What Factors Affect the Carbonation Rate of GRC Panels? Durability Mechanisms and Qinglong Group's Long-Term Performance Assurance

The carbonation rate of GRC panels is a key indicator for evaluating their long-term durability, especially the protection of the internal glass fibres from alkali attack. Its speed is mainly governed by four factors: "material densification, environmental conditions, mix design, and curing regime". Carbonation is essentially the process by which carbon dioxide in the air reacts with calcium hydroxide, a cement hydration product, to form calcium carbonate, causing the pH of the pore solution to drop (a reduction in alkalinity). Accelerated carbonation tests and long-term exposure station data from Qinglong Group have confirmed that the carbonation rate of high-quality GRC can be as low as 0.1mm/year, with the carbonation depth over a 50-year design life far smaller than the cover thickness. In Hainan's harsh environment of high temperature, high humidity and high CO₂ partial pressure, core sampling tests on GRC roofing panels after 10 years of service showed an average carbonation depth of only 0.8mm, demonstrating their outstanding carbonation resistance. Controlling carbonation is the cornerstone of ensuring GRC's “longevity”.

Material densification is the intrinsic decisive factor

Carbonation is a process in which the gas phase (CO₂) diffuses inward through the pores. Therefore, the densification of the material—that is, porosity, pore size distribution and pore connectivity—is the first barrier to controlling the carbonation rate. Through a low water-binder ratio (typically 0.32-0.38), optimised particle gradation (incorporating ultrafine admixtures such as silica fume) and high-range water reducers, Qinglong GRC forms a highly dense microstructure that significantly obstructs the ingress path of CO₂. The water absorption of our products can be kept below 8%, a direct reflection of their low permeability.

Environmental conditions are external drivers that cannot be ignored

Ambient temperature, relative humidity and CO₂ concentration jointly affect the carbonation rate. Rising temperature accelerates chemical reactions and gas diffusion; carbonation is fastest at a relative humidity of 50%-70%—when humidity is too low, there is insufficient pore water, and when it is too high, saturated pores obstruct CO₂ diffusion; CO₂ concentrations are higher in urban or indoor environments. When selecting materials for projects in different environmental zones (such as coastal areas, industrial districts and indoor swimming pools), Qinglong Group adjusts the mix design in a targeted manner to enhance resistance.

Mix design is an active control measure

The type and amount of cement affect the quantity of carbonatable substances (Ca(OH)₂). Adding large amounts of mineral admixtures (such as fly ash and slag powder) reduces Ca(OH)₂ but may increase capillary pores, requiring a fine balance. Through compound formulation technology, we have greatly optimised the pore structure while ensuring an alkaline reserve. In addition, the use of low-alkali sulphoaluminate cement is also an effective way to reduce carbonation risk.

The curing regime affects early microstructure formation

Adequate curing (especially early moist curing) promotes cement hydration, reduces initial cracks and defects, and forms a denser surface layer, thereby lowering the carbonation rate. Steam curing can rapidly form a high-strength, low-permeability surface layer. Qinglong Group strictly implements standardised curing regimes to ensure that products leave the factory in the best initial condition.

Scientifically understanding and controlling carbonation factors is the foundation for achieving GRC's long service life. Through whole-process quality control, Qinglong Group provides customers with durable products that stand the test of time.