Comparion Between Concretes Prepared With Three Types Of Cements Subjected To High Temperature

In this thesis, a comparative experimental investigation was conducted to study explosive spalling and residual mechanical properties of Portland cement concrete, sulphoaluminate cement concrete and high aluminate cement concrete at the same strength level at room temperature.The effect of cement and moisture content on spalling was investigated firstly. Concretes with seven moisture contents were prepared. After explosive spalling test, typical specimens that didn't encounter spalling were sawn into two pieces. Crack observation was carried out on the sawn surfaces of the specimens.After explosive spalling test, Residual mechanical properties and residual toughness of the three types of concrete were tested and compared with each.In the spalling test, Portland cement concrete and sulphoaluminate cement concrete suffered spalling, and sulphoaluminate cement concrete had a greater damage. No spalling occurred in high aluminate cement concrete.The results of the spalling test confirms the vapor pressure build-up mechanism. The critical moisture content of spalling for Portland cement concrete is between 63% and 75%, and spalling occurs at between 340℃and 450℃. While the critical moisture content of spalling for sulphoaluminate cement concrete is between 75% and 88%, and spalling occurs at between 330℃and 370℃.Residual mechanical properties of the three types of concrete decreases with the increase of temperature. Concretes with low w/b ratios lost more strength than concretes with high w/b ratios, and residual splitting strength performed more sensitively to high temperature than residual compressive strength.After exposure to 200℃, Compressive strength of both Portland cement concrete and sulphoaluminate cement concrete increased, but the degree of compressive increase of sulphoaluminate cement concrete was smaller. When temperature exceeded 400℃, sulphoaluminate cement concrete and Portland cement concrete had a similar residual compressive strength, and both of them were nearly broken at 1000℃. Compressive strength of aluminate cement concrete exposed to temperature below 400℃had a decrease, and the degree of compressive decrease of aluminate cement concrete was bigger than those of both Portland cement concrete and sulphoaluminate cement concrete. Residual compressive strength of aluminate cement concrete had little variation at temperature between 400℃and 800℃, when the temperature was up to 1000℃, Residual compressive strength had a sharp decrease.Residual toughness of the three types of concretes increased firstly and then had a sharp decrease as the temperature increases. In the group of cement concretes with high strength at room temperature, high aluminate cement concrete had the highest residual toughness. In the other group with low strength at room temperature, the three types of concretes exposed to temperature below 600℃had a similar residual toughness, but residual toughness of aluminate cement concrete was obviously higher than Portland cement concrete and sulphoaluminate cement concrete at temperature up to 600℃.