Engineering Properties of Cemented Paste Backfill with Full-Range Water-Reducing Admixture

This paper presents the effects of a full-range water-reducing (FRWR) admixture on the key engineering properties of cemented paste backfill (CPB). CPB samples with a certain slump are prepared with 4.5% cement by mass of the tailings and different dosages of an FRWR admixture (superplasticizer contents of 1%, 3%, and 5%) to evaluate their water demand during hydration, rheological properties, self-desiccation ability, and microstructural and mechanical properties. Moreover, cement paste samples with a high water-to-cement ratio (w/c = 2) which are used to model the cement matrix of the CPB are prepared for x-ray diffraction (XRD) scanning and thermal analyses (TAns). The results show that the addition of an FRWR admixture to the studied CPB can reduce its water demand by up to 23% and significantly increase its strength from 1.0 MPa to 2.38 MPa (by approximately 2.4 times) at 28 days. The pore volume of the CPB samples is also significantly reduced from 27.17 to 18.27% due to the capability of the FRWR admixture to reduce water demand. Also, the addition of an FRWR admixture to the CPB results in a substantial decrease (up to 83%) of its yield stress, thereby improving its flowability. The CPB samples with an FRWR admixture are found to have a higher negative pore water pressure, i.e., higher self-desiccation, than the CPB sample without an FRWR admixture. The microstructural analysis also shows that the FRWR admixture has an increasing effect on the hydration products in the CPB mixture.