Backfill Material Research Articles

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

A state-of-the-art review on delayed expansion of cemented paste backfill materials

A state-of-the-art review on delayed expansion of cemented paste backfill materials

The 3D response of a large-scale masonry arch bridge – Part II: Performance at failure

Masonry arch bridges continue to form a pivotal part of the transport networks of the UK and many other countries worldwide. However, their three-dimensional response (3D) under loading has to date been relatively little investigated. Here, details of a large-scale masonry arch bridge load tested to failure under laboratory conditions are presented. The bridge consisted of a brickwork arch barrel, abutments, spandrel walls, and compacted limestone as backfill material. Patch loading was applied to the surface of the backfill at the quarter and three-quarter span points to assess the failure mechanism, load-carrying capacity, and residual strength of the bridge. A range of sensors were employed to capture the 3D bridge response and ground-penetrating radar surveys were performed on both the virgin and load-tested bridge to compare its internal structure. The observed evolution of cracks and post-test deformed geometry demonstrated the presence of both a localised 3D mode of response in the arch barrel in the vicinity of the applied load and a global four-hinge mechanism. Failure-level load tests carried out first at the quarter span and then at the three-quarter span points showed that the load-carrying capacity of the bridge had reduced by only 10 % in the second test, though the stiffness of the bridge had decreased by around 35 %. During the failure-level load tests, significant in-plane and out-of-plane deformations of the spandrel walls were also observed, adding to the much smaller residual deformations recorded in low- and mid-level load tests.

Pengaruh Penggunaan Limbah Beton Sebagai (Agregat Halus) Terhadap Uji Kuat Tekan Paving Block

In Indonesia, the use of construction waste is usually not utilized properly most are simply dumped in open fields, and some are used as backfill material. The availability of such materials is vast. The purpose of this research is to determine the compressive strength value of paving blocks that utilize concrete waste with variations in the use of concrete waste, namely: 0%, 10%, 20, 30%, and the value of water absorption in paving blocks that utilize concrete waste with variations in the use of concrete waste, namely: 0%, 10%, 20, 30%. The test results showed that at 28 days of soaking, the compressive strength of normal paving blocks was 16.15 MPa, at 10% substitution of concrete waste for stone ash was 29.17 MPa, at 20% substitution of concrete waste to stone ash amounted to 39.32 MPa, and at 30% substitution of concrete waste to stone ash amounted to 22.66 MPa. From the results of the absorption test, it was found that the absorption value of normal paving blocks was 3.88%, at 10% substitution of concrete waste was 2.30%, at 20% substitution of concrete waste for stone ash was 1.89%, and at 30% substitution of concrete waste for stone ash was 2.80%.

Experimental Investigation on Hydrophobic Alteration of Mining Solid Waste Backfill Material

To address the issues of corrosion weakening of solid-waste-based backfill material caused by mine water, a novel hydrophobic solid waste backfill (HSBF) material was developed using polydimethylsiloxane (PDMS) and a silane coupling agent (SCA) as hydrophobic modification additives, and NaOH (SH) and sodium silicate (SS) as alkali activators. Fly ash and slag were chosen as the primary raw solid waste materials. The rheological properties of the hydrophobic-treated backfill slurries were measured, and the resulting physicochemical properties were compared with the unmodified reference group. This study reveals that the fresh HSBF slurry follows a Modified Bingham (M-B) model with shear-thinning characteristics. The addition of PDMS causes an increase in the water contact angle of the hardened HSBF material with F8S2 to up to 134.9°, indicating high hydrophobicity. Morphological observations indicated that PDMS mainly attaches to the inorganic particles’ surface through the bridging action of SCA for the hydrophobic modification of the backfill material. The overall strength of the HSBF materials was further ensured via fly ash–slag ratio optimization, and was found to be enhanced up to 98% by increasing slag content from 20% to 50%. This is mainly attributed to the hydration of slag, forming C-S(A)-H gel, which contributes to the increased strength. The novel HSBF material enables the elimination of cement in mine backfilling applications, demonstrating good economic benefits. Its excellent mechanical and hydrophobic properties can not only prevent overburden displacement in goaf areas, but can also mitigate water resource loss from overlying strata and simultaneously reduce the safety risks associated with long-term mine water deterioration.

