Vol. 4(6), pp. 184-191, June, 2013 DOI 10.5897/JCECT2013.0265 ISSN 1996-0816 2013 Academic Journals http://www.academicjournals.org/jcect Journal of Civil Engineering and Construction Technology Full Length Research Paper Reinforcing efficiency of glass fibres in low volume class F fly ash concrete V. M. Sounthararajan and A. Sivakumar* Structural Engineering Division, School of Mechanical and Building Sciences, VIT University, Vellore 632014, Tamilnadu, India. Accepted 27 May, 2013 This study reports the reinforcing efficiency of glass fibre addition in the low volume fly ash concrete upto 25% cement replacement level. Micro mechanical action of glass fibres in fly ash concrete are discussed with respect to different percentage of glass fibre addition. Glass fibres in concrete improves the matrix densification, refinement of microstructure, reduction of voids, minimize cracking due to stresses, and enhance durability to reinforcement corrosion, sulphate attack, and alkali-silica expansion. The experimental test results showed that 25% fly ash with 0.3% glass fibers addition in concrete provided highest compressive strength upto 51.45 at 28 days and a flexural strength of 5.15 MPa. Further tests on ultrasonic pulse velocity exhibited the quality of various concrete mixes and conform to the standard requirement for a high quality concrete. Key words: Compressive strength, fly ash, flexural strength, glass fibres, superplasticizer. INTRODUCTION The use of fly ash in large quantities have been used in mass concretes for long time, with the intention of reducing cost and controlling temperature rise in order to reduce cracking at early ages. Most current use of lowcalcium fly ash is in construction of pavements due to cost savings and improved surface quality of concrete against abrasive resistance. One of the main reasons for moving towards high strength is to obtain the later strength gain by replacing low volume of fly ash. The possible use of fly ash based concrete is increasing, however the delayed pozzolanic reaction restricts the large scale addition. Factors responsible for high strength concrete properties of cements, careful selection of mix ingredients, accelerators (chemical admixtures), fine aggregate and coarse aggregate volume fraction, high range water reducers. Fly ash and was particularly the cementing efficiency of fly ash depends on many of its characteristics. Pshtiwan et al. (2011), studied on glass fibre reinforced concrete used in construction. In this, the author compared the compressive strength and flexural strength by using cubes of varying sizes with and without glass fibres concrete. Various application of glass fibre reinforced concrete is also shown in this study. Also they concluded that by using 20 mm of coarse aggregate more air entraining is increased in the concrete which reduces the compressive strength of the concrete, only 10 mm coarse aggregate should be used to solve the problem of reduced flexural strength. Vijai et al. (2012) studied on properties of glass fiber reinforced geopolymer concrete composites. Compressive strength, split tensile strength and flexural strength of glass fiber reinforced geopolymer concrete composites decreases for the addition of 0.01 and 0.02% volume fraction of glass fiber resulted in the reduced mechanical properties. Krishna Rao et al. (2011) had made an investigation on the effect of size and shape of specimen on compressive strength of (GFRC). In this study the significance of compressive strength of concrete is due to the fact that the structural *Corresponding author. E-mail: sivakumara@vit.ac.in.
