How to Prevent Cracking of GRC Components During Setting?

Cracking of GRC components during the setting process directly affects structural safety and durability, and requires prevention from multiple dimensions including materials, technology, and environment. Based on 28 years of GRC production experience, Qinglong Group believes that the key to preventing cracking lies in controlling plastic shrinkage, drying shrinkage, and thermal stress. Through scientific mix design, curing regimes, and construction measures, the risk of cracking can be effectively reduced.

Controlling plastic shrinkage is the core of preventing early cracking. During the initial setting of GRC, excessively rapid evaporation of surface moisture increases capillary pressure and produces network cracks. In the Shenzhen Pingshan High-tech Zone Comprehensive Service Center project, Qinglong Group controlled the surface moisture evaporation rate below 0.5kg/m²h by spraying a curing agent (film-forming curing agent at 150-200g/m²) and covering with plastic film. At the same time, the mix proportion was optimized by adding cellulose ether (0.1%-0.2%) to improve water retention and extend setting time, avoiding plastic shrinkage cracks. In high-temperature, low-humidity environments, windbreak shelters and misting devices were installed to maintain ambient relative humidity at ≥80%.

Reducing drying shrinkage is the focus of medium- and long-term crack prevention. The drying shrinkage of GRC mainly results from hydration reactions and moisture loss. Qinglong Group controlled the drying shrinkage rate within 0.04% by adding an expansive agent (UEA dosage of 6%-8%) and reducing cement content (total cementitious materials not exceeding 400kg/m³). In the Wuhan Hanxiu Theater project, internal curing technology was adopted, incorporating pre-wetted lightweight aggregates to provide moisture from within, reducing the 28-day shrinkage value by 20%. The curing regime followed a three-stage method of "moisture retention – temperature control – slow drying", with initial wet curing of no less than 7 days and slow drying in the later stage to avoid concentrated shrinkage stress.

Thermal stress control is crucial. Massive GRC components develop temperature differences between the interior and exterior due to hydration heat, leading to thermal cracks. In the roof project of the Hainan International Convention and Exhibition Center, Qinglong Group adopted layered casting for components thicker than 100mm, controlling each layer to within 300mm at intervals of 2-3 hours. Temperature sensors were embedded to monitor internal temperature, and cooling measures were initiated when the temperature difference exceeded 20℃. Low-heat cement (C3A content ≤8%) was selected, and fly ash (20%-30%) was added to reduce hydration heat, keeping the temperature rise within 35℃.

Strengthening structural measures safeguards against cracking. Anti-crack steel mesh (4-6mm in diameter, spaced at 100mm) is added at stress concentration areas to improve tensile capacity. Qinglong Group applied fiber reinforcement (polypropylene fiber at 0.1% by volume) at weak points such as corners and openings to improve material toughness. Through systematic crack prevention measures, GRC components can achieve the crack-free quality target.