•Structural effect on compressive strength of cemented tailings backfill (CTB) was studied.•Increasing the filling time stages led to a remarkable decrease in CTB’s strength properties.•The CTB’s ...compressive strengths decreased gradually with increasing filling interval time.•The compressive strength showed an U-type distribution with increasing filling surface angles.•Some empirical equations were developed between CTB’s structural factors and strength gain.
In this paper, the influence of structural factors on the uniaxial compressive strength (UCS) of cemented tailings backfill (CTB) was experimentally investigated focusing on the filling time (FT), filling interval time (FIT) and filling surface angle (FSA). A number of CTB samples with a diameter × height of 50 mm and height of 100 mm were prepared at different FTs (1, 2, 3, and 4 stages), FITs (12, 24, 36, and 48 h), and FSAs (0, 15, 30, 45, and 60°) and subjected to UCS test to determine their mechanical strength performance. Results show that: (1) The UCS of the CTB samples decreased with the increase in FTs. The polynomial could represent the quantitative relationship between the backfill strength and FT. When the solid density (SD) within the CTB was constant, the value of the strength reduction coefficient k gradually decreased with the increase in FTs. When the SD was 65–75 wt%, the corresponding value of k remained between 0.592 and 0.967. (2) With the extension of the FIT, the UCS values of the CTB samples gradually decreased. The polynomial function could characterize the quantitative relationship between the UCS and FIT. The FIT only slightly influenced the strength performance of the CTB samples. The failure mode of the CTB samples may be tensile failure–transition from tensile failure to the shear failure-tensile shear pattern with the increase in the FIT. (3) The UCS showed a U-type distribution that decreased first and then increased with the increase in the FSAs. When the FSA changed from 0° to 60°, the UCS of the CTB samples first decreased and then increased with the FSA. The results presented in this study contribute to a better understanding of the effect of structural factors on CTB’s mechanical properties.
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•A novel method is proposed for predicting cemented paste backfill (CPB) strength.•Artificial neural network (ANN) and particle swarm optimization (PSO) are combined.•Dataset is ...collected from 396 unconfined compressive strength tests.•PSO was efficient in the architecture-tuning of the ANN.•The optimum ANN model was accurate at predicting CPB strength with R = 0.979.
Cemented paste backfill (CPB) has been widely used to prevent and mitigate hazards produced during the excavation of underground stopes. In practice, the strength of CPB is often an essential parameter for successful stope design. We propose an intelligent technique in this study for predicting the unconfined compressive strength (UCS) of CPB. This intelligent technique is a combination of the artificial neural network (ANN) and particle swarm optimization (PSO). The ANN was used for non-linear relationships modelling and PSO was used for the ANN architecture-tuning. Inputs of the ANN were selected to be the tailings type, the cement-tailings ratio, the solids content, and the curing time. A total of 396 CPB specimens under different combination of influencing variables were tested for the preparation of the dataset. The results showed that PSO was efficient for the ANN architecture-tuning. Also, comparison of the predicted UCS values with experimental values showed that the optimum ANN model was very accurate at predicting CPB strength.
Hydraulic fracturing is an effective method to improve the permeability of coal seams and enhance extraction of coalbed methane (CBM). Evolution of cracks in coal seam becomes increasingly complex ...when one borehole is drilled through multiple coal seams. In this work, physical models with two coal seams having different uniaxial compressive strength (UCS) ratios and height ratios were prepared to study the competitive initiation and extension of cracks based on pump pressure, acoustic emission (AE) source location, and crack morphology. The results showed that, a competitive relationship exists between the two coal seams in terms of crack extension. The pump pressure curves of all specimens presented four stages: (I) fluid-filling stage, (II) pressure rise stage, (III) pressure drop stage, and (IV) pressure stabilization stage. Compared with the pure specimen, the crack initiation pressure of specimens with two coal seams reduced generally. The AE source locations were first generated and mainly distributed in the softer coal seam, resulting in the formation of a complex crack network, whereas only a few cracks were generated in the harder coal seam, as observed after cutting the specimens. In seams with different height ratios, the AE source locations and tracers indicated that cracks preferentially developed and extended in the thinner coal seam. The higher the height ratio of the two coal seams, the more difficult it was for cracks to extend simultaneously in two coal seams. The research results will help improve the permeability of CBM reservoirs when subjecting multiple coal seams to hydraulic fracturing.
