To address the persistent challenge of accurately predicting the unconfined compressive strength(UCS)of cemented paste backfill(CPB)in underground mining,this study developed a hybrid intelligent model integrating quantum-behaved particle swarm optimization(QPSO)with a fully connected neural network(FCNN).A comprehensive database comprising 383 laboratory test samples was compiled,encompassing eight input variables:coefficient of uniformity(Cu),chemical composition(CaO and MgO),cement type(CT),tailings-to-cement(T/C)ratio,slurry mass concentration(MC),curing temperature(Temp),and curing time(Time).The QPSO algorithm was employed to perform a global optimization of critical hyperparameters,including hidden nodes,learning rate,regularization coefficient,dropout rate,and batch size.Subsequently,the Adam optimizer was applied for deterministic fine-tuning of network weights,yielding concurrent enhancements in convergence efficiency and predictive accuracy.Furthermore,SHAP,±10%perturbation analysis,and partial dependence plots(PDPs)were utilized to quantitatively evaluate the global importance,local marginal effects,and interactive sensitivities of input parameters.The proposed QPSO-FCNN model exhibited outstanding predictive performance,achieving an R2of 0.969,RMSE of 0.198 MPa,mean absolute erron(MAE)of 0.139 MPa,and a composite performance score(CPS)of 0.930,surpassing both conventional FCNN and QPSO-BPNN hybrid models.Sensitivity analysis revealed that T/C and Time were the most influential factors,while pronounced coupling effects occurred between Cu and MC,as well as between curing conditions and T/C.These results provide robust quantitative insights for optimizing the mix design and curing regimes of CPB,thereby enhancing its mechanical reliability in underground mining operations.
Aiming at the prominent problems of high cost of cementitious materials and low CO2sequestration efficiency in mine filling,this study systematically explored the influence mechanism of the mineral activator carbide slag(CS)and its composite activation with Na2SiO3(sodium silicate,SS)on the properties of low-activity electric arc furnace slag(EAFS)and granulated blast furnace slag(GBFS)-based cementitious materials.By preparing carbon-sequestering backfill materials with CS and CS–SSas activators,mineralization tests were conducted under controlled CO2curing parameters(pressure:0.2–0.4 MPa,concentration:20%–60%,curing duration:1–4 h).Comprehensive characterization via X-ray diffraction(XRD),Fourier-transform infrared spectroscopy(FTIR),thermogravimetry-differential scanning calorimetry(TG-DSC),and scanning electron microscopy(SEM)was performed to elucidate the evolution of hydration products and microstructures.It was revealed from the experimental results that,for the CS single-activation system,the 3-day and 7-day uniaxial compressive strengths(UCS)of the cementitious materials decreased with an increasing EAFS replacement ratio.The UCS peaked at 6.81 MPa(3-day)and 10.96 MPa(7-day)when EAFS replacement was 20%(with 20%or 30%CS,respectively).However,excessive CS reduced strength due to insufficient GBFS participation.The CS–SSsynergistic activation system exhibited superior early-age strength(17.66 MPa at 3-day or 22.01 MPa at 7-day),confirming the dominant role of SS in early hydration.Mineralization significantly enhanced the performance of the CS single-activation system:the 3-day strength increased by 1.90–2.77 times(reaching 11.60 MPa)compared to the control group(4.20 MPa),but it weakened the CS–SS synergistic activation system.It was identified via orthogonal analysis that CO2concentration(40%)was the primary factor influencing the 3-day strength of the CS single-activation system,followed by pressure(0.4 MPa)and curing duration(1 h).This validates that mineralization can be achieved under non-pure CO2and non-high-pressure conditions.Microstructural analyses showed that the CS single-activation system promoted the formation of C–(A)–S–H gel and CaCO3,whereas composite systems underwent decalcification of C–(A)–S–H gels during mineralization.This study uncovers the synergistic advantages of CS under CO2mineralization conditions and the incompatibility between the CS–SSsynergistic activation system and CO2mineralization curing,providing theoretical foundations and technical pathways for developing low-cost mine backfill materials with high CO2sequestration capacity.
This paper investigates the influence of mine tailings particle size and curing temperature on the rheological properties and strength development of cemented paste backfill(CPB).Laboratory experiments were conducted on CPB to evaluate their physical and mechanical behavior.A series of CPB samples with different mixture designs were prepared and cured for 28 days.The effect of curing temperature and particle size on mechanical properties was assessed using uniaxial compressive strength(UCS)tests.In addition,the influence of curing temperature(ranging from 5°C to 50°C)on CPB samples was studied through UCS testing.The microstructure of selected specimens was further analyzed using the mercury intrusion porosimetry(MIP)technique.The results indicate that:(i)the mechanical performance of CPB can be enhanced by reducing the proportion of fine particles in the tailings;(ii)the rate of strength gain increases with decreasing particle size,samples exhibiting faster strength development than CPB samples over the 28-day curing period;(iii)curing temperature has a significant impact on both the mechanical and microstructural properties of CPB;(iv)microstructural analysis revealed that reducing fine particles modifies pore size distribution and decreases overall porosity,thereby improving the mechanical behavior of CPB;and(v)MIP results showed that the reduction of particle size altered the microstructure,leading to a higher proportion of fine pores in CPB.
