Properties of High-Volume Fly Ash Concrete Reinforced with Natural Fibres

Rafat SIDDIQUE^1,* and El-Hadj KADRI²

¹ Faculty Affairs, Thapar University, Patiala - 147 004 (Punjab), India.

² Department of Civil Engineering, University of Cergy Pontoise, Rue Eragny Neuville sur Oise, Cergy Pontoise 95031, France.

Email: siddique_66@yahoo.com

* Coresponsable Author: Phone: (91) 175 239 3027O) ,3207 (H); Fax: (91) 175 239 3005

Abstract

Properties of high-volume fly ash concrete incorporating san fibres are presented in this paper. For this investigation, initially, three concrete mixtures were made with 35%, 45%, and 55% of Class F fly as partial replacement of cement. After this, three percentages (0.25, 0.50, and 0.75%) of san fibres (25 mm length) were added in each of the fly ash concrete mixtures. San is a natural bast fibre, and is also known as Sunn Hemp (Botanical name: Crotalaria Juncea). It is grown in Indian Sub-Continent, Brazil, Eastern and Southern Africa, and also in some parts of U.S.A. Tests were performed for compressive strength, splitting tensile strength, flexural strength, and impact strength at the ages of 28, 91 and 365 days. Tests were also performed for fresh concrete properties.

28 days test results indicated that san fibres reduced the compressive strength of high-volume fly ash concrete by 2 to 13%, increased splitting tensile strength by 6 to 26%, flexural strength by 5 to 14%, and enhanced impact strength tremendously (by 100 to 300%) depending upon the fly ash content and fibre percentage. Later age (91 and 365 days) results showed continuous increase in strength properties of high-volume fly ash concrete. This was probably be possible due to the pozzolanic action of fly ash, leading to more densification of the concrete matrix, and development of more effective bond between fibres and fly ash concrete matrix.

Keywords

Compressive strength; Concrete; Flexural strength; Fly ash; Impact strength; San fibres; Splitting tensile strength.

Introduction

The proportion of fly ash used as a cementitious component in concrete depends upon several factors. The design strength and workability of concrete, water demand and relative cost of fly ash compared to cement are particularly important in mixture proportioning of concrete. One of the major developments in the area of fly ash utilization in concrete has been the technology of high-performance, high-volume fly ash concrete by Malhotra and his associates [1, 2]. High-volume fly ash concrete has emerged as a construction material in its own right. These concretes generally contain more than 40% fly ash by mass of total cementitious materials. Malhotra [1-7] and Mehta [8] has reported extensively on high-volume fly ash concrete. Concrete containing high volumes of Class F fly ash exhibited excellent mechanical properties and good durability. Siddique [9-11] have explored the possibility of using Class F fly ash in concrete in high volumes, either as partial replacement of cement or fine aggregate. Results have indicated that Class F fly ash could be suitable used in concrete for certain applications. Berry [12] has reported about the hydration process in high volume of concrete and and Zhang [13] indicated the microstructure, crack propagation and mechanical properties of concrete made with high volumes of fly ashes. Influence of Class F fly ash on the abrasion resistance of concrete has been reported by Langan et al. [14], Langley et al. [15], Bilodeau and Malhotra [16], Tikalsky et al. [17]; Bilodeau et al. [18], and Langley et al. [19]. Poon [20] reported that concrete with a 28 days compressive strength of 80 MPa could be obtained with a low-calcium fly ash content of 45%.

The use of fly ash in concrete is found to affect strength characteristics adversely. A loss in strength of concrete can be retrieved to a large extent by incorporating fibres, which have proved their worth in enhancing the strength characteristics of concrete.

