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Avet F.,Ecole Polytechnique Federale de Lausanne | Snellings R.,Ecole Polytechnique Federale de Lausanne | Snellings R.,Flemish Institute for Technological Research | Alujas Diaz A.,Santa Clara University | And 2 more authors.
Cement and Concrete Research

The present paper introduces a new rapid, relevant and reliable (R3) 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 °C or for 1 day at 40 °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 °C and 400 °C. Very good correlations were found between the mortar compressive strength and both measures of chemical reactivity. © 2016 Elsevier Ltd. All rights reserved. Source

Kucharczyk S.,AGH University of Science and Technology | Zajac M.,Heidelberg Technology Center GmbH | Deja J.,AGH University of Science and Technology
Procedia Engineering

In the present contribution, the interaction between limestone and slag is investigated by a multi-method approach using chemical shrinkage, thermogravimetry, scanning electron microscopy (SEM) techniques and compressive strength measurements. The impact of limestone was investigated in blends containing synthetic slags of different alumina content. The results are correlated with the thermodynamic modelling in order to gain further insights into the physical and chemical processes governing the interaction between limestone, slag and Portland cement. Beyond 28 days of hydration, slag composites exhibit higher compressive strength values than their equivalent with quartz. Increasing the Al2O3 content from 8 to 12% in slag influenced compressive strengths positively at all hydration times. Further increase of alumina in slag to 16% has no positive effect on strength. Addition of limestone, results positively only on early compressive strengths. After 28 days and longer effect of limestone is either slightly negative or neutral. Only in the case of the slag containing 16% of alumina, limestone has positive impact on the late compressive strength. The effect of limestone has two main components: physical, so called filler effect and chemical that depends on the slag composition. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. Source

Whittaker M.,University of Aberdeen | Whittaker M.,University of Leeds | Zajac M.,Heidelberg Technology Center GmbH | Ben Haha M.,Heidelberg Technology Center GmbH | Black L.,University of Leeds
Construction and Building Materials

Slag cement pastes prepared with either 40% or 70% of slags by weight were prepared (W/B = 0.5) and subsequently exposed to a 3 g L-1 Na2SO4 solution. The slag cements were shown to be more resistant. Initially, ettringite levels rose, then plateaued upon carbonate AFm consumption, although monosulfate was also found to be in equilibrium with ettringite when using an Al-rich slag. Portlandite was initially consumed, to form ettringite, but leached out after prolonged attack until it was fully depleted, or nearly, with subsequently C-A-S-H being decalcified. Any excess aluminium released by the slag was bound to a calcium deficient C-A-S-H phase and hydrotalcite, sheltering the aluminates from ingressing sulfates. Mass balance further revealed that, if the slag in the blends were to fully dissolve to form C-A-S-H and hydrotalcite, there would have been insufficient aluminium and calcium to combine with sulfates to form ettringite. Rather, calcium from C-A-S-H would have continuously leached, leaving behind a silicate skeleton. © 2016 Elsevier Ltd. All rights reserved. Source

Link T.,Bauhaus University Weimar | Bellmann F.,Bauhaus University Weimar | Ludwig H.M.,Bauhaus University Weimar | Ben Haha M.,Heidelberg Technology Center GmbH
Cement and Concrete Research

This study investigates the production of highly reactive dicalcium silicate Ca2SiO4 (C2S). To that end, binders were synthesised by annealing of alpha-dicalcium silicate hydrate (α-C2SH) between 400 and 800°C. Two different heating sequences were tested. The phase compositions were determined by means of XRD. Depending on the annealing temperature and the heating conditions the cementitious materials consist of an X-ray-amorphous content as well as x-Ca2SiO4 (x-C2S) and γ-Ca2SiO4 (γ-C2S). The hydration kinetics of someselected binderswere investigated by means of isothermal calorimetry. The specific reactivity of thephases produced by means of annealing was determined during the first 40 h of hydration by use of XRD and TGA. The resulting binders show the highest reactivity when low annealing temperatures (<500°C) were used. After 72 h, degrees of hydration of about 89% are achieved. The most reactive component is the X-ray-amorphous content, followed by x-C2S. © 2014 Elsevier Ltd. All rights reserved. Source

Zajac M.,Heidelberg Technology Center GmbH | Bremseth S.K.,Norcem AS RandD | Whitehead M.,Heidelberg Technology Center GmbH | Ben Haha M.,Heidelberg Technology Center GmbH
Cement and Concrete Research

The effect of additions of limestone and dolomite powder on the properties of blended cements cured at 40 and 60 °C was investigated using a multi-method approach. The presence of limestone leads to the formation of hemi- and mono-carbonate and to the stabilization of ettringite at 40 °C. An increase of temperature to 60 °C results in the destabilization of ettringite and formation of monosulfate in the limestone cement. The dolomite is almost depleted in the cementitious matrix over the hydration time at the studied temperatures. As a result, the formation of hydrotalcite is observed which binds part of the alumina from clinker dissolution. At 60 °C, no monosulfate is found and the CSH contains less alumina in the presence of dolomite in comparison to when limestone is present. The dolomite dissolution increases the strength at higher temperatures as a result of the additional hydrotalcite formation. © 2014 Elsevier Ltd. Source

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