Novel Embedded Integrated Smart Elements and Coda Wave Analysis for Investigating GGBS Effects on Cement Hydration

Ground granulated blast-furnace slag (GGBS) is a typical supplementary cementitious material that can delay the early hydration of cement. In this study, a novel integrated sensor was employed to continuously monitor the hydration process of cementitious materials and to characterize the influence of GGBS addition on hydration behavior. The monitoring results show that the signal parameters, including amplitude, energy, and frequency domain, varied significantly during hydration. For plain cement paste (0% GGBS), the maximum signal amplitude after 24 h decreased by 28.2% compared with that at 0 h. As the GGBS content increased to 5%, 10%, 20%, 30%, 40%, and 50%, the amplitude reduction ratios increased to 34.1%, 38.1%, 36.8%, 53.1%, 47.4%, and 59.0%, respectively. A similar trend was observed for the signal energy, with corresponding decreases of 34.3%, 41.5%, 39.3%, 44.5%, 53.1%, 47.0%, and 59.5%. These results clearly indicate that the incorporation of GGBS delays the early hydration of cement and suppresses the evolution of ultrasonic response. Short-time Fourier transform analysis further confirmed that the main frequency peak shifted toward a later time with increasing GGBS content, demonstrating the retarding effect of slag on hydration kinetics. This study verifies the feasibility of using integrated sensors for in situ monitoring of the hydration delay process in GGBS-blended cementitious materials.