Study on Strength Characteristics of Hybrid Fibre Reinforced Concrete with Mineral Admixtures

  1. G. Nandini Devi

Department of Civil Engineering, Adhiyamaan College of Engineering, Hosur, Tamilnadu

  1. Corresponding author email

Associate Editor: Dr. Noor Danish Ahrar Mundari
Science and Engineering Applications 2016, 1, 15–21. doi:10.26705/SAEA.2016.1.12.15-21
Received 31 Aug 2016, Accepted 05 Sep 2016, Published 05 Sep 2016

Abstract

Concrete is a brittle material with a low tensile strength. Fibres when added to concrete increases strength, toughness and ductility. The addition of fibres improves the post-cracking behaviour of concrete. In this project, the strength characteristics of hybrid fibre reinforced concrete is studied experimentally by testing cubes, cylinders and prisms under compression, tension and flexure. Fibres used are glass and steel fibres. The combinations of different types of fibres potentially will improve the overall performance of concrete. Admixtures silica fume and fly ash improves workability of concrete. M25 grade concrete was investigated with addition of steel fibres and glass fibres with admixtures silica fume and fly ash. The test results shows that use of hybrid fibre reinforced concrete with admixtures improves compression, split tensile and flexural performance.

Keywords: Fibre Reinforced Concrete, Glass Fiber, Steel Fiber, Fly Ash, Silica Fume.

Introduction

Concrete is strong in compression but weak in tension. This weakness makes the concrete to crack at the tensile end thus leading to failure. Tensile strength of concrete is found to increase with the addition of fibres and also helps to convert the brittle characteristics of concrete to ductile. Fibres are metallic or non-metallic like steel, glass, synthetic and carbon.These short discrete fibres when uniformly distributed and randomly arranged act as crack arrestors and and provide crack resistance and crack control. Hybrid Fibre Reinforced Concrete (HyFRC) consists of two or more types of fibres of different sizes and shapes. Different types of fibres have different effects on the properties of fresh and hardened concrete. Addition of fibres to concrete improves the post cracking performance of concrete by improving strength, toughness, energy absorption capacity and ductility. The most used fiberis steel i.e. 50% of total tonnage used, then polypropylene (20%), glass (5%) and other fibers (25%).

Eswari et.al has investigated the influence of fiber content on the ductility performance of 100 X 100 X 500 mm hybrid fiber reinforced concrete specimens. A total of 27 specimens were tested to study modulus of rupture, ultimate load, service load, ultimate and service load deflection, crack width, energy ductility and deflection ductility. Fang Yuan et.al has studied high-performance fiber reinforced cementitious composite with strain hardening and multiple cracking properties. Manu Santhanam et.al has carried out an experimental study on high strength concrete reinforced with hybrid fibres (combination of hooked steel and a non-metallic fiber) up to a volume fraction of 0.5% using different hybrid fiber combinations – steel– polypropylene, steel–polyester and steel–glass.Nandini Devi have investigated the workability and mechanical properties of plain SCC and GFRSCC.For a given length of S-glass fibre, the compressive strength of GFRSCC increases when the content of the S-glass fibres in the mix increases. Singh et.al has investigated the strength and flexure toughness of HyFRC containing different combinations of steel and polypropylene fibres. The results indicate that compressive strength, flexural strength and flexural toughness of concrete containing a fibre combination of 75% steel fibres + 25% polypropylene fibres can be adjudged as the most appropriate combination. Vikranth et.al has concluded that concrete containing a fiber combination of 75% steel fibers + 25% polypropylene fibers can be the most appropriate combination to be employed in HFRC for compressive strength, flexural strength and flexural toughness. Yamin Patel et.al has investigated beam-column joint by using special hybrid fiber combination of steel and polypropylene fiber. The hybrid combination of 0.50% steel fiber and 0.50% polypropylene fiber has best performance considering the strength, energy dissipation capacity.

