The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morph...The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morphology differences between PC and AAS on micrometer to nano meter scale.The experimental results indicated that the AAS paste had soil like fracture texture and it was composed of mainly C-S-H gel but lacks of crystals,and it had a very strong tendency to shrink and crack.AAS paste is much denser and more homogeneous than PC,and on the nano scale C-S-H nano particle in the AAS paste is much smaller and packs much denser than PC paste.展开更多
This paper reports the development of an Alkali Activated Binder (AAB) with an emphasis on the performance and the durability of the AAB-matrix. For the development of the matrix, the reactive components granulated sl...This paper reports the development of an Alkali Activated Binder (AAB) with an emphasis on the performance and the durability of the AAB-matrix. For the development of the matrix, the reactive components granulated slag and coal fly ash were used, which were alkali activated with a mixture of sodium hydroxide (2 - 10 mol/l) and aqueous sodium silicate solution (SiO<sub>2</sub>/Na<sub>2</sub>O molar ratio: 2.1) at ambient temperature. A sodium hydroxide concentration of 5.5 mol/l revealed the best compromise between setting time and mechanical strengths of the AAB. With this sodium hydroxide concentration, the compressive and the 3-point bending tensile strength of the hardened AAB were 53.4 and 5.5 MPa respectively after 14 days. As a result of the investigation of the acid resistance, the AAB-matrix showed a very high acid resistance in comparison to ordinary Portland cement concrete. In addition, the AAB had a high frost resistance, which had been validated by the capillary suction, internal damage and freeze thaw test with a relative dynamic E-Modulus of 93% and a total amount of scaled material of 30 g/m<sup>2</sup> after 28 freeze-thaw cycles (exposure class: XF3).展开更多
This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaC...This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaCO3 as a stabilizer,and straw(for strengthening).The availability of raw materials for making Adobe presents the waste-stabilized Adobe as a potential product for a new alkali-activated binder.Waste-stabilized Adobe collected from an abandoned damaged building in the village of Inonu in Northern Cyprus,ground and calcined at the following temperatures:450,550,650,750,850,and 950℃.The calcination at each temperature was held for different durations 1,3,5,and 7 h.Raw and calcined waste stabilized Adobe structures were investigated using XRF,TGA-DTA,XRD,FTIR,and SEM.Considering technical and environmental views related to energy consumption,waste stabilized Adobe calcined at 750℃ for 1 h presented the most promising results regarding the production of a new precursor for alkali-activated binder.This study also presents the effect of ground granulated blast furnace slag(GGBFS)usage on the fresh and hardened properties of optimum calcined AB-based alkali-activated pastes cured at room temperature.GGBFS was used to partially replace AB to form a binary composite raw material system and seven experimental groups were designed according to replacement levels of 0%,5%,10%,15%,20%,25%and 30%(by mass).Alkali-activated high volume waste-stabilized Adobe-slag pastes prepared using Na2SiO3-to-NaOH ratio of 2 and 12 M concentration of Sodium Hydroxide.The fresh property as flowability and the hardened property as the compressive strength of the alkali-activated pastes with different GGBFS contents were investigated.The results indicated that the incorporation of GGBFS increased the flowability of fresh alkali-activated pastes.A 28-day compressive strength of 43.75 MPa can be obtained by a 30%replacement level of GGBFS.展开更多
We read with great interest the investigations conducted by Pourakbar et al.(2024)on the“Stabilization of clay soil using alkali-activated sewage sludge.”The authors have investigated the feasibility of utilizing al...We read with great interest the investigations conducted by Pourakbar et al.(2024)on the“Stabilization of clay soil using alkali-activated sewage sludge.”The authors have investigated the feasibility of utilizing alkali-activated sewage sludge(AASS)as a binder for stabilizing the clayey soil.Sewage sludge(SS)in varying proportions of 1.5%,2%,2.5%,3.5%,and 4.5%was utilized to prepare geopolymer binders using sodium and potassium-based alkali activators.Furthermore,unconfined compressive strength(UCS)and direct shear tests were conducted to examine the strength development of clayey soil stabilized with AASS.While the study presented some intriguing results,we have identified critical concerns regarding(i)the selection of SS as a precursor for alkali activation,(ii)technical inconsistencies associated with the compaction characteristics and microstructural analysis,and(iii)the feasibility of the proposed methodology for practical applications.Through our discussion,we seek to highlight these issues and provide constructive feedback to advance the understanding of alkali activation processes and their implications for soil stabilization.展开更多