AbstractMicrobially induced calcite precipitation (MICP) is a sustainable biological ground improvement technique that is capable of altering and improving soil mechanical and geotechnical ...engineering properties. In this paper, laboratory column studies were used to examine the effects of some key environmental parameters on ureolytic MICP mediated soils, including the impact of urease concentrations, temperature, rainwater flushing, oil contamination, and freeze–thaw cycling. The results indicate that an effective crystal precipitation pattern can be obtained at low urease activity and ambient temperature, resulting in high improvement in soil unconfined compressive strength (UCS). The microstructural images of such crystals showed agglomerated large clusters filling the gaps between the soil grains, leading to effective crystals formation. The rainwater flushing was detrimental to the biocementation process. The results also indicate that traditional MICP treatment by the two-phase injection method did not succeed in treatment of oil-contaminated soils, and the proposed premixing of bioflocs with soil can significantly improve UCS and stiffness of oil-contaminated soils. Finally, MICP-treated soils showed a high durability to the freeze–thaw erosion, which is attributed to the interparticle contact points and bridging of crystals formation.
The study is centered on optimizing graphene oxide (GO) concentration in M30 designer mix concrete, aiming to enhance its performance under elevated temperatures and fire conditions. The findings ...revealed a significant 40 % increase in compressive strength with the addition of 0.05 wt% GO to M30 grade concrete after 28 days of curing in water. GO played a crucial role in mitigating the impact of high temperatures under heating in furnace and fire exposure under flame, resulting in reduced crack formation and a delayed temperature rise during thermal loading. In heat resistance assessments, GO concrete exhibited a substantial delay in temperature rise compared to plain concrete under controlled furnace conditions, showcasing superior resistance to elevated temperatures. Thermogravimetric analysis and Differential TG analysis elucidated the superior retention of water and hydrated products in GO concrete, even after exposure to high temperatures. Fire exposure tests demonstrated that GO concrete exhibited a much lower surface temperature (less than 50 °C) opposite to the flame (flame temperature ∼ 700 °C) within a 15 cm width of concrete. Additionally, fewer and less severe cracks appeared in the GO concrete compared to plain concrete, showcasing its anti-spalling behavior. The altered matrix porosity of GO concrete, creating nano- and microscale channels, contributed to reduced vapor pressure and mitigated crack formation. This comprehensive study underscores the potential of GO as a versatile additive in concrete, offering enhancements in strength, heat resistance, and fire performance for sustainable and resilient infrastructure development.
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•0.05 wt% GO added M30 grade concrete showed 40 % increase in compressive strength.•GO concrete exhibited a substantial delay in temperature rise compared to plain concrete.•Heat treated GO concrete showed superior retention of water and hydrated products.•15 cm thick GO concrete exhibited much lower surface temperature (∼ 50 °C) under flame.
•Microstructure in the ITZ of lightweight concretes was studied.•Lightweight aggregates (LWA) contributed to the formation of a dense and thinner ITZ.•Lightweight structural concretes were developed ...and explained.
In this research both the microstructure and thickness of the interfacial transition zone (ITZ) in concretes of Portland cement and lightweight aggregates (LWA) are studied. It has been established that the microstructure in the ITZ strongly depends on the nature of the aggregate, specifically its porosity and water absorption. This study aims at researching the influence of physical properties such as density, porosity and morphology of lightweight aggregates such as pumice and expanded clays, on the microstructure and thickness of ITZ, and determine the effect that these factors have in turn on the mechanical properties as compressive strength of lightweight concretes (LWC). Lightweight aggregates were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Fluorescence (XRF), to determine their mineralogical, morphological and chemical characteristics. The characterization of ITZ by SEM-EDS, and conventional optical microscopy, was carried out on specimens of concrete manufactured with LWA and with a conventional aggregate, in order to evaluate its thickness; furthermore, to determine the porosity, digital image processing (DIP) was performed. Lightweight aggregates contributed to the formation of a dense and thinner ITZ, when compare to the ITZ of a conventional concrete. The lower porosity and greater amount of hydrated cement phases in the ITZ of lightweight aggregates are attributed to their physical, morphological properties and chemical and mineralogical composition; which contributed to the decrease of the wall effect, gestating from its surface the formation of C-S-H, achieving interlacing of hydrated phases on the surface of these aggregates with the cementitious matrix.
