Thermodynamic modeling of carbonated Portland cement under groundwater and seawater conditions

Abstract

This study aimed to investigate the phase assemblages of Portland cement (PC) samples and eluate compositions for various water compositions and liquid/solid (L/S) ratios using thermodynamic equilibrium calculations. Specifically, diverse groundwater and seawater compositions were selected as eluates to represent practical leaching conditions. Samples made of PC with carbonation degrees of 0, 10, 20, and 30 % were modeled under exposure to pure water, CO₂-rich and sulfatic groundwater, and normal and CO₂-rich seawater leaching conditions. The phase alterations, leached amounts of ions, and changes in the C-S-H compositions of normal or carbonated samples with exponentially increasing L/S ratios were observed. The carbonated samples showed decreased Ca leaching but accelerated decomposition of C-S-H due to the formation of calcite. In addition, the formation of thaumasite was significantly greater in the carbonated samples under the sulfatic groundwater and normal seawater leaching conditions. Subsequently, the modeling outcomes were compared with results from field studies reported in earlier literatures on the leaching of PC systems to bridge the calculations to realistic leaching behaviors.