Effect of cement content on the pore structure and imbibition rate of lime-cement mortars

Understanding the pore structure and water transport properties of cement-lime mortars has significant implications for the design of sustainable structures. By optimizing these properties, we can improve the compatibility between mortars and porous substrates such as building stones and bricks, as well as enhance the durability and efficiency of mortar in construction. This study provides a comprehensive analysis of the pore structure of cement-lime mortar mixtures and examines its implications for mechanical performance, natural carbonation, and capillary water uptake over time. For this purpose, the porosity of six cement-lime mortar mixtures was characterized using dynamic vapor sorption, mercury intrusion porosimetry, micro-computed tomography, capillary water uptake and water absorption under vacuum. It was found that cement-rich mixtures lead to a more refined pore network dominated by microcapillaries and decreased porosity with a unimodal pore size distribution, resulting in higher strength, while lime promotes the formation of macrocapillaries. Replacing 37-55 % of the binder mass with cement increases the primary capillary imbibition rate of lime mortars. However, this rate decreases when the cement content exceeds 55 %, likely due to the higher volume of microcapillaries formed by the addition of cement. The study highlights the importance of balancing lime and cement content to optimize the pore structure and water transport properties of mortars, which in turn affects their mechanical performance and durability.