Development of sustainable construction materials has been the focus of research efforts worldwide in recent years.Concrete is a major construction material;hence,finding alternatives to ordinary Portland cement is of...Development of sustainable construction materials has been the focus of research efforts worldwide in recent years.Concrete is a major construction material;hence,finding alternatives to ordinary Portland cement is of extreme importance due to the high levels of carbon dioxide emissions associated with its manufacturing process.This study investigates the geopolymerization process.Specimens with,two different water/binder weight ratios,0.30 and 0.35,were monitored using acoustic emission.Results show that there is a significant difference in the acquisition data between the two different water/binder weight ratios.In addition,acoustic emission can be used to beneficially monitor and investigate the early geopolymerization process.The acoustic emission data were processed through pattern recognition.Two clusters were identified,assigned to a specific mechanism depending on their characteristics.SEM observations were coincided with pattern recognition findings.展开更多
We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research resu...We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.展开更多
In order to study the characteristics of pure fly ash-based geopolymer concrete(PFGC)conveniently,we used a machine learning method that can quantify the perception of characteristics to predict its compressive streng...In order to study the characteristics of pure fly ash-based geopolymer concrete(PFGC)conveniently,we used a machine learning method that can quantify the perception of characteristics to predict its compressive strength.In this study,505 groups of data were collected,and a new database of compressive strength of PFGC was constructed.In order to establish an accurate prediction model of compressive strength,five different types of machine learning networks were used for comparative analysis.The five machine learning models all showed good compressive strength prediction performance on PFGC.Among them,R2,MSE,RMSE and MAE of decision tree model(DT)are 0.99,1.58,1.25,and 0.25,respectively.While R2,MSE,RMSE and MAE of random forest model(RF)are 0.97,5.17,2.27 and 1.38,respectively.The two models have high prediction accuracy and outstanding generalization ability.In order to enhance the interpretability of model decision-making,we used importance ranking to obtain the perception of machine learning model to 13 variables.These 13 variables include chemical composition of fly ash(SiO_(2)/Al_(2)O_(3),Si/Al),the ratio of alkaline liquid to the binder,curing temperature,curing durations inside oven,fly ash dosage,fine aggregate dosage,coarse aggregate dosage,extra water dosage and sodium hydroxide dosage.Curing temperature,specimen ages and curing durations inside oven have the greatest influence on the prediction results,indicating that curing conditions have more prominent influence on the compressive strength of PFGC than ordinary Portland cement concrete.The importance of curing conditions of PFGC even exceeds that of the concrete mix proportion,due to the low reactivity of pure fly ash.展开更多
This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The...This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes.To this end,binders including lime alone,LG(slag-based geopolymer),LGNM(nano-modified LG with NM)and LGNMF(LGNM/fiber)mixture were separately added to soft soil samples.The fabricated composites were then subjected to a set of macro and micro level tests.The results indicated that,adding LG binary with a 20%NM replacement can lead to a significant increase(by nearly 21 times)in soil strength and a remarkable decline(about 70%)in the compression index.In fact,NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric,which staggeringly improve the soil hydromechanical attributes.It was also observed that raising the curing temperature will effectively augment the polymerization kinetics,leading to a substantial increase(~2 times)in the soil solidification process.However,the stabilized composites containing NM may reveal a brittle nature under more intense stress.Such a potential drawback seems to be resolved by the integration of fibers within the matrix.LGNM combined with fiber would boost(≥10 times)the energy absorption capacity of the soil,notably enhancing its residual strength.Overall,LGNMF may not only feature a broader range of benefits(inc.economic,technical,environmental)compared to traditional binders but also promote the ductility of the GP materials.展开更多
This study used steel slag,fly ash,and metakaolin as raw materials(SFM materials)to create silica-alumina-based geopolymers that can solidify Hg^(2+)when activated with sodiumbased water glass.The experiments began wi...This study used steel slag,fly ash,and metakaolin as raw materials(SFM materials)to create silica-alumina-based geopolymers that can solidify Hg^(2+)when activated with sodiumbased water glass.The experiments began with a triangular lattice point mixing design experiment,and the results were fitted,analyzed,and predicted.The optimum SFM material mass ratio was found to be 70%steel slag,25%fly ash,and 5%metakaolin.The optimum modulus of the activator was identified by comparing the unconfined compressive strength and solidifying impact on Hg^(2+)of geosynthetics with different modulus.The SFM geopolymer was then applied in the form of potting to cure the granulated mercury tailings.The inclusion of 50%SFM material generated a geosynthetic that reduced mercury transport to the surface soil by roughly 90%.The mercury concentration of herbaceous plant samples was also reduced by 78%.It indicates that the SFM material can effectively attenuate the migration transformation of mercury.Finally,characterization methods such as XPS and FTIR were used to investigate the mechanism of Hg^(2+)solidification by geopolymers generated by SFM materials.The possible solidification mechanisms were proposed as alkaline environment-induced mercury precipitation,chemical bonding s,surface adsorption of Hg^(2+)and its precipitates by the geopolymer,and physical encapsulation.展开更多
