A study of alternative building materials and technologies for housing in Bangalore, India

Construction and Building Materials Vol. 9, No. 4, pp. 21 l-211, 1995 0 1995 Elsevier Science Limited

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A study of alternative building materials and technologies for housing in Bangalore, India Steven W. Harrison*

and Braj F?Sinhat

*Thorburn Colquhoun, UK tDepartment of Civil Engineering,

University

Received 7 April 1994; revised 5 January

of Edinburgh,

Edinburgh

1995; accepted 6 January

EH9 3JL, UK

1995

The purpose of the paper is to appraise alternative building materials and technologies for wall and roof construction. To this end, a study was undertaken of various options for housing in the city of Bangalore, India. An assessment is made of the cost of construction with these technologies as opposed to the conventional solutions normally adopted, indicating their suitability on this basis. In addition, other factors are highlighted which may effect the wide-scale adoption of the technologies. Keywords:

alternative;

building materials; wall

Most developing countries are facing an acute housing shortage and India is no exception. According to 1991 census data, the total population stood at 837 million, compared with just over 680 million in 1981. In fact, it is estimated that by the year 2000, India will overtake China as the most populated country in the world, with a projected total population in excess of 1 billion’. In the context of severe constraints on resources of all kinds, there is a growing awareness of the need to adopt measures for economy in the construction of shelter and low-rise buildings for housing the teeming millions in developing countries. In this quest for economy, the utilization of local materials, skills and manual techniques has been suggested for application in mass construction schemes and alternative materials and technologies are being promoted against conventional materials and technologies which have stood the test of time. A study of some alternative building materials and technologies was conducted in the city of Bangalore, India, to examine if the materials and technologies proposed are really economic in the short and longterm, and to establish any primary reasons for nonadoption in mass housing. The decision to examine the current housing situation in Bangalore was reached because the city is growing at an alarming rate due to rapid industrialization and migration of population from villages and other states in the search of better living conditions and improved job prospects. As a result, building activity within the city is more pronounced than in most other Indian cities2. Building materials and technologies For the materials to be appropriate to the needs of developing countries, they must be indigenous, locally Construction

available in abundance with low energy input in terms of production, maintenance and transportation costs, and be labour intensive. In a country like India with mass unemployment, it is essential to use labour intensive methods as it is estimated that the investment of 10 million rupees in housing construction generates direct employment on site of 565 man years of skilled and unskilled labour at 1983-84 wage rates3. In India, middle-class urban housing is generally constructed from bricks with a reinforced concrete roof. The choice of this roofing technology, although inappropriate to local climatic conditions, is seen as a way of conveying status in the community resulting in the demise of inclined tiled roofs. Therefore, the comparison of the alternatives will be made with this accepted norm. Clearly, the success of any proposed alternative will be influenced by several issues. The key factors for consideration are: (i) (ii)

(iii) (iv)

Cost. Can the use of an alternative be encouraged solely on these grounds? Technical input. Are the experts available to implement the technology successfully in housing the masses, bearing in mind that present forms of house construction are completed by employing local labour or labour contractors with no technical input. Availability of materials. Attitude. Do the views of the community aid or hinder the success of a proposed alternative; if the alternative is seen as inferior or not prestigious, the chances of adoption will be slim.

Of these issues, the question of cost to the user will receive the greatest attention in this paper. and Building Materials

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A study of alternative building materials: S. W. Harrison and 6. P. Sinha With these factors in mind, there now follows a description of the building materials and technologies employed in the houses investigated in terms of (i) (ii)

Indigenous materials used for the superstructure, i.e. the walls. Alternative roofing materials and technologies.

Materials used for superstructures The various walling materials described in this section.

used locally at present

are

Brick and cluy products Generally, brick and clay products are used in the conventional methods of house construction. A selection of the clay products adopted in the case study houses are represented in Figures I to 3. Soil cement blocks Soils can be used as a construction material for housing. The properties of the soil can be improved by adding one or more stabilizers. The purpose of the stabilizer is to prevent softening of the soil on absorption of moisture, the three main types of stabilizer being cement,

Figure 3

cement and lime, and lime”. It should be realized that there is no ‘miracle’ stabilizer that can be used in all cases, so that it is up to the builder to make trial blocks with various kinds and amounts of stabilizer which can be tested. In general, however, it may be stated that red sandy loams are ideal for stabilized soil blocks, the most important ingredients being 10 to 20% clay and 60 to 70% sand content. Although methods of block production may vary slightly, they all incorporate the same basic elements, namely sieving of the soil, pressing of the soil and chosen stabilizer by means of a machine, and curing of the resulting blocks for a specified period of time. Stone us u building muteriul

