Size Effect of Compressive Performance of Concrete under Elevated Temperatures: Tests and Meso-Scale Analysis

This study investigates the size effect of concrete under ambient and elevated temperatures through tests and numerical simulations. Compressive performance of prismatic and cylindrical concrete specimens with varying dimensions were tested at temperatures ranging from ambient temperature to 600 degrees C. Meso-scale finite element analysis (FEA), assuming that the mechanical properties of matrix and interfacial transition zones (ITZ) followed Weibull distribution, was employed to simulate the tested specimens and to conduct parametric analysis on specimens with larger or smaller sizes and under temperatures up to 800 degrees C. Both experimental and numerical results showed that the cracks on the specimen surface became finer and denser as an increase of specimen sizes under elevated temperatures. A noticeable decrease in concrete compressive strength with increasing specimen dimensions was observed below 600 degrees C, but peak strain and elastic modulus did not exhibit significant size effect. Size effect on strength diminished at temperatures exceeding 800 degrees C. Classic Size Effect Laws (SEL), such as Weibull's and Bazant's SEL, were applicable to characterize the size effect on strength of specimens within common lab test dimensions under elevated temperatures. Based on the results from experiments, FEA and Bazant's SEL, a stress-strain model under elevated temperatures considering size effect was proposed. The predicted results from this model showed good agreement with test results.