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Sustainable Materialisation of Residues from Thermal Processes into Construction Materials : Construction materials from stainless steel slags

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The amount of slag generated is almost athird of the total stainless steel produced. Owing to its mineralogy, a large partof the slag is produced as fines, which has a very low valorisation potentialand has to be landfilled. The present work is aimed at exploring the potentialof these slags to produce construction materials of higher economic value.To address the issue, two valorisationroutes were applied: 1) alkali-activation initiating binding reactions in theslag by the addition of alkali hydroxides and silicates, 2) carbonation initiating hardening reaction in the slag by the formation of alkalicarbonates. Two stainless steel slags, continuous casting (CtCs) slag and Argonoxygen decarburisation (AOD) slag, were targeted for valorisation.Initiation of hardening reactions in theslag was found to occur only under a combined treatment of alkali (Na and K)hydroxides and high temperature (80 &#176;C) which was provided by steam curing. However,only a moderate strength in the mortar specimens was observed under suchconditions along with appearance of efflorescence with NaOH for molaritiesabove 5 M. The problem of low strength and efflorescence in the mortar sampleswas eliminated by the introduction of silicates in the system along with thealkali hydroxides. The compressive strength of the slag mortars was found toincrease with the increase in the amount of silicates in the activatingsolution and with the increase of the curing temperature. The reaction productfrom the activation was found to be C-S-H as confirmed by thermogravimetric,QXRD, FTIR and 29Si NMR analysis.The slag was also found to develop strengthunder acceleration carbonation conditions which was provided under two environments:i) in a carbonation chamber, maintained at atmospheric pressure, 22 &#176;C, 5 vol.%CO2 and 80% RH; and ii) in a carbonation reactor, where the CO2partial pressure (pCO2)and temperature could be further increased. It was found that in thecarbonation chamber the compressive strength of the samples and the CO2sequestration continued to increase up to 3 weeks whereas in the reactor theoptimum for strength and CO2 sequestration was found at 80 &#176;C, 8 barpressure in 2.5 h. The major reaction product was found to be calcite indifferent morphologies.Three types of masonry blocks were preparedform the slag with the two valorisation routes: alkali-activated solid bricks,perforated carbonated bricks and alkali-activated aerated bricks. Thecarbonated bricks were found to have the best resistance to freeze-thaw,whereas the aerated bricks were found to have superior thermal resistivity values.The LCA showed that the environmental impact of the bricks is lower (negativefor carbonated bricks) than the conventional clay fired bricks and the impactof the aerated bricks was found to be similar to the conventional aeratedblocks available in the market. A SWOTanalysis highlighted the advantage of using these bricks in the form of lowerenergy requirement in its production, reduction of stress on the use of prime materialsand ease of metal recovery from the residual slag.The results of the dissertation show that thebinding potential of the stainless steel slags can be exploited as valorisedapplications in the construction industry by novel thermo-alkali activation andcarbonation processes.


Book
Targeted research action Environmentally friendly construction technologies : state-of-the-art and market review 1997/1998.
Author:
Year: 1998 Publisher: Brussels European council for construction research, development and innovation,

The Ecology of building materials
Authors: ---
ISBN: 0750654503 Year: 2003 Publisher: London Architectural press,

Handbook of sustainable building : an environmental preference method for selection of materials for use in construction and refurbishment.
Authors: --- ---
ISBN: 1873936389 Year: 1996 Publisher: London James & James


Book
Material revolution : sustainable multi-purpose materials for design and architecture
Author:
ISBN: 9783034606639 9783034605755 303460663X 3034610777 Year: 2011 Publisher: Basel : London : Birkhäuser ; Springer [distributor],

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Since it is now clear that in the future many raw materials will only be available to us in limited quantities, scientists have for some time been conducting intensive research into possible alternatives. Sustainability is the order of the day and the magic word for a better future in politics and industry. Moreover, environmental consciousness and a penchant for thinking in terms of material cycles have caught on with consumers: the use of environmentally compatible materials and production methods is desired, even taken for granted by the client. Designers and architects thus have a special

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