The escalating production of industrial solid waste,combined with the dwindling availability of natural resources,has intensified the focus on waste recycling.However,the heterogeneity and complexity of waste pose sig...The escalating production of industrial solid waste,combined with the dwindling availability of natural resources,has intensified the focus on waste recycling.However,the heterogeneity and complexity of waste pose significant challenges to determining process parameters.In this study,burnt coal cinder(BCC),granite powder(GP),and high-calcium fly ash(Class-C FA)were used as raw materials,and the response surface methodology(RSM)and single-factor experiments were applied to optimize the process parameters for geopolymer preparation.The optimized precursor powder composition was determined to be a mass ratio of 1.6:0.9:7.3 for BCC,GP,and Class-C FA.The NaOH-precursor powder ratio and liquid-solid ratio were adjusted to 0.084 and 0.222,respectively.The curing condition was set at 80℃ for 24 h.The resulting 28 d-aged multi-solid wastes-based geopolymer exhibited a high compressive strength of61.34 MPa.The microstructure,mineral phase,and atomic bonding of geopolymers were investigated using X-ray diffraction(XRD),thermal analysis(TA),Fourier transform infrared spectroscopy(FTIR),and scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS).Findings indicate that the compressive strength of geopolymer is most significantly influenced by the Class-C FA,followed by BCC.Furthermore,a minor addition of GP can optimize the structural density of the geopolymer.The Ca present in the Class-C FA participates in the geopolymerization,forming a hybrid N-(C)-A-S-H gel.RSM optimization facilitates the synergistic utilization of multi-solid wastes,ensuring an even distribution of gel and filler.This research establishes a theoretical framework for optimizing the preparation parameters of multi-solid wastes-based geopolymer and its subsequent applications;it holds significant scientific implications for the circular economy,resource transformation,and environmental conservation.展开更多
The waterproof performance,mechanical properties,chemical composition,microstructure,and pore structure of hydrophobically-modified geopolymer concrete are investigated before and after dry-wet cycles,to determine the...The waterproof performance,mechanical properties,chemical composition,microstructure,and pore structure of hydrophobically-modified geopolymer concrete are investigated before and after dry-wet cycles,to determine the long-term feasibility of using hydrophobically-modified geopolymer concrete in wet environments.We use two types of organic modifying agents:polydimethylsiloxane(PDMS)and sodium methyl siliconate(SMS).The experimental results show that incorporating 2%–6%PDMS or 5%–15%SMS can make the concrete hydrophobic,with water absorption and chloride transport rates decreasing by up to 94.3%.We also analyze the bonding modes of organic molecules and geopolymer gels,as well as their evolution mechanisms during dry-wet cycles.PDMS-modified geopolymer concrete is found to exhibit long-term waterproof performance that is not weakened by dry-wet cycles.This is attributed to the robust combination of organic components and the geopolymer gel skeleton formed through phase cross-linking.Meanwhile,PDMS-modified geopolymer concrete’s hydrophobicity,strength,and microstructure are essentially unaffected.In contrast,SMS-modified geopolymer concrete shows higher water sensitivity,although it does maintain efficient waterproof performance.Due to relatively low binding energy,the dry-wet cycles may lead to the detachment of some SMS molecules from the gel network,which results in a decrease of 18.6%in compressive strength and an increase of 37.6%in total porosity.This work confirms the utility of hydrophobically-modified geopolymer concrete as a building material for long-term service in wet environments,for instance,areas with frequent precipitation,or splash and tidal zones.展开更多
Metakaolin(MK)and sodium alginate(SA)were employed as raw materials to prepare SA-MK geopolymers,which were inorganic/organic composites.The microscopic morphologies,mineral phases,and chemical bonds of these composit...Metakaolin(MK)and sodium alginate(SA)were employed as raw materials to prepare SA-MK geopolymers,which were inorganic/organic composites.The microscopic morphologies,mineral phases,and chemical bonds of these composites were examined using mercury intrusion porosimetry,X-ray diffraction,Fourier-transform infrared spectroscopy,and scanning electron microscopy.And low-field nuclear magnetic resonance(LF-NMR)experiments were conducted to study the water forms at different curing ages.In addition,fluidity,bond strength,and compressive strength measurements were conducted to determine their macroscopic mechanical properties.The obtained results revealed that SA addition improved the viscosity and adhesion of the geopolymer slurry and increased the adhesion strength and density of the geopolymers with low Si/Al ratios.Nevertheless,it also reduced the fluidity of the mixed slurry and shortened the operation time.Adding the optimal amount of SA increased the compressive strength of the MK-based geopolymers.At a SA content of 1.5 wt%,the 7-day strength of the geopolymer reached its maximum value of 28.3 MPa,which was 74.6%higher than that achieved without the addition of SA.Furthermore,the presence of SA changed the water distribution and the pore structure of the MK-based geopolymers,which strongly affected their mechanical properties.展开更多
