Study On Fire-resisting Performance Of HPC

With fast economic development and rapid city growth, it is necessary to build high-rise buildings in cities with high population densities. Fire accidents may take place which results in building destruction and personal casualties. Concrete is one of the main structural engineering materials. It has a broad range of applications due to the technology and economical merits. So, it is important to study quantitatively the performance of concrete in the fire environment. With developing technology of concrete materials, HPC is replacing ordinary concrete. There are many influences on HPC at elevated temperature due to complexity of concrete. This thesis studies the influence of HPC with mineral admixture, chemical admixtures, polypropylene fiber, ? and investigates the change of micro/mecrocosmical structure by using SEM and MIP. The results are summarized as following:1) Concrete mixture with both slag and fly ash can improve the performance at elevated temperature. The residual strength is 1.2~4.0MPa higher than that of concrete with no mineral admixtures at 100°C, 200°C, 400°C, 600°C, 800°C and 900℃;2) By analyzing concrete with effective naphthalene water-reducing agent, polycarboxylate superplasticizer and air-entraining agent at the same water-cement ratio, it is shown that concrete with polycarboxylate superplasticizer has the best performance at elevated temperature and air-entraining agent can prevent cracking of concrete;3) Polypropylene fiber can efficiently prevent cracking and improve the bending strength of concrete if the heating temperature is lower than 400°C. But, it does not affect the bending strength of concrete significantly if the heating temperature is higher than 400°C;4) For the same water-cement ratio, the results show that concrete with waste-glass as aggregate has better performance than concrete with normal sand and gravel as aggregate at elevated temperatures. Concrete with waste glass as aggregate used at elevated temperature is economical and durable due to the loss of water, which prevents the occurrence of alkali-silica reaction;5) By analyzing the result of crack extension, pore structure and SEM images, adding polypropylene fiber into concrete can effectively prevent crack extension and ameliorate pore structure at elevated temperatures. The changes in the micro/macrostructure of concrete can explain the macroscopic performance of concrete at elevated temperature.