Modeling the durability of novel cementitious materials prepared with CEM II/C-M exposed to drying and carbonation

Abstract

The behavior upon exposure to CO2 of novel cementitious materials prepared with a low clinker cement CEM II/C-M (S-LL) is investigated in this paper. A simplified carbonation model considering the dissolution of a combined Ca-containing hydrate phase (CH, C-S-H, ettringite, monocarbonate, and Si-hydrogarnet) and the precipitation of calcite according to the evolution of phase assemblages calculated with thermodynamic modeling is applied to simulate accelerated carbonation tests in the laboratory. The dissolution rate of the Ca-containing hydrate phase is assumed to be determined by the water saturation degree, the partial pressure of CO2, and the fraction of its remaining volume compared to the initial one, which provides a way to predict the precipitation rate of calcite. Two mass conservation equations are considered in the model: water migration through the connected pores and diffusion of carbon dioxide in gaseous phases. Selected physical variables representative of the reactive transport properties are quantified from experimental measurements, including dynamic vapor sorption tests and drying experiments. The model response is compared to experimental data in terms of portlandite profiles from thermogravimetric analysis, and carbonation depth measurements using a pH indicator after specific times of accelerated carbonation. These experiments were also performed on a reference mortar prepared with the CEM II/A-S cement. All experimental results were simulated with the simplified carbonation model and the results compared to the response of the novel material.