External ammonium sulfate attack in concrete: Analysis of the current methodology

• DOI: 10.1016/j.conbuildmat.2021.122252
• Publication Date: 2021-01-26T10:11:19Z
• Authors: Monalisa C. Martins; Eloise A. Langaro; Gustavo Macioski; Marcelo H.F. Mede...
• Keywords: Cementitious; Silica fume; Ammonium sulfate; Sodium sulfate

Abstract The standards ASTM 1012 (2013) and NBR 13583 (2014) report the procedure for the evaluation of concrete subjected to sulfate attacks. However, the standards were based on sodium sulfate studies. This paper demonstrates that the methods suggested by the aforementioned standards may not be applicable to external attacks of ammonium sulfate. This paper aims to evaluate the effect of partial replacement (15%) of Portland cement by two supplementary cementitious materials (silica fume and rice husk ash). The concentration of the aggressive ammonium sulfate solution used in this study was 9.3%, as suggested by NBR 13583. The ASTM 1012 (2013) standard suggests half of this concentration. Complementary tests (mechanical and microstructural) were performed on samples that were monitored for 182 days. After this period, samples without addition and immersed in ammonium sulfate solution showed a 40% reduction in compressive strength when compared with reference samples. Samples with supplementary cementitious materials showed a reduction in the effects of degradation. However, these showed high precipitation of gypsum on the surface. The results of the microstructural tests demonstrated that the silica fume was more effective in the mitigation process. The expansion tests were inconclusive due to the sample surface degradation. Therefore, the results suggest that additional and more appropriate methods are needed for the evaluation of concrete when it is subjected to an external attack of ammonium sulfate.