To explore the distribution of and the mechanical properties(compressive strength)of the hardened body of alkali slag-fly ash cementitious materials,this study was conducted by using the XRD,FTIR,SEM/EDS,and other tes...To explore the distribution of and the mechanical properties(compressive strength)of the hardened body of alkali slag-fly ash cementitious materials,this study was conducted by using the XRD,FTIR,SEM/EDS,and other test methods in three conditions:airtight drying(AD),airtight immersion(AI),and airtight soaking(AS).The 1D distribution law of free of hardened body under standard curing conditions was explored.The experimental results show that under standard curing conditions,the 1D distribution of within 0d-3 d shows a∨-shaped distribution,within 3-7 d show a∧-shaped distribution,and within 7-28 d tends to be balanced.The test results of leaching rate show that the free was the most stable under AD conditions and the hardened body bound the most by XRD,FTIR and SEM/EDS.And the compressive strength of the hardened body was the highest.The compressive strength of 28th reached 95.9 MPa.The definite distribution of provides an important reference for the strength development and durability evaluation of the hardened body of alkaliexcited cementitious materials.展开更多
Alkali-activated slag concrete (AASC) is a new green building material. The amount of CO_(2) produced by AASC is 1/5th of that produced by ordinary Portland cement concrete (OPCC). In addition, AASC promotes the reuse...Alkali-activated slag concrete (AASC) is a new green building material. The amount of CO_(2) produced by AASC is 1/5th of that produced by ordinary Portland cement concrete (OPCC). In addition, AASC promotes the reuse of slag and other wastes and saves resources. Furthermore, the scope of use of slag has been expanded. The progress of the research on the hydration characteristics, microstructure, interfacial transition zone, and pore structure of AASC based on the relevant literatures was analyzed and summarized in this study. The influences of the slag composition, the type and dosage of the alkali activator, and the curing conditions on the hydration characteristics and the microstructure of the AASC were discussed. Relatively few research results on the microstructure of AASC are available, and the relevant conclusions are not completely consistent. Moreover, there are many constraints on the development of AASC (e.g., complex composition of raw materials of slag, large shrinkage deformation, and low fluidity). Therefore, further research is required.展开更多
The unconfined compressive strength(UCS)of alkali-activated slag(AAS)-based cemented paste backfill(CPB)is influenced by multiple design parameters.However,the experimental methods are limited to understanding the rel...The unconfined compressive strength(UCS)of alkali-activated slag(AAS)-based cemented paste backfill(CPB)is influenced by multiple design parameters.However,the experimental methods are limited to understanding the relationships between a single design parameter and the UCS,independently of each other.Although machine learning(ML)methods have proven efficient in understanding relationships between multiple parameters and the UCS of ordinary Portland cement(OPC)-based CPB,there is a lack of ML research on AAS-based CPB.In this study,two ensemble ML methods,comprising gradient boosting regression(GBR)and random forest(RF),were built on a dataset collected from literature alongside two other single ML methods,support vector regression(SVR)and artificial neural network(ANN).The results revealed that the ensemble learning methods outperformed the single learning methods in predicting the UCS of AAS-based CPB.Relative importance analysis based on the bestperforming model(GBR)indicated that curing time and water-to-binder ratio were the most critical input parameters in the model.Finally,the GBR model with the highest accuracy was proposed for the UCS predictions of AAS-based CPB.展开更多
In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated...In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated.The considered NaCl concentration is 3%.The effect of polypropylenefibers on the mechanical strengths is also examined.Scanning electron microscopy(SEM),thermogravimetry(TG)and X-ray diffraction(XRD)are selected to discern the mechanisms underpinning the NaCl-induced erosion.The obtained results indicate that the best results in terms of material resistance are obtained with admixtures containing 60%BFS and 40%FA in terms of mass ratio and 3%polypropylenefibers in terms of volume ratio.The maximum rates of decrease of theflexural,compressive and bonding strengths after 300 NaCl F-T cycles are 21.5%,20.3%and 22.6%,respec-tively.The corresponding rates of decrease due to NaCl D-W alternations are 28.1%,26.1%and 31.5%,respec-tively.The TG curves show that the alkali-activating activity of BFS is higher than that of FA.Moreover,in thefirst case,the microstructure of the hydration products is more compact.The results also show that NaCl F-T cycles lead to increasing cracks in the alkali-activated BFS.展开更多
Energy shortage and the emission of greenhouse gases have become a global problem of urgent concern.Therefore,there is an urgent need to develop a low carbon building material.Geopolymers have become a hot topic due t...Energy shortage and the emission of greenhouse gases have become a global problem of urgent concern.Therefore,there is an urgent need to develop a low carbon building material.Geopolymers have become a hot topic due to their environmental sustainability and the feasibility of immobilizing industrial waste.In this paper,steel slag(SS)fines were investigated as auxiliary materials of blast furnace slag(BFS)based geopolymer.The hydration heat properties,flowability,compressive strength,sorptivity coefficient,X-ray diffraction(XRD),and scanning electron microscopy(SEM)of the geopolymer pastes were determined.The results showed that the incorporation of SS weakened the reactivity of the BFS-based geopolymer paste and improved the flow values of the paste.The compressive strength of the geopolymer with 20%SS content reached 117 MPa at 28 d.The geopolymer specimens with high compressive strength showed a low sorptivity coefficient.The microscopic results showed that the addition of the appropriate amount of SS reduced the cracks,improved the density of the geopolymer,and produced a geopolymer composite with excellent mechanical properties.展开更多
