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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
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Nigeria: Appraisal of coir-fibre cement-mortar composite for low-cost roofing purposes*

* By Osondo J. Eze-Uzomaka, F.A.S. Professor of Civil Engineering and Head of Department of Civil Engineering, University of Nigeria, Nsukka, and O.O. Nwadiuto, B. Eng., M. Eng., Executive Engineer, Anambra State Rural Development Authority, Enugu.

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

Synopsis

Specific designations for various vegetable-fibre-reinforced matrices are proposed for clarity. By this designation system, vegetable-fibre-reinforced cement mortar is designated VEFICEM.

Coir-fibre is a monocotyledonous fibre and has variable physical and mechanical properties.

VEFICEM has superior strength, sound absorption, thermal insulation and handling characteristics, but, poorer fire resistance than plain cement-mortar. VEFICEM performs satisfactorily in rainshielding. It is, thus, concluded that VEFICEM is a viable roofing material, but more research and performance evaluation are required to improve the quality and utilization of the material.

A. Introduction

Following the pioneering work of Romualdi1 in 1964 on the reinforcing potentials of short-length fibres in concrete, there has been considerable enthusiasm in exploring the potentials of various types of fibres in a low-modulus matrix. Considering the industrial and economic constraints of developing countries, the interest in these countries has centred on vegetable fibres which are in abundance in such countries.

The most common matrix to which vegetable-fibre reinforcement has been applied were cement-based: cement paste (i.e., cement-water mixture), cement mortar (i.e., sand-cement-water mixture), and concrete (i.e., gravel-sand-cement-water mixture). These fibre- reinforced cement-based matrices have been indiscriminately referred to as "fibre-reinforced concrete" by various authors.

It has to be emphasized that these three types of matrices have different compositions, physical characteristics and engineering properties. Hence, it is necessary to distinguish between them. For clarity and uniformity in referencing, the designations given in table 1 have been adopted in this paper and are recommended.

Table 1. Proposed designations for vegetable-fibre-reinforced cement-based composites

Composite

Proposed designation

Vegetable-fibre-reinforced cement paste

VEFICEP

Vegetable-fibre-reinforced cement mortar

VEFICEM

Vegetable-fibre-reinforced cement concrete

VEFICON

The Swiss Centre for Appropriate Technology (SKAT) has collated and evaluated research and experiences on VEFICEM roofing2. The findings concluded that VEFICEM is indeed a promising roofing material. It was further noted that failures in VEFICEM roofing projects are traceable "to lack of/or improper know-how transfer, to missing knowledge concerning material properties, production technique and to the installation methods"2.

The foregoing finding regarding missing knowledge concerning material properties is understandable because published data on the properties of VEFICEM materials are very few and scanty. Consequently, this paper, as a contribution towards filling the gap, focuses on the relevant functional properties of VEFICEM.

A point of departure of this study from most other investigations into VEFICEM is the richness of the mortar mix. Hitherto, a sand-cement ratio of not greater than 1 has been adopted.3-5

The major aspiration in VEFICEM roofing lies in its cost-effectiveness, and since cement is the costliest single item of raw material, it was decided for the purposes of this study to use mortar with a sand-cement ratio of 2 or more.

B. Structure and physical properties of coir-fibre

1. General description

Coir-fibre is from coconut husk and it is light brown in colour. The cross-sectional geometry and length are variable, typical dimensions being as summarized in table 2.

Table 2. Summary of physical properties of coir-fibre

Fibre length (mm)

56

-

240

Fibre diameter (mm)

0.12

-

0.39

Specific gravity


1.35


Bulk density (kg/m3)


480


Water absorption in 24 hrs at 25.7°C (percentage)


66.42


Modulus of Elasticity (GPa)





(a) dry

2.24

(1.30-3.33)



(b) soaked in water

2.84

(2.10-4.00)



(c) soaked in Ca(OH)2

2.60

(1.40-4.00)


Ultimate tensile strength(MPa)





(a) dry

73.0




(b) soaked in water

86.0




(c) soaked in Ca(OH)2

71.0



2. Structure

Botanically, cocos mucifera lignin (coconut) is a monocotyledon and coir-fibre is a monocotyledonous fibre. In cross-section, coir-fibre consists of a vascular bundle surrounded by a large sheath of numerous thick-walled, narrow-lumened and strongly lignified schlerenchymatous fibres. Longitudinally, a fully mature coir-fibre consists of elliptically shaped parenchymatous xylem rays and numerous long, tapering schlerenchymatous fibres aligned in the direction of the rays.

