Analytical Model For Tensile Behaviors Of Ultra High Toughness Cementitious Composites

Ultra high toughness cementitious composites is a cement-based material added with polyvinyl alcohol (PVA) fiber, which has the strain hardening properties in the uniaxial tensile process that similar to metallic materials and has more capable in particular micro-cracks control than general fiber cement-based materials. This type of composites under tensile load has better strain capacity, more than 3% and maximum crack width below 0.1mm. This kind of composites help to overcome the shortcomings of concrete such as poor toughness and cracking easily. In this paper, for the macro tensile mechanical behavior of UHTCC, micro-mechanics and micro-fracture mechanics are employed to analyze the impact of parameters on the material properties.(1) This paper introduces the research background of the ultra high toughness cementitious composites and describes the theory of the strain hardening behavior. Then, highlights the research development process and engineering application of ultra high toughness cementitious composites.(2) The tensile process of ultra high toughness cementitious composite is divided into three stages through experiments and theoretical analysis. In order to establish the relationship between microscopic parameters and macroscopic properties of the materials, the author first introduces the single PVA fiber pullout test, then according to test results to establish a single PVA fiber pull model, based on which use the micro-mechanical analysis of the bond-slip relationship between single fiber and the matrix. Finally the stress-displacement of single fiber is founded.(3) Based on the single PVA fiber pull out, the ultra high toughness cementitious composite strength model is created with the analysis of the direct tensile test and microscopic parameters. Comparison of the results show that the analytical model and experimental strength are consistent, which proves the analytical results could reflect the tensile strength.(4) In view of relationship between microscopic parameters and macroscopic mechanical behavior, the influence of material parameters such as fiber volume fraction and interface strength on the composites cracking strength, ultimate strength, strain hardening behavior and other macro-mechanical properties is analyzed. (5) The multiple factors change which is made to improve to tensile strength of ultra high toughness cementitious composite,and satisfy the requirements of strain-hardening conditions. The results show that as far as possible without affecting ultra high toughness cementitious composite strain hardening properties, by improving the fracture toughness of the matrix and fiber strength to improve the tensile strength (in particular, first crack strength) is an effective way.