Effect of Sodium Sulfate Content on Engineering Properties of Artificial Aggregate Made from Cement and Fly Ash

This paper presents an experimental investigation in terms of sodium sulfate (Na2SO4) content effect on engineering properties of artificial aggregate made from Portland cement and a high amount of fly ash (i.e., artificial fly ash aggregate—FAA). The FAA was formed by a cold method with three ratios of fly ash-to-binder of 85%, 90%, and 95%, and several Na2SO4 contents of 0%, 1%, 2%, 3%, and 4% by mass of binder. After curing in water for 3, 7, and 28 days, the engineering properties including compressive strength of the FAA matrix, water saturation, crushing value, and density under saturated surface dry (SSD) condition of FAA were tested to find out the optimal fly ash-to-cement ratio and Na2SO4 content for FAA fabrication. The results showed that using Na2SO4 as an activator significantly improved the compressive strength of FAA matrix. Most of the FAA matrix using 2% Na2SO4 showed the significantly improved compressive strengths at 7, 14, and 28 days, while the FAA matrix with the ratio of fly ash-to-binder of 85% and 4% Na2SO4 gave the best compressive strength results at 14 and 28 days. When compared with the crushed stone, the water saturation of FAA was significantly higher about 12–27 times, its crushing value was 2–4 times higher, whereas its density in the SSD state was lower by 16.60–22.22%. In conclusion, the FAA made from 15% Portland cement and 85% fly ash activated by 2% Na2SO4 in this study had the acceptable engineering properties to partially replace crushed stone in the concrete production.