A study of the effect of displacement rate and moisture content on the mechanical properties of concrete: Use of acoustic emission

It is important to have an understanding of the behaviour of concrete under different displacement rates and moisture contents. This is because underground concrete structures are subjected to drying and wetting process and various loading condition including in situ stresses, induced stresses and earthquakes. In this research work, a program of systematic laboratory testing has been undertaken to determine the effect of displacement rates and moisture contents on concrete strength. A total number of 20 concrete specimens were tested. Axial strain, lateral strain and acoustic emission (AE) counts were recorded continuously until the specimens had failed. Findings from those results were used to conduct a detailed analysis of the crack closure, crack initiation, secondary cracking, crack damage and peak failure of dry, partially wet and fully wet concrete specimens at displacement rates corresponding to different loading rates (0.05, 0.10, 0.15, 0.20 and 0.25 mm/min). The results showed that when concrete were fully wet, the strength was dependent on displacement rate and the strength was significantly reduced in comparison with the strength of dry specimens at the same displacement rate (e.g. 25% reduction when the loading rate was 0.15 mm/min). The relationships between Young’s modulus and Poisson’s ratio with compressive strength were also studied and an increase of both with an increase in strength was observed.