Essau6 reports that cell walls show varying degrees of elasticity, plasticity and tensile strength in relation to their chemical composition and microscopic and submicroscopic structure. Because of its abundance in cell walls, cellulose has a major influence upon vegetable fibres. Frey-Wyssling7 also points out that tensile strength is one of the remarkable characteristics of cellulose. On the other hand, lignin increases the resistance of cell walls to pressure and protects the cellulose fibres from becoming creased.

3. Physical properties

The specific gravity, density and water absorption of the coir-fibre specimens were determined in accordance with relevant British Standards. A Hounsfield tensometer was used in determining the elastic modulus of the fibre. The fibre specimens were tested in three states: (a) dry; (b) after 7 days soaking in water; (c) after 7 days soaking in calcium hydroxide solution (pH -12). The purpose of these treatments is to assess the effects of such environments on the fibre modulus and ultimate strength. The calcium hydroxide simulates the alkaline effect resulting from the hydration of cement.

The results are summarized in table 2, while typical stress-strain curves are shown in figure 1.

The stress-strain relationships are curvilinear and the values of elastic modulus quoted above are the apparent initial target modulus as defined by Uzomaka.8 The variability in the elastic modulus within each group is such that the effect of the state of the specimen, if any, is masked. However, previous investigations by Uzomaka9 shows that akwara, which is of similar structure to coir-fibre, is not adversely affected by a cement environment.

Apart from the length and diameter the values quoted in table 2 differ from the corresponding values quoted in table 4 of SKAT. However, the values quoted by SKAT for sisal, for example, also differ from the corresponding values quoted in table 1 of Fageiri.4 These differences emphasize the variable-ness of the mechanical properties of vegetable fibres.

C. Strength characteristics of VEFICEM

Three types of tests were carried out for the purpose of assessing the effectiveness of coir-fibre in upgrading the strength of cement-mortar matrix. Details of the tests are summarized in table 3. In all cases in this project mixing was done by hand. Sand and cement were first mixed intimately and then the fibre was added and mixed as evenly as possible with the dry sand-cement mixture before water Was added and further mixing done. All specimen were cured in water for 28 days at an average temperature of 25.4°C.


Figure 1. Stress-strain relationship for coir-fibre

Table 3. Summary of strength test details

Type of Test

Size of specimen (mm)

Test equipment

Test method

Flexure

300 × 75 × 10

Triaxial machine with adaptation

Centre point loading

Tensile

Standard cement briquette as per BS 12

Hounsfield tensometer

Direct tension

Impact

250×150×15

Izod impact machine

Ballistic pendulum

The results are summarized in table 4. It is observed that coir-fibre upgrades modulus of rupture and impact resistance. On the other hand, fibre inclusion causes a reduction in tensile strength. The improvement in the modulus of rupture is noteworthy in view of earlier findings by Uzomaka8 and others showing that low-modulus vegetable fibres such as akwara (piassava) do not improve the modulus of rupture of concrete. The improvement observed here is likely to be due to the modulus rating of the cement-mortar matrix being of the same order as that of the fibre. For instance, inclusion of various types of vegetable fibres was also found by Uzomaka10 to have upgraded the strength of the specimen.

