Characteristics Of Explosive Spalling Behavior And Change In Permeability Of Steel-Fiber Reinforced Concrete Subjected To High Temperature

In this thesis, an experimental investigation was conducted to study explosive spalling and permeability of steel-fiber concrete subjected to high temperature.The effect of steel fiber on explosive spalling was investigated firstly. A series of concretes incorporated steel fiber at various dosages were prepared, and further processed to have various moisture contents. Explosive spalling test was conducted on plain concrete and steel-fiber concrete. After explosive spalling test, typical specimens that didn't encounter spalling were sawn into two pieces. Crack observation and interior permeability test were conducted on the sawn surfaces of the specimens. In addition, in order to make a comparative analysis of permeability between interior and near-surface of concrete, near-surface permeability of concrete after exposure to elevated temperature was measured.On the basis of these experimental results, permeability test was carried out on plain concrete and steel-fiber concrete after exposure to various cooling regimes. At the same time, a comparative experimental investigation on permeability properties of plain concrete, steel-fiber concrete, polypropylene-fiber concrete and hybrid fiber concrete was carried out by means of the same experimental method.The results of explosive spalling test indicate that moisture content has a dominant influence on the explosive spalling occurrence of high performance concrete. In addition, the higher the moisture content, the greater the frequency of spalling occurrence and the higher the degree of damage. Incorporating steel fiber to high performance concrete is an efficient way to avoid spalling of concrete exposed to high temperature.The results of the permeability test on specimens after heating and sawing indicate that the permeability increases significantly and exhibits an ascending trend with the increase of moisture content. Steel fiber can reduce the degree of permeability increment of concrete after exposure to high temperature. Interior permeability reflects the damage of concrete after exposure to high temperature more accurately.Cooling regime has a remarkable influence on the permeability of high performance concrete. Under the same target temperature, the permeability of high performance concrete subjected to quenching in water and spraying water for 30 minutes was both higher than that of natural slow cooling. The damage of concrete subjected to quenching in water is the most severe, characterized by a maximal permeability. The experimental results indicate that the addition of steel fiber to high performance concrete can efficiently reduce the degree of permeability increase of concrete after exposure to different cooling regimes from target temperature ranged from 200℃to 600℃.