Using acoustic emission to quantify damage in restrained fiber-reinforced cement mortars

This paper describes the use of acoustic emission (AE) for monitoring early-age cracking in restrained fiber-reinforced mortars. A steel-testing frame was used to prevent the length reduction associated with drying. AE sensors placed on both unrestrained and restrained specimens detected a high degree of activity that may be attributed to surface microcracking caused by moisture gradients that cause the surface to shrink more rapidly than the core. It was found that as the concrete neared the age of visible cracking, the acoustic waves generated in the restrained specimens had a greater amplitude and duration. For this reason, acoustic energy was utilized for these investigations. An increase in acoustic energy was detected before cracks were observed in the restrained specimens. It is believed that the role of fiber reinforcement is twofold. First, fibers arrest cracks thereby preventing unstable crack propagation, and second, they restrain the crack from opening preventing the cracking from becoming visible until a later age.