Strength Characteristics of Fiber Reinforced High Volume Fly Ash Concrete

Strength Characteristics of Fiber Reinforced High Volume Fly Ash Concrete

Shivakumara B

Prof and Head, Dept. of Civil Engineering

STJ Institute of Technology Ranebennur-581115, India

Dr. Prabhakara H R

Principal, University BDT College of

Engineering, Davangere 577 004 Karnataka, India,

Dr. Prakash K B

Principal, Government Engineering College,

Haveri 581 110, Karnataka, India,

Abstract

The dumping problem of fly ash has raised the alarming situation in the world which initiated towards consumption of fly ash in industry. The construction industry is one which consumes the cement for its pavement and other structures. The pavement will fail mostly due to excessive tensile stress. The use of plain high volume fly ash concrete (HVFAC) suffers from low tensile strength and limited ductility. These problems can be eliminated by introducing the reinforcement. When the fibers are mixed with concrete the tensile property of concrete is increased.

The aim of this work is to study the effect of variation of fiber content from 0% to 1.8% in high volume fly ash concrete. It is also aimed to study the effect of fibers on HVFAC with curing period. The studies cited in this paper, regarding fiber reinforced high volume fly ash concrete is making an attempt to study the strength characteristics up to 90 days curing. Locally available materials are used. Fly ash used is from Raichur thermal power plant and crimped steel fibers are used. The design of HVFAC mix was carried out as per the guidelines of CANMET[1]. hand book.

The study reveals the fact that the strength characteristics of fiber reinforced high volume fly ash concrete (FRHVFAC) show higher values at 1.4% addition of steel fibers.

Index Terms: Fly ash, HVFAC, FRHVFAC, Pavement, Compressive strength, Tensile strength. Flexural strength, Impact strength.

1. Introduction

   The main challenge before the construction industry is to serve the two important need of the society, namely, the protection of the environment and meeting the requirement of developing construction industry. The development of human activity results in environmental degradation. The main challenge is to

   minimise this degradation to a level consistent with sustainable development[2]. For civil engineers, the concept of sustainable development involves the use of high performance materials with reasonable cost with lowest possible environmental impact. The means of achieving it is to consume the waste products in construction industry.

   The production of fly ash is increasing with the coal utilisation and contributing to environmental degradation. This problem has raised the alarming situation in the world which initiated towards utilization of fly ash in construction industry.

   The large size of the concrete and cement industry is unquestionably the ideal place for economic and safe disposal of million tons of industrial byproduct fly ash due to its highly pozolonic and cementitious properties. Fly ash can be used in much larger amounts as cement replacement material in concrete than that being practiced today. The concrete containing 40 to 60 percentage of cement replacement by fly ash have shown the high strength and durability even at early ages. The study on suitability of superplasticized HVFA concrete for pavements showed that HVFA concrete with 50% – 60% fly ash can be designed to meet the strength and workability requirement of concrete pavements[3]. This has removed the strong objection of usages of high volume fly ash in concrete. The high volume fly ash utilization in concrete is highly advantageous in view of energy efficiency, durability, economy and overall ecological and environmental benefits[4].

   The use of high volume fly ash (HVFA) concrete fits in very well with sustainable development. High volume fly ash concrete mixtures contain lower quantities of cement and higher volume of fly ash (up to 60%)[5]. The use of fly ash in concrete at proportions ranging from 35% to 60% of total cementitious binder has been studied extensively over the last twenty five years and the properties of blended concrete are well documented. The replacement of fly

   ash as a cementitious component in concrete depends upon several factors. From the literature it is generally found that fly ash content in the cementitious material varies from 30-80% for low strength (20 MPa) to high strength (100MPa) of concrete [5].

   In India, fly ash mission has initiated projects on use of higher volume fly ash concrete construction. Gujrat Ambuja cements had laid down a high volume fly ash (50%) concrete road at their Ropar Plant, Punjab. The grade of the concrete was M-40 [6].

   The road construction industry is one which consumes the cement for its pavement and other structures. The pavement will fail mostly due to excessive tensile stress, which is the guiding factor of design [7]. Flexural strength of concrete is also an important property for concrete pavements. The rigid pavements are assumed to rest on a flexible soil subgrade and undergo mainly flexural stresses during service loads. The use of plain high volume fly ash concrete suffers from low tensile strength and limited ductility. These problems can be eliminated by introducing the reinforcement in tensile zone and prestressing the concrete. When the fibers are mixed with concrete, the post cracking behavior improves.

