Alkali-activated Cementitious Materials Research Articles

Study on the Properties and Hydration Mechanism of Calcium Carbide Residue-Based Low-Carbon Cementitious Materials

Alkali-activated cementitious materials, as an environmentally friendly cementitious material, can effectively reduce carbon emissions and improve the utilisation of solid wastes. However, traditional strong alkali activators have limitations such as high carbon emissions and poor safety. In order to overcome the defects of traditional strong alkaline activators and realise the high value-added use of calcium carbide residue (CCR), this paper adopts CCR as an alkaline activator to activate granulated blast furnace slag (GBFS)-steel slag (SS) cementitious systems for the preparation of alkaline-activated cementitious materials. The effects of CCR content and SS content on the compressive strength and working performance of CCR-GBFS-SS cementitious systems are analysed, along with the hydration process of CCR-GBFS-SS cementitious systems and the mechanism of action through the hydration products, their chemical structure and their microscopic morphology. The research results show that CCR-GBFS-SS cementitious systems have a 28-day compressive strength of 41.5 MPa and they can be controlled by the setting time; however, the flow performance is poor. The SS content can be increased to improve the flow performance; however, this will reduce the compressive strength. In CCR-GBFS-SS cementitious systems, CCR is the main driving force of hydration reactions, GBFS mainly provides active silica and aluminium and the amorphous C-(A)-S-H gel and ettringite formed by the synergistic action of multiple solid wastes are the main sources of compressive strength. With the extension of the curing time, the amount of hydration products in the cementitious systems gradually increases and the matrix of the cementitious systems gradually becomes denser. This study will provide a reference for the consumption of low-value solid waste such as CCR and the preparation of low-carbon cementitious materials from multi-component solid wastes.

Investigating the Performance of Alkali-Activated Cementitious Materials Under Temperature Cycling

Investigating the Performance of Alkali-Activated Cementitious Materials Under Temperature Cycling

Ultra-High-Performance Alkali-Activated Concrete: Effect of Waste Crumb Rubber Aggregate Proportions on Tensile and Flexural Properties

The declining availability of natural sand resources and the significant carbon footprint associated with the extensive use of cement are posing severe limitations on the advancement and application of ultra-high-performance concrete (UHPC). In this study, waste tyre-derived recycled crumb rubber particles (CR) were employed to replace quartz sand, and an alkali-activated cementitious material was used to produce waste tyre-alkali-activated UHPC (T-UHPAC). The influence of different CR replacement ratios (0%, 5%, 20%, 35%, 50%) on the tensile and flexural performance of T-UHPAC was investigated, and a predictive model for the stress–strain response considering the CR replacement ratio was established. An optimization method for improving the tensile and flexural performance of T-UHPAC was proposed. The results indicate that the effect of rough-surfaced CR on the interfacial properties of concrete differs from that of smooth quartz sand. A CR replacement ratio exceeding 35% led to a reduction in both the tensile and flexural strengths of UHPAC, while a replacement ratio at or below 20% resulted in a superior tensile and flexural performance of T-UHPAC. The established predictive model for tensile performance accurately forecasts the stress–strain behaviour of T-UHPAC under varying CR replacement ratios, with the accuracy improving as the CR replacement ratio increases. By utilizing CR to replace quartz sand in proportions not exceeding 20%, the production of low-carbon UHPC with exceptional comprehensive mechanical properties is achievable. Moreover, the development of T-UHPAC through the comprehensive utilization of waste tyres presents a promising and innovative approach for the low-carbon and cost-effective production of UHPC, thereby facilitating the sustainable development of natural resources. This research represents a significant step towards the widespread adoption and application of UHPC and thus holds substantial importance.

