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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 3, Number 4 (HABITAT, 1995, 46 p.)
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View the documentThe aim of the network and its journal
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View the documentEnergy efficiency in the production of building materials*
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Energy efficiency in the production of building materials*

By Baris Der-Pelrossian, UNCHS (Habitat). This article has been produced based on in-house research conducted earlier.

INTRODUCTION

Most developing countries have realized the significance of expanding the capacity of domestic production of building materials and have adopted or are in the course of adopting necessary policies to that effect. However, translating these policies into reality will depend first and foremost on the availability of the basic resource inputs for the production of a variety of basic building materials. The main inputs required for the production of building materials are:

(a) raw materials;
(b) labour;
(c) capital items such as machinery and tools; and
(d) energy.

All these inputs play vital roles in the production process and inadequate supply of any of them will jeopardize the success of any enterprise producing building materials. Yet, there are certain building materials - such as cement, lime and burnt-clay bricks - for which energy alone is an exceptionally crucial factor of production - in fact, so crucial that these materials can easily be classified as energy-intensive building materials. For instance, in the production of fired-clay bricks, the energy input is the only means of transforming the properties of the raw material (clay) into the desirable building brick which should possess certain characteristics in terms of strength, durability and resistance to water absorption. Similarly, in the production of lime and cement, energy is the only input which transforms the limestone into a material with cement properties.

In most developing countries, energy-dependent building materials are the key materials in the construction sector. Portland cement is the single most strategic material and, almost invariably, where there are near substitutes such as low-strength binders, they all tend to be energy-dependent. For the purpose of low-income housing, opportunities to expand the availability of walling materials beyond the range of cement-based materials are often restricted to another energy-dependent building material - tired-clay bricks. Roofing materials pose another problem of high-cost and scarcity but, unlike walling materials, the options are limited to a few energy-intensive materials: aluminium sheets, galvanized-iron sheets and asbestos-cement sheets. One material which can be explored to improve the availability of roofing materials to the low-income population is fired-clay tiles - another energy-intensive material.

Energy is probably the single most crucial factor required to improve the production of building materials in developing countries, yet it remains scarce, prohibitive in cost or not available. The main reason for this setback is obvious. The sharp increases in crude oil prices in the 1970s have since sustained a devastating trend in the energy situation, with the oil-importing developing countries being the most disadvantaged. The negative cycle in cost and supply of crude oil has had a similar effect on alternative forms of energy such as coal, firewood and electricity. The cost of energy in the production of a typical energy-intensive building material such as cement comprises 60 to 75 per cent of the direct manufacturing cost (1) - that is, if the source of energy is ever available at all.

In recent times, attention has continuously focused on ways and means of improving the energy situation to enhance the building-materials sector. Efforts in this direction are being made in both developing and industrialized countries, with outstanding achievements from the latter. Finland, for example, with minimal investments in ventilation technology has achieved about 30 to 75 per cent savings in energy consumption in the concrete industry. Hungary has achieved a 50 per cent reduction in energy consumption in the brick industry by renewing dryers and stoves and promoting efficiency in heat recovery (2). A few energy-saving technologies have also emerged in India and elsewhere. Thus, there is sufficient evidence that the negative trend in the energy sector is reversible. The purpose of this article is, therefore, to take account of the useful innovations towards improvement of the energy situation and, in particular, to stimulate research and development activities in an effort to ensure wide-scale production of local-building materials for the low-income population.

I. Energy Consumption in the Building-Materials Sector

Energy sources in the production of building materials can be classified as either primary sources - such as oil, coal, gas, other fuels and electricity, or as secondary sources - consisting of waste-heat which is generated during the production process.

