International Academic Institute for Science and Technology International Academic Journal of Science and Engineering Vol. 3, No. 5, 2016, pp. 98-106. ISSN 2454-3896 International Academic Journal of Science and Engineering www.iaiest.com Fiber Reinforced Concrete Pavement & Shrinkage Ali Kahidan a, Mohammad.r Shirmohamadian b, Wirya Rahmani c a Master Student, Department of Civil & Environment Engineering, University of Tarbiat Modares, Tehran, Iran. b Master Student, Department of Civil & Environment Engineering, University of Tarbiat Modares, Tehran, Iran c Master Student, Department of Civil & Environment Engineering, University of Tarbiat Modares, Tehran, Iran Abstract Cement concrete pavement provides durable service life and remarkable applicability for heavy traffic. Its purchase being easier than asphalt, cement concrete pavement offers excellent advantages in terms of durability and economic efficiency. However, adequate repair of this pavement is harder than asphalt concrete in case of degradation or damage. Cracking in the concrete pavement is the major cause of such disadvantages and the demand of repair on road sites is growing every day. This emphasizes the urgency to secure technologies for the control of early and longterm cracking. Accordingly, this study evaluates the drying and autogenous shrinkage strains regard to fiber reinforcement in order to reduce cracking of the concrete pavement mix so as to control the damage of the pavement by means of fiber reinforcement. The results show that the drying shrinkage strain can be significantly reduced to about 1/4 through the admixing of 0.2% volume ratio of NY fiber compared to the non-reinforced plain concrete, and that the hybrid fiber reinforcement mix H-N1-ST1 can realize remarkable reduction of the autogenous shrinkage. Keywords: Fiber Reinforced Concrete, Macro Fiber, shrinkage, Pavement, Hybrid Introduction Two techniques are generally used for road pavement: the asphalt concrete pavement that is ductile pavement and the cement concrete pavement that is rigid pavement. Cement concrete asphalt offers longterm service life and excellent applicability for heavy traffic. Its purchase being easier than asphalt, this pavement technique presents remarkable cost-effectiveness and durability. However, adequate repair of the cement concrete pavement is more difficult than the asphalt pavement in case of degradation or damage and demands works with a larger scale (Yang 2000; Um 2000). The typical causes of cracks in concrete pavement are the hydration cracking at early hydration state of concrete, the plastic shrinkage cracking, the environmental cracking caused by thermal changes at the top of the pavement, the drying shrinkage cracking according to the hardening of concrete, and the 98
cracking caused by the long-term process of alkali-silica reaction. The Korean research community has and is developing various solutions for the control of cracks (Naghizadeh rokni et al. 2016). The fundamental cause of the occurrence of cracks in concrete pavement is the poor resistance of the concrete pavement to bending, tension and cracking. Fiber reinforcement is a representative method for supplementing the bending tensile performance of concrete. To date, research on fiber reinforcement has been steadily conducted. The recent trend of research on fiber reinforcement focuses on studies dedicated to the plastic shrinkage cracking of fiber reinforced concrete with hybrid type of fibers and the tensile strength performance of steel fiber reinforced concrete (Won 2004; Kim 2005). Mehrian did an examination on fiberus structure and crack propagation in them. (Mehrian et. al., 2013, 2014, 2015, 2016). Research devoted to fiber reinforcement focuses mainly on the evaluation of the change of the mechanical performances according to the content and type of fibers in ordinary concrete and high strength concrete. However, poor interest is given to the fiber reinforcement effect with respect to the mix proportions of concrete. Especially, the quasi-absence of thorough study on the fiber reinforcement effect on concrete pavement of