Utilization of Copper–Molybdenum Tailings to Enhance the Compressive Strength of Alkali-Activated Slag-Fly Ash System

Utilizing a variety of solid wastes to prepare alkali-activated cementitious materials is one of the principal trends in the development of cementitious materials. Commonly used alkali activation precursors such as granulated blast furnace slag (GBFS) and fly ash (FA) will be less available due to resource pressures. Supply limitation is an important reason to research alternative precursors. To realize the high value-added utilization of copper–molybdenum tailings (CMTs), this study adopted the modified sodium silicate solution as an alkaline activator to activate GBFS-FA-CMTs cementitious system to prepare alkali-activated cementitious materials. The influence of CMTs content on the compressive strength of GBFS-FA-CMTs cementitious system was analyzed, and the mechanism of GBFS-FA-CMTs cementitious system was also analyzed through hydration product types, physical phase composition, and microscopic morphology. The results indicated that a paste with the incorporation of CMTs, S50F30C20 (50% GBFS, 30% FA, 20% CMTs), achieved the highest compressive strength of 79.14 MPa, which was due to the filling effect of the CMTs and the degree of participation in the reaction. Pastes with different contents of CMTs, while maintaining a constant CBFS content, exhibited similar strength development. Excessive amounts of CMTs could result in reduced compressive strength. Microstructural analysis revealed that the hydration products were structurally altered by the addition of CMTs. In addition to ettringite, quartz, C(-N)-S-H gel, and calcite, gaylussite was also formed; moreover, the mass of chemically bound water increased, and the microstructure of reaction products became denser. An excess of CMTs may restrict the growth of the hydration gel, leading to more microstructural defects. The study suggests that CMTs could enhance the compressive strength of hardened paste within an alkali-activated slag-fly ash system, possibly due to a filling effect and participation in the chemical reaction. This research confirms the feasibility of using CMTs in alkali-activated cementitious materials.

Effect of water quenched silicomanganese slag as fine aggregate on mechanical properties and microstructure characteristics of solid waste-based mortar and concrete

Research on water quenched silicomanganese slag (WQSMS) has primarily focused on grinding it into micro-powder to be used as auxiliary cementitious materials or to synthesize alkali-activated cementitious materials. However, there is a lack of research on utilizing WQSMS as fine aggregates instead of natural aggregates. Although its properties are similar to granulated blast furnace slag (GBFS), most studies investigating the use of GBFS as fine aggregates have mainly focused on mechanical properties rather than microstructure analyses. Meanwhile, to make full use of industrial solid waste, reduce CO2 emissions, and save energy consumption, solid waste cementitious material based on steel slag (SS), desulphurized gypsum (DG), and GBFS, as well as WQSMS as fine aggregate to replace ISO standard sand and washed-out sand (WOS) in various proportions(0%, 25%, 50%, 75%, and 100%) to prepare mortar and concrete, respectively. Analyses of workability, mechanical properties, and microstructure were carried out, and the improvement of mechanical properties of WQSMS was analyzed by SEM-EDS, SEM-BSE, and the microhardness test. The results show that with the increase of WQSMS, the workability of mortar and concrete decreased, while the mechanical strength increased first and then decreased. The mechanical strengths of them reached the peak when the WQSMS addition reached 50%. The flexural and compressive strengths of the mortar increased by 40% and 9.7%, respectively, while the tensile splitting strength and compressive strength of the concrete increased by 11.9% and 3.4%, respectively. The microstructure of the interfacial transition zone(ITZ) was greatly enhanced by WQSMS, which decreased the porosity by 10.49%, decreased the thickness by 27.27%, and increased the microhardness by 11.0%. However, when the content surpasses 50%, the mechanical strength of mortar and concrete declined due to the loose porosity and poor mechanical strength of WQSMS, and there was insufficient cementitious material to fill these holes. Nonetheless, with 100% content, the mortar maintained its high-performance status, with a flexural strength of 8.0 MPa and a compressive strength of 47.9 MPa, and the concrete still fulfilled the specifications of regular concrete C40. Both the fine aggregate and the cementitious material were composed of solid waste, showing potential environmental benefits and interesting green products for future studies.

