NANO-ENGINEERED NA-BENTONITE THIN FILM MEMBRANES FOR SUSTAINABLE WATERPROOFING OF CIVIL STRUCTURES

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Waterproofing remains a critical challenge in the durability and service life of concrete infrastructure, particularly in environments exposed to moisture ingress and shrinkage-induced cracking. Conventional bentonite-based systems, while effective, often require high material consumption and may exhibit limitations in performance consistency. This study explores the development of nano-Na-bentonite derived from Egyptian bentonitic clay through solvothermal (NBS) and precipitation (NBP) synthesis routes. By leveraging nano-scale engineering, the research aims to enhance swelling behavior, hydrophobicity, and crack-sealing efficiency, ultimately offering a sustainable and high-performance alternative for waterproofing civil structures.

Material Preparation and Nano-Modification Techniques

The starting Egyptian bentonite was subjected to activation and purification processes to ensure the removal of impurities and optimization of montmorillonite content prior to nano-modification. Two synthesis approaches—solvothermal (NBS) and precipitation (NBP)—were employed to achieve nano-scale refinement. These processes facilitated controlled crystallite formation, yielding particle sizes of approximately 10 nm for NBS and 50 nm for NBP. The comparative evaluation of these methods provides insights into how synthesis pathways influence structural refinement, morphology, and functional performance in waterproofing membranes.

Structural, Chemical, and Thermal Characterization

Comprehensive characterization techniques were utilized to investigate the physicochemical properties of NBS and NBP. X-ray diffraction (XRD) confirmed the preservation of montmorillonite as the dominant mineral phase, while X-ray fluorescence (XRF) validated the retention of essential chemical constituents. Fourier transform infrared spectroscopy (FTIR) identified characteristic functional groups associated with clay minerals, and TGA/DTA analyses demonstrated thermal stability and moisture-related mass changes. The nano-size effect was evident in the enhanced swelling capacities of 16.3 g/mm for NBS and 12 g/mm for NBP, significantly exceeding that of purified bentonite, thereby substantiating the influence of nano-engineering on performance enhancement.

Morphological Features and Swelling Behavior

Scanning electron microscopy (SEM) revealed that both NBS and NBP exhibit continuous wire-like morphologies with spherical and platelet nanostructures, contributing to improved surface area and interaction with water molecules. Micro-scale swelling measurements demonstrated remarkable volumetric expansion upon hydration, facilitating the formation of an impermeable gel layer. The reduced crystallite size in NBS particularly enhanced swelling kinetics, while NBP exhibited more uniform crack-sealing behavior. These morphological and swelling characteristics play a pivotal role in preventing water penetration and improving long-term waterproofing efficiency.

Hydrophobicity and Water Resistance Performance

Prototype thin film membranes fabricated from NBS and NBP were evaluated using water droplet contact angle analysis. Both membranes demonstrated excellent hydrophobic behavior, with contact angles ranging from 90° to 105° and low spreading coefficients between –81 and –86 mN/m. Notably, the membranes withstood 250–300 water droplets (1–1.2 mm height) without penetration, forming a stable protective gel layer on the surface. These findings confirm the enhanced water-repellent characteristics imparted by nano-scale modification and underscore their suitability for high-performance waterproofing systems.

Crack Morphology Analysis and Application Potential

Post-shrinkage crack morphology was assessed using USB digital microscopy to determine the crack-sealing efficiency of the membranes. The NBP membrane exhibited significantly reduced crack widths (0.09–0.18 mm) compared to NBS (0.22–0.58 mm), indicating superior crack mitigation capability. This suggests that precipitation-synthesized nano-bentonite may offer enhanced structural compatibility and sealing efficiency in concrete substrates. Overall, the performance of NBS and NBP thin film membranes highlights their potential as sustainable, low-consumption alternatives to conventional bentonite systems. Future investigations should focus on long-term durability, environmental exposure testing, and large-scale field implementation to validate their practical applicability in civil infrastructure.

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#ThinFilmMembrane
#HydrophobicCoatings
#SwellingClay
#StructuralEngineering
#BuildingMaterials
#InfrastructureInnovation
#MaterialCharacterization
#GreenConstruction
#AdvancedMaterials
#CrackSealingTechnology
#GeotechnicalEngineering
#SustainableInfrastructure

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