China is the largest producer and user of ordinary Portland cement(OPC),and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures.Alkali-activated materials...China is the largest producer and user of ordinary Portland cement(OPC),and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures.Alkali-activated materials(AAMs)are a new type of energy-saving and environmentally friendly building material with a wide range of potential applications.This paper compares the durability of AAMs and 0 PC-based materials un der sulfate attack,acid corrosion,carb on ation,and chloride penetratio n.Different AAMs have shown distinct durability properties due to different compositions being formed when different raw materials are used.According to the calcium(Ca)concentration of the raw materials,this paper interprets the deterioration mechanisms of three categories of AAMs:calcium-free,low-calcium,and calcium-rich.Conflicts found in the most recent research are highlighted,as they raise concerns regarding the consistenee and long-term properties of AAMs.Nevertheless,AAMs show better durability performances than OPC-based materials in general.展开更多
Lime and Portland cement are the most widely used binders in soil stabilization projects.However,due to the high carbon emission in cement production,research on soil stabilization by the use of more environmentally-f...Lime and Portland cement are the most widely used binders in soil stabilization projects.However,due to the high carbon emission in cement production,research on soil stabilization by the use of more environmentally-friendly binders with lower carbon footprint has attracted much attention in recent years.This research investigated the potential of using alkali-activated ground granulated blast furnace slag(GGBS)and volcanic ash(VA)as green binders in clayey soil stabilization projects,which has not been studied before.The effects of different combinations of VA with GGBS,various liquid/solid ratios,different curing conditions,and different curing periods(i.e.7 d,28 d and 90 d)were investigated.Compressive strength and durability of specimens against wet-dry and freeze-thaw cycles were then studied through the use of mechanical and microstructural tests.The results demonstrated that the coexistence of GGBS and VA in geopolymerization process was more effective due to the synergic formation of N-A-S-H and C-(A)-S-H gels.Moreover,although VA needs heat curing to become activated and develop strength,its partial replacement with GGBS made the binder suitable for application at ambient temperature and resulted in a remarkably superior resistance against wet-dry and freeze-thaw cycles.The carbon embodied of the mixtures was also evaluated,and the results confirmed the low carbon footprints of the alkali-activated mixtures.Finally,it was concluded that the alkali-activated GGBS/VA could be promisingly used in clayey soil stabilization projects instead of conventional binders.展开更多
In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract...In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract and alkali-activated slag(AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various Na Cl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.展开更多
To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 4...To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.展开更多
The paper investigates the second-order interactions of parameters in an alkali-activated mixture of paper production waste(PPW)and blast furnace slag(BFS)in Taguchi method.The PPW including lime mud(LM)and paper slud...The paper investigates the second-order interactions of parameters in an alkali-activated mixture of paper production waste(PPW)and blast furnace slag(BFS)in Taguchi method.The PPW including lime mud(LM)and paper sludge(PS).This paper provides the experimental models to assess the compressive and flexural strength of them at 7-day and 28-day.The results have shown that the second-order interactions between PPW and alkali-activated activator exists in each experimental model,and the significant interactions affect the selection of optimal compositions.Compared with the interactions between the PPW themselves,the interactions between PPW and alkali-activated parameters are the main significant factors affecting its physical properties.In each experimental model,the maximum compressive strength was 47.41 MPa in 7-day and 65.64 MPa in 28-day.Compared with the confirmatory experiments,the deviation of prediction calculated by experimental models was 3.08%and 0.56%,respectively.The maximum flexural strength was 5.74 MPa in 7-day and 5.96 MPa in 28-day;compared with the confirmatory experiments,the deviation of prediction calculated by experimental models was 5.40%and 0.17%.Considering the influence of circular materials,30%of PPW should be a suitable ratio to replace BFS as the raw material of alkali-activated slag(AAS).展开更多
The possibility of preparing cementitious materials by the alkali-activated method using Yellow River sediment(The second largest river in China)as raw material and the modification effect on different slag addition w...The possibility of preparing cementitious materials by the alkali-activated method using Yellow River sediment(The second largest river in China)as raw material and the modification effect on different slag addition were investigated.Sodium silicate and calcium hydroxide were used as the activator,and the specimens were prepared by the press molding method.The hydration process,hydration products,pore characteristics,and mechanical properties were investigated using SEM/EDS,FTIR,TG/DTG,XRD,MIP,and uniaxial compressive strength experiments,respectively.The results showed that the compressive strength of the modified yellow river silt-based cementitious material was significantly increased when the water glass dosage was 12 wt%(Ms=1.8)and the slag dosage was 40%,and its 90-day maximum compressive strength could reach 53 MPa.展开更多
