The Effect Of High Temperature On Micro Structure And The Vapor Pressure Of High Performance Concrete

Comparing with ordinary concrete, high performance concrete has preferable performance. Nowadays, it has been used in many projects which make people’s life more convenient, such as high-rise buildings, large span bridges and tunnels. However, comparing with ordinary concrete high performance concrete is easy to show different deterioration characteristics such as it may explode in the case of heating because high performance concrete has lower permeability and compact structure. The characteristics may affect the fire resistance of construction and cause great threat to the masses of people’s life and property safety. Therefore, analyzing the relationship between relate performance of high performance concrete and its temperature and researching the reasons of exploding after heating the high performance concrete have important meaning to improve the performance of concrete material and the fire resistance ability of structure. This report chooses appropriate design strength grade raw materials preparation of C60 high performance concrete according to the actual mix proportion of concrete used by a project, to study the mechanical properties of changing with the heating temperature and using the mercury injection hole measurement method and X-ray computed tomography(CT) scanning technology for its microstructure analysis along with the change of temperature. In the end, researcher analyzes the reasons of exploding of high performance concrete according to the experimental results. The main content includes:1. Summarizing the research progress of high performance concrete and the research condition of High temperature burst mechanism through looking up Chinese and abroad related literature.2. The influence of temperature on the basic mechanical property of high performance concrete. The main task is to test the compressive strength of concrete specimens, splitting tensile strength and compressive strength after different temperature burning, then analyze how the basic mechanical properties change along with the change of temperature. The results show that the mechanical properties of high performance concrete have obvious degradation tendency along with the rise of temperature. The concrete compressive strength degradation phenomenon performs more slowly when concrete heat under 500 ℃. However, concrete mechanics performance began to rapidly deteriorating, the trend of the compressive strength of concrete decreases obviously when concrete heat greater than 500 ℃.3. The rule of pore structure of concrete along with the temperature change. The main task is to test the pore structure of concrete before and after high temperature test using the method of mercury injection test hole, analyze the change rule of pore structure of high performance concrete along with before and after high temperature combing with geometry method of fractal dimension. At the same time, in order to observe the influence of temperature on pore structure of high performance concrete, this paper uses X-ray computed tomography(CT) scanning technology to observe concrete specimens. The results show that concrete porosity, average pore size and total pore volume shows great change with the increase of temperature, but the pore surface area had no obvious change; pore structure of concrete shows two different fractal characteristics based on the size of around 50 nm hole; mutations cause C60 high performance concrete pore distribution of threshold temperature at 350 ℃. In the end, discover the change trend of pore structure of concrete through disposing the CT scanning picture of concrete and through the concrete pore structure fractal dimension analysis by the similar change trend.4. The change rule of concrete pore water pressure along with the accepting temperature and heating position. This test uses homemade test apparatus to test and analyze the porosity of the concrete heats water vapor pressure. The main results include: the steam pressure from inside concrete shows the gradient decrease tendency with the concrete surface by fire. The time of producing steam pressure is different in each position of concrete, the side heating by firing begins to generate steam pressure firstly, then the maximum of steam pressure produced by concrete shows the rule of the change of gradient with the increase of heating time.5. The theoretical analysis of high performance concrete producing burst. It analyzes the related rule which includes the change rule of microscopic characteristics of pore structure of concrete with the change of temperature and the change rule of the pore water pressure of concrete with the change of temperature. The result indicates that the vapor pressure of concrete producing by the fire has significant influence on the burst of concrete.The main purpose is to research the influence of temperature on the vapor pressure of high performance concrete and micro structure. These researches provide some references for the research of the blowout phenomenon of high performance concrete under high temperature.