Sounthararajan and Sivakumar 185 Table 1. Cement and fly ash composition. Constituent Cement (OPC) % Class F Fly ash (%) SiO 2 21.03 57.55 Al 2O 3 4.73 21.34 Fe 2O 3 2.93 7.51 CaO 63.33 1.34 MgO 2.67 3.10 Na 2O 0.30 3.08 K 2O 0.65 1.99 SO 3 3.0 1.70 LOI 2.97 2.74 elements of compressive strength of concrete and different shapes and sizes are used. They proposed to investigate the effect of size and shape of the specimen on the compressive strength of the concrete. Ferrira et al. (2011), Bhuvaneshwari and Murali (2013) studied on GRC mechanical properties for structural applications. The results show that the presence of fibers may imply a loss of compressive strength of the material. However the presence of finer glass fibres in the matrix improved the strain hardening and crack arresting properties. Avinash et al. (2012) studied on the strength aspects of glass fiber reinforced concrete. From the study the author found the compressive strength of M40 concrete were 61.22 MPa with glass fibers 0.03% and 21.5 and 5.65 MPa for flexural and split tensile strength respectively. According to this study the author observed that the workability of the concrete decreases with the addition of glass fibers, but this difficulty can be overcome by using superplasticizers and the increase in compressive strength, flexural strength and split tensile strength for M20, M30, M40Grade concrete at 3, 7 and 28 days was 20 to 30%, 25 to 30%, 25 to 30% respectively. Swami et al. (2010) investigated on studies on glass fiber reinforced concrete composites strength and behavior. The compressive strength of CEMFIL crack High Dispersion glass fibers at 1.5% was found to be maximum with this percentage and there was an increase of 17.5% in compressive strength and, 65.45 and 45.56% increase in split tensile and flexural strength respectively. The ductility characteristics have improved with the addition of glass fibers, and also cracks can be controlled by introducing glass fibers. It also helps in controlling shrinkage cracks. Jagannadha et al. (2009) concluded that the maximum percentage of increase in compressive, split tensile and flexural strengths of concrete with 0% RCA were 6.08, 16.67 and 11.84 respectively while the maximum percentage increase in these strength for concrete with 50% RCA were 8073, 12.32, 16.43% respectively. From the investigation the author concluded that the maximum percentage of increased in mechanical properties such as compressive, split tensile and flexural strengths of concrete with 0% RCA were 6.08, 16.67 and 11.84 respectively while the maximum percentage increase in these strength for concrete with 50% RCA were 80.73, 12.32, 16.43% respectively. Yogesh et al. (2012) studied on performance of glass fibre reinforced concrete. The experiment consists of 0.45 water cement ratio and samples of concrete with 0.0, 0.5, 0.7, 0.9, 1.2, and 1.5% of fine aggregate had replaced by glass fibre. Based on the result author concluded that there was an increase of 30% in flexural strength when compared with 0% glass fibres. Research significance Experimental evaluations are made to investigate the performance of structural high strength grade concrete incorporating high volumes of low calcium fly ash with glass fibres. The conceptual mix design was used based on the fine to coarse aggregate ratio (F/C) and water to binder ratio (w/b) 0.3. Fly ash substitution based on total cement weight in the range of 0% and 25% by weight and inclusion of glass fibres was used 0% to 0.5% with and also maintained good workability up to 1.5% was used thought experimental works. METHODOLOGY Cement (OPC 53 grade) Ordinary Portland cement of chemical composition is given in the Table 1, the specific gravity value of 3.22 and basic properties of cement are given in the Table 2. Fly ash (class F) Low calcium fly ash was used as cement replacement material, the basic properties of fly ash are given in Table 2 and obtained from thermal power plant from ennure in Chennai and the specific gravity value of 2.42 is used. Fly ash particles passing through Indian Standard 90 micron sieve was used throughout the experimental works upto optimal level of replacement.
186 J. Civ. Eng. Constr. Technol. Table 2. Properties of 53 grade cement. Properties Cement Specific gravity 3.22 Initial setting time(min) 145 Final setting time(min) 255 Compressive strength of cement mortar (1:3) 7 days (MPa) 37.01 28 days (MPa) 48.90 Figure 1. Snap shot for glass fibres. Table 3. Finenesss modulus of fine aggregate. Sieve size Weight retained (gm) % of weight retained Cumulative % retained % passing 4.75 32 3.2 3.2 96.8 2.36 87.5 8.75 11.95 88.05 1.18 357.5 35.75 47.7 52.3 0.6 326.5 32.65 80.35 19.65 0.3 153 15.3 95.65 4.35 0.15 36 3.6 99.25 0.75 Pan 7.5 0.75 100 Fineness modulus 2.9 Glass fibres (E type) The glass fibers are alkali resistant with a modulus of elasticity 80 GPA, tensile strength 2.5 GPA, filament diameter consists of 14 micrometers and 6 mm long, having an aspect ratio of 600, specific gravity value of 2.68 and snap shot of glass fibers are shown in Figure 1. Fine aggregate The fine aggregate used was locally available in market. The fineness modulus of fine aggregate results is given in Table 3 and gradation curve for the coarse aggregate was drawn between practical size and percentage finer passing as shown in Figure 2. Coarse aggregate A coarse aggregate passing through 20 mm sieve was used in making concrete. The fineness modulus of coarse aggregate test results is given in Table 4 and the gradation curve for the coarse aggregate is drawn between particle size and percentage passing is shown in Figure 3.