Figure

1

Two walling systems employed the use of granite stone, namely the composite wall and modular granite slab system, this being in plentiful supply from the surrounding areas of Bangalore. The main properties of granite are a high compressive strength, resistance to most chemicals, and excellent durability. However, the stone is difficult to cleans. The modular system of granite slabs and concrete piers is developed around?

ii) (ii) (iii) (iv)

isolated, double-layer foundations of stone slabs for cast in situ hydrated lime-concrete block piers with slots on all sides to accommodate roughly dressed granite stone slabs forming the enclosing walls RC slabs.

Roofing technologies

Figure 2

212

The roof is the most essential part of a house. It is the part that predominantly costs the most, it is the part most exposed to the rigours of nature, and it is the part primarily responsible both for indoor comfort and for damage suffered during exposure to the detrimental effects of nature. Construction and Building Materials 1995 Volume 9 Number 4

A study of alternative building materials: S. W. Harrison and B. P. Sinha

Figure 4

Schematic representation

Ferrocement

of modified filler slab

Figure 6

Hollow blocks over prestressed panels

technologies

Ferrocement is principally the same as reinforced concrete (i.e. it incorporates wire mesh in the sections which are in tension, to supplement the low tensile strength of the mass and control thermal and shrinkage cracking), but has the following differences:7 (i) (ii) (iii) (iv)

its thickness rarely exceeds 25 mm; a rich Portland cement mortar is used; ferrocement has a greater percentage of reinforcement; its tensile-strength-to-weight ratio is higher than for reinforced concrete.

Shear connector

Ferrocement beam

ModiJed filler slab

The modified filler slab replaces concrete not used structurally in an attempt to reduce costs*. Lighter materials, in this case mangalore tile units, are positioned on a formwork allowing for reinforcement to run in ribs in perpendicular directions. Concrete is then cast between the ribs, covering the tiles. The system is particularly suited to warm climates as the existence of air voids between the tiles tends to increase the slab’s thermal insulation value. A schematic representation of this system is given in Figure 4.

Triangular stirrup ’ Tension rod

Figure 7

Precast roof and floor slabs The standard reinforced concrete slab may be designed to reduce or eliminate the need for formwork which is a costly and time-consuming part of the process of construction. Parts of the roof structure are precast in moulds on the ground or in a factory away from the site. These may be speedily assembled at the site once the supporting structure is in place. Three such systems employed in some of the case study houses use precast beams placed at such a spacing that, for example, hollow blocks can conveniently span between them*. These three systems, i.e. burnt clay hourdi tile roof, hollow blocks over prestressed panels, and composite reinforced concrete beam and cuddapah slabs, are illustrated in Figures 5 to 7, respectively. Arch roof

Figure 5

To eliminate the need for tension-carrying materials such as steel the principle of the arch can be employed, by which a roof can be constructed out of materials which can carry purely compressive forces. The technique of the arched panels over reinforced concrete joists as presented in Figure 8 makes partial use of this approach. The arched panels, which are prefabricated Construction and Building Materials 1995 Volume 9 Number 4

213

A study of alternative building materials: S. W. Harrison and 6. P. Sinha

Figure 8

Arched

panels over reinforced

concrete

Joists

at site ground level on earth formworks, consist of tiles with a layer of concrete on top. These are lifted to roof level and placed on the joists. For stability, the end walls need to be buttressed or alternatively the beams tied togethe?.

Figure 10

House no 2

Figure I1

House

no 3

Figure 12

House

no 4

Comparative cost analysis Tuhle 1 presents the houses examined in terms of the materials adopted for the walls and roofs, and the construction costs. The cost is compared against the norm, this being the brick walls and concrete roof. As the houses were built at different times. the cost was reworked for 1993 costs taking inflation into account. Instead of calculating the cost on a plinth area basis. it was felt that the surface area of the walls should be used. The reasoning behind this is that cost based on plinth area will include all the fittings, which may be highly variable between each house. External views of selected case study houses are indicated in Figurrs Y to 1-1. It can be observed from Tuble 1 that the cheapest walling material is the soil-cement block. with an average cost of approximately ~51.81 m-‘. All the alternative materials are cheaper compared to the plastered burnt clay brick walls. However, the claim of the