Granite residual soil (GRS) is a type of weathering soil that can decompose upon contact with water, potentially causing geological hazards. In this study, cement, an alkaline solution, and glass fiber were used to re...Granite residual soil (GRS) is a type of weathering soil that can decompose upon contact with water, potentially causing geological hazards. In this study, cement, an alkaline solution, and glass fiber were used to reinforce GRS. The effects of cement content and SiO_(2)/Na2O ratio of the alkaline solution on the static and dynamic strengths of GRS were discussed. Microscopically, the reinforcement mechanism and coupling effect were examined using X-ray diffraction (XRD), micro-computed tomography (micro-CT), and scanning electron microscopy (SEM). The results indicated that the addition of 2% cement and an alkaline solution with an SiO_(2)/Na2O ratio of 0.5 led to the densest matrix, lowest porosity, and highest static compressive strength, which was 4994 kPa with a dynamic impact resistance of 75.4 kN after adding glass fiber. The compressive strength and dynamic impact resistance were a result of the coupling effect of cement hydration, a pozzolanic reaction of clay minerals in the GRS, and the alkali activation of clay minerals. Excessive cement addition or an excessively high SiO_(2)/Na2O ratio in the alkaline solution can have negative effects, such as the destruction of C-(A)-S-H gels by the alkaline solution and hindering the production of N-A-S-H gels. This can result in damage to the matrix of reinforced GRS, leading to a decrease in both static and dynamic strengths. This study suggests that further research is required to gain a more precise understanding of the effects of this mixture in terms of reducing our carbon footprint and optimizing its properties. The findings indicate that cement and alkaline solution are appropriate for GRS and that the reinforced GRS can be used for high-strength foundation and embankment construction. The study provides an analysis of strategies for mitigating and managing GRS slope failures, as well as enhancing roadbed performance.展开更多
Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rat...Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.展开更多
The effect of the ground granulated blast-furnace slag （ GGBFS ） addition, the modulus n （ mole rutio of SiO2 to Na2O ） and the concentrution of sodium silicate solution on the compressive strength of the materi...The effect of the ground granulated blast-furnace slag （ GGBFS ） addition, the modulus n （ mole rutio of SiO2 to Na2O ） and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material （ AACCM for short ） was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% （ by mass ） ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.展开更多
Graphitic carbons with reasonable pore volume and appropriate graphitization degree can provide efficient Li+/electrolyte-transfer channels and ameliorate the sluggish dynamic behavior of battery-type carbon negative ...Graphitic carbons with reasonable pore volume and appropriate graphitization degree can provide efficient Li+/electrolyte-transfer channels and ameliorate the sluggish dynamic behavior of battery-type carbon negative electrode in lithium-ion capacitors(LICs).In this work,onion-like graphitic carbon materials are obtained by using carbon quantum dots as precursors after sintering,and the effects of alkali metal salts on the structure,morphology and performance of the samples are focused.The results show that alkali metal salts as activator can etch graphitic carbons,and the specific surface area and pore size distribution are intimately related to the description of the alkali metal salt.Moreover,it also affects the graphitization degree of the materials.The porous graphitic carbons(SGCs)obtained by NaCl activation exhibit high specific surface area(77.14 m^(2)·g^(-1))and appropriate graphitization degree.It is expectable that the electrochemical performance for lithium-ions storage can be largely promoted by the smart combination of catalytic graphitization and pores-creating strategy.High-performance LICs(S-GCs//AC LICs)are achieved with high energy density of 92 Wh·kg^(-1)and superior rate capability(66.3 Wh·kg^(-1)at10 A·g^(-1))together with the power density as high as10020.2 W·kg^(-1).展开更多
Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomech...Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomechanical performance of coral sand and meet the requirement of foundation construction in coastal areas,a novel alkali activation-based sustainable binder was developed.The alkaliactivated slag(AAS)binder material was composed of ground granulated blast-furnace slag(GGBS)and hydrated lime with the amendment of biochar,an agricultural waste-derived material.The biocharamended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical,physicochemical,and microstructural characteristics.Results show that adding a moderate amount of biochar in AAS could improve soil strength,elastic modulus,and water holding capacity by up to 20%,70%,and 30%,respectively.Moreover,the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand,especially at high biochar content.However,the resistance of the AAS stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar.Based on these observations,a conceptual model showing biochar-AAS-sand interactions was proposed,in which biochar served as an internal curing agent,micro-reinforcer,and mechanically weak point.展开更多
This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated product...This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca（OH）_2 content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of Na OH and gypsum. The products（C-S-H, ettringite and CaCO_3）, especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca（OH）_2, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.展开更多