   In this paper an attempt is made to study the effect of fibers and curing period on the strength properties of high volume fly ash concrete. The percentage replacement of cement by fly ash and aspect ratio of fibers are kept constant in the study.

2. Objective of the study

   There are numerous studies on the strength characteristic of concrete containing fly ash.

   However, there is little study in the literature regarding the strength of high volume fly ash concrete with fibers. Thus the main aim of this work is to study the effect of variation of fiber content from 0% to 1.8% in high volume fly ash concrete. It is also aimed to study the effect of fibers on HVFAC with different curing period. The studies are made to evaluate the compressive strength, tensile strength, flexural strength and impact strength.

   In this paper an attempt is made to study the effect of fibers and curing period on the strength properties of high volume fly ash concrete. The percentage replacement of cement by fly ash and aspect ratio of fibers are kept constant in the study.

3. Materials used

   1. Cement

      In the present research work ordinary Portland cement of 43 grade is used. The tests on cement were conducted in accordance with Indian standards confirming to IS: 8112 – 1989 [8]. The specific gravity of cement used is 3.15.

   2. Fly ash

      The fly ash used in the present study is taken from Raichur Thermal Power Station, Shakthinagar, Raichur, Karnataka. The physical and chemical properties of the fly ash used are reported in table 1 and table 2.

      Table: 1 Physical properties of fly ash

      Test conducted	Results	Requirement as per IS:3812-2003 [9]
      		Part 1	Part 2
      Specific gravity	2.5	–	–
      FinenessSpecific surface in m2/kg by Blaines Air- permeability method, (Minimum)	469	320	200
      Lime reactivity Average ompressive strength in N/m2, (Minimum).	4.6	4.5	—
      Comparative compressive strength at 28 days, percent, (minimum)	90	Not less than 80% of the strength to plain cement mortar cubes.
      Soundness by autoclave test, expansion of specimens in percentage, (maximum)	0.0025	34	50
      Residue on 45 micron sieve, percent,(Maximum)	28.5	34	50

      Table: 2 Chemical composition of fly ash

      Test conducted	Results	Requirement as per IS:3812:2003 [9]
      		Part 1		Part 2
      		Siliceous pulverized fuel ash %	Calcareous pulverized fuel ash %	Siliceous pulverized fuel ash %	Calcareous pulverized fuel ash %
      Silicon dioxide (SiO) plus aluminium oxide (Al2O2) plus iron oxide (Fe), percent by mass,(Minimum)	94.68%	70%	50%	70%	50%
      Silicon dioxide (SiO),percent by mass,(Minimum)	61.90%	35%	25%	35%	25%
      Magnesium oxide (MgO) percent by mass,(Maximum)	0.79%	5%	5%	5%	5%
      Total sulphur as sulphurtrioxide (SO3),percent bymass,(Maximum)	0.13%	3%	3%	5%	5%
      Loss on ignition, percent bymass, (Maximum)	0.47%	5%	5%	5%	5%

   3. Fine aggregate

      The fine aggregates used in this experimental program is procured locally from Tungabhadra river bed near Harihar. The test on sand is conducted according to IS:2386 1963 and IS:383-1970. The test results of sieve analysis confirmed the sand to zone II and fineness modulus 2.65. Properties of the fine aggregate used in the experimental work are tabulated in table 3.

      Table: 3 Physical properties of fine aggregate [10][11][12]

      Properties	Result	Reference code
      Specific gravity	2.66	IS:2386-(PART- III) – 1963
      Fineness modulus	2.65	IS:2386-(PART-I) – 1963
      Water absorption	0.91%	IS:2386-(PART- III) – 1963

   4. Coarse aggregate

      Locally available crushed granite coarse aggregates having the maximum size of 20 mm are used in the present work. The aggregates are tested as per Indian Standard Specifications IS: 2386-1963. The specific gravity was found to be 2.72 and fineness modulus 6.53.

   5. Superplasticizer

      Conplast- SP430, a concrete superplasticizer based on Sulphonated Naphthalene Polymer is used as a

      water-reducing admixture and to improve the workability of fly ash concrete.

   6. Steel f ibers

      Crimped steel fibers manufactured by M/s Stewols India (P) Ltd., Nagapur, are used in the present study. The average equivalent diameter is 0.75mm and average aspect ratio is 50.

4. Proportioning

   The design of HVFAC mix was carried out as per the guidelines of CANMET hand book[1]. These guidelines of CANMET have used the absolute volume method, which is the most common procedure of mix design. The trail batch mixes with 50% replacement of cement by fly ash are tested and mix proportion of 1:1.17:2.54 was arrived with water to binder ratio of 0.3 for M40 grade of concrete.

