Performance of carbonated calcium silicate based cement pastes and mortars exposed to NaCl and MgCl2 deicing salt

Abstract

This paper investigates the performance of two cementitious systems exposed to freezing or deicing salts. The first cementitious system is made using an ordinary portland cement (OPC) that reacts through hydration. The second cementitious system is made using a calcium silicate cement (CSC) that reacts and gains strength through carbonation (i.e., carbonated calcium silicate based cement (CCSC)). Two experimental techniques were used to evaluate the performance of these materials. The first technique measures the potential reactivity between the concrete paste and the deicing salt (NaCl and MgCl2) using a low temperature differential scanning calorimeter. The second technique uses a longitudinal guarded comparative calorimeter equipped with acoustic emission to assess the freeze–thaw performance of mortar samples saturated with water or deicing solutions. No chemical reaction is observed between CCSC paste and NaCl while a damaging reaction is observed between the OPC paste and NaCl due to the presence of calcium sulfoaluminate phases. A chemical reaction occurs for both the CCSC and OPC paste exposed to MgCl2: for the CCSC paste, this appears non-deleterious since relatively no reduction in dynamic elastic modulus is observed; for OPC paste, however, this is a damaging reaction due to formations of magnesium silicate hydrate and calcium/magnesium oxychloride. CCSC mortar sample saturated with water shows freezing in the large pores at approximately −5°C and smaller pores at approximately −28°C. Both the OPC and CCSC mortars show similar freeze–thaw performance when the system is water saturated. When the water in the pores of the mortar is replaced with a salt solution (NaCl and MgCl2), the CCSC mortar shows less freeze–thaw damage (mainly due to possessing a different pore structure) and more resistance to salt degradation (mainly due to possessing a different chemistry) than the OPC mortar does.