Wet granulation is a potential method to develop artificial aggregates.In this paper,the granulation of recycled alkali-activated slag powders with different particle size(d_(50) ranging between 12.9-127.7μm)distribu...Wet granulation is a potential method to develop artificial aggregates.In this paper,the granulation of recycled alkali-activated slag powders with different particle size(d_(50) ranging between 12.9-127.7μm)distributions were investigated in order to find how these affect on the engineering properties of the artificial aggregates.Blast furnace slag was added as co-binder in 10-30 wt.%during the granulation process and to enhance the properties,especially mechanical strength.The results show that the particle size of the raw material significantly affects the engineering properties of the produced aggregates,such as the crushing force(19-131.8 N),bulk density,water absorption,porosity and microstructure of the granules.The results show that granulation is a promising method to recycle alkali-activated materials as lightweight aggregates to replace natural aggregates.展开更多
The dielectric performance of alkali activated slag （AAS） cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste wer...The dielectric performance of alkali activated slag （AAS） cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste were mostly influenced by the fraction of free water in paste or absorbed water from ambient, but not including hydration water and microstructure. The free water was completely eliminated by heat treatment at 105 ℃ about 4 hours, and then its dielectric loss was depressed; but with the exposure time in air increasing, the free water adsorption in ambient air made the dielectric property of harden cement paste to be bad. The temperature and relative humidity of environment was the key factors of free water adsorption; hence, if the influence of free water on dielectric constant was measured or eliminated, the cement-based materials may be applied in humidity sensitive materials or dielectric materials domains.展开更多
Alkali activated binder, commonly known as geopolymer cement, has replaced Portland cement in the production of mortar and concrete globally over the past few years. The density, particle size distribution, and specif...Alkali activated binder, commonly known as geopolymer cement, has replaced Portland cement in the production of mortar and concrete globally over the past few years. The density, particle size distribution, and specific surface area (SSA) are important physical parameters affecting strength and durability of alkali activated binders. This study carried out tests for physical and chemical properties of the natural pozzolan and calcium hydroxide and then determines the influence of alkali solution (sodium silicate and sodium hydroxide) on strength development of natural pozzolan calcium hydroxide binders. The particle size distribution (PSD), relative densities (RD), and specific surface areas (SSA) of powder natural pozzolan and calcium hydroxide materials and for the mixture of natural pozzolan and calcium hydroxide were determined by using Blaine air permeability apparatus. The optimum proportion of 75% natural pozzolan and 25% calcium hydroxide was obtained which produces the compressive strength of 7.5 MPa at 28 days cured paste. The mixture of natural pozzolan and calcium hydroxide were further grinded at three different finenesses and the particle size gradation, specific densities, specific surface areas and mean particles sizes for the mixture were determined. The compressive strength of alkali activated binders increased with increasing curing period and fineness. The maximum compressive strength for 28 days cured specimens was 26.1 MPa which was obtained at a solution of 8 moles sodium hydroxide concentration. The test results showed that natural pozzolan materials can be used to make geopolymer binders for mortars and concretes. The geopolymer binders for mortars and concretes reduce green gas emission from cement factory but also it can be used to produce durable mortar and concrete with comparable strengths with mortars and concrete made from conventional Portland cement.展开更多
The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary enviro...The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content.Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water.The management of tailing dams requires expensive construction and careful control,and there is the need for stable,sustainable,and economically viable management technologies.Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings.Alkali activated materials are hardened,concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon,which fortunately,are the main elements in mining residues.Furthermore,alkali activation can immobilize harmful heavy metals within the structure.This review describes the research on alkali activated mine tailings.The reactivity and chemistry of different minerals are discussed.Since many mine tailings are poorly reactive under alkaline conditions,different pretreatment methods and their effects on the mineralogy are reviewed.Possible applications for these materials are also discussed.展开更多
By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing pr...By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm 3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na 2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.展开更多
High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitio...High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance （NMR） and scanning electron microscopy （SEM）. During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning （MAS） NMR of 27Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmet- rical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of 29Si with different treatments suggest that QO disappears, the quantity of Q2 increases, and the quantity of Q4 decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.展开更多
