Mechanical Properties Of Cemented Paste Backfill Research Articles

Experimental Study on Direct Tensile Properties of Cemented Paste Backfill

Cemented paste backfill (CPB) has been increasingly utilized in mines for efficient mineral obtaining and regional ground support. To guarantee the work performance, the mechanical properties of CPB have long been a topic of study among researchers. But the research progress on the tensile strength of CPB is limited, mainly because of the lack of an appropriate test method due to the low tensile strength of CPB. Therefore, instead of the conventional splitting indirect tensile strength test method, a new direct tension test method, which utilizes the specifically designed compression to tension load converter (CTLC) and dog-bone-shaped specimen, has been applied to study the direct tensile properties of CPB. In this study, the direct tensile strength (DTS) of 47 CPB mix designs were measured using CTLC, and the unconfined compressive strength (UCS) of the corresponding mix design was also tested. The experimental results showed that the increase in the binder content, solid mass content, and curing period led to higher CPB direct tensile strength, and the DTS of CPB was most sensitive to the binder content. Furthermore, the influence of the slurry mass solid content on the tensile strength of CPB was not linear. The influence of the binder content became increasingly notable with the increase in the solid content, especially if the binder content exceeded 75%. The effect of the curing period was found to be rather marginal due to the decreasing amount of un-hydrated cementitious materials left with the increase of the curing period. Overall, the DTS generated using dog-bone specimens and the CTLC apparatus are valid for better mine backfill designs. Finally, a linear correlative between UCS and DTS with a formula in the form of σDT (DTS) = 0.171 σc (UCS) was obtained, and the correlation was sufficient for further calculation of DTS using measured UCS.

Performance Investigation and Cost-Benefit Analysis of Recycled Tire Polymer Fiber-Reinforced Cemented Paste Backfill.

To alleviate the environmental problems caused by scrap tire and tailings disposal, the performance of recycled tire polymer fiber (RTPF)-reinforced cemented paste backfill (CPB) was investigated. Ordinary CPB, commercial poly-propylene fiber (CPPF) and reinforced CPB were also investigated for comparison. Slump tests, unconfined compression tests and a cost–benefit analysis were conducted. The results indicate that the flowability of the RTPF-reinforced CPB decreased with the increasing fiber content. The failure strain, unconfined compressive strength, and toughness values were generally higher than that of ordinary CPB (i.e., CPB without any fiber reinforcement). However, the mechanical properties would not be improved continuously with increasing RTPF content. It was found that the inclusion of RTPFs achieved the best improvement effect with the best mechanical properties of CPB at the fiber content of 0.6%. The failure mode of the RTPF-reinforced CPB was safer than that of the ordinary CPB. Microscopic observations indicated that the bond between RTPFs and the CPB matrix could affect the mechanical properties of the RTPF-reinforced CPB. From the cost–benefit analysis, the inclusion of RTPFs to reinforce CPB could gain relatively high mechanical properties with a low material cost.

Specific Mixing Energy of Cemented Paste Backfill, Part I: Laboratory Determination and Influence on the Consistency

Slump determination is widely used to assess the consistency and transportability of fresh cemented paste backfill (CPB). CPB consistency can depend on the mixing procedure for CPB preparation. In this paper, a method was developed to determine the specific mixing energy (SME) that is dissipated during the preparation of CPB mixtures and to analyze its effect on CPB consistency. For this purpose, CPB recipes were prepared using two tailings and the mixing parameters (mixing time and speed and load mass) were successively varied. SME was determined for each mixture using a power meter equipped with an energy recording system mounted on a laboratory Omcan mixer. Slump was also determined for each mixture. A semi-empirical model was then developed to predict SME as a function of the mixing parameters. Results showed that predicted SME compared well with measured SME during CPB preparation. Results also showed that slump increased with increasing SME. The influence of SME on the rheological and mechanical properties of CPB and practical applications are presented in a companion paper.

