Combined effects of high temperature and high strain rate on normal weight concrete

Abstract

Concrete in structures is possibly exposed to fire and blast due to occasional accidents or terrorist attack during the service life. Yet, there are few experimental studies on the responses of normal concrete structures subjected to high temperature and high strain rate loading simultaneously, although some high strain rate experiments were performed before or after fire exposure. This paper reports an experimental study of the combined effects of high temperature and high strain rate on normal concrete material, which is a preliminary basis for calculating and assessing the performances of RC structures in blast and fire. The dynamic properties of normal concrete at elevated temperature from 20 °C up to 950 °C were systematically studied using a specially manufactured microwave–heating automatic time-controlled Split Hopkinson Pressure Bar (MATSHPB) apparatus. The concrete specimens were first efficiently heated in a specially designed industrial microwave oven, and then rapidly loaded after quickly rolling to the SHPB system. Quasi–static and low strain rate tests at elevated temperatures were also carried out for comparative analysis. In contrast with previous experimental research, the test results showed that the dynamic strength and stress–strain curve of normal concrete at high temperature still experienced remarkable strain rate effects. Moreover, the failure appearances of normal concrete subjected to both high temperature and high strain rate loading were significantly different from those of concrete at ambient temperature. In contrast with quasi-static test data, a new empirical model on dynamic increase factor of strength and secant elastic modulus of concrete at elevated temperature (DIFTS, DIFTE) were established that can be used in a very wide range of application.