Effects of recycled carbon fibers on mechanical and piezoresistive properties and environmental impact in alkali-activated cementitious materials

The development of alkali-activated cementitious materials (AAM) reinforced with recycled carbon fiber (rCF) is of remarkable significance due to its cost-effectiveness compared to virgin carbon fiber, along with the sustainable reuse of solid waste serving as AAM. This study explores the integration of rCF and solid waste Ground Granulated Blast Furnace Slag (GGBS), aiming for cleaner construction practices. A novel approach involving a high-viscosity one-part GGBS slurry ensured homogeneous rCF dispersion, resulting in alkali-activated slag (AAS) mortars with outstanding overall performance at minimal dosage. At a minimum dosage of 0.1 vol%, rCF significantly enhanced flexural strength by 53.42% and reduced drying shrinkage by over 20%. The uniformly dispersed rCF acts as nucleation sites, boosting early compressive strength without compromising long-term performance. Furthermore, the connected rCF network established an exceptionally low percolation threshold (0.125 vol%) and demonstrated promising piezoelectric properties under cyclic loading, illustrating its potential as self-sensing concrete elements. Additionally, life cycle analysis (LCA) underscored the environmental benefits of rCF and GGBS, revealing their potential to remarkably cut carbon emissions (75.36%) and reduce costs (36.5%). These findings provide valuable insights into the development of rCF-reinforced self-sensing mortar with superior mechanical properties, showcasing the substantial potential of rCF in driving the construction industry toward carbon neutrality.

Experimental study on municipal solid waste incineration bottom ash as a component of alkali-activated coal gangue-based geopolymer.

This study explores the potential of municipal solid waste incineration bottom ash (MSWI BA) and coal gangue as precursors for alkali-activated cementitious materials (CG-MBA). An examination of the impact of MSWI BA content, NaOH/Na2SiO3 ratio, liquid-solid ratio, and NaOH concentration on strength and reaction through the application of diverse analytical methodologies. Results demonstrate that CG-MBA offers significant environmental benefits compared to conventional cement. When used as a construction filling material, CG-MBA exhibits a remarkable 74.5 ~ 79.2 wt% reduction in carbon dioxide emissions and 70.6 ~ 77.0 wt% reduction in energy consumption. Additionally, CG-MBA effectively immobilizes heavy metal ions in MSWI BA, with a fixation efficiency exceeding 56.0%. These findings suggest that CG-MBA is a promising sustainable solution for waste management, offering significant environmental benefits while demonstrating effective heavy metal immobilization. This approach contributes to pollution control and promotes environmental sustainability in the construction industry.

Synergy of micron graphite and fly ash for alkali-activated cementitious material: Electromagnetic absorption characteristics and mechanism

To attain a balance between compressive strength and electromagnetic wave absorption performance, this paper combined two electromagnetic wave loss mechanisms (magnetic loss and electrical loss), and prepared an environmentally friendly alkali-activated slag/fly cementitious material (ASFC) using micron graphite (MG) as the absorber and ground granulated blast furnace slag (GGBS) and fly ash (FA) as the precursors. The conductivity, electromagnetic wave absorption characteristics and compressive strength of ASFC with different ratios of GGBS and FA, MG size (800 mesh, 320 mesh, and 100 mesh), and content were investigated. The results indicated that when the ratio of GGBS and FA was 7:3, natural resonance and eddy current loss contributed to electromagnetic waves absorption at 8.2–11.0 GHz and 11.0–15.5 GHz range respectively. Additionally, the conductivity of MG/ASFC showed typical percolation characteristics, with the percolation threshold reached at a dosage of 3 wt%. In the 8.2–18.0 GHz, the incorporation of MG significantly augmented the conductive loss and polarization loss of ASFC. Furthermore, smaller-size MG was more beneficial for facilitating conductive loss of MG/ASFC among three different sizes. By adding 2 wt% of MG with 800 mesh, MG/ASFC can achieve a minimum reflection loss of −27.8 dB with a bandwidth of 3.0 GHz (Reflection loss ˂-7 dB). However, when compared to other cement-based absorbing materials reported, the MG/ASFC prepared in this experiment demonstrated better compressive strength and wave absorption properties. This finding contributing to a better understanding of green building materials with electromagnetic radiation protection capabilities.