This study focuses on the effect of ultrafine waste glass powder on cement strength,gas permeability and pore structure.Varying contents were considered,with particle sizes ranging from 2 to 20μm.Moreover,alkali acti...This study focuses on the effect of ultrafine waste glass powder on cement strength,gas permeability and pore structure.Varying contents were considered,with particle sizes ranging from 2 to 20μm.Moreover,alkali activation was considered to ameliorate the reactivity and cementitious properties,which were assessed by using scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),and specific surface area pore size distribution analysis.According to the results,without the addition of alkali activators,the performance of glass powder mortar decreases as the amount of glass powder increases,affecting various aspects such as strength and resistance to gas permeability.Only 5%glass powder mortar demonstrated a compressive strength at 60 days higher than that of the control group.However,adding alkali activator(CaO)during hydration ameliorated the hydration environment,increased the alkalinity of the composite system,activated the reactivity of glass powder,and enhanced the interaction of glass powder and pozzolanic reaction.In general,compared to ordinary cement mortar,alkali-activated glass powder mortar produces more hydration products,showcases elevated density,and exhibits improved gas resistance.Furthermore,alkali-activated glass powder mortar demonstrates an improvement in performance across various aspects as the content increases.At a substitution rate of 15%,the glass powder mortar reaches its optimal levels of strength and resistance to gas permeability,with a compressive strength increase ranging from 28.4%to 34%,and a gas permeation rate reduction between 51.8%and 66.7%.展开更多
Ultrafine copper tailings(UTCT) are a type of bulk solid waste containing heavy metals,discharged from copper refining industries.Large stockpiles of these tailings pose significant environmental risks and lead to the...Ultrafine copper tailings(UTCT) are a type of bulk solid waste containing heavy metals,discharged from copper refining industries.Large stockpiles of these tailings pose significant environmental risks and lead to the wastage of valuable mineral resources.To address this issue,this study has developed a backfill material(solidified ultrafine copper tailings,S-UTCT) for mine shaft rehabilitation.This material utilizes waste alkali exciters and UTCT as base components.The primary process involves thoroughly mixing the alkali exciter with UTCT,followed by injection into a mold or pit for curing.The optimized process parameters are as follows:UTCT solid content of 50wt%-60wt%,mixing duration of 6-8 min,alkali activator dosage of 30wt%-35wt%,water-to-solid weight ratio of 0.2,mixing speed of 400 r/min,and curing period of 28 d.Mechanistic analysis revealed that the alkali activator induces mineral phase reconstruction and morphological reconfiguration of UTCT,driven by mechanochemical activation during ball milling.This results in improved compressive strength and effective immobilization of heavy metals.This paper presents a novel cement-free and burn-free method for preparing cementitious materials for recycling resources in mines.展开更多
Environmental problems that came from the human activity have many facets,since pollution of the atmosphere arises from vehicles,industrial emissions while pollution of water could be from organic compounds,pesticides...Environmental problems that came from the human activity have many facets,since pollution of the atmosphere arises from vehicles,industrial emissions while pollution of water could be from organic compounds,pesticides etc.These can cause serious health effects,such as respiratory diseases,including asthma and lung cancer.Hence,in the present work,a kinetic study on the effective adsorption and photo degradation of methylene blue(MB)dye,under ultraviolet A(UVA)irradiation of an alkali activated inorganic polymer(geopolymer)with homogeneously dispersed titanium dioxide(TiO2)micro-particles is presented.In addition,antimicrobial testing of the alkali activated TiO2 material was performed showing a bacteriostatic effect.展开更多
The effect of sodium hydroxide （NaOH） amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH a...The effect of sodium hydroxide （NaOH） amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH and steel slag were analyzed based on setting time, volume stability, strength test, XRD and SEM analyses. The experimental results show that, NaOH as an alkali activator significantly reduces the cement setting time and improves the cement early strength. But the acceleration of hydration proces produces coarse crystalline hydration products and the osteoporosis structure of hardened paste, which has a negative effect on later age strength. The combination of 1% NaOH and 5% steel slag as alkali activating agents is optimal with respect to early and later age strengths. Overdose of NaOH not only decreases the cement strength at later age, but also may cause problem of volume stability.展开更多
基金Funded by the Open Foundation of National Key Laboratory of Green Building Materials(CBM-08-KF103)
文摘The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morphology differences between PC and AAS on micrometer to nano meter scale.The experimental results indicated that the AAS paste had soil like fracture texture and it was composed of mainly C-S-H gel but lacks of crystals,and it had a very strong tendency to shrink and crack.AAS paste is much denser and more homogeneous than PC,and on the nano scale C-S-H nano particle in the AAS paste is much smaller and packs much denser than PC paste.
