Novel nano-Na-bentonite membranes synthesized from purified Egyptian bentonitic clay for superior waterproofing of civil structures

This study investigates the synthesis and characterization of nano-Na-bentonite derived from Egyptian bentonitic clay via solvothermal (NBS) and precipitation (NBP), and evaluates its potential as a thin film membrane for waterproofing concrete structures. The starting bentonite underwent activation and purification prior to nano-modification. Comprehensive characterization techniques including XRD, XRF, SEM, FTIR, TGA/DTA and micro-scale swelling measurements were employed to elucidate the structural, chemical, thermal, and morphological properties of NBS and NBP. Prototype NBS and NBP membranes were fabricated and subjected to water droplet contact angle analysis to assess hydrophobicity and water resistance. Post-shrinkage crack morphology was examined using USB digital microscopy. The crystallite sizes of NBS and NBP were estimated to be 10 nm and 50 nm respectively, exhibiting substantially higher swelling capacities of 16.3 and 12 g/mm compared to purified bentonite. SEM revealed NBS and NBP possess continuous wire-like morphologies with spherical or platelet nanostructures. XRD, XRF, FTIR and TGA/DTA confirmed the preservation of montmorillonite as the primary mineral phase and chemical composition in NBS and NBP, attesting to the nano-size effect behind the enhanced properties. The NBS and NBP membranes demonstrated excellent hydrophobicity, withstanding 250-300 water droplets (1-1.2 mm height) on the surface without penetration, forming a protective gel layer. The low spreading coefficients (-81 to -86 mN/m) and contact angles (90-105°) further validated the water-repellent nature of NBS and NBP membranes. Microscopic analysis of post-shrinkage cracks showed significantly reduced crack widths in NBP (0.09-0.18 mm) compared to NBS (0.22-0.58 mm), indicating its superior potential in waterproofing applications. The performance of NBS and NBP thin film membranes highlights their promising utility as sustainable materials for waterproofing civil structures, potentially replacing conventional bentonite systems at significantly lower material consumption. Further research on long-term durability and field-scale implementation is warranted to realize the full potential of these nano-engineered clay membranes.