Not much research has been reported on the effects of natural fibres on the properties of mortar/concrete/fly ash concrete. Uzomaka [21] reported physical characteristics of natural fibre “akwara”, and akwara reinforced concrete, and concluded that akwara (i) is dimensionally stable in water; (ii) appears durable in cement matrix environment; (iii) stress-strain relationship is linear and the apparent initial tangent modulus is of the order of 2 KN/mm²; (iv) reduces compactability, mobility of fresh concrete and does not affect compressive and modulus of rupture; (v) enhances the impact resistance of the concrete. Lewis and Mirihagalia [22] conducted tests on mortar reinforced with natural fibres such as water reed, elephant grass, plantain, and musamba. Based on the test results they concluded that among the four types of natural fibres, elephant grass showed greatest promise as a reinforcing material. Castro and Naaman [23] used natural fibres Lechuguilla and Maguey of agave family as reinforcement in cement mortar. Based on their study they concluded that natural fibres of agave family have tensile strength up to 552 MPa, and fibres did not had significant difference in either mechanical properties or the reinforcing efficiency of Maguey or Lechuguilla fibres. Mawenya [24] reviewed the literature on sisal fibre reinforced concrete, and concluded that sisal fibres have significant mechanical properties that make them eligible as reinforcement for concrete. Fageiri[25] reported the results of an experimental investigation on the possibility of using kenaf fibres to reinforce rich cement sand mortar to produce corrugated sheets. He has concluded that the tensile properties of kenaf fibres are comparable to those of some natural fibres (sisal) and synthetics fibres (polypropylene) that are used to reinforce a low tensile strength matrix, and addition of kenaf fibres enhances the bending and impact resistance of sheets. Mwamila [26] has proposed the idea of reinforcing concrete beams with the twines made of sisal fibres.

Siddique [27-34] extensively reported the effects of natural san fibres on the properties of concrete and fly ash concretes. Siddique [28] reported the physical and mechanical properties of san fibres such as length, diameter, tensile strength, modulus of elasticity, tensile strength in alkaline environment, and dimensional stability in wet and dry conditions. Siddique [29] reported that presence of san fibre enhanced the static and impact strength of concrete sheets significantly.

Siddique [30] reported the effect of addition of various percentages and lengths of natural san fibres on compressive stress-strain characteristics of concrete. He concluded that ductility of concrete increased with the increase in percentage of fibres, and modulus of elasticity of san fibre reinforced concrete does not significantly differ from that of plain concrete. Siddique [31] concluded that san fibre did not significantly affect the compressive strength of concrete up to 0.75% of fibre content by volume of concrete, but beyond this fibre content, strength decreased sharply. Siddique [32] reported physical and mechanical properties of san fibre, and has also compared the experimental results of compressive strength, split tensile strength and flexural strength with the model based on law of mixture. Siddique [33] reported that the twines made of san fibres enhanced the load carrying capacity and ductility of concrete beams, and could be effectively used as reinforcement in concrete beams. Siddique [34] investigated the effects of natural san fibres on the flexural behavior of concrete beams reinforced with conventional steel reinforcement, and concluded that san fibres did marginally improved the flexural behavior of the reinforced concrete beams. In a recently published paper, Siddique [34] has reported the effects of san fibres on the properties of high-volume fly ash concrete at the age of 28 days.

Aim of the Research

Large volumes of fly ash are produced globally. Percentage utilization in concrete is still not much, probably because of strength reduction of concrete with the inclusion of fly ash at early ages. Natural fibres are found almost in every country, and its processing is not energy intensive. Fibres are known to have a positive impact on the strength properties and ductility of concrete. Present research aims to investigate the effect of natural fibres on the properties of concrete made with natural fibres.

Experimental Program

Materials

Ordinary Portland cement (equivalent to Type I cement per ASTM C 150) conforming to the requirements of Indian Standard Specifications IS: 8112-1989 [35] was used. Class F fly ash was obtained from thermal power plant. Chemical composition of the fly ash met ASTM C 618 requirements, and the results are given in Table 1.

Table 1. Chemical composition of fly ash

Chemical Analysis	Class F Fly Ash (%)	ASTM Requirement C 618 (%)
Silicon Dioxide, SiO₂	54.4	--
Aluminum Oxide, Al₂O₃	24.80	--
Ferric Oxide, Fe₂O₃	5.2	--
SiO₂ + Al₂O₃ + Fe₂O₃	84.0	70.0 min.
Calcium Oxide, CaO	5.1	--
Magnesium Oxide, MgO	2.5	5.0 max.
Titanium Oxide, TiO₂	1.4	--
Potassium Oxide, K₂O	0.8	--
Sodium Oxide, Na₂O	0.6	1.5 max.
Sulfur trioxide, SO₃	1.6	5.0 max.
LOI (1000^oC)	2.3	6.0 max.
Moisture	0.5	3.0 max.