Investigation into the alkali-activation of lithium slag: A sustainable alternative to conventional cement with optimized mechanical properties

Utilizing lithium slag as a precursor for alkali-activated cementitious materials offers a sustainable alternative to conventional cement, addressing both environmental pollution and land-use challenges posed by lithium slag waste. Additionally, this practice reduces energy consumption and CO2 emissions associated with cement production. This study presents a novel methodology involving high-temperature calcination and mechanical grinding to enhance the reactivity of lithium slag. Analytical techniques, such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), were employed to elucidate the mechanisms behind lithium slag's increased reactivity. Subsequently, these activated materials were used to formulate alkali-activated lithium slag cement composites (ALC). Various factors, including the calcination temperature, water-to-cement ratio, NaOH concentration, and lithium slag content, were investigated for their effects on the fluidity and mechanical properties of the mortar. Analytical techniques including XRD, scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), FTIR, and thermogravimetric analysis (TGA)/derivative thermogravimetry (DTG), were used to explore the hydration mechanisms. Results indicate that the optimal calcination temperature for lithium slag was 700 °C, while the optimal NaOH concentration was 1 mol/L. ALC exhibited robust mechanical properties, with compressive, flexural, and fluidity measures reaching 37.66 MPa, 10.13 MPa, and 200 mm, respectively. Predominant hydration products were found to be N-A-S-H and C-A-S-H. The production cost of 1 ton of ALC is $49.8, which is roughly 70% of the cost of producing 1 ton of OPC. Additionally, the total CO2 emissions and energy consumption of producing ALC amount to 60.56% and 64.95% respectively, compared to the total CO2 emissions and energy consumption of producing 1 ton of OPC.

磷渣基碱激发胶凝材料抗压性能研究

磷渣基碱激发胶凝材料抗压性能研究

Research on reactivity evaluation and micro-mechanism of various solid waste powders for alkali-activated cementitious materials

Alkali-activated cementitious material (AACM) based on the utilization of solid waste is a new type of environmentally friendly inorganic material, which has the advantages of early strength, fast hardening, high strength, and better durability. The reactivity of solid waste powder is a key factor for its appropriate utilization in alkali-activated cementitious materials, necessitating a rational evaluation of its reactivity. The reactivity evaluation was conducted on various solid waste powders, including fly ash (FA), red mud (RM), recycled micro-powder (RMP), red brick powder (RBP), coal gangue powder (CGP), and cement kiln dust (CKD). The effects of NaOH concentration, weight ratio of water to solid waste powder (W/P) and curing humidity on the compressive strength were investigated，then the compressive strength under optimal conditions was determined based on response surface analysis. The compressive strength under optimal conditions was used to evaluate the reactivity of solid waste powders. Moreover, microscopic tests (e.g., XPS test, ICP test, and NMR test) were carried to evaluate the reactivity of the solid waste. The relative number of bridging oxygen (RBO) measured by the NMR method in conjunction with chemical composition analysis serves as an effective method for evaluating the reactivity of solid waste powders. The leaching rate of Silicon (Si) and Aluminum (Al) ions in the ICP method depended mainly on the NaOH concentration and the elemental content in the raw material. In addition, the binding energies of O1s, Si 2p, and Al 2p tested by the XPS method had no particular correlation with the compressive strength.

Study on properties and soil solidification mechanism of alkali - activated cementitious materials

Due to the low strength and poor durability of soil, it is limited in engineering application. To improve its strength and durability, the alkali-activated (AA) cementitious materials were prepared using industrial wastes, and experiments were performed on AA cementitious materials and solidified soil, including mechanical properties tests, water stability tests, and microscopic properties tests. The results indicate that the content ratio of fly ash and slag can significantly affect the properties of AA cementitious materials, and the maximum 28d compressive strength reaches 36.1 MPa. With increasing AA cementitious materials content (up to 50%) and age, both the compressive strength and tensile strength of AA solidified soil enhance. The microstructure evolution process of soil after solidification includes four stages, including mineral material dissolution, silicon aluminum diffusion, polymerization of low polymer silicon aluminum salts, and polymer soil particle cementation and hardening. The mineral raw material particles and soil particles are effectively bonded due to the adhesion between the reaction products and the mineral material, which improves the performance of the AA solidified soil. The maximum 28d compressive strength of AA solidified soil was 3.6 MPa, the maximum tensile strength was 1.05 MPa, and the maximum water stability coefficient was 0.89.

