Abstract
The influence of the electrostatic precipitator ash “Zolest-bet” and silica fume on the sulfate resistance of Portland cement was studied. The evaluation criteria were the expansion, strength, density, and appearance of the samples, hardened in a 5% Na2SO4 solution starting from 3 days of age for 192 days at a temperature of 20 °C and 148 days at 40 °C. The mixture with the silica fume additive had the minimum expansion under the Na2SO4 action, and the mixture with the fly ash “Zolest-bet” additive had the greatest expansion. Zolest-bet ash in pure water shrank the mixture by 0.19 mm/m by the end of the hardening period, and it gave a linear expansion of 0.23 mm/m in a Na2SO4 solution after hardening. The mixture can be considered sulfate resistant at a given value of linear expansion. Despite the greatest expansion, the compressive strength of the samples with the Zolest-bet additive was found to be the highest at hardening in both environments. The flexural strength was found to be the highest after being in Na2SO4 solution. The sulfate resistance of the mixture with silica fume was higher than that of the mixture based on sulfate-resistant cement. This mixture did not have expansion in comparison with the initial length, instead it shrank, while the expansion of sulfate-resistant cement was 0.006% over the control period. The compressive strength of the mixture with the silica fume additive was slightly inferior to the strength of the mixture with Zolest-bet ash.
Highlights
The article contains research on sulfate resistance as a critical aspect of durability
Fly ash is used as a partial replacement for Portland cement to improve the strength and sulfate resistance of concrete [4,5,6], as well as to obtain artificial aggregates [7,8]
The hardening of all cement mixtures in water was accompanied by shrinkage
Summary
The article contains research on sulfate resistance as a critical aspect of durability. Fly ash is used as a partial replacement for Portland cement to improve the strength and sulfate resistance of concrete [4,5,6], as well as to obtain artificial aggregates [7,8]. There is evidence of a significant decrease in the diffusion rate in places where fly ash is present, as well as stabilization of calcium aluminate hydrates, which leads to an increase in resistance to sulfate attack. Fly ash is usually replaced by 15–35% of cement by weight. This range is acceptable for replacement without a significant negative impact on concrete performance. Fly ash is divided into low-calcium fly ash with a CaO content of no more than 18% (class F) and high-calcium fly ash with a CaO content of more than 18% (class C) according to ASTM C618 [10]
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