Natural sand with a 4.75 mm maximum size was used as fine aggregate and natural gravel with 12.5 mm maximum size was used as coarse aggregate. Both these aggregates were obtained locally. Both the aggregates met the requirements of Indian Standard Specifications IS: 383-1970 [36]. Their physical properties and sieve analysis results are given in Tables 2 and 3, respectively.

Table 2. Physical properties of aggregates

Property	Fine aggregate	Coarse aggregate
Specific gravity	2.58	2.60
Fineness modulus	2.41	6.52
SSD absorption, %	0.84	1.09
Void, %	33.2	37.2
Density, kg/m³	1678	1629

San is a natural bast fibre. It is also known as “Sunn Hemp.” Its scientific (botanical) name is Crotalaria Juncea. It is mostly grown in Indian Sub-Continent, Brazil, Eastern and Southern Africa, and also in some parts of U.S.A. (Hawaii, Florida). San (Sunn Hemp) plant is about 1 to 2.5 m in length and light green in color. The diameter of the plant varies from 10 to 30 mm. The stem of the plant is fully covered with thin layer of fibrous skin, which once extracted from the stem, is used as fibres. San fibres are used in making twines, rug yarns, tissue papers, canvas and cordage. In this investigation, san fibres having a length of 25 mm and three percentages (0.25, 0.50 and 0.75%) by volume of concrete were used. The physical and mechanical properties of san fibres are given in Table 4. A commercially available superplasticizer Centriplast FF90, based on melamine formaldehyde was used in all mixtures.

Table 3. Sieve analysis of aggregates

Fine aggregates			Coarse aggregates
Sieve No.	% passing	Requirement IS: 383-1970	Sieve size	% passing	Requirement IS: 383-1970
4.75 mm	97.3	90-100	12.5 mm	95	90-100
2.36 mm	92.4	85-100	10 mm	70	40-85
1.18 mm	81.2	75-100	4.75 mm	7	0-10
600 µm	63.2	60-79
300 µm	38.9	12-40
150µm	5.8	0-10

Table 4. Properties of san fibres

Property	Value
Diameter, mm	0.03 to 0.10
Tensile Strength, MPa	195 to 235
Elongation, %	1.19 to 1.36
Water absorption, %	85 to 120
Density, kg/m³	1010 to 1040

Mixture proportions

Initially, three high-volume fly ash concrete mixtures containing 35%, 45%, and 55% of Class F fly as replacement of cement were proportioned per Indian Standard Specifications IS: 10262-1982 [37] After this, three percentages (0.25, 0.50, and 0.75%) of san fibres by volume of concrete were added in each of the fly ash concrete mixtures. Mixtures proportions are given in Table 5.

Preparation, casting, and testing of specimens

Initially, cement and fly ash were dry mixed properly. After all the constituent materials were mixed, about 1/5 of the required water was added to the mixture. Small quantities of fibres were released manually and gradually taking care that the fibres were not mixed in bundles. After adding about 1/3of the quantity of fibres, some more water (about 1/3of the remaining quantity) was added to the mixer, and the remaining quantity of fibres was added again slowly and in small quantities. Finally, the remaining water was added, and the mixing was done till good homogeneous mixture, as visually observed, was obtained. If any lumping or balling was found at any stage, it was taken out, loosened and again added manually.

Table 5. Concrete mixture proportions

Mixture number	M-1	M-2	M-3	M-4	M-5	M-6	M-7	M-8	M-9	M-10	M-11	M-12
Fly ash, %	35	35	35	35	45	45	45	45	55	55	55	55
Fibres, %	-	0.25	0.50	0.75	-	0.25	0.50	0.75	-	0.25	0.50	0.75
Cement, kg/m³, C	260	260	260	260	220	220	220	220	180	180	180	180
Fly ash, kg/m³, FA	140	140	140	140	180	180	180	180	220	220	220	220
Fibres, kg/m³	-	2.6	5.2	7.8	-	2.6	5.2	7.8	-	2.6	5.2	7.8
Water, kg/m³, W	164	164	164	164	160	160	160	160	156	156	156	156
W/(C+FA)	0.41	0.41	0.41	0.41	0.40	0.40	0.40	0.40	0.39	0.39	0.39	0.39
SSD Sand, kg/m³	614	614	614	614	614	614	614	614	614	614	614	614
Coarse aggregate, kg/m³	1224	1224	1224	1224	1224	1224	1224	1224	1224	1224	1224	1224
Superplasticizer, L/m³	2.5	3.0	3.6	4.1	2.6	3.1	3.7	4.2	2.7	3.3	3.8	4.3
Slump, mm	85	70	60	40	90	75	60	50	100	75	65	50
Air content, %	3.4	3.6	3.8	4.0	3.3	3.5	3.7	3.9	3.4	3.6	3.8	3.9
Air temperature, °C	24	25	25	24	25	24	25	24	26	27	25	26
Concrete temperature, °C	26	26	27	26	27	26	27	26	27	28	27	28
Concrete density, kg/m³	2404	2408	2411	2414	2401	2404	2407	2410	2397	2400	2403	2406

