Measuring mortar shrinkage and cracking by pulse pre-pump Brillouin optical time domain analysis with a single optical fiber

Abstract

In this study, a new method to measure strain distribution and detect cracking with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA) is proposed. A mortar cylinder was cast in a corrugated polyethylene mold with two end plugs and tested according to ASTM C1698 for autogenous shrinkage. It was instrumented with two sensors made of a single optical fiber: one for combined strain and temperature measurement and the other for temperature compensation. The shrinkage-induced compressive strain was non-uniformly distributed over the sensor length. The average of the distributed strain was in excellent agreement with autogenous shrinkage that can be determined from the ASTM test. The location and magnitude of each peak of the distributed strain can be used to detect a corresponding invisible hidden crack.