Strength and suction development of nano-cemented paste tailings materials

This paper presents an experimental study of the strength and suction development of cemented paste backfill (CPB), which is an innovative cementitious construction material for mining (made by recycling mine waste into a construction material), and modified with nanoparticle (NP) additives. The effects of different amounts of four types of NP additives, including nano-silica (SiO₂), nano-calcium carbonate (CaCO₃), nano-iron oxide (Fe₂O₃), and nano-aluminum oxide (Al₂O₃), on the key engineering properties of CPB are investigated. An ether-based polycarboxylate superplasticizer (SP) is added to the backfill to help the NPs to better disperse in the mixture. Ordinary Portland cement is used as the binder in the CPB mixture. Uniaxial compressive tests (UCS) are conducted to determine the strength of the CPB, while suction monitoring experiments are performed to evaluate changes in suction with time. To understand the effects of the NP additives, different microstructural analyses and tests, including thermal analyses (thermogravimetry (TG), differential thermogravimetry (DTG)), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) are conducted on the nano-CPB and the cement paste of nano-CPB. The results indicate that the addition of NP additives in the absence of SP results in lower strength due to high likelihood of agglomeration. In contrast, samples with SP and NP additives show a higher UCS and more suction than the control sample at the early ages of curing. It has been observed that the addition of NP additives results in the generation of more hydration products which enhance the interparticle friction and packing density of the CPB structure. Higher strength is obtained by increasing the SP content (0.25%) with the same NP content (1%). Enhancement of the strength of CPB and increase in suction, particularly at early ages, can have great importance in speeding up the mining cycle and thus increasing mining productivity, which is obviously associated with financial benefits to the mine.