Table 4. Summary of strength test results

Volume fraction of fibre (percentage)

Modulus of rupture (N/mm2) at various water/cement ratios

Tensile strength (N/mm2) at various water/cement ratios

Impact strength (J/cm2) at various water/cement ratios

0.4

0.5

0.6

0.7

0.8

0.4

0.5

0.6

0.7

0.8

0.4

0.5

0.6

0.7

0.8

0

17.72

21.63

27.86

16.01

12.24

3.97

3.92

3.85

3.80

3.61

6.48

4.70

3.75

3.52

2.73

1

20.11

22.55

24.44

17.48

15.41

3.40

3.31

3.15

2.86

2.70

7.27

5.61

4.76

4.42

3.50

2

23.01

25.75

28.34

20.68

18.79

2.90

2.77

2.62

2.35

2.10

7.63

6.06

5.02

4.60

4.33

3

27.97

30.45

33.85

25.49

22.18

2.55

2.35

2.06

1.80

1.53

7.81

7.19

5.96

5.28

5.07

4

20.30

24.51

27.44

18.42

16.35

2.21

2.00

1.70

1.44

1.20

8.45

8.00

7.32

6.87

6.58

5

17.74

20.11

21.88

15.79

14.21

2.16

1.73

1.40

1.14

0.81

10.41

10.03

9.77

9.62

9.05

In all cases, increasing the sand/cement ratio for a given fibre volume fraction decreases the strength value. There is an observed sand/cement ratio, at which changing the water/cement ratio seems to affect the strength of the composite. This pattern occurs for all strength types. The point lies at a sand/cement ratio of between 3.0 and 3.5 for flexure and direct tensile strengths and at 6.0 for the impact strength.

D. Performance characteristics

1. Rain shielding

It is conventional to adopt the permeability test for the assessment of the resistance to water transmission through materials. Usually, however, the hydrostatic head over roofing materials in service is so low that given the pore structure of the cement-mortar matrix, the permeability test is not a sufficiently sensitive test in this context. Moreover, permeability tests on materials of very low permeability, such as hardened concrete, is generally coupled with inaccuracies due, mainly, to the problem of boundary flow.11

On the other hand, the absorption test assesses the degree to which water will infiltrate the material when both are in contact. Thus while the test assesses the affirmity of the pore structure of the material for water intake, it does not directly reflect the suitability of the material to rainwater passing through it during a rainstorm.

The rain-shielding requirement of a roofing material in service demands that when the material is inundated under rain, water shall not seep through it to wet its interior face and drop into the enclosure. The depth of troughs in corrugated asbestos- cement sheets is 55mm and during a rainstorm there is a standing head of water of 55mm on the roofing sheet for the duration of the rain storm. The rain simulation test equipment consists of a 100mm internal diameter plastic pipe plugged at its lower end with a 100mm diameter × 10mm thick coir-fibre cement-mortar disc which has been oven-dried for 24 hours and cooled to room temperature. Leakage at the pipe-disc interface is prevented with a bituminous seal. The test consists of maintaining a 110mm head of water in the plugged pipe for 7 days. The underface of the coir-fibre cement-mortar disc plug was inspected at regular intervals for dampness.

Nevertheless, for completeness permeability and absorption tests were also carried out. A falling-head permeameter was used for the permeability test. Boundary flow was checked by sealing the circumferential interface between the specimen and the permeameter ring with bitumen. A rubber ring was interposed between the permeameter cell-top and the upper surface of the specimen.

The permeability and absorption values are summarized in tables 5 and 6. The permeability values appear high and would suggest that boundary flow was not completely eliminated by the measures taken. On the other hand, the absorption values are compatible with published data for concrete.12 In any case the effect of increasing the volume fraction of fibre on both permeability and absorption values is logical. All the specimens used in the rain- simulation test (s/c =2; w/c = 0.6, VFF = 1 to 5 per cent) proved satisfactory as there was no dampness on their face after 7 days.

