Study On The Damage Mechanism And Mechanical Properties Of Fiber Reinforced Concrete With Slag Powder At Elevated Temperature

With a large number of tests of concrete at and after different target temperature, and the comparative analysis of SEM photographs of the microstructure of concrete after different temperature, the study was conducted in this paper about the effect and mechanism of temperature, slag powder, polypropylene fibers, steel fibers and concrete strength grade on the damage, burst and mechanical properties of concrete at elevated temperature, including:(1) Literature review was done on the state of the art research about the damage, burst and mechanical properties of concrete at elevated temperature, and approaches of improving the mechanical properties of concrete at elevated temperature were summarized.(2) By comparing and analyzing on the SEM photographs of concrete after different temperature, the research about the process and characteristics of the thermal decomposition of cement was conducted; the process and mechanism of tissue damage of concrete were shown intuitively. The result showed that the shrinkage of hydration products of the cement caused by dehydration was the key cause of concrete damage, and the tissue damage, the decay of mechanical properties and the burst of concrete were mainly caused by the activity of water in the concrete.(3) The formation, development and characteristics of the saturated steam within the tissue of concrete during being heated, was analyzed; with respect to the material properties of concrete and the relationship of saturated vapor pressure and temperature, this study explained the randomicity of concrete burst occurrence at high.temperature.(4) The effect and mechanism of temperature, slag powder content, steel fibers content, polypropylene fibers content and concrete strength grade on the weight loss rate and mechanical properties of concrete at elevated temperature were analyzed according to experiment results The result also showed that the decay of the mechanical properties and tissue of concrete worsened up gradually with the increasing of temperature, and when the temperature rise to more than 400℃, the decay was accelerated. Slag powder can improve the tissue properties and interface properties of concrete. Steel fibers can effectively improve the performance of concrete at elevated temperature; Polypropylene fibers mainly played a role of inhibiting the occurrence of the burst of concrete at high temperature. The characteristics and quantity of cement paste can mainly impact the effect of strength grade on the properties of concrete at and after different temperature.(5) Using the statistical analysis of the test results, the difference of the basic mechanical properties of concrete at and after high temperature was studied, and the result showed that the thermal stress wasn't the main cause of the damage and mechanical properties decay of concrete.