| BASIN - News No. 7 - Jan 1994: Waste utilization in building |
Building Advisory Service and Information Network
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Most joumals that deal with technological and developmental topics focus each issue on a special theme, and one of the themes that appears fairly often is "Waste" - in one form or other. It may deal with common household or municipal waste, agro-forestry or industrial waste, and may refer to the safe disposal of hazardous components, reprocessing of materials for other uses, partial or complete recycling, or to the environmental, social and political aspects. It is a very wide field, so only a few aspects can be dealt with each time.
This issue of BASIN-NEWS is mainly concerned with "Waste Utilization in Building", whereby some of the articles deal with "Waste" in a broader context (such as "Yemen's Environmental Problems " in the WA S SECTION, and "Municipal Solid Waste Management in Developing Countries" in the RAS SECTION). Nevertheless, they all have to do with human settlements in developing countries, and altogether help to acquire a multifaceted view of an extremely complex subject and one of the most burning issues of today - waste management.
Waste utilization is nothing new in developing countries. The article by Guido Ast explains how traditional recycling systems functioned in Yemen's cities and villages, and this is true for most other countries. Waste disposal started to become a problem, the moment the so-called "underdeveloped" countries decided to become "developing" countries, which in other words meant adopting western technologies and lifestyles, not knowing that they were also importing western problems. Of course, a number of other causes, such as uncontrolled population growth and urbanization, and the resulting social decline of the majority of the population, economic disasters, political disorder and several other factors, have all contributed to the present situation. But this issue of BASIN-NEWS was not conceived to investigate the causes - the main intention was to present possible solutions.
Waste Utilization or Recycling?
In this context, it seems necessary to explain the difference between "waste utilization" (which the articles in this issue deal with) and "recycling of waste". The wastes in the first case can be defined as by-products (of agricultural, forestry, industrial or even household processes), which do not essentially have anything to do with building, but which, with special processing and treatment, or in conjunction with other materials, can economically substitute (or even improve the quality of) conventional building materials, or help to economize in their production (eg "Using Waste Material as an Alternative Fuel for Firing Bricks in Zimbabwe").
Recycling of waste, on the other hand, means the reuse of a material or component for exactly the same purpose, for which it had been used previously. A classical example is the traditional pueblo house of the Hopi and Zuni Indians of Southwestern United States. The walls were made of adobe (mud) blocks, and the roofs were supported by thick cedar beams. Since timber is scarce in that region, the beams were not cut to the required lengths, but allowed to project through the face of the exterior walls. Thus they were used over again for hundreds of years, and the old mud walls were crushed, mixed with water and made into new adobe blocks for the new houses.
Demolition waste from conventional buildings today may continue to serve as building materials, but usually in a different way. Broken concrete may be used as aggregate in new concrete. Brick waste can be finely ground and used as a pozzolanic binder. It can also be crushed to a maximum size of 20 mm and used as coarse aggregate in concrete construction, which is especially important in countries, like Bangladesh, in which natural aggregate is scarce. However, when using waste material as aggregate, fresh cement is needed to make new concrete, while clay and fuel are needed to produce new bricks. Therefore, this is waste utilization - not recycling, as it is often called.
Recycling - in its true sense - is also possible in building construction today, but would need very careful consideration in the design stage. If components, such as windows, doors, lintels, beams, columns, slabs, pipes and so on, are designed and installed in a way that facilitates dismantling without destroying them, their reuse is possible. But also during the manufacturing process and during installation at the building site, excess material, clippings, etc should be avoided or reused within an internal recycling system to avoid producing waste.
Since recycling reduces the amount of new materials and components needed, it is the most desirable form of waste utilization from an environmental and economic point of view, but it will probably never be achievable for the entire building. Nevertheless, any form of waste utilization is worth consideration, in view of the evident advantages:
* Conservation of scarce and expensive resources, utilization of locally available materials and reduction of material and transportation costs.
* Reduction of environmental degradation of large areas, that would otherwise be destroyed by excessive quarrying, or disfigured by the establishment of additional manufacturing plants or waste dumps.
* Reduction of pollution by the use of materials that are difficult to dispose of, and avoidance of excessive production of new materials in polluting industrial processes.
* Considerable saving of energy, which would be required to produce new materials.
Limitations and Remedies
While all this makes good sense in theory - and the ideas are by no means new - there are several problems that make it difficult to introduce wastes as potential building materials:
* Although the total amount of available waste is large, it may be produced in numerous decentralized units, making collection extremely difficult.
* Handling of wastes can be dangerous, eg inhaling of fine particles; blisters, bums and illness from toxic substances; severe cuts from broken glass and metal scrap.
* Once a by-product becomes a useful building material, higher prices are often charged, so that the benefit of using cheap materials is quickly lost.
* Not all building materials based on wastes provide the same strength and durability as the materials they were designed to substitute (but if the price is low, this drawback can be accepted).
* The concept of using wastes and the fear of future problems that may arise due to inferior qualities of materials makes builders reluctant to use them.
* However, with a series of well-implemented measures, such as the following, most of the problems can be overcome:
* Producers of useful by-products need to be well instructed on appropriate methods of handling and storage of the material in order to facilitate collection.
* Careful supervision and strict observance of safety precautions (eg use of gloves, goggles, protective clothing) in handling waste is of vital importance to reduce injuries and health problems.
* Especially in the case of lesser known but promising waste utilization, considerable efforts are needed to demonstrate the technology and its advantages. Prototype structures (preferably important public buildings) that are constantly used can convince most doubters.
* The use of wastes for building offers a wide field of research and should be given priority - even in the more affluent countries - as there is a great need in all countries to save resources, energy and costs, and at the same time provide more affordable and appropriate shelter for the homeless.
Unfortunately, progress in the field of recycling or waste utilization is still rather slow at present. The practical implementation of these concepts is still in the developing stage in the industrialized countries, and more so in the developing world. This has a great deal to do with the general awareness of the problem.
How large is the proportion of the world's population that is really worried about depleting resources and environmental pollution and destruction? In most countries they are very small minorities. And wherever one can observe some form of activity aimed at saving scarce resources and protecting the environment, it is either
* traditional practice,
* a vital economic requirement, or
* enforced by legislation (with severe consequences for non observance).
Those who appear to act in this way on idealistic grounds, without any of the above reasons, in reality know that the economic and social benefits will ultimately be on their side, particularly in terms of resources saved, a healthy environment and greater chances of achieving peace and happiness, as there would be enough resources to share with others.
However, there is no use emotionalizing this issue and appealing to the peoples' conscience. The only way to achieve a breakthrough is by convincing them of the practical benefits that would result from waste utilization and recycling. And in that respect, there is much to be done.
The articles in this issue of BASIN-NEWS present a number of possible uses of wastes in the fields of wall building, cements and binders, roofing and earth construction. If many of these were to become normal practice, wherever the resources exist, we would be entering a new era in building technology. But that is still a long way off.
A great deal of research and development is needed to arrive at really practical solutions that involve all commercial disciplines, not only those of the building industry. If the same amount of money and effort were put into such research, as has been put into various other high tech industries, such as automobiles, computers, aviation, space and arms technologies, to name only some of the most obvious ones, a number of today's environmental problems would be solved, and the immense housing backlog would gradually diminish.
It is, therefore, up to the decision makers in governments and industries to provide the financial and technical means for increased research and development in the field of waste utilization and recycling. And it is up to the scientists, engineers, designers and other experts involved to exert all their creative energy to Find new and unconventional solutions.
Ideas could be taken up again, such as the one that was developed by a beer manufacturer in the 1960s, whereby the bottles were shaped like bricks, which were also used as such to build a prototype house. This idea could be carried further, such that all kinds of packaging (glass, metal, paper, synthetic materials) arc designed to be used in one way or other as a building material, after its original function has been fulfilled. The concept of using discarded car tyres for wall construction (as described in the EAS SECTION) is unconventional, but certainly an idea worth following up in places where old tyres normally end up on garbage dumps.
In Singapore, for instance, the problem of disposal of dewatered sewage sludge led to experiments in the production of bricks made of dried sludge or sludge ash, with astonishingly good test results compared to those of common burnt bricks. Admittedly, the idea of using sewage sludge may initially be unacceptable for many people, but with an intelligent marketing strategy, this problem can surely be overcome. In any case, the advantage of making a valuable resource out of a problem waste cannot be overrated.
More sophisticated technologies using heavy machinery which would not normally be considered appropriate technologies - should not be ruled out when it comes to reprocessing demolition waste, as there are indeed appropriate uses for them. In some industrialized countries, such technologies have been developed to separate and reprocess (usually crush and sieve) the waste, which - depending on the type of material - is successfully being used in road construction, or as concrete aggregate, or for the production of insulating material, light weight blocks and tiles, to name just a few uses. Such so-called "recycling plants" are also available as mobile units, which could be especially useful for the reconstruction of demolished buildings after natural disasters (earthquakes, hurricanes, etc), wars and other destructive events.
Improving the quality and durability of materials is also a form of waste management, as less waste results within a given period of time.
However, all these efforts to avoid or utilize waste materials in building cannot be implemented on a large scale, if the corresponding building codes, standards and specifications are not available. Architects, engineers, building technicians, decision makers in building authorities, suppliers of building materials and equipment, all have to be fully aware of the waste utilization and recycling options, their applications, advantages and limitations. Furthermore, such technologies must be integrated into the curricula of educational programmes and practical training courses on building technologies.
This shows that we still have a long way to go before waste utilization becomes a part of standard building practice. It may take another 50 or even 100 years -who knows? But in order to make sure that it does not take longer, we must intensify our efforts in achieving this goal - TODAY. And, until it is reached, there will be many more special issues on "Waste".
Kiran Mukerji Starnberg, Germany
He is an architect and consultant to the Wall Building Advisory Service since the establishment of BASIN.
WAS - Wall Building Advisory Services at GTZ/GATE, Section 4130, Dag-Hammarskj"ld-Weg 1, D-6236 Eschborn 1, Germany
Amongst the many things man consumes in daily life, building materials happen to be the largest in terms of weight, being about 5 tonnes per capita per year - next only perhaps to water. Hence, in the wake of mounting pressures on basic materials like cement, bricks, stone and timber - mostly from natural sources - due to construction activities in various sectors of the economy, we cannot avoid looking for alternate, allied and complementary building materials, if the rapidly rising problems of shelter are to be tackled for a sustainable future.
Man and his activities produce a lot of wastes: agricultural and industrial wastes as well as urban and rural wastes. As a rough estimate - since organized data is not available - about 300 million tonnes of agricultural wastes were produced annually in India in 1985-86, while the industrial and mineral wastes were estimated to be about 50 million tonnes per year. In the same period, the total amount of urban and rural wastes (sweepings, garbage, kitchen waste, night-soil, animal wastes) was estimated to be over 1000 million tonnes per year. With such a large quantity of wastes around us - and the figures are increasing constantly - the magnitude of the problem of utilizing them usefully means taking into account aspects of the environment, economy, technology and energy.
Of primary importance are the environmental aspects of the problem. For example, the production of one tonne of cement utilizes one and a half tonnes of limestone, thereby disturbing one and a half to two tonnes of natural deposits. On the other hand, in producing one tonne of paper, the plant produces half a tonne of lime sludge, the disposal of which is a problem. On the whole, the country produces 10 to 12 tonnes of lime sludge from a number of industries, but their disposal need not be a problem, because technologies have been developed to use the lime sludge for manufacturing lime-based building materials. Thus the waste from one industry can become a resource for another industry.
