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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 2, Number 1 (HABITAT, 1992, 50 p.)
View the document(introduction...)
View the documentThe aim of the Network and its journal
View the documentForeword
View the documentSignificance of information exchange in promoting the local building-materials sector in developing countries
View the documentNigeria: Pozzolana - the cheap alternative to Portland cement*
View the documentMauritius: A study of the potential use of Mauritian bagasse ash in concrete*
View the documentMalawi: The use of rice-husk and bagasse ash as building material*
Open this folder and view contentsTechnology profiles
View the documentPublications review
View the documentEvents
View the documentBack cover

(introduction...)


United Nations Centre for Human Settlements (Habitat)
Nairobi, 1992

Women contribute significantly in shelter construction.


Figure


Figure

The aim of the Network and its journal

The Network of African Countries on Local Building Materials and Technologies has the objective of strengthening local technological capacity through facilitating information flow, regional cooperation and the transfer of appropriate technologies in lowcost and innovative building-materials sector among African countries.

The Journal of the Network, currently published biannually, seeks to provide a channel for information that is available and could be of use by professionals, technicians, researchers and scientists, as well as policy and decision makers. It is a medium for information exchange and facilitator for acquisition of suitable technologies and know-how by needy countries.

Efforts are made to compile, process and publish articles and technical papers originating, mainly, in the African region. However, as deemed appropriate and subject to availability, research findings and technological information from countries outside the African region are also included to stimulate interregional cooperation as well.

CONTRIBUTIONS TO THE JOURNAL

This Journal welcomes information or articles on lowcost innovations in building materials technology. Information in the form of technical and policy papers, illustrations, news items and announcements of events can be sent from individuals or institutions in the private or public sectors, from within and outside the African region. All correspondence on the Journal should be addressed to the Chief, Building and Infrastructure Technology Section, Research and Development Division, UNCHS (Habitat), P.O. Box 30030, Nairobi, Kenya.

The views expressed in this Journal do not necessarily reflect those of the United Nations. Mention of firm names and commercial products do not imply the endorsement of UNCHS (Habitat). The reprinting of any of the material in this publication is welcome, provided that the source is mentioned and one copy sent to UNCHS (Habitat).

National network institutions

Cyprus Organization of Standards and Control of Quality
Ministry of Commerce and Industry
Cyprus

Department of Civil Engineering
University of Addis Ababa
Ethiopia

Building and Road Research Institute (BRRI)
Kumasi University
Ghana

Housing and Building Research Institute (HABRI)
College of Architecture and Engineering
University of Nairobi
Kenya

Department of Civil Engineering
The Polytechnic University of Malawi
Malawi

Department of Architecture and Civil Engineering
University of Malta
Malta

School of Industrial Technology
University of Mauritius
Mauritius

Nigerian Building and Road Research Institute (NBRRI)
Lagos
Nigeria

Faculty of Engineering
Fourah Bay College
University of Sierra Leone
Freetown
Sierra Leone

Geological Survey Mines Department
Ministry of Lands and Mines
Entebbe
Uganda

Building Research Unit
Dar-es-Salaam
United Republic of Tanzania

Ministry of Public Construction and National Housing
Harare
Zimbabwe

Foreword

One of the important factors that hinder the development of the local building materials sector in most developing countries is the inability of research institutions to translate their research findings into commercial production. One way of tackling this constraint is through effective information exchange. Information exchange is an important tool for the development of any sector. It increases awareness among various actors involved in the sector, facilitates transfer and diffusion of technology and stimulates intercountry or interinstitutional cooperation in a variety of areas.

In the past few decades, quite a number of research institutions and universities have been established in Africa and considerable research work is being carried out in them. However, in the absence of effective information exchange mechanisms, most research results and innovations in the building materials sector have remained inaccessible to many African countries. Prospective entrepreneurs or industrial promotion agencies looking for new technologies will need all the available technical information about a production process and its output. They would also be interested in knowing whether the technology has proved a commercial success elsewhere, particularly, under similar conditions of application.

A major reason for the present unsatisfactory situation is that building research institutions in many developing countries remain preoccupied with basic research work and the important task of disseminating research information to the industry is not given requisite priority. Consequently, the industry, as a whole, has very little access to information on new and innovative technologies appropriate to its needs. The limited information available from equipment suppliers are also often biased in favour of large-scale technologies, of little relevance to the vast majority of small-scale producers of building materials.

The Network of African Countries on Local Building Materials and Technologies, through this Journal, is attempting to bridge this information gap by collecting, processing and disseminating information on appropriate technologies and materials among African countries. The previous two issues of the Journal focused on roofing and walling materials. The theme selected for this issue is binding materials. There is no doubt that both walling and roofing materials are crucial for the construction of a low-cost house, however, none of them could be produced without the use of appropriate binding materials. Binders are essential components in the production of mortars for masonry, in plastering walls, in stabilizing soil and in making concrete. Among the different types of binding materials, Portland cement, with its proved suitability in all types of construction work, has remained practically inaccessible to many low-income house builders in developing countries because of its scarcity and high cost. Many research institutions, in the recent past, have devoted efforts to finding solutions to replace cement with such alternative binders as lime and natural pozzolanas, and binders produced from agricultural and industrial wastes, and other materials. What remains now is to stimulate the industrial sector to make use of such research findings, to increase commercial production, and, by innovative marketing programmes, to increase the acceptability of such lowcost binders among individual house builders and contractors.

In this issue of the Journal a number of technical articles on research findings and innovations for the production and use of lowcost binders have been compiled, and I hope that they will be of interest and use to the readers. In this connection, I would like to acknowledge and thank all the authors and institutions in the countries whose papers are included in this issue and hope that all these efforts will assist in meeting our common objective: to facilitate better shelter for all.

Dr. Arcot Ramachandran
Under-Secretary-General
Executive Director


A good foundation is important for ensuring durability of low-cost houses


Side view of a lime kiln

Significance of information exchange in promoting the local building-materials sector in developing countries

Introduction

One of the main barriers in technology transfer among developing countries is related to the limited amount of information exchange. The absence of any systematic information flow between developing countries has led to a trend of wasting scarce resources and a general lack of progress in the area of local building materials. Information exchange is a vital component and sometimes the backbone to technology transfer, a process which has proved to be viable in attaining self-sufficiency in many developing countries in the building-materials and construction sectors.

In both developing and developed countries, there is abundant information on low-cost building-materials technologies which should be sufficient enough to promote the wide adoption of the building materials. However, in most cases, the bulk of the information originating from developing countries is not processed or published. The dissemination of the information is yet another key problem. Even when the information is processed and published, there are deficiencies in the eventual dissemination. This problem is common to information on low-cost building materials originating from all sources, developing countries, developed countries and relevant international organizations. The information is hardly ever disseminated to the target groups: those who would ultimately make practical use of the information such as site supervisors, technicians in charge of machine-fabricating workshops, small-scale entrepreneurs and practitioners who are actually involved in the day-to-day operations in the production and use of building materials. There is also the question of how to repackage information to a comprehensible level for artisans in rural areas who may not understand the rather complex technical publications which characterize most available information on low-cost building materials.

This article is meant to examine the major shortcomings in and solutions to information exchange. Section A analyses information needs. Section B describes the various sources of information relevant to the building-materials sector. Section C gives a brief overview on the services which should be rendered to users. Sections D and E examine the current situation and the obstacles to the flow of information and give some solutions on how to overcome the barriers.

A. Analysis of information needs

Generally, there exists a direct relationship between information needs and the ultimate use of information, i.e., information needs define exactly the type of information required by a specific user-group or individual. Information has value only when it is used. No information can be processed or used effectively, if it does not satisfy the needs of the user, if the user does not trust the source of information, or if the processor of information does not know who would be the ultimate user of information. The information flow, therefore, will not succeed if these prerequisites are not satisfied.

The major user-groups could be categorized as follows.

1. Decision/policy-makers

The information requirements of decision- and policy-makers involve the directions and priorities of planning and programming. Decision-makers need to draw on many sources of concise, authoritative and up-to-date information which can be fed with confidence into planning models with due consideration to sociological, economic and environmental factors which are often very complex.

The major types of specific information required are:

(a) State-of-the-art of available technological capacity in the country; the performance of the industry, its adaptability and application characteristics;

(b) Data on geological surveys of available and potential natural resources suitable for production of building materials;

(c) Data on current and projected demand of building materials and forecasting;

(d) Studies on the compatibility of the use of innovative local building materials with existing social and cultural patterns and on the environmental impact of their use.

2. Researchers

Most research institutions in developing countries are concerned with applied research which might lead to industrial application. The bulk of researchers need information on results achieved at other research institutions which have had an impact on the commercial production of building materials. Up-to-date and accurate information on research activities world-wide could be of considerable help to research institutions in developing countries in selecting the most relevant research project, even though, the selection procedure for research projects normally is based on a policy of priorities.

The specific information requirements are:

(a) Types of research being carried out world-wide and, in particular, in developing countries. In view of the geographic and climatic resemblances of some countries in one region, regional information is more relevant and useful;

(b) Existing research experience and findings; laboratory test results, physical and chemical properties of raw materials and end-products; machinery design, efficiency and performance; costing and cost-benefit analysis reports;

(c) Proceedings of conferences, seminars, workshops and other similar events.


Research institutions need information for their activities

3. Trainers

Training and education are the backbone of any type of development; training at the grass-roots level is crucial, because the skilled labourers are the ones who are directly involved in the day-to-day work of production. Universities and high-level technical and vocational training centres are in existence in many developing countries; however, the training of artisans and other craftspeople has unfortunately not yet reached the level of expectation. Trainers in this category are always in need of information related to the various methods of training and skill upgrading.

The specific needs of those involved in training are:

(a) Basic textbooks; manuals on the production of building materials; simple and illustrative technical notes; fact sheets; etc.;

(b) Current awareness bulletins/journals reporting sources as well as trends and developments in various applications;

(c) Literature surveys; conference and seminar proceedings and periodical journals;

(d) Audio-visual aids;

(e) Evaluated data on sources, material and methods.


Audio-visual materials are important information sources for trainers

4. Entrepreneurs and professionals

Building-materials production plants, construction firms and professionals and technicians working in such facilities are indeed the main actors directly involved in the manufacture and use of building materials. These groups are the largest among the others mentioned earlier, and in a broad sense, their experience, endeavours and achievements very often establish the basis for a number of peripheral activities such as research and training, among others. Therefore, furnishing suitable technical information to these user-groups would significantly improve their operations. In fact, these groups are usually the main sources of information generation, which, if processed and disseminated among, and used by different groups, would help considerably in the promotion of the building-materials and construction industries in every country. The major information requirements of these groups are:

(a) Directories of institutions and firms involved in research and in the design of buildings, in the production of building materials and in construction;

(b) Directories of firms and workshops involved in the manufacture of machinery and equipment for the production of building materials;

(c) Periodical journals, technical reports and other types of publications covering innovations, case-studies and applied research results in the building materials and construction sector;

(d) Standards and specifications for building-materials production and application.

B. Survey of sources of information

The diversity of various institutions and individuals concerned with low-cost building materials and construction technologies is reflected in the pattern of information provision, both through informal exchange and formal information service provision. This institutional diversity and the very rapid growth of interest and activity have resulted in a situation where mechanisms for information exchange currently available are widely recognized as being inadequate.

Among the major information sources, the following are considered as the most relevant ones.


Conferences and workshops are important for interpersonal communication

1. Conferences, meetings and workshops

Among the various means of information transfer, interpersonal communication through participation in meetings, conferences or workshops is preferred. Over the past few decades the increase in the number of conferences and different types of meetings of international and regional scope, in all areas of building materials and technologies, has been large, and the published proceedings of such events are heavily cited in the review of literature. In fact, such events are good sources of information, because they establish forums for the exchange of views, provide exhibits, permit site visits, and facilitate personal contacts among different groups having mutual interests.

Even though interpersonal communication through meetings is regarded as being very effective, there is clearly a limit to the extent to which this kind of information transfer can be generalized and extended, if only for the financial burden, both for the organizers and the participants.


Meetings are important for exchange of views

2. Directories

The importance of identifying institutions and individuals as potential sources of information on building materials and construction is well recognized. Collection and dissemination of such information is usually organized through published directories or databases developed in relevant libraries and/or documentation centres.

Directories are meant not only to provide a roster of names and contact addresses, but also to stimulate intercountry cooperation. Recognizing the need for better knowledge of, and closer links between institutions dealing with human settlements issues, UNCHS (Habitat) undertook, as early as 1978, the preparation of a series of directories and guides to information sources on institutions, organizations and individuals involved in the field of human settlements. Each directory and information source deals with a different aspect of human settlements such as: training, financing, and construction materials, among others. The most comprehensive and up-to-date directory published by UNCHS (Habitat) is the Habitat Directory (HS/106/86)* which lists 1784 names of organizations dealing with human settlements, in three languages.

