Autonomous Crack Sealing
Gel-based polymerisation chemistry added to the mix as a dry admixture at the batch plant. The precursor particles distribute uniformly throughout the cementitious matrix — dormant until a crack opens and moisture contact triggers the reaction. No separate application, no monitoring, no access to the element after placing.
Gel precursor distribution
The GX healing system consists of gel precursor compounds added to the concrete mix as a dry additive at the batch plant. The precursor is distributed as micron-scale particles throughout the cementitious matrix. During normal hydration and curing, the precursor particles remain dormant — encapsulated in a hydrophobic shell that protects them from premature activation.
The precursor system is designed to target uniform distribution throughout the mix cross-section, including the transition zone between aggregate and paste — a common crack initiation site in high-stress concrete elements.
Crack formation
Thermal, mechanical, or shrinkage-induced cracking ruptures the hydrophobic shell of precursor particles in the crack zone. The particle matrix is exposed.
Moisture activation
Water ingress through the crack channel contacts exposed precursor particles. A controlled chain polymerisation reaction begins at the crack faces. Gel volume increases as the reaction progresses.
Crack bridging & set
The expanding gel fills the crack void from both faces inward. On reaching the full crack width, continued polymerisation transitions the gel to a set solid phase. Subsequent drying reduces volume minimally — the set phase retains bridging contact.
Moisture-triggered polymerisation
Activation is triggered by liquid water contact — not humidity alone. This threshold is intentional: relative humidity fluctuations during normal exposure do not activate the precursor. The system is designed to activate when the crack has opened sufficiently to allow water ingress — the condition that marks the beginning of durability deterioration in conventional concrete.
The activation reaction is exothermic at small scale — measurable with embedded thermocouples during laboratory characterisation. The reaction rate is designed to target a 7–28 day completion window at ambient temperatures in the design range, allowing the gel set phase to develop over a controlled cure period rather than a rapid flash-set that could trap air voids.
All values below are design targets and aspirational performance goals. They represent intended specification ranges, not certified test results. GX systems are not yet ASTM-certified products.
| Parameter | Target Range | Basis | Notes |
|---|---|---|---|
| Target crack width — max effective sealing | 0.05 – 0.40 mm | Designed to meet | Wider cracks may require partial bridging; narrower cracks may rely on autogenous cement hydration |
| Activation temperature range | 5°C – 40°C | Design target | Reaction rate decreases below 10°C; performance below 5°C is under development |
| Target sealing time — 0.20 mm crack at 20°C | 14 – 28 days | Design target | Indicative; influenced by crack geometry, water availability, and temperature |
| Compressive strength — 28-day compliance target | Designed to target C30/37 (EN) / 4,500 psi (ASTM) | Design target | GX additive designed to have minimal impact on baseline compressive strength of host mix |
| Chloride diffusion resistance | Target Dc < 3 × 10⁻¹² m²/s at 28 days | Design target | Tested per NT Build 443 protocol — results pending external laboratory confirmation |
| Repeat cycle capacity | Targeting ≥ 3 independent crack-heal cycles | Aspirational target | Limited by precursor concentration in the healed zone; available precursor per zone decreases with each cycle |
Specification note: GX concrete is specified as a performance-based admixture addition. The specification section should define the target maximum crack width, the exposure class, and the minimum cure period — GX is not a proprietary product name specification. Our technical team confirms the appropriate GX grade, dosage rate (kg/m³), and any mix design adjustments for the host concrete. We do not specify by product name; we specify by performance parameters with a defined framing that the specifier controls.