Influence of fly ash and curing on cracking behavior of concrete by acoustic emission technique

• Acoustic emission study during compression testing of plain and fly ash concrete.
• Unstable cracking is delayed in fly ash concrete as compared to plain concrete.
• Effect of curing on unstable cracking load is examined.
• Cracking mode in concrete is affected by fly ash replacement.

This study aims to investigate the crack growth behavior of plain and fly ash concretes with different curing periods during uniaxial compression testing using acoustic emission (AE) technique. Compressive strength of plain and fly ash concrete increase with curing periods and it becomes almost same order for 56 days curing. AE results have shown three distinct stages of AE activity in both concretes. The AE generated from the three stages has been attributed to crack closure/microcracking, steady crack propagation and unstable crack propagation. Fly ash concrete with proper curing produces evident filling effect for the pores and the occurrence of pozzolonic reaction leads to reduction of microcracking and corresponding decrease in amplitude of AE activity in the initial loading of fly ash concrete. The results showed that fly ash concrete specimen can withstand higher stress and strain without unstable crack propagation. An attempt has been made to compare types of cracking in both plain and fly ash concrete using AE parameters and it has been correlated with SEM images and final cracking pattern.