Mechanical Properties Of Hybrid Fibre Reinforced Composite Concrete. (HyFRCC)

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1 Mechanical Properties Of Hybrid Fibre Reinforced Composite Concrete. (HyFRCC) 1, 2, a *Wan Amizah Bt Wan Jusoh 1, b, Izni Syahrizal Bin Ibrahim 1 Faculty of Civil Eng, Universiti Teknologi Malaysia (UTM), Malaysia, Johor Bahru,Malaysia. 2 Faculty of Civil & Env. Eng, Universiti Tun Hussein Onn Malaysia (UTHM), Malaysia, Parit Raja,Johor, Malaysia. a amizah@uthm.edu.my; b iznisyahrizal@utm.my Abstract :The concept of hybridization can offer more attractive mechanical engineering properties by adding two or more types of fibre into concrete. For this purpose, type hooked-end deformed steel fibre (SF) with 60mm length and polypropylene fibre (PPF) type fibrillated virgin polypropylene with length 19mm were chosen as a compliment with C30 grade concrete. The specimens incorporated steel and polypropylene fibres in the mix proportions of 100-0%, 75-25%, 50-50%, 25-75% and 0-100% with total volume fraction (V f ) 1.5%. The research methodology were focused on experimental program to determine mechanical properties 28 days of hardened concrete HyFRCC such as compressive strength, flexural strength,splitting tensile and flexural toughness. With combination of two fibres in concrete, it will delay micro and macro crack formation with SF was found to enhanced flexural strength, tensile strength, ability to resist cracking and spalling meanwhile PPF will contributed in tensile strain capacity, compressive strength and delay micro cracks. The result found that fibre in concrete helps in bridging the crack growth. For (V f ) 1.5%, the fibre mix proportion 75% of ST fibre and 25% of PP fibre which gives highest value of flexural strength, tensile splitting, and 100% of ST fibre and 0% of PP fibre contributed highest value for compressive strength and flexural toughness. Keywords: Hybrid Fibres, Hooked-End, Steel Fibre, Fibrillated, Polypropylene 1.0 Introduction Concrete are the second most consumed construction materials after water with twice as much concrete used across the world rather than all other construction material. Concrete meanwhile in its certain common characteristic is strong in compression and weak in tension (Mindess, 1990). Concrete also associated with creep and drying shrinkage which induced cracking problems and deterioration. Reinforcement of concrete with short randomly distributed fibres can address some of the concerns related to concrete brittleness and poor resistance to crack growth (P.N.Balaguru, 1992). When utilizing with single type of fibre may improve of properties to a limited level. However by hybridization with two or more different type of fibre in concrete will known as hybrid fibre reinforced composite concrete HyFRCC. In a HyFRCC, two or more different types of fibres can be properly combined to produce a composite, whose mechanical and physical performances take benefits from each type of fibres and from a possible synergistic response 1

2 (Banthia & Gupta, 2004).The combination of fresh concrete mixes with steel fibre (SF) and fibrillated polypropylene fibre (PPF) might have improved the different mechanical properties of concrete as reported by (Qian & Stroeven, 2000). 2.0 Scope and Objective This research will covered the performance characteristics of HyFRCC through the combined use of different types of fibre in concrete. As shown in figure 1(a) and 1(b) the fibre has been used in this study. At the micro-level, fibres inhibit the initiation and growth of cracks, and after the micro-cracks coalesce into macro-cracks, fibres provide mechanisms that abate their unstable propagation, provide effective bridging, and impart sources of strength gain, toughness and ductility (Mindess, 1990; P.N.Balaguru, 1992). (a) Figure 1:(a) Fibrillated polypropylene fibre (b) Hooked end steel fibre (b) Tadepalli, Mo, Hsu, & Vogel, (2009) in his research on the effects of steel fibre reinforcement on found that the most effective shape for energy absorption capacity is the hooked end type fibres. Steel fibre with higher modulus of elasticity should be used V f within 0.5% to 1.5% as the additional fibre then may reduces the workability of mix and cause balling or mat which will be extremely difficult to separate by vibration (ACI Committee 544, 2010) Additional steel fibre looked as a better idea to prevent cracking and early thermal contraction right after placing the fresh concrete in the formwork (Ibrahim & Che Bakar, 2011). 2