which the mix proportion is limited to a specific weight and is prescribed to adopt coarse aggregates with granulometry different to that of concrete pavement is noteworthy. Accordingly, this study intends to evaluate the drying shrinkage and autogenous shrinkage strains with respect to the fiber reinforcement in order to reduce cracking of the concrete pavement mix. Fiber reinforced concrete specimens are fabricated with the type and content of fiber chosen as test variable to select the type and quantity of fiber effective for shrinkage control. To that goal, the shrinkage strain of concrete is measured. Three types of macro fibers with length longer than 30 mm and small aspect ratio together with micro nylon fibers with length of 12 mm and aspect ratio larger than 1000 are selected for the tests. Both reinforcement with a single type of fiber and hybrid reinforcement involving micro and macro fibers were executed, and the fiber volume ratio was set to 0.2 to 0.3% of the concrete pavement mix. Using the so-fabricated specimens, the change of the length caused by drying shrinkage and autogenous shrinkage of concrete is analyzed comparatively. Test 2.1. Test planning and test variables The detailed mix proportions of the concrete pavement in this study are listed in Table 1. Fig. 1 describes the designation of the variables, and Table 2 presents the test variables and their explanation. Table 3 arranges the experimental setup. In the tests on fresh concrete, the slump was measured in compliance with KS F 2402, the air content was measured according to the specifications of KS F 2421, and the change of length by drying shrinkage and autogenous shrinkage was measured in compliance with the stipulations of KS F 2424 and KS F 2586. Type W/C S/a (%) (%) Table 1: Mixture proportions of concrete AE/C (%) SP/C W (%) (kg/m 3 ) Max. coarse Volume mixing aggregate size (Ɛ/m 3 ) (mm) C S G Pavement 42.3 39 0.02 0.28 150 32 113 270 422 Table 2: Parameter and fiber volume fractio n 99
Specimen Mixture Fiber dosage (%) Nylon PP PVA ST Plain Pavement concrete - - - - S-N2-00 0.2 - - - S-00-PP2-0.2 - - S-00-PV2 - - 0.2 - Single fiber S-00-ST2 - - - 0.2 H-N1-PP1 0.1 0.1 - - H-N1-PV1 0.1-0.1 - H-N1-ST1 0.1 - - 0.1 H-N13-PP07 0.133 0.066 - - H-N07-PV13 0.066-0.133 - H-N07-ST13 0.066 - - 0.133 H-N2-PP1 0.2 0.1 - - H-N1-PV2 0.1-0.2 - H-N1-ST2 0.1 - - 0.2 Figure 1: Specimen description 100
Factors Table 3: Experimental plan Levels Fresh concrete Experiments Hardened concrete 2.2. Materials and test methods 3 2 ɁSlump ɁAir content ɁConsistency (Vebe test) ɁDrying Shrinkage length variation (1, 7, 14, 28, 56 days) ɁAutogenous Shrinkage length variation (1,2,3...28 days) Table 4: Physical properties of Ordinary Portland Cement Density Blaine Soundness Setting time (min) Compressive strength (MPa) (g/cm 3 ) (cm 2 /g) (%) Ini. Fin. 3 days 7 days 28 days 3.15 3 165 0.18 235 320 20.4 29.4 38.7 Table 5: Physica aggregate s Type Density (g/cm 3 ) Fineness modules Absorption ratio (%) River sand 2.65 2.86 2.63 Crushed sand 2.50 2.62 1.42 Coarse agg. 20 mm 2.71 7.01 1.18 Coarse agg. 32 mm 2.70 6.88 0.58 Table 6: Physical properties of fiber Property NY PP PVA ST Density (g/cm 3 ) 1.16 0.91 1.30 7.86 Aspect ratio 1000 75~100 45 65 Length (mm) 12 30 30 35 101
Diameter (mm) 0.012 0.3~0.4 0.66 0.54 Tensile strength (MPa) 896 250~1000 900~1600 1200 Modulus of elasticity (GPa) 3.9~4.9 3~30 23~41 200 2.3. Test Results 2.3.1. Variation of length by drying shrinkage Figure 2: Drying shrinkage of fiber reinforced concrete Fig. 2 plots the variation of length by drying shrinkage with respect to the age per single fiber type. First, plain specimen experiences a strain of about 400u10 6 at 56 days, while concrete reinforced with a single type of fiber shows a change of length smaller than plain at all levels. Especially, the micro NY fiber reinforcement provides the most remarkable shrinkage control effect with a very small strain below 100u10 6. Among the macro fibers, S-00-PV2 offers the most effective performance with a drying shrinkage ratio of 200u10 6. 102