Phenolic foam(PF)has attracted growing attention in plugging areas due to its lightweight,flame retardancy and high fillability,yet its friable character and high reaction temperature severely weaken its potentials to...Phenolic foam(PF)has attracted growing attention in plugging areas due to its lightweight,flame retardancy and high fillability,yet its friable character and high reaction temperature severely weaken its potentials toward practical coal mining applications.Herein,a novel phenolic composite material filled with modified fly ash(MFA)geopolymer has been proposed to address the above issues.By modifying fly ash(FA)particles with siloxanes,robust interfacial bonding between the organic PF polymer and inorganic geopolymer network has been established,which enables modulation of their micro-morphologies to optimize their macro performances.The foam structure of PF evolves from an open-cell to a closed-cell morphology with the incorporation of MFA,leading to a decreased pulverization ratio(41%)while enhanced mechanical properties(15%).Compared with neat PF,the composite exhibits faster gelation dynamics during curing,with a maximum reaction temperature as low as only 40°C.PF/MFA composite show high reliability against gas leakage during a laboratory designed coal mine plugging test.Furthermore,the formation of a silica hybrid char layer with higher graphitization degree and a multiple continuous closed-cell structure following the combustion of PF/MFA effectively inhibits the release of combustible volatiles and toxic gases.It is provided that this strategy of geopolymer filled polymer cross-linking networks with tunable morphology opens up an avenue for advanced mining phenolic filling materials.展开更多
The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several...The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several composite structure models,including a concrete lining structure(CLS)without foam geopolymer and six foam geopolymer composite structures(FGCS)with different backfill parameters,to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading.Pressure,strain,and vibration responses at different locations were synchronously tested.The damage modes and dynamic responses of different models were compared,and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed.The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading,reducing the strain in the liner structure by 52%and increasing the pressure attenuation rate by 28%.Additionally,the foam geopolymer backfill reduced structural vibration and liner deformation,with the FGCS structure showing 35%less displacement and 70%less acceleration compared to the CLS.The FGCS model with thicker,less dense foam geopolymer backfill,having more pores and higher porosity,demonstrated better compression and energy absorption under dynamic impact,increasing stress wave attenuation efficiency.By analyzing the stress wave propagation and the compression characteristics of the porous medium,it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77%lower than that of CLS,and the transmitted wave energy was 90%lower.The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.展开更多
The performance of roller compacted concrete(RCC)was greatly influenced by variations in material proportion,optimum moisture content,density of mixes and methodology adopted making it different from conventional conc...The performance of roller compacted concrete(RCC)was greatly influenced by variations in material proportion,optimum moisture content,density of mixes and methodology adopted making it different from conventional concrete mixes.Even though RCC has gained popularity,the complex phenomenon involved in developing the RCC mixes limits it from large-scale applications.In this study,reclaimed asphalt pavement(RAP)incorporated roller-compacted geopolymer concrete(RGC)mixes were developed herein with different compaction techniques such as vibratory hammer(VH),modified proctor(MP),vibration table(VT)and compression machine(CM)are studied and compared with control mixes of natural aggregates.Initially,the effect of alkali solutions such as sodium hydroxide(SH)and sodium silicate(SS)on the physical properties.During,the second phase mechanical properties such as dry density,compressive,flexural and split-tensile strength,modulus of elasticity and microstructure properties will be investigated.The test results revealed that compaction efforts were greatly influenced by the alkali solution.Furthermore,the poor bond characteristics between RAP and the binder matrix had a significant effect on strength properties.Also,the various compaction techniques affected the mechanical properties of mixes developed herein.In Comparison with various compaction efforts,VH and MP produced comparable results,whereas the VT method underestimated and overestimated the various strength properties.Although,the CM method reports comparable results but difficult to maintain consistency in strength aspects.Therefore,optimization of various parameters influencing the concrete properties needs to be achieved for field density.展开更多
