Assessing lightweight aggregate efficiency for maximizing internal curing performance

Abstract

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