3 Polypropylene fibre has a characteristic with low modulus of elasticity,low fire resistance and low durability. It is a synthetic hydrocarbon polymer which is made using extrusion process. PPF fibre cannot prevent the formation and propagation of high stress level and cannot prevent larger cracks. To improved potential crack control, necessary that have great deal by mixing steel fibre and polypropylene fibre in concrete to reduce crack growth on structure element in construction industry. The objective of this study to investigate the mechanical properties of HyFRCC in terms of compressive strength, flexural strength, tensile split and ability of HyFRCC in terms of energy absorption and ductility response. 3.0 Experimental Programme 3.1 Materials, concrete mix, specimen preparation and testing The mechanical properties of HyFRCC based on their performance condition at fresh and hardened state. Slump test as a tool measurement to determined workability of fresh state of HyFRCC. At 28 days with C30 grade concrete, four test has been conducted to determine the strengths of HyFRCC under compression test, tensile splitting, flexural strength and flexural toughness as a mechanical performance of the composite material. Table 1 shows the fibre mix proportion of SF and PPF fibres used in HyFRCC with total volume fraction, V f 1.5%. The physical properties such density of SF and PPF was 7850 kg/m3 and 460 kg/m3 respectively. Aspect ratio (l/d) of PPF within range of and SF have an aspect ratio, (l/d) of between 55 and 60. The materials used in this study are listed in Table 2. The ratio of water added to the cement was w/c=0.55. In order to have proper mixture the design mix were refer to design of environment method (DOE). The proportion of water, cement, fine and coarse aggregates and super plasticizer were mixed same portion each batch as per designed.the use of fibre is well known to effect the 3

4 Concrete Batch Steel Fibre Hooked End (Kg) Fibrillated Polypropyle ne Fibre (Kg) Design Compressiv e Cube Strength at 28-days Ordinary (N/mm 2 ) Portland Cement (Kg) Fine Aggregate (Kg) Coarse aggregate (max size of 10mm) (Kg) Water (Kg) Super plasticizer (ml) workability and flow ability of concrete, However, to overcome this problem, superplasticizer were used to improved workability when high volume fraction of fibre mixed with concrete. The mixing of the materials was done specific sequence as stated in BS EN 206-1:2000. Figure 2 shows that the process of fibre added into wet concrete mixes. In the production of concrete, the aggregate and sand was put into mixer and mixed for a few minutes followed by cement and water were added into mix. Fibres were added in small amount to avoid fibre balling effect and to produce with uniform material consistency and good in workability. Table 1: Dosage of fibre proportion by volume Type of Fibres Total Volume Fraction, V f =1.5% Steel Fibre (ST) Polypropylene Fibre (PPF) (a) Figure 2 : Fibre added into wet concrete mixes Table 2: Concrete mixture proportion Plain (100-0) (75-25) (50-50) (25-75) (0-100)

5 A total of six concrete mixes were prepared with plain concrete as control and concrete with different fibre combination as shown in Table 2. For each mix, 150x150x150mm cubes, 100x300mm cylinder,100x100x500mm and 100x100x350mm prism were prepared for compressive strength (BS EN :2009),Splitting tensile strength (BS EN :2009) and flexural strength (BS EN 12390:2009) and flexural toughness (ASTM C1609/C1609M-12) respectively. The experimental setup has been conducted at laboratory as shown in figure 3. (a) (b) (c) Figure 3: Experimental setup at laboratory (a) Compression Test, (b) Splitting tensile test, (c) Flexural Strength Test (d) Flexural Toughness 4.0 Result and Discussion Figure 4 shows the relationship between the concrete slump and fibre proportion at V f 1.5%.Comparing the design slump between 60mm and 180 mm, the test results show that V f 1.5% almost below the design slump within 32-40mm. This shows that for longer fibre used such SF with 60mm and PPF with 19mm also affect the concrete workability reduces. The higher fibre quantity causes congestion in the concrete mix and also ability of PPF absorb water, thus reduced the workability. 5

6 The result of f cu conducted on control mix and hybrid fibres with different fibre volume fraction are presented in table 3 and figure 5. The result shows that there are an increase of f cu up to 13% when the fibre percentage at V f 1.5 % with 100 SF and 0% PPF. However it shows slight decrease on the value of compressive strength of V f 1.5 % with 0% SF and 100% PPF obtained 33.2Mpa. All the compressive values obtained after 7 and 28 days curing. This will concluded for SF also contributed to increase the important part of strength of concrete. PPF showing the average result 33.2Mpa also still higher then design of normal concrete strength f cu. The splitting tensile strength result shows in table 3 and figure 6. The result shows the maximum value of Mpa at fibre combination of 75% SF and 25% PPF. This value of f t was increase of 20% as compare with control sample. The cracking pattern was also observed for each fibre proportion batch. The f t values obtained after 28 days curing. Table 3 shows the variation result of HyFRCC for indirect tensile test. From the result in table 3, almost f t of combination fibre give the high tensile strength compare control sample. The flexural strength test result for various proportion of fibre mix are presented in table 3 and figure 7. The result show that the fibre combination of 75% SF and 25% PPF at volume fraction 1.5% give the highest f ct with 37% as compare to the control sample. The reason of this, when structure were subjected to flexural loading, the shorter fibre bride the micro cracks and prevent the expansion of the structure and when the shorter fibre fail the longer fibre will keep bridging the cracks until its fail which resulted in increase of flexural strength. However, the result shows the decrease 15% of the value ft for 0% SF and 100% PPF because of concrete with short fibre like PPF may result with non uniform fibre distribution and when load is applied on specimen, the short fibres were pulling out from the matrix which resulted in the lowest flexural strength. 6

