Acoustic Emission in the Drying of Hardened Cement Paste and Mortar

Acoustic emission (AE) during the drying of cement and mortar was studied extensively; AE in direct fracture of notched beams was also measured. A new method for observing the hydration of cement by measuring acoustic conductivity was developed and used to aid in the interpretation of the drying experiments. Acoustic emission due to drying increased rapidly with the time of hydration. It reached a maximum value at ∼60 days for hardened cement paste and 240 days for a standard mortar. It is shown to be caused by fractures in structures that develop, at least in part, during the drying process.