Extensive research work on HyFRC has established that the behaviour of HyFRC depends on aspect ratios, distributions, orientations, geometrical shapes and mechanical properties of fibres. By adding two different types of fibre one being nonmetallic, it is observed that fresh concrete properties like workability and hardened concrete properties like strength, toghness can be improved as each type of fibre function individually to yield optimum performance. The hybrid combination of low and high modulus fibres i.e. metallic and non-metallic fibres offers potential benefits to arrest the micro and macro cracks and improves overall properties of concrete with reduced cost of concrete. Most researchers limit volume of fibres to 4.0% and aspect ratio to 100 to avoid unworkable mixes.This paper investigates the influence of admixtures like silica fume and fly ash and various volume fraction of fibre content on fresh and hardened properties of concrete. Steel fibres (metallic fibre) and glass fibres (nonmetallic fibre) are used.

MATERIALS AND METHODOLOGY

Materials Used

Materials used are cement, fine aggregate, coarse aggregate, silica fume, fly ash, steel frber, glass fiber and water. For conventional concrete, proportional mix of cement: fine aggregate: coarse aggrgateas recommended by IS 456:2000 for M25 Grade is used i.e. 1:1:2 with water-binder ratio of 0.45.

Coromandal king OPC 53 Grade cement having specific gravity 3.12 and standard consistency 32% was used. Fine aggregate used is river sand conforming to Zone III and specific gravity of 2.62. Coarse aggregate of 20mm size, crushed angular in shape with specific gravity of 2.69 was used. The aggregates are free from dust before used in the concrete. Fibres selected were steel fibres (crimpled) and glass Fibres (straight). From investigations, it can be found out that good results are obtained at an aspect ratio around 80 for glass fibers. Keeping that in view we have considered fibres with aspect ratio of 80 (Length 12 mm and Diameter 0.4 mm). Steel fibres have length 60 mm, width of 3 mm and thickness of 1mm have been used. Fly ash for the study is taken from Tuticorin Thermal Power Plant(TTPP) at Tuticorin. The physical properties of silica fume used is its diameter is about 0.1 micron to 0.2 micron, surface area about 30,000m2/kg and density is about 550kg/m3. The chemical composition are it contains more than 90 percent silicon dioxide with other constituents like carbon, sulphur and oxides of aluminium, iron, calcium, magnesium, sodium and potassium. Potable tap water available in laboratory with pH value of 7.0±1 and conforming to the requirement of IS 456:2000 was used for mixing, casting the concrete and curing the specimen as well. Cubes, cylinders and prisms were casted, cured using water and tested.

Mix Proportioning

From literatures it is found that optimum replacement of silica fume and fly ash is 10% and 20% by weight of cement repectively. Fiber combination adopted was 50% steel fiber and 50% glass fiber for fiber volume content variation from 0.5, 1.0,1.5, 2, 2.5%.Table.1 gives the mix proportion.

Table 1: Quantities of Materials Used

Mix CC CA CF CFA-0.5 CFA-1.0 CFA-1.5 CFA-2.0 CFA-2.5
Design Grade of concrete M 25(1:1:2) M 25 M 25 M 25 M 25 M 25 M 25 M 25
Cement (kg) 24.66 17.262 24.66 17.262 17.262 17.262 17.262 17.262
Fine Aggregate(kg) 24.66 24.66 24.66 24.66 24.66 24.66 24.66 24.66
Coarse Aggregate (kg) 49.32 49.32 49.32 49.32 49.32 49.32 49.32 49.32
Fly Ash (kg) - 4.932 - 4.932 4.932 4.932 4.932 4.932
Silica Fume (kg) - 2.466 - 2.466 2.466 2.466 2.466 2.466
Steel Fibre (kg) - - 0.185 0.061 0.123 0.185 0.246 0.308
Glass Fibre (kg) - - 0.185 0.061 0.123 0.185 0.246 0.308
w/b ratio 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45

The total dosage of fibres was maintained at 1.5% primarily from the point of view of providing good workability.