Considerable work has been done by research institutions and industries to develop appropriate technologies for the production of building materials from different types of wastes. The need for the scientific disposal of such wastes and by-products was perhaps a desirability in the past, but today it is a compelling necessity. Building materials manufacturers, therefore, should come out in a big way to set up small-scale decentralized enterprises, based on environmentally sound and appropriate technologies, if we have to realize our targets of shelter in a sustainable manner.
In order to promote such innovative technologies, the Govemment of India set up the Building Materials and Technology Promotion Council (BMTPC) in 1990, under the aegis of the Ministry of Urban Development, with the aim of bringing together scientific research, technological advancements and enterprise. The Council undertakes functions such as the scaling of technologies from the pilot to the commercial stage, entrepreneural development, facilitating venture/risk capital support to new industrial units, absorption and indigenization of imported technologies, preparation of location specific feasibility reports, ensuring market support through building materials estates and adoption by public and private agencies.
One of the principal areas of activity is the promotion of production units of building materials and components based on fiyash, phosphogypsum, red mud, blast furnace slag, lime sludge, and other industrial and agricultural wastes. It is proposed to develop a national programme, in co-ordination with the Ministry of Energy and other Central Ministries, to identify such innovative technologies, demonstrate them through pilot plants and a growing national network of building centres, provide technical and financial assistance to entrepreneurs, exempt certain products from levy of excise duty, and implement other facilitating measures.
Some of the main applications of wastes currently being promoted by the BMTPC are listed below.
*Manufacture of various types of cement (Portland pozzolanacement, lime-pozzolana masonry cement, slag-flyash cement, etc).
*Production of lightweight aggregates for concrete components.
*Production of aerated lightweight cellular blocks and slabs.
*Production of clay-fiyash burnt bricks and tiles.
*Production of flyash-sand-lime bricks.
*Utilization of fiyash as structural fill for roads, land reclamation, abandoned mines, etc.
Production of hydraulic binder and supersulphated cement.
Production of plaster boards, partitionp anels, ceiling tiles and boards, fibre boards, artificial marble, etc.
Production of fired bricks and tiles from a mixture of red mud and clay.
Production of lightweight aggregate for concrete from pelletized and fired red mud.
Production of lightweight roofing sheets.
Production of polymer composites for door panels, partitions, etc.
Blast furnace slag
Manufacture of various types of cement (slag cement, supersulphated cement, slag-flyash cement,
metallurgical cement, etc).
Production of lightweight aggregat- for concrete.
Production of refractories and ceramics.
Utilization of blast furnace slag as structural fill for roads, land reclamation, abandoned mines, etc.
Production of lime-pozzolana binders and masonry cement.
Production of sand-lime bricks.
Production of cement fibre roofing sheets, using a variety of natural fibres, such as coir waste, sisal
fibre, wood wool and other agro-forestry by-products.
Production of pozzolanic binders from rice husks and other agricultural wastes.
Production of wood substitutes (particle board and fibre board) from various agro-forestry by-prod-
ucts, such as bagasse, cotton stalks, water hyacinth, rice husks, bamboo, etc).
Production of lightweight concrete and thermal insulation components, using aggregates made from
agricultural wastes, such as coconut, oil palm and peanut shells, carbonized grains, etc.
T. N. Gupta
Building Materials & Technology Promotion Council
G-Wing, Nirinan Bhavan New Delhi 110011 / INDIA
The Kurehwasekwa Co-operative, based in Epworth, a peri-urban, unplanned settlement on the outskirts of Harare, is a clay brick making group with a membership of seven men and three women. It has been in operation since 1988, making farm bricks from ant hills, on the basis of a six-monthly renewable contract issued by the local authority. Until ITDG's intervention through its Outreach Programme, the Co-operative had been using firewood with a small addition of unsieved boiler waste or ash to fire its slop moulded bricks. A farm brick is generally an underfired brick of irregular shape, characterized by low compressive strength, low hardness, high water absorption and typical light orange colour.
The Building Materials Outreach Programme, on the strength of its acquired bank of knowledge, is specifically geared to providing technical assistance to small scale building materials producers - starting by clearly identifying problems, and then seeking appropriate solutions in a participatory manner. The problems identified at the Kurehwasekwa Co-operative dealt with the scarcity and high costof firewood, poor product quality in terms of strength and water absorption, high green and fired breakage rates.
The Co-operative was finding the cost of coal prohibitive for purposes of firing bricks. Thus focus was directed towards the use of boiler waste or ash, as the only possible alternative to wood as an energy source.Boiler waste or ash is the solid refuse from stoker boilers, which use coal for heat generation.
The availability of coal in abundance in Zimbabwe accounts for its extensive use in power stations, as well as in most processing plants employing steam or oil as a medium of conducting heat, eg the chemical and foodprocessing industries, sugar refineries, soap and oil manufacturing plants. tobacco curing farms. to mention just a few.
The efficiency of operation of these boiler plants determines to a large extent how much energy is being extracted from the coal, and how much is being left in the residual product - boiler waste. Thus boiler ash collected from different places will always vary in terms of residual energy value, depending on the efficiency of the source boiler plant. Consequently, the ash from inefficient boilers has proved to be a viable energy option for firing clay bricks on a small scale basis.
Given below is an approximate analysis of boiler waste being used by the Kurehwasekwa Co-operative to fire its bricks in field clamps, in comparison with wood and coal.
1.2 - 12.8 %
Gross calorific value (Mega Joules 1 kg)
The above analysis indicates that, in terms of energy value, the boiler waste which Kurehwasekwa is using compares favourably with both wood and coal, and would fall a little short of being equivalent to coke. It indicates a high degree of inefficiency of the boiler plant that supplies the ash, and one gets the impression that it is functioning more like a coke making plant rather than a heat generating plant.
Clamp firing temperatures attained and Implications on the quality of the product
Using fuclwood as the prime source of energy plus some unsieved boiler waste, maximum firing temperatures achieved have ranged from 650' to 800'C, whilst withsieved boilerwaste as the sole source of energy and a different clamp arrangement, maximum temperatures of 950' to 115OOC were achieved. This shows that by using a rich boiler waste, it is possible to reach vitrification temperatures, which for most soils are around 110°C.
The firing temperatures have a strong bearing on the quality of the brick, as the following test results on bricks from the Kurehwasekwa Co-operative clearly show (Case I used firewood plus some boiler ash; while
Case 2 used only boiler ash):
Water absorption by weight
Hence increase in compressive strength
(6.98 - 3.81) x 100 13.81
Reduction in water absorption levels
(21.1 - 13.7) x 100 121.1
Thus, from producing a farm brick, the Co-operative is now almost producing a common brick, satisfying the minimum standard specifications set by the Standards Association of Zimbabwe, such as: average compressive strength of 7 MPa; water absorption by weight, under certain controlled testing conditions, of less than 15 %.
As a result of the improved quality of bricks it has been possible for Kurehwasekwa Co-operative to increase the selling price of their bricks from $ 160 to $ 250 per 1000 bricks without extra effort, whilst neighbouring brick making groups are selling at prices ranging from $ 150 to $ 180, with low sales figures per month.
However, it must be noted that the price increase has been gradual. In turn, this has also enabled the Co-operative members to increase their average monthly allowance/ wage from $ 100 to $ 200. It is also worth-while noting that the monthly allowance/wage is not predetermined, but is performance oriented, which is definitely a motivating factor,
Savings in using boiler waste
If it were taking Kurehwasckwa Co-operative 160 manhours to build and man a clamp with firing tunnels, using firewood and boiler waste, it now takes 120 man-hours to do the same work with sieved boiler waste as the only fuel, and a different field clamp arrangement with the provision of kindling fireplaces only. This is because in the latter case the need to incorporate firing tunnels and to replenish the clamp with firewood for at least 3 days after the clamp is fired has been obviated.
The cost of fuel prior to using boiler waste as the only energy source was as follows:
1. Eight loads of firewood $ 80 per load
2. One load of boiler waste $ 300 per load
Total cost of fuel per clamp
Using only boiler waste, the corresponding cost is now $ 500, which is basically only the transportation cost, as the ash is obtained free from the manufacturing plants. Thus, expressed in percentages, the savings in labour costs is 25 %, while the fuel cost savings amounts to 46.8 %.
The breakage rate of bricks in field clamps designed with firing tunnels/arches was high. In fact, it was approximately 15 %, due to various factors: the quality of the green bricks, the nature of stacking bricks in the clamp with fuel wood and the low firing temperatures attained. On the other hand, the use of sieved boiler waste obviates the need to create firing tunnels in clamp building, and also results in stronger bricks being obtained, because of the higher firing temperatures, which has led to a significant reduction of the breakage rate of bricks on the clamps to a mere 2 %. This translates to a breakage savings rate of 86.7 %.
Complete use of the boiler waste
The fine particles of the boiler ash are normally sieved out before building a clamp, for which only the coarse particles are used. These permit an efficient air flow within the clamp, achieving uniform and higher temperatures all over. The material that is sieved out is not thrown away, but is used as an additive or blending material before moulding, especially to soils with high clay content. The boiler ash distributed within the brick ensures uniform burning, reduces the amount of external energy required, and makes the bricks lighter, as the burnt ash leaves small cavities, which in addition gives the bricks heat insulating properties.
Environmental and economic impact analysis
The use of boiler waste, instead of firewood, is very much in line with the national thrust to conserve the natural vegetation. In addition, the fact that there are virtually no volatiles in boiler ash, and that technical advice from the ITDG Building Materials Outreach Progrwnme puts a lot of emphasis on clamp firing efficiency, has meant that smoke emission levels from Kurehwasekwa Co-operative clamps are very low.
In a country going through an economic structural adjustment programme, with its attendant inflationary problems and demands for competitiveness, the cost savings derived from using boiler ash is extremely important.
This reduction of fuel cost and the benefits accrued from selling a quality brick at a higher price, have been greatly welcomed by Kurehwasekwa Co-operative, whose appreciation of business copiousness has also been greatly enhanced. There is tremendous scope for disseminating this knowledge, as other groups in the Epworth area are now showing growing interest in these developments, with a view to implementing the process at their own sites.
To date this technology has already been adopted in the Ringa Resettlement area, in Beatrice, about 80 km from Harare, using boiler waste from surrounding commercial tabacco farms. Initial results of this work, which is being closely monitored by the Building Materials Outreach Programme, are very promising. To facilitate appreciation of the use of boiler waste in clamp firing, two people from Ringa have been attached to Kurehwasekwa Co-operative for a period of one week.
Realizing that boiler waste collected from different places will always vary in terms of residual energy content, there ia need to establish the minimum residual energy content required to adequately fire bricks in a field clamp. It is most likely that, on completion of the research component of this work, we will hold a field workshop on the use of boiler waste in firing bricks as a dissemination strategy.
I would like to sincerely thank Kurehwasekwa Co- operative for permission to use data from their production and financial records, and the Institute of Mining Research U.Z. for the analytical data on Hwange coal.
Project Officer, ITDG Shelter Programme
A report on the problems caused by uncontrolled littering and sewage disposal in the historical mud cities of the Republic of Yemen
World Cultural Heritage Sana'a
Everyone who visits the Republic of Yemen complains about the plastic blossoms that decorate the breathtaking terraced landscape. Garbage heaps and wrecked cars are scattered around the city gates and architectural masterpieces. Sewage ponds greet the visitor at Sana'a airport, and their sweetish-foul smell accompanies him on his joumey through the crystal clear highland air to the mecca of culture fans and generations of architects.
World Cultural Heritage Sana'a!
