Laboratory Investigation of Internal Curing Potential in Stiff Mortar Mixtures Using Expanded Clay Aggregates

Abstract

The low water-to-cement (w/c) ratios of stiff paving mixtures such as roller-compacted concrete (RCC) pavements often pose significant challenges in moisture retention and proper curing which can lead to concrete shrinkage cracking. Traditional curing methods (e.g., external water curing) often prove insufficient as a result of RCC’s denser matrix and low permeability. As RCC pavement is a stiff and dry mixture, inadequate curing and adverse weather conditions can further lead to early structural and functional issues. The use of internal curing (IC) technology can be a solution to mitigate early cracking, particularly in stiff mixtures such as RCCs. This study investigates the effects of lightweight expanded clay aggregates (ECA) as an internal curing agent in mortar mixtures for RCC paving applications. Natural fine aggregates were partially replaced by pre-soaked ECAs at varying proportions that is, 5%, 10%, 15%, and 20%; their influence on stiff mortar’s water absorption and desorption capacities, degree of hydration (DOH), mechanical strength, and microstructural characteristics were investigated. The water absorption, desorption (release) potential, and mercury intrusion porosimetry (MIP) test results confirmed the suitability of ECA aggregate as an IC agent. The DOH improved by 24% to 38% and 2.8% to 13% for water and sealed curing, respectively, at varying ages. Subsequently, the compressive strength and flexural strength were found to have improved for both water curing and sealed curing. Microstructural analysis revealed a decrease in porosity while an increase in the calcium-silicate-hydrates (CSH) gels, particularly near the interfacial transition zone (ITZ) was observed. This study demonstrates that ECA can be an effective internal curing agent to mitigate water retention problems in RCC pavements, contributing to its enhanced early-age strength characteristics.