An Investigation into the effect of plastic fibre on plastic shrinkage cracking of concrete

• Main Authors: Ke-Ling Shih, 施克陵
• Other Authors: 詹穎雯
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/tnq8w5

碩士 === 國立臺灣大學 === 土木工程學研究所 === 106 === Plastic shrinkage occurs within several hours after casting and this type of shrinkage causes early age cracking which is known as plastic shrinkage cracking. Concrete with a large surface area compared to its volume are usually tend to form plastic shrinkage cracking. Aggressive substance may enter the cracks, which accelerate the deterioration of concrete and it also induces the exposure of reinforcement causing it to corrode faster. These phenomena will have an impact on the aesthetic value, durability, serviceability and mechanical properties of the concrete structures. There are many factors influencing plastic shrinkage cracking such as mix proportion of concrete, bleeding, initial setting time, environment conditions and restraint. These factors influence each other and change continuously with time, so they complicate the mechanism of plastic shrinkage cracking. To prevent plastic shrinkage cracking, curing the concrete surface directly after casting is a method that usually adopted. It can keep the surface of concrete wet and avoid capillary pressure to build up causing plastic shrinkage cracking. Adding plastic fibers into concrete is another preventive method. The interfacial shear bond stress between fibers and concrete paste is used to increase the tensile strength of concrete under plastic state and reduce the formation of plastic shrinkage cracking. As the awareness of environmental protection rises, plastic fibers made of recycled materials are applied to concrete, which will gradually proceed in the future. This study will discuss the relationship between plastic fibers and plastic shrinkage cracking area. In this study, the bleeding test, the measurement of evaporation, the setting time test and the plastic shrinkage cracking test were carried out to investigate the effects on the plastic shrinkage cracking of concrete with different water-cement ratios, environmental conditions and restraints. The appropriate conditions were selected to carry out the plastic shrinkage cracking test of concrete with low volume of fibers. The crack prediction value was obtained by using all the above test results, and the value as well as the final crack area were put into the crack prediction model to compare the severity of plastic shrinkage cracking. Finally, the final crack area and the crack prediction values of fiber concrete mixed with the plastic fibers used in this study are compared to the values of general concrete. The fiber risk reduction values of plastic fibers used in this study with different volume substitution were obtained and applied to the equation of crack prediction value.