Influence of Curing Type and Duration on the Resistance to Accelerated Carbonation and Its Relation to Natural Indoor and Outdoor Sheltered Carbonation

Abstract

The assessment of the resistance to carbonation of cement based materials is, because of practical considerations, mostly based on accelerated carbonation tests at elevated CO2 concentrations. However, experimental research already pointed out that results originating from accelerated carbonation tests are not completely representative for the natural carbonation resistance. This is caused by the altered reaction mechanisms due to the elevated CO2 concentrations resulting in deviating reaction products (e.g. CaCO3 polymorphs), an increased amount of water released during carbonation, etc. Moreover, the maturity of a cement paste matrix prior to exposure has a greater impact in case of accelerated carbonation compared to natural carbonation. Especially when adding supplementary cementitious materials (SCMs) to partially replace Portland clinker, the pozzolanic or latent-hydraulic behaviour might result in a less developed microstructure at early ages. As a consequence, extrapolated and/or converted results from accelerated carbonation tests on young mortar may misrepresent the performance under natural carbonation. This paper reports on the influence of curing type (sealed versus water) and duration (13, 28 and 90 days) on the carbonation rate of CEM I, CEM II/B-V and CEM III/B mortar exposed to 1 vol% CO2. Moreover, a comparison was made with carbonation rates based on natural carbonation of the same mixes both in an indoor and outdoor sheltered environment and sealed cured for 13 days prior to exposure. In general, the outcomes indicate that the reference water curing in combination with accelerated carbonation at 1 vol.% CO2 best represents the natural behaviour for the different cement types.