In situ continuously monitoring the early age microstructure evolution of cementitious materials using ultrasonic measurement

The early age microstructure evolution was continuously monitored by using a specially improved ultrasonic monitoring apparatus. The influence of water-to-binder ratios, mineral admixtures, aggregates and temperature were systematically investigated. The experimental results show that concrete can be clearly classified into four stages, while only the three stages can be observed without coarse aggregates. In addition, pre-percolation threshold, percolation threshold and full connectivity of the solid phase were identified. The microstructure formation is promoted with the reduced water-to-binder ratios, increased temperature, silica fume and aggregates addition, while the reverse phenomenon is observed when fly ash and slag are incorporated.