CO2 RICH ENVIRONMENT AS A CURING METHOD FOR COMMERCIAL FIBRE-CEMENT CORRUGATED SHEETS

This work presents a pilot-scale curing method based on accelerated carbonation. Commercial corrugated sheets, reinforced with cellulose and polypropylene fibres, produced by the Hatschek process were evaluated after the curing method in a CO₂ rich environment and compared with air-cured corrugated sheets. The curing was carried out in a chamber similar to an autoclave with 8 m³ of internal volume specially designed for fibre-cement sheets curing. Three different manometric pressure conditions were tested: (I) sub-atmospheric (-0.5 bar); (II) atmospheric; (III) super-atmospheric (5 bar). The results for the three conditions were similar in several characteristics, standing out the super-atmospheric condition in some of them. Carbonation degrees of up to 38%, which means about 107 g of CO₂ incorporated per kg of dry composite, resulted in the increase of bulk density and the decrease of apparent porosity and water absorption. In terms of reinforcement, polypropylene fibres are challenging due to their low modulus of elasticity and poor fibre to matrix adhesion. The accelerated carbonation cured sheets showed a better fibre to matrix interface. The mechanical strength of the accelerated carbonation cured sheets increased by about 15%. The modulus of elasticity (6.3 GPa) and limit of proportionality (4.4 MPa) increased about 40% compared to air-cured sheets, leading to more rigid products. The dimensional stability evaluated by controlled drying shrinkage tests revealed dimensional variation around 1 mm/m in the accelerated carbonation cured sheets. The consumption of calcium hydroxide during the carbonation process at early ages of the composite, leading to lower matrix pH, is also a benefit that may decrease the cellulose fibre degradation under the alkaline environment. The benefits of the curing method also mitigated the defects by clogging the open pores and micro-fissures, providing higher physical-mechanical performance than the air-cured sheets. This curing method opens viable perspectives for CO2 capture in fibre-cement composites and polypropylene as reinforcement fibre for new technologies of fibre-cement.