Research on the interaction between trench material and pipeline under fault displacement

With the large-scale construction of oil and gas pipelines, the safety issues of long-distance buried pipelines in the service and construction have become increasingly prominent. The complex geological and topographical conditions of the special zone will put forwards extremely high requirements on pipe trench laying backfill materials and construction technology. For example, pipelines are inevitable to cross the active fault, while the trench backfilled with soil has limitations in protecting them from failure under the active fault displacement caused by the earthquake. Therefore, it is necessary to study the pipe–soil interaction mechanism, determine the stress state of the pipeline and propose a new backfilling material that can protect the pipeline from failure. Foam concrete (FC) provides a new choice to backfill the buried pipeline trench due to its high-homogeneity, lightweight, controllable-strength, and self-compacting. To further determine the applicability of the FC, the pipe-FC interaction mechanism is studied. Then, a FE model of the FC-pipeline-soil interaction system is established by Abaqus to quantitatively analyze the applicability of the FC based on the experimental data of the mechanical performance of the FC. It proves that using FC as trench backfill material has a noticeable protective effect on the pipeline under the earthquake-induced displacement of the normal fault. Furthermore, FC has a better protective effect on the pipeline subjected to compressive than tensile. Therefore, the reference for applying FC in trench backfilling of pipelines crossing normal fault is provided.

A Critical Review of Soil Models and Factors Affecting Earth Retaining Structures Design

Earth retaining structures, ERSs, are used in many engineering fields. Special considerations and technical knowledge in geotechnical engineering should be adopted in the modeling, analysis, and design of ERSs. Some of these considerations are related to the soil models, and (quality, settlement, and inclination) of the backfill and foundation soils of the retaining wall, RW, as presented in this critical review. This review shows that the analysis and design of ERSs are highly affected by model adopted for soil behavior, and the quality and characteristics of backfill materials. The backfill materials affect the selection of material type and performance of the ERSs, furthermore, they impact the soil interaction with RW. In selecting an appropriate model, it is important to consider the effect of soil history and stress changes that may the soil experience in the future. The design of some types of ERSs, backfilled with a material predominantly finer than the coarse sand grain size, should be conducted with precautions due to the possibility of lateral earth pressure (LEP) changing from active state to at-rest state after construction. It is worthwhile to consider both short-term and long-term settlements in the analysis and design of ERSs as there are specific types of ERSs that can tolerate large short-term settlements but cannot tolerate large long-term settlements. Finally, under both static and dynamic loadings, the angle of inclination of the backfill soil greatly affects the distribution of LEP and the value of the resultant force behind the RW.

Assessing the Performance of CO2-Mineralized Underground Backfilling Materials through the Variation Characteristics of Infrared Radiation Temperature Index

Assessing the Performance of CO2-Mineralized Underground Backfilling Materials through the Variation Characteristics of Infrared Radiation Temperature Index

Thermodynamic performance of SiC-enhanced MicroPCM backfill based on response surface methodology

The functional backfilling in mining achieves synergistic co-mining of deep-earth deposits-geothermal, and the development of functional filling materials with suitable phase change parameters and excellent physicochemical properties is imminent. This study aims to investigate the optimal composition of phase change energy storage backfill material based on MicroPCM. To address the issues of reduced compressive strength and specific heat capacity of MicroPCM-backfill, silicon carbide (SiC) is introduced to prepare MPSC-backfill. Box-Behnken Design (BBD) is proposed to design and analyze according to four factors (ash-sand ratio, slurry concentration, MicroPCM, SiC), three levels (compressive strength, thermal conductivity, specific heat capacity) and three center points. Based on the Response Surface Methodology, the multivariate quadratic polynomial model was used to perform multiple linear regression and binomial fitting analysis to explore the optimal ratio. Combined with SEM-EDS (Scanning Electron Microscope with Energy-Dispersive X-ray Spectroscopy) analysis, the following conclusions were drawn. SiC exhibits an overall enhancement of the compressive strength of the backfill, and the thermal conductivity tends to increase almost linearly. The specific heat capacity grows in a small amount of silicon carbide doping, but excessive amounts lead to a decrease, with an overall limited impact. The addition of SiC does not affect the phase change ability of MicroPCM. And within a certain range of added quantities, it optimizes specific heat capacity, thermal conductivity, and compressive strength. Experimental validation based on the obtained optimal composition shows errors within a 5% margin, indicating the response model's good accuracy and predictability. High and low-temperature cyclic tests confirm the long-term thermal energy storage stability of MPSC-backfill during phase change cycles.

