Abstract
Effects of disodium EDTA (EDTA-2Na) on hydration and mechanical properties of calcium sulphoaluminate-belite cement (CSBC) were investigated systematically. Results show that EDTA-2Na addition leads to visible changes in CSBC strength development. 0.50 % EDTA-2Na significantly enhances the compressive strength by 18 % and 23 % compared with the blank specimens at 7 d and 28 d, while reducing the strength at 8 h and 1 d. The content of the main hydration product (AFt) determines the strength development. At the early hydration stage, EDTA-2Na delays hydration of ye'elimite to form AFt, thus decreasing the early hydration degree of CSBC and increasing the porosity to reduce strength. In the presence of EDTA-2Na, the morphology changes of amorphous aluminum hydroxide (AH3) facilitate the AH3-C2S-CaSO4 reaction to increase AFt content and form a more condensed structure, thus enhancing the late strength. In this way, the strength development of CSBC mortars can be modified and regulated by EDTA-2Na.
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