Influence of lime on the evolution of cement mortars carbonation and hydration processes

Abstract

Using additional binders such as hydrated lime in cement-based systems implies changes in the development of chemical processes such as hydration and carbonation, having a clear impact in the rheological and mechanical properties of the material. This paper aims to study the impact of different amounts of hydrated lime (0, 50 %, and 66.7 % of lime as binder by volume), different curing ages (from 7 to 180 days), and evolution of the exposure front for the chemical processes in cement-based mortars. Moisture diffusion and mercury intrusion porosimetry (MIP) were performed to obtain information related to porosity, while phenolphthalein and thermogravimetric tests allowed the determination of the carbonation rate and the analysis of the temporal evolution of C-S-H, AFm, AFt, portlandite, and calcium carbonate phases, respectively. The results evidenced that adding lime to cement-based mortars accelerated the carbonation rates at long-term. Cement-lime-based mortars exhibited a higher carbonation efficiency, as evidenced by significant increases in the calcium carbonate quantities compared to portlandite after 28 days of curing. However, at early stage, pure cement-based mortars showed a faster penetration of CO2 and subsequent carbonation due to the low amount of available portlandite and early exposure to an environment prone to carbonation.