7 Figure 4: Relationship between Slump concrete (mm) and fibre proportion (%) Figure 5: Relationship between cube compression strength (f cu ) and fibre proportion (%) Figure 6: Relationship between concrete splitting tensile strength (f ct ) and fibre proportion (%) Figure 7: Relationship between concrete flexural strength (f t ) and fibre proportion (%) 7

8 Table 3: Result of compressive strength, flexural strength test and splitting tensile test Batch Compression Test (f cu ) 7 Days 28 Days Average Average Plain (100-0) (75-25) (50-50) (25-75) (0-100) Flexural Strength Test (f ct ) Batch 7 Days 28 Days Average Plain (100-0) (75-25) (50-50) (25-75) (0-100) Splitting Tensile Test (f t ) Batch 7 Days 28 Days Average Plain (100-0) (75-25) (50-50) (25-75) (0-100) Table 4: Flexural toughness indices Volume Fraction (%) 1.5 % Volume Proportion (SF-PPF) P 600 (kn) P 150 (kn) f 600 (MPa) f 150 (MPa) T 600 (J) Control T 150 (J) 8

9 Figure 6: Relationship load versus deflection for plain and hybrid fibres at V f of 1.5%. Result from flexural toughness on control sample and hybrid fibres composites with a V f of 1.5%. are shown in figure 8 and table 3.Flexural toughness was followed ASTM C1609/C1609M-12 and its defined as the ratio of area of load deflection graph up to 3 times the deflection at first crack and area of load deflection graph corresponding to first crack. Based on 9

10 the load deflection graph, apparent toughness indices were calculated for all prism specimens as shown in table 4.The pattern for graf plotted load versus deflection also shown that behavior of ductility when mixed with hybrid fibre in concrete. Combination of 100% SF and 0% PPF shown the ductility when sample not break into two and still give value of deflection after first crack until failure. As compare with 75% SF and 25% PPF, graph pattern shows steep slope after first crack and leading decrease with deflection value when load also decrease. So 100% PPF used in concrete not give much in term ductility response and sample break into two after first crack. 5.0 Conclusion As the main conclusion drawn from this study, the workability of fresh concrete was found to decrease with an increase in the fibre content. Too much PPF in concrete will affect low workability cause of the potential PPF ability to absorb water in concrete. The fibre in concrete helps in bridging the crack growth and the combination of 75% SF and 25% PPF give the high value of flexural strength and tensile splitting and for 100% SF and 0% PPF contributed in compression strength and flexural toughness. The additional of SF causes durability of concrete compare with plain concrete. When concrete subjected to load, the steel fibre will absorb more energy before its fails. When observation during experimental work, plain concrete will split into two suddenly when its subjected to loading because its characteristic as a brittle material. Compare with hybrid fibre concrete it s slowly break into two when loading increase. Acknowledgement A special thanks goes to all staffs in the Structural & Material Laboratory, Faculty of Civil Engineering, Universiti Teknologi Malaysia for their valuable help and supports. Much appreciation for study leave sponsorship by Universiti Tun Hussein Onn Malaysia, Batu Pahat, 10

11 Johor and scholarship SLAI by Ministry of Higher Education. Also, special thanks to Supplier for the supply of steel fibre and polypropylene fibre. References ACI Committee 544. (2010). Report on the Physical Properties and Durability of Fiber- Reinforced Concrete. BS EN (2009).Compressive Strength of Test Specimens.Testing Hardened Concrete BS EN (2009).Tensile Splitting Strength of Test Specimens.Testing Hardened Concrete BS EN (2009).Flexural Strength of Test Specimens.Testing Hardened Concrete C 1609/C 1609M (2008). Standard Test Method for Flexural Performance of Fibre-Reinforced Concrete (Using Beam with Third-Point Loading). Annual Book of ASTM Standards, ASTM Committee. C Banthia, N., & Gupta, R. (2004). Hybrid fiber reinforced concrete ( HyFRC ): fiber synergy in high strength matrices, 37(December), Ibrahim, I. S., & Che Bakar, M. B. (2011). Effects on Mechanical Properties of Industrialised Steel Fibres Addition to Normal Weight Concrete. Procedia Engineering, 14, doi: /j.proeng Mindess, B. and. (1990). Fibre Reinforced Cementious Composite. Fibre Reinforced Cementious Composite. Elsevier Applied Science,London,UK. P.N.Balaguru, S. P. S. (1992). Fiber Reinforced Cement Composite. In Mc Graw Hill-Inc. New York. Qian, C. X., & Stroeven, P. (2000). Development of hybrid polypropylene-steel fibre-reinforced concrete. Cement and Concrete Research, 30(1), doi: /s (99) Tadepalli, P. R., Mo, Y. L., Hsu, T. T. C., & Vogel, J. (2009). Mechanical Properties of Steel Fiber Reinforced Concrete Beams. Structures Congress 2009, doi: /41031(341)115 11

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