How to Prevent Cracking of GRC Components During Setting?

Cracking of GRC components during setting and hardening is mainly the result of multiple interacting factors, including “plastic shrinkage, drying shrinkage, thermal stress, and structural restraint.” Crack prevention is a systematic project that must run through the entire process of material design, production curing, and installation detailing. In the production of 30,000 square meters of GRC curtain wall for the Comprehensive Service Center of Shenzhen Pingshan High-Tech Zone (a Luban Award project), Qinglong Group successfully achieved the goal of “zero through cracks” on a large-scale project through the integrated application of low-shrinkage formulations, precise curing regimes, and rational structural detailing. A scientific prevention strategy can reduce cracking risk to a minimum.

Optimizing Material Mix Proportions to Reduce Shrinkage at the Source

Controlling shrinkage is fundamental to crack prevention. Qinglong takes a multi-pronged technical approach: 1) Reducing the water-cement ratio: lower the water-cement ratio as much as possible while ensuring workability (usually kept below 0.32), reducing the total amount of evaporable water. 2) Adding shrinkage-reducing admixtures: incorporating high-efficiency shrinkage-reducing agents can effectively reduce capillary pore tension and lower drying shrinkage values. 3) Optimizing aggregate gradation: using continuously graded aggregates to increase packing density and reduce the amount of cement paste. 4) Using low-alkali cement: selecting sulfoaluminate cement with relatively low shrinkage or incorporating large amounts of mineral admixtures. These measures reduce the driving force of shrinkage at the material level.

Implementing Scientific Curing to Control Early Moisture Loss

Curing during the early stage of setting and hardening is crucial—it is the critical window for preventing plastic shrinkage cracks. Qinglong strictly implements the curing principles of “timely, sufficient, and continuous”: components are covered with plastic film immediately after forming to prevent surface moisture evaporation, and cured in a standard curing room (temperature 20±2°C, humidity ≥95%) for no less than 7 days. For mass components, “curing in the mold” is adopted to provide external restraint and slow the drying rate. In hot, dry regions such as Hainan, the frequency and duration of moist curing must also be increased.

Improving Structural Detailing to Release Shrinkage Stress

Rational structural detailing can effectively “channel” rather than “rigidly resist” shrinkage stress. 1) Controlling the size of individual components: avoid producing overly long or large panels, keeping the total shrinkage deformation within a reasonable range. 2) Installing induced joints: preset “induced joints” at points of stress concentration or abrupt geometric change to guide cracks to occur regularly at predetermined locations. 3) Optimizing reinforcement: place alkali-resistant glass fiber mesh or a small amount of steel reinforcement within components to improve crack resistance. Qinglong uses finite element software to simulate shrinkage stress during the detailed design stage, optimizing component segmentation and reinforcement schemes.

Controlling Temperature Differences Between Production and Installation Environments

Sudden temperature changes cause thermal expansion and contraction stresses. During production, control workshop temperatures and avoid exposing components to high heat. After curing, components should be stored at temperatures close to their service environment to reduce thermal stress at delivery. During installation, avoid working under extreme high or low temperatures, and ensure that the connections between GRC components and the main structure have a certain degree of movement capacity to accommodate thermal deformation.

Preventing cracking of GRC during the setting period is a combination of materials science, process technology, and refined management. By establishing a crack prevention control system covering the entire process, Qinglong Group ensures that every GRC component leaving the factory possesses excellent volume stability and integrity.