Effect of hydrogel on mitigating drying shrinkage induced cracking in carbonation cured calcium silicate binders

Abstract

Carbonation cured calcium silicate binders can be considered an alternative material to reduce the carbon footprint of the construction industry. Carbonation at elevated temperatures is used to enhance carbonation reaction; however, it accelerates drying, which could result in drying shrinkage induced cracking. The effect of hydrogel on the microstructure and properties of carbonated wollastonite pastes was discussed in this paper. The teabag test and flow test showed that hydrogel absorption was notably higher in wollastonite paste than in OPC paste. The phase analysis based on Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), revealed calcite as the primary polymorph of calcium carbonate in the carbonated product. The micro-CT analysis showed crack formation in the control pastes while no or significantly fewer cracks were observed in the hydrogel modified pastes. The hydrogel modified pastes exhibited lower water loss and drying shrinkage compared to the control paste at early carbonation stage. The above results provided evidence that cracking was caused by drying shrinkage in the control carbonated pastes and hydrogel was effective in mitigating such cracking by lowering water loss at early stage of carbonation. The results of the nitrogen adsorption test indicated a higher specific surface area and pore volume in the hydrogel modified pastes. The hydrogel modified pastes exhibited a slightly reduced compressive strength due to the presence of hydrogel macrovoids in these pastes.