An acoustic emission (AE) technique was applied for early detection, characterisation and time progress description of cracking phenomenon caused by the corrosion of Al encapsulated in cement matrix. The study was conducted on an ordinary Portland cement (OPC) system encapsulating high purity Al bar. Acoustic signals were generated and released during immersing of the sample in deionised water. A computer controlled PCI-2 based AE system processed the signals detected by piezoelectric transducers. A subsequent comparative study of the AE data collected with those obtained from a reference OPC sample has been applied. Recorded AE activity confirmed that the process of initiation and development of At corrosion causes significant mechanical stresses within the cement matrix. Our analysis demonstrated possibility to differentiate AE signals based on their characteristics, and potentially correlate detected AE with the fracture processes in the cement system encapsulating Al. (c) 2006 Elsevier B.V. All rights reserved.