文摘This paper reports the development of an Alkali Activated Binder (AAB) with an emphasis on the performance and the durability of the AAB-matrix. For the development of the matrix, the reactive components granulated slag and coal fly ash were used, which were alkali activated with a mixture of sodium hydroxide (2 - 10 mol/l) and aqueous sodium silicate solution (SiO<sub>2</sub>/Na<sub>2</sub>O molar ratio: 2.1) at ambient temperature. A sodium hydroxide concentration of 5.5 mol/l revealed the best compromise between setting time and mechanical strengths of the AAB. With this sodium hydroxide concentration, the compressive and the 3-point bending tensile strength of the hardened AAB were 53.4 and 5.5 MPa respectively after 14 days. As a result of the investigation of the acid resistance, the AAB-matrix showed a very high acid resistance in comparison to ordinary Portland cement concrete. In addition, the AAB had a high frost resistance, which had been validated by the capillary suction, internal damage and freeze thaw test with a relative dynamic E-Modulus of 93% and a total amount of scaled material of 30 g/m<sup>2</sup> after 28 freeze-thaw cycles (exposure class: XF3).
文摘This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaCO3 as a stabilizer,and straw(for strengthening).The availability of raw materials for making Adobe presents the waste-stabilized Adobe as a potential product for a new alkali-activated binder.Waste-stabilized Adobe collected from an abandoned damaged building in the village of Inonu in Northern Cyprus,ground and calcined at the following temperatures:450,550,650,750,850,and 950℃.The calcination at each temperature was held for different durations 1,3,5,and 7 h.Raw and calcined waste stabilized Adobe structures were investigated using XRF,TGA-DTA,XRD,FTIR,and SEM.Considering technical and environmental views related to energy consumption,waste stabilized Adobe calcined at 750℃ for 1 h presented the most promising results regarding the production of a new precursor for alkali-activated binder.This study also presents the effect of ground granulated blast furnace slag(GGBFS)usage on the fresh and hardened properties of optimum calcined AB-based alkali-activated pastes cured at room temperature.GGBFS was used to partially replace AB to form a binary composite raw material system and seven experimental groups were designed according to replacement levels of 0%,5%,10%,15%,20%,25%and 30%(by mass).Alkali-activated high volume waste-stabilized Adobe-slag pastes prepared using Na2SiO3-to-NaOH ratio of 2 and 12 M concentration of Sodium Hydroxide.The fresh property as flowability and the hardened property as the compressive strength of the alkali-activated pastes with different GGBFS contents were investigated.The results indicated that the incorporation of GGBFS increased the flowability of fresh alkali-activated pastes.A 28-day compressive strength of 43.75 MPa can be obtained by a 30%replacement level of GGBFS.
文摘We read with great interest the investigations conducted by Pourakbar et al.(2024)on the“Stabilization of clay soil using alkali-activated sewage sludge.”The authors have investigated the feasibility of utilizing alkali-activated sewage sludge(AASS)as a binder for stabilizing the clayey soil.Sewage sludge(SS)in varying proportions of 1.5%,2%,2.5%,3.5%,and 4.5%was utilized to prepare geopolymer binders using sodium and potassium-based alkali activators.Furthermore,unconfined compressive strength(UCS)and direct shear tests were conducted to examine the strength development of clayey soil stabilized with AASS.While the study presented some intriguing results,we have identified critical concerns regarding(i)the selection of SS as a precursor for alkali activation,(ii)technical inconsistencies associated with the compaction characteristics and microstructural analysis,and(iii)the feasibility of the proposed methodology for practical applications.Through our discussion,we seek to highlight these issues and provide constructive feedback to advance the understanding of alkali activation processes and their implications for soil stabilization.
基金the support provided by the National Natural Science Foundation of China(Grant Nos.52278336 and 42302032)Guangdong Basic and Applied Research Foundation(Grant Nos.2023B1515020061).
