Chemical Activation of Metakaolin in Cement-Based Materials

摘要

Metakaolin (MK) comes from the calcination of kaolinite at temperatures ranging from 700℃ (1292°F) to 850℃ (1562°F). The resulting dehydroxylation of kaolinite produces an amorphous material (metakaolin) that is usually very reactive in alkaline media such as cement-based materials. However, the reactivity generally takes effect after a few days, so poor short-term performance is obtained, which is a disadvantage in cases where the concrete needs to be rapidly stripped of its formwork. The aim of this work was to test different chemical activators for metakaolin, in order to obtain short-term strength similar to that obtained without metakaolin. Twelve activators were selected and tested in mortars at different concentrations, using two modes of introduction (in solution and in solid form). Four cements were used in the experiments (2 CEM I and 2 CEM Ⅱ). Workability and compressive strength tests were carried out (at 16 h, 24 h, 48 h, 7 d, and 28 d). The results show disparities in the efficiency of the activation. Products very active at early ages often led to a decrease in strength at 28 days of age, compared to activator-free mixtures.