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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 | Year: 2016

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.

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 | Year: 2014

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.

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 | Year: 2016

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.

Kucharczyk S.,AGH University of Science and Technology | Zajac M.,Heidelberg Technology Center GmbH | Deja J.,AGH University of Science and Technology
Procedia Engineering | Year: 2015

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.

Kucharczyk S.,AGH University of Science and Technology | Deja J.,AGH University of Science and Technology | Zajac M.,Heidelberg Technology Center GmbH
Journal of Advanced Concrete Technology | Year: 2016

This work investigates the role of alumina content in the slag and presence of limestone in composite cement on the hydration and compressive strength evolution of composite cement. A coupled experimental and modeling approach was applied. Increasing A1;0; content of slag from 8 % to 12 % has pronounced impact on slag kinetics while further increase from 12 % to 16 % has a limited effect. However, this increase affects the hydrates assemblage across the whole composi-Tional range investigated; the composition of the C-S-H phase and hydrotalcite is modified. Additionally the AFm and AJFt phases content changes. Presence of limestone has a pronounced impact on the hydration, being more pronounced for the slags of high alumina content. Tins is related to the formation of hemi-And mono-carbonate and stabilization of ettringite. Despite of these changes, the pore size distribution is similar among the investigated cements. Thermody-namic modelling matches favorably the experimental data and enables calculating the evolution of the pore volume over the time. A relationship between calculated porosity and compressive strength is proposed and verified. Tins relationship shows that all hydrated phases have a similar impact on compressive strength and the strength is mainly related to the pore volume. © 2016 Japan Concrete Institute.

Whittaker M.,University of Leeds | Zajac M.,Heidelberg Technology Center GmbH | Ben Haha M.,Heidelberg Technology Center GmbH | Bullerjahn F.,Heidelberg Technology Center GmbH | Black L.,University of Leeds
Cement and Concrete Research | Year: 2014

The effects on composite cements of the aluminium content of slag, plus that of additional sulfate, have been investigated. Samples containing cement or composites with 40% replacement by one of 2 different slags, differing in aluminium contents, were prepared. A further blended sample was prepared with additional anhydrite replacing 3% w/w of binder. Slag blended mortars showed comparable strengths to the neat cement system at later ages. Adding slag changed the hydration kinetics of the clinker phases. The addition of sulfate had no effect on slag reactivity but increased that of alite. Slags richer in aluminium resulted in greater incorporation of aluminium into C-S-H and encouraged the presence of hemicarboaluminate over monocarboaluminate. The Ca/Si ratios of the C-S-H formed were comparable between the two blends, being marginally lower than that of the neat system. The addition of anhydrite resulted in the adsorption of sulfate onto the C-S-H, plus stabilisation of ettringite. © 2014 Elsevier Ltd.

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 | Year: 2015

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.

Zajac M.,Heidelberg Technology Center GmbH | Skocek J.,Heidelberg Technology Center GmbH | Bullerjahn F.,Heidelberg Technology Center GmbH | Ben Haha M.,Heidelberg Technology Center GmbH
Cement and Concrete Research | Year: 2016

The retardation of calcium-sulpho-aluminate (CSA) type cements by three common retarders - sodium gluconate, sodium-potassium tartrate and borax is investigated at a 2% addition rate. Each of the retarders has a different effect on the early-age hydrate assemblage, as shown by quantitative X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and pore solution analysis. Regardless of the retarder used, the hydration starts with mainly the dissolution of ready soluble (calcium) alkali sulphates and ye'elimite, followed by the formation of ettringite and aluminium hydroxide, whereby the specific clinker mineral dissolution as well as ettringite-forming reaction is delayed in different ways depending on the retarder used. The results showed that the retardation is mainly caused by preventing hydrates formation in the case of tartrate and gluconate. Contrary, borax retards the hydration by preventing to a certain extent the dissolution of ye'elimite and lowers the initial pH. Furthermore, the morphology of ettringite is altered depending on the type of the retarder used. © 2016 Elsevier Ltd. All rights reserved.

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