While both sources of energy are important in the search for energy-efficiency in building materials production, the primary sources of energy are fundamental to the energy crisis and, perhaps, deserve more attention. There is a distinction between thermal energy resources, which are responsible for the main energy transformation process in the production cycle, vis-a-vis energy for electrical power to run machines for ventilation, grinding of raw materials and similar functions. Thermal-energy consumption normally outweighs that of electrical power. For instance, in cement manufacture, fuel consumption accounts for about 75 to 90 percent of the total primary energy used in a plant while electrical power accounts for the remaining 10 to 25 per cent(3). In some small-scale technologies for production of lime and fired-clay bricks, energy requirements could sometimes be accounted for only by fuel consumption in the firing process.

Comparison between various building materials in terms of their energy-consumption patterns should take into consideration variations between countries and even within one country; consideration should also be given to variations between production technologies for the same building material. This is a very complex task and, in the absence of comprehensive universal data in this areas, an attempt has been made in table 1 to provide an indication of relative energy consumption for selected building materials in India.

Table 1. Energy consumption in the manufacture of building materials in India

Classification of material

Energy consumption in MJ/kg of material

I

Burnt-clay tiles

3.00

II

Burnt-clay bricks

1.43


Hollow-concrete blocks

1.20


Sand-lime blocks

1.03

III

Reinforced concrete

2.00-8.00


Unreinforced concrete

1.20


Aerated concrete

2.89

IV

Portland cement

6.70


Hydrated lime

4.21


Gypsum plaster

1.52


Calcined-clay pozzolana

1.39

V

Steel

26.00


Aluminium

144.00

VI

Wood products

3.00

Source: Fog, M. H. and Nadkarni, K. L., reference No. 1

The energy values given in table 1 can only be meaningful if comparisons are made between materials with similar functions in construction. For instance, cement, lime and gypsum are comparable within the limits to which they can be used in construction for identical purposes. This phenomenon is illustrated in tables 2 and 3, using walling materials and binders as examples. These consumption values become even more meaningful when translated into cost values relative to total cost of production as indicated in table 4.

Table 2. Energy consumption in materials for walling

Element

Energy content of 1 sq. m in MJ

Wall made of

bricks:

118.0 kg

278.5

hollow-clay bricks,

cement:

2.5 kg

10.0

18 cm × 10 cm × 30 cm

lime:

6.4 kg

57.6

21 cm thick

sand:

0.043m

314.2




360.3

Wall made of

bricks:

73.1 kg

172.5

hollow-clay bricks,

cement:

2.0 kg

8.0

8 cm × 18 cm × 30 cm

lime:

5.2 kg

46.8

13 cm thick

Sand:

0.035m3

11.5



238.8;

Wall made of

bricks:

127.0 kg

660.4

solid-clay bricks,

cement:

1.8 kg

7.2

12 cm × 16 cm × 25 cm

lime:

4.5 kg

40.5

15 cm thick

sand:

0.03 m3

9.9



718.0

Wall made of

bricks:

255.0 kg

1326.0

solid-clay bricks,

cement:

4.4 kg

17.6

12 cm × 16 cm × 25 cm

lime:

11.1 kg

99.9

30 cm thick

sand:

0.074m3

24.4



1467.9

Wall made of adobe,

adobe:

800.0 kg

1.5

40 cm × 10 cm × 20 cm

cement:

1.6 kg

6.4

43 cm thick

lime:

4.2 kg

37.8

sand:

0.028m3

9.4



55.1

Wall made of adobe,

adobe:

400.0 kg

0.75

20 cm × 40 cm × 40 cm

cement:

1.6 kg

6.4

23 cm thick

lime:

4.2 kg

37.8

sand:

0.028m3

9.3



54.25

Wall made of concrete

cement:

52.4 kg

209.6

blocks, 20 cm × 20 cm

lime:

7.0 kg

71.1

× 40 cm 23 cm thick

sand:

0.159m3

52.5

stone:

0.107m3

35.3



368.5

Source: Rai, M. Energy Conservation in the Development and Production of Building Materials, reference No. 7

Table 3. Energy consumption of selected binders (basis 1m3 wet mortar)

Composition of binder

Energy requirement as percentage of 1:6 cement-sand mortar

Cement: sand (1:6)