Figure 3: Drying shrinkage of hybrid fiber reinforced concrete Figure 4: Variation of drying shrinkage strain of hybrid fiber reinforced concrete at 56 days Fig. 3 plots the variation of length by drying shrinkage with respect to the age per hybrid fiber type. The variation of length is reduced by more than 2 times at all reinforcement levels compared to the nonreinforced plain specimen when hybrid fiber reinforcement is adopted. Mix H-N1-ST1 shows the smallest strain. As shown in Fig. 4, the effect of the variation of the fiber content by 0.2~0.3 is practically nonexistent. Compared to the results for the 0.2% volume reinforcement ratio by NY fiber, the mix H- N2PP1 with hybrid reinforcement by NY fiber at 0.2% and macro fiber at 0.1% exhibits much larger drying shrinkage, which reveals that synergy of both micro and macro fibers did not apply in the reduction of the drying shrinkage. For a small fiber content of about 0.2~0.3%, NY fiber provides the most remarkable shrinkage reduction effect. 103
2.3.2. Variation of length by autogenous shrinkage Figure 5: Autogenous shrinkage of fiber reinforced concrete Figure 6: Autogenous shrinkage of hybrid fiber reinforced concrete Fig. 5 plots the variation of length by autogenous shrinkage with respect to the age per single fiber type. The plain mix experiences an autogenous shrinkage strain of about 100u10 6 at 28 days. For the fiber reinforced mixes, specimen S-N2-00 tends to show large autogenous shrinkage at early age but, at later age, the autogenous shrinkage becomes nearly identical to that of plain and S-00-PP2. Specimen S-N2-00, which developed the most remarkable performance during the evaluation of the drying shrinkage, provides performance similar to plain in the evaluation of the autogenous shrinkage. This means that the improvement of the performance brought by NY fiber reinforcement cannot be developed for the autogenous shrinkage. The most effective mix in reducing the autogenous shrinkage is S-00-PV2, which reveals the largest autogenous reducing effect of PVA fiber. 104
Figure 7: Variation of autogenous shrinkage strain of hybrid fiber reinforced concrete at 28 days Fig. 6 plots the variation of length by autogenous shrinkage with respect to the age per hybrid fiber type. The plain mix shows an autogenous shrinkage strain of about 100u10 6. The variation of the shrinkage is sensitive to the change of the fibers. Specimen H-N2-PP1 presents the largest autogenous shrinkage of approximately 130u10 6 while mixes H-N1-ST1 and H-N-PP1 shows the smallest shrinkage strains with value of about 70u10 6. Fig. 7 compares the autogenous shrinkage at 28 days. The mix proportions with fiber content of 0.2% shows shrinkage reducing effect generally equivalent or superior to the mixes with fiber content of 0.3%. The most remarkable fiber ratio is 1:1. Conclusions This study analyzed comparatively the shrinkage performance of concrete pavement according to fiber reinforcement. It was seen that mix S-N2-00 with single fiber reinforcement provides the largest reduction of the drying shrinkage while mix H-N1-ST1 with hybrid fiber reinforcement developed the smallest shrinkage. The most remarkable performance for the autogenous shrinkage was provided by specimen S-00-PV2 with single fiber reinforcement and mixes H-N1-ST1 and H-N1-PP1 with hybrid fiber reinforcement. References Kim MH, Kim JH, Kim YR, Kim YD(2005). An Experimental Study on the Mechanical Properties of HPFRCCs Reinforced with the Micro and Macro Fibers. Journal of Korea Concrete Institute, Vol. 17, No. 2, pp. 263-271. Li VV and Stang H(1997). Interface property characterization and strengthening mechanisms in fiber reinforced cement based composites. J. Advanced cement based Materials, Vol. 6, No. 1, pp. 1-20. Olivito RS, Zuccarello FA(2010). An experimental study on the tensile strength of steel fiber reinforced concrete. Cement & concrete composite, composites: Part B 41, pp.246-255. Sivakumar A, Manu Santhanam(2007). A quantitative study on the plastic shrinkage cracking in high strength hybrid fibre reinforced concrete. Cement & concrete composite, 29, pp.575-581. 105
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