Table 5. Permeability values for coir-fibre cement-motor composite sand/cement ratio = 2

Volume fraction of fibre (percentage)

Permeability (10-5 cm/sec) at various water/cement ratios


0.4

0.5

0.6

0.7

0.8

0

1.75

1.90

1.96

2.31

2.50

1

1.90

2.10

2.30

2.70

2.95

2

2.10

2.38

2.48

2.60

2.86

3

2.35

2.47

2.65

2.90

3.20

4

2.60

2.85

3.15

3.33

3.70

5

3.05

3.35

3.60

4.05

4.40

Table 6. Water absorption values for coir-fibre cement-motor composite sand/cement ratio = 2

Volume fraction of fibre (percentage)

Water absorption (percentage) at various water/cement ratios


0.4

0.5

0.6

0.7

0.8

0

1.30

2.51

2.60

3.07

3.61

1

1.71

3.00

3.23

3.78

4.42

2

2.01

3.07

3.41

4.02

4.43

3

2.16

3.69

4.00

4.27

4.80

4

3.28

4.56

4.85

5.22

5.91

5

4.90

5.92

6.15

6.76

7.11

2. Thermal insulation

Roofing materials are required to shield the enclosure from heat in a hot climate and retain the heat within the enclosure in a cold climate. Thus, roofing materials should provide thermal insulation to the enclosure. The thermal-insulation quality of a material is a function of its thermal conductivity, the latter being a measure of the ability of the material to conduct heat. The diffusivity values obtained in this study are summarized in table 7. It is seen that fibre inclusion has a considerable effect in reducing the thermal diffusivity of the plain matrix.

Table 7. Thermal diffusivity values for coir-fibre/cement-mortar composite

Volume fraction of fibre (percentage)

Thermal diffusivity (m2/sec) at various water/cement ratios


0.4

0.5

0.6

0.7

0.8

0

8.96

8.45

7.23

6.25

5.21

1

8.06

6.61

5.98

4.76

3.72

2

5.50

4.72

3.81

2.98

2.22

3

4.28

3.51

2.82

1.96

1.15

4

3.66

2.84

2.00

1.35

0.72

5

3.20

2.33

1.54

1.06

0.45

3. Fire resistance

Specimens measuring 250mm × 75mm × 10mm were used. They were dried to a constant mass in an oven and allowed to cool. The specimens were then fired in a furnace at a temperature of 650°C for periods of 20, 30,40, 50 and 60 minutes and then tested immediately after removal from the furnace for load-deflection characteristics. The results are presented in figure 2.


Figure 2a

It was observed that the coir-fibre cement-mortar composites produced dark smoke within 10 minutes of furnace treatment, probably due to the charring of the fibres, in contradiction to the plain cement-mortar speciments. On cooling, after furnace treatment, all specimens lost their load-carrying capacity and VEFICEM specimens disintegrated. Examinations of the results show that fibre reinforcement degraded the fire-resistance rating of the plain specimen.


Figure 2b


Figure 2c


Figure 2d

E. Handling characteristics

1. Characteristics considered

Handling characteristics are conceived to refer to those characteristics of the material which affect the case of their installation. These characteristics are summarized below.

2. Density

The variation of density with the volume fraction of fibres is given in figure 3 (see next page), from which it is seen that fibre inclusion reduced the density of the composite and hence makes it lighter and easier to handle.

3. Sawability and nailability

150mm × 150mm × 10mm specimens having a sand/cement ratio of 2, water/cement ratio of 0.6 and volume fractions of fibre of 0-5 per cent were cast. The specimens were sawn with an ordinary carpenters saw and 50 mm nails were driven into some sheets to assess their nailability.

All the specimens proved difficult to saw. Plain cement-mortar sheets could not be nailed and they split on nailing. The coir-fibre/cement-mortar composites cracked on nailing, although the cracks were arrested by the fibres and therefore did not spread excessively. VEFICEM roofing materials are therefore not amenable to sawing and nailing.

F. Conclusions

1. Types of fibre-reinforced cement-based matrices should be properly distinguished and adequately defined and not indiscriminately referred to as fibre-reinforced concrete.

2. Vegetable-fibre-reinforced cement-based matrices should be designated VEFICEP for the cement paste, VEFICEM for the cement-mortar, and VEFICON for the concrete.

3. Coir-fibre is a monocotyledonous fibre with variable cross-sectorial geometry (dia. 0.12-0.39mm) and variable length (56mm-240mm).

4. Coir-fibre used in this study has a specific gravity of 1.35, bulk density of 480kg/m3 and a water absorption of 66 per cent.