Thirty years ago, this country was still uninfluenced by westem civilization, but the Yemeni people, though very firm in religious, family, dressing and dietarytraditions, have now fully accepted the "blessings" of our consumer society. Cars, the larger the better (no wonder - petrol being cheaper than drinking water in plastic bottles) are the new status symbols, in place of the proudly decorated houses. Water supply and sewage pipes coverthe beautifully adorned facades, and the roofs are crowned with TV antennas, or nowadays with satellite dishes, next to water tanks, often shaped likejet fighters. Colourful wrappings of foodstuffs and household articles - and above all, half a million PVC water bottles every day - are the main sources of the plastic and paper wastes that litter the roads and landscape.
The uncoordinated water supply system, which has been developed according to westem standards over the last thirty years - mainly with international assistance - apparently did not provide for adequate sewers and sewage plants, with the result that much of the waste water is disposed of directly into the ground, polluting the groundwater, destabilizing the soil around the buildings and thus causing irreparable damage to them. Furthermore, the indiscriminate use of the limited resources has led to an immense drop of the groundwater level (up to 500 m in the Sana'a basin), and wastage of water due to faulty plumbing, dripping taps and WCs, mismanagement, etc, accounts for 40 to 60 % loss of the precious liquid - in a country that cannot afford to lose even a drop.
Traditional waste disposal
Imported solutions for imported problems
Garbage and sewage problems were unknown to Yemen in the past. Goats, sheep, chicken, cats and dogs were fed with household wastes. Each floor of the tall buildings has a toilet next to a vertical shaft. The faeces dropthrough the hole in the squatting slab, down the shaft to a chamber at streetlevel. Here the excreta dries quickly, becomes odourless and diminishes in volume. Occasionally public bathhouse employees remove the faeces, which are dried together with animal excreta, and used instead of firewood for heating water in the public baths (hammams). This way any pathogenic organisms contained in the faeces are destroyed, so the ashes were safely used as fertilizer in the fields-
Since water had to be carried all the way home from the mosque well, or had to be pulled up from self-owned wells to the top floors of the multi-storeyed houses, water consumption was relatively low. The resulting small amount of waste water from households and religious washings before prayers (five times daily) was used to water gardens. No detergents were used, hence the soil and groundwater remained unpolluted. Thus, it used to be a perfect recycling system that ecologists nowadays can only dream of.
Today, goumama (the Arabic word for garbage) rarely bothers anyone. The Leftovers of the sumptuous meals of Yemeni men are eaten by the women and children - or thrown away - while the men retire to chew qat (a mild stimulant leaf) and discuss more important issues.
Indeed these "qat meetings", which take place on the top floor of the building, in the afternoon reception room, called the mafraj (literally translated as "the place where ones forgets one's worries"), are of particular importance to Yemeni men. They never come with empty hands: on their traditional curved dagger, called jambia - the pride of every man - hangs a rosary and a plastic bag with fresh qat leaves, in their hands a plastic bag with a water bottle and a few packets of cigarettes.The more they bring along, the higher is their status and the greater the respect earned.
However, when they leave the room, the place is littered with green nibbled-off qat leaves (only the soft tips are chewed), mixed with plastic bags, half empty water bottles and empty cigarette packs. Between them the filled spittoons and used hookahs (water-pipes), and above all of it - thick air. It is then up to the women to clean up the mess. Whatever is not eaten by the goats (they too love qat), is thrown out into the street, into the garden, or wherever it can be deposited out of sight.
These waste disposal problems came with imported consumer goods; therefore, imported solutions are needed. Numerous projects of international development co-operation are now dealing with urban waste disposal. Apart from establishing garbage collection systems, which can only be maintained by continuous foreign aid, foreign workers - typically from Bangladesh - are required to do the dirty work for a monthly pay of US $ 30.
But other strategies are also needed to reduce the increasing volume of garbage, particularly that of the plastic waste, which is the major pollutant - above all the plastic water bottles. A promising strategy is to use the trucks, that deliver the water bottles, to transport the empty bottles back to the water factory. In order to achieve this, the people should get an attractive discount on the new bottles purchased, if they bring back clean empty bottles, which can be recycled. Surely not all botdes will be returned, but even if the number of bottles thatland on the garbage heaps is reduced just by 50 %, it would be a great achievement. Then there are the poor people in the streets, who can collect the discarded bottles and return them for say I Rial apiece. The difficulty, however, is that dirty bottles cannot be reclycled if they are not cleaned, which naturally means more water consumption for cleaning them. In any case, in order to avoid additional restraints due to bureaucratic problems, private companies should be involved in such a scheme.
In case it comes to a recycling system, efforts should also be made to save production costs. One important way would be to do away with the paper labels, which incur costs in the production phase and cause problems in the recycling phase. Thus, it would be better to produce the bottles with the brand name and production date incorporated in the form.
This shows that a great deal can and has to be done as soon as possible. Even the GTZ-DED project Planning Assistance for Urban Development has made efforts to assist the local authorities in solving the garbage and sewage problems in Yemen's urban areas, by producing technical manuals and conducting pilot projects and training courses. However, despite all these efforts, it is still very uncertain whether a solution can be found which will be able to catch up with the pace of garbage and sewage production and ultimately overtake it.
Teamleader of the GTZ-DED Development Co-operation Project
Planning Assistance for Urban Development in Yemen
Part ll: Dissemination
This is the second part of an article series describing a research and development project carried out jointly by the Housing and Building Research Institute (HABRI), University of Nairobi, Kenya, and the Institute for Tropical Building, Starnberg, Germany (on behalf of GATE). Part I of this series appeared in BASIN-News No. 4 (July 1992) and described the tests and demonstration phase of the project.
Foreign Imports In building
In construction, building materials constitute the main input, sometimes accounting for as much as 75 % of the cost of a low cost house. And even so, a majority of developing countries continues to import significant amounts of building materials and components. For large conventional and "modem" projects, import levels can range from 5 to 10 % for countries like Greece and Mexico, through about 60 % for Kenya and Ivory Coast, to more than 60 % for the Republic of Yemen.
In a survey of import content on construction works in the Umoja II housing project (a modest house owner-ship estate in Nairobi), it was revealed that at least 37 % of the project cost demanded foreign currency for purchasing building materials, equipment and fuel. Against this background, it is crucial that rational cost effective, foreign exchange saving methods are used, utilizing locally developed technologies and labour intensive local building materials production.
Therefore, to have a meaningful impact, building materials and technologies should fulfil most of the following criteria:
* take into account the existing climatic conditions;
* use local, readily available, cheap materials, which are easy to work with;
* incorporate indigenous techniques and skills; apply indigenous building form;
* let the existing need be identified by the local community;
* apply materials with a low energy consumption;
* avoid the use of heavy machines for production, transport and lifting gear.
Technology transfer mechanisms
Given the above scenario on conventional construction practices and the implications of appropriate technology on housing, a number of agencies in Kenya have adopted various dissemination approaches. A relatively large number of local and foreign institutions and individuals have been involved in one way or another in search of ways and methods to impart alternative building techniques to target communities. Some of these agencies include (though not exclusively): HABRI, the Village Improvement Programme (VIP) of the National Christian Council of Kenya (NCCK), ActionAid/ Kenya, AHF, AMREF, Canadian Save the Children, various women groups in Kenya, school committees, and a numberof othercommunity based organizations (CB0s), NG0s and private individuals. Appropriate technologies that have been disseminated by these organizations for various projects include stabilized soil blocks, rammed earth walling technology, fibre concrete roofing tiles, improved sanitation and water collection methods.
Development and promotion of Indigenous building materials and construction techniques -The HABRI Experience
HABRI has five main objectives, two of which are:
- to explore social, technical and economic problems of housing and community planning, and
- to help establish appropriate policy guidelines";
- to disseminate information to the public and researchers on various aspects on which the Institute has competence".
In BASIN-News No. 4, the first article (Part 1: Tests and Demonstration) dealt primarily with the first objective quoted, while this part focusses on the dissemination of the technologies developed in the Kenyan-Gennan technical co-operation project.
It was initially decided to use the youth polytechnics in Kenya, which are described as low cost training centres in rural areas. They aim at giving school leavers in their localities skills, understanding and values, which make them able to seek money-making opportunities where they live, and to contribute to rural development by building up the economic strength of their own communities. Through these institutions, over 200 trainees and their instructors have been trained in the production and use of innovative walling and roofing materials, and alternative sanitation and water systems. In the four major climatic zones, eight instructors' houses were built as demonstration structures. The training workshops and the resultant houses have generated a lot of interest in their respective areas. Some work groups have been formed to venture into the production of these alternative building materials. A further eight instructors' houses were built as a result of four other training workshops in four training centres.
The demonstrations in the later phase changed from youth polytechnics to other community based organizations and institutions. The most notable of these is the Kipkaren primary school in Eldoret Municipality. It entails the construction of classrooms and teachers' houses in a school strategically located in a low income site and service scheme. The local community participated by providing labour on a self-help basis, after training sessions by HABRI. The local authority was also actively involved in the project, which is beneficial for the future of the technology in the area. The last phase of dissemination works with a more diversified clientele and an equipped mobile demonstration van to reach out to requests for training in remote rural centres and educational institutions.
Currently, in this last phase of the HABRI/GATE project, a number of schools and needy women organizations are being trained on production and construction, using alternative building materials, and are assisted with equipment to build demonstration structures, either classroom blocks or houses. Specific training workshops fordifferent cadres of society, both local and from outside Kenya are carried out upon request, Well over 30 tailor-made training courses/ workshops have been carried out in the last three years. Development and popularization of appropriate simple field tests and quality control mechanisms have also been part and parcel of the dissemination strategy.
HABRI has developed into a regional resource centre, with a large specialized documentation. Numerous enquiries about appropriate building technologies are received every month, and printed infonnation material has been prepared on various subjects, and sent out in response to such enquiries.
Furthermore, HABRI is represented by the Director and other research staff on several technical working groups and committees, including the Kenya Bureau of Standards Technical Committee on Building Materials. Two specification standards have been approved on the use of FCR and Stabilized Soil Blocks. The standard on SSB was gazetted at the beginning of 1993 as KS02-1070. HABRI is actively represented in the technical committee deliberating on the code of practice for the production and use of stabilized soil blocks. HABRI's field experiences with demonstration and training workshops will be a valuable asset in these deliberations.
But it has been very encouraging to observe that, even without the direct involvement of HABRI or other research institutions, several building projects around Nairobi and other parts of Kenia, have been implemented using such technologies. These are, for instance, private builders and church administrators, particularly in St. Joseph's parish in Kangemi, Nairobi, where all the new buildings (housing, workshops, schools, church, etc) are being built with stabilized soil walls and FCR roofing, for which all the blocks and tiles are produced in their own workshops. This shows that the dissemination phase has been successful and the technologies are being accepted by the local people.
Peter N. Muturi (M.Arch. - KULeuven)
HABRI University of Nairobi
Cements and Binders Advisory Service provided by Intermediate Technology Development Group (ITDG), Myson House, Railway Terrace, Rugby CV21 3HT, UK
There are a number of waste materials which are either pozzolanic, reacting with lime to form a binder, or have intrinsic binding properties. Some, such as pulverised fuel ash (pfa) from coal burning power stations, are now used widely, but others find little application - in spite of extensive research work - largely for economic or technical reasons. For example, it is not economical to collect waste if it is produced in small quantities at a large number of widely dispersed sites. Particular technical difficulties of waste utilization include contamination by unwanted materials, which is why materials such as phosphogypsum from fertilizer production and lime from acetylene gas production or as a by-product of the sugar industry have not found wider application. Another factor is variation in properties of the material, such as of burnt clay pozzolana from pulverising waste underfired bricks and tiles. Refining such wastes to reduce these problems introduces an additional stage in the process and can lead to their utilization becoming uneconomic.
