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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 1, Number 3 (HABITAT, 1991, 46 p.)
View the document(introduction...)
View the documentForeword
View the documentThe role of a Network in strengthening local technological capacity in the production of Building Materials
View the documentMalawi: Production process, application and acceptance of fibre concrete roofing products*
View the documentNigeria: Natural-fibre Shwishcrete technology for low-cost roofs*
View the documentNigeria: Appraisal of coir-fibre cement-mortar composite for low-cost roofing purposes*
View the documentMalawi: Improved concrete roof tiles and roof-tile machines*
View the documentEast African roof thatching techniques being tested in India*
View the documentCorrugated roofing sheets from coir-waste or wood-wool and Portland cement*
View the documentPublications review
View the documentEvents
View the documentBack Cover

Nigeria: Natural-fibre Shwishcrete technology for low-cost roofs*

* Submitted by Prof. Bayo Olateju, Department of Building, Faculty of Environmental Design and Management, Obafemi Awolomo University, Ile-Ife, Nigeria.

Abstract

The performance of four locally available vegetable fibres, namely, kenaf, pineapple, screwpine and sponge, is described in this paper. The study involved the use of short-chopped fibres in a Shwishcrete matrix, to produce roofing sheets for self-help low-cost housing projects. The approach used includes an investigation of material performance characteristics for both the fibres and the fillers individually and in matrix. The manufacturing process involves preparation, casting and testing of prototypes for strength, durability, permeability, water absorption etc.

Introduction

The roof is one of the most expensive building components, because its cost ranges between 25 and 50 per cent of the total cost of a house. Therefore, one of the problems in low-cost housing development is finding a cheap roofing material which satisfies basic requirements of durability, impermeability, low thermal conductivity, high strength etc.

Shwishcrete is basically a laterite stabilized with cement. Extensive research has shown that stabilization enhances the strength and other physical characteristics. Moreover, reinforcement with natural fibres improves its ductility, which allows it to be formed into various shapes.

Materials

There are three materials involved in the preparation of Shwischcrete roofing sheets. They are laterite, cement and fibres. Natural fibres can be classified into three types, namely, cotton, bast and hard vegetable fibres. The hard vegetable fibres include manila, sisal, henequen, mauritius, coir, kenaf, pineapple and cabuya.

The best fibres grown in Nigeria today include remie, sunn, hemp, rossele, jute, bolobolo, cheyi and yawa. Fibre production is controlled by climatic factors, such as rainfall and temperature. The majority of Nigerian fibres are annual types and are used in indigenous weaving.

Characteristics of the fibres investigated

Kenaf (hibiscus canabinus) is an annual plant which belongs to the malvaceae family. It grows in the wild in northern Nigeria where it has been an export commodity for several years.

Sponge (Luffa aeagyptiaca), locally known as kanin kanin or Okun gambari, belongs to the cucurbitaceae family. It is an annual plant which is available in southern Nigeria and the tropics. It can be a climbing or a prostrate plant, the skeleton of which is used for sponge or rope after retting.

Screwpine (panadanus candelabrum) is a swamp plant which is used for mats in Nigeria. Aerial propped roots, which protrude from the branches as well as the main trunk, support the trunks, and both root and trunk form fibres. The leaves and the fibres are used for clothing, matting, thatch and baskets.

Pineapple (Annanas Sativus) is a single-fruit erect plant which grows to a height of between 0.6 and 1.2m. The leaves accommodate the fibres which are of small uniform diameters, very long and elastic.

Preliminary laboratory investigations, using micrometer screw gauge and magnifying glass, indicate that kenaf has a diameter of 0.16 m whilst the pineapple, the screwpine and the sponge have diameters of 0.27 µm, 0.5 µm and 0.265 µm. The tensile strengths for pineapple, screwpine and sponge are 21.2, 15.9 and 15.5 N/mm2 respectively. The studies reported here were carried out using chopped fibres. The kenaf was chopped to 12mm lengths, whilst the other three were chopped to lengths between 12mm and 25mm.

The fibres can be used in the chopped form (lengths less than 50mm) or in long forms (up to 1.4m). They should not be used in the twisted form but as individual strands, to expose each fibre to the surrounding matrix.