* Symbols in parentheses are the sales numbers of the publication.


Bibliographies and directories are important sources of information

3. Referral services

Referral services are meant to supply appropriate information to other dissemination centres or individuals. The major functions of a referral service are:

(a) To collect, on a world-wide basis, information about date and information resources on a specific subject;

(b) To prepare a comprehensive inventory of the kinds of data/information/services available from these sources with a detailed subject index for access;

(c) To guide users to the appropriate sources of the required date or information.

4. Bibliographic references

Bibliographies are considered as being among the most relevant information sources for all those who, in one way or another, are involved in a specific sector of the building industry. Undoubtedly, all actors involved in the building sector, who want to keep abreast of developments in the building-materials and construction industries, need up-to-date reference material in their day-to-day work.

UNCHS (Habitat), in its endeavour to achieve its objective of fostering technology exchange and information dissemination, has produced a series of bibliographies on topics related to human settlements. Among these bibliographies which relate to the building industry are:

- Bibliography on Local Building Materials, Plants and Equipment (HS/22/82E)

- Bibliography on Small-scale Building Materials Production (HS/154/89E)

- Bibliography on Earth Construction (HS/169/89E)

- Bibliography on Passive Solar Systems in Buildings (HS/173/89E)

5. Periodicals and other technical publications

During the past few decades, a number of international, national and non-governmental organizations, in an attempt to collect and disseminate information, have launched programmes for publishing periodicals, such as journals, news bulletins, and books, which are considered quite satisfactory and effective for the user-communities.


Exhibitions could be good sources of information

Even though, publishing specialized periodicals has a very long history in developed countries, the process, particularly in the field of low-cost building materials and technologies, is in its infancy in most developing countries and the number of publications dealing only with the problems of developing countries in this subject is very limited. Commercial publishers, in recent years, are showing an increased interest in texts relevant to developing countries, but much of their outputs tend to consist of case-studies which attract limited interest outside the country concerned. Moreover, by their very volume, journals being published world-wide may be presumed to contain much information on specialized topics, yet, there is often a considerable amount of duplication and of publication for the sake of doing so. Therefore, in order to improve the quality of the journals specializing in the low-cost building-materials sector, there is need for increased cooperation between the relevant institutions in developing countries and the publishing organizations.

6. Technical assistance programmes as information sources

An examination of technical assistance programmes, both international and bilateral, indicates that the experience gained in them provides a potentially valuable source of information to and about developing countries. The extent to which the information generated might be generally available is hardly known. However, much of it warrants systematic and wider dissemination, especially at the regional level and in terms of technical cooperation among developing countries (TCDC).

In the context of technical assistance programmes initiated by the United Nations system, the establishment of regional and global networks in specialized areas, as a means for collecting information and establishing databases, is considered as one of the most effective methods, and if operated on a sustainable basis, could become a vital source of information in a specific subject area. These networks, in order to function effectively, would obviously need various types of means such as: equipment and hardware; software; personnel; and premises. It is difficult, however, to estimate in quantifiable terms the extent of the means necessary for the operation of a network or one of the documentation centres in the network. This would depend on the number and characteristics of the users to be served, the volume of documentation to be processed, the documentation method used, the services to be provided etc. Therefore, as a preliminary step to each case, these various elements must be the subject of a detailed assessment and analysis making it possible to estimate in quantitative terms what means are required.

C. Services to the users **

** In the preparation of this section, the use of the Handbook for Information Systems and Services (ISBN 92-3-101457-9), published in 1977 by the United Nations Educational, Scientific and Cultural Organization, as reference and source, is acknowledged.

If a successful flow of information has to be realized, then services such as searching and retrieval, dissemination, notification, translation and document reproduction, to mention only a few, have to be rendered to the users. Information may be recorded in a document whether public or confidential, or it may exist in the memory or notebook of a personal source. Information services are usually composed of primary sources as well as compendia and a variety of traditional retrieval guides. As no document collection is self-sufficient, it must identify other sources of information through catalogues and directories. Between information and its user there are the operations of the information service, such as dissemination which is initiated by the information services, and searches and retrieval, which can be initiated by the user. The main categories of user groups, in this regard, could be defined as: those expressing individual queries and those expressing wider and more permanent interests that are to be regularly matched against new acquisitions in the documentation services. Either type of group consists of a set of keys which should be compared with document profiles. The simplest form of matching is to require that all user keys must be present in the profile of a document before the latter's location is reported.

Another important function that an information service should carry out in order to render services to users is reviewing publications upon their receipt for the purpose of selecting information pertinent to the programme of a specific user-group and to note individual items to be brought to the attention of users. This is generally known as “current-awareness” service. A refinement of the current-awareness idea is the selective dissemination of information that is designed to serve the individuals directly.


Technical co-operation projects are potential sources of information

Translation and document-reproduction services are also considered important services that should be provided to the user communities. Translation of documents, very often, imposes great barriers to the transfer of information. Whether the actual translation occurs in the processing or dissemination phase, the information service may be expected to provide full document translations or vernacular summaries of foreign language material. Document reproduction, similarly, cannot be considered as a purely technical matter. Therefore, the level of reproduction facilities and capabilities has a direct bearing on the effective service that a documentation service can provide to its users.

The figure shown below is a chart of the flow of information to a scientific and professional user.

D. Examination of the present situation and the obstacles to the flow of information

In the context of developing countries, even though information exchange in the building-materials sector is not the sole prerequisite for intercountry cooperation for promoting the sector, it is a vital input to the complex and resource-demanding process of technology transfer. Some developing countries have over the years been engaged in various levels of activity to promote low-cost building materials, sometimes involving projects which are complementary to one another, at other times involving straightforward duplication of projects. The issue worth emphasizing is that the remaining developing countries would not need to invest in any primary research but to build upon existing experiences and innovations.

For almost every conceivable building material which is likely to have an impact on low-income housing, there is a proved and appropriate technology. Despite this, and in view of a general lack of a systematic flow of information, the majority of developing countries are still stuck with huge resource outlays on the fundamentals of research into innovations in low-cost building materials and often achieving results of no consequence at all to the worsening shelter crisis. The logical step, following the few correct approaches to the promotion of low-cost building materials should obviously be a process of information exchange among these countries to preclude this wasteful trend.

The process of information collection and dissemination through specialized information services and data centres in developing countries is undergoing gradual development. Special libraries and documentation centres are already established in most countries and are usually attached to government ministries or universities. The specialized information and data centres are organized in different ways according to the system chosen and local conditions. State-run centres and non-governmental centres play different roles in specific conditions. However, the assignments of these centres are often not closely linked to each other and in the process of collecting and disseminating information, each centre uses resources from abroad. Moreover, the availability and dissemination of information via data centres are, in general, handicapped by the isolated location of these centres and their local production of national data. Therefore, most scientists are obliged to search for their information needs personally, which is a time-consuming effort.


A model of flow of information to a scientific and technical user. This figure is a reproduction of figure 5.6.1. from UNESCO, Handbook for Information Systems and Services (Paris, 1977).

In the past few decades a number of information and documentation centres in the areas of building-materials and construction industry have been set up and are in operation in several developed countries. The mandate accorded to these information centres are, in many cases, very similar which is to collect, process and store systematically research activities and their findings and retrieve and supply them to the interested parties upon request. Some of them are also established merely to provide technical advice on innovative technologies relevant to developing countries.

These information centres, even though, having contributed considerably in collecting and disseminating information, and while possessing sophisticated and computerized facilities to process information, have, unfortunately, not been able to satisfy fully and effectively the information needs of many developing countries, and, in particular many countries of the African region. Although digital linkages and communication exchange have been successfully implemented, the transfer of technical and scientific research information into practice has not yet been implemented successfully and systematically in many developing countries, and in some cases the existence of successful research results is seldom brought to the attention of users. There are a several reasons for these problems, the main ones being the almost non-existence of well-organized and - equipped information centres at both the national and regional levels, a scarcity of trained and experienced professional staff in developing countries to manage these centres, a lack of adequate policies and strategies to promote the information flow, and, obviously, the existence of financial constraints prevailing in many countries.

Also, there are non-coherent patterns of building-materials production between the formal and informal sectors, the latter generally being characterized by small- and medium-scale producers. However, considering the industry as a whole, there is a lack of appropriate mechanisms for information flow so as to promote the linkages between these two sectors leading to balanced growth, and to bridge the gap between the demand for and supply of building materials. Therefore, national and sub-regional information centres, to facilitate increased awareness among professionals and decision-makers, are considered to be equally important as international or regional information centres.

E. Solutions to the barriers in information exchange

In the preceding sections, a brief analysis of information needs, information sources and obstacles to the flow of information relevant to developing countries has been presented. In view of the multidisciplinary character of information exchange and its importance in the promotion of the low-cost building-materials sector, tackling the obstacles confronting systematic information flow, and devising precise guidelines and solutions, would require a more comprehensive examination of the sector which should be carried out, possibly, in conjunction with some case studies. However, in the context and limits of this article, some proposed solutions may be summarized as follows:

(a) National, regional and international information centres/networks should be established, and, if in existence, their capabilities to coordinate and to work in liaison with research institutions and successful entrepreneurs in the area of building materials and technologies, should be strengthened.

(b) All national research institutions, universities and any establishment involved in the building-materials industry should be aware of the existence of relevant information centres and should be committed to cooperate with them in regularly supplying relevant information on their activities and work progress.

(c) The information centres should have professional competence and should be in a position to process the information gathered from various institutions and to store it properly for easy retrieval.

(d) Governments of developing countries, donor countries, and non-governmental and international organizations should support the information centres during their initial stages and up to the time when they can become self-supportive in their operations.

(e) The information centres should devise guidelines and evaluation procedures for the institutions and/or individuals who are suppliers of information, so that wasteful efforts in compiling and processing of information could be minimized/eliminated.

(f) In view of the poor communication systems prevalent in many developing countries for the efficient flow of information from information centres to the user-communities, it is the vital role of the information centres to ensure a systematic flow of information between the suppliers and users of information. In this regard, information needs must be examined from the following aspects:

(i) The aim of the information (for what use, by whom, in which type of institutions);

(ii) The nature of the information needed;

(iii) The form in which information is, or might be, delivered.

(g) The information centres/networks should endeavour to publish and disseminate periodicals, journals, technical notes, audio-visual material and any other suitable publications with the aim of informing the user-communities on research results, innovations, case studies etc.

(h) The information, technical data and case studies published must include relevant and useful material. They should avoid duplication and should be simple and able to be understood by specific categories of user-communities.

(i) Conferences, seminars, workshops, exhibitions and similar events are important tools for the purpose of information exchange. Therefore, efforts should be made to encourage their organizers and increase the number of such events.

(j) Referral material such as bibliographies, directories, compendia etc. needs to be published and disseminated, and if already in existence should be updated as appropriate.

F. Conclusions

Information exchange is a vital component of technology transfer and an important input to the process of promoting the building-materials industry.

Existence of national information services, in order to facilitate translation of research findings into industrial production, and create necessary linkages between research and development institutions on the one hand, and entrepreneurs, on the other, are considered as important as the regional and international information centres.

In the process of collecting and disseminating information, the needs of specific categories of the user-communities should be taken into consideration, e.g., the type of information needed by professionals or researchers should be different from the information needed by policy-makers. Likewise, the user-communities must be made aware of the sources of information. They must be furnished with such information as could be deemed useful and relevant to their area of specialization.

Organization of conferences, workshops and similar events as a medium for information exchange, as well as publication of directories, bibliographies, journals and the like, on specific aspects of building materials and related technologies, are very useful tools in facilitating increased awareness among various categories of user-communities.

In the past few decades some non-governmental and international agencies in developed countries have established databases and information systems on the general building and construction industries, with very few of them specializing in the areas of low-cost building materials and related technologies. Even though their achievements are highly appreciated and accepted by different categories of user-communities, their efforts have not yet been effective in stimulating and improving the process of information exchange in many developing countries, in particular, in the countries of the African region. This is, mainly, because of the poor communication systems in many developing countries, a lack of coherent and sustainable links among various institutions in different countries and a lack of sound management on the part of the information centres.

Nigeria: Pozzolana - the cheap alternative to Portland cement*

* By Dotun Adepegba, Professor of Structural Engineering, University of Lagos, Nigeria.

