Title: Investigating Dual Sulfate Attack Mechanisms using Unidirectional Penetration Approach

Author(s): Qiao Wang, William Wilson, and Karen Scrivener

Publication: Symposium Paper

Volume: 349

Issue:

Appears on pages(s): 623-628

Keywords: Degradation ; Humidity ; Sulfate attack ; SEM ; Unidirectional approach

DOI: 10.14359/51732777

Date: 4/22/2021

Abstract:
Sulfate attack is generally classified into chemical and physical sulfate attack. It is significantly different from lab ponding tests, instead, so called physical sulfate attack dominates in semi-immersed conditions which primarily occurred in field. However, due to its greater complexity, it has been strongly neglected and less investigated. This paper concerns developing a new test approach for physical sulfate attack degradation investigation and understanding the mechanisms behind it. The new test setup allowing unidirectional flow that enables to study it under controlled conditions (i.e., constant wicking action over fixed thickness with fixed relative humidity). To imitate the real field condition, sodium sulfate solution was used in contact with one side and refreshed every month, on the other side the relative humidity was controlled at 55 %. portland cement paste specimens were used with the proposed setup in the semi-immersed conditions to investigate the effect of w/c on sulfate attack. After several months of exposure to 30 g/L sulfate solution, the profile of sulfate ingression and phase assemblage was investigated by SEM-EDS and XRD, respectively. The lateral expansion and physical appearance of the samples were tracked over time. The results indicated physical and chemical sulfate attack occurred simultaneously on both sides of single sample and mechanisms and parameters involved were further discussed.