Additionally, a large number of waste materials could be used as aggregate in concrete mixes for a variety of applications. These materials include rice husks, mine tailings, burnt coal or coke, broken glass, brick and tile wastes and demolition wastes. However, waste materials as aggregate are often inferior to sand, gravel and crushed rock and their use is only really justified where conventional aggregate is difficult to obtain or where extraction of conventional aggregate causes serious environmental damage.
Another application of largely organic wastes is in boards and sheets formed under heat and pressure with the addition of a small quantity of resin. Some organic wastes, for example, straw from wheat, barley and rice have intrinsic binding properties which are activated by heat and pressure. However the boards produced without addition of resin generally have low strength and their main use is for insulation.
In the following articles, an overview of the research work of the Central Building Research Institute (CBRI) in India on waste utilization in cements and binders is presented first. CBRI are one of the leading research organisations in this field worldwide. The second article describes a specific feasibility study and pilot project on introducing rice husk ash cement production in Kenya. Finally there is a short article on producing sodium silicate, a lesser known binder, from waste rice husks and utilizing it in low-cost building. These three articles give an indication of the range and diversity of possibilities of using waste materials in binders thus potentially saving the use of millions of tonnes of Portland cement, a scarce and expensive material in many areas.
The Central Building Research Institute (CBRI) has been at the forefront of research and development work on utilization of agro-industrial by-products for cementitious binders for several years and has developed products and processes which are now described. The following table gives information on the availability of by-products in India with potential for use for cementitious materials.
Annual Production (MillionTonnes)
DEVELOPMENT OF CEMENTITIOUS BINDERS
Cementitious binders from rice husk and lime sludge.
A hydraulic binder has been developed from rice husk and by-product lime from sugar, acetylene, paper and other industries. The binder holds promise as a substitute to Portland cement in certain applications.
Method of preparation
The lime sludge and rice husk were mixed together in equal proportion by weight when dry along with 10-12% of plastic clay. After adding water the mixture was made into balls or cakes (fig.1). After drying in the sun, the balls/cakes were ignited in a trench or clamp or on a grating (figs. 2 and 3). The rice husk ash which is produced is rich in silica and can react with the lime. The maximum temperature recorded during firing was 900-950Ã¸C, producing a soft powder. As the reactivity of hydraulic binders increases with fineness the material is then ground in a ball mill.
Properties of the binder
The strength development of the binder is based on the lime-pozzolana reaction. Physical properties of the binder were determined according to methods described in the Indian standards.
The binder was found to conform to the compressive strength requirements of the standard on quick-setting lime-pozzolana mixtures and to have acceptable time limits for setting as a hydraulic cement. It also exhibits improved water retention, workability, water tightness and other properties, compared with lime-based compositions.
The binder has been found suitable in applications such as masonry mortars, plasters, foundation concrete and concrete for sub-flooring and terracing.
Since the binder is prepared entirely from industrial and agricultural wastes and its manufacture does not involve special skill and machinery it can be used as a partial substitute for cement, and would be particularly suitable for rural and low-cost housing programmes.
GRANULATED BLAST FURNACE SLAG
In India about 10 million tonnes of blast furnace slag is produced every year, of which about 2.5 million tonnes is being granulated. Granulated blast furnace slag is a glassy material and possesses good hydraulic properties. Its main uses are in the production of sulphate-resisting cements, that is slag cement and super-sulphated cement.
Slag cement can be produced by controlled blending of granulated blast furnace slag, Portland cement clinker and a small amount of gypsum to regulate the setting time. The hardening of slag cement is due to two processes - hydration of Portland cement, which releases lime, and then the slower process of slag activation with lime. The properties of the slag cementref.2 prepared from Indian slags conform to the Specifications for Portland slag cement IS 455-1989.
Supersulphated cement is an intimate blend of granulated slag (70-80%), gypsum anhydrite (20-25%) and a small amount of Portland cement (5-10%), which acts as an activator. CBRI has developed a supersulphated cementref.3 using Indian slags. These slags have relatively low lime and high alumina contents and their sulphate activation has been studied to optimize the manufacture of supersulphated cements. The optimum amount of activator (gypsum anhydrite) was found to be 20-25 per cent as against the commonly recommended value of 10-15 per cent. The cement thus prepared conforms to the Specifications of supersulphated cement IS: 6909-1990. The manufacturing technology is available indigenously and there is good demand for this type of cement. The initial strength of this cement is obtained by the formation of ettringite but the final strength is achieved by formation of hydrated calcium silicates as with Portland cement.
Advantages of slag cement include cheapness and saving in energy, increased resistance to sulphates and lower heat of hydration compared to Portland cement. The concretes made from slag cements can be used successfully in marine and underground foundations and in dams.
In India the production of fly ash by coal-fired power stations has been increasing and a large amount of this ash is being dumped, which causes severe pollution. Fly ash can be used in preparing cementitious binders in two ways.
Fly ash being a pozzolanic material can be used for the production of Portland-pozzolana cement which can be prepared by inter-grinding it with Portland cement clinker. Investigations have shown that the fly ash component can be as high as 25 per cent for the cement to still conform to the Specification for Portland-pozzolana cement IS: 1484:1976ref.4.
The Portland-pozzolana cement can be used in most situations, where ordinary Portland cement is used and reduces the heat of hydration, water permeability and alkali-aggregate reaction while improving resistance to attack by contaminated waters.
Activated lime fly ash mixtureref.5
Extensive study of lime-pozzolana binders with fly ash as the pozzolana has been carried out by CBRI. It was observed that most Indian fly ash possesses poor reactivity with lime with long setting and hardening times.
A process for improving the properties of lime and fly ash mixtures has been developed by CBRI, thus enhancing the rate of reaction between lime and fly ash so promoting faster setting and rapid development of strength of mortars and plasters. The exact composition of such a lime-pozzolana mixture depends upon the type of lime used and the reactivity of the fly ash. The complete process is shown schematically in fig.4. This uses chemical additives and grinding and compounding of constituents. Tests indicate that such mixtures can comply with the specification for Quick setting lime-pozzolana mixture IS 10772-1983.
Huge quantities of gypsum (CaSO4.2H2O) are produced by phosphoric acid, super phosphate and hydrofluoric acid industries. Also gypsum anhydrite (CaSO4) is obtained during the manufacture of hydrofluoric acid by the treatment of fluorspar (CaF2) with sulphuric acid. These by-products contain impurities of free acid, fluorides and phosphates which may affect their properties as binders. However, the amount of impurities can be reduced simply by washing with water.
Cementitious binders from fluorogypsum anhydrite
(a) Plastering material
A cementitious binderref.6 from gypsum anhydrite has been developed which is suitable for plasters. Gypsum anhydrite itself does not react with water. It needs an accelerator, generally a sulphate. Results of trials of a number of different accelerators show that 2% K2SO4 or NaHSO4 gives the required setting time. The effect of free acid in the anhydrite can be neutralized by the addition of a small amount of lime (2.5%) at the time of blending.
(b) Supersulphated Cementref.8
Due to the scarcity of high grade gypsum anhydrite for the manufacture of supersulphated cement, efforts have been made to utilize by-product gypsum anhydrite. Studies have shown that supersulphated cement made with the by-product conforms to the standard Specifications of supersulphated cement IS: 6069-1990.
Cementitious binder from phosphogypsumref.9
Investigations have been made to produce a durable gypsum binder based on calcined phosphogypsum, fly ash, Portland cement and a retarder and the properties of such a binder have been tested.
BAGASSE ASH BASED CEMENTITIOUS BINDERref.10
Investigations indicate that bagasse ash has good pozzolanic activity. It was found to consist of about two-thirds silica, most of which is in an amorphous state.
An attempt has been made to produce a quick-setting lime and bagasse ash mixture by intergrinding a hydrated lime, bagasse ash, 10% Portland cement and 4 per cent gypsum in a ball mill to a fineness of 90% passing through a 200 mesh (75Ã¦) sieve.
Such a mixture would have potential application as a mortar or plaster, particularly in rural areas.
A variety of cementitious binders can be produced from different types of agro-industrial by-products. The binders developed are of varying grades and can be utilized depending upon the situation. The technologies involved in their production do not require special skill and machinery. Therefore they can be manufactured and used as a partial substitute for high energy Portland cement on a small scale.
1. Dass, A. and Malhotra, S.K. A New Hydraulic Binder from Waste Lime and Rice Husk: Part 1 - Basic Properties Research and Industry, 22 (3) 1977 P.149.
2. Chopra, S.K. Investigation on the Utilisation of Indian Iron Blast Furnace Slag Part II, Bulletin of Central Building Research Institute, Roorkee. 3 (2) 1955 P.72.
3. Chopra, S.K. & Lal, K. The Manufacture of Supersulphated Cement from Indian Slag Indian Concrete Journal, April 1961. P/144.
4. Rehsi, S.S. and Garg, S.K. Proportioning Concrete Mix Containing flyash Journal of Institution of Engineer (India), Vol. XLV Pt CEl, Sept. 1964, P.68.
5. Dave, N.G., Malhotra, S.K. and Verma, M.L., Improved Lime Fly Ash Mixtures and their Manufacture Proc. of National Workshop on Utilisation of Flyash, Roorkee, May 19-20, 1988, P.93.
6. Teneja, C.A. and Shukla, C.V. Plaster from By-product Anhydrite Research and Industry, 20 (4) 1974, P.194.
7. Physical Testing of Gypsum Plasters and Gypsum Concrete ASTM Part 13, 1974.
8. Taneja, C.A. and Malhotra, S.K. Supersulphated Cement From Waste Anhydrite Research and Industry 19 (2) 1974 P 51.
9. Singh, M. and Garg, M., Investigation of Durable Gypsum Binder for Building Materials Construction and Building Materials 6(1) 1992, P 52.
10. Mehrotra, S.P. and Masood, I. Pozzolanic Behaviour of Bagasse Ash Building Research and Information 20 (5) 1992, P 299.
This article is based on a report made available to CAS by Dr. S.K. Malhotra, Scientist at : Central Building Research Institute - CBRI, Roorkee - 247672, India.
Ed. Note - Unfortunately, due to limitations of space it has not been possible to include the whole of Dr. Malhotra's article. However, CAS would be pleased to send any reader a complete copy of it, including test result data, on request.
Ordinary Portland Cement (OPC), the most widespread binder produced in Kenya, is becoming increasingly unaffordable for low-cost housing applications. After having concentrated on the development and dissemination of cost-effective alternatives for walling and roofing materials, the Housing Research and Development Unit (HRDU) of the University of Nairobi is now, with the help of GTZ (German Technical Assistance), developing alternative binders to increase the use of locally-produced binders and reduce dependency on Portland cement.
Although rice husk ash (RHA) has been used in several parts of the world as a pozzolanic cement extender, its potential for such use in Kenya has remained largely untapped, despite the ever increasing accumulation of rice husks - an agro-waste from rice processing. However, recent research on use of RHA as a pozzolanic cement extender in Kenya so far shows positive indications of economic and technical feasibility.
2. CONVENTIONAL BINDERS
Over the last three years the price of OPC has more than tripled, from KSh 98 per bag in 1990 (US$ = KSh 22) to KSh 345 in 1993 (US$ = KSh 60). This has been mainly caused by the devaluation of the Kenya Shilling (KSh) against hard currencies and the decontrolling of prices. The consumers' incomes have not followed this inflationary trend, resulting in an alarming loss of purchasing power making cement an increasingly unaffordable building product.
Although produced in Kenya, OPC has still an import cost component of about 24%. This covers mainly equipment, spare parts and furnace oil. Cement replacement should, therefore, also be examined in terms of the expected amount of foreign exchange saved.