文摘Granite residual soil (GRS) is a type of weathering soil that can decompose upon contact with water, potentially causing geological hazards. In this study, cement, an alkaline solution, and glass fiber were used to reinforce GRS. The effects of cement content and SiO_(2)/Na2O ratio of the alkaline solution on the static and dynamic strengths of GRS were discussed. Microscopically, the reinforcement mechanism and coupling effect were examined using X-ray diffraction (XRD), micro-computed tomography (micro-CT), and scanning electron microscopy (SEM). The results indicated that the addition of 2% cement and an alkaline solution with an SiO_(2)/Na2O ratio of 0.5 led to the densest matrix, lowest porosity, and highest static compressive strength, which was 4994 kPa with a dynamic impact resistance of 75.4 kN after adding glass fiber. The compressive strength and dynamic impact resistance were a result of the coupling effect of cement hydration, a pozzolanic reaction of clay minerals in the GRS, and the alkali activation of clay minerals. Excessive cement addition or an excessively high SiO_(2)/Na2O ratio in the alkaline solution can have negative effects, such as the destruction of C-(A)-S-H gels by the alkaline solution and hindering the production of N-A-S-H gels. This can result in damage to the matrix of reinforced GRS, leading to a decrease in both static and dynamic strengths. This study suggests that further research is required to gain a more precise understanding of the effects of this mixture in terms of reducing our carbon footprint and optimizing its properties. The findings indicate that cement and alkaline solution are appropriate for GRS and that the reinforced GRS can be used for high-strength foundation and embankment construction. The study provides an analysis of strategies for mitigating and managing GRS slope failures, as well as enhancing roadbed performance.
基金supported by the Key Research and Development Special Tasks of Xinjiang,China (No.2022B01051-2)the National Natural Science Foundation of China (Nos.U23B2091,42372328,and 52478253)+1 种基金the Natural Science Foundation of Jiangsu Province,China (No.BK20240209)the Science and Technology Program Special Fund of Jiangsu Province (Frontier Leading Technology Basic Research) Major projects,China (No.BK 20222004)
文摘Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.
基金Supported by the National "863"Research Project of China(No.2002AA335050) ,the National Natural Science Foundation ofChina( No.50409011) and the High-level University ConstructionProject of South China University of Technology (No.B09-224)
文摘The effect of the ground granulated blast-furnace slag （ GGBFS ） addition, the modulus n （ mole rutio of SiO2 to Na2O ） and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material （ AACCM for short ） was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% （ by mass ） ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.
基金the National Natural Science Foundation of China(No.51804344)the Program of Huxiang Young Talents(No.2019RS2002)+1 种基金the Innovation and Entrepreneurship Project of Hunan Province,China(No.2018GK5026)the Innovation-Driven Project of Central South University(No.2020CX027)。
文摘Graphitic carbons with reasonable pore volume and appropriate graphitization degree can provide efficient Li+/electrolyte-transfer channels and ameliorate the sluggish dynamic behavior of battery-type carbon negative electrode in lithium-ion capacitors(LICs).In this work,onion-like graphitic carbon materials are obtained by using carbon quantum dots as precursors after sintering,and the effects of alkali metal salts on the structure,morphology and performance of the samples are focused.The results show that alkali metal salts as activator can etch graphitic carbons,and the specific surface area and pore size distribution are intimately related to the description of the alkali metal salt.Moreover,it also affects the graphitization degree of the materials.The porous graphitic carbons(SGCs)obtained by NaCl activation exhibit high specific surface area(77.14 m^(2)·g^(-1))and appropriate graphitization degree.It is expectable that the electrochemical performance for lithium-ions storage can be largely promoted by the smart combination of catalytic graphitization and pores-creating strategy.High-performance LICs(S-GCs//AC LICs)are achieved with high energy density of 92 Wh·kg^(-1)and superior rate capability(66.3 Wh·kg^(-1)at10 A·g^(-1))together with the power density as high as10020.2 W·kg^(-1).
基金supported by the Hawaii Department of Transportation(Grant No.2020-4ReSUPP)National Natural Science Foundation of China(Grant No.42007246)Fundamental Research Funds for the Central Universities.
