SodiumBentonite
Highly expansive volcanic clay capable of swelling 15-20 times its dry volume when in contact with water. Confined in geocomposites, it forms an indestructible self-healing gel, making it the most reliable underground waterproofing system for concrete structures.
Fig. 01 — GCL Geocomposite. Confined between soil and wall, the swelling of bentonite creates a positive impermeable pressure that physically blocks water table infiltration.
In the field of waterproofing in water table or below-ground applications, bituminous systems can fail through ageing or tearing. Sodium Bentonite overturns this limitation: it is an active and millennial material that uses water itself as a motor to seal the building.
Sodium bentonite is a volcanic clay. Its ‘sodium’ variant (natural or activated) is composed of over 75% Montmorillonite, a layered mineral. Water penetrates between these lamellae, causing extraordinary swelling of 15–20 times its dry volume. When confined between wall and backfill, the bentonite transforms into an impenetrable gel, creating an absolute hydraulic barrier.
The bentonite powder is encapsulated between two layers of geotextile to form a GCL (Geosynthetic Clay Liner). This is nailed directly against the foundation wall. The greatest advantage over plastic membranes is its self-healing capacity. If the concrete wall cracks due to structural settlement (micro-cracks up to 2 mm), the bentonite gel expands autonomously inside the crack, sealing it permanently.
Standards
European and international references applicable.
Physical properties
Usage environment
Bentonite works EXCLUSIVELY in compression. If left unconfined (not held by heavy backfill or a concrete counter-wall), contact with water will simply turn it into an ineffective muddy mass. RISK: in contaminated soils (landfills) or coastal zones (saltwater), sodium is chemically replaced by calcium ions, blocking expansion. Use polymeric bentonite GCL in these cases.
Documented applications
TAV. DRetaining Walls and Foundation Slabs
Waterproofing of underground garages, basements and continuous foundation slabs before backfilling.
Tunnels and Culverts
Sealing of the extrados of cut-and-cover tunnels where constant soil pressure is guaranteed.
Landfills (Capping)
Final capping or base lining of landfill basins to prevent leachate from contaminating the water table.
Artificial Ponds and Water Features
Placed on the bottom of excavated earth and covered with sand or gravel to create watertight artificial ponds.
Swelling Capacity (Volume increase % on contact with water)
TAV. EUnlike a PVC membrane that, if punctured by a stone during backfilling, allows water through, sodium bentonite uses the water itself that is trying to penetrate to expand and cure the tear.
Used in these systems
TAV. SOperational documents from this sheet
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