Effect of accelerated carbonation on the microstructure and physical properties of hybrid fiber-cement composites

• The content of Ca(OH)2 decreased after accelerated carbonation of the fiber-cement.
• C–S–H and calcium sulfoaluminates contents decreased after accelerated carbonation.
• CaCO3 formed from the carbonation is precipitated in the pore structure of the matrix.
• The interface between the cellulose fibers and the matrix in the carbonated composites was improved.
• Accelerated carbonation can be effective to mitigate the degradation of cellulose fibers in fiber-cement.

Carbonation takes place in the fiber-cement composites through the diffusion of carbon dioxide (CO2) through the unsaturated pores of the cement matrix, and through its reaction with the hydration products of the Portland cement (mainly calcium hydroxide and CSH phases). The use of this technology in the fiber-cement production consists of an interesting procedure to prematurely decrease the alkalinity of the cement matrix, which is potentially harmful to the cellulose fiber reinforcement. It is also an initiative to CO2 sequestration and partial replacement of petroleum-based fibers. Therefore, the objective of the present work is to show the impact of accelerated carbonation on the microstructure and physical properties of fiber-cement composites reinforced with cellulose pulp and synthetic fibers. The effectiveness of the accelerated carbonation was confirmed by thermogravimetric (TG) analysis. Accelerated carbonation increased bulk density (BD) and decreased apparent porosity (AP). The SEM micrographs show that the calcium carbonate (CaCO3) formed from the carbonation reaction is precipitated in the pore structure of the matrix. The interface between the cellulose fibers and the cement matrix in the carbonated composites was improved, decreasing the typical voids around the cellulose fibers that prejudice the fiber-cement performance at long term.