Alkali-activated cement(AAC)is either clinker-less or free,and it is also environmentally friendly due to its low carbon footprint and wide range sources.Industrial wastes,like steel slag and blastfurnace slag,usually...Alkali-activated cement(AAC)is either clinker-less or free,and it is also environmentally friendly due to its low carbon footprint and wide range sources.Industrial wastes,like steel slag and blastfurnace slag,usually have latent hydraulic reactivity,and can be used as precursors of AAC.Both clinkerless and clinker-free AAC were prepared from the mixture of steel slag and blastfurnace slag by using water glass as an activator,and four different recipes which satisfied the strength requirement of 42.5R Portland cement were obtained.Each recipe of AAC exhibited better resistance to sulfate attack and frost attack than Portland cement.AAC showed huge drying shrinkage,but it was equivalent to that of Portland cement as steel slag content increased to 40%.The AAC also had quite low risk of alkali-aggregate reaction.Microstructure analysis showed that the major products were calcium silicate hydrate(C–S–H),calcium aluminosilicate hydrate(C–A–S–H)and zeolite-like phases.Ettringite was also detected in the binder when gypsum was contained in the precursors.展开更多
Self-compacting concrete(SCC)has gained huge attention recently due to its high workability which eliminates the need for vibration and makes its placement easier compared to conventional concrete.However,the producti...Self-compacting concrete(SCC)has gained huge attention recently due to its high workability which eliminates the need for vibration and makes its placement easier compared to conventional concrete.However,the production of Portland cement(PC)which is the main binder in SCC is energy-intensive and one of the major contributors to the world’s carbon dioxide emission.On the other hand,the use of alkali-activated binders(AABs)in concrete has been reported to reduce the energy consumption and carbon emission of concrete by more than 50%.Therefore,the use of AAB as a binder in SCC can help to achieve an eco-friendlier concrete.This paper gives a short overview of the performance of SCC made with AABs.The effect of various factors on the performance of alkali-activated self-compacting concrete(AASCC)was discussed and a simplified sustainability assessment of AASCC was carried out.Discussions from this paper showed that AASCC with acceptable fresh and hardened properties can be achieved with the proper selection of materials.In addition,the evaluation of the embodied energy and carbon of different types of concrete showed that AASCC is more sustainable.However,more research in this field is required to encourage its universal acceptance and large-scale application.展开更多
Fibre can enhance the mechanical properties of cement-based composites,but fibre also degrades their workability.However,the quantitative effects of fiber content and length-diameter ratio on alkali-activated material...Fibre can enhance the mechanical properties of cement-based composites,but fibre also degrades their workability.However,the quantitative effects of fiber content and length-diameter ratio on alkali-activated materials are still unclear.Various aspect ratio,volume fraction of polyvinyl alcohol fibre(PVAF),and various water-binder ratio were employed to prepare a total of 26 groups of fibre reinforced alkali-activated composite(FRAAC).The influence of PVAF fibre factor(product of fiber volume fraction and length-diameter ratio)on flowability,compactness,strength,and crack fractal dimension of FRAAC was researched.The influence of water-binder ratio on the plastic viscosity of FRAAC was more significant than that on the yield stress.When fibre factor was lower than critical value of 150,the influence of fibres could be overlooked.The reason was that the space between fibres was distant,so the flowability of FRAAC was not impacted by PVAF.At this time,fibres were challenging to restrict the cracks in matrix and increase their mechanical properties.When fibre factor was higher than critical value 150 and lower than density packing value 450,the flexural strength,compressive strength and crack fractal dimension of FRAAC were considerably enhanced,and the FRAAC could still flow easily under dead weight.When fibre factor were above 450,noteworthy fibre balling considerably decreased the flowability,leading to poor solidity and reduced compressive strength.Hence,the ideal content of PVAF in alkali activated composite is between 150/(l/d)and 450/(l/d).展开更多
In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unb...In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state.Test on flexural behavior of these four beams was performed.Moreover,normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained.Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM.Based on the experimental results and theoretical study,computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM.Formula of bending rigidity calculation was founded which results are in good agreement with testing data.展开更多
To solve the energy consumption and CO_(2) emission during cement production,the new binders must be developed as an alternative to cement.CaO/CaSO_(4)-activated slag binder is an eco-friendly and safe cementitious ma...To solve the energy consumption and CO_(2) emission during cement production,the new binders must be developed as an alternative to cement.CaO/CaSO_(4)-activated slag binder is an eco-friendly and safe cementitious material;however,its low strength during initial stages limits its applications.In this study,colloidal nanosilica(CNS)was employed as an additive to improve the strength of CaO/CaSO_(4)-activated slag binder,and the effects of CNS on the workability,hydration kinetics,hydration products(type,quantity,and polymerization degree),and binder microstructure were thoroughly investigated.A moderate CNS content,through its nucleation effect,significantly increased the hydration rate of the nucleation and crystal growth(NG),phase boundary interaction(I)and diffusion(D)processes,which generated large quantities of calcium aluminosilicate hydrate(C-A-S-H)gel in the initial hydration stage.Meanwhile,the addition of CNS improved the polymerization degree of C-A-S-H gel.This amorphous reactant well-filled the pore space between slag particles and yielded a compact microstructure,consequently enhancing the binder strength.Considering the reduction in fluidity and the increase in production cost,the CNS mass fraction was controlled as3%,and the binder reached the satisfactory strengths of 3.87,24.47,31.43,and 41.78 MPa at 1,3,7,and 28 d,respectively.展开更多
