Behavior of cementitious mixtures with filler carbonate subjected to accelerated carbonation

Calcium carbonate limestone filler is used as a partial replacement for clinker in cements to reduce carbon dioxide emissions and fill the voids in the cement paste. However, concrete durability conditions depend on the composition and the water/cement ratio, one of the major origin of concrete´s porosity. The objective of this study was to evaluate physical and chemical effects of calcium carbonate limestone filler in mortar pastes subjected to accelerated carbonation. Composite formulations were elaborated with three proportions of filler substitution (15%, 25% and 35%) and three water/cement ratios (0.42, 0.50 and 0.58). Physical, chemical and mineral characterizations were performed on Portland cement PC V and calcium carbonate limestone. The resulting mortar paste formulations were evaluated with respect to mechanical strength and capillary water absorption both for samples without carbonation and with accelerated exposure conditions. In the latter, carbonation depth penetration was also ascertained. Carbonation effects were determined from X-ray diffraction and thermogravimetric analysis. Results on compression strength and water absorption determined that a 25% filler substitution achieved the best performance with 40.72 MPa and an absorption of up to 7% for the water/cement ratio of 0.42. The carbonation coefficient was primarily affected by the water/cement ratio rather than substitution level. Thermal and mineral analysis indicated that carbonation consumed portlandite and formed calcite. Further calcium carbonate polymorphs were identified after 28 days of accelerated carbonation as a result so far unreported in studies of Portland cement.