Understanding the microstructural evolution of hypersaline cemented paste backfill with low-field NMR relaxation

Cemented paste backfill (CPB) comprising mineral tailings, binders and mixing water is an important potential support material in the mining industry. As the mechanical properties of CPB are significantly influenced by its microstructural characteristics the development of measurement tools to better understand its pore structure evolution is important for its increased utilisation. This study reports the application of low-field nuclear magnetic resonance (NMR) relaxation time measurements to characterise the microstructural evolution of CPB materials over 56 days of hydration, contrasting common tap water and hypersaline water (~22 wt% salt) as mixing water. Distinct NMR relaxation time populations were evidenced within each CPB sample, revealing the presence of both capillary (T1,2 ≈ 10 ms) and gel pore water (T1,2 ≈ 300–500 μs), with time-dependent relaxation measurements facilitating characterisation of capillary pore structure evolution over the hydration period assessed. Hypersaline samples demonstrated a time-lag in this measured capillary pore evolution, relative to those hydrated with tap water, while pore structure evolution rates were observed to increase with increased CPB binder content. Further, both T1 and T2 NMR relaxation times were found to correlate with the uniaxial compressive strength of the CPB materials investigated, facilitating the formulation of a predictive correlation function between NMR relaxation characteristics and mechanical properties.

Correlation of coupled effects of curing stress and curing temperature on the mechanical and physical properties of cemented paste backfill based on gray relational analysis

For the effective disposal of tailings and to improve the safety of mines, cemented paste backfill (CPB) technology has been widely applied worldwide. The mechanical and physical properties are the key measurements for the filling stopes. However, no study has addressed the correlation with the effect of curing stress and curing temperature on the mechanical and physical properties. In this paper, a novel method of gray relational analysis (GRA) is applied to evaluate the correlation between these parameters, based on laboratory experiment results. The curing stress and curing temperature are selected as the influencing factors, and the uniaxial compressive strength (UCS), porosity, Ca(OH)2 content and dry density are the output data. The results show that the compactness and pore structure are significantly influenced by the curing stress, and the hydration reaction degree and hydration products are significantly affected by the curing temperature. The results show that the GRA method can be efficiently applied for evaluating the correlation of curing stress, curing temperature and mechanical properties of CPB, which can provide certain guidance for the design of CPB in underground mines.

Coupled effects of curing stress and curing temperature on mechanical and physical properties of cemented paste backfill

In order to disposal the tailings and improve the safety of mines, the cemented paste backfill (CPB) technology has been widely applied to the mines all over the world, and the index of uniaxial compressive strength (UCS) for CPB is one of the most important factors to guarantee the safety of the filling stopes. However, there is little information regarding the coupled effects of curing stress and curing temperature. This study is aimed to investigate the coupled effects of curing stress and curing temperature on the physical and mechanical properties of CPB. Thus, the CPB samples were cured at different curing stress and curing temperature, also the mechanical and physical parameters were frequently tested, the microstructure of CPB was tested by the X-ray diffraction (XRD) and thermal gravity analysis (TGA). The results show that both the curing stress and curing temperature can affect the cement hydration reaction rate, resulting in more hydration products, which is contribute to the UCS acquisition. On the other hand, the water content, dry density and stress-strain curve of CPB were greatly influenced. The results demonstrate that the coupled effects of curing stress and curing temperature should be considered when designing a cost-effective and safety CPB in the underground mines, which can provide technical guidance for the mines.