The porous structure and honeycombed structure of granulated blast furnace slag formed by alkali activation(AGBFS)can be used as a promising photocatalysts substrate for the photocatalytic removal of atmospheric or wa...The porous structure and honeycombed structure of granulated blast furnace slag formed by alkali activation(AGBFS)can be used as a promising photocatalysts substrate for the photocatalytic removal of atmospheric or water pollutants.In this study,photocatalytic activated slag granules were synthesized by loading TiO_(2)on AGBFS with immersion method.The physicochemical properties and NO_(x)removal performance of activated slag granules/TiO_(2)photocatalysts were studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and photocatalytic performance test.The effects of slag particle sizes and nano-TiO_(2)loading concentrations on photocatalytic efficiencies of NO_(x)removal were also investigated.It was found that the De-NO_(x)performance of activated slag granules/TiO_(2)photocatalyst increased with the increasing of slag particle size in low TiO_(2)loading concentration situation,while increasing the TiO_(2)loading concentration would result in the opposite De-NO_(x)performance as slag size increased.Nevertheless,for the same size activated slag,the photocatalytic efficiency of activated slag granules/TiO_(2)photocatalyst gradually improved with the increase of loading concentration of TiO_(2).展开更多
Geopolymer is a new environment-friendly cementitious material, and the development of geopolymer can reduce the carbon dioxide emission caused by the development of cement industry. Geopolymer materials not only have...Geopolymer is a new environment-friendly cementitious material, and the development of geopolymer can reduce the carbon dioxide emission caused by the development of cement industry. Geopolymer materials not only have excellent mechanical properties, but also have a series of excellent properties such as fire resistance and corrosion resistance. Most industrial solid waste and waste incineration bottom ash are piled up at will, which not only occupies land resources, but also has a bad impact on the environment. Recycling them can be used as raw materials for preparing geopolymers. Geopolymer materials can effectively adsorb heavy metals, dyes, and other radioactive pollution, which is very beneficial to society's future development. However, due to the excellent properties of geopolymer materials, its application goes beyond that. Some useful information about geopolymer materials was introduced in this paper. The paper included the geopolymerization, the source of raw materials, the types of activators, the preparation methods, and the different application fields of geopolymer materials. The factors affecting the fresh properties and mechanical properties of geopolymer materials were discussed. In this paper, the shortcomings and application limitations of geopolymer materials were summarized, and their progress was summarized to lay a theoretical foundation for the long-term development of geopolymer materials.展开更多
Experimental evaluations were conducted to determine the water sorptivity,setting time,and resistance to a highly acidic environment,of mortar with alkali-activated ground granulated blast furnace slag(GBS)binder and ...Experimental evaluations were conducted to determine the water sorptivity,setting time,and resistance to a highly acidic environment,of mortar with alkali-activated ground granulated blast furnace slag(GBS)binder and also of combinations of fly ash and GBS binders.Binders were activated using mixtures of NaOH and Na_(2)SiO_(3)solutions.The molarity of NaOH in the mixtures ranged from 10 mol·L^(−1)to 16 mol·L^(−1),and the Na_(2)SiO_(3)/NaOH ratio was varied from 1.5 to 2.5.Mortar samples were produced using three binder combinations:1)GBS as the only binder;2)blended binder with a slag-to-fly ash ratio of 3:1;and 3)mixed binder with 1:1 ratio of slag to fly ash.Mortar samples were mixed and cured at(22±2)°C till the day of the test.The impact of activator solution alkalinity,activator ratio Na_(2)SiO_(3)/NaOH,GBS content on the rate of water absorption were evaluated.After 7,28,and 90 d of immersion in a 10%sulfuric acid solution,the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight.The influence of solution alkalinity and relative fly ash content on setting times was investigated.Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations,at each curing age,and for mortars made with each of the NaOH alkaline activator concentrations.Mortar sorptivity decreased with age and sodium hydroxide concentrations,suggesting the production of geopolymerization products.No reduction in weight of sample occurred after immersion in the strong acid H_(2)SO_(4)solution for three months,regardless of binder combination.This was due to the synthesis of hydration and geopolymerization products in the presence of curing water,which outweighed the degradation of the geopolymer matrix caused by sulfuric acid.展开更多
基金Funded by the Natural Sciences Foundation of China(No.51808025)the Pyramid Talent Training Project of BUCEA(No.JDYC20200329)。
文摘To explore the distribution of and the mechanical properties(compressive strength)of the hardened body of alkali slag-fly ash cementitious materials,this study was conducted by using the XRD,FTIR,SEM/EDS,and other test methods in three conditions:airtight drying(AD),airtight immersion(AI),and airtight soaking(AS).The 1D distribution law of free of hardened body under standard curing conditions was explored.The experimental results show that under standard curing conditions,the 1D distribution of within 0d-3 d shows a∨-shaped distribution,within 3-7 d show a∧-shaped distribution,and within 7-28 d tends to be balanced.The test results of leaching rate show that the free was the most stable under AD conditions and the hardened body bound the most by XRD,FTIR and SEM/EDS.And the compressive strength of the hardened body was the highest.The compressive strength of 28th reached 95.9 MPa.The definite distribution of provides an important reference for the strength development and durability evaluation of the hardened body of alkaliexcited cementitious materials.
