Fatigue Performance and Multiscale Mechanisms of Concrete Toughened by Polymers and Waste Rubber

For improving bending toughness and fatigue performance of brittle cement-based composites, two types of water-soluble polymers (such as dispersible latex powder and polyvinyl alcohol powder) and waste tire-rubber powders are added to concrete as admixtures. Multiscale toughening mechanisms of these additions in concretes were comprehensively investigated. Four-point bending fatigue performance of four series concretes is conducted under a stress level of 0.70. The results show that the effects of dispersible latex powder on bending toughness and fatigue life of concrete are better than those of polyvinyl alcohol powder. Furthermore, the bending fatigue lives of concrete simultaneously containing polymers and waste rubber powders are larger than those of concrete with only one type of admixtures. The multiscale physics-chemical mechanisms show that high bonding effect and high elastic modulus of polymer films as well as good elastic property and crack-resistance of waste tire-rubber powders are beneficial for improving bending toughness and fatigue life of cementitious composites. 1. Introduction With the rapid development of high-rise building and long-span concrete bridges in China, demands of high strengths and high toughness of concrete materials are more and more highlighted in the latest decade. Because of the obvious brittleness, high strength concrete structures are always suddenly fractured without any warning under fatigue and earthquake actions. Besides, cracks introduced by these dynamic loads are entrance of corrosion ions such as chloride, dioxide, and sulfate, which would make durability of concrete structure degraded. Therefore, upgrading toughness is a necessary way to improve the durability of cement-based composites. It has been noted that material toughness depends on material components, microstructure morphology and mechanics, and so forth. Because of shrinkage, random microcracking could not be prevented inside of concrete. That means the optimized cost-effective methodologies for toughness improvement of concrete is a big challenge so far. Many scientists (Dry [1], Ye [2], Guneyisi et al. [3], etc.) have done many researches to decrease porosity, homogenize microstructure, enhance bond strength between aggregate and hardened cement paste, and decelerate crack growth through fiber reinforcement, polymer toughening, and nanoparticles. However, fibers and nanomaterials are too expensive to be applied in practice in wide range. Instead, polymers and reactive industry waste particles or powder could be better choice even though a