What Factors Are Related to the Carbonation Rate of GRC Panels?

The carbonation rate of GRC panels is a key indicator for evaluating their long-term durability and predicting their ability to protect the internal glass fibers. Carbonation is essentially the process by which carbon dioxide reacts with calcium hydroxide, a hydration product of cement, to form calcium carbonate, causing the alkalinity (pH value) of the pore solution to decline. Through long-term research and accelerated testing, Qinglong Group has grouped the core factors affecting carbonation rate into four major categories: material density, environmental conditions, time, and stress state. Understanding and controlling these factors is the scientific basis for producing long-life GRC products.

The Density of the Material Itself Is the Decisive Internal Factor

The diffusion rate of carbon dioxide in GRC depends directly on the material's pore structure and permeability. Qinglong substantially reduces the carbonation rate through the following measures: 1) Reducing the water-binder ratio: This is the most effective measure; lowering the water-binder ratio from 0.4 to 0.3 can reduce the carbonation rate several-fold. 2) Incorporating active mineral admixtures: Silica fume, fly ash, and similar materials refine capillary pores and consume calcium hydroxide, though it should be noted that they may slightly reduce early-stage alkalinity. 3) Ensuring adequate curing: Sufficient moist curing promotes hydration, generating more hydration products that block the pores. The 28-day carbonation depth of Qinglong GRC can typically be controlled within 1mm.

Environmental Conditions Are External Factors That Cannot Be Ignored

1) Ambient CO₂ concentration: Concentrations are higher in urban industrial areas than in rural areas, and indoor levels may be higher than outdoor levels. 2) Ambient temperature and humidity: The carbonation reaction is fastest at a relative humidity of 50%-70%; humidity that is too high or too low will inhibit it. Rising temperatures accelerate the reaction. 3) Wetting-drying cycles and salts: Wetting-drying cycles intensify moisture and ion transport, and aggressive media such as chloride ions have a synergistic destructive effect with carbonation. For coastal projects, Qinglong specifically enhances its formulations' resistance to the combined attack of carbonation and chloride ions.

Long-Term Effects of Time and Stress State

Carbonation depth is roughly proportional to the square root of time. If GRC panels remain in tension or bending for extended periods in service, microcracks may develop, opening fast channels for CO₂ and significantly accelerating carbonation. Therefore, controlling drying shrinkage cracks and load-induced cracks in GRC panels is essential. Qinglong minimizes crack formation through measures such as adding fibers, optimizing reinforcement, and incorporating shrinkage joints.

Consequences of Carbonation and Protective Measures

Carbonation itself does not directly damage GRC, but the resulting drop in alkalinity (pH falling from above 13 to below 9) deprives the alkali-resistant glass fibers of their alkaline protection and may trigger fiber corrosion over time. Therefore, delaying carbonation is key to protecting the fibers and ensuring long-term strength. In addition to optimizing the material, applying a high-quality protective coating (such as a silicone-based water repellent) to the GRC surface to form a barrier is a cost-effective supplementary protective measure. Qinglong can provide customers with carbonation depth predictions and protection schemes based on the design service life.