13th International Conference on Fracture June16–21, 2013, Beijing, China -1UHPC Precast Product under Severe Freeze-Thaw Conditions Ming-Gin Lee1, Kun-Long Lee1,MangTia2 1 Department of Construction Engineering, Chaoyang University of Technology, Taichung 41349, Taiwan, ROC 2 Department of Civil and Coastal Engineering, University of Florida, Gainesville, FL32611, USA * Corresponding author: mglee@cyut.edu.tw Abstract In this study, ultra high performance concrete (UHPC) was used to investigate the effect of UHPC and its precast product by the severe freeze-thaw testing. The UHPC to be used as a precast product material contains a large amount of cement and cementitious materials, a large amount of superplasticizer, and a very small amount of water. The UHPC mixes with eight different volumes of steel fibres were tested and evaluated to find the optimum quality of precast production. The results show that the mechanical properties of UHPC possess high strength, ductility, and bond stress. The results also indicate that most of UHPC specimens presented a steady decrease in compressive and flexural strength after freeze-thaw testing. The 2.5, 3.0 and 3.5% steel fibres by volume were chosen and used in UHPC precast products, after UHPC specimens were tested and finished on their performance evaluations. The results show that the loading capacity of UHPC precast products increased significantly after 600 free-thaw cycles. As a result of freeze-thaw resistance, the appropriate mixes of UHPC applied in the precast products have been obtained; it would provide a reference manufacturing for the UHPC products. Keywords: Ultra high performance concrete, UHPC, Freeze-thaw, Product 1. Introduction Many severe circumstances are the result of extreme climate conditions such as low temperature, freeze–thaw action, fire attack, and exposure to deicing salts. Because of this, the environmental durability of both the construction materials and methods used in severe conditions and applications are of utmost importance. For example, a small fire can reach 250°C, while a common blaze can easily produce temperatures of around 800°C. In major conflagrations the temperature can even reach 1100°C. At this level, the heat affects most materials, provoking the spontaneous combustion of some of them and affecting the resistance of others. However, very little research has been performed in evaluating the environmental durability of construction materials for UHPCmembers. Very little work has been done on the effects of freeze–thaw cycling on UHPCmaterials and UHPC precast products too. The process of degradation of concrete due to freeze-thaw cycling is known as occurring due to the expansion of pore water in the cement paste as it freezes to ice. The expansion of water into ice is approximately 9%. This results in the ice pushing water to take up the extra volume and in turn creates hydraulic pressure inside the concrete matrix when it has no more room to expand. Micro-crack or local crack is caused if the expansive forces exceed the tensile strength in the concrete during the freeze-thaw cycling. The effect of freeze-thaw cycling has a significant effect on cement concrete and it causes cracking and scaling and ultimately failure [1].
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