Standard 150 mm cubes for compressive strength, cylinders of 150×300 mm for splitting tensile strength, 101.6×101.6×508 mm beams for flexural strength were cast per the provisions of Indian Standard Specifications IS: 516-1959 [38]. For impact strength, concrete sheets of size 500×500×30 mm were cast. The specimens were covered immediately for complete moisture retention. The specimens were demoulded after 24 hours of casting, and were then placed in a water-curing tank at temperature of 26 ± 1°C. The specimens were tested at the ages of 28, 91 and 365 days.

Compressive strength, splitting tensile strength and flexural strength were determined per Indian Standard Specifications IS 516-1959 [38]. For impact strength measurement, a set-up was designed. Impact strength test was carried out by a falling weight method. In this test a cylindrical metallic piece of weight 40 N was dropped from a constant height (1000 mm). The number of blows required to fail the specimens gives the impact strength of the slabs. Since damage inflicted by the blows of impact load stays during the subsequent blows, it was assumed that the slabs absorb impact energy imparted by the drop of load. The cumulative energy imparted to the slab in kN-m to cause failure is expressed as mgh × average number of blows.

Results and Discussion

Compressive strength

Compressive strength test results of concrete mixtures containing 35, 45, and 55% fly ash, and the effects of san fibres on the compressive strength of high-volume fly ash concrete are shown in Fig 1.

Figure 1. Compressive strength development with age

At the age of 28 days, concrete Mixtures M-1 (35% fly ash), M-5 (45% fly ash), and M-9 (55% fly ash) achieved compressive strengths of 26.7, 24.7 and 23.1 MPa, respectively. Compressive strength of concrete Mixtures M-1, M-5, and M-9 increased substantially at the later ages (91 and 365 days). Mixture M-1 (35% fly ash) achieved strength of 33.5 MPa at the age of 91 days, and 38.6 MPa at the age of 365 days, an increase of 25.5 and 44.5%. Similarly, Mixtures M-5 (45% fly ash) and M-9 (55% fly ash) achieved strengths of 30.1 MPa and 27.7 MPa at the age of 91 days, and 34.4 MPa and 32.1 MPa at the age of 365 days. The increase in compressive strengths of fly ash concrete mixtures was probably due to significant pozzolonic reaction of fly ash.

It is evident from Fig. 1 that for a particular fly ash percentage, compressive strength of high-volume fly ash concrete mixtures decreased with the increase in fibre percentage at all ages (28, 91, and 365 days). However, the reduction in compressive strength with the addition of fibres continued to decrease with an increase in percentage of fly ash content from 35 to 55%. At the age of 28 days, the reduction in compressive strength was between 8 and 13% for Mixture M-1 (35% fly ash), between 3 and 7% for Mixture M-5 (45% fly ash), and between 2 and 8% for Mixture M-9 (55% fly ash). At the age of 91 days, the reduction in compressive strength was between 2 and 8% for Mixture M-1 (35% fly ash), between 4 and 8% for Mixture M-5 (45% fly ash), and between 3 and 10% for Mixture M-9 (55% fly ash). At 365 days, the reduction in compressive strength was between 5 and 11% for Mixture M-1 (35% fly ash), between 6 and 9% for Mixture M-5 (45% fly ash), and between 3 and 9% for Mixture M-9 (55% fly ash).

Generally, presence of fibres induces porosity and reduces the compressive strength. However, in this case, addition of fibres reduced the compressive strength between 1 and 13% depending upon the fly ash content, fibre percentage, and age of testing, which was not significant decrease, considering contributions of fibres in enhancing tensile and impact strengths.

Splitting tensile strength

Splitting tensile strength of high-volume fly ash concrete mixtures, and effects of san fibres on its splitting tensile strength is shown in Fig 2.

