Metakaolin as aluminum source in Supersulfated Cement

Reference Presenter Authors
04-043 Caroline Angulski da Luz Volkweis, L.(UTFPR); Angulski da Luz, C.(UTFPR); Pereira Filho, J.I.(UTFPR); Bortolozzo, P.H.(UTFPR); Mantelli, D.F.(Universidade Tecnológica Federal do Paraná); Perardt, M.(UTFPR); Metakaolin is a material derived from the calcination of kaolinite clays (kaolin) whose predominant composition is hydrated aluminum silicate (Al2Si2O5(OH)4). While kaolin is widely employed by the ceramic industry, the use of metakaolin has been growing in the cement industry as pozzolanic material in Portland cements. Considerable attention has been given to special cements, which can reduce CO2 emissions and, consequently, reduce the impacts caused by the cement industry. Supersulfated cements (SSCs) are composed from blast furnace slag (90-80%), calcium sulfate (10-20%) and an alkaline activator, which may be Portland cement or hydroxides. SSCs have their performance influenced by the percentage of alumina present in blast furnace slag. Slags with higher alumina content (greater than 13%) form more hydrated product and less pores, resulting in a higher compressive strength. In Brazil, the slag has a medium content of alumina (7 to 11%). The goal of this article was to investigate the metakaolin as source of alumina in supersulfated cements in order to achieve greater compressive strength. SSCs were prepared with 85% blast furnace slag, 15% calcium sulfate and 5% of Portland cement (as activator). The metakaolin was used as a replacement of slag in 5, 10 and 20%. The compressive strength and the formation of the hydrated compounds were investigated at 7 and 28 days. It is expected that SSC with higher proportions of metakaolin present higher formation of ettringite and consequently higher compressive strength.
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