Effect of Portuguese metakaolin on hydraulic lime concrete using different curing conditions

Hydraulic lime concrete with the addition of metakaolin in various percentages and cured under different conditions was studied in order to evaluate the effect of the pozzolanic additions over time (7, 28, 90 and 360 days). This study was performed using NHL 5, a metakaolin of Portuguese origin, siliceous sand and calcareous coarse aggregate, with increasing percentages of substitution of hydraulic lime by metakaolin in weight. In order to evaluate the pozzolanic effect, compressive strength test were performed and analysed by relative strength–time plots and by the application of different indexes such as the index of specific strength and the pozzolanic index. Thermogravimetric analysis was performed at the age of 28 days in order to evaluate the phases present in the concrete specimens. As main conclusions metakaolin is an adequate material for application in concrete with hydraulic lime binder as a pozzolanic addition providing an increase in mechanical strength for the studied substitutions of 20% and 30%. Testing should be performed at 28 days when portlandite consumption is complete.