New Publication: NOx uptake capacities and sequestration pathways by hydrated cementitious phases
This study seeks to quantify NOx sequestration by individual hydrated cementitious phases (C-S-H, AFm-SO4, and Ca (OH)2), establish a fundamental understanding of the reaction pathways, and reveal the effects of carbonation (CaCO3 and AFm-CO3). For uncarbonated phases, the highest NOx uptake was measured in C-S-H, with the produced nitrite/nitrate physically bound on solid surface. For AFm-SO4, an anion exchange process was observed, where nitrite/nitrate substitute for sulfate and form new AFm-NO2/NO3. Ca(OH)2 showed undetectable NOx uptake, which may be due to the relative low temperature and relative humidity. For carbonated phases, CaCO3 exhibited an improved NOx uptake compared to uncarbonated phases, with uptake capacity three times higher than that of C-S-H. The result of AFm-CO3 indicates that carbonation could potentially inhibit the anion exchange process that was observed in AFm-SO4. These findings provide guidelines for the rational design and optimization of cement-based materials for enhanced NOx sequestration.