An investigation on the use of zeolite aggregates for internal curing of concrete

Shrinkage of concrete may lead to cracking and ultimately to a reduction of the service life of concrete structures. Among known methods for shrinkage mitigation, internal curing with porous aggregates has been successfully utilized in the last couple of decades for mitigating autogenous, drying and plastic shrinkage. In this paper, performance of LECA (Lightweight Expanded Clay Aggregate) and natural zeolite aggregates from Iran to act as internal curing agents was studied. While LECA is well recognized as an excellent internal curing agent in the literature, according to a few studies also some kind of zeolite aggregates may be used as internal curing agents. However, no in depth investigations on the microstructure of zeolite aggregates and on their desorption properties are available. first part of this paper, the microstructure of LECA and natural zeolite aggregates (clinoptilolite) from Iran are investigated and compared, with special focus on their pore structure and on their water absorption and release behavior. In the second part, the efficiency of internal curing in mortars incorporating these porous aggregates is examined. The results show that opposite to LECA, the zeolite aggregates examined in this research are not efficient as internal curing agents. While LECA showed high absorption and was able to release the water at high relative humidity, zeolite aggregates absorbed most of the water in nm-sized pores and retained the water down to low relative humidity levels. The performance of porous aggregates to act as internal curing agents is directly related to their internal microstructure and resulting desorption properties, with zeolite aggregates performing poorly for mitigating early-age shrinkage.