Effect of alkanolamines in kaolinitic calcined clays pozzolanic reactivity.

Abstract

Five kaolinitic clays with different amounts of kaolinite, ranging between ~70 wt% and ~30 wt%, have been studied to unravel the possible activation effect of alkanolamines on the aluminate fraction of calcined clays. This is of interest for enhancing the reactivity of LC3 binders. These clays were calcinated at 860ºC for 4 h and ground to particle sizes of DV,50 ~10 μm. Three alkanolamines were selected: triisopropanolamine (TIPA), triethanolamine (TEA) and methyldiethanolamine (MDEOA), added in two dosages, 0.025 and 0.050 wt% (by weight of calcined clay, bwcc). The role of alkanolamines as activators in calcined clays was assessed following the ASTM c1897 standard bases on R3-tests. Concretely, first by measuring the heat evolved due to the pozzolanic reaction of the calcined clay and Ca(OH)2 (i.e. R3 mixture) by isothermal calorimetry at 40ºC during 7 days, and second, the bounded water by measuring the weight loss of R3 mixture after heating them at 350ºC.This study concludes that there is no significant activation of the pozzolanic activity of kaolinitic calcined clays just by adding alkanolamines. However, a mild activation was observed, i.e., higher heat evolved up to 7 days, by adding 0.05 wt% bwcc of TIPA, TEA and MDEOA to a high kaolinite content disordered metakaolin with high specific surface area calcined clay.