The basic characteristics of paste backfill materials based on highly active mineral admixtures: Part I. Preliminary study on flow, mechanics, hydration and microscopic properties

The cost performance of backfill materials in coal mines has long limited the widespread use of backfill technology. Therefore, developing backfill materials that are both cost-effective and high-performing is a pressing scientific issue that requires immediate attention. This study proposes replacing ordinary Portland cement (OPC) with highly active mineral admixtures, such as mineral powder and limestone powder, to prepare a green, low-cost, and high-performance coal mine backfill material. The use of mineral admixtures can improve the performance of the backfill material while reducing its environmental impact. The proposed approach is cost-effective and environmentally friendly. The study employed experimental tests and microscopic characterization methods, such as the slump test, hydration heat test, uniaxial compressive strength test, and microstructure test, to clarify the synergistic reaction mechanism of highly active mineral admixture-based paste backfill material (HAM-PBM). This clarification is helpful in regulating the macroscopic properties of hardened paste. The results show that: (1) The rheological properties of fresh HAM-PBM slurry are consistent with the Herschel-Bulkley model, and its fluidity meets the technical requirements for coal mine backfilling. The slump of fresh HAM-PBM slurry ranges from 140 to 145 mm, and the yield stress ranges from 3.188 to 12.819 Pa. (2) Highly active mineral admixtures significantly affect the early hydration process of HAM-PBM. The parameters of the hydration characteristics during the initial dissolution stage, acceleration stage, deceleration stage, and stabilization stage gradually decrease, while the duration of the induction stage gradually increases. This confirms that the early hydration activity of mineral powder (MP) and limestone powder (LF) is lower than that of OPC. (3) The uniaxial compressive strength (UCS) of the MP series exhibits an "anti-hook" change pattern, while the UCS of the LF series shows a decreasing change pattern. The microstructure, including the number of hydration products, microscopic density, and other characteristics, follows the same change pattern as the UCS. (4) Based on the synergistic reaction mechanism of hardened slurry, it is recommended that MP replace a maximum of 10 % of OPC and LF replace a maximum of 5 % of OPC. The need for composite replacement of OPC with MP and LF is clarified, resulting in a cost-effective coal mine backfill material. This study has contributed to the national "double carbon" policy and the low-cost backfilling application of coal mines.

Feasibility of using superelastic shape memory alloy in plastic hinge regions of steel bridge columns for seismic applications

AbstractThis paper contributes to the further development of seismic resilient infrastructure by introducing a novel prototype bridge which integrates tubular steel piers with superelastic shape memory alloy (SMA). The proposed bridge pier is composed of a circular steel tube which is bonded to a superelastic SMA tube in regions of high stress. The pier is distinguished by its ability to minimize residual drifts following inelastic deformations induced by cyclic loading. Three‐dimensional continuum finite element (FE) models are utilized to examine its lateral behavior. Experimental data is used to demonstrate the effectiveness of the continuum FE procedure in replicating the cyclic response and capturing both global and localized behaviors. A novel composite material model is proposed to represent the degradation of strength and accumulation of irreversible strains in the cyclic response of superelastic SMAs. An iterative procedure for the calibration of this material is presented. Investigations, employing the calibrated FE procedure, focus on the quasi‐static cyclic response of steel piers with superelastic SMA in the plastic hinge zone, aiming to identify the optimal length of the SMA tube for achieving a self‐centering response with reduced residual deformation. The study is then further expanded to examine the seismic response of a bridge structure incorporating such piers. Development of the FE model for the prototype bridge includes the modelling of the piers using continuum elements, while the superstructure, bearing units, abutment walls, and backfill material are modelled using discrete elements. Nonlinear time history analyses are undertaken to investigate the effects of column wall thickness and materials used in the plastic hinge zones of the piers. Dynamic FE study results indicate that bridges employing such piers are capable of returning to their original position, provided the SMA tube is of adequate length.

Preparation and Properties of Expansive Backfill Material Based on Municipal Solid Waste Incineration Fly Ash and Coal Gangue

