The role of the alumina content of slag, plus the presence of additional sulfate on the hydration and microstructure of Portland cement-slag blends

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract: The effects on composite cements of the aluminium content of slag plus that of additional sulphate, has 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 sulphate 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 hemicarbonate over monocarbonate. 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 sulphate onto the C-S-H, plus stabilisation of ettringite. Corresponding Author 8 9 The Role of the Alumina Content of Slag, plus the Presence of AdditionalAbstract 10 The effects on composite cements of the aluminium content of slag plus that of additional sulphate, 11 has been investigated. Samples containing cement or composites with 40% replacement by one of 2 12 different slags, differing in aluminium contents, were prepared. A further blended sample was 13 prepared with additional anhydrite replacing 3%w/w of binder. Slag blended mortars showed 14 comparable strengths to the neat cement system at later ages. Adding slag changed the hydration 15 kinetics of the clinker phases. The addition of sulphate had no effect on slag reactivity but increased 16 that of alite. Slags richer in aluminium resulted in greater incorporation of aluminium into C-S-H and 17 encouraged the presence of hemicarbonate over monocarbonate.

Phase modification induced drying shrinkage reduction on Na2CO3 activated slag by incorporating Na2SO4

“…Besides, hemicarboaluminate (PDF #00-036-0129), also named hemicarbonate, is also observed [35]. The existence of this phase indicates that the system is abundant with aluminum because the Mg content is not sufficient to consume all Al 2 O 3 , forming hydrotalcite [35][36][37]. Similar phenomenon was also reported by Ke et al [35], which is due to the preference of forming layered double hydroxide structures.…”

Current knowledge of external sulfate attack

“…The work found an optimum sulfate content, beyond which sample resistance worsened due to increased susceptibly to volume instability. The use of additional gypsum favours ettringite precipitation over AFm phases at early ages, before the occurrence of sulfate attack (Whittaker et al, 2014). With more of the original aluminium now bound, less is available to subsequently react with sulfates.…”

Effect of Slag Reactivity Influenced by Alumina Content on Hydration of Composite Cements

“…The dissolution of the clinker phases was mathematically described using the Parrot and Killoh equations (Parrot and Killoh 1984). The parameters of the equations were adapted to the kinetics of the cement clinker dissolutions shown in paper (Whittaker et al 2014) that investigates similar systems. For all three investigates slags, the same kinetics of cement clinker was calculated.…”

“…Blast furnace slags contain more Al 2 O 3 than Portland cement clinker, however, significantly less Al 2 O 3 than fly ash or metakaolin. Despite the lower alumina content, more AFm and AFt phases might be formed in the Portland cement -slaglimestone blends due to the higher hydration degree of the slag (Kocaba et al 2012;Whittaker et al 2014;Hoshino et al 2006) when compared to the fly ash. This effect is counter by the fact that more Al is bound in the C-S-H and hydrotalcite like phase (Richardson and Groves 1997;Taylor et al 2010;Lothenbach et al 2011).…”