Influence of fly ash with low content of 3CaO·Al2O3 on the sulfate resistance of Portland cement

Abstract

This paper presents an investigation of the resistance to the influence of sulfate solutions conducted on three kinds of Portland cement with rather high content of 3CaO·Al2O3 (5.45-11.84 wt%). Also, the paper considers the resistance of all cements blended with 30 wt% of fly ash whose 3CaO·Al2O3 content was almost negligible so as to lower the 3CaO·Al2O3 content of the mixtures to 3.82-8.29 wt%. Experiments were conducted on a 3×2 series of test samples prepared in accordance with Kind's method (GOST 4798-69). Then, they were exposed to the influence of aggressive solutions with 1 and 2 kg/m3 of SO42- ions as well as 0.320 kg/m3 of NH4+ ions. Also, pure water was used as a neutral fluid. The experiments lasted six months, while flexural strengths were measured after 1, 2, 4 and 6 months. By dividing the flexural strength of corroded samples with the strength of a referent ones a kind of corrosion resistance factor was obtained as a numerical quantifier of a sample's quality. The results were analyzed separately; no-ash samples and ash samples were considered to be two different systems. The behaviour of each (under the influence of both ions from the solutions in two concentrations) was considred. The samples with fly ash proved generally more resistant for all concentrations and durations of the degradation.