Mechanism of Crack Development and Strength Deterioration in Controlled Low-Strength Material in Dry Environment

The continuous expansion at the urban scale has produced a lot of construction waste, which has created increasingly serious problems in the environmental, social, and economic realms. Reuse of this waste can address these problems and is critical for sustainable development. In recent years, construction waste has been extensively recycled and transformed into highly sustainable construction materials called controlled low-strength materials (CLSMs) in backfilling projects, pile foundation treatment, roadbed cushion layers, and other applications. However, CLSMs often experience shrinkage and cracking due to water loss influenced by climatic temperature factors, which can pose safety and stability risks in various infrastructures. The purpose of this paper was to study the mechanism of crack formation and strength degradation in a CLSM in a dry environment and to analyze the deterioration process of the CLSM at the macro- and micro-scales by using image analysis techniques and scanning electron microscopy (SEM). The test results show that with the drying time, the CLSM samples had different degrees of cracks and unconfined compressive strength (UCS) decreases, and increasing the content of ordinary Portland cement (OPC) reduced the number of cracks. The addition of bentonite with the same OPC content also slowed down the crack development and reduced the loss of UCS. The development of macroscopic cracks and UCS is caused by the microscopic scale, and the weak areas are formed due to water loss in dry environments and the decomposition of gel products, and the integrity of the microstructure is weakened, which is manifested as strength deterioration. This research provides a novel methodology for the reuse of construction waste, thereby offering a novel trajectory for the sustainable progression of construction projects.