5. Experimental results

   1. Compressive strength test results

      Table 4 gives the overall results of compressive strength of FRHVFAC. Also it gives the percentage increase or decrease of compressive strength with respect to reference mix. Variation in the compressive strength can be depicted in the form of graph as shown in fig. 1.

      Table 4 Overall results of compressive strength for FRHVFAC

      Percentage of fiber	7 days compressive strength (MPa)	Percentage increase or decrease of 7 days compressive strength with respect to reference mix.	28 days compressive strength (MPa)	Percentage increase or decrease of 28 days compressive strength with respect to reference mix.	90 days compressive strength (MPa)	Percentage increase or decrease of 90 days compressive strength with respect to reference mix.
      0.00 (Ref. mix)	19.56	.-	43.33	.-	51.11	.-
      0.20	20.00	2.00	44.74	3.00	52.74	3.00
      0.40	20.78	6.00	46.07	6.00	54.37	6.00
      0.60	21.33	9.00	47.41	9.00	56.00	10.00
      0.80	22.26	14.00	49.19	14.00	58.22	14.00
      1.00	22.74	16.00	50.37	16.00	59.41	16.00
      1.20	22.89	17.00	50.37	16.00	59.70	17.00
      1.40	22.96	17.00	50.96	18.00	60.00	17.00
      1.60	22.67	16.00	50.37	16.00	59.41	16.00
      1.80	22.59	16.00	50.22	16.00	59.26	16.00

      60

      55

      Compressive strength (MPa)

      Compressive strength (MPa)

      50

      7 days strength

      28 days strength

      90 days strength

      7 days strength

      28 days strength

      90 days strength

      45

      40

      35

      30

      25

      20

      0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

      Percentage of fibers

      Fig. 1 Variation of compressive strength of FRHVFAC

   2. Tensile strength test results

      Table 5 gives the overall results of tensile strength of FRHVFAC. Also it gives the percentage increase or

      decrease of tensile strength with respect to reference mix. Variation in the tensile strength can be depicted in the form of graph as shown in fig. 2.

      Table 5 Overall results of tensile strength for FRHVFAC

      Percentage of fiber	7 days tensile strength (MPa)	Percentage increase or decrease of 7 days tensile strength with respect to reference mix.	28 days tensile strength (MPa)	Percentage increase or decrease of 28 days tensile strength with respect to reference mix.	90 days compressive strength (MPa)	Percentage increase or decrease of tensile strength with respect to reference mix.
      0.00 (Ref. mix.)	1.74	.-	2.35	.-	3.30	.-
      0.20	1.86	7.00	p>2.65	13.00	3.30	0.00
      0.40	1.91	9.00	2.74	17.00	3.37	2.00
      0.60	2.02	16.00	2.83	21.00	3.54	7.00
      0.80	2.09	20.00	3.02	29.00	3.57	8.00
      1.00	2.22	27.00	3.17	35.00	3.62	10.00
      1.20	2.32	33.00	3.27	39.00	3.86	17.00
      1.40	2.41	38.00	3.30	41.00	3.94	19.00
      1.60	2.38	36.00	3.28	40.00	3.87	17.00
      1.80	2.31	32.00	3.21	37.00	3.82	16.00

      4.0

      Tensile strength (MPa)

      Tensile strength (MPa)

      3.5

      3.0

      2.5

      7 days strength

      28 days strength

      90 days strength

      7 days strength

      28 days strength

      90 days strength

      2.0

      1.5

      0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

      Percentage of fibers

      Fig. 2 Variation of tensile strength of FRHVFAC

   3. Flexural strength test results

      Table 6 gives the overall results of flexural strength of FRHVFAC. Also it gives the percentage increase or

      decrease of flexural strength with respect to reference mix. Variation in the flexural strength can be depicted in the form of graph as shown in fig. 3.

      Table 6 Overall results of flexural strength for FRHVFAC.