Mix 1: Conventional concrete with 0% fibre and no admixtures – CC

Mix 2: Concrete with 0% fibre and with admixtures - CA (70% cement, 20% fly ash and 10% silica fume by weight)

Mix 3: Concrete with fibre and with no admixtures – CF-1.5 (concrete with 0.75% Steel fiber and 0.75% glass fiberby weight of cement)

Mix 4: Concrete with fibre and with admixtures – CFA-0.5 (70% cement, 20% fly ash, 10% silica fume, 0.25% steel fiber and 0.25% glass fiber)

Mix 5: Concrete with fibre and with admixtures – CFA-1.0 (70% cement, 20% fly ash, 10% silica fume, 0.5% steel fiber and 0.5% glass fiber)

Mix 6: Concrete with fibre and with admixtures – CFA-1.5 (70% cement, 20% fly ash, 10% silica fume, 0.75% steel fiber and 0.75% glass fiber)

Mix 7: Concrete with fibre and with admixtures – CFA-2.0 (70% cement, 20% fly ash, 10% silica fume, 1% steel fiber and 1% glass fiber)

Mix 8: Concrete with fibre and with admixtures – CFA-2.5 (70% cement, 20% fly ash, 10% silica fume, 1.25% steel fiber and 1.25% glass fiber)

Casting of Specimens

For casting the specimens, standard cast iron moulds of size 150mm x150mm x150mm cubes, cylinders of 150mm diameter and 300mm height, prisms 100mm x100mm x 500mm are used. The moulds have been cleaned of dust particles and applied with mineral oil on all sides, before the concrete is poured into the moulds. Thoroughly mixed concrete is filled into the mould in three layers of equal heights followed by tamping. Then the mould is placed on the table vibrator for compaction. The specimens are removed from the moulds after 24 hours and cured in clean and fresh water.

Test on Concrete

Tests on Fresh Concrete

Tests on fresh concrete was to study its workability which is measured by Slump test Compaction factor test and Vee-bee consistometer. Figure.1 shows measuring workability.Table.2 shows measurement of workability.

[2456-2793-1-12-1]

Figure 1: Measurement of Workabilty

Table 2: Measurement of Workability

Mix Slump in mm Compaction Factor Vee Bee Time in Seconds Degree of Workability
CC 39 0.87 13 Good
CA 34 0.85 12 Good
CF-1.5 25 0.80 33 Low
CFA-0.5 37 0.85 12 Good
CFA-1.0 32 0.81 12 Good
CFA-1.5 29 0.83 18 Good
CFA-2.0 27 0.80 20 Low
CFA-2.5 26 0.79 22 Low

Tests on Hardened Concrete

a). Cube Compression Test

This test was conducted as per IS 516-1959. The cubes of standard size 150 mm x150 mm x 150 mm were casted to find the compressive strength of concrete. Specimens were placed on Compression Testing Machine (CTM) of capacity 1000kN without eccentricity and a uniform rate of loading of 140kg/cm2 per minute was applied till the failure of the cube. The maximum load was noted (figure.2). Cube compressive strength (fck) in MPa= P/A, where, P= cube compression maximum load, A= area of the cube on which load is applied.

[2456-2793-1-12-2]

Figure 2: Testing of Specimens

b). Split Tensile Test

Concrete cylinders of size 150mm diameter x 300mm height were casted. The test was carried out by placing a cylindrical specimen horizontally between the loading surface of a compression testing machine and the load is applied until the failure of the cylinder, along the vertical diameter. Apply the load continuously without shock at a rate of approximately 14- 21kg/cm2 /minute which corresponds to a total load of 9900kg/minute to 14850kg/minute. Note down the breaking load(P). When the load is applied along the generatrix, an element on the vertical diameter of the cylinder is subjected to a stress of = 2P/πld, where, P is the compressive load on the cylinder, l is the length of the cylinder, d is diameter of the cylinder.

c). Flexural Test

Prisms of size 500x100x100mm are tested using a flexure testing machine. The specimen is simply supported on the two rollers of the machine which are 600mm apart, with a bearing of 50mm from each support. The load shall be applied on the beam from two rollers which are placed above the prism with a spacing of 200mm. The load is applied at a uniform rate such that the extreme fibres stress increases at 0.7N/mm2 /min i.e. the rate of loading shall be 4 kN/min. The load is increased till the specimen fails. The maximum value of the load applied is noted down. The modulus of rupture is calculated,σs=Pl/bd2 where, P = load in N applied to the specimen, l = length in mm of the span on which the specimen is supported, b = measured width in mm of the specimen, d = measured depth in mm of the specimen at point of failure.

