Paste Curing Effectiveness with Contactless Sensing and 2D Wavefield Analysis

Abstract

The serviceability and performance life of concrete pavement are improved by temperature and moisture management during the initial cement reactions, which has been done successfully by various curing methods and compounds. However, the effectiveness of all curing compounds and methods has been difficult to measure spatially and rapidly in the field. In this paper, a new contactless ultrasonic testing system (UTS) and 2D wavefield analysis are introduced to evaluate the effectiveness of curing methods and compounds through monitoring of the near-surface damage of early-age hydrating paste. Cement paste specimens were cast and exposed to elevated drying conditions (23 C air temperature, 46% humidity, and 6.6 m/s wind speed) while subjected to no curing, plastic cover curing, and a wax- based compound. The UTS employed a fully contactless 50kHz ultrasonic transmitter and an array MEMS receivers. The paste specimens were monitored at ages 1, 4, 7 days after casting for the evolution of near-surface cracking. The non-contact UTS monitored the energy of leaky Rayleigh waves (LR-waves) signal over time and analyzed the frequency-wave number (f-k) domain to characterize the quantity of near-surface damage in the cement paste specimens. An ultrasonic surface damage index (USDI) was defined from f-k wavefield domain based on the ratio of the non- propagating and forwarding LR-waves. The contactless sensing and 2D wavefield analysis easily distinguished the specimen damage differences between the no curing surface, the plastic sheet cover cure, and the wax-based curing. Surfaces with low surface damage had little to zero non-propagating wave energy, which was seen in the wax-based curing specimens and the unexposed bottom surfaces of all cast specimens.