To realize the large-scale utilization of municipal solid waste incineration (MSWI) fly ash in the field of building materials and to reduce the cost of coal mine backfill mining, the effects of the mixing ratio of cementitious materials, the particle size distribution of aggregates, and the amount and mass concentration of cementitious materials on the properties of backfill materials were experimentally investigated, and the microstructure of the hydration products was analyzed. The results showed that as the mass ratio of MSWI fly ash to bottom ash increased, the rate of expansion of the cementitious system continued to increase, and the compressive strength of the cementitious system continued to decrease. The Al (aluminum) and AlN (aluminum nitride) in the fly ash reacted with water to generate gas, causing the expansion of the cementitious materials; NaOH increased the alkalinity of the solution, which promoted the formation of more bubbles, thereby improving the expansion performance of the cementitious material. When the content of NaOH was 0.9%, the sample rate of expansion could reach 15.9%. The addition of CaCl2 promoted the early hydration reaction of the cementitious material, forming a dense microstructure, thus improving the early strength and rate of expansion of the cementitious material. The compressive strength of the backfill body increased as the fractal dimension of the aggregate particles increased, and the particle grading scheme of group S1 was optimal. The 1-day, 3-day, and 28-day strengths of the backfill body of group S1 reached 0.72 MPa, 1.43 MPa, and 3.26 MPa, respectively. It is recommended to choose a backfill paste concentration ranging between 78.5% and 80% and a reasonable amount of cementitious material between 20% and 25%. After the MSWI fly ash was prepared as a backfill material, the leaching of potentially harmful elements in the fly ash was greatly reduced, and the concentration of dioxin was reduced to 13 ng TEQ/kg. This was attributed to the dilution of the cement, the physical encapsulation of gel products, and the isomorphous replacement of Ca2+ in calcium aluminate chloride hydrate.

A Critical Review of Methods for Backfill Soil Modulus in Design of Flexible Culverts

Flexible culverts made of corrugated steel or plastic are cost-effective and environmentally friendly alternatives to conventional small road and railway bridges. These structures interact with the backfill by deflecting when subjected to overburden loads, enabling them to utilize the surrounding soil by carrying loads in ring compression. In low soil cover situations, the relationship between bending and backfill soil (stiffness) modulus increasingly influences bearing capacity, and therefore must be considered in design. Backfill soil modulus is a direct result of the execution of the backfilling, and recognized as the most important design parameter because of local uncertainties during construction and material variability. This paper gives a review of some of the existing methods for determining backfill soil modulus. It covers development history, theoretical approximations, aspects of crushed rock materials and their quality, and ease of use in routine design. By applying the methods on different materials and comparing the end results with a compilation of large-scale compression tests and materials from various origins, the performance of the reviewed methods is evaluated. It is found that the reviewed methods have specific drawbacks depending on the actual stress condition and backfill material being applied. In addition, most methods are based on reference laboratory tests carried out on specific and sometimes high-quality materials, and therefore fail to reflect how the quality of rock materials influences the backfill modulus. These shortcomings are used to suggest a new outlook that should be considered in future research on backfill design.

An Experimental Study on the Mechanical Properties and Microstructure of the Cemented Paste Backfill Made by Coal-Based Solid Wastes and Nanocomposite Fibers under Dry-Wet Cycling.

The mechanical properties and microstructure of the cemented paste backfill (CPB) in dry-wet cycle environments are particularly critical in backfill mining. In this study, coal gangue, fly ash, cement, glass fiber, and nano-SiO2 were used to prepare CPB, and dry-wet cycle tests on CPB specimens with different curing ages were conducted. The compressive, tensile, and shear strength of CPB specimens with different curing ages under different dry-wet cycles were analyzed, and the microstructural damage of the specimens was observed by scanning electron microscopy (SEM). The results show that compared with the specimens without dry-wet cycles, the uniaxial compressive strength, tensile strength, and shear strength of the specimens with a curing age of 7 d after seven dry-wet cycles were the smallest, being reduced by 40.22%, 58.25%, and 66.8%, respectively. After seven dry-wet cycles, the compressive, tensile, and shear strength of the specimens with the curing age of 28 d decreased slightly. The SEM results show that with the increasing number of dry-wet cycles, the internal structure of the specimen becomes more and more loose and fragile, and the damage degree of the structural skeleton gradually increases, leading to the poor mechanical properties of CPB specimens. The number of cracks and pores on the specimen surface is relatively limited after a curing age of 28 d, while the occurrence of internal structural damage within the specimen remains insignificant. Therefore, the dry-wet cycle has an important influence on the both mechanical properties and microstructure of CPB. This study provides a reference for the treatment of coal-based solid waste and facilitates the understanding of the mechanical properties of backfill materials under dry-wet cycling conditions.

Study on size effect and crushing characteristics of gangue-filling material under the confined compression

ABSTRACT The diameter, particle size distribution, and diameter-height ratio of coal gangue backfill material directly affect its mechanical behavior. This study investigated the influence of different particle sizes on the bearing characteristics and particle breakage of coal gangue backfill material under constrained compression through orthogonal experiments. A numerical model of randomly geometrically filled stones under compression was developed to reveal the micro-damage mechanism of coal gangue backfill material under different particle size effects. The results indicate that the diameter Rd of coal gangue backfill material has the greatest impact on its mechanical behavior, followed by the particle size distribution Rg, with the diameter-height ratio Rd-h having the least impact. The diameter significantly affects the compressive strength of the samples, with larger diameters leading to poorer initial force chain stability and lower compressive strength. The particle size distribution has a significant impact on sample breakage, with the breakage rate and fractal dimension increment being negatively correlated with the initial particle size distribution. Particle breakage in the samples gradually progresses from the periphery towards the center, with tensile failure being the primary mode of damage.

