Severe scaling and spalling are commonly observed on tunnel lining surfaces in sulfate-rich environments. Due to humidity gradients, sulfate solution in rock fissures migrates through capillary action to the concrete exposed face, leading to physical crystallization precipitation at free-face zone and chemical sulfate attack at soil-facing zone, resulting in concrete expansion and crack. Existing models focus on full immersion or wet-dry cycles, which have obvious errors in predicting concrete damage under similar partial immersion. Considering the time- varying characteristics of saturation, porosity, calcium leaching and crack, a transport-reaction-expansion model for lining concrete under dual sulfate attacks and water evaporation was established. The spatiotemporal distribution of phase composition and the influence of modeling parameters on concrete expansion were revealed. The expansion strain caused by dual sulfate attacks and changes in the water evaporation zone was discussed. These findings provide a theoretical foundation for the durability design of lining concrete in sulfate- rich environment.

Increasing soil salinization and microplastics (MPs) pollution of farmland have become global agricultural issues that have to be faced, destabilizing plant-soil systems and bringing threats to ecosystems. Few studies have focused on the effects of MPs on saline soil water evaporation and desiccation crack formation, and the underlying influencing mechanisms of MPs and salts in soils. A mechanism test was conducted to explore the effects of MPs concentrations (0.5 %, 1 %, 3 %, w/w) on the simultaneous changes of water evaporation and cracking patterns of saline soils with different salinities (0, 0.1 %, 0.3 %, 0.5 %, w/w). Quantitative findings showed that (1) the MPs significantly reduced saturated conductivity by 14.9-46.8 % and 4.6-54.5 % in non-saline soil and lightly saline soil, respectively, which showed a decreasing trend with increasing MPs concentration; besides, soil salts also significantly reduced saturated conductivity, but the inhibition weakened with increasing soil salinity. (2) The MPs significantly reduced total porosity by 2.2-7.9 % and 1.8-6.6 % in non-saline and saline soils, respectively, which exhibited a slight decreasing trend with increasing MPs concentration. (3) The MPs reduced total evaporation by 0.4-6.1 % and 0.9-6.5 % in non-saline and saline soils, respectively. As the MPs concentration increased, the total evaporation of non-saline soil decreased, and the total evaporation of saline soils firstly decreased and then increased. After evaporation, both soil salt and MPs inhibited cracking. Correlations indicated that the presence of soil salt and MPs and their interactions explained more than half of the variability of soil and water characteristics and crack parameters. Mechanism exploration suggested that the MPs affect the evaporation process and crack behavior by changing soil pore size distribution, damaging soil structure, and the water repellency of the MPs particles; besides, the salts inhibit the soil water evaporation and surface cracking through increasing osmotic suction, blocking soil macropores, and promoting inter-microaggregate cementation. Our findings provide evidences for MPs influences on saline soil physical properties, water evaporation, and crack development, deserving attentions to the regulations and developments of soil-crop systems that facing salinization and plastic pollution.