Manufacture of alkali-activated cementitious materials using municipal solid waste incineration fly ash (MSWIFA): The effect of the Si/Al molar ratio on fresh and hardened properties

Due to the escalating production of municipal solid waste and the widespread adoption of incineration technology, there is a substantial demand for secure disposal of municipal solid waste incineration fly ash (MSWIFA). In this research, alkali-activated MSWIFA via combination with metakaolin (MK) and cement was used to produce an eco-friendly composite. The influence of Na2O content and modulus (Ms) of alkali activator on the early compressive strength and setting time of the composites was investigated, and 4 wt% Na2O content was found to be the most appropriate alkali content. Then, the influence of the Si/Al ratio (2.35–3.18) on the fresh properties (initial setting time, rheology properties, and hydration heat) and hardened properties (compressive strength and shrinkage performance) of composite materials was studied. The microscopic mechanism of the effect of the Si/Al ratio on material properties was explained by XRD, TG, and SEM-EDX. The results showed that the compressive strength of the composite can reach 16.4 MPa at 28 days, which met the quality standard of MU15 (GB/T 25779–2010) of load-bearing concrete perforated brick. With the increase of the Si/Al ratio, the setting time of the slurry is prolonged and the rheological property has deteriorated. The composites with a lower Si/Al ratio (2.35) have the densest structure and the lowest degree of drying shrinkage, which leads to a higher strength. This study provides a potential solution for MSWIFA solidification in low-carbon construction applications.

Alkali-activated geopolymer materials prepared from coal gangue and municipal solid waste incineration byproducts

Coal gangue and municipal solid waste incineration byproducts (fly ash and bottom ash) are considered as solid and hazardous waste, respectively, and the accumulation of these wastes leads to significant environmental issues. Coal gangue is rich in Si and Al but lacks of Ca, making it challenging to create alkali-activated cementitious materials with good mechanical performances. Fly ash and bottom ash are abundant in Ca. The feasibility of using fly ash and bottom ash as calcium sources for preparing alkali-activated coal gangue-based geopolymers is investigated in the present work. The unconfined compressive strength (UCS) test and microscopic tests (XRD, FTIR, TGA, SEM and ICP-OES) are conducted to study the strength and reaction mechanism of coal gangue and fly ash/bottom ash (CGFA/BA) geopolymers. The results show that the strength of CGFA/BA geopolymers initially increases and then decreases with an increase in fly ash and bottom ash content, and the optimal dosage of fly ash and bottom ash is 15% and 30%, respectively. The liquid-solid ratio and alkali solution (NaOH/Na2SiO3) ratio have a significant influence on the strength of the CGFA/BA geopolymers and the optimal alkali solution ratio is 25:75, while the liquid-solid ratio of 0.45 and 0.60 is recommended for CGFA and CGBA geopolymers, respectively. The CGFA geopolymer with 15% fly ash, 25:75 alkali solution ratio, 0.45 liquid–solid ratio and 8 mol/L sodium hydroxide concentration obtains the highest UCS of 30.28 Mpa. The heavy metal immobilization efficiency (IE) of the CGFA geopolymer is better than that of the CGBA geopolymer. The IE of heavy metals of the CGFA geopolymer is larger than 84.66% and that of the CGFA geopolymer is larger than 55.95%. In the CGFA geopolymer, the IE is Hg>Pb>Zn>Cd>Cr>Ba, while in the CGBA geopolymer, the IE is Hg>Cd>Ba>Cr>Zn>Pb.