At the age of 28 days, Mixtures M-1 (35% fly ash), M-5 (45% fly ash), and M-9 (55% fly ash) achieved splitting tensile strengths of 3.0, 2.6 and 2.2 MPa, respectively. Mixture M-1 (35% fly ash) achieved strength of 3.8 MPa at the age of 91 days, and 4.3 MPa at the age of 365 days. Similarly, Mixtures M-5 (45% fly ash) and M-9 (55% fly ash) achieved strengths of 3.3 MPa and 2.6 MPa at the age of 91 days, and 3.8 MPa and 3.0 MPa at the age of 365 days. Like compressive strength, increase in splitting tensile strength at later ages is due to the pozzolonic reaction of fly ash.

Figure 2. Splitting tensile strength development with age

The effects of san fibres on the splitting tensile strength of high-volume fly ash concrete are shown in Fig 2. It is clear from this figure that for a particular fly ash percentage, splitting tensile strength of fly ash concrete mixtures increased with the increase in fibre percentage at 28, 91, and 365 days. At the age of 28 days, increase in the splitting tensile strength was between 6 and 20% for Mixture M-1 (35% fly ash), between 10 and 26% for Mixture M-5 (45% fly ash), and between 9 and 18% for Mixture M-9 (55% fly ash).

At later ages (91 and 365 days), splitting tensile strength of concrete mixtures continued to increase. At 91 days, it was between 8 and 21% for Mixture M-1 (35% fly ash), between 12 and 27% for Mixture M-5 (45% fly ash), and between 7 and 22% for Mixture M-9 (55% fly ash). At 365 days, it percentage increase in strength was between 10 and 25% for Mixture M-1 (35% fly ash), between 10 and 29% for Mixture M-5 (45% fly ash), and between 10 and 23% for Mixture M-9 (55% fly ash). Increase in strength at later ages was probably due to the pozzolanic action of fly ash, leading to more densification of the concrete matrix, and development of more effective bond between fibres and fly ash concrete matrix.

Flexural strength

Flexural strength test results of concrete mixtures containing 35, 45, and 55% fly ash, and the effects of addition of san fibres on the flexural strength of high-volume fly ash concrete are shown in Fig 3. At the age of 28 days, Mixtures M-1 (35% fly ash), M-5 (45% fly ash), and M-9 (55% fly ash) achieved flexural strengths of 2.9, 2.5 and 2.3 MPa, respectively. Mixture M-1 (35% fly ash) achieved strength of 4.5 MPa at the age of 91 days, and 5.0 MPa at the age of 365 days. Similarly, Mixtures M-5 (45% fly ash) and M-9 (55% fly ash) achieved strengths of 3.9 MPa and 3.1 MPa at the age of 91 days, and 4.2 MPa and 3.3 MPa at the age of 365 days. Like compressive strength and splitting tensile strengths, increase in flexural strength at later ages is due to the pozzolonic reaction of fly ash.

Figure 3. Flexural strength development with age

It is clear from Fig. 3 that for a particular fly ash percentage, flexural strength of fly ash concrete mixtures increased with increase in fibre percentages at the ages of 28, 91, and 365 days. At 28 days, increase in the flexural strength was between 7 and 14% for Mixture M-1 (35% fly ash), between 5 and 11% for Mixture M-5 (45% fly ash), and between 5 and 9% for Mixture M-9 (55% fly ash). At later ages (91 and 365 days), flexural strength of mixtures further increased. At 91 days, it was between 6 and 14% for Mixture M-1 (35% fly ash), between 7 and 13% for Mixture M-5 (45% fly ash), and between 6 and 13% for Mixture M-9 (55% fly ash. At 365 days, percentage increase in strength was between 10 and 17% for Mixture M-1 (35% fly ash), between 8 and 17% for Mixture M-5 (45% fly ash), and between 6 and 13% for Mixture M-9 (55% fly ash).

Impact strength

Results of impact strength are shown in Fig 4. It is clear from this figure that for all fly ash concrete mixtures, addition of san fibres enhanced the impact strength significantly with an increase in percentage of fibres. For concrete Mixtures M-1 (35% fly ash), improvement in impact strength was between 2 and 3 times at the age of 28 days, whereas it was between 2 and 3.5 times at 91 days, and between 2.5 and 4 times at 365 days.

