Utilization of cenospheres as an internal curing material for autogenous shrinkage mitigation of ultra-light-weight concrete

Autogenous shrinkage of ultra-light-weight concrete (ULWC) can cause severe cracking at early-age reducing the service life of the structure. This paper proposes a method to mitigate autogenous shrinkage of ULWC using pre-saturated cenospheres. ULWCs with densities of 800 kg/m³, 900 kg/m³ and 1000 kg/m³ were prepared using both pre-saturated and pre-dried cenospheres. Low-field nuclear magnetic resonance was applied to characterize the water state evolution during hardening of the ULWC. The results demonstrated that the pre-saturated and pre-dried cenospheres behave in different absorption and desorption behaviors in ULWC which dominate the deformation of ULWC at the first few hours. The pre-dried cenospheres absorb water in the mixing stage and the first few hours. This leads to a rapid increase of shrinkage. On the other hand, a considerable amount of water is released from the pre-saturated cenospheres in the first few hours leading to an expansion phase. In case of ULWC with density of 800 kg/m³, the pre-saturation method reduced autogenous shrinkage by 81.7 %, and improved 7-day compressive strength by 11.9 % compared to the pre-dried method.