文摘Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomechanical performance of coral sand and meet the requirement of foundation construction in coastal areas,a novel alkali activation-based sustainable binder was developed.The alkaliactivated slag(AAS)binder material was composed of ground granulated blast-furnace slag(GGBS)and hydrated lime with the amendment of biochar,an agricultural waste-derived material.The biocharamended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical,physicochemical,and microstructural characteristics.Results show that adding a moderate amount of biochar in AAS could improve soil strength,elastic modulus,and water holding capacity by up to 20%,70%,and 30%,respectively.Moreover,the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand,especially at high biochar content.However,the resistance of the AAS stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar.Based on these observations,a conceptual model showing biochar-AAS-sand interactions was proposed,in which biochar served as an internal curing agent,micro-reinforcer,and mechanically weak point.
基金Funded by the National Natural Science Foundation of China(No.51578108)the Ministry of Water Resource of the People’s Republic of China(No.201501003)
文摘This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca（OH）_2 content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of Na OH and gypsum. The products（C-S-H, ettringite and CaCO_3）, especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca（OH）_2, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.
基金support received for the project DeConcrete Eco-Efficient Arctic technologies cooperation funded by kolarctic CBC initiative of European Union(KO 4068).XRD analysis was performed at the Center of Microscopy and Nanotechnology(University of Oulu).The authors would like to thank Jarno Karvonen and Elisa Wirkkala for their assistance with the laboratory experiments.
文摘Wet granulation is a potential method to develop artificial aggregates.In this paper,the granulation of recycled alkali-activated slag powders with different particle size(d_(50) ranging between 12.9-127.7μm)distributions were investigated in order to find how these affect on the engineering properties of the artificial aggregates.Blast furnace slag was added as co-binder in 10-30 wt.%during the granulation process and to enhance the properties,especially mechanical strength.The results show that the particle size of the raw material significantly affects the engineering properties of the produced aggregates,such as the crushing force(19-131.8 N),bulk density,water absorption,porosity and microstructure of the granules.The results show that granulation is a promising method to recycle alkali-activated materials as lightweight aggregates to replace natural aggregates.
文摘The dielectric performance of alkali activated slag （AAS） cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste were mostly influenced by the fraction of free water in paste or absorbed water from ambient, but not including hydration water and microstructure. The free water was completely eliminated by heat treatment at 105 ℃ about 4 hours, and then its dielectric loss was depressed; but with the exposure time in air increasing, the free water adsorption in ambient air made the dielectric property of harden cement paste to be bad. The temperature and relative humidity of environment was the key factors of free water adsorption; hence, if the influence of free water on dielectric constant was measured or eliminated, the cement-based materials may be applied in humidity sensitive materials or dielectric materials domains.
文摘Alkali activated binder, commonly known as geopolymer cement, has replaced Portland cement in the production of mortar and concrete globally over the past few years. The density, particle size distribution, and specific surface area (SSA) are important physical parameters affecting strength and durability of alkali activated binders. This study carried out tests for physical and chemical properties of the natural pozzolan and calcium hydroxide and then determines the influence of alkali solution (sodium silicate and sodium hydroxide) on strength development of natural pozzolan calcium hydroxide binders. The particle size distribution (PSD), relative densities (RD), and specific surface areas (SSA) of powder natural pozzolan and calcium hydroxide materials and for the mixture of natural pozzolan and calcium hydroxide were determined by using Blaine air permeability apparatus. The optimum proportion of 75% natural pozzolan and 25% calcium hydroxide was obtained which produces the compressive strength of 7.5 MPa at 28 days cured paste. The mixture of natural pozzolan and calcium hydroxide were further grinded at three different finenesses and the particle size gradation, specific densities, specific surface areas and mean particles sizes for the mixture were determined. The compressive strength of alkali activated binders increased with increasing curing period and fineness. The maximum compressive strength for 28 days cured specimens was 26.1 MPa which was obtained at a solution of 8 moles sodium hydroxide concentration. The test results showed that natural pozzolan materials can be used to make geopolymer binders for mortars and concretes. The geopolymer binders for mortars and concretes reduce green gas emission from cement factory but also it can be used to produce durable mortar and concrete with comparable strengths with mortars and concrete made from conventional Portland cement.
基金financially supported by the project“Steps toward the use of mine tailings in geopolymer materials”funded by the Academy of Finland(No.292526)。
文摘The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content.Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water.The management of tailing dams requires expensive construction and careful control,and there is the need for stable,sustainable,and economically viable management technologies.Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings.Alkali activated materials are hardened,concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon,which fortunately,are the main elements in mining residues.Furthermore,alkali activation can immobilize harmful heavy metals within the structure.This review describes the research on alkali activated mine tailings.The reactivity and chemistry of different minerals are discussed.Since many mine tailings are poorly reactive under alkaline conditions,different pretreatment methods and their effects on the mineralogy are reviewed.Possible applications for these materials are also discussed.
