The leaching-deterioration properties and leaching mechanism of cement mortar under dry-wet cycles

Abstract

The dry–wet cycle in cement mortar is essential for accelerating ion transport; however, it results in an increase in severity of durability damage. Leaching damage is a primary-contributing factor that reduces durability. Studies on calcium corrosion degradation of cement-based materials and its inhibition process during dry–wet cycles are lacking. In this work, the frequency of dry–wet cycles, concentration of soaking liquid, reduction of water–cement ratio, and incorporation of silica fume on the corrosion deterioration of cement mortar were studied. Using NH4Cl solution as the corrosion medium, the variation in leaching depth, calcium-ion dissolution, compressive strength, flexural strength, phase composition, and microstructure was analyzed. The results showed that calcium dissolution occurs during dry–wet cycles, hence the mechanical properties of the cement mortar declines, and pore expansion occurs. With the shortening of the dry–wet cycles, leaching damage increased and the dissolution rate gradually deviated from Fick's law. Increasing the concentration of NH4Cl solution significantly increased the leaching depth of mortar and accelerated the reduction of the compressive flexural strength. Reducing the water–cement ratio or adding a proper amount of silica fume effectively inhibited the dissolution rate of cement mortar and the deterioration of compressive strength and flexural strength. The results of this study provide a new insight and deeper understanding of the leaching-degradation properties and mechanisms of cement-based materials during dry–wet cycles. Furthermore, the results may be used for the inhibition of cement-based material dissolution during dry–wet cycles.