Ettringite

About: Ettringite is a research topic. Over the lifetime, 2702 publications have been published within this topic receiving 67056 citations. The topic is also known as: woodfordite.

Effect of Gypsum on the Early Hydration of Cubic and Na-Doped Orthorhombic Tricalcium Aluminate

Abstract: The tricalcium aluminate (C3A) and sulfate content in cement influence the hydration chemistry, setting time and rheology of cement paste, mortar and concrete. Here, in situ experiments are performed to better understand the effect of gypsum on the early hydration of cubic (cub-)C3A and Na-doped orthorhombic (orth-)C3A. The isothermal calorimetry data show that the solid-phase assemblage produced by the hydration of C3A is greatly modified as a function of its crystal structure type and gypsum content, the latter of which induces non-linear changes in the heat release rate. These data are consistent with the in situ X-ray diffraction results, which show that a higher gypsum content accelerates the consumption of orth-C3A and the subsequent precipitation of ettringite, which is contrary to the cub-C3A system where gypsum retarded the hydration rate. These in situ results provide new insight into the relationship between the chemistry and early-age properties of cub- and orth-C3A hydration and corroborate the reported ex situ findings of these systems.

Limestone Addition in Cement

Abstract: Addition of fine limestone provides an excellent means to reduce the amount of clinker in cement. It is now well accepted that limestone partially reacts in cementitious systems with C3A to produce hemi- and monocarboaluminate phases and as a consequence more sulfate is available to form ettringite and the total volume of hydrates increases. The mechanism by which limestone affects the hydration is crucial in understanding its influence on the properties of cementitious materials. Laboratory and Commercial Cements with two different types of clinker, low and high C3A with different gypsum and limestone addition, were investigated. Hydrated pastes and mortars were investigated in terms of kinetics, phases assemblage, microstructure development, porosity, mechanical properties and durability (sulfate attack and sorptivity). An improvement in sample preparation for XRD measurement was made, which allows preferential orientation to be avoid and improves Rietveld Analysis quantification. The elastic modulus was found to correlate well with compressive strength and could be used as a nondestructive method to measure compressive strength. Monocarboaluminate formation was found to increase with increasing C3A. For high C3A cement it is visible at 2 days of hydration and at 720 days 4.5% of monocarboaluminate is measured in the system. For Low C3A cement it is visible at 7 days of hydration and at 720 days 1.6% of monocarboaluminate is measured in the system. Mc is formed only after all gypsum, which is more reactive than limestone is consumed to produce ettringite. No monosulfate is observed in the limestone systems. The optimum gypsum, was found to have as much effect at early ages on the hydration as 10% of limestone addition. Consequently variations in the gypsum level were investigated but it was difficult to quantify differences between samples with increasing gypsum addition. Studies of behavior in sulfate solution indicated that C3A is the dominant factor. Limestone addition produces slight changes in the form of degradation but do not fundamentally change whether deterioration takes place or not.

Calcium sulphate anhydrite based composite binders; effect of Portland cement and four pozzolans on the hydration and strength

Abstract: The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with Portland cement and pozzolans Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and pulverized fuel ash were characterized The composite binders showed hydraulic behavior The use of Portland cement favoured the strength, which was also higher with the incorporation of siliceous nanometric pozzolans compared to the micrometric silicoaluminate pozzolans The nanoparticles enhanced the early hydration and changed the gypsum morphology promoting denser matrices of hydration products The geothermal waste pozzolan was the most effective, while one of the composites with metakaolin showed formation of ettringite and strength losses The heat of hydration of the composites was considerably lower than that of the neat Portland cement