Understanding of the deterioration characteristic of concrete exposed to external sulfate attack: Insight into mesoscopic pore structures

Abstract

Sulfate attack-induced deterioration on concrete begins with significant expansive forces generated at the narrow mesoscopic pore-level. However, the corresponding mesoscopic deterioration characteristic of concrete under different types of sulfate exposure remains uncertain. This experimental study devoted to provide a fundamental understanding on the possible alteration of the mesoscopic pore structures in concrete caused by chemical sulfate attack (CSA) and physical sulfate attack (PSA), by using a nondestructive testing technology. Results indicated that at the early stage of sulfate exposure (0–3 months), the sulfate attack reaction products attempted to fill most categories of mesoscopic pore structures (most categories of pores and pore throats) in concrete specimens exposed to CSA, but they preferred to abundantly accumulate in relative larger pores (e.g. Detrimental Pore III, DP-III) in concrete suffered from PSA. At the middle and later stages of exposure (3–9 months), the deterioration of concrete specimens under PSA was characterized by the rapid formation of the smaller pores (DP-I and DP-II) and the smaller pore throats (PT-I and PT-II), while the situation was just the reverse under CSA condition. In addition, suggestion was made that intentional reducing the initial volumes of DP-III (pores with 1–100 µm in diameter) in concrete by appropriate methods may significantly enhance the sulfate resistance of concrete materials suffered from physical attack.