Advanced Materials Research Vol. 804 (2013) pp 8-11 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.804.8
Review of Mechanical Properties and Durability of PVA Fiber Reinforced Cement Based Composite Materials Xiaobing Daia, Peng Zhangb and Jixiang Gaoc College of Water Conservancy and Environment Engineering, Zhengzhou University, Zhengzhou, Henan, 450001, China a
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Keywords: Cement based composite, PVA fiber, Mechanical properties, Durability.
Abstract. As a kind of high performance cement based construction materials, because of good mechanical performance and durability, PVA fiber reinforced cement based materials have been paid more and more attention in the field of civil structure engineering. To grasp the characteristics of PVA fiber reinforced cement based composite materials and promote a better application of PVA fiber reinforced cement based composite in practical engineering, a series of research works on the mechanical properties and durability of PVA fiber reinforced cement based composite were introduced systematically. Introduction Addition of fibers in cement based composite materials can improve the toughness, impact resistance and shrinkage cracking resistance of the materials in effective ways. The research and application of synthetic fibers reinforced concrete began in the 1960s, which obtained the considerable development in the 1970s. Because the synthetic fibers can effectively control the cracks of the structures of cement mortar and concrete, the fibers have been applied on a large scale new works and repair works in the 1980s. The traditional fiber reinforced cement based composite materials have low tensile strain resistance, and in recent years, great achievements in the research have obtained to change this brittleness, most of which are concentrated in changing fiber contents. Though the fracture toughness of materials can be improved by this means, the construction cost will be increased and great inconvenience will be brought to the construction. With the development of research of fiber reinforced cement based composite materials in recent years, the fiber of polyvinyl alcohol (PVA) fiber with high strength and high modulus has been an ideal fiber applying in cement based materials. Mechanical Properties of PVA Fiber Reinforced Cement Based Composite Materials PVA fiber is a new fiber with high tensile, high elastic modulus, good hydrophilicity, and especially the compatibility with Portland cement. Xue Huiqing et al. verified the uniaxial tensile and flexural toughness through experiments in order to obtain the PVA fiber reinforced cement based composites with high toughness and large deformation [1]. Their results show that PVA fiber can improve the cracking resistance and the resistance to deformation of the matrix materials, and PVA fibers can obviously improve the flexural toughness of concrete. Furthermore, flexural toughness index of PVA fiber concrete was obviously higher than that of polypropylene (PP) fiber concrete. PVA fiber has the common advantages of chemical fiber, and it has relatively low prices and high elastic modulus. However, because the research on PVA fibers used in the cement concrete is very little, this fiber has not been fully used. The effect in theory of PVA fiber in cement bases material includes restricting the extension of the original defects in the matrix (micro-cracks), delaying the appearing of new cracks and improving the deformation capacity. Wang Yongbo et al. found that PVA fiber can effectively improve the crack resistance of cement base material and that the quantity of 0.9 kg/m3 of PVA fiber content in cement mortar can make the crack control rate be more than 80% through a series of experiments of PVA fiber reinforced concrete [2]. For PVA fibers have strong All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 123.15.57.134, Zhengzhou University, Zhengzhou, China-08/08/13,17:54:16)
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cohesive force with the cement based materials, they can be used in building engineering to effectively improve the crack resistance of mortar and concrete. The addition of PVA fiber effectively improved the toughness of cement concrete, and the experimental results show that the toughness can be improved by 67%. Zhan Binggen et al. have conducted the toughness research by applying low dosage (fiber volume fraction of 1% - 2%) of high strength and high elastic modulus PVA fiber, and analyzed the effect of the material composition parameters (PVA fiber volume fraction, fiber length to diameter ratio, interfacial modifier and sand cement ratio, etc.) on the toughness of high strength and high elastic modulus PVA fiber reinforced cement base material [3]. The results indicate that the toughness of PVA fiber reinforced cement base material was increased with the increase of fiber volume ratio and the decrease of the ratio of sand. Concave soil improved the interface performance between the fiber and matrix, and thus it also improves the toughness of the PVA fiber reinforced cement based materials, however the dosage has an optimal value. High length to diameter ratio of PVA fiber reinforced cement base material has a