Effect of proteins on the mineralization, microstructure and mechanical properties of carbonation cured calcium silicate

The effect of five proteins with different physicochemical properties on the mineralization, microstructure, and mechanical properties of carbonated wollastonite pastes was examined. The negative surface charge of wollastonite particles increased as the result of protein adsorption. The flow of fresh paste was shown to increase in the pastes with proteins due to the enhanced electrostatic repulsion of the wollastonite particles as a result of the adsorption of negatively charged proteins, the ball bearing effect of the proteins in the pore solution, and formation of air bubbles. While calcite and amorphous calcium carbonate were the primary phases of calcium carbonate in all pastes, other polymorphs including aragonite and vaterite were present, to a small extent, in the microstructure of most of the pastes modified with proteins. The calcium carbonate content was shown to be higher in some of the pastes modified with proteins and this was attributed to the delayed water loss to evaporation and presence of free water due to hydrophobization of pastes modified with proteins. The X-ray micro-computed tomography (micro-CT) analysis revealed the formation of cracks in the control and some of the protein modified pastes resulting from drying shrinkage. It was demonstrated that the increased microstructure hydrophobicity was the reason for the absence of cracks in the pastes with the proteins that did not show cracks. Overall, the carbonated pastes with proteins exhibited higher compressive strength compared to the control paste. Absence of cracks, enhanced interfacial strength between carbonated products in the microstructure and organic-inorganic composite formation are suggested to be responsible for the increased compressive strength of the carbonated pastes with proteins.