Influence of chemical additives and curing conditions on the mechanical properties and carbonation resistance of alkali-activated slag composites

Abstract

The main aim of the presented work is to investigate the effect of the addition of air-entraining (AEA) and shrinkage-reducing agents (SRA) on the mechanical properties and carbonation resistance of alkali-activated slag (AAS). The materials used for the sample preparation were blast-furnace slag activated using sodium silicate and AEA or SRA in various amounts. The samples were cured in various conditions (air curing under laboratory conditions and water curing at the same temperature) and the influence of these was also studied. The prepared samples (specimens with dimensions of 100 mm × 20 mm × 20 mm) were tested for compressive and bending strengths. The experimental results show that the addition of AEA did not have a significant influence on the mechanical properties, while the addition of SRA had a negative effect. However, the carbonation resistance markedly decreases with an increase of both agents. The same is true for air curing, as mechanical strengths are lower compared to those samples cured in water, and the ratio of the strength of the air-cured composite and that of the water-cured composite decreases with an increase in the content of SRA. Keywords: alkali-activated slag, carbonation resistance, chemical additives, mechanical properties Glavni namen tega dela je preiskava vpliva dodatka za zmanj{anje vsebnosti zraka (angl. AEA) in dodatka za zmanj{anje kr~enja (angl. SRA) na mehanske lastnosti in odpornost na karbonacijo z alkalijami aktivirane`lindre (angl. AAS). Materiali za pripravo vzorcev so bili plav`na`lindra, aktivirana z natrijevim silikatom in razli~nim dodatkom AEA ali SRA. Vzorci so bili strjeni pri razli~nih pogojih (strjevanje na zraku v laboratorijskih pogojih in strjevanje v vodi pri enaki temperaturi) in {tudiran je bil njihov vpliv. Pripravljeni vzorci, z merami 100 mm × 20 mm × 20 mm, so bili preizku{eni na tla~no in upogibno trdnost. Rezultati preiskav ka`ejo, da dodatek AEA ni imel pomembnega vpliva na mehanske lastnosti, medtem ko je dodatek SRA nanje vplival negativno. Vendar pa se je odpornost na karbonacijo mo~no zmanj{ala z ve~anjem vsebnosti obeh dodatkov. Enako velja za strjevanje na zraku, saj so mehanske lastnosti slab{e v primerjavi z vzorci, strjenimi v vodi in se razmerje trdnosti vzorcev strjenih v vodi in razmerje trdnosti na zraku strjenih kompozitov, zmanj{a s pove~anjem vsebnosti SRA. Klju~ne besede: z alkalijami aktivirana`lindra, odpornost na karbonacijo, kemijski dodatki, mechanske lastnosti

Some Issues of Shrinkage-Reducing Admixtures Application in Alkali-Activated Slag Systems

“…The coarser pore structure of SRA1.0 specimens compared to those without SRA led to a modified weight loss development, with accelerated weight loss rate during the first days of drying. A slight increase in weight beyond the third day of dry air exposure is probably caused by the intense carbonation which was, together with the relatively low strengths of these air-stored specimens, presented in [ 53 ]. The importance of the pore size distribution for drying shrinkage was emphasized by Collins and Sanjayan [ 18 ] and it can thus be concluded that the great reduction of drying shrinkage induced by 1% of SRA is attributed to coarser pores, where the shrinkage forces are not so high.…”