Hydration of C(3)A-gypsum systems

Hydration of C(3)A-gypsum systems with different gypsum additions was investigated in terms of the phase assemblage, kinetics and microstructural development. The second stage of the reaction, which begins after the depletion of gypsum, was of particular interest. From in-situ X-ray diffraction results, it was seen that the dissolution of ettringite and C(3)A to form monosulfoaluminate and/or hydroxy-AFm phases is a rapid reaction that occurs right after the depletion of gypsum. The observation of the calorimetric curves obtained for the different gypsum additions leads us to the conclusion that the mechanism controlling the hydration rate during this period is the nucleation and growth of the AFm phases. The microstructural study showed that the formation of AFm phases occurs in the space between the C(3)A grains but also within the boundaries of the original C(3)A grains. Hydrogarnet was observed growing as a shell around the C(3)A grains. (C) 2012 Elsevier Ltd. All rights reserved.

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Alexandra Quennoz, Karen Scrivener
2012
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https://infoscience.epfl.ch/record/180155?ln=en

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Impact of Annealing on the Early Hydration of Tricalcium Silicate

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It was recently proposed that the induction period observed during the hydration of tricalcium silicate could be explained by the build-up of ions in solution. Due to the importance of defects in this mechanism, this work describes the effect of different annealing effects on the defect structure and hydration behavior of C3S. The impact of annealing on the crystal structure was checked by X-ray diffraction and the defect structure studied by transmission electron microscopy. The hydration kinetics were followed by isothermal calorimetry of pastes. Scanning electron microscopy was used to look at the microstructure formation. It was observed that grinding created a highly deformed layer on the surface of the grains, which disappeared after annealing. The defect structure was closely related to the length of the induction period observed in pastes by calorimetry. There was no observable effect on the morphology of C-S-H during hydration, but the number of calcium hydroxide nuclei was less in pastes from annealed material.

Wiley-Blackwell2014

Development of a new rapid, relevant and reliable (R-3) test method to evaluate the pozzolanic reactivity of calcined kaolinitic clays

Adrian Alujas Diaz, François Henri Avet, Mohsen Ben Haha, Karen Scrivener, Ruben Anton Snellings

The present paper introduces a new rapid, relevant and reliable (R-3) test to predict the pozzolanic activity of calcined clays with kaolinite contents ranging from 0 to 95%. The test is based on the correlation between the chemical reactivity of calcined clays in a simplified system and the compressive strength of blends in standard mortar. The simplified system consists of calcined clay portlandite and limestone pastes with sulfate and alkali levels adjusted to reproduce the reaction environment of hydrating blended cements. The pastes were hydrated for 6 days at 20 degrees C or for 1 day at 40 degrees C. The chemical reactivity of the calcined clay can be obtained first by measurement of the heat release during reaction using isothermal calorimetry and second by bound water determination in a heating step between 110 degrees C and 400 degrees C. Very good correlations were found between the mortar compressive strength and both measures of chemical reactivity. (C) 2016 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2016

, ,

The effect of limestone on the hydration and microstructural development of ultra high performance concrete (UHPC) with different levels of replacement (34%, 54% and 74% by volume) was investigated. Up to 54% replacement of cement by limestone the mixes showed better workability and higher compressive strength (170 MPa at 56 days for 54% addition) compared to a classical mix (155 MPa) with no limestone replacement. The kinetics of hydration were compared for different replacement levels using isothermal calorimetry. The phase development was quantified by X-ray diffraction with Rietveld method combined with thermal gravimetric analysis. The pore structure was examined by mercury intrusion porosimetry. The composition of hydration products was determined by scanning electron microscopy with energy dispersive X-ray analysis. The results showed that the hydration degree of the cement is increased from 39% for classical UHPC to 66% for the UHPC with 54% of limestone. (C) 2016 Elsevier Ltd. All rights reserved.

Elsevier2017