Sounthararajan and Sivakumar 187 120.00 100.00 % of pasing 80.00 60.00 40.00 20.00 0.00 0.01 0.1 1 Particle size (mm) Figure 2. Gradation curve for fine aggregate. Table 4. Fineness modulus of coarse aggregate. Sieve size Weight retained (g) % of weight retained Cumulative % retained % passing 40 0 0 0.00 100.00 20 1774 1774 35.48 64.52 16 2463 4237 84.74 15.26 13.2 655 4892 97.84 2.16 12.5 29 4921 98.42 1.58 10 79 5000 100.00 0.00 9.5 0 5000 100.00 0.00 4.75 0 5000 100.00 0.00 pan 0 - - Fineness modulus 6.16 Superplasticizer The modified polycarboxylate ether based superplasticizer was used for improving the workability of concrete mixes. A high range water reducing admixture was used for dispersion of particle suspensions effectively at low dosage. The basic properties of superplasticizer are given in Table 5. These polymers are used as dispersants to avoid particle aggregation, and to improve the flowing ability characteristics. Water and concrete mixture proportions Normal potable water was used throughout the works. Mix design was carried out using conceptual mix design was adopted and are presented in Table 6. The main variable was arrived at based on the trial and error methods such as water to binder ratio of 0.35 (w/b) and Fine to Coarse aggregate ratio (F/C) 0.6. A total six different mixes (M, M1, M2, M3, M4 and M5) were prepared using cement replaced by fly ash with 0 and 25% (by weight of cement) and inclusion of glass fibres at different percentage varying from 0, 0.1, 0.2, 0.3, 0.4 and 0.5%. Preparation of casting and testing The compression testing of concrete samples were carried out on 100 100 100 mm size cast iron mould. Split tensile strength of concrete were casted in standard size of 100 mm diameter and 150 mm height and flexural member of standard size of 100 100 500 mm, for testing all hardened concrete specimens. Fresh concrete was placed into the moulds and compacted using table vibrator for 30 s and top surface was leveled smoothly using trowel and after that the moulds were securely placed in the room temperature for 24 h. After 24 h the hardened concrete cubes were demoulded for all specimens were kept in the normal portable curing tank for concrete for hydration with different curing days 7 and 28 days. The specimens were tested according to IS 516-1959 and IS 1199 to 1959. From the demoulding date the specimen should be tested and its strength using compressive flexural testing machine as shown in Figures 4, 5 and 6.
188 J. Civ. Eng. Constr. Technol. % finer 120 100 Percentage of passing 80 60 40 20 % finer 0-20 0, 0 0 10 20 30 40 50 Partical size(mm) Figure 3. Gradation curve for coarse aggregate. Table 5. Chemical properties of super plasticizer. Label Specific gravity P h value Air entrainment Chloride content Amount of SP Superplasticizer 1.225 5.7 1% Nil 1.50% by weight of binder content Table 6. Various mix proportions. Mix Id w/b ratio Glass fibres (%) F/C ratio Cement (kg/m 3 ) Fly ash Fine aggregate content Coarse aggregate Water Super plasticizer (%) M 0.35 0 0.6 400 0 672 1113 140 1.5 100 M1 0.35 0.1 0.6 300 100 672 1113 140 1.5 95 M2 0.35 0.2 0.6 300 100 672 1113 140 1.5 93 M3 0.35 0.3 0.6 300 100 672 1113 140 1.5 92 M4 0.35 0.4 0.6 300 100 672 1113 140 1.5 91 M5 0.35 0.5 0.6 300 100 672 1113 140 1.5 89 Slump (mm) RESULTS AND DISCUSSION Fresh concrete properties The workability of fresh concrete containing fly ash with glass fibres concrete up to optimum level of dosage exhibited good workability with the addition of superplasticizer. However, in the case of increased addition of glass fibres at 0.4 and 0.5% showed loss in consistency and the mix was harsh which necessitated additional time for vibration of fresh concrete mixtures. Compressive strength The experimental test result is given in Table 7; the compressive strength of concrete with different mixture proportions was determined at the ages of 7 and 28 days as shown in Figure 7. It can be concluded that the reference concrete for compressive strength without fly ash and glass fibres strength attainment was 36.50 MPa and 44.10 MPa at 7 and 28 days respectively. Whereas concrete mixe M2 which had 25% fly ash with 0.1% glass fibres showed marginally increased compressive strength