基金would like to acknowledge the National Natural Science Foundation of China(51590914 and 51608432)Natural Science Foundation of Shaanxi Province(2019JQ-481).
文摘Alkali-activated slag concrete (AASC) is a new green building material. The amount of CO_(2) produced by AASC is 1/5th of that produced by ordinary Portland cement concrete (OPCC). In addition, AASC promotes the reuse of slag and other wastes and saves resources. Furthermore, the scope of use of slag has been expanded. The progress of the research on the hydration characteristics, microstructure, interfacial transition zone, and pore structure of AASC based on the relevant literatures was analyzed and summarized in this study. The influences of the slag composition, the type and dosage of the alkali activator, and the curing conditions on the hydration characteristics and the microstructure of the AASC were discussed. Relatively few research results on the microstructure of AASC are available, and the relevant conclusions are not completely consistent. Moreover, there are many constraints on the development of AASC (e.g., complex composition of raw materials of slag, large shrinkage deformation, and low fluidity). Therefore, further research is required.
基金funded by the Natural Sciences and Engineering Research Council of Canada(NSERC RGPIN-2017-05537).
文摘The unconfined compressive strength(UCS)of alkali-activated slag(AAS)-based cemented paste backfill(CPB)is influenced by multiple design parameters.However,the experimental methods are limited to understanding the relationships between a single design parameter and the UCS,independently of each other.Although machine learning(ML)methods have proven efficient in understanding relationships between multiple parameters and the UCS of ordinary Portland cement(OPC)-based CPB,there is a lack of ML research on AAS-based CPB.In this study,two ensemble ML methods,comprising gradient boosting regression(GBR)and random forest(RF),were built on a dataset collected from literature alongside two other single ML methods,support vector regression(SVR)and artificial neural network(ANN).The results revealed that the ensemble learning methods outperformed the single learning methods in predicting the UCS of AAS-based CPB.Relative importance analysis based on the bestperforming model(GBR)indicated that curing time and water-to-binder ratio were the most critical input parameters in the model.Finally,the GBR model with the highest accuracy was proposed for the UCS predictions of AAS-based CPB.
基金supported by 2023 University-Level Scientific Research Project of Ningbo Polytechnic(NZ23002)the First Batch of Ningbo Construction Scientific Research Projects in 2023(20230106).
文摘In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated.The considered NaCl concentration is 3%.The effect of polypropylenefibers on the mechanical strengths is also examined.Scanning electron microscopy(SEM),thermogravimetry(TG)and X-ray diffraction(XRD)are selected to discern the mechanisms underpinning the NaCl-induced erosion.The obtained results indicate that the best results in terms of material resistance are obtained with admixtures containing 60%BFS and 40%FA in terms of mass ratio and 3%polypropylenefibers in terms of volume ratio.The maximum rates of decrease of theflexural,compressive and bonding strengths after 300 NaCl F-T cycles are 21.5%,20.3%and 22.6%,respec-tively.The corresponding rates of decrease due to NaCl D-W alternations are 28.1%,26.1%and 31.5%,respec-tively.The TG curves show that the alkali-activating activity of BFS is higher than that of FA.Moreover,in thefirst case,the microstructure of the hydration products is more compact.The results also show that NaCl F-T cycles lead to increasing cracks in the alkali-activated BFS.
基金Funding Statement:This work was supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Energy shortage and the emission of greenhouse gases have become a global problem of urgent concern.Therefore,there is an urgent need to develop a low carbon building material.Geopolymers have become a hot topic due to their environmental sustainability and the feasibility of immobilizing industrial waste.In this paper,steel slag(SS)fines were investigated as auxiliary materials of blast furnace slag(BFS)based geopolymer.The hydration heat properties,flowability,compressive strength,sorptivity coefficient,X-ray diffraction(XRD),and scanning electron microscopy(SEM)of the geopolymer pastes were determined.The results showed that the incorporation of SS weakened the reactivity of the BFS-based geopolymer paste and improved the flow values of the paste.The compressive strength of the geopolymer with 20%SS content reached 117 MPa at 28 d.The geopolymer specimens with high compressive strength showed a low sorptivity coefficient.The microscopic results showed that the addition of the appropriate amount of SS reduced the cracks,improved the density of the geopolymer,and produced a geopolymer composite with excellent mechanical properties.