      Percentage of fiber	7 days flexural strength (MPa)	Percentage increase or decrease of flexural strength with respect to reference mix.	28 days flexural strength (MPa)	Percentage increase or decrease of 28 days flexural strength with respect to reference mix.	90 days flexural strength (MPa)	Percentage increase or decrease of flexural strength with respect to reference mix.
      0.00 (Ref. mix.)	2.21	.-	3.37	.-	5.77	.-
      0.20	2.77	25.00	4.20	25.00	6.29	9.00
      0.40	3.07	39.00	4.63	38.00	6.64	15.00
      0.60	3.15	42.00	4.96	47.00	7.05	22.00
      0.80	3.43	55.00	5.18	54.00	7.11	23.00
      1.00	3.81	72.00	5.77	71.00	7.13	24.00
      1.20	3.84	75.00	5.87	74.00	7.32	27.00
      1.40	3.97	80.00	5.99	78.00	7.44	29.00
      1.60	3.93	78.00	5.94	76.00	7.40	28.00
      1.80	3.87	75.00	5.91	79.00	7.37	28.00

      7.5

      7.0

      6.5

      Flexural strength (MPa)

      Flexural strength (MPa)

      6.0

      5.5

      5.0

      4.5

      4.0

      3.5

      3.0

      2.5

      2.0

      7 days strength

      28 days strength

      90 days strength

      7 days strength

      28 days strength

      90 days strength

      0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

      Percentage of fibers

      Fig. 3 Variation of flexural strength of FRHVFAC.

   4. Impact strength test results

      Table 7 gives the overall results of impact strength of FRHVFAC. Also it gives the percentage increase or

      decrease of impact strength with respect to reference mix. Variation in the impact strength can be depicted in the form of graph as shown in fig. 4.

      Table 7 Overall results of impact strength for FRHVFAC.

      Percentage of fiber	7 days impact strength (N-m)	Percentage increase or decrease of 7 days impact strength with respect to reference mix.	28 days impact strength (N-m)	Percentage increase or decrease of 28 days impact strength with respect to reference mix.	90 days impact strength (N-m)	Percentage increase or decrease of 90 days impact strength with respect to reference mix.
      0.00 (Ref. mix.)	1348.61	–	2060.95	–	2458.71	–
      0.20	2178.52	62.00	3326.56	61.00	3968.59	61.00
      0.40	2558.90	90.00	3893.67	89.00	4645.15	89.00
      0.60	3084.51	129.00	4682.09	127.00	5585.73	127.00
      0.80	3561.71	164.00	5415.18	163.00	6460.30	163.00
      1.00	3575.54	165.00	5435.92	164.00	6485.06	164.00
      1.20	3969.75	194.00	6030.69	193.00	7194.62	193.00
      1.40	4156.48	208.00	6293.50	205.00	7508.14	205.00
      1.60	3872.92	187.00	5885.46	186.00	7021.35	186.00
      1.80	3298.90	145.00	5014.05	143.00	5981.76	143.00

      8000

      7500

      7000

      6500

      Impact strength (N-m)

      Impact strength (N-m)

      6000

      5500

      5000

      4500

      4000

      3500

      3000

      2500

      2000

      1500

      1000

      7 days strength 28 days strength 90 days strength

      7 days strength 28 days strength 90 days strength

      0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

      Percentage of fibers

      Fig. 4 Variation of impact strength of FRHVFAC

6. Observations and discussions

   Following observations were made based on the studies conducted on FRHVFAC.

   It is observed that the compressive strength of FRHVFAC increases as the percentage of steel fibers in it increases up to 1.4%. Thereafter the compressive strength shows a decreasing trend. Thus the higher

   value of compressive strength may be obtained by using 1.4% steel fibers. This is true for 7 days, 28 days and 90 days compressive strength. At 1.4% addition of steel fibers the percentage increase of days, 28 days and 90 days compressive strength are found to be 17%, 18% and 17% respectively. It is also observed that a small percentage addition of fibers have improved the compressive strength of high volume fly ash concrete. (Table 4 and fig 1)

   It is observed that the tensile strength of FRHVFAC increases as the percentage of steel fibers in it increases up to 1.4%. Thereafter the tensile strength shows a decreasing trend. Thus the higher value of tensile strength may be obtained by using 1.4% steel fibers. This is true for 7 days, 28 days and 90 days tensile strength. At 1.4% addition of steel fibers the percentage increase of 7 days, 28 days and 90 days tensile strength are found to be 38%, 41% and 19% respectively. Also it is observed that a small percentage addition of fibers have improved the tensile strength of high volume fly ash concrete. ( Table 5, and fig 2)

   It is observed that the flexural strength of FRHVFAC increases as the percentage of steel fibers in it increases up to 1.4%. Thereafter the flexural strength shows a decreasing trend. Thus the higher value of flexural strength may be obtained by using 1.4% steel fibers. This is true for 7 days, 28 days and 90 days flexural strength. At 1.4% addition of steel fibers the percentage increase of 7 days, 28 days and 90 days flexural strength are found to be 79%, 78% and 29% respectively. Also it is observed that a small percentage addition of fibers have improved the flexural strength of high volume fly ash concrete. ( Table 6, and fig 3)

