Traditional Chinese sticky rice–lime mortar, a key material for restoring historic masonry buildings, suffers significant degradation under combined salt erosion and freeze–thaw cycling. This study experimentally investigated the coupled effects of chloride, sulfate, and freeze–thaw action on sticky rice–lime mortar under simulated service conditions. Specimens prepared using traditional methods were subjected to freeze–thaw cycling in pure water, 5% Na2SO4 solution, 5% NaCl solution, and 5% NaCl + 5% Na2SO4 solution. Their mechanical properties, phase compositions, and pore structures were characterized through compressive, dynamic elastic modulus, X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests. After six freeze–thaw cycles, the relative dynamic elastic modulus (0.72, 0.58, 0.57, 0.55), mass loss (1.7%, 3.69%, 4.82%, 5.60%), and compressive strength loss (30.05%, 43.90%, 47.56%, 52.43%) progressively worsened from pure water to Na2SO4 to NaCl to compound salt conditions, indicating that under the same concentration, the deterioration induced by sodium chloride freeze–thaw is more severe than that caused by sodium sulfate, while the compound salt freeze–thaw condition leads to the most severe deterioration. Under compound salt freeze–thaw, the deterioration mechanisms include expansion due to gypsum formation, salt crystallization, ice formation, and the dissolution of cementitious phases driven by CaCl2 attack. Furthermore, clear correlations are observed among the mass loss rate, compressive strength loss rate, and relative dynamic elastic modulus, as well as between the peak strain and secant modulus. These findings provide valuable insights for improving the durability of historic restoration mortars.
Jiang et al. (Fri,) studied this question.