Sulphate induced changes of rheological properties of cemented paste backfill

Abstract

The rheological properties of cemented paste backfill (CPB) are important properties, which determine its flow ability or ease of transport in pipelines to fill underground voids. However, no research has been conducted to understand the effects of the sulphate content in CPB on its rheological properties, even though sulphate ions are usually found in CPB mixtures. Evaluating and understanding the effect of sulphate on the rheological properties of fresh CPB are important in carrying out backfilling with cemented paste. Therefore, the objective of this paper is to experimentally study the effects of the initial sulphate content on the rheological properties of CPB. Samples made with two different types of tailings (silica tailings and polymetallic tailings) with an initial sulphate content of 0, 5000, 15,000 and 25,000 ppm are prepared and cured at room temperature (20 °C). Their yield stress and apparent viscosity at different curing times of 0, 0.15, 1, 2, and 4 h are determined and then analyzed. Additional tests or measurements are carried out to further investigate the experimental results, which include monitoring through electrical conductivity (EC), measuring the pH and zeta potential as well as conducing thermal and XRD analyses. The results show that the initial sulphate concentration can significantly affect the rheological properties of CPB. The initial sulphate concentration can cause different microstructural or chemical changes in fresh CPB, such as inhibition of the cement hydration process or affecting the repulsive forces between particles. These changes significantly affect the yield stress and apparent viscosity of CPB. More specifically, the yield stress shows a trend of decline as the initial sulphate concentration is increased, while the apparent viscosity shows the opposite trend. The findings of this research demonstrate the significance of sulphate and its effects on the rheological behaviors or properties of CPB and can significantly contribute to the optimization of the transport of CPB through pipelines.