100

Cement: lime: sand (1:1:6)

135

Lime: burnt-clay pozzolana (1:2)

172

Lime: burnt-clay pozzolana: sand (1:1:1)

133

Lime: flyash or rice-husk ash (1:2)

94

Lime kiln reject: flyash or rice-husk ash (1:2)

25

Source: Rai, M. Energy Conservation in the Development and production of Building Materials, reference No. 7

Table 4. Cost of energy relative to production cost of selected materials

Material

Energy cost as percentage of total material cost

Cement

43.0 - 53.0

Lime

47.9 - 59.5

Gypsum products

11.1 - 16.6

Bricks and tile

29.7 - 36.5

Other structural

23.7

Clay products

35.2

Concrete blocks

3.6 - 6.5

Timber sawmills

2.2 - 4.1

Source: UNIDO - The building materials industry in developing countries, an analytical appraisal, sectoral studies series No. 16 vol. 1, Vienna 1985 p. 98.

Another important but often neglected component in energy consumption in the building- materials sector is in relation to transportation or distribution of the finished product for construction. Building materials are produced solely for construction so that their energy consumption computations can only be finalized at the point of use. In fact, there are some developing countries where the cost of transporting building materials outweighs the actual cost of production. In Botswana, Honduras and Sudan, after 100 miles, the cost of transporting cement is higher than the manufacturing cost(4).

II. Prevailing energy-inefficient production systems

Despite the high cost and scarcity of energy, there is a considerable degree of wastefulness in the use of energy in the production of building materials, especially regarding energy-dependent building materials. To some extent, energy loss in this context can be attributed to basic human error or negligence in the production process. However, a fundamental reason for wastefulness in energy utilization can be attributed to two related factors:

(a) production technology; and
(b) scale of production.

The extent to which the choice of technology determines the efficiency of energy utilization can be illustrated with the following examples:

(a) Cement production

Cement production is basically a choice between rotary kiln technology and vertical shaft kiln technology. The rotary kiln is more popular, due to several technical advantages. However, on account of energy consumption alone, the shaft kiln is more efficient - as illustrated in table 5.

Table 5. Typical energy consumption patterns of cement manufacturing processes in Europe (fossil fuel only)

Type of kiln

Energy consumption in kcal/kg of clinker

Shaft kiln

750

Rotary kiln types

Dry (long kiln)

860

Wet (long kiln)

1300

Dry (suspension pre-heater)

790

Source: Spence, R.J.S. Small-scale Production of Cementitious Materials, I.T. Publications Ltd., London, 1980.

In a similar development in India, it was established that while a vertical shaft kiln consumed around 750 kcal/kg of clinker, a rotary kiln consumed up to 2000 kcal/kg of clinker. In addition to the advantage of low-fuel consumption, the vertical shaft kilns are known to have operated efficiently on a variety of solid fuels, sometimes with an ash content as high as 50 per cent (5). Even within the rotary kiln technology, there are variations between the wet process and the dry process, with implications for energy-efficiency. For instance, a wet process could consume 1400 kcal/kg of cement compared to 750 kcal/kg of cement energy consumption in the dry process - a difference of about 86 per cent (6).

(b) Lime production

Fuel consumption in alternative technologies for production of hydrated lime tends to show the importance of choice of technology in achieving energy efficiency. Using the case-study of the Federal Republic of Germany in table 6, an energy saving of about 40 per cent is achieved when rotary kiln technology is adopted in place of a traditional vertical kiln. A similar trend applies to India, where energy efficiency of the CBRI improved shaft kiln has been achieved through the principles of uniformity of heat distribution over the cross section of the kiln plus the provision of a good draught system. In detail, the CBRI kiln is a tall cylindro-conical structure constructed of masonry material with an internal lining of fired-clay bricks. The effective height of this kiln for a 10 tonne per day capacity is 11 m and the calcining zone maintains a temperature of 950°C to 1100°C (7).

Table 6. Fuel consumption in lime production using different technologies

Country

Type of kiln

Proportion of production cost

Primary energy consumption MJ/kg quicklime


Traditional vertical kiln

35

4.760

Federal Republic of Germany

Ring annular kiln

22

4.865


Rotary kiln

20

6.715


Traditional kiln

-

12.60

India

Conventional

-

9.03


Improved shaft kiln (CBRI)

-

6.24

Source: UNCHS (Habitat), Technical note No. 12, 1987

(c) Fired-clay bricks

The theoretical energy requirement for firing clay bricks in small-scale kilns is about 20 to 35 per cent of the actual energy consumption in production practice. Thus, most existing brick production technologies are by definition energy-inefficient. Despite this trend, large-scale kilns are more efficient in energy consumption than traditional kilns as exemplified in table 7.

Since transportation of bricks from the point of production to the point of use accounts for a significant amount of energy consumption, it could be argued that the scale of production is a crucial determinant of efficiency in energy utilization. Building materials, by their nature, tend to have a low value-to weight ratio so that they are excessively costly to transport even over short distances. This situation is worsened in most developing countries where the scarcity and prohibitive cost of oil are rampant and where the infrastructure or facilities for transportation are under-developed. Large-scale production technologies predetermine high-energy consumption for distribution of building materials because a single plant often has a wide catchment zone, sometimes an entire country. Large-scale brick industry is an example of prevailing error in choice of scale of technology as far as energy-efficiency in transportation is concerned.

III. Innovations for energy-efficient building materials production technologies

There are at least four ways in which the building materials sector can realize improvements in terms of energy-efficiency. These are:

(a) extensive use of those building materials which can be produced with hardly any expenditure on thermal energy or electrical power;

(b) innovative technologies to improve or minimize fuel consumption in energy-intensive building materials production;

(c) innovations related to use of cheap and renewable forms of energy as fuel or electrical power; and

(d) promotion of small-scale technologies to minimize energy consumption in transportation of materials.

The four strategies outlined above are interrelated rather than independent. Thus a comprehensive approach to the energy crisis may require the implementation of all four approaches concurrently.

The following parts of this article show the specific merits of each.

(a) No-energy building materials

In principle, building materials which can be produced without the use of any type of thermal energy and electrical power should form the cornerstone of the building materials sector in countries facing scarcities and high cost of energy. Unfortunately, there are only a limited number of such building materials. Typical examples are unstabilized soil blocks, fibre-reinforced soil blocks, manually produced bamboo walling and thatch roofing.

Table 7. Energy consumption in brick-making technologies

Technology

Scale of production
(No. of bricks)

Labour required (man-hr for 1000 solid bricks)

Over-all energy consumpion (MJ/1000 solid bricks)

Small-scale production, all manual methods, clamps, scoves, scotch kilns

2,000

20 to 30

7,000 to 10,000

Small-scale production, all manual methods, up draught and down draught kilns

2,000

30 to 40

10,000 to 15,000

Medium-scale production, all manual methods, bull's kilns

20,000

30 to 40

4,000

Medium-scale production, semi-mechanized method, Hoftmann on zig-zag kiln

30,000

30 to 35

3,000 to 3,500

Large-scale production, full mechanized tunnel kiln 1

150,000

10 to 15

3,000 to 4,000

Source: UNCHS (Habitat), Technical Note No. 12.

(b) Innovative technologies to improve fuel consumption in energy-intensive building materials

Some energy-intensive building materials are indispensable to construction so that any improvements in their supply and cost should depend on feasible innovations to optimize the energy consumption patterns in the production process.

Fortunately, recent innovations have proven that energy utilization in the production of materials such as cement, lime, concrete and fired-clay bricks can be optimized with considerable benefits in energy savings. Using Portland cement as an example, table 8 gives an indication of some interesting innovations.