Results and Discussion

Measurement of Workability

Workability of concrete is measured in terms of slump, compaction factor and vee bee time and the results are tabulated in Table. 2.

As volume fraction of fibres are increased, the workability of concrete decreases. For volume fraction of 1.5%, it is seen that with addition of admixtures, the workability of concrete is improved.

Compressive Strength

Cubes were tested for compressive strength at 7th, 14th and 28th day. The compressive strength results of 7th , 14th and 28th day are tabulated in Table.3, 4 and 5 respectively. It is found that compressive strength increases to 51.48% with addition of 2.5% fiber to conventional concrete. For 1.5% addition of fiber, concrete with admixture is 3.7% higher than concrete without admixtures. Figure.3 shows cube compressive strength of different mix.

[2456-2793-1-12-3]

Figure 3: Cube Compressive Strength of Different Mix

Table 3: Compression Test on Cube at 7th day

Mix Initial crack load, kN Average failure load, kN Compressive strength, N/mm2 % Increase in strength with CC
CC 215 355 15.77 -
CA 187 386 17.26 9.45
CF-1.5 272.5 368.5 16.54 4.88
CFA-0.5 190 357.5 15.90 0.82
CFA-1.0 248 396 17.60 11.60
CFA-1.5 316 408.5 18.16 15.16
CFA-2.0 314 427 19.02 20.61
CFA-2.5 321 497 22.10 40.14

Table 4: Compression Test on Cube at 14th day

Mix Initial crack load, kN Average failure load, kN Compressive strength, N/mm2 % Increase in strength with CC
CC 368 474 21.00 -
CA 392.5 498.5 22.60 7.62
CF-1.5 329 546 24.27 15.57
CFA-0.5 306 478.5 21.26 1.24
CFA-1.0 335 528 23.47 11.76
CFA-1.5 341 567.5 25.22 20.10
CFA-2.0 367.5 590 26.22 24.86
CFA-2.5 378 612 27.20 29.52

Table 5: Comparison on Compressive Strength of Cube at 28th Day

Mix Initial crack load, kN Average failure load, kN Compressive strength, N/mm2 % Increase in strength with CC
CC 416 615 27.33 -
CA 460.5 682 30.31 10.90
CF-1.5 512 783 34.80 27.33
CFA-0.5 437 660 29.33 7.32
CFA-1.0 520 738 32.80 20.01
CFA-1.5 567 812 36.10 32.09
CFA-2.0 658 865 38.44 40.65
CFA-2.5 705 931 41.4 51.48

a). Comparison of Compressive Strength at 7th day

Comparison on Split Tensile Strength at 28th day

Cylinders were tested for split tensile strength at 28th day. The results are tabulated in Table.6. It is found that split tensile strength increases to 45.6%with addition of 2.5% fiber. As observed earlier, for 1.5% addition of fiber, concrete with admixture is 19.1% higher than concrete without admixtures. Figure.4 shows split tensile strength of different mix.

Comparison on Flexural Strength at 28th day

Prismswere tested for flexuralstrength at 28th day. The results are tabulated in Table.7. It is observed that flexural strength increases to 48.72% with addition of 2.5% fiber. For 1.5% addition of fiber, concrete with admixture is 8.7% higher than concrete without admixtures. Figure.5 shows flexural strength of different mix.

[2456-2793-1-12-4]

Figure 4: Split Tensile Strength on Cylinder at 28th day

[2456-2793-1-12-5]

Figure 5: Flexural Strength on Prism at 28th day

Table 6: Comparison of Split Tensile Strength of Cylinder at 28th Day

Mix Average failure load, kN Split Tensile Strength, N/mm2 % Increase in strength with CC
CC 175 2.5 -
CA 183.5 2.65 6.00
CF-1.5 193 2.77 10.80
CFA-0.5 229 3.23 29.20
CFA-1.0 231 3.27 30.80
CFA-1.5 233 3.30 32.00
CFA-2.0 248 3.51 40.40
CFA-2.5 257 3.64 45.60

