Reactivity and Performance of Limestone Calcined-Clay Cement (LC3) Cured at Low Temperature

Karen Scrivener, Franco Alberto Zunino Sommariva
SPRINGER, 2018
Article de conférence

Limestone calcined-clay cements (LC3) take advantage of the synergetic effects of calcium carbonate reaction with the additional aluminium provided by the calcined clay. As temperature decreases, calcium carbonate solubility increase, therefore, the early-age hydration kinetics and the optimal proportioning of the ternary cement system are modified. This study explored the reactivity and mechanical performance of different LC3 systems cured at 10 and 20 degrees C. Mixtures containing PC, PC-limestone and a LC3 blends with 50% clinker factors and 2:1 clay-to-limestone ratio were cast and compared. Hydration kinetics were assessed using isothermal calorimetry at each of the temperatures. The evolution of porosity was studied during hydration by MIP. Compressive strength was measured over time on cement paste cubes. Phase assemblage was monitored using XRD.

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Karen Scrivener, Franco Alberto Zunino Sommariva
SPRINGER, 2018
Article de conférence

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https://infoscience.epfl.ch/record/263308?ln=fr

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Pozzolanic reactivity of low grade kaolinitic clays: Influence of calcination temperature and impact of calcination products on OPC hydration

Adrian Alujas Diaz, Rodrigo Fernandez Lopez, Karen Scrivener

The influence of thermal activation temperature in the pozzolanic reactivity of low grade kaolinitic clay and the impact of calcination products in OPC hydration are assessed in this paper. The raw material, with approximately 40% kaolinite and 40% of 2:1 clay minerals, was calcined to temperatures ranging between 500 and 1000 degrees C. The clay and its calcined products were characterized by XRD, XRF, FTIR, TGA-DTA, Al-27 NMR, PSD and BET. The pozzolanic reactivity of the calcined products and its impact on hydration of blended systems was assessed by compressive strength in mortars with 30% substitution of OPC and heat output from lime-pozzolan pastes. The influence of calcined clays on OPC hydration was characterized by XRD, Al-27 NMR and Si-29 NMR, and Isothermal Calorimetry. The increase of pozzolanic reactivity with the increase of activation temperature is limited not only by recrystallization above 900 degrees C, but also by the decrease of the specific surface that occurs between 800 and 900 degrees C. Highest pozzolanic reactivity is reached when calcined at 800 degrees C, a temperature representing the best compromise between structural disorder of the clay fraction and its specific surface. The impact of calcined clays on the hydration of blended systems is a combination of a filler effect at early ages and the pozzolanic reaction. Calcined clays favor the formation of AFm-type phases and C-A-S-H with longer chains, in which Al is substituting for Si. The experimental results indicate that clays with moderate contents of kaolinite constitute a potential source of high reactivity pozzolanic materials. (C) 2015 Elsevier B.V. All rights reserved.

Elsevier Science Bv2015

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Effect of cement substitution by limestone on the hydration and microstructural development of ultra-high performance concrete (UHPC)

Wei Huang, Karen Scrivener, Wei Sun

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

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Assessing the Effect of Calcite Impurities in Clay on Optimal Dehydroxylation Parameters for Enhanced Reactivity

Karen Scrivener, Franco Alberto Zunino Sommariva

This study focused on understanding the influence of different amounts of calcite impurities (0 to 10% by mass) on the optimal parameters for clay dehydroxylation and the reactivity of the final calcined clay. A surface response experimental design was used to study the effect of maximum temperature, residence time and calcite content on different experimental responses. Specific surface and particle size distribution were used to characterize the physical properties of the calcined-clays. SEM coupled with EDS was selected to study the particle morphology and the composition of the amorphous phase formed, while XRD was used to assess the mineralogical composition after calcination. TGA analysis was used to measure the remaining amounts of kaolinite and calcite after calcination, while isothermal calorimetry was used to assess the reactivity of the different calcined-clays obtained. It was observed that specific surface area is the most sensitive parameter to variations in calcite content.

SPRINGER2018

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