Another innovation regarding energy-savings in cement production is the technology of blended cements. The blending of certain carbonaceous materials such as granulated slag, fly-ash and other pozzolanas with cement makes it possible to produce more cement from the same amount of clinker and thus reduce the final consumption of energy per ton of cement produced. Experience has shown that up to 20 per cent of clinker can be replaced by fly-ash and up to 25 per cent by blast furnace slag without changing the performance of blended cements in comparison to Portland cement for general application in construction. In some countries, this mode of production has led to an estimate of 20 to 40 per cent savings in fuel consumption. Further examples of innovations in production technology related to energy savings for a variety of building materials are given in table 9. Fortunately, most of the materials identified in this table are abundantly available in most developing countries; indeed, they exist as waste products which pose a disposal problem. One way to enhance the wide-scale use of these innovative technologies is to promote effective and economic strategies for collection and distribution of these waste materials.

(c) Innovations related to use of cheap and renewable sources of energy for fuel and electrical power.

Table 8. Selected examples of improvements in energy conservation and in specific energy consumption in cement production

Plant type/location

Energy savings

Measure taken

A. Energy conservation


Wet process

Savings of 150 kcals/kg

Adding a vent air recirculation system toclinker cooler thereby reducing dustwastage and increasing heat recuperation.

Long-dry process

Savings of 512 toe/year, Preheating of fuel oil by using clinker cooler waste heat from heat exchanger inside the cooler.

Preheater-dry

Savings of 625 toe/year, Use of coal mine tailing as substitute processof fuel oil

Semi-dry process

Savings of 625 toe/year

Use of clinker cooler vent air as primary air to hot air furnace.

Dry process

Savings of 14 kcals/kg, Addition of new kiln seal at discharge end to cut out air infiltration.

B. Lowering specific energy consumption

Wet process (Canada)

10 per cent (from 1,416 kcals/kg to 1,280 kcals/kg)

Recirculating clinker cooler air.

Wet process (Canada)

9 percent (from 1,441 kcals/kg to 1,280 kcals/kg)

Slurry thinner to lower slurry moisture to 1,280 kcals/kg) from 35.8 per cent to 31.2 per cent with increase in clinker production by 9 per cent.

Wet process (USA)

17 per cent (from 1,876 kcals/kg to 1.560 kcals/kg)

Reduction in slurry moisture, new seals and closing holes, new cooler grates, and fans, new chain system.

Wet process (Brazil)

11 per cent (from 1,841 kcals/kg to 1,637 kcals/kg)

Changing clay component, modifying chain system.

Wet Process adding (USA)

15 per cent (from 1,617 kcals/kg to 1,381 kcals/kg)

Slurry water reduction, lifters insulating bricks, raw feed chemistry control, chain maintenance, and cooler modification.

Source: Fog, M. H. and Nadkarni, K.L. reference No. 1.

It can be argued that the most important strategy to tackle the energy situation relates to the availability and use of substitutes to coal, oil, gas and firewood. In the search for cheaper alternatives to conventional forms of energy, one should aim first and foremost at those options which are easily achievable within the resource capacities of developing countries -preferably energy options related to waste materials. For choosing the energy sources, the criteria should thus initially ignore disadvantages in rate of energy consumption using "new" forms of energy vis-a-vis conventional forms of energy.

On the basis of the above, one could summarize the innovations worth promoting as follows:

(i) development of energy from bio-mass based on agricultural residues and in a form which could be transported, i.e., by pyrolytic conversion of bio-mass into liquid and gaseous energy or charcoal;

(ii) use of agricultural and industrial wastes such as rick husk, directly as forms of solid fuel;

(iii) recycling and/or incineration of municipal-solid wastes - glass, aluminium, paper, plastics, wood and rubber;

(iv) development of suitable forms of energy from the sun, ocean, wind and geo-thermal power for direct heating or drying processes or for conversion into electrical power.

Table 9. Utilization of industrial and agricultural wastes for production of building materials in energy-saving technologies

Type

Supply of material

Mode of utilization

Energy Saving (percentage)

1. Granulated blast furnace slag

Iron and steel industry

Up to 45 per cent additive to cement to produce blended cement

35 to 40 per cent of energy consumption in manufacturing of ordinary Portland cement

2. Air-cooled and foamed blast

same

Substitute to conventional coarse aggregate.

