Assessing lightweight aggregate efficiency for maximizing internal curing performance

Internal curing (IC), which has been extensively investigated in the last decade, has been shown to enhance hydration, diminish autogenous shrinkage, and mitigate early-age cracking due to selfdesiccation in high-performance concrete. It also increases the internal porosity of concrete, however, which might reduce mechanical properties. Thus, a better understanding of what makes a lightweight aggregate (LWA) effective and efficient for IC is fundamental to maximize the gains and minimize the shortcomings. This study analyzes the performance of a wide set of LWAs for IC, including artificial and natural LWAs. The water uptake, water release, and pore structure of the LWAs were determined, as well as their performance in concrete, which was assessed using the degree of hydration, compressive strength, chloride ion permeability, and autogenous shrinkage. The results showed that natural LWAs possess higher, coarser, and more interconnected porosity than artificial LWAs. This allows natural LWAs to store more water and present higher and faster water release for IC. Natural LWAs produced concrete with a similar or better performance than that of artificial LWAs in spite of requiring lower dosages. When selecting an LWA for IC, it is important to consider not only its effectiveness in reducing autogenous shrinkage, but also its efficiency and other performance criteria, such as transport properties and compressive strength.