This paper was presented to the Seminar on Local Materials for Housing, Third International Seminar of the African Network of Scientific and Technological Institutions (ANSTI), Civil Engineering Subnetwork, held at the University of Mauritius, Reduit, March 1990. ANSTI is a UNESCO-sponsored Network

Abstract

The paper is aimed at introducing new entrants into researches on pozzolanas. Reference is made to the past efforts of the industrial countries in research work leading to the development and commercialization of local pozzolanas in their environs, and how Africa, albeit having abundant potential for pozzolanas, has not yet succeeded in making effective use of the only known cheap alternative to Portland cement. The paper enumerates the physical and chemical characteristics of a presumed pozzolanic material. It gives the state-of-the-art of research methods in the area of pozzolanic materials without utilizing sophisticated laboratory equipment. With the help of the test results, new methods for the physical and the chemical combination of pozzolanas, to produce the best blend, are introduced. The methods could be used in laboratories and industry, especially when there is need to improve pozzolanic activity or produce blended cement. Emphasis is laid on the need for African Governments to persuade the existing Portland cement factories in Africa to undertake pozzolana production as a new line. The examples of Rwanda and the United Republic of Tanzania are highlighted with a view to encouraging other African countries to adopt the experiences of developed countries in the production of pozzolana as an alternative to Portland cement for masonry work.

Introduction

Pozzolana is a natural or artificial material which contains silica and alumina or ferruginous materials in a reactive form. The natural pozzolanas are of volcanic origin, such as volcanic ashes, tuffs and other diatomaceous earths, and agricultural and mine wastes. Pozzolanic materials are not cementitious in themselves but, when finely ground, contain some properties which at ordinary temperatures will combine with lime and shale in the presence of water to form compounds which have a low solubility character and possess cementitious properties.

There are various types of pozzolanas depending on their composition. Portland pozzolana is a blend of Portland cement and pure pozzolana such as volcanic ashes or rice-husk ash. Lime pozzolana is a blend of natural pozzolana with lime. Clay pozzolana is a blend of shale or clay with pure pozzolana. There has not been a report yet on whether pure pozzolanas are combined to form pozzolana cement. There are already a number of pozzolanas of African origin apart from those which derived their sources from volcanoes. The mine wastes, such as bauxite wastes, riget cake, riget stone, magnetite, ash of dry stalks of palm bunch, coal ash and ilmonite are new additions to the family of pozzolana of African origin. They are mainly from tin, aluminium and coal mines.

Pozzolana is not a new binder. It was used by the early Egyptians, centuries ago. The Greeks used the volcanic tuff from the island of Thera and the Romans used the red volcanic tuff found in the Bay of Naples. The best variety of the tuff was found around Pozzuoli, hence it was called pozzolana.

The high cost of production of Portland cement and the resulting high cost of construction, led some countries in Europe and America to manufacture pozzolana cements so as to reduce the demand on Portland cement. Countries that use pozzolanas are Australia, Greece, India, the Russian Federation, Spain, the United States of America and Yugoslavia. However, there are inherent problems in the manufacture of pozzolana cements which could raise the cost of their production to almost the same level as Portland cements. Some of the problems are: the refusal of the existing Portland-cement factories to adopt pozzolana cement as one of their lines of production; a lack of sufficient quantity of pozzolanic materials; the high temperature demand by some pozzolanic materials to improve pozzolanic activity; and the extremely low rate of strength development characteristic of some pozzolanas due to a deficiency of essential elements.

In Africa however, Rwanda and the United Republic of Tanzania have gone into trial production of pozzolana. Organization of a small pilot plant for the manufacture of lime-pozzolana was reported by Apers and others (1). The base material is volcanic ash, found in north-western Rwanda. The lime deposit was found near the site for the factory at Runhengeri. The production cost of lime pozzolana was about RwF6000 (RwF100 = US$1) per ton, whereas the production cost of Portland cement was about RwF30,000 per ton. The lime-pozzolana cement costs about one fifth the cost of Portland cement. This is possible because pozzolana formed about 60 per cent of the content, 20 per cent was lime and the remaining 20 per cent was Portland cement.

Kawiche (2) reported the efforts of the Government of the United Republic of Tanzania in persuading the Mbeya Portland Cement Factory to produce pozzolana cement as one of its lines of production. There is not a single African country that is devoid of pozzolanic materials. The most common pozzolanic materials in Africa are laterite, limestones, clay and shales. Evidence is also available that agricultural wastes with pozzolanic characteristics are available in large quantities in Africa.

Comparison of pozzolanas with Portland cement

Pozzolanas do not develop strength at the same high rate as Portland cement. The strength which an ordinary Portland cement will attain in 14 days may not be attained by untreated pozzolanas in 60 days. The problem is that all pozzolanas have a low content of calcium oxide and a high content of silicon dioxide. This imbalance is responsible for the low rate strength development.

Tables 1 and 2 show the efforts of Lea (3) who analysed some pozzolanas that were found in Europe and the United States of America. It is pertinent, therefore, to collate pozzolanas of African origin with a view to combining one or two of them if necessary, for the improvement of pozzolanic activity or for volumetric purposes. The Africa Pozzolana Research Depository (APRD) which is located in the Civil Engineering Department of the University of Lagos, could be a focal point for this purpose. APRD has been involved in research, since 1985, on the exploration of local pozzolana, and is prepared to provide information and help, and carry out tests and analysis of any presumed pozzolanic material that is available in any part of Africa. In this regard, communications can be addressed to the author.

Table 1. Percentage composition of volcanic ash pozzolanas

Pozzolana

Ignition loss

SiO2

Al2O3

Fe2O3

TiO2

CaO

MgO

Na2O

K2O

SO3

Rhenish trass

10.1

54.6

16.4

3.8

0.6

3.8

1.9

5.1

3.9

0.4

Rhenish trass

8.5

54.8

17.2

4.4

0.6

2.3

0.9

7.0

3.8

0.1

Bavarian trass

14.0

57.0

10.9

5.6

0.5

6.0

2.2

1.8

1.5

0.2

Santorian earth

4.9

63.2

13.2

4.9

1.0

4.0

2.1

3.9

2.6

0.7

Santorian earth

3.1

65.2

12.9

6.3

-

3.2

1.9

2.6

4.2

-

Rome Segni

9.6

44.1

17.3

10.7

-

1.2

2.0

1.4

3.1

-

Rome Segni

5.3

48.2

21.9

9.6

-

7.5

3.2

-

-

0.3

Sao Paolo

4.1

45.2

2.0

10.7

-

9.8

3.8

-

-

0.3

Naples: Bacoli

4.8

55.7

19.0

4.6

-

5

1.3

3.4

-

-

Baia

14.4

59.5

19.3

3.3

-

2.1

0.2

-

-

0.2

Romanian trass

13.9

62.5

11.6

1.8

-

6.6

0.7

-

-

-

Crimean tuff

11.7

70.1

10.7

1.0

-

2.5

0.3

-

-

-

United States Rhyolithic

3.4

65.7

15.9

2.5

-

3.4

1.3

5

1.9

-

Pumicite

4.2

72.3

13.3

1.4

-

0.7

4.0

1.6

5.4

Trace

Table 2. Percentage composition of some artificial pozzolanas

Pozzolana

Ignition loss

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O+K2O

SO3

Burnt clay

1.6

58.2

18.6

9.3

3.3

3.9

3.9

1.1

Burnt clay

1.3

60.2

17.7

7.6

2.7

2.5

4.2

2.5

Spent oil shale

3.2

51.7

22.4

11.2

4.3

1.1

3.6

2.1

Raw gaize

5.9

79.6

7.1

3.2

2.4

1.0

-

0.9

Burnt gaize

-

88

6.4

3.3

1.2

0.8

-

Trace

Raw moler

5.6

66.7

11.1

7.8

2.2

2.1

-

1.4

Burnt moler

-

70.7

12.1

8.2

2.3

2.2

-

1.5

Raw diatomite

8.3

86

2.3

1.8

Trace

0.6

0.4

-

Burnt diatomite

0.4

69.7

14.7

8.1

1.5

2.2

3.2

-

Fly ash (United States)

1.2

47.1

18.2

19.2

7.0

1.1

3.95

2.8

Fly ash (United States)

7.5

44.0

18.4

11.2

11.6

1.1

3.14

2.0

Fly ash (United Kingdom)

0.9

47.4

27.5

10.3

2.1

2.0

5.7

1.8

Fly ash (United Kingdom)

4.1

45.9

24.4

12.3

3.6

2.5

4.2

0.9

Rice-husk ash

-

85.6

2.5

0.3

1.0

1.0

2.5

1.5

Simple method for measurement of pozzolanic activity.

In order to determine whether or not a material is pozzolanic, the first test to be carried out is the standard consistency test on a paste made from finely ground powder of the material. This test is used to determine the standard consistency of the paste for use in the tests for the initial and the final setting times of the paste. The standard consistency test gives the indication of the quantity of water to be added to the dry powder of the material being tested to produce the type of paste to be used in the VICAT apparatus. The quantity of water required for a consistent paste is an indirect measure of the degree of fineness of the powder. The finer the powder, the more water it will require to produce a consistent paste.

The initial and the final setting times of the consistent paste is also an indication of pozzolanic activity. The nearer the initial and the final setting times of a pozzolanic material to that of Portland cement, the greater the pozzolanic activity. Two typical brands of Portland cement were tested, one at the Civil Engineering Department, University of Lagos, and the other at the Civil Engineering Department, City University, London. The two brands were ordinary Portland cement manufactured to the specifications of BS 12. The test in London was carried out in the winter and the test in Lagos in the dry season when the temperature was about the highest. The initial setting time for the test in London was 3.40 hours and the test in Lagos was 2.30 hours. The final setting time for the test in London was 4.27 hours whereas, the test in Lagos gave 3.95 hours. The well-known behaviour of cement, setting slower in cold weather than in hot is clearly demonstrated. The same phenomenon is expected from pozzolanic materials. Therefore, if a test on pozzolanic material is carried out in the cold period the result cannot be comparable with the test carried out in the hot period, if, setting time is the determinant. However, setting times are just one of the factors that determine the degree of pozzolanic activity of materials.

The chemical composition of finely ground powder is the next step in the test to identify a pozzolana, whether or not the setting times are suspicious. The need to examine the chemical composition is to find out if the principal elements which normally exist in pozzolanas are present. There are several methods to determine the composition of materials. The major constituents expected in a pozzolana are silica, lime, alumina and iron oxide, although others like magnesia, calcium sulphate, potassium, titanium, sulphur and copper have been found to be present, depending on the source of materials. Generally, most pozzolanas have a very high content of silica as is evidenced in tables 1 and 2. The second highest is alumina. In most cases, untreated pozzolanas are deficient in calcium which is needed to promote pozzolanic activity in combination with silica and alumina.

Physical state - new method to combine pozzolanas for maximum activity

The degree of pozzolanic activity can be increased by two major methods, viz., the physical method and the chemical/calcination method. The chemical and physical mechanisms by which pozzolanas develop cementitious properties are complex. In the physical method of increasing pozzolanic action, one or two, or even more pozzolanas can be combined to produce an entirely new pozzolana. The combination may be as a result of the non-availability of a sufficient quantity of one or two pozzolanas. A combination of these pozzolanas may produce increased quantity but not necessarily increased pozzolanic activity. The combination may, otherwise, be due to a balancing of elements having found that the element that is low or absent in one pozzolana is abundantly present in the other. For example, if the fly ash, with 11.6 per cent of calcium oxide, is combined with the rice-husk ash with 1 per cent calcium oxide (see table 2) a material with higher pozzolanic activity than the fly ash and the rice-husk ash may result. There is a graphical method of scientifically combining any number of pozzolanas to produce a single pozzolana, having a property, very close to an ideal composition which is the Portland cement. Suppose, there are three pozzolanic materials A, B and C with the following chemical compositions:

Pozzolanic material

Percentage composition


Fe2O3

Al2O3

SiO2

CaO

A

14

26

48

5

B

11

18

44

12

C

3

18

30

30

Portland cement

3

5

22

65

Plot the points as shown in figure 1, with the elements arranged in the ascending order of the percentage content of the element in the ideal material, which in this case is the Portland cement. The curve with the lowest percentage content of calcium oxide is for material A. The curve with the next percentage content of calcium is material B and the curve next to that is for material C. The highest content of calcium oxide occurs in the ideal material which is always the Portland cement for any exercise of combining pozzolanas.

Join the foot of curve A to the head of curve B with a dash-and-dot line. Join the foot of curve B to the head of curve C with a dash-and-dot line. The dash-and-dot line which joins the foot of curve A to the head of curve B intersects the Portland cement curve at 13 per cent which means that material A will form 13 per cent of the new material produced by combining materials A, B and C. Similarly the dash-and-dot line which joins the foot of curve B to the head of curve C intersects the Portland cement curve at 24 per cent which means that material B will form 24 per cent of the new material produced by combining materials A, B and C. Therefore, material C will form the balance which is 63 per cent. This arrangement will produce the best combination of the three materials for the best pozzolanic activity.


