Durability of an innovative self-healing geopolymer vertical barrier under dry-wet cycles

Microcapsules have great potential in developing more durable and reliable cutoff wall materials. This study produced two types of microcapsules, including single-walled and double-walled, using sodium silicate as the core material, which demonstrated advantageous chemical structures, thermal stability, and rheological properties. An innovative self-healing geopolymer cutoff wall backfill (SHGCWB) has been synthesized based on this. The evolution of durability was evaluated macroscopically through dry-wet cycle test. The self-healing effect and durability enhancement mechanism of microcapsules were revealed microscopically by MIP and SEM-EDS tests. The hydraulic conductivity of SHGCWB can remain below 1E-8 m/s before the 4th dry-wet cycle, and fluctuate around 1E-8 m/s in the subsequent cycles. The true determinant of permeability is the proportion of micropore (< 0.05 μm), mesopore (0.05–0.1 μm), and macropore (> 0.1 μm). One can promptly estimate the hydraulic conductivity of SHGCWB based on ultrasonic pulse velocity (UPV) and the first ultrasonic pulse amplitude (UPA). This study can provide a new technical solution to further improving the long-term durability and serviceability of cutoff wall.