Investigations on deteriorations of concrete from surfaces to interiors under temperature gradient effects

In this investigation, in order to understand deterioration processes of concrete from surfaces to interiors under temperature gradient effects, 150mm cubic concrete specimens were heated without temperature-rising stages at 800° for 20min, 40min, 60min, 90min and 120min and then cooled with running water. For the purpose of evaluating deterioration characteristics of the heated concrete, compressive strengths and cracking conditions of heated concrete specimens, microstructural morphologies of concrete constituents, as well as dehydration degrees of concrete matrix from surfaces to interiors were determined. Results showed that during heating process, deterioration of concrete matrix from surfaces to interiors could be divided into a heat-influenced area, a semi heat-influence area and a heat-uninfluenced area. In heat-influenced area, dehydration degrees of hydration products were extremely severe, and the corresponding microstructural integrity almost completely lost. With increasing heating durations, heat-influenced areas gradually expanded towards concrete interiors, making the semi heat-influenced areas gradually become heat-influenced areas, and heat-uninfluenced areas become semi heat-influenced areas. Consequently, with increasing heating durations, compressive strengths of the heated concrete gradually decreased.