5. Apparent initial tangent modulus ranging from 1.3 GPa to 4.00 GPa and ultimate tensile strength ranging from 71 MPa to 86 MPa were measured in this study for coir-fibre.

6. VEFICEM has a higher modulus of rupture than plain cement mortar and there is an optimum fibre volume fraction of 3 percent.

7. VEFICEM has lower ultimate tensile strength than plain cement-mortar.

8. VEFICEM has much higher impact resistance than plain cement-mortar.

9. VEFICEM has higher permeability and absorption than plain cement-mortar, but VEFICEM appears to perform satisfactorily in rain-shielding of enclosures as adjudged by the rain- simulation test.

10. VEFICEM has better lower thermal diffusivity than plain cement-mortar and would therefore also provide better thermal insulation.

11. The fire-resistance quality of plain cement-mortar is better than that of VEFICEM.

12. VEFICEM is lighter than plain cement-mortar but it is difficult to saw and to nail.

13. Thus the overall assessment of VEFICEM is that it is a viable roofing material but more research and performance evaluation are still required to improve upon the quality and utilization of the material.


Figure 3. Variation of density with volume fraction of fibre

References

1. Romualdi, J.P., and Mandel, J.A., "Tensile strength of concrete affected by uniformly distributed and closely spaced short lengths of wire reinforcement". Journal of the American Concrete Institute, Proceedings, vol. 61, No. 6, June 1964, pp. 657-671.

2. Beck, V., Gram, H.E., and Wehrle, K., "Fibre concrete roofing: towards a mature technology", FCR-News, April 1987 (St. Gallen, Swiss Centre for Appropriate Technology (SKAT), pp. 1-3.

3. Gram, H.E., and others, A Comprehensive Report on the Potential of Fibre Concrete Roofing (St. Gallen, Swiss Centre for Appropriate Technology, (SKAT), 1987), p. 91.

4. Fageiri, O.M.E., "Use of kenaf fibres for reinforcement of rich cement-sand corrugated sheets". Symposium on Appropriate Building Materials for Low Cost Housing (New York, E. and F.N. Spon Ltd., 1983), pp. 167-176.

5. Castro, J., and Haaman, E.A., "Cement mortar reinforced with natural fibres", Journal of the American Concrete Institute, Title No. 78-6,1981, pp. 69-78.

6. Essau, K., Plant Anatomy (New York, John Wiley & Sons. Inc., 1965), pp. 55-56.

7. Frey-Wyssling, A., Die Pflanzliche Zellwand (Berlin, Springer-Verlag, 1959).

8. Uzomaka, O.J., "Characteristics of akwara as a reinforcing fibre". Magazine of Concrete Research, vol. 28 (1976), No. 96, pp. 162-167.

9. Uzomaka, O.J., "Discussion: Characteristics of akwara as a reinforcing fibre", Magazine of Concrete Research, vol. 29, No. 100, September 1977, pp. 161-164.

10. Uzomaka, O.J., "Performance characteristics of plain and reinforced soil blocks". Proceedings, International Conference on Materials of Construction for Developing Countries, Bangkok, Thailand, August 1978, pp. 911-925.

11. Uzomaka, O.J., "Permeability testing of plastic concrete", Proceedings, International Conference on Recent Developments in Accelerated Testing and Maturity of Concrete. Transportation Research Board 558 (Washington, D.C., National Research Council, 1975), pp. 93-103.

12. Neville, AM., Properties of Concrete (Pitman Paperbacks), p.331.

13. Thompson, N.E., "A note on the difficulties of measuring the thermal conductivity of concrete". Magazine of Concrete Research, vol. 20, No. 62, March 1968. pp. 45-49.

14. Tye, R.P., Thermal Conductivity (London, Academic Press Inc. Ltd.), vol. 2, pp. 149-201.

15. Joos, G., and Freeman, I.M., Theoretical Physics (3rd edition) (New York, Hafner Publishing Company).

16. Nwadiuto, O.O., "The potentials of coir fibre-mortar composites for roofing in low cost housing projects", M. Eng. Thesis, University of Nigeria, Nsukka, Department of Civil Engineering, August 1988.