Performance Evaluation of Steel Slag and Construction and Demolition Waste as Reinforced Earth Backfill Materials Under Cyclic Loading Conditions

Performance Evaluation of Steel Slag and Construction and Demolition Waste as Reinforced Earth Backfill Materials Under Cyclic Loading Conditions

Sol–gel-stabilized CO2 foam for enhanced in-situ carbonation in foamed fly ash backfill materials

AbstractA novel highly stable aqueous foam was synthesized using CO2, sodium silicate (SS) and anionic surfactant of sodium dodecylbenzene sulfonate. The influence of CO2 foam on the mechanical properties and its underlying mechanisms of foamed backfill material was investigated. The experimental results revealed that the addition of CO2 and SS effectively reduced the drainage of the foam while strengthening the liquid film of the Plateau borders, which stabilizes the foam. The excellent stability is attributable to the gel network developed after SS exposed to CO2, that adhere to the foam surface. Furthermore, due to the interaction between encapsulated CO2 and hydration products, micro CaCO3 formed and filled the pore wall; thus, precast foam forms robust pore structures in the hardened foamed backfill.

Feasibility and mechanism of high alumina cement-modified chlorine saline soil as subgrade material

Soil salinization is a serious problem during ground improvement and foundation construction around the coastal region. This study used high alumina cement (HAC) as a soil stabilisation agent to modify the coastal chlorine saline soil as roadbed backfilling materials. In addition, Ordinary Portland cement (OPC), slaked lime (SL) and fly ash (FA) were used to better the understanding of the chlorine fixation and roadbed performance. The microstructures of different hydration products were investigated through the utilization of the X-ray diffraction and scanning electron microscope equipped with an energy dispersion spectrometer. The HAC-SL-modified soil depicts that the aluminium and calcium phases are beneficial to the formation of Friedel’s salt and hydration products. The optimal chlorine fixation is approximately 20.5% at 6% HAC-SL incorporation (3% of HAC and 3% SL). At the early stage of curing, the strength of the HAC-treated soil is high. However, with a prolonged curing period, there is a slight decrease in the strength because the porosity will increase during the transformation of metastable CAH10 and C2AH8 into stable and dense C3AH6. This evolution can be prevented by incorporating SL to enrich calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). Furthermore, it is of key importance to mention that HAC reaction is quick, therefore, the compaction should be undertaken instantly to ensure the road performance.

A backfill material without cementitious material: Carbonation curing magnesium slag based full solid waste backfill material

A backfill material without cementitious material: Carbonation curing magnesium slag based full solid waste backfill material

Innovative synthesis of low-carbon cemented backfill materials through synergistic activation of solid wastes: An integrated assessment of economic and environmental impacts

The accumulation of large amounts of steel slag (SS) and oil shale residue (OSR) causes serious pollution due to the lack of effective ways to utilize them. In this study, OSR, SS, and soda residue (SR) were used to synergistically prepare all-solid-waste low-carbon cemented backfill material (ALCCB). No cement and chemical additives were added to this material, and synergistic activation enabled full utilization of the solid wastes. The total solid waste utilization rate was 100 %. The mechanical characteristics of the ALCCB and the heavy metal leaching rates were determined. The unconfined compression strength of the ALCCB after 28 days was 5.97 MPa, while the slump was 205 mm. These results met the performance requirements for a filling material. The leaching rates for the heavy metals after 28 days conformed to the guidelines for Class III groundwater quality. The mechanism underlying synergistic hydration of the solid wastes was analyzed at the micro- and macroscale with X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results indicated that hydration of the ALCCB occurred continuously during curing, and the faster early hydration reaction stabilized heavy metal curing at 7 d. In addition, ALCCB offers greater economic and environmental advantages than cementitious materials. Notably, the economic and environmental benefits of ALCCB were found to supersede those of cement-based materials, with a cost reduction of 42.6 % and a CO2 emission reduction of 86.9 %. This innovative low-carbon mine backfill material effectively promotes the utilization of solid waste resources and supports sustainable development.