Effect of sulfonated acetone formaldehyde on the properties of high-fluid backfill materials

Abstract

High-fluid backfill materials (HFBMs) can overcome the limitations of traditional backfills and increase the utilization rate of construction spoils, whose necessary step is to obtain a suitable water-reducing agent, which can reduce water consumption and improve the performance of backfills. However, polycarboxylate superplasticizers (PCE) cannot effectively reduce water consumption in soils. Therefore, sulfonated acetone formaldehyde (SAF) was mixed with HFBMs to investigate their working performance, mechanical properties, and microstructure. The water reduction mechanism was also addressed. The results show that unlike PCE, SAF did not fail in the presence of soil. Moreover, it was able to adsorb and disperse soil and cement particles, thereby reducing mixing water requirements which was verified by the experiments of absorption properties of montmorillonite, particle size analysis and zeta potential of spoil sample. The working performance, mechanical properties, and pH of the leaching solution were enhanced at a higher SAF content. The mixing water requirement decreased by 41.67% at a SAF content of 3.0% for similar working fluidities (190 ± 5 mm). The compressive strength and dry density of the testing block were 2.32 MPa and 1628 kg/m3, respectively. The highest pH of the leaching solution led to a larger content of gelatinous material and needle-rod ettringite crystals with a compact microstructure. However, longer setting times were obtained when SAF was added in excess, due to the formation of an oil film on the surface and retarding ability of cement hydration. The shortest setting time was obtained at a SAF content of 1.5%. An engineering test demonstrated that the strength of an extracted testing block was approximately 500 kPa. In addition, a backfill section obtained with the samples exhibited a dense foundation, few cracks and cavities, and an excellent performance.