New insights into determining the "time zero" of autogenous shrinkage in low water/binder cement-based composites (LW/B-CC) system based on relaxation theory

This study proposes a novel insight to accurately determine the time zero of autogenous shrinkage in low water/binder cement-based composites (LW/B-CC) based on relaxation theory. Firstly, low-field nuclear magnetic resonance (NMR) technology is used to study the process of water consumption inside the LW/B-CC and clarify the evolution of capillary tension to determine the time zero of autogenous shrinkage. Then, the Laplace equation is used to establish the relationship between water consumption, capillary tension, and autogenous shrinkage in LW/B-CC. The results show that the time corresponding to the development of capillary tension and water consumption in pores is considered as "time zero" of autogenous shrinkage. Furthermore, the capillary tension generated by internal water consumption, about 100 KPa similar to 200 KPa, can cause enormous autogenous shrinkage, which easily leads to cracking. In addition, expansion products produced by calcium sulfoaluminate cement (CSA) hydration facilitate the formation of the matrix skeleton and reduce autogenous shrinkage in LW/B-CC. In general, low-field NMR technology is an effective tool to determine the time zero of autogenous shrinkage.