Figure 1. Combination of three types of pozzolana

Chemical state

The chemical conversion of pozzolana is highly technical and requires experience. Care must be taken not to introduce chemicals which are strange to the chemistry of cement and which are likely to be deleterious to pozzolana cement when in use. The chemical process cannot be complete without calcination. But calcination involves clinkerization which can put extra cost in the production process. The chemical process must essentially be followed by two tests: (a) determination of the free lime, which is the same thing as the soundness test for cement by Le Chatelier; (b) determination of the sulphate content. The chemical process and calcination can be applied to the physical state, i.e., after the combination of one or two pozzolanas, if the result is still not satisfactory. In most cases carbonates of metals are recommended for the chemical conversion of pozzolanas for improved pozzolanic activity.

Amorphous silica was reported by Malquori (4) to react much more rapidly than the crystalline form because its structural bonds are weak and unstable, thus, making it vulnerable to calcium hydroxide. For example, in clay materials, annihilation of the bonds between silica and alumina, due to calcination, has made silica and alumina more reactive with calcium hydroxide. This process may not achieve good results in materials formed from crystallization in which silica and alumina are strongly held in their lattices. A good and easily improved pozzolanic material must have a great percentage of its silica in the amorphous form.

Mechanical state

Mechanical tests involve the determination of the compressive and the tensile strengths on a short- and long-term basis. It is advisable to test the paste as well as the concrete made from the presumed pozzolanic material. In order to avoid results that are not reproducible the following points are important and must be noted:

(a) Temperature and humidity at the time of casting of the specimens must be recorded in order to quantify the effect of these variables on the test results.

(b) Test specimens prepared from pozzolanic materials should be cured under wet sacks and not immersed in water. Concrete, mortar or paste made from pozzolanas must be kept damp for a minimum of 60 days during which time it must have developed the full strength of an ordinary Portland cement. If pozzolanic specimens are immersed in water, especially at the early ages, there is a tendency to absorb water, which may increase the water of hydration and thereby reduce the strength of the specimen.

(c) Curing under wet sacks may continue for 90 days because some pozzolanas give compressive strengths which are higher than those of ordinary Portland cement at about that age.

Pozzolanas set slowly and, therefore, develop very low heat of hydration. This makes them very useful for non-structural construction in hot countries. Pozzolanas are more suitable for use in hot countries than in cold because higher pozzolanic activity can be developed in hot countries than in cold by the same materials.

References

(1) Apers, J., Pletinck, M., and Verschure, H., “A pozzo-lime industry in Rwanda”, in Proceedings of Symposium on Appropriate Building Materials for Low-cost Housing, Kenya, 1983, vol. 2, pp. 86-92.

(2) Kawiche, G. M., “Production of Portland-pozzolana cement in Tanzania”, in Proceedings of Symposium on Appropriate Building Materials for Low-cost Housing, Kenya, 1983, vol. 2, pp. 95-104.

(3) Lea, F. M., The Chemistry of Cement and Concrete (London, Edward Arnold Limited, 1938), p. 141.

(4) Malquori, G., “Portland-pozzolana cement”, in Proceedings of 4th International Symposium, Washington, vol. II, pp. 983-1006.

Acknowledgement

Acknowledgment is due to the University of Lagos Central Research Committee, for providing the funds for this research which is part of the exploration of pozzolanas in Nigeria for the purpose of finding a cheap alternative to expensive ordinary Portland cement.

Mauritius: A study of the potential use of Mauritian bagasse ash in concrete*

* By B. K. Baguant and G.T.G. Mohamedbhai, Department of Civil Engineering, University of Mauritius

This paper was presented to the seminar on Local Building Materials for Housing, Third International seminar of the African Network of Scientific and Technological Institutions (ANSTI), civil engineering subnetwork, held at the university of Mauritius, Reduit, March 1990. ANSTI is a UNESCO-sponsored Network.

Abstract

Bagasse is the fibrous residue of sugarcane after crushing and extraction of juice. Bagasse ash is the waste product of the combustion of bagasse for energy in sugar factories. An estimated 20,000 tons of bagasse ash are produced every year in Mauritius, of which about 11,000 tons are potentially usable.

This paper investigates the technical feasibility of using bagasse ash as a partial replacement of cement in concrete (i.e., as a pozzolana), and as a fine aggregate in concrete. The low chemical reactivity of the ash is demonstrated. Its use as sand in concrete shows no adverse effects on strength or strength development up to one year. However, the longer-term properties of the concrete, such as shrinkage and durability need to be further investigated.

Introduction

The economy of Mauritius, a small, 1800 km2, Indian Ocean island, has been and is still very much dependent on the cultivation of sugarcane. The production of sugarcane varies from year to year, the main factor for such variations being climatic conditions, the average annual yield being about 5.6 million tons (1). Bagasse, the residue of sugarcane after crushing and extraction of juice, consists of water (about 50 per cent), fibres (above 48 per cent) and relatively small amounts of soluble solids. Nearly all bagasse produced in Mauritius is burnt for energy needed for sugar processing. The surplus energy is convened into electricity. Only a very small amount (about 3750 tons per year) is used for making resin-bonded boards.

Bagasse ash is at present considered to be a waste product with little or no use. It has negative value, in that, the sugar factories have to spend money to dispose of it. Moreover, it is a potential environmental pollutant. It is estimated that about 20,000 tons of bagasse ash are produced every year. This represents about 0.3 per cent of cane crushed or about 2.8 per cent of the dry weight of bagasse.

Since all cement used in Mauritius is imported, the prime use of bagasse ash in concrete would be as pozzolana, that is, as a partial replacement for cement. Another possibility is its use as a fine aggregate, even though the quantities available are small compared with the national annual consumption of about 1.2 million tons of fine aggregate. The latter requirement is currently being satisfied by crushing basalt rock and quarrying in dwindling reserves of natural coral sand.

Although Mauritius is sparing little effort in developing its industrial sector, its economy will continue to depend heavily on sugar production for many years to come. The sugar factories on their side, will continue to depend entirely on bagasse burning for energy. The supply of bagasse ash is, therefore, ensured for years ahead.

Characteristics of bagasse ash

Types and availability

The sugar factories in Mauritius use two types of bagasse-fired water-tube boilers: a hearth-type and a suspension-burning type (2). In the former, bagasse fed in at the top of the furnace falls in a pile on the floor of the hearth, while cold or hot air is blown on to the burning bagasse. This type of burning produces three types of ash:

(a) Furnace bottom ash, which accumulates on the floor of the hearth and is removed manually at every weekend shutdown.

(b) Hopper ash, which is blown by horizontal air blasts into hoppers situated at the back of the furnace.

(c) Fly ash, which is carried by the exhaust gases up the chimney and is partially removed by sprays of water.

In the suspension-burning type, bagasse fed in from the sides is distributed by a spreader-stoker on to the plan area of the combustion chamber, while primary air is blown upwards through a grate enabling the bagasse to burn in suspension in air without heaps forming on the grate. This type of furnace also produces three types of ash:

(a) Grate ash, which accumulates on the grate and is removed by tilting the grate every six to eight hours.

(b) Hopper ash, which is blown into hoppers by secondary air fed in from the sides of the furnace.

(c) Fly ash, which is carried up the chimney.

Of the estimated 20,000 tons of bagasse ash produced every year, about 4000 tons are fly ash (2). The remainder consists mainly of grate ash (about 11,000 tons).

Table 1. Chemical composition of bagasse ash (excluding fly ash) from different sources

Constituents

Percentage composition


Ref. 9

Ref. 10

Ref. 11

Ref. 2

Dundee, Hopper ash

Dundee grate ash

SiO2

74.2

75.0

71.4

73.07

50.19

57.61

Al2O3

12.12

3.6

1.6

12.00

10.12

10.11

Fe2O3

12.12

2.7

1.9

12.00

15.75

10.79

CaO

3.93

3.9

4.3

4.3

4.94

4.58

MgO

0.32

4.1

3.8

2.66

8.14

5.31

K2O

1.67

7.1

11.0

2.65

5.56

6.22

Na2O

0.36

0.2

0.8

0.16

0.41

0.29

P2O5

5.58

2.3

3.4

2.57

2.09

2.38

SO3

0.20

0.3

-

0.23

-

-

Cl2

0.07

-

-

0.01

-

-

MnO

-

-

-

-

0.26

0.29

TiO2

-

-

-

-

1.57

1.46

L.O.I*

1.63

1.65

-

1.30

1.23

1.24

* Loss-on-ignition

Chemical composition

Results of chemical tests on grate and hopper ashes carried out in Mauritius and at the University of Dundee are shown in table 1. The local data were obtained using classical laboratory techniques whereas the Dundee results were obtained by an X-ray fluorescence (XRF) method of oxide analysis.

The results indicate a fairly high degree of variability in chemical composition of the ashes, with the Dundee data showing marked departures from typical results. But, in general, the grate and hopper ashes have a high silica content, which, if present in an amorphous chemically reactive form, could enable the ashes to exhibit pozzolanic properties. Also, being alkaline, the ashes are compatible for mixing with Portland cement.

The grate and hopper ashes have reasonably low loss-on-ignition values (see table 2), with the exception of ashes from fuel where the factory burns pulverized coal in addition to bagasse for energy production. Fly ash has a high carbon content. It is also soft, compressible and highly absorptive. It is, therefore, not suitable for inclusion in concrete.

Table 2. Loss-on-ignition (L.O.I) values of bagasse ashes from various sources


Type of ash

Factory

Grate

Hopper

Fly

Mon Desert Alma

3±0.5

1±0.3

71±3

Belle Vue

4±0.3

1±0.2

-

F.U.E.L.

14±1

4±0.3

80±2

Rose-Belle

3±0.5

1±0.2

7±0.5

Table 3. Specifications of BS 3892 for pulverized fuel ash (pfa) for use in concrete

Property

Limit (percentage)

Fineness (expressed as the mass proportion retained on a 45 micron sieve)

Not greater than 12.5

Loss-on-ignition

Not greater than 7

Water requirement of a mixture of pfa and ordinary

Not greater than 95 of that of OPC

Portland cement (OPC)


Pozzolanic activity index

Not less than 85

Physical properties

The grate and hopper ashes are granular, rough, vascular particles whose maximum sizes can vary extensively as the material forms lumps in the furnace. The relative density of the ashes on a saturated surface dry basis range between 1.90 and 2.12. The ashes also have very high absorption values of 10 ± 2 per cent.

The grading of the ashes can be extremely variable, the percentage passing 600 um sieve ranging from 14 per cent to 80 per cent. But, in general, the ashes tend to be rather coarse, with 15-25 per cent passing the 600 µm sieve (2,3).

Pozzolanic activity

There is no national or international standard for testing bagasse ash. The specifications of BS 3892 (4) for pulverized fuel ash (pfa) for use in concrete (see table 3) were therefore, used to establish whether bagasse ash could be an effective pozzolanic material for use in concrete.

Samples of grate ash and hopper ash obtained from one factory were used in all the tests. Fly ash was excluded because of its high carbon content The ash samples were oven-dried, ground in a ball-mill and sieved through a 45 µm test sieve. The samples thus automatically satisfied the fineness requirement. The loss-on-ignition values for grate ash varied between 1.4 and 1.7 per cent and those for hopper ash between 0 and 0.2 per cent. These values are well below the 7 per cent specified in BS 3892.

The water requirement of grate ash (110 per cent) and hopper ash (104 per cent) were greater than the 95 per cent specified in BS 3892, probably because of greater friction between the particles of ash compared with pfa (5). The greater angularity of grate ash particles compared with hopper ash is reflected in its higher water requirement to give the same flow characteristics as that of hopper-ash mortar.

The pozzolanic activity index values for grate-ash and hopper-ash mortars were found to be 68 per cent and 65 per cent, respectively, which are much lower than the specified minimum of 85 per cent in BS 3 892, showing the relatively poor reactivities of the ashes. This is not too surprising in view of the relative absence of cenospheres revealed by the scanning electron microscope (SEM) photographs. However, many pozzolanas are known to exhibit low reactivities at early ages and yet develop significantly higher strengths at later ages. It was therefore, decided to investigate the strength development with time of concrete specimens incorporating ground grate-and hopper-ashes. The mix proportions of the normal, grate-and hopper-ash concretes (see table 4) were such that the cement content was kept constant and the natural sand was reduced by an amount equal to the volume of ash added. The strength results of the specimens tested over a period of one year are shown in figure 1 and in table 5.