OPC is often unnecessarily used for applications where other binders could offer satisfactory alternatives. A cheaper cement option would be one of the most cost-effective means possible to increase availability of building materials for the low-cost sector of the housing market in Kenya.
Lime is not extensively used in the construction sector, except in some parts of the coastal area. Most of the limited lime production from the existing plants is consumed in other sectors of the economy, and the price for good quality lime has doubled over the last three years.
The above factors clearly demonstrate the need for innovative approaches to production of cementitious materials in Kenya.
3. RAW MATERIALS : RICE HUSKS
Kenya is producing about 40,000 tonnes of rice paddy annually. The maximum amount of rice husks available therefore is about 8,000 tonnes per year. This is expected to triple by the end of this decade. In the Mwea area the Mwea Rice Millers (MRM) process most of the rice. Around Kisumu, there are more dispersed and smaller millers. The Tana River scheme is still in development but will become by far the biggest in the country when completed. Still, when compared to some other countries, Kenya is only a very small producer.
It should be stressed that in Kenya the husks are not only a by-product but also a real waste product. The husks are neither used as fuel for commercial boilers nor transformed into animal fodder. The husks represent both a real cost to the rice millers and an environmental hazard in the dumping area (Fig.1).
In the absence of feasible alternative uses, the rice mills are interested in the binder project, and are willing to sell the husks at a nominal value.
Overall in Kenya the potential total amount of binder which could be produced from RHA, is very low compared with the general consumption of cement. The processing of RHA cement could account for at most 4% of the total cement consumption in the rice growing areas, but within specific zones in these areas there is potential for more widespread application of RHA cement.
4. BURNING THE HUSKS
The husks are burnt in a controlled manner in a special purpose-built low-cost incinerator measuring 1.2m x 1.2m x 2.4m. The materials used for building the kiln are : concrete for the foundation, burnt bricks for the walls, and an iron sheet hood. The kiln has a number of iron bars inside, lined with a mosquito gauze to prevent the ash falling down. Studies to improve the kiln design should look at a more durable netting material and should consider how to make optimum use of the fuel value of the husks.
About 200 kg of husks are needed to fill the kiln with a light compacting effort. A fire is then started at the bottom of the kiln with small pieces of wood and paper. After this no other fuel is added for combustion of the husks.
Temperatures were recorded with a digital pyrometer (Fig.2). The average temperature over the peak period (between 20 and 30 hours of firing) is around 540Ã¸C, with maxima between 580Ã¸C and 660Ã¸C. Temperature control is achieved by variable air inlets.
XRD (X-ray diffraction) spectra analysis shows that, if the temperature is kept below 700Ã¸C, the controlled RHA samples are amorphous. The resulting ash has a colour ranging from dark grey to white, depending on the residual carbon content. Very light grey ash was obtained when RHA was allowed to cool to ambient temperature in the kiln. However, ash which is removed from the kiln after burning and cooled in the open, so cooling at a faster rate, is dark grey.
Chemical analysis reveals that the total percentage of the oxides of silica, iron and aluminium, ranges between 86% and 91%. This indicates that the Kenyan RHA is potentially suitable as a pozzolanic material.
5. GRINDING THE ASH
The ball mill (Fig.3), which is used for grinding the ash, is an essential part in the production plant. A cylinder-type ball mill (0.5m diameter, 0.5m length) was fabricated by a Nairobi metal engineering firm and installed at the HRDU workshop. The mill is electrically driven by a 4kW motor. The balls, which occupy about 55% of the section of the cylinder, are recycled truck bearings with diameter ranging from 12 to 25mm. When full the laboratory ball mill takes about 27 kg of ash. For a commercial plant a ball mill with a bigger cylinder (1.5m x 1.0m diameter) and a capacity of 325 kg per batch would be required. The milling is done for 3 to 4 hours. Samples are taken every hour to monitor the fineness of the ground ash.
It was found that the Blaine fineness gradually increases from 200 Blaine (m2/kg) to 420 when grinding between 2 and 4 hours. The common standard of fineness of Kenya Standard cement is 355 m2/kg. When grinding over longer periods, the fineness did not significantly increase. Since there is a direct relationship between fineness, strength and electricity requirements, it is essential to optimise the grinding period of the ash, and probably alternative grinding agents should be considered to speed up the grinding process.
The milled ash is packed in bags, kept in a dry place and transported to the construction site. On site, RHA and OPC are thoroughly mixed according to the required ratios before the other mortar components are added.
6. PRODUCTION COSTS
An economical feasibility analysis has been done for the three rice areas, with levels of production varying between 1 and 10 tonnes of RHA per day. A possible set-up for the Mwea area for production of 2 tonnes/day would require a capital cost of KSh 400,000 including a bank of 12 incinerators and two medium-size ball mills. A team of eight labourers would be employed with one supervisor. Burning would be done in 48-hour cycles with grinding at three batches per day.
The calculations indicate that, depending on the size and location of the production unit, RHA can be produced at approximately 25% of the price of OPC. Production units with higher capacities (for example four tonnes/day) would be able to further reduce production costs. This takes into account all inputs, including depreciation of investment, interest on loans, materials, bagging, transport, labour, supervision, marketing costs, allowances for waste, profit and tax. Also on a macro-economic level, there will be definite savings on foreign currency since there is no fuel involved in the production process and because the grinding equipment is manufactured locally.
Variables which influence the viability to a great extent include the production capacity, the organizational structure of the plant, the value of the husks, and the distance to the building sites. All these are very sensitive to the competitiveness of RHA in the market for binders. The integration of the RHA plant within a rice mill (as a subsidiary firm) would improve the commercial viability of a project because of drastic reduction of transport and overhead costs.
7. PERFORMANCES AND COST OF MORTAR MIXES
The figures on production costs are not conclusive without looking at the cost and quality of the final products. The choice of correct mortar mixes should aim at lowering the cost while resembling the quality of conventional mortars.
In terms of compressive strength it was found possible to replace up to 30% of OPC (by weight) in a mortar mix by RHA without losing any strength.
The conventional 1:6 (cement:sand) mix for plasters was modified by progressively reducing the amount of cement and adding RHA and/or lime. Attention was paid to the use of simple volumetric relations between the different components which are easy to measure on the building site.
For each mix, the relation between strength and mortar cost was established. The preferred mix with 50% of OPC replaced by RHA (by volume) has strength characteristics which are almost identical to conventional OPC mortar and achieves a cost saving of 33%.
Of other important properties of mortars, it was noted that slightly more water was needed for mixes with large amounts of RHA to maintain the required workability. RHA cement mortar also appears to lose moisture faster than the control mixes. Hence with this mortar there is need for consistent watering during the first days after plastering. There was no shrinkage or efflorescence in walls and floors where RHA was used.
It is very important to be aware of such differences when using RHA binders. Therefore, when commercially produced as an additive to OPC binders, the ash should be packed in a clearly different manner from OPC to avoid confusion. Clear mixing instructions should be indicated on the bags in order to avoid improper use of RHA.
8. EXISTING AND POTENTIAL APPLICATIONS
To test the response of RHA-cement to environmental conditions, 10 different formulations based on laboratory tests and a literature survey were used as mortars in 12 different residential buildings in two districts. In some cases, complete walls were plastered with the same mix and in others, different mixes were used in longitudinal strips on one wall to compare the performance of different plasters in similar exposure conditions (Fig.5).
Mortars containing RHA have been used for the following building components: internal plaster, external plaster, keying, screeding, floor top finish, door and window edges, wall corners, base course, lintel finish, and rendering of chimneys. Recipient walls for renders have included those of natural stone, burnt bricks, stabilized and sun-dried soil blocks (Fig.6).
It is expected that RHA/OPC cement can be used as a binder for masonry mortars, floor slabs, fibre cement tiles, stabilized soil blocks, precast elements, watertanks, and in concrete. Some of these potential applications are currently being tried out.
9. CONCLUDING REMARKS
The development of RHA binders should only be considered provided the following conditions are met :-
(a) rice must be produced in sufficient quantities,
(b) there should be no viable alternative for the use of the husks,
(c) OPC must be relatively expensive and
(d) there must be a need for an increased stock of binder.
These conditions are met only to a limited extent in the rice growing areas of Kenya because the quantities of rice produced are rather small and because the demand for cementitious binders is increasing at a rate which cannot be met by RHA cement alone.
Performance of the product
Burning the husks at peak temperatures of less than 700Ã¸C guarantees the amorphous nature and reactivity of the ash. The fineness after four hours grinding is higher than OPC fineness. Tests have also confirmed that it is possible to replace up to 50% (by volume) of cement by RHA without significantly affecting the characteristics of the mortar. Provided attention is paid to curing, the RHA plasters perform well for a large variety of building applications.
The most successful mortar mix can be 33% cheaper than the control while maintaining the same strength, but optimum mixes and actual cost savings will vary from area to area. Mixes with a considerable amount of lime do not seem to give adequate cost benefits. On the macro-economic level there can be a saving in foreign exchange and less capital required for production and employment creation.
Marketability and dissemination
Despite the apparent advantages of the limited application of RHA-based binders in Kenya there is often a hesitant attitude in using any new building product. To counter this appropriate marketing strategies are needed.
HRDU initially intends to promote RHA cement at shows, seminars and well-established youth polytechnics, but the main thrust of dissemination will be aimed at local artisans, who can influence the opinion of consumers considerably. The HRDU laboratory will continue to produce RHA until investment by private company can be arranged, possibly as a joint venture with a rice milling plant. The long-term aim is to positively influence Government and NGO agencies with building programmes in rice growing areas in favour of RHA cement.
Other types of pozzolanic binders
The use of RHA should not be isolated from the search for high reactivity natural pozzolana (volcanic ash, tuffs, scoria) for blended cements and lime-pozzolana binders. Initial investigations show that the scale of the impact could be much larger than RHA, but that the variation in reactivity is likely to complicate quality control procedures. Both RHA and natural pozzolana would have potential application in other parts of East African. Fragmented efforts towards the development of alternative binders are underway in several countries, but there is as yet no coherent policy to stimulate research and investment initiatives.
Tuts, R., Pre-feasibility study on the use of rice husk ash as a cementitious binder in Kenya. HRDU, 1990.
Wahome, E.R., Properties of local pozzolanic materials for use in concrete. MSc, thesis, University of Nairobi, 1990.
Hammond, A.A., Research on rice husk ash binders low-cost housing technology. HRDU, 1991.
Tuts, R., Potentialities and constraints for using pozzolanas as alternative binders in Kenya. Stoneleigh, ITDG, 1991.
Mbindyo, J.K., Chemical characteristics of rice husk ash and its applications. MSc thesis, University of Nairobi, 1992.
Tuts, R., Mbindyo, J.K., Application tests on Rice Husk Ash Binders. HRDU, 1992.
This article is based on a report made available to CAS by Raf Tuts, formerly of HRDU at the University of Nairobi, Kenya, but currently at PGCHS - KU-Leuven, Kasteel Arenberg, B-3001 Heverlee, Belgium. Fax.Ã¿+32-16-29-14-34, and the presented research work on RHA was done by A.A. Hammond
On the subject of rice husk ash CAS has learnt of an interesting project in the Chikwawa District of Malawi in which rice husk ash is reacted with caustic soda (sodium hydroxide) and water in a tank of hot steam to produce sodium silicate. The project is being financially supported by Danchurchaid through the Christian Service Committee of the Churches in Malawi and DESWOS, the German Development Assistance Association for Social Housing.