Sounthararajan and Sivakumar 189 Figure 4. Snap shot for mixture machine. Figure 6. Test set up for Flexural testing machine. using indirect method; the experimental test result are given in Table 7. From that test result, it showed that reference concrete without fly ash and glass fibres strength was 3.65 MPa at 28 days but in the case of M3 that is 25% of fly ash with 0.3% glass fibres, the strength was 4.40 MPa at 28 days, when compared to reference concrete strength which was increased upto 20.55% at 28 days. Flexural strength Figure 5. Test set up for compressive testing machine. up to 7.12% for 7 days and 8.59% for 28 days, when compared to reference concrete but in such a case of M3 (25% fly ash with 0.3% glass fibres the strength at 7 days was 41.15 MPa and 51.45 MPa at 28 days, It can be noted that, when compared to reference concrete the strength was increased up to 13.01 and 16.66% for 7 and 28 days respectively. The significant improvement on the strength was noticed at optimum level of fly ash addition with optimum dosage level of glass fibres in concrete. The flexural strength evaluations of different glass fibre concrete mixes after 7 and 28 days of curing subjected to two point load are presented in Table 7. From experimental test result showed that the flexural strength of reference concrete, the strength was 3.65 MPa for 7 days and 4.12 MPa for 28 days. It can be also concluded that the strength up to optimum level of 25% fly ash with 0.3% glass fibres showed an increase of 20.55% for 7 days and 25% for 28 and was found to be higher compared to the reference concrete as shown in Figure 8. This significant increment in flexural strength with increase in optimal level (0.3%) of glass fibres content might be due to the random orientation of fibres, the strength ability of the fibres to take up maximum ultimate load on the flexural member, which leads to good bonding action between fibres and concrete. The length to diameter ratio of glass fibres and also Polycarboxylic ether based superplasticizer which plays a major role of flexural member due to effect of reinforcing agents. Split tensile strength Commonly, concrete strong in compression and weak in tension, can be measured as the split tensile strength Ultrasonic pulse velocity Pulse velocity technique is an important assessment for predicting the quality of concrete for different mixture
190 J. Civ. Eng. Constr. Technol. Table 7. Strength Properties for different mixture proportion of concrete at 7 and 28 days. Mix Id Fly ash (%) Glass fibres (%) Compressive strength (MPa) Split tensile strength (MPa) Flexural strength (MPa) 7 days 28 days 28 days 7 days 28 days M 0 0 36.50 44.10 3.45 3.65 4.12 M1 0.1 36.15 46.20 3.52 3.90 4.01 M2 0.2 39.10 47.89 3.65 4.10 4.85 M3 25 0.3 41.13 51.45 3.90 4.40 5.15 M4 0.4 31.50 39.40 0.00 3.31 4.05 M5 0.5 29.75 35.75 3.55 3.40 3.95 7 days 28 days 1 day 3 days 7 days 28 days Compressive strength (MPa) 60 50 40 30 20 10 0 0% 0.10% 0.20% 0.30% 0.40% 0.5% Ultrasonic pulse velocity (m/s) 4,500 4,000 3,500 3,000 M M1 M2 M3 M4 M5 Percentage of Glass fibres Figure 7. Variation of compressive strength with 25% of fly ash based concrete. Different Mix Id Figure 9. Ultrasonic pulse velocity for various mixture proportions of concrete. Flexural Strength (MPa) 6.00 5.00 4.00 3.00 2.00 1.00 0.00 7 days 28 days 0.0% 0.1% 0.2% 0.3% 0.4% proportion of concrete. The ultrasonic pulse velocity values for all rice husk ash based concrete with respect to different curing ages are given in the Table 7. The investigation test results showed that good hardening properties of the concrete was noticed for optimized rice husk substitutions as observed in Figure 9. The ultrasonic pulse velocity values showed an increasing trend for different concrete mixes with the pulse velocity values in the range from 3500 to maximum range of 4500 m/s (Table 8). However, higher UPV values (4430 m/s) was obtained for F/C ratio of 0.6 with w/b 0.35 for 25% of fly ash with 0.3% glass fibres at 28 days and all the values showed satisfactory performance levels as per IS (Indian standard) 13311 part 1 1989. 0.5% Different Percentage of Glass Fibers Figure 8. Flexural strength for various mixture proportions of concrete. Conclusion A Portland cement concrete, designed for compressive strength at 28 days (51.3 MPa) was used as a reference concrete. Concrete mixes, containing low-calcium fly
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