The development of micro‐cellular foams with ultra‐high compressive strength and high volume expansion ratio (VER) is a challenging task. Herein, polyamide 12T (PA12T) micro‐cellular foams with ...ultra‐high compressive strength were fabricated via in situ polytetrafluoroethylene (PTFE) fibrillation using supercritical CO2 foaming technology and a chain extender. The resulting branched structure showed considerably improved viscoelasticity and foaming performance, thus improving the cell morphology of the PA12T foam and exhibiting high VER. The PTFE fibrillation network induced melt strength enhancement, crystallization nucleation, and cell nucleation. The branched PA12T foam with 1.5 wt% PTFE exhibited the smallest cell diameter (15 μm) and highest cell density (3 × 109 cells/cm3). The compressive strength of the foam (0.50 MPa under 5% strain) was 70% higher than that of pure PA12T. This research offers an effective method for producing high‐VER PA12T foams with adjustable micro‐cellular structures and excellent mechanical properties.
Polyamide 12T micro‐cellular foams with ultra‐high compressive strength via in situ polytetrafluoroethylene fibrillation.
Na2SO4 (NS)-activated slag as a kind of alkali-activated slag (AAS) had great development potential in low carbon cementitious materials field, because NS could be obtained from natural resources ...with much lower CO2 emissions than NaOH and water glass. However, the main issue was its slower strength development at both early and later ages. With intention to mitigate this problem, ultra-fine slag was used, and the increased CO2 emissions caused by ultra-fine slag expected to be balanced by the use of fly ash (FA). In the present study, NS-activated ultra-fine slag/FA was designed. Effects of NS dosage and FA content on the compressive strength were researched, and the activated process was assessed by chemical shrinkage, XRD, TGA, pH value, ion concentration, NMR, and SEM. Finally, CO2 emissions were evaluated. Results showed that compressive strength of slag with D50 = 3.1 μm activated by 4% Na2O-E of NS reached 36.2 MPa and 77.3 MPa at 28 d and 90 d age. The main hydrates of NS-activated slag were ettringite and C-(N)–S–H. Moreover, in the NS-activated ultra-fine slag/FA mortars, 20% FA significantly reduced the 3 d compressive strength, but slightly increased the 28 d compressive strength. CO2 emissions of this blend seemed much lower than that of NaOH or water glass-activated slag. These results suggested one alkali-activated binder with low carbon emissions.
•Slag with D50 = 3.1 μm was efficiently activated NS at ambient temperature.•The increase in NS accelerated the production of C–N–S-A-H and ettringite.•Strength of slag with 20% FA could reach 41.5 MPa and 60.8 MPa at 28 d and 90 d age.•CO2 emissions of NS-activated slag/FA was lower than that of the common AAS system.
The above article, published online on 29 December 2022 in Wiley Online Library (wileyonlinelibrary.com) has been retracted by agreement between the journal's Editor‐in‐Chief, Professor Luc Taerwe, ...the fib, and John Wiley & Sons Ltd. The retraction has been agreed given the journal has received evidence confirming that the peer review process of this paper was manipulated. As a result, the conclusions reported in the article are not considered reliable.
Compressive strength of concrete is one of the most determinant parameters in the design of engineering structures. This parameter is generally determined by conducting several tests at different ...ages of concrete in spite of the fact that such tests are not only costly but also time-consuming. As an alternative to these tests, machine learning (ML) techniques can be used to estimate experimental results. However, the dependence of compressive strength on different parameters in the fabrication of concrete makes the prediction problem challenging, especially in the case of concrete with partial replacements for cement. In this investigation, an extreme learning machine (ELM) is combined with a metaheuristic algorithm known as grey wolf optimizer (GWO) and a novel hybrid ELM-GWO model is proposed to predict the compressive strength of concrete with partial replacements for cement. To evaluate the performance of the ELM-GWO model, five of the most well-known ML models including an artificial neural network (ANN), an adaptive neuro-fuzzy inference system (ANFIS), an extreme learning machine, a support vector regression with radial basis function (RBF) kernel (SVR-RBF), and another SVR with a polynomial function (Poly) kernel (SVR-Poly) are developed. Finally, the performance of the models is compared with each other. The results of the paper show that combining the ELM model with GWO can efficiently improve the performance of this model. Also, it is deducted that the ELM-GWO model is capable of reaching superior performance indices in comparison with those of the other models.
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