RESUMO
C4AF is considered the least reactive main clinker phase, but its reactivity may be affected by adding supplementary cementitious materials (SCMs). Pure C4AF was synthesised in a laboratory furnace, and the role of silica fume without gypsum on its early hydration properties was monitored. Burning was carried out in four stages to achieve 99% purity of C4AF. Heat flow development was monitored by isothermal calorimetry over 7 days of hydration at 20°C and 40°C. The role of silica fume on hydrogarnet phase katoite (Ca3Al2(SiO4)3 - x(OH)4 x x = 1.5-3) formation during early hydration was studied. Rapid dissolution of C4AF, formation of metastable C-(A,F)-H and its conversion to C3(A, F)H6 was evidenced by isothermal calorimetry as a large exotherm. Changes in microstructure during early hydration were documented by SE micrographs, EDS point analyses, X-ray mapping and line scans by SEM-EDS. The phase composition was characterised by DTA-TGA and QXRD after 7 days of hydration. The katoite diffraction pattern is similar for the reference sample and sample with silica fume, but substitution in its structure can be revealed by X-ray microanalyses. The composition of katoite is variable due to the various extent of substitution of 4OH- by SiO4 4- due to silica fume.
RESUMO
The mineralising effect of CuO on microstructure and phase composition of SO3 -doped clinker was studied by a combination of phase analysis, light and scanning electron microscopy and QXRD. Results show proportionally higher C4 AF content in clinker interstitial matter due to CuO doping. CuO also lowers the SO3 incorporation in main clinker phases C3 S and C2 S. Observation in back-scattered electrons revealed that Cu crystallises mainly as a Cu-rich phase in the clinker interstitial matter and inclusions in crystals of C2 S with distorted structure. CuO partially inhibits the incorporation of Fe2 O3 in C2 S.