Table 4. Mix proportion of normal, hopper- and grate-ash concrete

Concrete mix

Normal

Hopper ash

Grate ash

Cement (kg/m3)

320

320

320

20 mm gravel (kg/m3)

744

744

744

10 mm gravel (kg/m3)

372

372

372

Natural sand (kg/m3)

744

558

558

Ash (kg/m3)

-

95

60

Water (kg/m3)

200

200

200

Total (kg/m3)

2380

2289

2254

Slump (mm)

85

50

70

Table 5. Strength development with time


Compressive strength

Age (days)

Normal concrete

Hopper-ash concrete

Grate-ash concrete


N/mm2

Percentage

N/mm2

Percentage

N/mm2

Percentage

3

19.9

48.3

21.5

48.5

20.4

46.9

7

30.3

73.5

30.9

69.7

29.9

68.7

28

41.2

100.0

44.3

100.0

43.5

100.0

90

45.4

110.2

50.1

113.1

47.8

109.9

180

45.2

109.7

50.7

114.4

48.4

111.3

365

45.9

111.4

51.5

116.2

51.5

118.4


Figure 1. Strength development as a percentage of 28-day strength

The strengths of both grate- and hopper-ash mixes were comparable with those of the normal mix at all corresponding ages. There was no evidence of any significant additional strength development due to pozzolanic activity. These results confirm the poor reactivity of the ashes and make it most unlikely that bagasse ash in Mauritius will ever be used as pozzolana in concrete.

Bagasse ash as sand replacement in concrete

Characteristics of ash selected

Grate ash is granular requiring no grinding for use as sand, whereas hopper ash usually contains clinkery lumps which must be ground. Also, because grate ash is available in larger quantities than hopper ash, it was decided to use grate ash in this series of investigations.

Table 6. Series 1: Concrete mixes with basalt sand

Mix

Free water/cement ratio

Cement content (kg/m3)

Basalt sand content (kg/m3)

Coarse aggregate content (kg/m3)

1.1

0.41

561

747

912

1.2

0.48

480

800

940

1.3

0.59

390

878

952

1.4

0.67

343

939

939

1.5

0.84

274

1031

915

Table 7. Series 2: Concrete mixes with grate ash

Mix

Free water/cement ratio

Cement content (kg/m3)

Grate ash content (kg/m3)

Coarse aggregate content (kg/m3)

2.1

0.41

561

498

912

2.2

0.48

480

553

940

2.3

0.59

390

585

952

2.4

0.67

343

626

939

2.5

0.84

274

688

915

The ash was oven-dried for 24 hours and then passed through a BS 4.75 nun standard test sieve to remove the coarser particles. Tests were carried out on grate ash and crushed basalt sand to determine their grading, relative density, and water absorption in accordance with BS 812 (6).

The grading of grate ash was coarser (20 per cent passing a 600 um sieve) than that of basalt sand (41 per cent passing a 600 um sieve). The relative density of the ash (2.00) was about two thirds that of basalt sand and the replacement of the sand by the ash was carried out by volume rather than by weight in order not to affect the volume stability of the concrete. The absorption value of the ash (10 ± 2 per cent) was very high compared with that of basalt sand (0.40 ± 0.01 per cent).

Compressive strength tests

Three series of tests were carried out.

Series 1: These tests consisted of five concrete mixes prepared with ordinary Portland cement, basalt sand and 12 nun maximum size basalt aggregate. These mixes were designed in accordance with the United Kingdom Department of the Environment (DOE) (7) design procedure for normal concrete mixes so as to obtain a range of 28-day strengths varying between 20 and 60 N/mm2 and a slump of 30-60 mm. The aggregates used were oven-dried and the actual amount of water added to each of the five mixes was the sum of the free water and the absorption of the aggregates. The cement content of the mixes ranged from 274 kg/m3 to 561 kg/m3 and the corresponding free water/cement ratio varied from 0.84 to 0.41 (see table 6).

Table 8. Series 3: Concrete mixes with grate ash and superplasticizer

Mix

Free water/Cement ratio

cement content (kg/m3)

Grate ash content (kg/m3)

Coarse aggregate content (kg/m3)

Superplasticizer content (kg/m3)

3.1

0.29

561

498

912

17

3.2

0.34

480

533

940

14

3.3

0.41

390

585

952

12

3.4

0.47

343

626

939

10

3.5

0.58

274

688

915

8

Table 9. Compressive strength results of mixes in the three series, 28-day cube strength (N/mm2)

Mix

Series 1 (basalt sand)

Series 2 (grates ash)

Series 3 (grate ash + plasticizer)

1

(0.41)

62

(0.41)

33

(0.29)

70

2

(0.48)

53

(0.48)

28

(0.34)

65

3

(0.59)

42

(0.59)

21

(0.41)

55

4

(0.67)

34

(0.67)

14

(0.47)

45

5

(0.84)

24

(0.84)

8

(0.58)

35

(Figures in brackets indicate the free water/cement ratios)

Table 10. Average initial absorption


Average initial surface absorption (ml/m2/s)

Time (Minutes)

Series 1 (basalt sand)

Series 2 (grate ash)

Series 3 (grate ash + plasticizer)

10

0.150

0.143

0.045

30

0.117

0.073

0.022

60

0.070

0.058

0.015

120

0.067

0.033

0.010

Series 2: In these test specimens, basalt sand in each of the five mixes was totally replaced, by volume, by grate ash (see table 7). The free water/cement ratios were kept the same but the total amount of water for each mix was adjusted to take into account the higher absorption value of grate ash. Nevertheless, a reduced slump of 0-10 mm was obtained.

Series 3: A water-reducing superplasticizer (Melment L10 - a modified condensate product of melamine and formaldehyde) was added to the mixes of series 2. The cement, ash and coarse aggregate contents of series 2 and series 3 mixes were, thus, the same (see table 8). Preliminary tests were carried out to determine the optimum dosage of superplasticizer to be used, that is, the amount of superplasticizer for which no further significant water reduction was observed. This was found to be about 3 per cent by weight of cement, and this was the amount used in each of the five mixes of series 3, causing a 22 per cent reduction in the total amount of water used, but again giving a slump of 0-10 mm. Three 100-mm cubes were prepared from each of the five mixes in each of the three series. The cubes were stored in water and tested in compression at the age of 28 days. The results are shown in table 9 and figure 2.

Shrinkage


Figure 2. Change of strength with change in cement content


Figure 3. Shrinkage - time graph

Shrinkage tests were carried out using standard 300 × 75 × 75 mm prisms, in accordance with BS 1881 (8), on mix 3 of the three series of concrete described earlier. After storing the specimens in water for seven days, they were removed and shrinkage readings were started. Shrinkage was recorded over a period of 49 days during which the specimens were continuously stored in air.

The results (see figure 3) showed that shrinkage increased with age in all the three series but the increase was more marked in grate-ash concrete (with or without superplasticizer) (3).

Although both concrete mixes had the same free water contents, the total water contents in the mixes were significantly different because of the higher absorption of the grate ash. This could have been responsible for the greater drying shrinkage in the ash concrete. The superplasticizer caused only a slight reduction (about 12.5 per cent) in the shrinkage of the ash concrete.

Permeability

Permeability of concrete, that is the measure of the ability of liquids or gases to penetrate the material, is an indirect measure of its durability.

There are various methods of measuring permeability and the one used in this study was the initial surface absorption test (ISAT) described in BS 1881. The test measures the rate of flow of water, under a small constant head, into oven-dried concrete per unit surface area after a stated interval of time from the beginning of the test. The initial surface absorption of concrete decreases with time until no more water is absorbed and the surface has reached saturation.

Tests were carried out on concrete cubes of mix 3 in each of the three series of concrete. Three cubes, at the age of 28 days, were tested in each series. The average initial surface absorption values of the three series are shown in table 10. (3)

Discussion

The variability in the chemical and physical characteristics of bagasse ash is an important consideration in the evaluation of the material for potential use in concrete. Hopper ash and grate ash are fairly similar in chemical composition, whereas fly ash has a very high carbon content. Grate ash is fairly granular, which makes it quite suitable for use as a fine aggregate in concrete. Hopper ash tends to form clinkery lumps which would need grinding or crushing before incorporation in a concrete mix. Fly ash is soft, compressible and highly absorptive, which makes it quite unsuitable for mixing into concrete. Quantities also favour the use of grate ash in concrete in preference to the other ashes.

Although both grate ash and hopper ash satisfy the requirements of BS 3892 for loss-on-ignition, silica, magnesia and sulphuric anhydride contents, they fail to meet the specification for water requirement and pozzolanic activity index. Moreover, the ashes require grinding before they can comply with the fineness requirements.

There appears to be no adverse effect on the strength or strength development of concrete incorporating bagasse ash over a period of up to one year. Further tests are required to assess the longer-term effects, in particular the shrinkage and durability properties.

Grate-ash concrete has significantly lower strength than the corresponding basalt sand concrete. The 28-day strength of the ash concrete varies from about half to one third of the equivalent control mix. However, the addition of a superplasticizer to the grate-ash concrete causes a considerable increase in strength. With the latter concrete, strengths about three times those of unplasticized ash concrete and about 35 per cent higher than those of basalt-sand concrete are obtained. Also, the plasticized grate-ash concrete appears to reach a strength limit at about 70 N/mm2.

In the fresh state, the ash-concrete mixes show lower workability. The slump decreases from 30-60 mm in the basalt-sand concrete to 0-10 mm in the grate-ash concrete (with or without superplasticizer). This is due to the coarse grading of the ash and to the rough angular nature of the grate-ash particles which increase aggregate friction and interlock. This results in poor cohesion of the fresh concrete, the workability of which hardly improves even with further addition of water.

Conclusions

Bagasse ash in Mauritius shows too poor reactivity with Portland cement to make it an effective pozzolana in concrete.

Bagasse ash can be effectively used as a fine aggregate in concrete to produce a range of compressive strengths up to about 70 N/mm2. However, generally reduced workability is observed in the fresh concrete, due to the coarse grading and angular texture of the ash particles.

The shrinkage of bagasse-ash concrete is not excessively higher than that of normal concrete. However more data are required to assess this property of the concrete.

The initial surface absorption characteristics of bagasse-ash concrete do not give any indication of low durability in comparison with basalt-sand concrete.

The addition of a superplasticizer significantly reduces the initial absorption capacity of bagasse-ash concrete.

Acknowledgement

The invaluable contribution of Dr. R.K. Dhir, Reader in Civil Engineering, Department of Civil Engineering, University of Dundee, in connection with this project is gratefully acknowledged.

References

1. Mohamedbhai, G.T.G., and Baguant, B.K., “Possibility of using bagasse ash and other furnace residues as partial substitute for cement in Mauritius”, Revue agricole et sucri de l'Ile Maurice, vol. 64, no. 3, September-December 1985.

2. Li Pin Yuen, L.Y.N.G., “Availability of bagasse ash and its characteristics in Mauritius”, B. Tech. final year project (Reduit, University of Mauritius, 1986).

3. Kim Currun, G.S., “The effects of plasticizer on bagasse ash concrete”, B. Tech. final year project (Reduit, University of Mauritius, 1988).

4. British Standard, BS 3892: 1982, Pulverised fuel ash.

5. Choollun, V.K., “Pozzolanic activity of bagasse ash and a laterite”, B. Tech. final year project (University of Mauritius, 1988).

6. British Standard, BS 812: 1975, Methods for sampling and testing of mineral aggregates, sands and fillers.

7. Department of the Environment, Design of Normal Concrete Mixes (Garston, Building Research Establishment, Transport and Road Research Laboratory, 1975).

8. British Standard, BS 1881: 1990. Methods of testing concrete.

9. Uteene, A.F., “Investigation into the properties of bagasse ash cement”, B. Tech. final year project (Reduit, University of Mauritius, 1980).

10. Cementia Engineering and Consulting Ltd., A Report on Tests Carried out on Bagasse Ash from Mauritius, 1978.

11. Paturau, J.M., By-products of the Cane Sugar Industry. An Introduction to Their Industrial Utilisation, Sugar Series, 3 (Elsevier Scientific Publishing Company).

Malawi: The use of rice-husk and bagasse ash as building material*

* By Uffe Leinum, Architect/planner, building materials and low-cost

In Malawi, about 45,000 tons of rice are milled every season but only a small proportion of the remaining husks is used by some of the large industrial concerns as fuel energy, and, thereafter, the rice-husk ash is usually discarded as a waste product. It is already common knowledge that rice-husk ash contains the highest proportion of silica compared with that derived from any other ashed natural plant material, and it is thus, an immediately available asset and under-developed source of wealth.

