Freeze–thaw behavior of air entrained cement paste saturated with 10 wt.% NaCl solution

• The air entrained cement pastes were pre-saturated with 10% NaCl solution.
• The strains of pastes were measured under freeze–thaw loading.
• A poroelastic model including the effect of water activity was established.
• Density changes and the thermal contraction dominate strains during freezing.

By experimental measurement and poroelastic approach, the present study attempts to assess the freeze–thaw (F–T) behavior of air entrained cement pastes saturated with 10 wt.% NaCl solution. The strains of cylindrical cement pastes were measured under undrained cyclic F–T loading. Six distinct stags of the strains for one whole F–T cycle were identified. Meanwhile the specific strains of thermal contraction, hydraulic expansion, ice nucleation expansion and residual expansion were analyzed. A poroelastic model involving thermodynamic equilibrium between ice crystal and pore solution, pore size distribution and constitutive poromechanical equations was developed to quantify the strain sources. The obtained results indicated: 1, air-void entrainment tends to decrease the thermal contraction but to increase the hydraulic expansion, ice nucleation expansion and residual expansion; 2, the established poroelastic approach can capture the experimental data; 3, changes of salt concentration, water activity and fusion energy play minor roles on the strains of the porous material, while density changes as water crystallizes and the thermal contractions remain the dominative factors.

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