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

Abstract

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 FT-IR 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.