Enhanced Internal Curing for Ultra-High-Performance Concrete Using Reactive Curing Solution

Autogenous shrinkage in ultra-high performance concrete (UHPC) caused by its low water-to-cement ratios and the dense particle packing within the mixture poses a critical challenge for the material. Providing additional moisture through internal curing shows a great potential in addressing this challenge. However, existing studies found that more internal curing water is needed for UHPC to avoid self-desiccation than that needed for high performance concrete. To address this issue, this study proposes an enhanced internal curing technology which can drastically reduce the autogenous shrinkage without using more internal curing water and compromising mechanical properties. This is achieved by using perforated cenospheres (PCs) as the internal curing agent and replacing internal curing water with carbamide solutions. In addition to replenishing water, the carbamide solutions can react with portlandite after being released into the cement paste. CaCO3 can be produced by this reaction, which has a larger volume and much higher elastic modulus than portlandite. In this way, chemical shrinkage of the cement paste is reduced and the stiffness of the paste is enhanced, both contributing to reductions in the autogenous shrinkage. As a result, the reduction in autogenous shrinkage of the UHPC is enhanced from less than 50% using water to over 90% using 3% carbamide solution to replace water in PCs.