Figure 9

214

House no

I

designer of the modular granite slab system (house no. 3) of a 40% reduction in cost cannot be substantiated on the basis of these calculations. A saving of 13% in the cost of the superstructure can be justified at the expense

Construction and Building Materials 1995 Volume 9 Number 4

Soil-cement blocks

Soil-cement blocks

Soil-cement blocks

Soil-cement blocks

Soil-cement blocks

Perforated blocks

Soil-cement blocks

Perforated

4 (1988)

5 (1990)

6 (1991)

7 (1991)

8 (1991)

9 (1991)

10 (1992)

11 (1992)

Rs. 45/-

Concrete block pillars with granite slabs

3 (1991)

f 1.OOis approximately

Composite masonry: size stone masonry/ soil-cement blocks

2 (1991)

clay blocks

and hollow clay

Burnt clay bricks

Superstructure

1 (1992)

House number (year of construction)

Hourdi clay blocks on prestressed joists

Arched panels on RC joists

Hollow clay blocks over prestressed joists

Modified filler slab

Reinforced concrete roof

Reinforced concrete roof

Composite reinforced concrete beam and cuddapah slabs

Burnt clay Hourdi tile roof

Reinforced concrete roof

Tiled and concrete arched panels on ferrocement ribs

Reinforced concrete roof

Roof

N/A

N/A

5777

2517

4850

8513

1785

6815

11666

13555

7075

N/A

N/A

9.62

6.91

8.90

8.68

6.39

7.21

10.41

9.07

9.66

N/A

N/A

2.08

1.65

1.79

1.55

1.82

1.70

3.76

3.95

4.33

Cost at time of construction Total cost Roof Walls (f m-2 plinth) (f m-2 (f ) surface area)

12444

8000

6673

2908

5602

9832

2268

10478

2538

15656

8172

11.46

14.60

11.12

7.99

10.26

10.02

8.11

8.68

11.43

10.46

11.15

2.35

1.93

2.14

1.70

1.86

1.60

1.90

1.84

3.83

4.07

4.40

Estimated cost for 1993 Total cost Roof Walls (f m-2 plinth) (f m-2 (0 surface area)

Table 1 Alternative materials and technologies adopted in case study houses and their cost

A study of alternative

Figure 13

building materials: S. W. Harrison and B. P. Sinha

Houseno 9

of visual impact or aesthetic appeal. If the quality of available bricks can be improved and the walls left unplastered, then there will be a reduction in cost from 4.40 to f2.82 rnm2,a saving of 36%. This requirement is not that difficult to achieve and implement. The implication of this improvement means that all the alternative technologies of composite external granite and internal soil cement block wall (house no. 2) and modular granite system (house no. 3) become more expensive than the technology they are attempting to replace. Only soil-cement blocks still remain cheaper, but the saving is reduced from 56% to 34%. Since in many parts of India good quality bricks are available, these alternatives do not offer any savings. Reinforcing this point, examples exist of railway buildings constructed several years ago with unplastered bricks throughout the country which have proved durable and have stood the test of time. The performance of the alternative roofing technologies compared to that of the reinforced concrete slab vary markedly. The average approximate cost of the RC slab is f 10.76 m-*, the greatest saving resulting in the use of the modified filler slab with mangalore tile filler units (house no. 5) - costing f7.99 rne2, a saving of 26%. The performance of the other technologies is less than convincing, with only marginal savings being obtained. If the walls of the conventional house (house no. 1) are replaced with the cheapest alternative, namely the soil-cement blocks, the introduction of a saving of 58% in walling costs would appear to be an attractive proposition to any householder. Therefore replacing the walls, the total saving in cost for the house as a whole is 8”/1 (i.e. original cost f8172; reduced price f7520). However, if it is assumed that the burnt bricks are of adequate quality to remain unplastered, the saving becomes 3% (i.e. original cost f7764; reduced price f7520). This constitutes a significant reduction in possible savings. Performing a similar operation to the type of roof employed, i.e. the modified filler slab replaces the reinforced concrete slab, a total saving in the cost of the house is 2.5%, based upon plastered burnt bricks (i.e. 216