Figure 4. Impact strength development with age

For concrete Mixtures M-5 (45% fly ash), improvement in impact strength was between 1.5 to 2.5 times at the age of 28 days, whereas it was between 2 and 3 times at 91 days and between 2 and 3.5 times at 365 days. For concrete Mixtures M-9 (55% fly ash), improvement in impact strength was between 1 and 2 times at the age of 28 days, with the increase in percentage of fibres, whereas it was between 1.5 and 2.5 times at 91 days, and between 1.5 and 3 times at 365 days.

Conclusions

The following conclusions are drawn from the present investigation:

§ Compressive strength, splitting tensile strength and flexural strength of high-volume fly ash (HVFA) concrete increased with age in comparison with 28-day strength. Increase in the strengths of HVFA concrete clearly indicated the pozzolanic reaction of fly ash.

§ San fibres did not significantly affect the compressive strength of high-volume fly ash concrete. At the age of 28 days, reduction in compressive strength was between 2 and 13% depending up on the fly ash content and fibre percentage. At 91 and 365 days, compressive strength of san fibre reinforced high-volume fly ash concrete increased, which is clearly due to pozzolanic reaction of fly ash.

§ San fibres enhanced the 28 days splitting tensile strength of high-volume fly ash concrete mixture by 7 to 26% depending upon fly ash and fibre percentage. At later ages (91 and 365 days), there was further improvement in the splitting tensile strength of high-volume fly ash concrete. This was probably due to the pozzolanic reaction of fly ash, leading to more densification of the concrete matrix, and development of more effective bond between fibres and fly ash concrete matrix.

§ Addition of san fibres marginally increased the 28 days flexural strength of high-volume fly ash concrete by 5 to 14%, depending upon the fly ash content and fly ash percentage. Flexural strength of high-volume fly ash concrete also increased with age.

§ Use of san fibres significantly enhanced the 28-day impact strength (1 and 3 times) of high-volume fly ash concrete with the increase in percentage of fibres. With the increase in age, improvement in impact strength was of the order of 1.5 to 3.5 times at the age of 91 days, and between 1.5 to 4 times at the age of 365 days.

References

1. Malhotra V.M., Ramezanianpour A.R., Fly ash in concrete, 2^nd Edition, CANMET, Energy, Mines and Resources Canada, Ottawa, Canada, 1994, 307 pp.

2. Malhotra V.M., CANMET investigations dealing with high volume fly ash concrete- advances in concrete technology, 2^nd Edition, CANMET, Ottawa, 1994, p. 445-482.

3. Malhotra V.M., High-performance HVFA concrete: a solution to the infrastructural needs of India, Indian Concrete Journal, 2002, 76(2), p. 103-107.

4. Malhotra V.M., Durability of concrete incorporating high-volume of low-calcium (ASTM class F) fly ash, Cement & Concrete Composites, 1990, 12(4), p. 271-277.

5. Sivasundram V., Carette G.G., Malhotra V.M., Long-term strength development of high-volume fly ash concrete, Cement & Concrete Composites, 1990, 12(4), p. 263-270.

6. Haque M.N., High fly ash concrete, ACI Materials Journal, 1984, 81(1), p. 54-60.

7. Swamy R.N., Mineral admixtures for high strength concrete, Indian Concrete Journal, 1991, 65(6), p. 265-271.

8. Mehta P.K., Concrete structure, properties and materials, Prentice-Hall International Series in Civil Engineering and Engineering Mechanics, 3^rd Edition, 1986.

9. Siddique R., Performance characteristics of concrete containing high-volumes of class f fly ash, Cement and Concrete Research, 2004, 34(3), p. 487-493.

10. Siddique R., Effect of fine aggregate replacement with class f fly ash on the abrasion resistance of concrete, Cement and Concrete Research, 2003, 33(11), p. 1877-1881.

11. Siddique R., Effect of fine aggregate replacement with class f fly ash on the mechanical properties of concrete, Cement and Concrete Research, 2003, 33(4), p. 539-547.

12. Berry E.E., Hydration in high-volume fly ash concrete binders, ACI Materials Journal, 1994, 91(4), p. 382-389.

13. Zhang M.H., Microstructure, crack propagation, and mechanical properties of cement pastes containing high-volumes of fly ashes, Cement and Concrete Research, 1995, 25(6), p. 1165-1178.