The sodium silicate produced has been used as a waterproofing coating, or mixed as a dilute solution with mud for plastering, or, similarly, added to soil to produce an adobe brick/block of improved quality and strength for use in a low-cost rural housing programme. When used as a waterproofing agent a primary coat of diluted sodium silicate solution should be applied to adobe brick/block plastered walls prior to decoration with calcium stearate paint containing red iron oxide powder as a colouring agent. The calcium stearate paint is also derived from rice husk ash.
Unlike with rice husk ash cement the husks do not need to be burnt under controlled conditions so it is possible to use ash which is a residue from burning husks as fuel.
The cost of using sodium silicate is said to compare favourably with other binders. The sodium silicate can be produced locally on a small-scale, the only significant import component being the caustic soda.
There could also be potential for using bagasse waste from sugar production, after burning to ash - for sodium silicate production - although the silica content of bagasse ash is somewhat lower than that of rice husk ash.
CAS would be very interested to learn from BASIN News readers about any work on producing or using sodium silicate. CAS receives a few enquiries a year on sodium silicate and needs to assess the benefits and limitations of this material and whether it has potential to become a widely used binder. Any opinions on this subject are also welcome. It is hoped to publish a synopsis of all contributions received on this subject in a future issue of BASIN News.
Roofing Advisory Services at SKAT - Swiss Centre for Development Cooperation in Technology and Management, Vadianstr.42, CH-9000 St.Gallen, Switzerland
As the quantity of urban solid waste is increasing rapidly, affecting both public health and the environment, efficient and sustainable Solid Waste Management (SWM) must be considered as a most pressing issue on the agenda of both, many developing countries as well as governments world-wide.
Besides conventional scavenging, organised reclamation and utilisation of solid refuse are increasingly being considered as important alternatives to waste disposal. The re-use of materials gained from solid waste reduces degradation of living environment (which is the initial objective of SWM). It also contributes to the conservation of resources, provides economically favourable solutions and creates jobs.
Appropriate solutions for developing countries are often determined based on technical and economical considerations only. In future, however, more emphasis will also have to be given to environmental aspects . The utilisation of solid wastes for building materials can be a valuable contribution in this respect . Although the recovery and recycling of Municipal Solid Waste (MSW) has been introduced in many countries, with the involvement of the informal sector, relatively little is known about the utilisation of MSW for building materials, especially for commercial roofing.
In view of the above, the RAS input to this edition of BASIN-News includes
* description by the International Reference Centre for Wastes Disposal (IRCWD), Dbendorf, Switzerland, of general problems and issues of solid waste management in developing countries, and
* highlights possibilities and limitations of the utilisation of solid wastes in roofing materials
Municipal Solid Waste Management in Developing Countries: Problems and Issues; Need for Future Research by Roland Schertenleib and Werner Meyer
During the International Drinking Water and Sanitation Decade, proclaimed by the UN for 1980 -1990, the main emphasis was placed on the improvement of water supply and the safe disposal of human excreta in developing countries (DCs). Solid Waste Management (SWM) received comparatively little attention.
Today, urban SWM is considered to be one of the most immediate and serious environmental problems confronting urban governments in DCs. This is mainly due to the rapid urbanization taking place on an enormous scale in Asia, Africa and Latin America.
Inadequate management and disposal of solid waste is an obvious cause for the degradation of the environment in most cities of the developing world. Many cities face serious environmental degradation and health risks due to uncollected domestic refuse on streets and in public areas, clogged urban drainage systems by indiscriminately dumped refuse, and by contamination of water resources near uncontrolled dumping sites.
Inadequate collection and disposal of solid waste is a major factor in the spread of gastrointestinal and parasitic diseases, primarily caused by the proliferation of insect and rodent vectors. Mostly low-income communities, where uncollected domestic refuse is often mixed with human and animal excreta and piles up on the street, are affected by inadequate SWM systems. Besides public health protection measures, important objectives of a SWM system should be the conservation of natural resources (water, air, soil), minimization of the use of nonrenewable resources (energy and raw material) and of imported material (financial resources and products), as well as general improvement of the standard of living by a control of the aesthetic problems like dirt, odour and smoke.
This article identifies the main problems and issues related to the highly unsatisfactory situation of municipal SWM encountered in most DCs, and suggests some possible approaches for improving the present situation.
2. IDENTIFICATION OF TYPICAL PROBLEM AREAS
Based on extensive literature reviews, observations and discussions in a number of DCs, five typical problem areas have been identified: (a) inadequate coverage of the population to be served; (b) operational inefficiencies of municipal SW services and management; (c) limited utilization of the informal and formal private sector in recycling activities; (d) specific problems related to final disposal of solid waste; and (e) problems concerning the management of (non-industrial) hazardous waste.
a) Inadequate coverage of the population to be served
Existing municipal solid waste management schemes generally serve only part of the urban population. In a "typical" urban area, the municipal service picks up about 50 to 70 percent of the refuse and serves less than 50 percent of the population. The low-income peri-urban areas usually make up the unserved population.
The lack of adequate institutional arrangements and the low financial and technical sustainability of existing collection systems are the main reasons why this kind of situation prevails in urban areas of DCs. The waste generated by the fast growing cities is increasingly beyond the collection capacity and financial limitations of most municipal administrations. Usually, not even the operation costs of the collection services are covered by adequate fees, and the available funds from the central budget are insufficient to finance adequate levels of service to all segments of the population. In a situation where resources are scarce, priority is usually given, mainly for political reasons, to middle and high income areas. In addition, many urban poor live in unplanned and unauthorized areas (often outside the municipal boundaries) and are, therefore, not eligible for municipal services.
Even though low-income areas are grossly neglected by municipal collection services, low-income communities have proved willing to make some investments in cleaning up streets and improving drainage. The question is how much are they willing/able to pay, under what conditions and for what kind of service.
b) Operational inefficiencies
Although municipalities in DCs expend substantial resources on waste management (often 20 to 30 percent of municipal operating revenues), they tend to do a poor job operationally.
Operational inefficiency is due primarily to the inefficient institutional arrangements common to municipal governments in DCs. In addition, waste management services generally receive little attention from top city officials, and are usually assigned to the lower echelons of municipal government or to health departments. However, the more a city grows, the more the solid waste collection becomes complex and requires top level planning and sophisticated engineering and management skills.
c) Limited utilization of the capacity of the informal and formal private sector in recycling activities
The informal sector has been playing traditionally an important role in SWM schemes, especially with regard to recycling activities. However, while being basically beneficial to the environment and supporting large numbers of poor workers, these recycling activities by the informal sector can conflict with efficient waste management practices. These activities also pose serious health problems to the worker community. The formal private sector has so far been rather reluctant to participate in recycling activities, although the materials recovered from the waste stream are marketable.
The recovery of all kinds of material from municipal solid waste by the informal sector is not only a fact of life which cannot be ignored or even abolished, it also offers opportunities to incorporate resource recovery into solid waste management schemes. Scavenging as a whole not only provides a source of income to one of the poorest segments of the population, but it also reduces the need for highly sophisticated and costly recovery systems. Therefore, these recycling activities should by no means be discouraged, particularly since resource recovery is now becoming a recognized component of municipal solid waste management strategies in industrialized countries.
Although material recovery from the waste stream has a great potential for private sector involvement (the outputs are marketable), in industrialized countries as well as in DCs the formal private sector has been playing a minor role in recycling activities. The reasons are manifold and interrelated: (a) the market for recovered material, which is often controlled by cartels, leads to oligopolistic situations; (b) prices for recovered materials are subject to large fluctuations and are not predictable; (c) tipping fees are generally too low to create an economic incentive for private firms to reduce the volume of solid waste by material recovery and recycling of the putrescible components (composting). As long as this situation prevails, the formal private sector will probably only be involved through contractual agreements with municipalities.
d) Specific problems related to the final disposal of solid waste
The solid waste in DCs is generally disposed of in uncontrolled open dumps. Although the environmental consequences of inadequate disposal are often quite evident, they are seldom dealt with.
Financial and institutional constraints are the main reasons for such a situation. If financing of solid waste collection services poses a problem, the financing of safe disposal of solid waste poses an even greater problem. Although most people are willing to pay for the removal of the refuse from their immediate environment, they are generally not concerned with its ultimate disposal. In addition, since the important physical components of the environment (air, water, soil) are public goods, their utilization is not controlled by simple market mechanisms.
The present situation is expected to deteriorate even more. Due to rapid urbanization, the existing dumping sites, often former quarries originally located at a safe distance outside the municipal boundaries, are increasingly encircled by settlements and housing estates. They are subjected to growing opposition from the public. On the one hand, the central location of the dumping sites; i.e., close to the collection area, has enabled local governments to dispose the municipal SW at little cost. On the other hand, it is becoming increasingly difficult to find new landfill sites which find the approval of the public, and which are located at a reasonable distance from the collection area. Many of the recently selected landfill sites in larger cities (e.g. Jakarta, Manila) are in fact located at distances between 20 to 40 km from the central collection areas. This results in high transfer and transportation costs as well as in additional investments in the infrastructure of roads.
e) Problems related to collection and disposal of (non-industrial) hazardous waste
Although most hospitals officially require the burning of their pathogenic waste, most of the existing incinerators are out of order due to a lack of fuel and/or spare parts. Consequently, pathogenic waste products often enter the MSW stream and cause serious health risks.
Hospitals and especially the growing number of health institutions such as primary health care centres and dental and veterinary clinics spread throughout the cities and produce infectious medical waste. They generally lack appropriate collection and disposal services. Consequently, pathogenic waste products often enter the MSW stream and pose serious health risks to the public (e.g. children playing with toys recovered from MSW products), to scavengers and collection crews, and to workers at the landfill.
3. Possible approaches to solve the most urgent problems and need for future research
a) Increase in coverage
As long as solid waste collection services are not sustainable in the sense that the beneficiaries are not able/willing to pay for the kind of service offered to them, it is obvious that it will be increasingly beyond the resources of the municipal administrations to collect the growing amount of solid waste generated by the rapidly expanding cities in DCs. This basically means that the people in low-income communities have to assume the responsibility of the municipality with regard to the handling of their garbage, and to set up a system appropriate to their economic situation. This can take different forms; i.e., the community/neighbourhood is either paying private collectors, within or without the community, or the population will have to partly carry out the work themselves. In other words, those who cannot afford to pay in cash will still be provided with SWM services by paying in kind.
b) Improving operational efficiency
It is often argued that privatization of SWM activities is the best method to improve the poor efficiency of existing SWM systems. A preliminary study comparing the latest cost data of the urban waste management services in Rio de Janeiro and Sao Paulo revealed that taxpayers in Rio de Janeiro pay for a similar level of service at least twice as much as taxpayers in Sao Paulo. This difference is attributed to the fact that the services in Rio de Janeiro are provided by a government agency in contrast to Sao Paulo, where private firms have been contracted to collect the refuse and operate processing plants and disposal facilities. There is strong evidence that the productivity and efficiency of the services delivered by private firms in Sao Paulo is higher.
However, privatization has also serious limitations. Although in most cities of Francophone West Africa (e.g. Dakar, Abidjan, Lom‚, Douala), private firms have been in charge of SW services for many years, there is no indication that the municipal authorities and/or the taxpayers in these cities pay less for their SW services. This is probably because these private firms basically have a monopoly without any competition.
In this context, it is important to note that the organizational structure and management of the refuse collection agency are the most important factors affecting the efficiency of the system.
c) Better utilization of the capacity of the informal and formal private sector in resource recovery from MSW
The crucial question with regard to informal sector involvement in SWM systems is how can the above mentioned problems associated with scavenging be reduced or even eliminated without jeopardizing the benefits of these activities. A possible approach is to regard improved scavenging as an integral component of solid waste management planning and implementation.
