Effect of elevated temperatures on compressive strength of concrete

• Published in: Construction & building materials 2019-12, Vol.229, p.116846, Article 116846
• Main Authors: Shen, Jiarong, Xu, Qianjun
• Format: Article
• Language: English
• Subjects: Compressive strength; Drying; Elevated temperatures; Mathematical model; Moisture content; Porosity
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2019.116846

•Compressive strength tests were conducted to examine the mechanical properties of concretes after heating at different elevated temperatures.•The pore structures of concrete were characterized by mercury intrusion porosimetry (MIP) and N2 adsorption.•During drying, the strength first decreased and then increased with a decrease in the moisture content. The moisture content at the minimum strength decreased with an increase in temperature.•Based on the equation proposed by Ryshkewith, a mathematical model was proposed, derived from Griffith’s fracture theory. Our proposed experimentally based model agrees 97% for concrete exposed to elevated temperatures. Concrete structures can sometimes be exposed to elevated temperatures for different durations. This study aims to quantitatively determine the effect of temperature on the compressive strength of concrete. During drying, the moisture content of concrete varies from full saturation to completely dry. The porosity of concrete increases with temperature. The evolution of the porosity at elevated temperatures was characterized by mercury intrusion porosimetry (MIP) and N2 adsorption. The changes in the moisture content and porosity led to variations in the concrete strength. In this study, the compressive strength of concrete during drying at elevated temperatures (40 °C, 105 °C, 150 °C, 200 °C, and 250 °C) was tested. The results showed that the compressive strength first decreased and then increased with a decrease in the moisture content. The moisture content at the minimum strength decreased with an increase in temperature. Moreover, the compressive strength of concrete with the same moisture content decreased with an increase in the heating temperature. Then, the effects of microcracks and capillary pressure on the evolution of the compressive strength during drying were analyzed. Finally, based on the equation proposed by Ryshkewith, a mathematical model was proposed, derived from Griffith’s fracture theory. The new model had better agreement with experimental results, and the correlation coefficient was 0.97, which demonstrated that the proposed model provided better predictions for concrete exposed to elevated temperatures.