Effect of moisture conditioning of expanded clay aggregates on fresh and hardened properties of structural lightweight self-compacting concrete

Abstract

This study addresses the influence of the initial moisture condition of lightweight expanded clay aggregates (LECA), an important parameter that remains insufficiently quantified, particularly regarding how controlled pre-saturation duration influences the interfacial transition zone (ITZ) and, consequently, the fresh and hardened properties of structural lightweight self-compacting concrete (LWSCC). LECA moisture conditions, from dry to pre-saturated states, were investigated for their effects on fresh properties, mechanical performance, and capillary water absorption. Results reveal a pronounced non-linear response to aggregate moisture. Dry LECA increased compressive strength and stiffness due to local water absorption and a reduced effective water-to-cement ratio, but impaired workability and increased blockage risk. High moisture contents led to excess free water, promoting segregation and a fragile, porous interfacial transition zone. The 5-min pre-saturation condition (PS-5min) provided the optimal balance, improving slump flow by over 30%, halving T500 time, reducing capillary absorption, and maintaining compressive strength within 8% of dry aggregates. SEM observations indicate that these macroscopic behaviours are closely related to the evolution of the ITZ, which becomes denser and more homogeneous under controlled pre-saturation conditions. This highlights the critical role of controlled LECA moisture in achieving balanced fresh and hardened properties.