Abstract

Freeze–thaw cycle (FTC) deterioration is one of the major durability concerns for concrete structures in cold climates. While many studies focus on fully saturated conditions, real structures often undergo FTCs under unsaturated conditions, where damage mechanisms are not well understood. This study investigates FTC damage in mortar under controlled unsaturated conditions to improve understanding of moisture-driven deterioration. Mortar specimens with water-to-cement (W/C) ratios of 0.50 and 0.75 were cast in thin specimens (100 mm × 100 mm × 10 mm) to promote rapid thermal response and enhance moisture redistribution, allowing for early detection of expansion. Specimens were preconditioned to specific degrees of saturation derived from preliminary simulations, and hermetically sealed to prevent moisture loss. Expansion and temperature were continuously monitored during FTCs using embedded mould gauges. Mercury intrusion porosimetry and image analysis were conducted to evaluate porosity, pore size distribution, and air content. Results indicate that both the degree of saturation and W/C ratio affect FTC damage under unsaturated conditions. In all samples, expansion increased with saturation. At 84% saturation, small but measurable expansion was observed, which increased progressively to 97% saturation. The fully saturated specimens exhibited the highest expansion, reaching approximately 600 and 950 μm for the 0.50 and 0.75 W/C mortars, respectively. Mortars with a 0.75 W/C ratio exhibited earlier and more severe expansion than those with a 0.50 W/C ratio. These findings suggest that FTC deterioration can begin well below full saturation due to ice formation in capillary pores. Therefore, durability assessments should consider unsaturated conditions to reflect in-service performance more accurately.

Keywords

freeze–thaw cycles, unsaturated condition, mortar durability, water-to-cement ratio, spacing factor.

DOI

10.5703/1288284318129

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Experimental Study on Freeze–Thaw Cycles Response in Mortar under Controlled Partially Saturated Conditions

Freeze–thaw cycle (FTC) deterioration is one of the major durability concerns for concrete structures in cold climates. While many studies focus on fully saturated conditions, real structures often undergo FTCs under unsaturated conditions, where damage mechanisms are not well understood. This study investigates FTC damage in mortar under controlled unsaturated conditions to improve understanding of moisture-driven deterioration. Mortar specimens with water-to-cement (W/C) ratios of 0.50 and 0.75 were cast in thin specimens (100 mm × 100 mm × 10 mm) to promote rapid thermal response and enhance moisture redistribution, allowing for early detection of expansion. Specimens were preconditioned to specific degrees of saturation derived from preliminary simulations, and hermetically sealed to prevent moisture loss. Expansion and temperature were continuously monitored during FTCs using embedded mould gauges. Mercury intrusion porosimetry and image analysis were conducted to evaluate porosity, pore size distribution, and air content. Results indicate that both the degree of saturation and W/C ratio affect FTC damage under unsaturated conditions. In all samples, expansion increased with saturation. At 84% saturation, small but measurable expansion was observed, which increased progressively to 97% saturation. The fully saturated specimens exhibited the highest expansion, reaching approximately 600 and 950 μm for the 0.50 and 0.75 W/C mortars, respectively. Mortars with a 0.75 W/C ratio exhibited earlier and more severe expansion than those with a 0.50 W/C ratio. These findings suggest that FTC deterioration can begin well below full saturation due to ice formation in capillary pores. Therefore, durability assessments should consider unsaturated conditions to reflect in-service performance more accurately.