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
Pergamon-Elsevier Science Ltd, 2016
Journal paper

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.

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Adrian Alujas Diaz, François Henri Avet, Mohsen Ben Haha, Karen Scrivener, Ruben Anton Snellings
Pergamon-Elsevier Science Ltd, 2016
Journal paper

Abstract

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https://infoscience.epfl.ch/record/221774?ln=en

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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

Rapid, Robust, and Relevant (R3) Reactivity Test for Supplementary Cementitious Materials

François Henri Avet, Xuerun Li, Karen Scrivener, Ruben Anton Snellings

Although supplementary cementitious materials (SCMs) are now commonly accepted and widely used, consensus has not been reached for methods to test their chemical reactivity. A multitude of test methods exist but often fall short on one or more of the key features of a proper test-that is, width of scope, practicability, reproducibility, and relevance of the result. A rapid, robust, and relevant chemical reactivity test applicable to a wide range of SCMs would therefore not only serve as global benchmark but it would also remove present ambiguities in regards to classification. In response, a new, so-called "R3" test was conceived at Ecole Polytechnique Federale de Lausanne and is now being further developed and tested in RILEM TC 267 TRM, The test method was initially based on a screening of calcined clays in portlanditealkali-sulfate systems by isothermal calorimetry. Subsequently, the system formulation was more systematically studied and compared to strength development of blended cement mortar bars for a wide range of calcined kaolinitic clays. Remarkably good correlations between strength development and heat release were found. This was confirmed for other Sells and other measurable system properties. In particular; bound water content and chemical shrinkage correlated remarkably well to the isothermal calorimetry results. The origin of this correspondence can be traced back to the hydration reaction. Indeed, it is the solidification of water that directly links heat release; chemical shrinkage; and, obviously, bound water content. This contribution traces back the origins and the first inroads leading up to the present state of development of the test method and concludes on future perspectives.

AMER CONCRETE INST2019

Hydration of C(3)A-gypsum systems

Alexandra Quennoz, Karen Scrivener

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.

2012

Clay

Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, Al2Si2O5(OH)4). Clays develop plasticity when wet but can be harde

Compressive strength

In mechanics, compressive strength (or compression strength) is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loa

Kaolinite

Kaolinite (ˈkeɪ.ələˌnaɪt,_-lɪ- ) is a clay mineral, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms t