Title: Evaluating Alternative Binder Materials for Sewer Collection System Concrete Structures to Reduce Fat, Oil, and Grease Related Sanitary Sewer Overflows

摘要

The accumulation of fat, oil, and grease (FOG) in sewer pipes reduces its carrying capacity and results in Sanitary Sewer Overflows (SSOs). Previous studies have shown that FOG deposits are formed from a saponification reaction between calcium and long chain free fatty acids (LCFFA). This study aims to evaluate the contribution of FOG deposit formation from the corrosion of concrete materials. In particular, we explore the use of class F Fly Ash (FA) as an alternative binder material that can reduce or eliminate calcium leaching from sewer line construction materials and eventually reduce FOG related SSOs. In this study, two High Volume Fly Ash (HVFA) portland cement paste samples CP50FA, CP75FA with 0.42 water to cement (w/c) ratio were cast using 50% and 75% replacement of cement by fly ash (FA), respectively. Pure cement paste specimens (CPOFA) were also cast. Among the various constituents of cement, calcium hydroxide (CH) is the major component releasing calcium ion readily. A pozzolanic reaction between alumino-silicates from FA and Calcium Hydroxide (CH) from cement takes place to transform CH into a stable constituent known as Calcium-Silicate-Hydrate (CSH). Thermogravimetric Analysis (TGA) tests were performed on both HVFA samples and pure cement paste and results revealed that the CH content of CP50FA and CP75FA samples at the age of 135 days was 9% and 1%, respectively, compared to 24% for the pure cement paste sample. A dissolution test was performed for 40 days at pH 7 to assess the calcium leaching potential of the samples. After 40 days, the leachate calcium concentration of CPOFA, CP50FA, and CP75FA were 14.0, 4.3 and 2.5 mg/l/g respectively. The preliminary results of this study suggest that a significant decrease in calcium release can be achieved through the use of fly ash as cement replacement for the production of alternative binder materials with low calcium content. This strategy could be a sustainable solution for the reduction of FOG related SSOs, maintenance, and clean-up costs. Additionally, this study, if incorporated, would be able to reduce potential adverse environmental effects from coal-fired power plants by-products by recycling FA.