14. Langan B.W., Joshi R.C., Ward M.A., Strength and durability of concrete containing 50 percent Portland cement replacement by fly ash and other materials, Canadian Journal of Civil Engineering, 1990, 17, p. 19-27.

15. Langley W.S., Carette G.G., Malhotra V.M., Structural concrete incorporating high-volumes of class F fly ash, ACI Materials Journal, 1989, 86(5), p. 507-514.

16. Bilodeau V.M. Malhotra, Concrete incorporating high volumes of ASTM class F fly ashes: mechanical properties and resistance to deicing salt scaling and to chloride-ion penetration, ACI Special Publication (SP-132), 1992, p. 319-349.

17. Tikalsky P.J., Carrasquillo P.M., Carrasquillo R.L., Strength and durability considerations affecting mix proportions of concrete containing fly ash, ACI Materials Journal, 1988, 85(6), p. 505-511.

18. Bilodeau V. Sivasundram, Painter K.E., Malhotra V.M., Durability of concrete incorporating high volumes of fly ash from sources in the US, ACI Materials Journal, 1994, 91(1), p. 3-12.

19. Langley W.S., Carette G.G., Malhotra V.M., Strength development and temperature rise in large concrete blocks containing high volumes of low-calcium (ASTM class F) fly ash, ACI Materials Journal, 1992, 89(4), p. 362-368.

20. Poon C.S., Study on high strength concrete prepared with large volumes of low calcium fly ash, Cement and Concrete Research, 2000, 30(3), p. 447-455.

21. Uzomaka O.J., Characteristics of akwara as a reinforcing fibre, Magazine of Concrete Research, 1976, 28(96), p. 162-167.

22. Lewis G., Mirihagalia P., Natural vegetable fibres as reinforcement in cement sheets, Magazine of Concrete Research, 1979, 31(107), p. 104-108.

23. Castro J., Naaman A.E., Cement mortar reinforced with natural fibres, American Concrete Institute Journal, 1981, 1, p. 69-78.

24. Mawenya A.S., Development in sisal fibre reinforced concrete, Proceedings on Appropriate Building Materials for Low Cost Housing, Nairobi, Kenya, Nov 1983.

25. Fageiri O.M.E., Use of kenaf fibres for reinforcement of rich cement-sand corrugated sheets, Proceedings on Appropriate Building Materials for Low Cost Housing, Nairobi, Kenya, Nov 1983.

26. Mwamila B.L.M., Reinforcement of concrete beams with low modulus materials in the form of twines, Proceedings on Appropriate Building Materials for Low Cost Housing, Nairobi, Kenya, Nov 1983.

27. Siddique R., Study of structural characteristics of natural fibre reinforced concrete, Ph.D. Thesis, BITS, Pilani, India, 1993.

28. Siddique R., Venkataramana J., Use of san fibre in cement concrete sheets. Thin reinforced concrete products & systems, ACI Special Publication (SP-146), 1994, p. 69-78.

29. Siddique R., Compressive stress-strain curves of natural fibre reinforced concrete, Indian Journal of Engineering & Material Science, 1994, 1, p. 237-239.

30. Siddique R., Compressive strength of natural san fibre reinforced concrete, NICMAR Journal of Construction Management, 1995, 9(4), p. 287-292.

31. Siddique R., Characteristics of concrete reinforced with san fibres, Journal of Ferrocement, 1996, 26(1), p. 1-10.

32. Siddique R., Concrete beams reinforced with twines of natural fibres, Journal of Ferrocement, 1997, 27(2), p. 119-126.

33. Siddique R., Flexural behavior of reinforced concrete beams with san fibres, Journal of Ferrocement, 1999, 29(1), p. 17-28.

34. Siddique R., Properties of concrete incorporating high volumes of class f fly ash and san fibres, Cement and Concrete Research, 2004, 34(1), p. 37-42.

35. IS: 8112-1989, Specifications for 43-Grade Portland cement, Bureau of Indian Standards (BIS), New Delhi, India.

36. IS: 383-1970, Specifications for Coarse and Fine Aggregates from Natural Sources for Concrete, Bureau of Indian Standards (BIS), New Delhi, India.

37. IS: 10262-1982, Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards (BIS), New Delhi, India.

38. IS: 516-1959, Indian Standard Code of Practice- Methods of Test for Strength of Concrete, Bureau of Indian Standards (BIS), New Delhi, India.