基金Financial support from the National Natural Science Foundation of China(51778003,51878263,and 51608004)Opening Foundation of State Key Laboratory of High Performance Civil Engineering Materials(2018CEM002)+1 种基金Anhui Provincial Education Department(gxfxZD2016134)Anhui Province Higher Education Revitalization Program([2014]No.11).
文摘China is the largest producer and user of ordinary Portland cement(OPC),and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures.Alkali-activated materials(AAMs)are a new type of energy-saving and environmentally friendly building material with a wide range of potential applications.This paper compares the durability of AAMs and 0 PC-based materials un der sulfate attack,acid corrosion,carb on ation,and chloride penetratio n.Different AAMs have shown distinct durability properties due to different compositions being formed when different raw materials are used.According to the calcium(Ca)concentration of the raw materials,this paper interprets the deterioration mechanisms of three categories of AAMs:calcium-free,low-calcium,and calcium-rich.Conflicts found in the most recent research are highlighted,as they raise concerns regarding the consistenee and long-term properties of AAMs.Nevertheless,AAMs show better durability performances than OPC-based materials in general.
基金supported by Chem Concrete Pty.Ltd.Australia,Abadgaran Negin Jonoobshargh Company(ANJ Co.),Iran(Grant No.118/3C-1399)。
文摘Lime and Portland cement are the most widely used binders in soil stabilization projects.However,due to the high carbon emission in cement production,research on soil stabilization by the use of more environmentally-friendly binders with lower carbon footprint has attracted much attention in recent years.This research investigated the potential of using alkali-activated ground granulated blast furnace slag(GGBS)and volcanic ash(VA)as green binders in clayey soil stabilization projects,which has not been studied before.The effects of different combinations of VA with GGBS,various liquid/solid ratios,different curing conditions,and different curing periods(i.e.7 d,28 d and 90 d)were investigated.Compressive strength and durability of specimens against wet-dry and freeze-thaw cycles were then studied through the use of mechanical and microstructural tests.The results demonstrated that the coexistence of GGBS and VA in geopolymerization process was more effective due to the synergic formation of N-A-S-H and C-(A)-S-H gels.Moreover,although VA needs heat curing to become activated and develop strength,its partial replacement with GGBS made the binder suitable for application at ambient temperature and resulted in a remarkably superior resistance against wet-dry and freeze-thaw cycles.The carbon embodied of the mixtures was also evaluated,and the results confirmed the low carbon footprints of the alkali-activated mixtures.Finally,it was concluded that the alkali-activated GGBS/VA could be promisingly used in clayey soil stabilization projects instead of conventional binders.
基金financially supported by the National Natural Science Foundation of China (Nos.51461135001 and 51678144)the Major State Basic Research Development Program of China (No.2015CB655100)+2 种基金the Natural Science Foundation of Jiangsu Province (No.BK20161420)the Industry-University Research Cooperative Innovation Fund of Jiangsu Province (No.BY2013091)the China-Japan Research Cooperative Program by Ministry of Science and Technology of China (No.2016YFE0118200)
文摘In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract and alkali-activated slag(AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various Na Cl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.
文摘To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.
基金This work was supported by Ministry of education of Taiwan(Grant No.H108-AA09)for funding,CHP for materials provision,and NCKU C-Hub for space and instruments.
文摘The paper investigates the second-order interactions of parameters in an alkali-activated mixture of paper production waste(PPW)and blast furnace slag(BFS)in Taguchi method.The PPW including lime mud(LM)and paper sludge(PS).This paper provides the experimental models to assess the compressive and flexural strength of them at 7-day and 28-day.The results have shown that the second-order interactions between PPW and alkali-activated activator exists in each experimental model,and the significant interactions affect the selection of optimal compositions.Compared with the interactions between the PPW themselves,the interactions between PPW and alkali-activated parameters are the main significant factors affecting its physical properties.In each experimental model,the maximum compressive strength was 47.41 MPa in 7-day and 65.64 MPa in 28-day.Compared with the confirmatory experiments,the deviation of prediction calculated by experimental models was 3.08%and 0.56%,respectively.The maximum flexural strength was 5.74 MPa in 7-day and 5.96 MPa in 28-day;compared with the confirmatory experiments,the deviation of prediction calculated by experimental models was 5.40%and 0.17%.Considering the influence of circular materials,30%of PPW should be a suitable ratio to replace BFS as the raw material of alkali-activated slag(AAS).
基金Funded in part by the Joint Funds of National Natural Science Foundation of China(No.U20A20324)National Natural Science Foundation of China(No.51878116)+3 种基金Liaoning Province Key Project of Research and Development Plan(No.2020JH2/10100016)Dalian Science and Technology Innovation Fund Project(No.2020JJ26SN060)the National Natural Science Foundation of China(No.51809109)the National Key Research and Development Projects(No.2017YFC0504506)。
文摘The possibility of preparing cementitious materials by the alkali-activated method using Yellow River sediment(The second largest river in China)as raw material and the modification effect on different slag addition were investigated.Sodium silicate and calcium hydroxide were used as the activator,and the specimens were prepared by the press molding method.The hydration process,hydration products,pore characteristics,and mechanical properties were investigated using SEM/EDS,FTIR,TG/DTG,XRD,MIP,and uniaxial compressive strength experiments,respectively.The results showed that the compressive strength of the modified yellow river silt-based cementitious material was significantly increased when the water glass dosage was 12 wt%(Ms=1.8)and the slag dosage was 40%,and its 90-day maximum compressive strength could reach 53 MPa.
