Water Treatment Sludge-Calcium Carbide Residue Geopolymers as Nonbearing Masonry Units

In this research, water treatment sludge (WTS) calcium carbide residue (CCR) geopolymers were evaluated as a sustainable masonry nonbearing unit. The WTS was a by-product from a water treatment plant, whereas CCR was a by-product from an acetylene gas factory in Thailand. Sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3) were used for the geopolymerization process. The unconfined compressive strength (UCS), water absorption, and durability of WTS-CCR geopolymer were studied in this research. The test results indicate that the optimal liquid alkaline activator (L)/CCR ratios provided the maximum unit weight decrease with CCR contents for all of the Na2SiO3/NaOH ratios evaluated. The optimal L/CCR ratios were found to be 16, 8, 5.33, 4, 3.2, and 2.67 for CCR contents of 5, 10, 15, 20, 25, and 30%, respectively. The Na2SiO3/NaOH ratio of 70: 30 was found to give the highest maximum unit weight and UCS among all of the WTS/CCR ratios tested. Three zones of UCS development with CCR content were evident: the active, inert, and deterioration zones. In the active zone, the UCS increased significantly as the CCR content increased, and the maximum UCS was attained at 10% CCR. In the inert zone, the UCS development was gradual. When the CCR content was more than 20% in the deterioration zone, a subsequent strength decrease was observed. The wet-dry (w-d) cycle strength, UCS(w-d), depends primarily on the initial soaked strength, UCS0. A UCS(w-d) predictive equation was proposed for the assessment of initial strength to attain the required w-d strengths. Based on the UCS and water absorption requirements, an optimum ingredient consisting of 10% CCR and 70:30 Na2SiO3/NaOH at room temperature curing can be recommended for nonbearing masonry units. (C) 2017 American Society of Civil Engineers.