In order to determine the suitability of a particular type of local fibre, a test of matrix reactivity was carried out. This was done by soaking the fibres in water for two hours, preparing cement paste made of ordinary water and the presoaking water, and comparing the times of setting of both. A reactive fibre takes considerably longer to set.

Lateritic soils

Two types of laterite soils (samples A and B), available around the laboratory, were investigated. The materials were first sieved to ensure that particles greater than 2 mm were eliminated. Various physical tests, including both wet and dry sieving, hydrometer analysis and specific gravity, were carried out on the samples.

The matrix

To investigate the properties of the fibre-shwishcrete matrix, 50mm × 50mm cubes were cast using three different cement/laterite mixes, namely, 3:1, 2:1 and 1:1, and fibre contents of 1 per cent to 5 per cent by weight. The specimens were tested for strength after 7,14,21 and 28 days.

During casting of specimens incorporating fibres, it was noted that additional water was needed to achieve the same consistency of paste as for unreinforced samples. Fibre content tended to make the mix "ball" and reduce the weight of the specimen. These preliminary tests revealed the optimum fibre content and the effect of the presence of fibre on the mixing water demands for uniform workability.

Results

Various material characteristics were revealed from the preliminary tests. The grain-size analysis showed that sample.

A contained sand, silt and clay panicles in the proportions of 47 per cent, 30 per cent and 23 per cent, respectively, whilst sample B contained 57 per cent, 28 per cent and 15 per cent, respectively.

Figure 1 shows the influence of fibre-content variation with the water/cement ratio. Figures 2 and 3 show the influence of fibre content on specimen weight as well as compression strength at various curing ages for 1:1 mix at 3 per cent (optimum) fibre content for kenaf fibres. The other fibres show exactly similar shapes, to distinguish a value between 2.9 per cent and 3.1 per cent as optimum fibre content.


Figure 1. Variation of fibre content with water-cement ratio


Figure 2. Influence of fibre content on specimen weight

Source: Olateju (1)


Figure 3. Compressive strength for various ages of specimen for 1:1 mix at optimum fibre content

Source: Olateju (1)

The results of these preliminary tests indicate the following:

(a) The four fibres tested do not possess matrix-fibre reaction and can be used in sheet-making;

(b) The tensile strengths of the fibres are inversely proportional to the diameters - the lower the diameter, the higher the tensile strength;

(c) The optimum fibre content is about 3 per cent - this can be compared with that of asbestos-cement which is between 10 and 15 per cent;

(d) Even though a low strength was achieved for 1:1 mixes of Shwishcrete, it was still high enough for structural use;

(e) Fibre reinforcement decreased the weight of specimens but increased their strength (average bending strengths for samples with kenaf, screwpine, pineapple and sponge reinforcements are 23.3N/mm2, 25.53N/mm2, 23.76N/mm2 and 22.02N/mm2, respectively, as opposed to 16.8N/mm2, for unreinforced specimen).

Casting of prototypes

Fresh fibre-Shwishcrete matrix can be cast in various ways to produce various shapes and sizes. The shapes used in this investigation included flat, circular-corrugated and standard corrugated sheets. The kenaf matrix was used in casting the three shapes, whilst the other fibres were cast with only flat and circular-corrugated sheets.

Prototype production

The screwpine fibre, which was prepared almost a year earlier, was soaked for two hours to reduce brittleness. The materials were, then, weighed according to the mix ratios. The initial results indicated excessive cracking with the 2:1 and 3:1 mixes. Subsequent castings were limited to the 1:1 mixes.

A polythene sheet was first spread on the mould, and the paste was, then, spread evenly by hand and tamped to achieve some compaction. The other half of the form was then placed on top of the lower half and pressed, using a wooden platform and known weights to achieve additional compaction. Care was taken in aligning the forms to ensure that a uniform thickness was achieved throughout. The cast specimen was, then, allowed to set for 24 hours, after which the polythene sheet was removed, and the sheets demoulded for curing.

Testing and evaluation of prototypes

The specimens were tested for strength after 28 days. The testing programme included density, permeability, flexural strength, water absorption, thermal conductivity and accelerated durability. The kenaf-fibre specimens, which were used as pilot specimens, were tested for nailing and accelerated durability.