The existing situation with regard to scavenging activities at dump sites and/or transfer stations/points could be improved significantly for example by (a) physically separating the area where scavenging is taking place from the actual disposal site. This would prevent interference with the tipping operation at the landfill; (b) providing manual or very simple mechanical sorting tools and operational training to the scavengers. Which would lead to more efficient material recovery; (c) incorporating processing activities to add market value to the recyclables; (d) providing washing and sanitary facilities in the areas where controlled scavenging is taking place; and (e) providing education, housing and health facilities to the scavenger community. In cases where collection and recovery are closely linked; i.e., where scavengers are actually given the task to collect the solid waste, it is essential to have formal agreements between the authority in charge of SWM, the households and the scavengers, and to put in place appropriate payment mechanisms. This again requires scavengers to be organized in formally acknowledged groups.
Since the formal private sector has so far been rather reluctant to enter the recycling market, investigations on market and price mechanisms of secondary raw materials are urgently needed. In this context, the question of prime interest is how do direct and indirect subsidies of virgin and/or imported raw material influence the prices of recyclables.
d) Improving the situation with regard to the final disposal of MSW
The following three basic measures are suggested to improve the present situation with regard to the final disposal of MSW in landfills: (a) Institutional and financial models for waste disposal activities as an integral part of SWM have to be found and applied. Landfill operation costs have to be covered by the collection fees. (b) Appropriate guidelines for the operation of landfills in DCs have to be developed. These guidelines should not be based primarily on the existing requirements of sanitary landfills in industrialized countries but mainly take into account the basically different physical and economic situation prevailing in DCs. (c) Increased recycling of the organic putrescible component, which accounts for the largest fraction of the MSW produced in DCs, will reduce the amount of waste to be disposed of, lower landfill operation costs and prolong their lifespan.
e) Improving the management of pathogenic hospital waste
Most of the wastes generated by hospitals and clinics are similar to the domestic and commercial wastes produced by other institutions; i.e., they are not hazardous and do not require special attention. In order to minimize the amount of waste to be handled in a special way, the small portion of infectious and hazardous waste should always be kept separate from the other waste stream (e.g. separation at the source). Nevertheless, appropriate guidelines have to be developed for the special handling and safe disposal of the relatively small portion of hazardous pathogenic waste from hospitals and clinics.
Urban SWM is one of the most serious environmental problems confronting the governments in DCs. Inadequate collection and disposal of solid waste are major reasons for the environmental degradation and health risks in the fast growing urban areas of DCs. The above mentioned five typical problem areas are related to institutional, financial and technical issues.
The most promising approach to improve the collection coverage is the introduction of community-based waste management schemes which involve the local communities in the collection, sorting and recycling activities. Research is needed to determine how such schemes can be implemented under different kinds of condition.
Operational efficiency of SW services can be improved by increasing the participation of the private sector. However, future research should not only address the question of what should be the role of the private sector in SWM, but also how the performance of public enterprises can be improved and what should be the role of the public (government) sector vis-…-vis the private sector.
The benefits of the recycling activities by the informal sector should be officially recognized. Instead of being outlawed, these activities should be improved and encouraged. However, informal recycling systems have to be thoroughly studied before changes are introduced. Investigation on market and price mechanisms of secondary raw materials are also necessary to determine how the capacity of the informal and formal private sector in resource recovery from municipal solid waste can be improved.
In order to improve the present situation of final disposal, three basic measures are suggested: (a) institutional and financial models for waste disposal activities as an integral part of SWM have to be found and applied; (b) appropriate guidelines for the operation of landfills in DCs have to be developed; and (c) recycling of the large organic putrescible MSW fraction needs to be increased.
There is a need for appropriate guidelines for the handling and safe disposal of hazardous pathogenic waste from hospitals and clinics in DCs.
The International Reference Centre for Waste Disposal (IRCWD) is a section within the Swiss Federal Institute for Environmental Science and Technology (EAWAG). IRCWD is mainly involved in applied research, consulting and teaching in the field of Water Treatment, Sanitation and Solid Waste Management (SWM) in economically less developed countries. Its main task is to evaluate and support the development of sustainable, low-cost technical solutions appropriate to the local and cultural conditions.
In the field of water treatment, IRCWD has been conducting during the last few years a R&D project on the application of roughing filters for the pretreatment of highly turbid surface water.
Some of IRCWD's main activities of the last years in the field of sanitation have been devoted to the development of new guidelines on the reuse of wastewater and excreta in agriculture and aquaculture. In the current R&D sanitation projects, IRCWD is studying different alternatives with regard to emptying pit latrines and septic tanks and the treatment, disposal and/or reuse of their content in a hygienically safe and still affordable way.
Compared to water treatment and sanitation, solid waste management (SWM) is a relatively new field in the activities of IRCWD. In an initial phase, important typical current problems in municipal SWM have been analyzed and identified. Based on this review and based on the availability of its financial and human resources, IRCWD selected the following three areas for future R&D activities:
a) Community-based primary solid waste collection this project component, information is being collected and analyzed on existing primary SW collection schemes where the local community has assumed responsibility for setting up and/or organising the primary SW collection. The overall objective is to propose and disseminate approaches on how to increase Municipal Solid Waste (MSW) service coverage, especially in low-income areas.
b) Decentralized composting of municipal solid waste
This component of the research project will analyze existing experiences of decentralized composting systems. The overall objective is to propose and disseminate approaches on how to reduce economic and financial costs of municipal SWM. The main reasons for introducing decentralized composting are the recovery of the high proportion of organic material in municipal SW and/or the reduction of transportation and disposal costs.
c) Development of "realistic" and safe guidelines for sanitary landfills
The objective of this research component is to bridge the gap between the existing standards and guidelines for sanitary landfills, developed mainly in industrialized countries, and the crude open MSW dumping practice used by most municipalities of lower income economies. The project will develop minimal requirements and guidelines for environmentally safe and still financially affordable MSW landfill disposal.
People/institutions who are interested in collaboration with the IRCWD in some of the above mentioned research areas are kindly invited to contact:
1. Requirements of a Roof
As the roof represents an important, if not the most important part of a building, special care has to be given in preparing its elements. A roof has to fulfil various functions simultaneously. Being a form of physical barrier between man and the climate, the comfort of the occupants of a house or building largely depends on the efficiency with which this physical barrier fulfils its functions. These functions are:
* to protect from rain or to collect rainwater in areas where water is precious;
* to provide thermal insulation and shade;
* to provide extra living or storage space (to span space);
* to protect from other climatic influences, such as wind, snow, hail, etc.
A sloped roof can be divided into two parts, namely the roof structure (under or supporting structure) and the roof cover (tiles, sheets, etc.). In order to construct a reliable roof, not only must the covering material be of high quality, but the roof structure and the roof cover together must function as a coherent system, and thus special care also has be taken with the under structure. The technology for roofing (including under structure) should be adapted to local conditions including:
- sociocultural aspects,
- economic aspects,
- climatic & geographical situation,
- existing institutions and entrepreneurs in the R&D area,
- available skills and existing know-how.
It is generally accepted that roofing materials must be of a high standard, because a sub-standard and badly designed roof may not only result in a defective roof, but may ultimately cause severe damage to the whole building. In this light the potentials and limitations regarding the utilisation of waste materials for roofing have to be analysed.
2. Available Waste Materials
In the table below, a catalogue of solid wastes which could be considered for re-use in the building sector is listed according to their origin.
The recent and gradual changing of the composition of the urban solid waste (e.g. more plastic products and paper) provides new options for roofing materials from this waste.
For the development of sustainable waste technologies it is important that they be adapted to the local situation. The amounts, fractions and quality of available solid wastes and their actual utilisation should be analysed. If a need for a roofing material is identified and affordable materials are available, then a detailed feasibility study, based on the requirements described in chapter one, should be done.
3. Potential and Limitations of Waste Materials for Roofing
RAS knows of comparatively few experiences in developing countries concerning the successful re-use of waste materials, particularly in roofing. Some of the main reasons for the reluctance in such re-use could be:
- extreme requirements for roofing materials, i.e. high physical stress (higher than for most other building parts);
- waste materials for building purposes have a relatively low acceptance, especially for the users;
- the reuse of recycled materials, especially for roofing materials, involves comparatively high technologies, thus resulting in generally high investment costs for entrepreneurs, dependence on industrialised countries and expensive products;
- the building market, particularly entrepreneurs, is very conservative with regard to new materials;
- lack of marketing strategies;
- suitable and sufficient waste materials such as paper or cardboard not available.
As known from experience (shanty towns, slums, biddon- villes), the re-use of solid wastes for housing purposes has a direct relation to the social status of users. The settlement structure, as shown in the table below is an indicator which determines the degree of processing required and the type of reusable waste.
In this light, the utilisation of waste materials in roofing has a big potential, but also strong limitations.
It is assumed that much research work is being done in the re-use of waste materials in roofing, even if world-wide not many successful products are known. Many problems can be avoided if the research is demand-oriented and based on the local situation (requirements of a roof, availability of waste, marketability, etc.). Products made in and for industrialised countries should not be introduced in developing countries without appropriate adaptation.
4. Examples of Roofing from Waste Materials
4.1 Manufacturing asphalted roofing sheets from waste paper
With a reasonable life span roofing sheets made of waste paper, waste cardboard (cellulose) and bitumen (a by-product of the distillation of mineral oil) have proved to be a successful roofing product in industrialised countries. They are water resistant and are very durable. The life span can only be guaranteed if the selection of raw materials and the production process is closely followed up by highly skilled professionals. So far this product has only been successfully produced in Europe and is mainly exported. This capital intensive production process has recently been introduced in Rwanda, using locally grown papyrus and imported bitumen. Due to severe energy constraints on a national level, a breakthrough in this production has not been reached yet.
4.2 Manufacturing Micro Concrete Roofing Sheets with Waste Paper/Cardboard
These asbestos-free cement sheets are reinforced with natural mineralized fibre (cellulose fibres, e.g. from pulped banana-boxes). The cellulose fibres have to be neutralized in a high-tech procedure which has to be closely controlled. Experience has shown that production without a meticulous quality control results in a considerable reduction in durability, so that the life span of the product is reduced to a few years.
4.3 Other Roofing Materials From Waste Materials
- Roof cladding from the re-use of car tyres could be a possible alternative. Even if no experience is known in this field this option should be further analyzed.
- Rice Husk Ash (RHA) is often mentioned as an additive in cement products, but experience has shown severe limitations for its utilisation in tile production. Although a good quality can be obtained under laboratory conditions, RHA seems inadequate for tiles/sheets production. Main constraints are a slow production process, slow curing and an unsatisfactory performance over time (cracks after 2-3 years).
- Other options are possible but need further investigation.
5. Conclusions and Recommendations
The rapid increase in municipal solid wastes in urban areas in developing countries, the increasing tendency of using throwaway products, as well as the availability of manpower, provide a great potential for using waste materials in construction and also as roofing materials.
The objective is not to support 'waste production', but to promote technologies which are based on an efficient and effective utilisation of locally produced waste materials. It is hoped that developing countries can be made aware of the growing problem and at the same time the local housing market be provided with alternative, valuable and locally made products.
The study of literature and inquiries amongst potential producers and users have revealed that very little is known about economically feasible and qualitatively adequate production of materials for the roof cover, as well as for the roof structure, from recycled or re-used solid waste materials.
Experience has shown that theoretically feasible solutions are commercially inadequate, as investment costs are too high or the products are not marketable, e.g. because of strong competition and/or low acceptance of the new products.
Increased research is required in this field, but it should, however, go hand in hand with practical application, based on a clear demand and on existing experience. Only technically, economically and environmentally sound solutions are sustainable.