Approximately 8500 tons of high-silica rice husks are obtainable each year from three ricemills, namely Blantyre, processing 13,000 tons of milled rice, Karonga, 6000 tons, and Nkhotakota, a further 6000 tons. Yet this potential source, for use in building-materials industry, has received very little attention within the economy. In Malawi, a continuing study of this naturally occurring waste material has been carried out over several years, and a low-cost plant capable of manufacturing sodium silicate (waterglass) solution from rice-husk ash was designed and built in the laboratory. One of the prototype installations is at present being used in conjunction with work on a large low-cost housing project financially supported by the Danchurchaid and the German Development Assistance Association for Social Housing (DESWOS). Sodium silicate (waterglass) solution can be shown to have a considerable number of advantages when applied to building materials, and may eventually help to increase durability and lower the costs of low-cost housing construction throughout the country.

Cement

Cement has proved to be a very expensive commodity for use in many recent low-cost housing programmes in Malawi, 50 kg is priced at MK 29.00 (1992 price). It is estimated that 1800 tons of ash could be produced annually in relation to the present milling capacity of approximately 45,000 tons of rice, as 1 ton of rice yields about 40 kg of ash as a by-product. However, because of the limited quantities which would be readily available, it was decided that any ash that was produced should be used for the manufacture of sodium-silicate (waterglass) solution rather than dealt with as an extender for cement, owing to the fact that the former product could have a much more extensive application in the construction industry.

Waterproofing liquid

liquid coating of sodium-silicate (waterglass) solution dries into a hard vitreous film with a “varnished” type finish that is both protective of the outward appearance and water-resistant. An application to the surface of porous concrete, burnt bricks, compressed soil and sun-dried building blocks produces an additional hardness and renders the material waterproof. In addition, this material is suitable for preserving thatched roofs and also gives considerable protection against fire in existing buildings.

Bricks

It has proved practicable to mix rice husks with clay in order to produce strong and more resistant burnt bricks or blocks, and bricks and blocks containing this mixture have been found to be very suitable for use in the construction of foundations and floors. As the quality of clay differs considerably from place to place, a test of the mixture should be carried out at the specific locality prior to manufacture, although reasonable results have usually been obtained when incorporating 10 per cent rice husk by volume. Both burnt bricks and sun-dried blocks are easily manufactured locally, but it must always be borne in mind that a considerable amount of firewood is used for firing - in fact, approximately 1 cubic metre for every 1000 bricks produced, which puts an additional stress on the economy of a rural community, as wood is inevitably used extensively for cooking. Because of the urgent need to conserve these finite resources, the use of burnt bricks is recommended mainly for foundation works and where the external walls tend to suffer from extreme exposure to rain. However, they may be considered in small quantities for decorative purposes, such as below windows, a detail which has been incorporated in existing designs for rural low-cost houses recently built in Malawi.


Figure 1. When applied as a paint coat, the sodium-silicate sludge has been found to he extremely useful for foundation plinths (Habitat)

Paint and adhesive

A sodium-silicate (waterglass) solution can be used as a protective coating or paint for solid walls, with the addition of extenders, such as limestone, clay or iron oxide. The decorative finish achieved by this process has proved to be considerably cheaper than any surface treatments obtained by using imported paints or waterproofing. The liquid also has the properties of a general adhesive and can be used as a gluing agent for metal, wood and concrete products, such as roofing tiles, as well as being capable of fixing various glass and ceramic materials.

Varnish

Where the groundwater table is very high, the application of a sodium-silicate (waterglass) solution on bricks or concrete will quite satisfactorily substitute for a waterproof membrane and inhibit rising damp. At the same time, it provides a decorative surface finish which is both hard-wearing and easy to keep clean.

Adobe plaster for external walls

As a result of tests, it has been proved that the addition of between 0.5 per cent and 1 per cent sodium-silicate (waterglass) solution in the mixing water used for the preparation of mud plaster produces a hard surface finish, but, in order to make the facing material totally resistant to driving rain, a further coat of solution is required. This also acts as a good undercoat, prior to decoration with a “home-made” product - calcium stearate/cement paint.

Adobe blocks and stabilized sun-dried block walls

For centuries, soil has been used as a basic material for the construction of walls throughout the civilized world, and these will often last indefinitely, provided they receive proper maintenance and preservation. In rural areas of Malawi, the use of adobe blocks for walls is quite common, and these structures, built out of soil in the shape of sun-dried building blocks, have adequate strength under any conditions and can be very durable, in spite of rain and/or a humid climate, if supported on a good foundation. An additional design factor that can be incorporated is the provision of a generous overhang to the roof. In order to withstand a humid atmosphere, an economical means of giving protection to the sun-dried block is to stabilize the soil content with a diluted sodium-silicate (waterglass) solution. This process enables an unskilled labour force to cast small and comparatively cheap sun-dried building components, without the conventional use of either cement or lime additives, both of which are expensive to purchase. The compressive strength of each block can be doubled by the addition of 0.5 per cent sodium-silicate (waterglass) solution to the mixing water. Walls can be either plastered with mud plaster which has had incorporated between 0.5 and 1 per cent sodium-silicate solution as a stabilizer, and/or then decorated by means of a protective coating consisting of calcium stearate/cement paint combined with a sodium-silicate (waterglass) solution.


Figure 2. Application of waterproof cement paint on adobe wall (Chikwawa, Malawi).

The recommended procedure to be adopted prior to decoration is as follows:

(a) One priming coat consisting of sodium-silicate (water-glass) solution to cover the mud-plaster surface;

(b) One finishing coat (coloured if required) of calcium stearate/cement paint. The cement paint is rendered much more durable if it is protected with further application of sodium silicate.

Calcium stearate/cement paint

Although materials such as waterproof paint are available for use on mud-brick/block walls, they are usually produced with imported elements. By using materials which are readily at hand in the locality and then made up in accordance with the formula developed by Uffe Leinum, consultant architect to the Christian Service Committee of the Churches in Malawi, overall costs can be greatly reduced. A programme consisting of the construction of five demonstration houses was undertaken, with a recommendation for on-site manufacture of waterproof cement paint. The water-repellent paint contains the following essential ingredients: Portland cement, hydrated lime, calcium stearate (a fat coated with lime) and rice-husk ash.

Calculations relating to the approximate cost of 10 kg of paint with an optimum covering capacity of 20 square metres are as follows:

A mixture of home-made waterproof paint weighing 1 kg would be expected to cover 2 square metres of wall surface at a nominal thickness of 0.5 mm. However, if an initial application of sodium-silicate (waterglass) solution is used as a priming coat, coverage of up to 4 square metres of wall surface should be achieved. A comparison with the cost of equivalent commercial products will show a net saving of 80 per cent even when a relatively expensive pigment is incorporated as a colouring agent.

Item

Amount (kg)

Cost in MK

Portland cement

7.5

4.35

Hydrated lime

1.5

0.54

Calcium stearate

0.5

0.20

Silica ash

0.5

0.00

Firewood

0.5

0.50

Red oxide (colouring agent)

1.0

3.50

Total cost


9.09


Estimated cost of equipment (oil drum, scales and hand tools)


450.00


Relative expenditure per square metre excluding equipment


MK

“Home-made” red paint


0.45

Red PVA paint


2.54

“Home-made” grey paint


0.28

grey PVA paint


2.19

White cement


4.90

Sugarcane (bagasse) as a waterproofing agent

Adjacent to one of the selected development areas in the Southern Region, the Sugar Corporation of Malawi (SUCOMA) has a large plant for the production of refined sugar and sugar by-products. Investigations have already confirmed that the wax obtained from sugarcane has excellent waterproofing properties and, if prepared, is suitable for external application to walls. Molasses is known to be an efficient binder for clay and soil. It also has a comparatively long-lasting waterproofing effect on these products, as well as endowing the clay/molasses mixture with additional compressive strength. Elsewhere, the sugarcane crop is already being converted into a wide range of products, from monosodium glutamate for the food industry to hardboard for furniture; but the possible diversification of sugarcane waste into an increased supply of bagasse (the cane fibre), which remains after the sugar-extraction process has been completed, appears to be particularly advantageous.

Given the escalating costs of fuel and its scarcity, using any local asset, such as bagasse, is becoming increasingly relevant and important. The ash produced after burning the bagasse has a comparatively high silica content, although somewhat less than rice-husk ash, but it is equally suitable and can be used quite economically in producing sodium-silicate (waterglass) solution for general use in the building industry. Sugar production is increasing to an extent that an estimated 480,000 tons of bagasse might soon become available. This amount would yield between 16,800 and 24,000 tons of ash per annum after it had been used as fuel/energy.


Figure 3. Storage of bagasse for fuel (Sugoma, Malawi)


Figure 4. Diagram of sodium-silicate plant

Production of sodium silicate (waterglass)

Production of sodium-silicate (waterglass) solution is at present being carried out at a materials-production industries' centre attached to a large low-cost rural housing programme in the Chikwawa district of Malawi, where the basic raw materials are waste rice-husk ash and bagasse. Most of the rice-husk ash for the project has been obtained from a large industrial plant, after it had been used with other combustible materials, such as wood and cotton waste, for fuel/energy. This specific mixture of substances prior to firing has resulted, in the presence of black carbon, which settles as “sludge” after the manufacturing process is completed to provide an extremely useful material for applying as a paint coat to brick foundation plinths. It is a completely satisfactory and cheap alternative to the use of cement rendering or imported bituminous paint.

The whole operation maximizes the use of a surplus material to advantage, as well as eliminating all traces of waste, although if pure, non-contaminated rice-husk ash is used, the “sludge” left behind has proved to be minimal. Unfortunately, caustic soda is still required for the manufacturing process - an imported raw material costing currently about MK 6.50 per kg (1992 price).

In order to produce a marketable quality of sodium-silicate (waterglass) solution, the various ingredients are introduced into the reactor vessel (drum): caustic soda, rice-husk ash as industrial waste, and water, in predetermined and controlled proportions. The production time required for obtaining 200 litres of material from one reactor vessel, which includes preparation and lighting up the boiler, cooking and cooling periods, complete with tapping off, is estimated at approximately 24 hours. However, a small-scale plant combining several production vessels connected to one boiler, could yield up to 1000 litres in a day (see figure 4).

Basic design for processing plant

Either rice-husk or bagasse ash is fed into the reactor vessel, where steam from the boiler can be led into the container. After the correct amount of caustic soda and water has been added to the ash deposit, the reactor vessel is subjected to the boiling process for approximately one hour. The resultant liquid can then be cooled, filtered and placed in containers ready for use on site.

Estimated manufacturing cost of filtered waterglass

Per 200 litre drum

Malawi Kwacha

1. Caustic soda

77.50

2. Fibrewood

7.50

3. Labour - two men

5.00

4. Water - 250 litres

0.40

5. Transport 25 per cent

24.86

6. Depreciation of machinery 10 per cent

9.04


Total manufacturing costs

124.30


7. Profit at 15 per cent

18.65


Total production costs

142.95

Therefore, the estimated costs for sodium-silicate (waterglass) solution will be:

Volume of drum (litre)

MK

200

142.95

5

7.88

1

1.58


Figure 5. Sodium-silicate (waterglass) plant (Chikwawa, Malawi). Patent application has been filed

These calculations are based on the use of a single production vessel of 200 litres capacity and, therefore, present the worst example financially, as normally a multiple unit would be engaged in this operation. Production levels can then quite easily be brought up to five times the former amount, at the same fixed costs and workforce level. The paint coverage that can be anticipated for concrete floors, sun-dried blocks or burnt brick walls is about 14 square metres per litre, but a two-coat application is recommended for all sun-dried block-work, at an estimated cost of MK 0.10 per square metre.

Safety factors

1. When burning rice husks in large quantities, it is very difficult to determine if combustion is occurring at the centre of the pile. Because of this particular factor, a safety fence should be erected around the bonfire site, in order to permanently restrict access by children playing in the area.

2. Rubber gloves should always be worn for weighing out the caustic soda, as any contact with the skin is harmful.

3. The reactor vessel must be fitted with a lid, as, during the initial 20 minutes, the substances are alkaline and should not be allowed contact with the eyes. When the final stages of the manufacturing process have been reached, the mixture is only as caustic as lime. Soap and water should be used for cleaning skin surfaces.


Figure 6. Boiling calcium strearate for paint (Chikwawa, Malawi).


Figure 7. Reactor vessel


Figure 8. Boiler unit


Figure 9. Construction of a chimney stack/boiler roof (Georgetown, Guyana).


Figure 10. Steam heater and boiler unit under construction (Georgetown, Guyana).