   It is observed that the impact strength of FRHVFAC increases as the percentage of steel fibers in it increases up to 1.4%. Thereafter the impact strength shows a decreasing trend. Thus the higher value of impact strength may be obtained by using1.4% steel fibers. This is true for 7 days, 28 days and 90 days impact strength. At 1.4% addition of steel fibers the percentage increase of 7 days, 28 days and 90 days impact strength are found to be 208%, 205% and 205% respectively. Also it is observed that a small percentage addition of fibers have improved the impact strength of high volume fly ash concrete substantially. (Table 7 and fig 4)

   The improvement in the properties of HVFAC may be due to the fact that additions of fibers improve the stiffness of concrete. Also, addition of 1.4% fibers will fill all the major voids resulting in dense mass. Addition of more than 1.4% steel fiber result in lowering the strength characteristics, since it affect the workability of concrete seriously. Mixing and compaction operations become difficult when more

   than 1.4% steel fibers are added in high volume fly ash concrete. Substantial improvements are found in tensile strength, flexural strength and impact strength when 1.4% steel fibers are added to high volume fly ash concrete, and marginal increase is found for compressive strength.

   Thus, there is a clear indication that the use of steel fibers in high volume fly ash concrete can modify the properties to suit it for rigid pavement construction.

7. Conclusions

Following conclusions can be drawn based on the study conducted

1. Compressive strength of FRHVFAC shows an increasing trend up to 1.4% addition of steel fibers. Thereafter compressive strength shows a decreasing trend. The percentage increase of 7 days, 28 days and

   90 days compressive strength for 1.4% addition of steel fibers are found to be 17%, 18% and 17% respectively.

2. Tensile strength of FRHVFAC shows an increasing trend up to 1.4% addition of steel fibers. Thereafter tensile strength shows a decreasing trend. The percentage increase of 7 days, 28 days and 90 days tensile strength for 1.4% addition of steel fibers are found to be 38%, 41% and 19% respectively.

3. Flexural strength of FRHVFAC shows an increasing trend up to 1.4% addition of steel fibers. Thereafter flexural strength shows a decreasing trend. The percentage increase of 7 days, 28 days and 90 days flexural strength for 1.4% addition of steel fibers are found to be 79%, 78% and 29% respectively.

4. Impact strength of FRHVFAC shows an increasing trend up to 1.4% addition of steel fibers. Thereafter impact strength shows a decreasing trend. The percentage increase of 7 days, 28 days and 90 days impact strength for 1.4% addition of steel fibers are found to be 208%, 205% and 205% respectively.

5. Use of steel fibers in high volume fly ash concrete can modify the strength properties. Therefore FRHVFAC can be recommended in the construction of rigid pavements.

References

[1]. CIDA, NRCAN, CII. High Volume Fly Ash Concrete Technology, Best practice Guidelies. New Delhi : Confidaration of Indian Industry (CII), 2005.

[2]. Cindy, K. Estakhri, Donald Saylak Reducing greenhouse gas emissions in Texas with high- volume fly ash concrete. URL: Transportation Research Record No. 1941, 2005: 167-174.

[3]. Kumar B., etal, Evaluation of properties of high volume fly ash concrete for pavements., Journal of Material in Civil Engineering, 2007, Vol 19.

[4]. Malhotra, V.M.,and Gjrov, O.E., Properties of cement concrete containing fly ash and condensed silica fume., Cement and Concerete Research,12, 1982.

[5]. Report No. T(S) 006, January, 2005, Use of higher volume fly ash in concrete for building sector, CBRI, Roorkee.

[6]. CANMET, CII. High volume fly ash concrete technology hand book. New Delhi : CII, 2005. 3rd eddition

[7]. Yoder, Witczak. Principles of pavement design.

New York : John Wiley and sons, Inc., 2007.

[8]. Bureau of Indian standard., 43 Grade Ordinary Portland Cement Specification IS: 8112 – 1989. New Dheli.

[9]. Bureau of Indian standard., Specification for fly ash for use as pozzolana and admixture.,IS:3812- 2003. New Dheli.

[10].Bureau of Indian standard., Specification for Coarse and Fine Aggregates from Natural Sources for Concrete, IS:383-1997., New Dheli.

[11].Bureau of Indian standard.,Methods of Test for Aggregates for Concrete Part Ill Specific Gravity, Density, Voids, Absorption and Bulking, IS:2386(Part-III)1963., New Dheli.

[12].Bureau of Indian standard., Methods of Test for Aggregates for Concrete Part I Particle Size and Shape, IS:2386(Part-I)1963., New Dheli.