The accelerated durability test involved using 1 per cent solution of sulphuric acid and immersing measured lengths of roofing sheets in the solution for 24 hours, using 75 × 200 mm pieces sawn from the specimens. The specimen was then placed in a 105° oven for 24 hours, was removed and weighed again, before the immersed portion was brushed with a hard plastic brush and reweighed. It was, then, immersed in water for one hour, dried in an oven for two hours and allowed to cool to room temperature, before the cycle was repeated. It is estimated that each cycle is equivalent to two years' durability. For comparison, specimens of locally produced asbestos sheets were tested in the same manner for nailing and durability.

During the nailing process, it was observed that the asbestos-cement sheets cracked, whereas the fibre-Shwishcrete components did not. Further, the durability test on the kenaf sheets showed lower weight reduction than the asbestos sheets, whereas the newly-cast specimens showed higher weight reduction than the asbestos sheets, but were still durable over 10 cycles i.e., over 20 years' life. Table 1 shows characteristics of Shwishcrete sheets.

Table 1. Comparison of roof-sheet characteristics


Asbestos

Pineapple

Screw pine

Sponge

Kenaf

Normal thickness (mm)

4.5

5.0

5.0

5.0

5.0

Weight per sheet (kg/m2)

9.0

9.62

9.63

10.72

10.4

Density (kg/m3)

1500.00

1885.71

1842.86

1804.76

1944.4

Water absorption (percentage)

25.00

10.78

10.60

18.6

12.2

Bending strength (N/mm2)

16.00

22.86

21.32

20.09

17.3

Thermal conductivity (w/m°C)

0.35

0.71

0.67

0.74

0.87

Durability (minimum yrs)

20

20

20

20

20

Conclusions

From the foregoing analysis, the following conclusions can be drawn:

1. The use of fibres reduces the dead weight of Shwischcrete sheets with increased bending strength.

2. The optimum fibre content tested is 3 per cent, as compared with asbestos-cement fibre content of 10-15 per cent.

3. The bending strength achieved is a function of the size of the fibre, varying inversely as the diameter decreases.

4. Satisfactory and portable form work can be made to produce sound Shwishcrete specimens.

5. Fibre-Shwishcrete sheets are more ductile, and resist impacts from nailing better than asbestos-cement sheets.

6. The performance of fibre-Shwishcrete roofing sheets are satisfactory, compared with that of asbestos-cement sheets.

7. Apart from kenaf, fibres can be obtained at almost no cost. Further, all of them are regenerative materials which can be cultivated and produced in large quantities. The fibre-manufacturing process requires no energy consumption, and the sheet-production technology does not require trained personnel, machinery, electricity or any other cost-intensive high technology.

References

Adeleke, A., and Holgate. R.A., A Review of the Fibre Materials Available in Nigeria, Lagos, Federal Ministry of Commerce and Industry, 1964.

Landaeta, G., and Larsson, S. Roofs in the Warm-Humid Tropics of South-East Asia. Lund, Lund Committee on Habitat and Development Studies, 1987, p. 10.

Olateju, Bayo, "Kenaf fibre-Shwishcrete composite for low cost roof construction". International Journal for Housing Science and Its Applications, xiii, 2. 1989 pp. 127-136.

Olorode, Omotoye, "Dicotyledonous plants with corolla fused ovary inferior", Taxonomy of West African Plants. London, Longman Group, Ltd. 1984, pp. 92-94.

Ogunleye, S.J., "Development of fibre Shwishcrete roofing material", (Unpublished occasional research reports) Ile-Ife, Department of Building, Obafemi Awolowo University, 1989.

Persson, H., and Skarendahl, A. "Sisal-fibre concrete for roofing sheets and other purposes", Appropriate Industrial Technology for Construction and Building Materials. New York, United Nations, 1980.

Rowley, R.D., and Miner, D.F. "Non-metal fibres". Handbook of Engineering Materials. Toronto, Wiley Engineering Handbook Series, 1956 pp. 97-120.

Schreckenback, H., and Abankwa, J.G.K., Construction Technology for a Tropical Developing Country. Eschborn, Agency for Technical Cooperation, n.d.