Note

The sodium-silicate solutions described in this report are inorganic, non-inflammable, non-explosive, non-toxic and are not regarded as hazardous chemical substances. It is partly the relatively low environmental risks, which are already associated with soluble silicates, that account for their ever-increasing world-wide application.

Technology Profile No. 1: Mini-cement production*

* This technology has been developed by Regininl Research Laboratory (RRL), Jorhat, India.

A mini-cement plant is one the total installed capacity of which is not greater than 200 tons per day, including one or more kilns on one site. The case for developing mini-cement plants in India has arisen from the high cost of installing viably-sized conventional cement plants, the large number of small deposits of limestone dispersed at various parts of the country and the versatility of mini-cement plants in matching the limited availability of power, water and other inputs. By meeting the demands of local captive markets, mini-cement plants also provide for participation of local small entrepreneurs and, thus, help in building up local economies.

Major advantages of mini-cement plants are:

- Less capital-intensive;
- Short gestation period;
- Quick return of investment;
- Utilization of small deposits of limestone;
- Low transport costs, as product can be consumed locally;
- Attractive to young entrepreneurs with limited financial resources.

A mini-cement plant of capacity 20-10.0 tons per day, based on vertical-shaft-kiln (VSK) technology, has been developed by Regional Research Laboratory (RRL), Jorhat, India. The technology package is licensed through the National Research Development Corporation of India, and the plant is set up by a number of consultants, appointed for the purpose, on a turn-key basis. The product conforms to IS: 269 - 1976, the specification for ordinary Portland cement. Mini-cement plants, with technical know-how from RRL and licence from the National Research Development Corporation, New Delhi, have started commercial production successfully in several parts of the country. Complete detailed engineering reports can be offered for a 25 ton/day VSK plant. Basic design and process know-how is available from the RRL, Jorhat.

Figures 1 and 2 show outside views of two mini-cement plants in India.


Figure 1. Prag Shiva mini-cement plant in Guwahati Assam, India.


Figure 2. Bhagyanagar mini-cement plant in Nandigram, Hyderabad, India.

Production processes

Some of the processes on which mini-cement production could be based, are:

(a) VSK;
(b) Rotary kiln;
(c) Lurgi sinter bed;
(d) Belt kiln.

Processes 1 and 2 are established as commercially viable, while processes 3 and 4 are of theoretical interest. The development of the VSK process for cement production can be traced back to 1824, At that time, this process did not receive much attention, as the operations were highly labour-intensive, the clinkers produced were of non-uniform quality, and the overall economics were unfavourable. However, with the development of the pan-type nodulizer, which ensures a uniform-quality product, the situation has radically changed.

The kiln consists of a cylindrical shell with a conical sintering zone lined with refractory bricks. A rotary discharge grate at the bottom of the shell coupled with its drives and air sealing device takes care of the uniform rate of discharge of clinker. The green nodules thus move down gradually and encounter hot flue gases. In the sintering zone, nodules are calcined and oxides recombine to form the essential cement phases. The clinkers thus formed move further downward, encounter incoming air and become cooled. Finally the clinkers exit through the rotary discharge grate and reciprocating discharge gate. The RRL shaft kiln is highly efficient in calorie consumption (1030±50 kCal/kg of clinker).

The cement clinkers are then pulverized after admixing with the required amount of gypsum in a cement mill to a minimum fineness of 2250 sq cm/g.

Figure 3 shows a view of a VSK designed by RRL, and figure 4 shows another VSK designed by Cement Research Institute (CRI), India, for a 20 ton/day capacity plant.

The VSK process of cement production which is a semi-dry process consists of the following major operational steps:

(a) Primary crushing of limestone, clay and other additives, if any, to a fineness of about 12-15 mm.

(b) Pulverizing of the raw meal (stated in 1 above) and coke breeze to a fineness of 90 per cent below 170 mesh BSS.

(c) Blending of the pulverized material in suitable proportions, to ensure desired uniform-quality product.

(d) Preparation of nodules, by the addition of water to the raw meal in the nodulizer.

(e) Feeding of nodules into the VSK wherein the nodules undergo drying, calcining, sintering and cooling, resulting in the formation of cement clinkers.

(f) Grinding of clinker and blending of the ground clinker with gypsum, to obtain quality Portland cement.

Figure 5 shows a nodulizer of a VSK mini-cement plant and figure 6 shows a raw material balancing and grinding section.


Figure 3. View of a VSK


Figure 4. General arrangement of CRI type VSK for Visvakarma mini-cement plants.

(This figure is reproduced from Monograph on Appropriate Industrial Technology, Appropriate Industrial Technology for Construction and Building Materials, No. 12 (New York, United Nations Industrial Development Organization, 1980), p. 66, fig. 1.)


Figure 5. Nodulizer of VSK mini-cement plant. Pioneer Cement Plant, Ltd. Hyderabad, Andhra Pradesh, India.

The principal equipment in a VSK process for a typical plant of 25 tons per day capacity is given in table 1.

Table 1. List of equipment for a 25 ton/day VSK mini-cement plant

Equipment

Quality

Capacity

Limestone crusher

1

6 ton/h

Limestone conveyor

1

6 ton/h

Hammer mill

1

6 ton/h

Belt conveyor

1

6 ton/h

Limestone elevator

1

3 ton/h

Coke-breeze, clay and additive elevator

1

2 ton/h

Table feeders (1 each)

4

(a) 2 ton/h



(b) 120 kg/h



(c) 300 kg/h



(d)100 kg/h

Belt conveyor for raw material

1

4 ton/h

Raw material elevator

1

4 ton/h

Raw material grinding mill

1

3 ton/h

Screw conveyor

1

3 ton/h

Raw meal elevator

1

4 ton/h

Homogenizer

2

10 ton/h

Raw meal feeder

1

3 ton/h

Nodulizer

1

3 ton/h

Nodule screen

1

3 ton/h

Nodule elevator

1

3 ton/h

Vertical shaft kiln

1

25 ton/day

Clinker elevator

1

4 ton/day

Clinker and gypsum elevator

1

4 ton/day

Gypsum feeder

1

50 to 150 kg/h

Clinker feeder

1

1-4 ton/h

Cement mill

1

2 ton/h

Cement elevator

1

4 ton/h

Screw feeder

1

4 ton/h

Weighing machine

1

0-100 kg

A process flow diagram of a VSK mini-cement plant is shown in figure 7 and a typical layout of 50/100 ton/day-capacity VSK cement plant is shown in figure 8.

Raw materials, including fuel

Limestone:



CaO

45 per cent minimum


SiO2

12 per cent maximum


Al2O3

4 per cent maximum


Fe2O3

2-4 per cent maximum


MgO

2.0 per cent maximum

Clay/fly-ash/shale:



SiO2

60-66 per cent


Al2O3

12-18 per cent


Fe2O3

5-9 per cent


Plasticity

Medium plastic

Coke breeze (fuel):



Calorific value

6000 kCal/kg minimum


Ash

30 per cent maximum


Volatile matter

8 per cent maximum

Gypsum:



CaSO4 2H2O

80 per cent minimum

The typical consumption pattern of these raw materials per ton of product is as follows:

(a) Limestone

1.36 T

(b) Clay

0.17 T

(c) Coke-breeze

0.25 T

(d) Gypsum

0.04 T

Utilities

Consumption of utilities per ton of product is as follows:

(a) Power

About 135 kWh

(b) Water

About one cubic metre

Product specifications

Physical


Specific surface:

2250 cm2/g minimum

Setting time:



(a) Minimum

30 minutes


(b) Maximum

600 minutes

Soundness:



(a) Le Chatelier

10 mm maximum


(b) Autoclave

0.8 per cent maximum

Compressive strength (kg/cm2):



(a) 3 days

160 minimum


(b) 7 days

220 minimum


(c) 28 days

330 minimum

Chemical



Loss-of-ignition

5.00 per cent maximum


Insoluble residue

4.00 per cent maximum


SO3 content

2.75 max., when C3A <7 per cent 3.00, when C3A >7 per cent


MgO content

6.00 maximum


Alumina ratio

0.66 minimum


Lime saturation factor

Between 0.66 and 1.02

Special requirements:



(a) C3A

less than 7 per cent


(b) SO3

2.75 per cent maximum

Characteristics of cement IS: 269-1976 limits

Specific surface area:



3100-3300 cm2/g

Minimum 2250 cm2/g

Setting time (min.):



Initial 106-130 minutes

Not less than 30 min.


Final 220-260 minutes

Not more than 600 min.

Compressive strength:



3 days 190-220 kg/cm2

Minimum 160 kg/cm2


7 days 280-310 kg/cm2

Minimum 220 kg/cm2


28 days 405-450 kg/cm2

Minimum 330 kg/cm2

Le Chatelier expansion:



1-2 mm

10 mm maximum

Autoclave test:



0.05-0.2 per cent

0.8 per cent maximum


Figure 6. Raw material balancing and grinding section. Bhagyanagar Cement Plant Ltd., Nandigram, Hyderabad, Andhra Pradesh, India.


Labour


50 ton/day

100 ton/day

Skilled

45

50

Unskilled

75

80

Designation



Managing director

1

1

Works manager

1

1

Shift-in-charge

4

4

Plant operator

8

8

Nodulizer operator

8

8

Raw mill operator

4

4

Cement mill operator

4

4

Senior chemist

1

1

Junior chemist

3

3

Storekeeper-cum-accountant

1

1

Electrician

2

2

Mechanic fitter

2

2

Peon

2

2

Driver

-

2

Guards

4

4

Helper

-

3

Unskilled labour

35

35

Unskilled contract labour

40

45

Total

120

130


Figure 7. Process flow diagram of a VSK mini-cement plant.


Figure 8. Typical layout of a 50/100 ton/day VSK cement plant.

Technology Profile No. 2: Production of lime*

* This technology has been developed by the Central Building Research Institute (CBRI), Roorkee, India

Production of lime is a simple process in which limestone is calcined at elevated temperatures. Theoretically, 900°C is a sufficiently high temperature to carry out the process. However, in practice, it has been found necessary to maintain the temperature at a much higher level than this to complete the chemical reaction. In the absence of adequate temperature over sufficient time, the lime produced will be of inferior quality: it might be underburnt or overburnt. The success of the process, therefore, lies in maintaining proper conditions for calcination.

Kiln design

Lime kilns of various designs have been used. However, vertical-shaft types are thermally the most efficient. Consequently, their use results in savings in fuel. In India, different types of kiln have been employed through the ages, but investigations carried out at the Central Building Research Institute (CBRI) have shown that most of the traditional designs produce an inferior quality of product with a higher consumption of fuel. CBRI, in recent years, has developed lime kilns of several types, which are being offered for exploitation by the industry. The smallest kiln has about a 5 ton/day capacity below which hardly any efficiency can be expected. Figure 1 shows a lime kiln developed by CBRI.

Some salient features of the kilns

(a) The kilns are of brick or stone masonry;

(b) The kiln designs ensure smooth running and periodic withdrawal of lime;

(c) The kilns lend themselves to a fair degree of instrumentation, if required;

(d) They work on natural draft and have an arrangement for their control;

(e) They work continuously but can be adapted for day working only;

(f) They are thermally efficient, and heat losses are minimal;

(g) They produce a uniform quality lime, by avoiding overburning or underburning;

(h) Under standard working conditions, these kilns produce very little core or unburnt material;

(i) They can be operated by trained unskilled labour;

(j) Contamination of lime with fuel is minimal.

Raw material and chemical composition

The impurities in limestone are primarily SiO2, Al2O3 and Fe2O3. They are non-volatile in nature and remain as contaminants in the lime produced. Limestone generally contains some MgCO3 also. Calcite stone usually contains CaCO3 exceeding 95 per cent, and dolomitic stone has an MgCO3 content of 35-40 per cent. In the burning operation, the carbonates are converted to their corresponding oxides. Dolomitic lime is used largely in refractories where a high MgO content is essential.

The principal reactions involved in the calcination of calcitic and dolomitic limestones are:

CaCO3 ® CaO + CO2
(Calcite)

CaCO3 MgCO3 ® CaO.MgO. + 2CO2
(Dolomite)

The average dissociation temperatures for the above two types of limestone at atmospheric pressure are 900° and 725°C respectively. Certain materials, such as sulphur dioxide, present in the stone or fuel tend to react with lime and oxygen to form CaSO4 which is unstable at high temperatures. Al2O3 and SiO2 combine with CaO and MgO to form various silicates and aluminates at very high temperatures. These compounds are water-insoluble and are undesirable, as they decrease oxide values and also coat the lime particles and so reduce its reactivity.

