Humidity evolution in cement-based materials is monitored using fluorescent molecular humidity-sensitive responses

Abstract

In situ detection technology for cement-based materials typically produces unclear physical meanings, which limits research on durability issues such as heat-moisture transfer, dry-wet cycles and microcrack propagation. Taking the external thermal insulation system of building exterior walls as an example, this paper explores in-situ fluorescence sensing techniques for moisture evolution of cementitious materials using the quenching effect caused by the aggregation of fluorescent molecules. This study includes the monitoring of fluorescence intensity under humidity evolution and a stability study of fluorescence intensity under different temperatures and humidity cycles. Results showed that the gradual transition of the polymeric state of fluorescent molecules led to the first increase and then decrease of fluorescence intensity with increasing humidity (0 % RH-95 % RH). The fluorescence intensity peaked at 65 % RH, decreases at high humidity due to aggregated caused quenching effects, and maintained good stability after 8 humidity cycles. With regard to ambient temperature, the fluorescence intensity decreased with increasing temperature (5 °C – 40 °C), and the fluorescence intensity peaked at 5 °C. The temperature sensitivity of the fluorescence is weakened by the methyl effect of the rhodamine 6G fluorescent molecules and the thermostatic properties of the insulation boards. Fluorescence sensing technology for humidity evolution of cement-based materials has moisture sensitivity and fluorescence stability, and thus has a wide range of applications in the sensing of humidity evolution of civil engineering materials.