Table 7: Comparison of Flexural Strength of Prism at 28th Day

Mix Average failure load, kN Flexural Strength, N/mm2 % Increase in strength with CC
CC 10.35 4.31 -
CA 12.125 4.97 15.31
CF-1.5 13.8 5.51 27.84
CFA-0.5 12.1 4.83 12.06
CFA-1.0 12.7 5.09 18.10
CFA-1.5 14.6 5.99 38.98
CFA-2.0 15.4 6.19 43.62
CFA-2.5 16.0 6.41 48.72

Conclusions

From experimental investigations, it is found that compressive strength increases to 51.48%, split tensile strength increases to 45.6%, flexural strength increases to 48.72% with addition of 2.5% fiber to conventional concrete. For 1.5% addition of fiber, concrete with admixture has compressive strength 3.7% higher, split tensile strength19.1% higher and flexural strength8.7% higher than concrete without admixtures. Workability and mechanical properties of concrete is found to improve with addition of silica fume and fly ash.

References

  1. Banthia N (2012),”FRC: Milestone in international Research and development”, proceedings of FIBCON2012, ICI, Nagpur, India, February 13- 14, pp 48.
  2. Davallo.M, Pasdar.H, (2009) “Comparison of Mechanical Properties of Glass-Polyester Composites Formed by Resin Transfer Moulding and Hand LayUp Technique’’, International Journal of ChemTech Research, Vol.1, No.3, pp 470-475, July-Sept 2009.
  3. Fang Yuan, Jinlong Pan, ZhunXu and C. K. Y. Leung, ‘A comparison of engineered cementitious composites versus normal concrete in beam-column joints under reversed cyclic loading’, Materials and Structures, January 2013, Volume 46, Issue 1-2, pp 145-159.
  4. Manu SanthanamandA. Sivakumar, ‘Mechanical properties of high strength concrete reinforced with metallic and non-metallic fibres’, Cement and Concrete Composites, Volume 29, Issue 8, September 2007, pp 603–608.
  5. Nandini Devi G, ‘Experimental Study on Properties of Glass Fibre Reinforced Self-Compacting Concrete’, International Journal of Earth Sciences and Engineering (IJEE), October 2014, Vol.7, No.5, pp. 1906-1917.
  6. Ravichandran A.,Suguna K., And Ragunath P.N.(2009),” Strength Modeling of High-Strength Concrete with Hybrid Fibre Reinforcement”, American Journal of Applied Sciences, vol 6(2), pp:219-223.
  7. S. Eswari, P.N. Raghunath and K. Suguna, ‘Ductility Performance of Hybrid Fibre Reinforced Concrete’, American Journal of Applied Sciences, 2008, vol. 5 (9), pp 1257-1262.
  8. Sivakumar.A, (2011), ‘Influence Of Hybrid Fibres On The Post Crack Performance Of High Strength Concrete: Part I Experimental Investigations’, Journal of Civil Engineering and Construction Technology Vol. 2(7), pp. 147- 159, July 2011.
  9. S.P. Singh, A.P. Singh and V. Bajaj, ‘Strength And Flexural Toughness Of Concrete Reinforced With Steel – Polypropylene Hybrid Fibres’, Asian Journal Of Civil Engineering (Building And Housing) Vol. 11, No. 4 (2010), pp 495- 507.
  10. Yamin Patel, Elizabeth George and Sumant Patel, ‘Utilization of Hybrid Fiber Reinforced Concrete for Beam-Column Joint Analysis’, Indian Journal Of Applied Research, Vol: 3, Issue: 5, May 2013, pp 277-279.

© 2016 G. Nandini Devi ; licensee Payam Publishing Pvt. Lt..
This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The license is subject to the Science and Engineering Applications terms and conditions: (http://www.jfips.com/saea)

Keep In Touch

RSS Feed

Subscribe to our Latest Research Articles RSS Feed.

Subscribe

Follow the Science and Engineering Applications

LinkedIn

Twitter: @SAEA

Facebook: Facebook

 
Back to Article List