Construction

reduced price f7965). Again, if the bricks are taken to be unplastered, the saving becomes 2.66% (i.e. reduced price f7557). If the wails and roof of house 1 are both replaced by the cheapest alternatives, and assuming the bricks can be left unplastered, the total saving in the cost of the house as a whole is 5.8% (i.e. reduced cost f7313), still a reasonable saving. If the walls are originally plastered, the possible saving is 10.7% (i.e. reduced cost f7296). These figures do not, however, take account of the price of land which, after all, is a resource requiring capital expenditure from the house-owner and so, a consideration in the calculation of any cost reductions. The price paid for the house plot by the owner of house I in 1990 was f 1777, with construction following in 1991. Therefore, based on 1991 construction costs and including land, the total saving incurred by the adoption of these alternatives for the case of the plastered burnt brick walls is 9% (i.e. original cost f8853; reduced cost f8019). The possible saving with the burnt brick walls unplastered is only 5.1%. Secondary technical issues These savings not only represent a marked difference from the individual savings in wall and roof costs, but also the optimum reductions possible based upon the available data. With a saving of 5%, it may be considered appropriate to employ soil-cement blocks in place of clay bricks. However, there are hidden problems which affect the eventual cost of applying such a technology. For instance, unlike the more conventional methods 0,‘ construction, the use of soil-cement blocks requires a high degree of technical input to produce satisfactory results. When these technical issues are properly addressed, stabilized soil blocks represent an attractive proposition for adoption in mass housing programmes. One such successful implementation of the technology was initiated by the Military Engineering Services (the largest Indian governmental construction agency) in the construction of three buildings during 1990-91 in Bangalore for the Defence Research and Development Organization. These structures were inspected during June 1993 and found to be performing satisfactorily although some cracks had developed in the two-storey buildings, predominantly on the external walls subjected to the greatest climatic changes. However, if technical supervision and adequate standards are not enforced, the results can be disastrous. The point is most clearly illustrated by the Yelahanka Housing Project which involved the construction of some 770 houses of soil-cement blocks. Due to a disregard for the technical considerations involved in producing the blocks, the subsequent houses were of such a poor quality that the project was abandoned before completion, a loss which a developing country can ill afford. Since such technical difficulties cannot be attributed to burnt clay bricks, it is somewhat unclear as to whether these savings are significant enough to increase the use of such alternatives.

and Building Materials 1995 Volume 9 Number 4

A study of alternative building materials: S. W. Harrison and B. P. Sinha

Conclusions

Acknowlegements

On the basis of this study, the following conclusions can be drawn:

The authors are extremely grateful to both the Institution of Civil Engineers, the University of Edinburgh, and the Carnegie Trust of Scotland, whose financial support made this study possible. Also, many thanks to Professor Jagadish and his colleagues of the Department of Civil Engineering, Indian Institute of Science, Bangalore, and the Central Building Research Institute, Roorkee, for their technical input. Finally, to all those who gave their valuable time to be interviewed, your contributions can never be underestimated.

The replacement of a conventional technology with an alternative material must be measured against the cost of the building as a whole. An optimum overall saving of approximately 5% may not be a significant enough incentive for people to alter the choice of materials used in their homes. If the quality of burnt clay bricks can be improved to a level where the need for plaster finishes is negated, all the adopted alternative technologies for the construction of houses become expensive except for soil-cement blocks as a walling material. The modified filler slab, with a saving of 36% compared to the conventional RC slab, may be adopted in roof construction. The Government of India and research institutes must also play a part to ensure that any technology is thoroughly investigated, hence minimizing the risk of its failure when applied in the field. For any alternative technology to be successful proper training must be given to craftsmen and professionals, which is not as important in traditional materials and technologies with high factors of safety.

References Financing human settlement development and management in developing countries: A comparative overview of case studies. United Nations Centre for Human Settlements (Habitat) (HS/174/89E), Nairobi, 1990 Jagadish, K.S. Interview, 1992 Sinha, B. P. Historical Development of Structural Brickwork, Its Potential and its Relevance to India, Constrado, India, 1987 Jagadish, K. S. and Reddy, B. V. V. The production of stabilised mud blocks. Lecture notes for the short term course organ&d by ASTRA on Earth Construction Technologies, Bangalore, 1991 St&, R. Appropriate Building Materials: A Catalogue of Potentiol Solutions, Intermediate Technology, Shaftesbury, UK, 1988 Kanade, S. N. A Revolutionary Statement in Stone, unpublished, 1992 Appropriate Building Materials, op. cit. Spence, R. J. S. and Cook, D. J. Building Materials in Developing Countries, Wiley, Chichester, UK, 1983

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