基金supported by the Natural Science Foundation Project of Chongqing(cstc2020jcyj-msxmX0954)the Chongqing Outstanding Youth Project(cstc2019JCYJQX0024)the National Natural Science Foundation of China(52204415.U1902217)。
文摘Alkali-activated cement(AAC)is either clinker-less or free,and it is also environmentally friendly due to its low carbon footprint and wide range sources.Industrial wastes,like steel slag and blastfurnace slag,usually have latent hydraulic reactivity,and can be used as precursors of AAC.Both clinkerless and clinker-free AAC were prepared from the mixture of steel slag and blastfurnace slag by using water glass as an activator,and four different recipes which satisfied the strength requirement of 42.5R Portland cement were obtained.Each recipe of AAC exhibited better resistance to sulfate attack and frost attack than Portland cement.AAC showed huge drying shrinkage,but it was equivalent to that of Portland cement as steel slag content increased to 40%.The AAC also had quite low risk of alkali-aggregate reaction.Microstructure analysis showed that the major products were calcium silicate hydrate(C–S–H),calcium aluminosilicate hydrate(C–A–S–H)and zeolite-like phases.Ettringite was also detected in the binder when gypsum was contained in the precursors.
文摘Self-compacting concrete(SCC)has gained huge attention recently due to its high workability which eliminates the need for vibration and makes its placement easier compared to conventional concrete.However,the production of Portland cement(PC)which is the main binder in SCC is energy-intensive and one of the major contributors to the world’s carbon dioxide emission.On the other hand,the use of alkali-activated binders(AABs)in concrete has been reported to reduce the energy consumption and carbon emission of concrete by more than 50%.Therefore,the use of AAB as a binder in SCC can help to achieve an eco-friendlier concrete.This paper gives a short overview of the performance of SCC made with AABs.The effect of various factors on the performance of alkali-activated self-compacting concrete(AASCC)was discussed and a simplified sustainability assessment of AASCC was carried out.Discussions from this paper showed that AASCC with acceptable fresh and hardened properties can be achieved with the proper selection of materials.In addition,the evaluation of the embodied energy and carbon of different types of concrete showed that AASCC is more sustainable.However,more research in this field is required to encourage its universal acceptance and large-scale application.
基金funding of Henan Province Transportation Science and Technology Plan Project(2021J3).
文摘Fibre can enhance the mechanical properties of cement-based composites,but fibre also degrades their workability.However,the quantitative effects of fiber content and length-diameter ratio on alkali-activated materials are still unclear.Various aspect ratio,volume fraction of polyvinyl alcohol fibre(PVAF),and various water-binder ratio were employed to prepare a total of 26 groups of fibre reinforced alkali-activated composite(FRAAC).The influence of PVAF fibre factor(product of fiber volume fraction and length-diameter ratio)on flowability,compactness,strength,and crack fractal dimension of FRAAC was researched.The influence of water-binder ratio on the plastic viscosity of FRAAC was more significant than that on the yield stress.When fibre factor was lower than critical value of 150,the influence of fibres could be overlooked.The reason was that the space between fibres was distant,so the flowability of FRAAC was not impacted by PVAF.At this time,fibres were challenging to restrict the cracks in matrix and increase their mechanical properties.When fibre factor was higher than critical value 150 and lower than density packing value 450,the flexural strength,compressive strength and crack fractal dimension of FRAAC were considerably enhanced,and the FRAAC could still flow easily under dead weight.When fibre factor were above 450,noteworthy fibre balling considerably decreased the flowability,leading to poor solidity and reduced compressive strength.Hence,the ideal content of PVAF in alkali activated composite is between 150/(l/d)and 450/(l/d).
基金Sponsored by the Changjiang Scholars Program of China(Grant No.2009-37)the National Natural Science Foundation of China(Grant No.50678050)
文摘In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state.Test on flexural behavior of these four beams was performed.Moreover,normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained.Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM.Based on the experimental results and theoretical study,computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM.Formula of bending rigidity calculation was founded which results are in good agreement with testing data.
基金supported by Natural Science Foundation of Shandong Province(No.ZR2019BEE075)Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents(No.2019RCJJ007)+1 种基金Young Science and Technology Innovation Program of Shandong Province(No.2020KJD001)Youth Science and Technology Talent Growth Program of Guizhou Province(No.KY[2018]466).
