Using EDTA-2Na to inhibit sulfate attack in slag cement mortar under steam curing

This paper explored a novel method to inhibit sulfate attack in slag cement mortar under steam curing, by using ethylenediaminetetraacetic acid disodium (EDTA-2Na) to chelate calcium ions. 0.5 and 1% EDTA-2Na were used in slag cement mortars to evaluate the inhibition effect in sulfate solution (7.5% Na2SO4 and MgSO4 solution) for 360 days. The weight variation, compressive strength, along with FTIR spectroscopy, XRD and DTG, were conducted to analyze the sulfate degradation. Additionally, the isothermal calorimetry was measured to study the effect of EDTA-2Na on the hydration of cement. Results indicated that 1% EDTA-2Na retarded the cement hydration distinctly. The EDTA-2Na enhanced the resistance of steam-cured slag mortar against sulfate attack. For the Na2SO4 attack, the enhancing effect of 1% EDTA-2Na was higher than that of 0.5% EDTA-2Na. For the MgSO4 attack, 0.5 and 1% EDTA-2Na was both beneficial. The EDTA-2Na decreased the amount of calcium hydroxide due to the chelation, retarding the formation of gypsum and secondary ettringite. (C) 2020 Elsevier Ltd. All rights reserved.