Effect of calcined zeolite on the shrinkage and mechanical properties of lightweight engineering cementitious composites

Lightweight engineering cementitious composites (LECCs) show great promise for weight-sensitive structures such as bridges, high-rise buildings, and floating platforms. However, the large quantities of cement used in LECCs cause significant shrinkage, which leads to debonding of LECCs from the original structural interface during structural strengthening and repair, severely compromising its strengthening efficiency. To address this issue, we investigated the use of zeolite as an internal storage source to compensate for water loss during the hydration of LECCs, focusing on the relationship between the mechanical and dry-shrinkage properties of LECCs after the introduction of zeolite. XRD and SEM were used to reveal the microscopic mechanisms of zeolite action in the LECC matrix. The results showed that the compressive and tensile strengths of LECCs were improved by the internal care of the zeolite, and the optimum strength was achieved with 5% zeolite addition. In addition, zeolite doping significantly improved the drying shrinkage of LECCs, which was reduced by 31.2% at a 2.5% replacement compared with that of the control group. Microscopic analysis showed that the reduction in shrinkage and increase in strength of the LECC matrix were mainly attributed to the role of the volcanically active zeolite in the later stages of cement hydration, which provided sufficient water to promote further hydration of the hydration products, resulting in a slightly swollen dense microstructure such as that of hydrated calcium silicate aluminate.