文摘To solve the energy consumption and CO_(2) emission during cement production,the new binders must be developed as an alternative to cement.CaO/CaSO_(4)-activated slag binder is an eco-friendly and safe cementitious material;however,its low strength during initial stages limits its applications.In this study,colloidal nanosilica(CNS)was employed as an additive to improve the strength of CaO/CaSO_(4)-activated slag binder,and the effects of CNS on the workability,hydration kinetics,hydration products(type,quantity,and polymerization degree),and binder microstructure were thoroughly investigated.A moderate CNS content,through its nucleation effect,significantly increased the hydration rate of the nucleation and crystal growth(NG),phase boundary interaction(I)and diffusion(D)processes,which generated large quantities of calcium aluminosilicate hydrate(C-A-S-H)gel in the initial hydration stage.Meanwhile,the addition of CNS improved the polymerization degree of C-A-S-H gel.This amorphous reactant well-filled the pore space between slag particles and yielded a compact microstructure,consequently enhancing the binder strength.Considering the reduction in fluidity and the increase in production cost,the CNS mass fraction was controlled as3%,and the binder reached the satisfactory strengths of 3.87,24.47,31.43,and 41.78 MPa at 1,3,7,and 28 d,respectively.
基金Funded by the China National Key R&D Program(No.2018YFE0106300)the Natural Science Foundation of China(No.51802238)the Fundamental Research Funds for the Central Universities(Nos.WUT2018IVA011,WUT2018III022,2019IVB060,2020-zy-015,and 2020-zy-016)。
文摘The porous structure and honeycombed structure of granulated blast furnace slag formed by alkali activation(AGBFS)can be used as a promising photocatalysts substrate for the photocatalytic removal of atmospheric or water pollutants.In this study,photocatalytic activated slag granules were synthesized by loading TiO_(2)on AGBFS with immersion method.The physicochemical properties and NO_(x)removal performance of activated slag granules/TiO_(2)photocatalysts were studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and photocatalytic performance test.The effects of slag particle sizes and nano-TiO_(2)loading concentrations on photocatalytic efficiencies of NO_(x)removal were also investigated.It was found that the De-NO_(x)performance of activated slag granules/TiO_(2)photocatalyst increased with the increasing of slag particle size in low TiO_(2)loading concentration situation,while increasing the TiO_(2)loading concentration would result in the opposite De-NO_(x)performance as slag size increased.Nevertheless,for the same size activated slag,the photocatalytic efficiency of activated slag granules/TiO_(2)photocatalyst gradually improved with the increase of loading concentration of TiO_(2).
基金supported by the National Natural Science Foundation of China (51978070)the Shaanxi Natural Science Basic Research project (2020JM-265)。
文摘Geopolymer is a new environment-friendly cementitious material, and the development of geopolymer can reduce the carbon dioxide emission caused by the development of cement industry. Geopolymer materials not only have excellent mechanical properties, but also have a series of excellent properties such as fire resistance and corrosion resistance. Most industrial solid waste and waste incineration bottom ash are piled up at will, which not only occupies land resources, but also has a bad impact on the environment. Recycling them can be used as raw materials for preparing geopolymers. Geopolymer materials can effectively adsorb heavy metals, dyes, and other radioactive pollution, which is very beneficial to society's future development. However, due to the excellent properties of geopolymer materials, its application goes beyond that. Some useful information about geopolymer materials was introduced in this paper. The paper included the geopolymerization, the source of raw materials, the types of activators, the preparation methods, and the different application fields of geopolymer materials. The factors affecting the fresh properties and mechanical properties of geopolymer materials were discussed. In this paper, the shortcomings and application limitations of geopolymer materials were summarized, and their progress was summarized to lay a theoretical foundation for the long-term development of geopolymer materials.
基金This project was funded by the Office of Research and Sponsored Programs at Abu Dhabi University(Nos.19300460 and 19300643)The project is also funded by ASPIRE Award for Research Excellence(AARE),Abu Dhabi,UAE。
文摘Experimental evaluations were conducted to determine the water sorptivity,setting time,and resistance to a highly acidic environment,of mortar with alkali-activated ground granulated blast furnace slag(GBS)binder and also of combinations of fly ash and GBS binders.Binders were activated using mixtures of NaOH and Na_(2)SiO_(3)solutions.The molarity of NaOH in the mixtures ranged from 10 mol·L^(−1)to 16 mol·L^(−1),and the Na_(2)SiO_(3)/NaOH ratio was varied from 1.5 to 2.5.Mortar samples were produced using three binder combinations:1)GBS as the only binder;2)blended binder with a slag-to-fly ash ratio of 3:1;and 3)mixed binder with 1:1 ratio of slag to fly ash.Mortar samples were mixed and cured at(22±2)°C till the day of the test.The impact of activator solution alkalinity,activator ratio Na_(2)SiO_(3)/NaOH,GBS content on the rate of water absorption were evaluated.After 7,28,and 90 d of immersion in a 10%sulfuric acid solution,the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight.The influence of solution alkalinity and relative fly ash content on setting times was investigated.Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations,at each curing age,and for mortars made with each of the NaOH alkaline activator concentrations.Mortar sorptivity decreased with age and sodium hydroxide concentrations,suggesting the production of geopolymerization products.No reduction in weight of sample occurred after immersion in the strong acid H_(2)SO_(4)solution for three months,regardless of binder combination.This was due to the synthesis of hydration and geopolymerization products in the presence of curing water,which outweighed the degradation of the geopolymer matrix caused by sulfuric acid.
