Contents lists available at ScienceDirect Ultrasonics journal homepage: www.elsevier.com/locate/ultras Ultrasonic evaluation of strength properties of cemented paste backfill: Effects of mineral admixture and curing temperature Haiqiang Jiang a,b , Hongshun Yi a , Erol Yilmaz c, ⁎ , Shiwei Liu d , Jingping Qiu a a Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang, China b Backfill Engineering Laboratory, Shandong Gold Mining Co., Ltd., Laizhou 261441, China c First Quantum Minerals Ltd., Cayeli Bakir Isletmeleri A.S., PO Box 42, Madenli, Cayeli, Rize TR53200, Turkey d School of Water Conservancy and Hydroelectric Power, Hebei University of Engineering, Handan 056038, China ARTICLE INFO Keywords: Mine tailings Cemented paste backfill Ultrasonic behavior Unconfined compressive strength Curing conditions Mineral admixtures Microstructural properties Curve fitting analyses ABSTRACT This paper presents the findings of a research study designed and conducted to investigate the effects of mineral admixture and curing temperature on uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) behavior of laboratory-prepared cemented paste backfill (CPB) samples. A total of 290 CPB samples were pre- pared at different replacement rates (10–80%), cured at various temperatures (10–50 °C), and respectively subjected to both UPV and UCS testing after curing times of 3, 7, 14, 28, 56 and 90 days. The obtained ex- perimental results show that the addition of fly ash (FA) can lead to an increase or decrease trend in UCS and UPV behavior of CPB samples, depending on the replacement level of admixtures. There is a competition be- tween the strength-increasing factor (micro-filler effect of FA) and strength-decreasing factor (lower amount of cement hydration products induced by replacement ratio). Both UPV and UCS are found to decrease with in- creasing blast furnace slag (Slag) replacement level mainly attributable to its low pozzolanic reactivity. Besides, the curing temperature has a significant influence on UCS and UPV behavior, depending on the curing time. Results also suggest that UPV is less sensitive to the variation in the admixture dosage and curing temperature than UCS. As a result, there exists a clear linear relationship between UPV and UCS behavior of both CPB samples prepared with FA and/or Slag admixtures, and CPB samples tested at each curing temperature. The main findings of this research study suggest that the UPV test can be reliably used for predicting CPB’s strength properties, saving money and time to mine operators. 1. Introduction Mining extracts valuable minerals and/or other geological materials from an ore-bearing body. Mining and processing of the mineralized ore generate considerable volumes of solid wastes (e.g., tailings and waste rocks) and underground voids, which can cause serious environmental and geotechnical hazards [1–3]. Mining operations may indeed create the negative impacts, both during the mining activity and after the mine has closed, if necessary precautions are not taken seriously [4,5]. Accordingly, increasing public awareness coupled with increasingly stringent regulations forces the mining industry to adopt more com- petent and efficient techniques to better manage their destructive tail- ings and underground voids [6,7]. One of these emerging techniques is called cemented paste backfill (CPB) which offers better technical and economic advantages over other filling methods like rock/slurry fills [8]. These advantages include ground support for underground structures, surface disposal of tailings, increased mine production and mining cycle, and reduced ore dilution, surface subsidence and re- habilitation costs [9–11]. CPB is a high-density, non-segregating, non-Newtonian fluid, and composite material which is made up of wet process tailings (70–85 wt % solids), a hydraulic binder (3–7% by mass of total solids), and mixing water [12]. As a secondary ground and wall support element, the me- chanical stability is one of the most important performance criteria of CPB structures [13,14]. Once placed into mine stopes, CPB must satisfy certain dynamic/static load resistance requirements to ensure a safe underground working environment and remain stable during the ex- traction of ore from neighbor stopes [15]. The most common and vital parameter which is directly used to assess the mechanical stability of CPB structures is uniaxial compressive strength (UCS) [16,17].A number of researchers have examined experimentally the effects of influencing variables (as internal and external factors) on UCS https://doi.org/10.1016/j.ultras.2019.105983 Received 22 December 2018; Accepted 18 August 2019 ⁎ Corresponding author. E-mail address: yilmazer@fqml.com (E. Yilmaz). Ultrasonics 100 (2020) 105983 Available online 19 August 2019 0041-624X/ © 2019 Elsevier B.V. All rights reserved. T