Determination of the pozzolanic activity of mortar's components by thermal analysis

Historic lime mortars are complex multicomponent system whose mineralogical and chemical composition changes over time. With age, hydraulic phases are converted by carbonation process to calcium carbonate and reactive silicon and aluminium oxides. The consolidation of lime mortars is usually based on the dotation of the Ca(OH)(2) into its matter so pozzolanic reaction may possibly take place. The study was aimed to explore pozzolanic potential of sand grains and degraded binder with respect to renewal of hydraulic phases which could contribute to mortar's mechanical strength and therefore prolong its durability. For this purpose, pastes of mortar components with lime hydrate were prepared and stored in wet conditions (RH = 99 +/- 1 %, T = 30 +/- 1 degrees C) for 180 days. Pozzolanic reaction products were studied at different ages using thermal analysis and X-ray diffraction. With respect to sand grains pozzolanic activity, both methods confirmed the presence of newly formed monocarboaluminate as an only hydraulic phase; moreover, CSH and hydrocalumite have been found in degraded binder pastes. CSH, stratlingite and monocarboaluminate were detected as products of pozzolanic reaction of silicate and metakaolin with calcium hydroxide.