Does lack of CO2 control in environmental chambers influence the strength and stiffness of hydraulic lime mortars?

Abstract

This study investigates the influence of carbon dioxide (CO2) control in environmental chambers, where hydraulic lime mortar specimens are typically cured before strength testing according to EN1015-11:2019. To do this, three sets of identical mortar samples were cast. Two sets were cured in an environmental chamber that offered the same temperature and relative humidity but different CO2 conditions. In the first chamber, carbonation reactions used the ambient CO2 trapped in the hermetically sealed chamber air. The second chamber was connected to an external carbon dioxide supply, which maintained a constant CO2 concentration, above ambient laboratory levels, during curing. A third set of samples was cured under laboratory conditions to serve as a reference. Following the 35-day curing period, the dynamic elastic modulus and flexural and compressive strengths of sample sets were obtained. Subsequent X-ray diffraction analysis gives additional insights into the material composition for each curing regime. Results indicate that controlling carbon dioxide to above ambient levels leads to noticeably higher stiffness and strength in samples. This suggests that implementing CO2 control as a part of standard curing conditions may enable more reliable estimates of strength and stiffness development in lime mortars, with respect to laboratory conditions.