10 to 15 per cent compared to stone aggregate.

3. Fly-ash

Thermal power plants using coal

Up to 30 per cent additive to cement to produce blended cement

25 to 30 per cent of energy consumption in manufacture of ordinary Portland cement.

4. Fly-ash

same

20 to 40 per cent interground with clay to produce fired-clay bricks

25 to 30 per cent equivalent of energy consumed in firing bricks consumed in firing bricks with coal or wood

5. Colliery waste

Coal washing plants

10 to 25 per cent In interground with clay to produce fired-clay bricks

20 to 25 per cent comparison to normal energy requirements using coal

6. Mineral tailing

Residues of iron, cooper, zinc, tin, lead, gold, silver

Constitutes 20 to 50 per cent of raw materials for production of fired-clay bricks, masonry cement, cellular concrete and sand-lime bricks

15 to 30 per cent Compared to energy consumption in normal production system

7. Calcium carbonate sludge

Fertilizer, tannery, sugar, paper and acetylune industries

As raw material for lime manufacture

10 to 15 per cent Compared production from traditional raw materials

8. Bauxite waste (red mud)

Aluminium or bauxite industry

50 per cent additive inter-ground with clay in production of fired-clay bricks

5 to 10 per cent compared to energy consumption in normal production systems

9. Husks of rice, groundnut, coffee, maize

Various plant sources

10 to 25 per cent additive interground with clay and coconut pithin production of fired-clay bricks. The husks when incinerated into ashes can be mixed with lime to produce low-strength binders of blended with ordinary Portland cement to produce masonry cement.

15 to 25 per cent equivalent of coal consumption in normal production process

Source: UNCHS (Habitat), Technical Note No. 12.

(d) Promotion of small-scale production units

This strategy is the only logical means of ensuring distribution of building materials to the ultimate point of use with minimal demands on fuel for transportation. Fortunately, recent innovations have made it possible for almost every building material to fit into varying scales of production defying the monopoly of large-scale production systems which certain sectors such as the cement, steel and aluminium industries used to enjoy. For instance, in some countries, the introduction of mini steel plants utilizing scrap metal as raw material has led to noticeable savings in energy consumption in the steel industry.

CONCLUSIONS

The indispensable role of energy as a factor of production in the building-materials sector is undermined by the crippling trend of its scarcity and high cost in most developing countries. However, as indicated in this article, there is proven know-how to deal with this negative situation. In fact, some of the technological options for energy-efficiency in building materials production are so simple and basic that it may not be too difficult to put them into actual practice. What remains to be done is to find an effective means of promoting the requisite technological innovations at the local level either through transfer of know-how from external sources or even technology transfer within a given country. Normally, information dissemination through written materials such as this article, is not in itself an end to realizing practical achievements in technology transfer or technology innovation. Nevertheless, the existing gap in information flow related to technology innovation in developing countries, makes the information in this article note of relevance to overall development efforts -hopefully it will serve as the framework for designing effective field implementation programme on this subject.

REFERENCES

1. Fog, M. H. and Nadkarni, K. L., Energy efficiency and fuel substitution in the cement industry, World Bank, Washington, 1983.

2. Economic Commission for Europe, Energy savings in the production of building materials and in the construction process, seminar on modern building technologies, Poland, 1985.

3. Ibid, reference No. 1

4. UNIDO, The building materials industry in developing countries, sectoral studies series No. 16, Vol.1 Vienna, 1985.

5. Spence, R. J. S., Small-scale production of cementitious materials, I.T. Publications Ltd., London, 1980.

6. Ibid, reference No. 1.

7. Rai, M., Energy conservation in the development and production of building materials, proceedings of the International Workshop on Energy Conservation in Building, C.B.R.I. Roorkee, India, 1984.

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