Investigation of spatial stratified heterogeneity of cemented paste backfill characteristics in construction demolition waste recycled aggregates

This paper discusses the application of construction demolition waste (CDW) in the field of backfill mining as an efficient way of increasing the CDW utilization rate. But much of the research on cemented paste backfill (CPB) with the CDW has been conducted in the laboratory which cannot accurately explain the spatial differentiation characteristics and mechanism of onsite CPB. To this end, this study uses fractal theory, image processing, and scanning electron microscopy (SEM) to analyze the spatial stratified heterogeneity (SSH) of recycled aggregates and the mechanical properties of the CPB under the natural flow of slurry. The spatial distribution mechanism of the CPB’s performances is also explained. The results indicate that the compressive strength reaches a maximum of 4.07 MPa on the top of the upper segment and a minimum of 1.6 MPa on the bottom of the upper segment, with a mean value of 2.4 MPa in the whole tunnel. This satisfies the requirements of field applications. The maximum and minimum mean particle sizes appear on the bottom of the upper segment and the lower segments of the tunnel, and the multifractal parameters are shown to indirectly reflect the distribution of recycled aggregate size. According to the test results of sampling point, the spatial distribution of CPB’s strength and recycled aggregate along the flow direction of slurry are regressed, allowing the tunnel to be divided into five distinct regions. Finally, the PSD of recycled aggregates and microstructures has a profound impact on the mechanical properties of CPB, but the motion characteristics of the recycled aggregates are the main reason for the SSH of the CPB properties.

Effects of coupled sulphate and temperature on internal strain and strength evolution of cemented paste backfill at early age

Cement hydration is a volume reduction reaction which can result in negative pore water pressure while strengthening the structural stiffness of cemented paste backfill (CPB). Both sulphate and temperature significantly affect the hydration process and thus influence the internal volume change and mechanical properties of CPB. The expansive hydration products produced in sulphated CPB may create an increase in volume which subsequently weakens the CPB. This paper presents an experimental study conducted to evaluate the coupled effects of sulphate and curing temperature on the internal strain evolution of early aged CPB. CPB samples of various initial sulphate concentrations (0, 5000 and 25,000 ppm) were prepared and cured at various temperature (20 °C and 35 °C) at early ages (≤7 days). Mechanical tests were conducted on the samples as internal strain was monitored by Fiber Bragg Grating (FBG) sensors. The results indicate that the FBG sensor is sufficiently sensitive to detect the internal strain development of sulphated CPB mixtures during the hydration process. At sulphate concentration of 25,000 ppm, the expansive strain occurred at curing temperature of 35 °C due to the internal expansive force of the expansive materials. The final internal strain value corresponds closely to the strength of the sulphated CPB. As the internal strain of sulphated CPB decreased, the uniaxial compressive strength and tensile strength showed similar trends throughout the experiment. When expansive strain emerged after the initial thermal strain stage, however, there was a higher ratio of uniaxial compressive strength to tensile strength. This phenomenon merits careful consideration in the stability analysis of exposed CPB in underground mines.

Experimental Investigation on Mechanical Properties of Cemented Paste Backfill under Different Gradations of Aggregate Particles and Types and Contents of Cementing Materials

Obtaining the optimal gradation of aggregate particles is beneficial for improving the strength of cemented paste backfill (CPB). Consequently, the uniaxial compression tests with acoustic emission (AE) monitoring were performed on CPB, for which the aggregate particles satisfied the Talbot grading theory. The effects of the Talbot indices of aggregate particles and types and contents of cementing materials on the mechanical properties of CPB were analyzed. The AE characteristics and stress-strain behaviors of CPB were discussed. The results show that the specific Talbot index reflected the optimal strength and deformation properties of CPB is 0.45, and the maximum UCS is 7.6 MPa. The mechanical properties of CPB also can be optimized by changing the type of cementing material and increasing the content of cementing material. The effects of the Talbot indices of aggregate particles and types and contents of cementing materials on the crack damages reflected by the AE signals of CPB are mainly observed in the oa stage and ab stage during the loading process.

Experimental investigation of mechanical and microstructural properties of cemented paste backfill containing maple-wood filler

This experimental study investigates the influence of maple-wood sawdust addition on the mechanical and microstructural properties of cemented paste backfill (CPB). Mechanical properties of CPB were determined by uniaxial compressive strength (UCS) tests and microstructural changes were evaluated by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) analysis. Results indicate that the addition of 12.5% maple-wood sawdust (by dry mass of binder) improves the strength development of CPB specimens at later hydration age (91 curing days). However, at a higher maple-wood sawdust content of 14.5%, the UCS showed lower improvement. Moreover, MIP and SEM analysis results revealed that the 12.5% wood filler addition made the CPB material less porous and more compact by increasing the mineral content formed by cement hydration. The positive influence of maple-wood sawdust on CPB was associated with higher binder content (⩾5%) and mid- to long-term curing times (⩾56days).