Prediction of compressive strength and feature importance analysis of solid waste alkali-activated cementitious materials based on machine learning

This study examines the analysis and treatment of diverse types of solid waste alkaline-activated cementitious materials utilizing machine learning techniques. To account for the variability of solid waste alkaline-activated cementitious materials, three crucial chemical components (aluminum trioxide, calcium oxide, and silicon dioxide) were chosen as representative features. A total of 274 pertinent datasets were collected and split into training and testing sets with an 80% to 20% ratio for analysis. Six machine learning models, including multilayer feedforward neural network, genetic algorithm neural network, support vector machine, random forest, radial basis function neural network, and long short-term memory network, were employed to construct predictive models. The optimal hyperparameters were identified via grid search. The performance of the models was assessed using the training and testing sets, revealing that all models exhibited strong predictive and generalization capabilities on both sets. Among the models, the support vector machine model achieved the highest performance, yielding an R2 value of 0.9054, MAE of 4.1460, and NRMSE of 0.0997. Through the utilization of SHAP (Shapley Additive Explanations) analysis, the interplay between factors and the significance of features were examined. Calcium oxide, water-to-binder ratio, silicon dioxide, modulus of water glass, and aluminum trioxide were recognized as the primary factors that influence the compressive strength. The research findings offer guidance for optimizing the performance of alkaline-activated cementitious materials made from solid waste.

Experimental Study on the Application of Recycled Concrete Waste Powder in Alkali-Activated Foamed Concrete.

The alkali-activated cementitious material was prepared by partially replacing slag with recycled concrete powder (RCP). The influence of RCP substitution rates (10%, 20%, 30%, 40%, and 50% mass fraction) on the performance of alkali-activated slag-RCP-based (AASR) foamed concrete was studied. The fluidity, water absorption, softening coefficient, compressive strength, flexural strength, drying shrinkage, thermal conductivity, and frost resistance of AASR foamed concrete were studied. The results show that the fluidity and softening coefficient of AASR foamed concrete decreases with the increase in RCP content, and the fluidity range is 230-270 mm. Due to the porous structure of the RCP, the water absorption of AASR increases. With the increase in the curing age, the strength of AASR foamed concrete increases. The addition of RCP reduced the mechanical properties of AASR foamed concrete. Compared with the control group, the compressive strength of AASR50 decreased by 66.7% at 28 days, and the flexural strength decreased by 61.5%. However, the 28 d compressive strength of AASR foamed concrete under all RCP replacement rates still meets the standard value (0.6 MPa). The addition of RCP effectively reduces the thermal conductivity of the AASR foamed concrete, and when the RCP content is 50%, the thermal conductivity is lowest, 0.119 W/(m·K); the drying shrinkage of the AASR foamed concrete can be improved by adding RCP, and the drying shrinkage value is lowest when the RCP is 30%, which is 14.7% lower than that of the control group. The frost resistance of AASR foamed concrete decreases with the increase in the RCP content. When the recycled micropowder content is 20-50% and after 25 freeze-thaw cycles, AASR foamed concrete has reached freeze-thaw damage.

Distribution of Na+ and Mechanical Properties of Hardened Body of Alkali-activated Cementitious Materials

Distribution of Na+ and Mechanical Properties of Hardened Body of Alkali-activated Cementitious Materials

Workability and mechanical properties of GGBS-RFBP-FA ternary composite geopolymer concrete with recycled aggregates containing recycled fireclay brick aggregates

