Deterioration of Cementitious Materials in Wastewater Treatment Plants’ Pumping Stations and Sand-Trap Structures

Abstract

Wastewater treatment plants (WWTPs) are critical infrastructures for wastewater management, and their durability is crucial. Due to their excellent water tightness and strength, cementitious materials are used to build WWTPs. However, the performance of these materials is affected by aggressive environments. There are few in situ experiments in the literature regarding the deterioration of cementitious materials in WWTPs. This paper investigates their deterioration mechanisms in a sewage pumping station and a sand-trap structure of a WWTP. In situ experiment was conducted by exposing cement specimens in both locations for 1, 2, 3 and 7 months. The physical and morphological changes of the specimens were examined using stereo microscopy and scanning electron microscopy, whereas the mineralogical/solid phase changes were examined using X-ray diffraction. The results showed that the specimens from the pumping station formed colored surface products, which were confirmed to be secondary minerals (i.e., gypsum and ettringite), whereas there were no colored surface products in the sand-trap structure. The results demonstrated that cementitious materials subjected to wastewater vapors (in a pumping station) had higher deterioration effects than those subjected to wastewater liquid (in a sand-trap structure), suggesting that the wastewater vapors are more aggressive toward cementitious materials than wastewater liquids.