Study of physico-chemical and mechanical characteristics of consolidated and unconsolidated cemented paste backfills

Streszczenie W ostatnich latach obserwuje się, że wydajność i jakość próbek zawiesin nasyconych cementem (CPB - Cement Paste Backfill) in situ są stale niższe niż tych samych próbek przygotowanych w plastikowych formach w laboratorium. Może to wynikać z braku w laboratorium skutecznego narzędzia mogącego naśladować zawiesiny in situ, warunki ich utwardzania jak również rozmiary i geometrię próbek. W celu wypełnienia tej luki, w la­boratorium opracowano nowe narzędzie o nazwie CUAPS (Curing Under Applied Pressure System), wytworzone i wykorzystane do zbadania wpływu ciśnienia na podstawie skutecznego nacisku na właściwości fizykochemiczne i mechaniczne CPB, jak również próbek otrzymanych z plastikowych form. Badania porównawcze przeprowa­dzono zarówno dla próbek CUAPS jak i próbek otrzymanych w laboratorium, zawierających lepiszcza (cementu) 3,45 i 7% wag. po 7, 14 i 28 dniach utwardzania. Wyniki wskazują, że wydajność próbek konsolidowanych CUAPS są zawsze bardziej prawdziwe (realistyczne) niż próbek otrzymanych w laboratorium, głównie z powodu odprowadzania wody w wyniku konsolidacji. Ostatecznie metoda CUAPS powoduje korzystny wpływ na utwar­dzenie CPB dzięki zawartości wody (separacja wody od świeżej zawiesiny odpadów z cementu) i połączeniu części wody zasobowej z zawiesiną w zrobach.

A contribution to understanding the effects of curing temperature on the mechanical properties of mine cemented tailings backfill

Increasing usage of cemented paste backfill (CPB) in underground mines combined with the fact that every single mine or backfill structure is unique with regards to their temperature conditions require a need to clarify and quantify the effect of curing temperature on the mechanical properties of CPB. Hence, the main objective of this study is to use an experimental approach to study the influence of curing temperature and combined effect of temperature and CPB components on the main mechanical properties (strength, modulus of elasticity, and stress–strain behaviour) of CPB. Thus, different types of CPB specimens are tested at different curing times and temperatures (2 °C, 20 °C, 35 °C, and 50 °C). The compressive and split tensile strength, modulus of elasticity, stress–strain behaviour and microstructure are evaluated by laboratory tests. The results show that the curing temperature has a significant influence on the mechanical properties of CPB. Moreover, the effect of temperature on these properties depends on the binder type, W/C ratio, tailings type and curing time. The study demonstrates that the mine and backfill temperatures are an important parameter that should be considered in mine backfill operations.

Thermal conductivity of cemented paste backfill material and factors affecting it

Cemented paste backfill (CPB) is extensively used in underground mine operations. Several studies have been conducted to investigate the mechanical properties of CPB. However, little attention has been devoted to the thermal conductivity of CPB. The knowledge of this thermal property is vital for the design of cost-effective and durable CPB materials. This article presents the results of a comprehensive laboratory study on the thermal conductivity of CPB. Influencing factors on the thermal conductivity of CPB were quantitatively investigated. The measurements of thermal conductivity were performed by using the KD2 Thermal Properties Analyser. Valuable results with regards to the effects of CPBs mix components, curing time and temperature, and water saturation degree on the thermal conductivity of CPB were gained. It is felt that the present study would contribute to the better optimisation of CPB mixtures and the design of more cost-effective and durable CPB underground structures.