With urbanization developing, various construction and demolition wastes (CDWs) have emerged, causing environmental and social issues. Green concrete materials, such as recycled aggregates concrete (RAC) and alkali-activated cementitious materials, propose for their environmentally friendly construction. In this study, the ground granulated blast furnace slag (GGBS), recycled fireclay brick powder (RFBP), and fly ash (FA) ternary composite geopolymer concrete with recycled aggregates (GRAC) containing recycled fireclay brick aggregates (RFBA) proposed at first. Then, this study investigated the fresh and hardened properties of this concrete. The experimental variables included the two types of ternary composite geopolymer concrete with recycled fireclay brick aggregates (GRA-RFBAC) mix ratios, five replacement ratios of recycled coarse aggregate, and four replacement ratios of RFBP. The workability and mechanical properties of GRA-RFBAC were studied, respectively. Moreover, the micro-structures and hydration mechanisms of GRA-RFBAC were also studied. The results showed the feasibility of applying RFBP and recycled aggregates containing recycled fireclay brick aggregates (RA-RFBA) in geopolymer concrete, i.e. GRA-RFBAC exhibited good workability and mechanical properties. The addition of RFBP could improve the workability of GRA-RFBAC. GRA-RFBAC with 10% RFBP replacement ratio of was found to have the best mechanical properties. The addition of RA-RFBA has a detrimental effect on both the workability and mechanical properties of the GRA-RFBAC. The stress-strain relationship model of GRA-RFBAC was give and the stress-strain curves of GRA-RFBAC were similar to those of Ordinary Portland cement concrete with recycled aggregates.

Manufacture of alkali-activated cementitious materials using municipal solid waste incineration (MSWI) ash: Immobilization of heavy metals in MSWI fly ash by MSWI bottom ash

Based on the purpose of safe solid waste recycling, this work proposed a new method of co-treatment of municipal solid waste incineration fly ash (MSWIFA) and municipal solid waste incineration bottom ash (MSWIBA). The alkali-activated binder was synthesized from MSWIFA and MSIWBA by Ca/Si ratio design. The results showed that the maximum compressive strength of the samples at 56 d reached 8.8 MPa. A low concentration of alkali (6% Na2O dosage) favors the development of compressive strength when more MSWIFA is used in the binder system. The C-S-H gel is the main gel product in this case. In contrast, a high concentration of alkali (8% Na2O dosage) is required in the MSWIBA-based binder system. And C-(A)-S-H gels and N-A-S-H gels coexist under this condition. The results of leaching tests showed that after 56 d of curing, the reaction products limited the migration and leaching of potentially toxic elements from MSWIFA by physical encapsulation or chemical bonding. The immobilization efficiency of heavy metals such as Cd, Cr, Cu, Ni, Pb and Zn were above 98%, and their leaching concentrations were below the limits of the relevant Chinese standards.

Study on strength characteristics and thickening characteristics of classified-fine cemented backfill in gold mine

For some new mines, the utilization rate of tailings is not satisfactory when using unclassified tailings as backfill aggregate for cemented backfill. At the same time, with the progress of mineral processing technology, the tailings discharged by the concentrator gradually become finer. Therefore, cemented filling with fine-grained tailings as aggregate will become the development direction of filling technology in the future. In this paper, the feasibility of fine particle tailings backfill is studied by taking the particle tailings of-200 mesh as aggregate in Shaling gold mine. The calculation shows that the utilization rate of tailings is increased from 45.1% to 90.3% by using-200 mesh tailings as filling aggregate. The response surface central composite design method (RSM-CCD) was used to study the strength of backfill with alkali-activated cementitious material as binder by taking the mass concentration of backfill slurry and sand-binder ratio as input factors. The results show that the 28-day strength of the backfill with graded fine-grained tailings as filling aggregate can reach 5.41 MPa when the sand-binder ratio is 4, which can fully meet the needs of the mine for the strength of the backfill. The thickening test of-200 mesh fine particle tailings was carried out by static limit concentration test and dynamic thickening test. In the case of adding 35 g/t BASF 6920 non-ionic flocculant, the concentration of 64.74% tail mortar can reach 67.71% after 2 h of static thickening, and the concentration can reach 69.62% after 2 h of static thickening. The feeding speed of thickener should be controlled between 0.4 and 0.59 t/(m2 h). In this case, the underflow concentration of thickener is relatively high, which is 64.92–65.78%, and the solid content of overflow water is less than 164 ppm. The conventional full tailings thickening process was improved by using the design of high-efficiency deep cone thickener and vertical sand silo. The feasibility of fine-grained tailings as filling aggregate was demonstrated by combining the filling ratio test of fine-grained tailings, the data of thickening test and the improved thickening process. The research results can provide reference for other mines to use fine-grained tailings as filling aggregate to design filling system.