Noncontact stress measurement technique for concrete structure using photoluminescence piezospectroscopy

Photoluminescence piezospectroscopy (PLPS) is a laser-based noncontact and nondestructive stress measurement technique but has not been studied extensively in the field of civil structural health monitoring. Using the PLPS technique, the stress level can be measured by emitting a laser source onto a target's surface. In this study, PLPS was attempted for noncontact stress measurement of concrete. Alumina is one of the chemical components of Portland cement, and is a highly sensitive material for PLPS. Therefore, alumina in concrete can be used as a passive stress sensor by PLPS. To investigate the spectral detectability at different alumina rates, cement mortar specimens were prepared with increasing concentrations of additional alumina. It was determined that spectral detectability increases with increasing alumina concentration. Then, uniaxial compression tests were conducted to investigate the relationship between stress level and spectral shifts. It was ascertained that compressive stress and spectral shifts have a negative linear relationship. Then, the effective piezospectroscopic coefficients were calculated to be - 0.1574 cm(-1)/MPa and - 0.1468 cm(-1)/MPa for the R1 and R2 bands, respectively. The experimental results reveal that application of PLPS to concrete can provide essential information for structural health monitoring and allow for preventive measures to be taken before collapse of cement structures.