6. Call for Contributions
RAS is interested in promoting successful technologies for roofing based on solid waste materials. Individuals or institutions interested in sending information or in participating in R+D are welcome to contribute.
Any information on this subject is welcome and can be sent to the following address:
CH-9000 St. Gallen
The Lake of Yojoa conservation area in Honduras was an enchanting site for the second Latin American seminar of Teja Micro Concreto TMC. Some forty representatives from thirteen countries, ranging from experienced TMC producers and project directors to newcomers, participated in four days of intense discussion.
Reviewing the situation of each country revealed a general progress in the region. More than one million square metres of TMC tiles have been produced up to date, 800,000 of it in Honduras and around 380 jobs created. With the tremendous expansion of the technology in Honduras, the annual capacity of production in Latin America is now approaching 800,000 square metres.
The main interest of the participants was the exchange of experiences in quality control, dealing with equipment made in Cuba and technical aspects of production, but the seminar also covered items like the first steps toward establishment of producers associations and marketing of TMC.
Relations and friendships developed and renewed among producers from various countries and discussions of controversial approaches have been an important result of networking
The conclusions of the seminar were:
- The Latin American seminar and the network are of great importance for the development of the technology in the region. The network will be further developed as an instrument for the exchange of experiences among its members and activities still better coordinated. The next seminar will be held in Cuba in 1995.
- Experience in Latin America proves that TMC (MCR) tiles are a good roofing material for all segments of the roofing material market, though the technology needs constant development and a still higher level of productivity must be reached.
- Diffusion of TMC should be accelerated through implementation of technology in further countries of Latin America. All countries intend to establish producers associations or national centres responsible for quality control, training, credit lines, diffusion of technology and marketing.
- The MEPI-system (a Monitoring, Evaluation, Planning and Implementation tool for all FCR/MCR projects world-wide) has been introduced and first results are expected for end of 1993.
Kathrin Rhyner Pozak, Roland Stulz
ROOF COVER GUIDE, FCR/MCR Toolkit Element 25, P. Gut, SKAT/ILO, 1993, 25.- SFr.
This guide provides the necessary information on the design and construction of FCR/MCR tile roof cover. Emphasis is given to basic roof forms.
The guide aims at helping to do proper detailing, and to build and maintain the roof cover in a sound manner. It deals with the different roof cover types, gives information about tile requirements and provides detailed solutions to technical tile laying praxis.
The guide is addressed to architects and engineers involved in the design of buildings with FCR/MCR tile roofs, and also to builders, site engineers and overseers, who are implementing construction.
Producers of roof cover materials can use the guide as a basis for advising their costumers on the successful use of their products. The guide is also useful as a teaching aid.
Roof Structure Guide, FCR/MCR Toolkit Element 24, P. Gut, SKAT/ILO, 1993, 35.- SFr.
This guide provides information on how to design and build a roof structure for light weight and even (non-curved) roof cover materials. Although it is part of the FCR/MCR Toolkit series, it is equally applicable in the case of other roof cover materials such as clay tiles, slates, sheets etc.
The guide explains also the basic principles of building statics and structural design. Constraints determining the roof shape and earthquake and storm proof construction are discussed.
The guide deals in brief with all the commonly known materials for roof structures with special emphasis on timber technology.
The guide is addressed to architects and engineers involved in the design of buildings with FCR/MCR tile roofs, and also builders, site engineers and overseers, who are implementing construction.
Producers of roof cover materials can use the guide as a basis for advising their costumers on the successsful use of their products.
CRATerre - International Centre for Earth Construction, Centre Simone Signoret / BP 53, F - 38090 Villefontaine, France
Earth is one of the raw materials which is extremely adaptable as far as compatibility with waste materials from various sources is concemed. Such waste materials can serve as a support, be processed into a stabilizer or actually be processed using a moulding process proper to building with earth.
Some of these processes are described below.
When acetylene is made from carbide, a residue is obtained which is in fact pure lime in the form of a paste.This can be used with earth as a stabilizer. It is mostly used as a mortar intended for masonry or renders.
Alginate is an alginic acid salt and is a by-product of algae treatment. Its use as a stabilizer can be of interest in coastal regions.
Banana tree fibres
It has long been known that the sap and fibres of banana trees have a stabilising effect. In Brazil, scientific research is being carried out on the use of the banana tree fibres which are the waste material of the agricultural industry.
Blast furnace slag
Blast furnace slag consists of scori a composed ofsilicates which float on the surface of molten metal and is a by-product of casting in iron ore foundries. In its chemical composition, blast furnace slag closely resembles Portland cement. Slag is made up mainly of three oxides:CaO, SiO2 and A12 03 (90 - 95%). One should take account of the fact that certain types of slag can be more active and others almost entirely incapable of forming a hydraulic bond. This depends of the structure of each type of slag after cooling. Slag induces some flocculation in the stabilization process which can be carried out with almost all soils. Their characteristics are very similar to those of the classic soil-cement.
Used car tyres areavailable in enormous quantities and it is often a real headache to know how to deal with them.They can be used for building. Once in place, they are filled with earth, one row on top of another. The earth must be carefully compacted inside the tyres. This gives a house with a very massive structure, with excellent thermal performance in most cases. For aesthetic and structural reasons, such houses are then rendered (illustration 1).
Coalmine waste materials are piled up to form enormous slurry heaps; as they naturally contain a certain amount of clay, they have some cohesive power. Several experiments to transfonn this "earth" into blocks intended for building have been successfully carried out.
An incredible amount of bottles can often be found around small and large towns. Bottles and other glass waste can be ground down into powder, which can in turn be incorporated into earth components, e.g. compressed earth blocks, adobe blocks, etc. Glass powder makes such bricks very hard and virtually impregnable to termite attack. A relatively limited number of blocks used in the footings of a house can effectively protect it from termite attack.
Iron salts are coagulant electrolytes produced by the mining industry. These products can stabilize soil, but this would require very large quantities because of their very slow dissipation. Their use is therefore restricted to mining areas.
Lignosulphate is the organic substance which permeates the cells, fibres and vessels of wood and certain plants and which renders them impermeable and non-extensible. For stabilization, one can use lignosulphates or lignosulphites which are by-products of wood processing (as well as straw or alfa) in the paper industry. Lignosulphite, for example, is poured away into the rivers of producing countries at a rate of several million tons a year. Their composition varies very greatly depending on the nature of the basic product used and the chemical reaction; the waste matter can be used as a gluing or dusting agent. But used in this way, they remain almost entirely water soluble. If the lignosulphite solution is mixed (by a process of oxidation) with hexavalent chromium salts, principally potassium bichromate or sodium bichromate, a thick gel is obtained which is an insoluble compound: chromolignin.
When stabilizing a soil with suitable characteristics, 4% lignosulphite and 1% bichromate should be used.
Lignin is found in the following materials:
24 - 28%
29 - 35%
Lime sucrates are not by-products of sugar refinery, but the final products of the transformation of sugar sap during refining. Lime sucrates can be used as a soil stabiliser. They are of particular interest in regions where growing and processing sugar cane are highly developed. These products can not be mixed with cement and may attract termites. Compressive strength is improved and capillary rise is greatly reduced. 5% is effective for sandy soils. When using clayey soils, small quantities of lime need to be added to obtain the equivalent effectiveness.
Certain kinds of molasses, which are by-products of plant processing, can be used for stabilization, e.g. wood molasses (see lignin), sugar molasses (see lime sucrates). Sugar aldehydes from dehydrated molasses can be polymerized at high temperatures with phenolic catalysts. The resinous material obtained has characteristics similar to that of a naturally occuring asphalt and synthetic resins.
This kind of gypsum, which is an industrial waste, behaves like plaster. It is an attractive stabilizer for rather sandy soils, but is not recommended for clayey soils. One should not exceed 15% proportion of stabilizer. Because of the danger of rapid setting, the earth must be worked in small quantities. The plaster can be combined with lime in proportions of around 1: 1.
It should never be used in combination with cement, however. Despite a definite stabilizing effect, such products remain vulnerable to damage from water.
Dust from concrete aggregate quarries is generally considered to be an unusable industrial waste product. Itcan, however, beused to thin soils with too high a clay content, thus making them perfectly suitable for use in the field of building with earth.
The raw material for production of aluminium is bauxite. When bauxite is refined, it yields alumina, which in turn is smelted into aluminium. The red or brown mud is a waste product from alumina production and constitutes a considerable environmental problem because there is so much of it - 30-40 million tonnes per year worldwide. Unless disposed of properly, it can contaminate the ground water and spread red dust over wide areas. Even when correctly managed, the unesthetic effect and the mere space requirement of the vast mud ponds motivate the continued search for economic uses.
UNIDO has undertaken a number of technico-economic studies on industrial use of red mud waste. These studies have been used to develop the technology used in China and for similar projects in India and Jamaica.
In Shandong in the People's Republic of China, the traditional local brickmaking factories are able to use a mixture of brown mud from the Shandong alumina plant and fly ash from the neighbouring coal-fired power station to make bricks and tiles.
Rice husk ash
Along-side with the production of rice paddy, are the by-products such as rice straws and husks, which are being disposed of as wastes. When properly burnt (400- 500 'C) the resultant ash can be used as a stabilizer, with pozzolanic properties.
The mineral waste products from the demolition of buildings can sometimes be perfectly suited to being mixed with clayey soils which act as natural binding agents. It is in this way that a large area of the centre of Lisbon, that of the Marquis of Pombal, was rebuilt after it had been destroyed in an earthquake,
The shea is a tree (Butyrospermum parkii of the sapotaccae family) which grows in the Sahara, and its seeds provide a fatty substance known locally as "karit‚" butter. The waste materials of the process, which still contain appreciable quantities of oil, can be successfully used in the composition of earth renders intended for earth building production.
Sodium chloride is a by-product of the manufacture of sodium carbonate. It can be used successfully with clayey soils to reduce their plastic characteristics. The effect obtained cannot, however, be qualified as stabilization.
Sugar press mud
The sugar will employing carbonation process are producing about 6-8 tons of press mud for every I 00 tons of sugar-cane processed by them. Its disposal is a big problem for the factories. Much useful land in their proximity is being wasted by dumping this material.
Press mud can be added to fine soils with high quantities of clay and/or silt, resulting into dramatic improvements of the characteristics of these soils.
Mortar prepared from this sugar press mud as such and mixed with 3 to 4 % bitumen can be used for rendering walls.
Used engine oil
Used engine oil can be used as a water-proofing agent within the material itself or on the surface. One should bear in mind that such oil will wash out with water. It is not therefore enormously efficient. As surface protection, its must be regularly renewed to achieve viable protection.
Enormous quantities of wood shavings are produced by our wood industries. In certain specific circumstances, wood shavings can be mixed with earth to form a perfectly stable and durable material, with remarkable insulating properties.
Dozens of other applications for using waste materials certainly exist. Do not hesitate to inform us of your own experiences which you can share with your colleagues through BASIN-News.
"Appropriate Building Materials" was first published in 1981 and quickly established itself as one of the most important source books in the field of building materials for the Third World. Up to this date, this book is in very high demand and used by various groups such as: engineers, architects, planners, practitioners, government officials, as well as do-it-yourself builders etc. SKAT still receives many letters, comments and also enquiries. Relevant journals reviewed the book and since then, almost any publication about appropriate building materials refers to it and/or includes it in the bibliography.
In 1993 a new print became necessary. This opportunity has been made use of by a mini revision (third revised edition) to add certain information such as Micro Concrete Roofing (MCR), new equipment and machine designs as well as new addresses. Only a mini revision was made, because the content of the second edition is still very much up to date with the prevailing situation in the field of appropriate building materials .
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