Influence of air entrainment and aggregate type on freeze–thaw–induced changes in the coefficient of thermal expansion of Portland cement concrete

The coefficient of thermal expansion (CTE) plays a critical role in the thermal stress development and long-term performance of Portland cement concrete (PCC) pavements. While extensive research has focused on factors such as aggregate type, mix composition and moisture content, the influence of freeze–thaw (F/T) deterioration on the CTE of concrete has not been fully clarified. This study examines the evolution of concrete CTE under repeated F/T cycles through a controlled laboratory program involving six mixtures with varying aggregate types and air contents. The results show that freeze–thaw exposure significantly increases the CTE of concrete—by as much as 32% for non–air-entrained specimens—due to progressive microcracking and internal damage. The inclusion of air-entraining agents (AEA) mitigated this effect, limiting the CTE increase to less than 10% in the most durable mixes. The relative dynamic modulus of elasticity (RDME) exhibited a clear inverse correlation with CTE, indicating that thermal expansion behaviour can serve as a sensitive indicator of freeze–thaw damage. A predictive model linking CTE increase to RDME loss was developed and validated. The proposed relationship provides a practical framework for incorporating freeze–thaw effects into mechanistic–empirical pavement design and durability assessment of PCC materials.