better improvement on toughness. Gao Shuling et al. studied the difference of the uniaxial compressive stress-strain curve between the normal concrete and PVA fiber reinforced cement matrix composites with the PVA fiber volume content of 2% applying cylinder specimens with the size of Φ76×152 mm, and analyzed the stress-strain curve, mechanical properties and the failure pattern of the fiber reinforced composites [4]. Their results show that the compressive strength of the composites is 20-40 MPa, and the strain at the peak stress can reach 0.8%-1.5%, which is 4-7 times of that of the concrete, and the ultimate compressive strain is 5-10 times of that of the concrete. Chen shengping et al. carried out the mechanical properties study through uniaxial compression tests, direct tensile tests, four-point bending tests and bending tests with different ratio and different shape of specimen of the PVA fiber reinforced cement base composite material. The results show that the compression strength of PVA fiber cement-based composite materials is increased not too much, the growth ratea of which is bout 10%, while the tensile strength and bending strength increase a lot, and there appears a lot of tiny cracks, and presents the strain hardening characteristics, and the limit tensile strain can reach 1.8% [5]. The test results are much more accurate applying the monoblock type specimens than shank type specimens to carry out the direct tensile test, and the test operation of monoblock type specimens is much easier. Their test results verified that the PVA fiber reinforced cement matrix composites have wonderful toughness Gao Shuling et al. preliminary prepared PVA fiber cement-based composite materials, and the performance of raw materials, mixing procedure and mixing process are described in detail [6]. Based on the measure of the values of slump flow of each mixture, the cause why the flowability decreases after adding fibers is revealed that there are hydrophilic PVA fibers, the surface of which adsorbs a great deal of free water molecules. The hardening stress-strain full curves were obtained by applying external clip-on uniaxial direct tensile tests, and the limit tensile strain reached 0.7%, which is about 70 times of that of the concrete. Furthermore, according to the effect of the matrix and fiber content on the ultimate tensile strain, peak stress and fracture energy, the stress-strain full curves of false hardening were analyzed. Wang Youkai et al. carried out four-point bending test on PVA fiber reinforced cement based composites (PVA-FRCC), and they obtained the load deflection curves, and further analyzed the deformation properties of PVA-FRCC. The results indicate that the deformation ability of PVA-FRCC is significantly improved compared with the matrix concrete [7]. The failure of PVA-FRCC is changed from suddenly brittle failure into ductile damage with better toughness, and a large number of cracks come into being when the damage occurs. PVC fibers reinforced cement based composites with high elastic modulus can replace the traditional reinforced cement based materials to obtain false characteristics of strain hardening and multiple slit, so as to improve the durability of the structures. Chen Xue et al. studied the bending properties of fiber reinforced cement based materials (ECC) by three point bending test under different ratio of fibers. The results show that the larger of water cement ratio, the lower of the
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bending strength of ECC, however, the smaller water cement ratio can reduce flowing property of the matrix, which is not conducive to construction operations; with the increase of fiber mass fraction, the bending capacity of the ECC increased at first, and then decreased; the ECC with larger fiber length to diameter ratio has better bending performance [8]. Durability of of PVA Fiber Reinforced Cement Based Composite Materials Freezing and thawing, salt erosion and other environmental factors are the major factors leading to degradation in structure performance and shortening in service life of concrete and other cement base material structures. When summarizing the research progress of concrete durability in the last 50 years, Mehta pointed out that the main reason that the concrete was damaged today can be ranked in order of decreasing importance: reinforcement corrosion, freezing damage, corrosion effect [9]. Therefore, improving the frost resistance of concrete is of great significance to improve its durability. Based on the data derived from the quick frozen experiment, Liu Shuguang et al. analyzed the damage principle and features of PVA fiber cement base composite materials in the frozen environment of salt to verify the proposed concrete freezing-thawing parabolic damage model on the basis of the damage principle, and the life of PVA fiber cement-based composites in salt frozen environment were predicted based on the parabolic model [10]. Their results indicate that the salt frost damage of PVA fiber cement based composite materials is produced by static water pressure and seepage pressure, and the failure process is result from the internal damage accumulation under the action of the repeated action of the