文摘By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm 3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na 2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.
文摘High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance （NMR） and scanning electron microscopy （SEM）. During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning （MAS） NMR of 27Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmet- rical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of 29Si with different treatments suggest that QO disappears, the quantity of Q2 increases, and the quantity of Q4 decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.
基金the National Natural Science Foundation of China(No.51709097).
文摘This study focuses on the effect of ultrafine waste glass powder on cement strength,gas permeability and pore structure.Varying contents were considered,with particle sizes ranging from 2 to 20μm.Moreover,alkali activation was considered to ameliorate the reactivity and cementitious properties,which were assessed by using scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),and specific surface area pore size distribution analysis.According to the results,without the addition of alkali activators,the performance of glass powder mortar decreases as the amount of glass powder increases,affecting various aspects such as strength and resistance to gas permeability.Only 5%glass powder mortar demonstrated a compressive strength at 60 days higher than that of the control group.However,adding alkali activator(CaO)during hydration ameliorated the hydration environment,increased the alkalinity of the composite system,activated the reactivity of glass powder,and enhanced the interaction of glass powder and pozzolanic reaction.In general,compared to ordinary cement mortar,alkali-activated glass powder mortar produces more hydration products,showcases elevated density,and exhibits improved gas resistance.Furthermore,alkali-activated glass powder mortar demonstrates an improvement in performance across various aspects as the content increases.At a substitution rate of 15%,the glass powder mortar reaches its optimal levels of strength and resistance to gas permeability,with a compressive strength increase ranging from 28.4%to 34%,and a gas permeation rate reduction between 51.8%and 66.7%.
基金financially supported by the Major Science and Technology Special Project of China Energy Construction Corporation(No.CEEC2021-ZDYF-03)the National Key Research and Development Program of China(No.2020YFC1806401)the Postdoc Matching Fund Scheme of The Hong Kong Polytechnic University(No.P0045785)
文摘Ultrafine copper tailings(UTCT) are a type of bulk solid waste containing heavy metals,discharged from copper refining industries.Large stockpiles of these tailings pose significant environmental risks and lead to the wastage of valuable mineral resources.To address this issue,this study has developed a backfill material(solidified ultrafine copper tailings,S-UTCT) for mine shaft rehabilitation.This material utilizes waste alkali exciters and UTCT as base components.The primary process involves thoroughly mixing the alkali exciter with UTCT,followed by injection into a mold or pit for curing.The optimized process parameters are as follows:UTCT solid content of 50wt%-60wt%,mixing duration of 6-8 min,alkali activator dosage of 30wt%-35wt%,water-to-solid weight ratio of 0.2,mixing speed of 400 r/min,and curing period of 28 d.Mechanistic analysis revealed that the alkali activator induces mineral phase reconstruction and morphological reconfiguration of UTCT,driven by mechanochemical activation during ball milling.This results in improved compressive strength and effective immobilization of heavy metals.This paper presents a novel cement-free and burn-free method for preparing cementitious materials for recycling resources in mines.
文摘Environmental problems that came from the human activity have many facets,since pollution of the atmosphere arises from vehicles,industrial emissions while pollution of water could be from organic compounds,pesticides etc.These can cause serious health effects,such as respiratory diseases,including asthma and lung cancer.Hence,in the present work,a kinetic study on the effective adsorption and photo degradation of methylene blue(MB)dye,under ultraviolet A(UVA)irradiation of an alkali activated inorganic polymer(geopolymer)with homogeneously dispersed titanium dioxide(TiO2)micro-particles is presented.In addition,antimicrobial testing of the alkali activated TiO2 material was performed showing a bacteriostatic effect.
文摘The effect of sodium hydroxide （NaOH） amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH and steel slag were analyzed based on setting time, volume stability, strength test, XRD and SEM analyses. The experimental results show that, NaOH as an alkali activator significantly reduces the cement setting time and improves the cement early strength. But the acceleration of hydration proces produces coarse crystalline hydration products and the osteoporosis structure of hardened paste, which has a negative effect on later age strength. The combination of 1% NaOH and 5% steel slag as alkali activating agents is optimal with respect to early and later age strengths. Overdose of NaOH not only decreases the cement strength at later age, but also may cause problem of volume stability.