The reaction of quicklime is also influenced by high operating temperatures and retention times. With an increase in temperature, the reaction rate increases, and, consequently, the reaction time decreases. However, the maintenance of high temperatures beyond an optimum limit causes overburning of the lime.

Production process

Limestone is broken to a size of about 75 to 125 mm, and coal to half this size. These are mixed in mixers near the kiln. To initiate fire, a layer of firewood is first laid. Above this, some steam coal is spread. Thereafter, the kiln is filled with previously mixed coal and limestone. Generally, the coal requirement is 12-15 per cent that of limestone, but this varies, depending upon the type of limestone and the quality of coal. Fire is introduced from the bottom and rises. Charging and discharging are so adjusted that the firing zone is maintained in the middle of the kiln.


Figure 1. Lime kiln.


Figure 2. Production process of quicklime.

Scheme for the production of quicklime

(a) The manufacturing process is shown in a flow chart in figure 2.

(b) Production scale

(i) Rate of production

10 tons per day of three shifts,
3000 tons per year of 300 working days

(ii) Inputs

Land

3000 sq m

Building

20 sq m

Shed

200 sq m

Machinery and

1 lime kiln

equipment

1 feeding device

Electric power

50,000 kWh per year

Water

1000 kl per year

Coal (steam)

900 tons per year

Limestone

6000 tons per year

Labour

1 manager


3 operators


4 skilled labourers


2700 work days labour


2 guards

Technology Profile No. 3: Hydrated lime*

* This technology has been developed by the Central Building Research Institute (CBRI), Roorkee, India.

Lime produced by the calcination of limestone in a kiln is known as quicklime. Before using it in construction, it needs to be hydrated. Chemically the process is:

CaO + H2O ® Ca(OH)2

In this process, if any magnesia is present, it may also be hydrated partially or fully as:

MgO + H2O ® Mg(OH)2

Although the conversion of quicklime into hydrated lime appears to be a simple process, the reaction is governed by numerous factors which affect the properties of the final product. It is, therefore, desirable that the manufacture of hydrated lime is carried out in a factory under controlled conditions, rather than in the field where hardly any control can be effected.

Process of hydration

Lime samples hydrated in the machine during trial runs were evaluated for their physical and chemical properties.

The chemical properties of hydrated lime are shown in table 1.

Table 1. Chemical properties of hydrated lime

Chemical constituents

Percentage composition

SiO2

2.5 - 4.6

Al2O3

0.7 - 5.5

CaO

82.0 - 96.3

MgO

0.56 - 5.86

CO2

1.65 - 1.89

Loss-on-ignition (LOI)

23.45 - 25.75

Some of the physical properties of hydrated lime are shown in table 2.

Table 2. Physical properties of hydrated lime

Constituents

Properties

Residue on 2.36 mm sieve

0.0

Residue on 850 micron sieve

1.2 - 1.46 per cent

Residue on 300 micron sieve

1.6 - 3.97 per cent

Residue on 212 micron sieve

3.64 - 3.80 per cent

Soundness (Le Chatelier)

0.5 - 1.0 mm

Workability

40 - 44 per cent

The above results show that the hydrator can be used for producing class B and C limes.

Advantages of the use of hydrated lime

The use of hydrated lime has the following advantages.

(a) Properly manufactured and carefully packed hydrated lime possesses definite and uniform properties;

(b) There is hardly any deterioration even after long storage, if the material is properly packed;

(c) It is easy to handle, store and transport and can be used without any further processing at the site;

(d) It can be incorporated in mortars in exact proportions;

(e) The plasticity of lime putty can be improved, if so desired, by soaking it in water.


Figure 1. Lime hydrator.

Hydrated lime, possessing definite advantages, is finding increasing demand in construction and various other industries, such as paper, sugar, leather tannery and agriculture, among others. That is why, there is always a considerable demand for a suitable indigenous machine for hydrating quicklime.

Lime hydrating machine

Based on extensive research work carried out at the Central Building Research Institute (CBRI), Roorkee, a lime hydrating machine has been developed, which is commercially produced in two different sites. Special features of the CBRI lime hydrating machine are:

(a) The machine has three tiers with consequent saving of space;

(b) Each of the three tiers of the machine has a well-defined function:

(i) The first tier acts as mixer;

(ii) The main process of hydration takes place in the second tier;

(iii) In the third one the hydration process is completed and the final product is dried.

(c) The design of the machine has been kept flexible so that movement of materials and, consequently, the contact period for the reaction between lime and water can be adjusted to achieve complete hydration;

(d) Steam generated during hydration is used for pre-heating the water used for hydration and thereby speed of the reaction is accelerated;

(e) The smaller model is transportable as one unit and, hence, it is possible to carry it to the site of use;

(f) Lime obtained is in an almost dry state;

(g) The machine is suitable for high-calcium and soft-burnt dolomite lime;

(h) Machines capable of hydrating about three, five and ten tons of quicklime per shift of eight hours have been designed, fabricated and tested in the laboratory. They have also been commissioned in the field.

Scheme for the production of hydrated lime

The manufacturing process is shown in the flow chart (see figure 2).

The production scale is as follows:

Rate of production

22 tons per day of 2 shifts
6600 tons per year of 300 working days

Land and building



sq m


Land

2000


Building

20


Shed

250



Machinery and equipment





Crusher for quick lime

1


Lime hydrator

1


Bucket elevator

1


Vibrating screen

1


Storage Bins

2


Belt conveyor for quick lime

1



Raw materials





Quicklime

6000 tons per year



Utilities





Electric power

100,000 kWh per year


Water

10,000 kl per year



Workforce requirement





Plant supervisor-cum-manager

1


Chemist-cum-analyst

1


Mechanic-cum-operator

6


Electrician-cum-mechanic

2


Storekeeper

1


Clerk-cum-typist

1


Skilled labour

12

Energy consumption for a day's production*

Machinery/equipment

Energy


Electrical

Thermal

Crusher, lime hydrator, bucket elevator, vibrating
Screen, belt conveyor




334 kWh


* Requirement for 22 tons of hydrated lime


Figure 2. Production process of hydrated lime.

Publications review

Published by UNCHS (Habitat)

Bibliography on Passive Solar Systems in Buildings

Nearly half of the world's commercial energy is consumed in buildings in order to provide indoor comfort. However, the natural environment can be used to reduce energy requirements in buildings by making use of passive energy systems which can contribute to indoor comfort. In order to promote standards and technologies for the provision of economically efficient infrastructure, the United Nations Centre for Human Settlements (Habitat) has prepared this bibliography to provide professionals, such as designers, architects and engineers concerned with construction and rehabilitation of buildings, with information on passive solar systems and allied subjects from the available literature, to encourage them to make maximum use of energy-conserving devices and systems.

The bibliography lists selected references on passive solar systems in buildings. It includes information for those concerned with the reconstruction and retrofitting of buildings, especially in developing countries. The bibliography covers the following parts: (a) general reading list; (b) bibliography by topics, covering passive solar technology, heating, cooling, building materials and construction techniques and solar radiation and climate; (c) annotated bibliography; and (d) descriptor index to part (b). The list of literature covered is in the form of books, conference proceedings, journals, reports, papers and articles. There is also an annex which lists references of specialist publishers.


68 pp. HS/173/89: ISBN 92-1-131094-8

Corrosion Damage to Concrete Structures in Western Asia

With the present-day understanding of the problem, it is possible to prevent corrosion by a proper choice of materials admixtures and by following sound construction practices that will produce concrete of good quality. It is also possible to prevent corrosion by providing, where the importance of the structure justifies, cathodic protection which reverses the electrochemical process that causes corrosion.

This monograph explains the phenomenon of corrosion and deals with the repair of structures damaged by corrosion, corrosion-monitoring techniques, and the steps to be taken to prevent corrosion.


33 pp. HS/204/90E: ISBN 92-1-131122-5

Executive Summary of the Global Report on Human Settlements

The Global Report on Human Settlements was prepared by UNCHS (Habitat) and published by Oxford University Press in 1987. The Global Report was prepared under the General Assembly's mandate and documents world-wide settlements conditions and trends so as to assist governments in improving their settlements policies, plans and programmes. It is dedicated to those who, in spite of limited means and the financial and physical odds with which they are confronted, are at this moment building or improving their own habitat, to those whose wisdom and inspiration prompted the world community to embrace the concept of human settlements, and to the planners and builders who believe that the world can become a better place to live in.

The executive summary highlights the main issues and findings of the Global Report on Human Settlements and is considered as a synthesis of the main topics covered in the main report.


45 pp. HS/129/88E: ISBN 92-1-131055-5

Energy for Building - Improving Energy Efficiency in Construction and in the Production of Building Materials in Developing Countries

The link between energy production and use and the local and global environment is causing increasing concern world-wide. There is also a growing demand for environmental impact assessments of all building projects which should include consideration of embodied energy.

This publication examines the question of energy efficiency in building materials from the point of view of producers of building materials, building designers and builders. Producers will want to know how they can change their production processes so as to reduce energy consumption (and cost), how energy consumption can be reduced by changing the raw materials and the product mix specification used, and how energy costs can be reduced by changing to different energy sources.

Producers and builders will also want to know what techniques are available for application now, and what techniques are currently under development or might become available in the near future. The publication is also intended to be of use to policy-makers in the field of housing and construction who will be interested in the conclusions of the report about the most effective actions to be taken by each group.


104 pp. HS/250/91E: ISBN 92-1-131174-8

Events

Expert Group Meeting on Appropriate, Intermediate, Cost-effective Building Materials, Technologies and Transfer Mechanisms for Housing Delivery, Madras, India, 4-7 February 1992

The Commission on Human Settlements, in its decision 13/24 of 7 May 1991, requested the Executive Director of the United Nations Centre for Human Settlements (Habitat) to prepare a theme paper entitled “Appropriate, intermediate, cost-effect building materials, technologies and transfer mechanisms for housing delivery”, for its consideration during the fourteenth session to be held in mid-1993. The purpose of the theme paper is to submit for consideration of the Commission an objective appraisal of the performance of the building materials industry in developing countries, focusing on the major problems and constraints that currently hinder the adequate supply of basic building materials at prices that can be afforded by average house-builders. The paper should also highlight available policy options and submit a framework of action, at both national and international levels.

The Expert Group Meeting, organized by UNCHS (Habitat) brought together more than 10 experts and had the objective of identifying the suitable structure and format of the draft, produced the preliminary outline of the paper. It also defined ways and means on how to acquire and analyze necessary data and information and the type of inputs which would be required from member governments.

Workshop on the Second Issue of the Global Report on Human Settlements, Nairobi, Kenya, 2-6 December 1991

The main objective of the Global Report is “to provide a complete review of human settlements conditions, including an analysis of major forces and trends accounting for both their present developments and their continuing creation, maintenance and improvement”. The prime purpose is to analyse world-wide regional development trends and future prospects in the field of human settlements and, in this way, assist governments to implement the recommendations for national action made at Habitat: United Nations Conference on Human Settlements.

The workshop, organized by UNCHS (Habitat), brought together experts from Africa, Asia, North and South America and Europe and was intended to provide suggestions to UNCHS (Habitat) on the contents and format of the second issue of the Report.

International Seminar on Housing Indicators, Nairobi, Kenya 27-30 January 1992

More than 50 participants from 27 countries of Africa, Asia, North America, and Western and Eastern Europe, as well as representatives of the World Bank and UNCHS (Habitat) participated in the four-day seminar which was organized by UNCHS (Habitat). The Seminar was organized in response to the question, which arose after the formal adoption of the Global Strategy for Shelter to the Year 2000, of setting in place suitable mechanisms and guidelines for monitoring progress in achieving the Strategy's goal of adequate shelter for all by the year 2000 - a task which was a fundamental part of the Strategy itself.

Housing indicators were on the agenda of 10 sub-regional intergovernmental meetings organized by UNCHS (Habitat) on national shelter strategy formulation and implementation. These meetings revealed the interest of Member States in acquiring tools for monitoring their progress in addressing the Strategy's national goals and offered useful suggestions on how this task could be approached.

The discussions during the Seminar focused mainly on such topics as: quantity and price indicators, housing quality indicators, housing demand indicators, housing supply indicators, the regulatory audit and lessons learned from the extensive survey. Moreover, the participants had the opportunity to discuss and deliberate on the preliminary results of the housing indicators programme in their respective countries.

Back cover


UNITED NATIONS CENTRE FOR HUMAN SETTLEMENTS (Habitat)
PO Box 30030, Nairobi, KENYA. Telephone: 230800, 520600
Cable: UNHABITAT; FAX (254) 2 226473, 226479; Telex: 22996 UNHAB KE


Figure