hydrostatic pressure and osmotic pressure inside the material. Besides, the concrete damage model based on damage mechanics can be applied to PVA fiber reinforced cement based composite materials, which has high accuracy, and the validation of the model can provide the basis for life prediction and the damage law of PVA fiber cement-based composite materials in freezing-thawing environment in further research. Furthermore, the fiber volume content of 1.5% PVA fiber cement base composite material has good salt frost resistance. In order to study the effect of PVA fibers on the properties of shrinkage cracking of cement-based composite materials, Zhou Zaiquan et al. conducted the shrinkage properties of PVA reinforced concrete through the ring shrinkage test with mortar powder content of 0%, 0.75%, 1.5% of mortar powder and fiber content of 0.9% [11]. The test results show that the addition of PVA fiber evidently improved the drying shrinkage resistance of the mortar, and a large number of cracks appeared, and the maximum crack width was controlled within 0.1 mm. From the shrinkage strain and the maximum crack width, it can be seen that PVA fiber reinforced concrete is obviously better than the normal concrete. Through the fast freeze-thaw test in chlorine salt environment, Liu Shuguang et al. studied the number of freezing-thawing cycles, fiber volume dosage, fly ash and silica fume, on the salt frost resistance of PVA fiber cement-based composite materials, and the change rule of the internal microstructure with the change of the salt frost effect, PVA fiber distribution in cement matrix and the interface bonding condition were observed by scanning electron microscope [12]. The experimental results show that the addition of PVA fibers can obviously improve the salt frost resistance of cement-based composite materials, and PVA fiber has good dispersibility in the matrix and good combination with the cement matrix, however, the addition of fly ash, silica fume can’t obviously improve the salt frost resistance of PVA fiber cement base composite materials. The water permeability of PVA fiber reinforced cement-based composites depends on the degradation speed of the PVA fiber cement-based composites to some extent. Based on darcy's law, Liu Shuguang et al. derived the calculation model of permeability coefficient of the water inside the PVA fiber cement based composite materials on the basis of experimental study, and analyzed the effect of fiber volume ratio, fly ash, silica fume on the anti-permeability of PVA fiber reinforced cement-based composites [13]. Their research results indicate that the PVA fibers can obviously improve the permeability performance of cement-based composite materials, and the addition of fly ash and silicon powder reduced the anti-permeability of PVA fiber reinforced cement-based composites.
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Conclusions From the above-mentioned related research results on the properties of PVA fiber reinforced cement based composites, it can be concluded that PVA fiber has good cracking resistance and toughening effect, and they can significantly improve the deformation ability of the composites. Besides, PVA fibers can obviously improve the flexural toughness of concrete, and the flexural toughness index of PVA fiber reinforced concrete is obviously higher than that of PP fiber reinforced concrete. The toughness of cement based materials reinforced by PVA fiber with high length to diameter ratio can be well improved by the fiber. Furthermore, the addition of PVA fibers can improve the salt frost resistance, drying anti-cracking performance and anti-penetrability performance of cement based composites. Acknowledgments The authors would like to acknowledge the financial support received from National Natural Science Foundation of China (Grant No. 51208472) and China Postdoctoral Science Special Foundation (grant no. 2012T50603). References [1] Q. Xue, Z. Deng and J. Li: Journal of Zhengzhou University (Engineering Science). Vol. 30 (2009), p. 92 [2] Y.B. Wang and H. Luo: Chongqing Construction. Vol. 7 (2005), p. 46 [3] B.G. Zhan, X.S. Lin and T. Chen. Journal of Hefei University of Technology (Natural Science Edition). 30 (2007), p. 1178 [4] S.L. Gao and S.L. Xu: Concrete and Cement Products. 36 (2009), p. 43 [5] S.P. Chen and S.H. Li: Journal of Hubei University of Technology. Vol. 26 (2011), p. 108 [6] S.L. Gao and S.L. Xu: Journal of Dalian University of Technology. Vol. 47 (2007), p. 233 [7] Y.K. Wang and L. Cao: Journal of Henan University of Science and Technology (Natural Science Edition). Vol. 30 (2011), p. 85 [8] X. Chen, Q.Y. Sun, L.S. Cui and C.M. Xu: New Building Materials. 35 (2008), p. 175 [9] P.K. Mehta: Proceeding of Second International Conference on Concrete Durability. American Concrete Institute, ACISP126-1 (1991). [10] S.G. Liu, Z.W. Wang, C.W. Yan, J. Zhang and M. Yan: Concrete and Cement Products. 39 (2012), p. 46 [11] Z.Q. Zhou and Q.H. Cui: Engineering Quality. 26 (2008), p. 31 [12] S.G. Liu, M. Yan, C.W. Yan and R.Y. Guo: Journal of Jilin University (Engineering Science). 42 (2012), p. 63 [13] S.G. Liu, X.M. Zhao, C.W. Yan and J. Zhang: Journal of Inner Mongolia University of Technology. 30 (2011), p. 414
