Investigation on the potential utilization of zeolite as an internal curing agent for autogenous shrinkage mitigation and the effect of modification

This paper presents an experimental investigation on the potential utilization of one natural zeolite as an internal curing agent for mitigation of self-desiccation and the subsequent autogenous shrinkage of cement paste with low w/b ratio (0.25). Incorporation of 20% zeolite by mass leads to higher internal relative humidity (90.4%) during the first 7 d compared to that of control sample (78.1%). It is indicating that the zeolite under investigated shows partially elimination effect on the self-desiccation and the autogenous shrinkage as well based on the time-zero defined by the onset of internal relative humidity drop. To obtain improved internal curing property, attempts have been done to modify the pore structure of zeolite by acid treatment and/or thermal treatment. However, both nitric acid treatment and thermal treatment shows negative effect on the improvement of internal curing property of zeolite. Because nitric acid treatment tends to increase the BET surface area of zeolite by increasing the volume of 2–7 nm pores, and the thermal treatment tends to reduce the porosity rather than to enlarge the pore size of zeolite.