The strength and microstructural analysis of recycled geopolymer are presented in this paper.Five kinds of geopolymers containing 0%,20%,50%,80%and 100%of recycled geopolymer powder were prepared using metakaolin as t...The strength and microstructural analysis of recycled geopolymer are presented in this paper.Five kinds of geopolymers containing 0%,20%,50%,80%and 100%of recycled geopolymer powder were prepared using metakaolin as the source material.The alkali activator solution was a mixture of sodium silicate(Na_(2)SiO_(3))and 12 M sodium hydroxide(NaOH).The change laws of compressive and flexural strength of recycled geopolymer specimens were investigated.And the microscopic characteristics were carried out by SEM,XRD and FTIR to observe the internal morphology and analyze changes in components of recycled geopolymers at different substitution rates.The results show that,with the increase of substitution rate of recycled geopolymer powder,the mechanical properties of recycled geopolymers degenerate and the looser structure are formed.When the substitution rate is less than 50%,the recycled geopolymer specimen meets the use requirements of heavy traffic load class.And the specimen with 80%of substitution rate satisfies the requirements of plastering mortar.展开更多
In this study,the feasibility of producing eco-friendly bricks by using geopolymer technology and a waste grinding wheel(WGW)from the grinding wheel industries was investigated.Nowadays,in order to meet industrial nee...In this study,the feasibility of producing eco-friendly bricks by using geopolymer technology and a waste grinding wheel(WGW)from the grinding wheel industries was investigated.Nowadays,in order to meet industrial needs,for instance,in Taiwan,approximately 500,000 grinding wheels are used annually.That is,a large number of“waste”grinding wheels are produced.Furthermore,few studies have been conducted on the use of WGWs as raw materials in geopolymer applications.The use of geopolymer technology to form bricks can avoid the utilization of clay and cement and even prevent the use of a high-temperature process in kilns.Moreover,it can decrease CO_(2) emission and energy consumption and thus,protect the environment.In this study,the following three major factors were considered:press-forming pressure(70 and 100 kgf/cm2),NaOH molar concentration(2 and 4M),and the ratio of binder fineaggregate(1:3,1:4,and 1:5).Under these conditions,the specimens were tested using the compressive strength test,water absorption test,microstructure analysis,a freezing–thawing test and toxicity characteristic leaching procedure test.The optimal formulation was composed of 1:4 binder fine-aggregate ratio,4M NaOH concentration,and 100-kgf/cm2 pressure.Furthermore,we used a WGW and achieved a compressive strength of 50.6 MPa after 28 days,which was greater than 32 MPa and conformed to the Grade A brick standard of National Standards of the Republic of China(13295).In conclusion,this brick fabrication method based on geopolymer technology was not only beneficial to the environment but also improved the efficiency of reutilizing WGW.展开更多
The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations.One example is the use of coal ashes from thermalelectrical plant...The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations.One example is the use of coal ashes from thermalelectrical plants in the production of geopolymer–a green cement made by mixing aluminosilicate with alkaline activator.In this study,fly and bottom ashes from a thermal-electrical unit were used as sources of aluminosilicate in the synthesis of geopolymers.A mixture of sodium hydroxide(10 mol/L)and sodium silicate(SiO_(2)/Na_(2)O ratio of 2.2)was used as the alkaline activator.The type(fly or bottom ash)and content of the ash were the variables in the synthesis.The ashes were characterized by X-ray fluorescence(XRF),X-ray diffraction(DRX),particle size distribution(PSD),specific surface area(BET),and thermal analysis(DTA/TGA).The ash-based geopolymer samples were measured to obtain their compressive strength after curing.The evolution of the geopolymerization process was also assessed based on final alkali concentration measurements.The results show that it is possible to obtain geopolymers using coal ashes as raw materials with high solid content.The compressive strength for the bottom ash geopolymer after 90 days of curing is 35 MPa.The low concentration of unreacted alkalis after curing(1.5×10^(-3)e 3.5×10^(-3)M)corresponds to high efficiency of the geopolymerization reaction.展开更多
The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content...The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content.A series of tests including X-ray diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,physical adsorption and unconfined compressive strength were used to investigate this effect.The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer,so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a“peak shifting”phenomenon,i.e.,the higher the water-to-binder ratio,the higher the optimum mass ratio.Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems;higher addition of sodium sulfate,however,could cause the symmetrical stretching vibration of Si—O and the symmetrical stretching vibration of Si—O—Si and Al—O—Si,and promote the formation of N-A-S-H gels.Furthermore,the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously.The maximum strength of geopolymer curing at ambient temperature was 52 MPa.This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content.The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated,and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.展开更多
In this study,a new GVS(Ground Volcanic Scoria)lunar regolith simulant was produced.The similarity between GVS and lunar soil was proved by comparison with Apollo lunar soil samples and other commercial lunar soil sim...In this study,a new GVS(Ground Volcanic Scoria)lunar regolith simulant was produced.The similarity between GVS and lunar soil was proved by comparison with Apollo lunar soil samples and other commercial lunar soil simulants.Then,GVS lunar regolith simulant was investigated as the source material for preparing geopolymer to produce building material for lunar colony construction.To study the possibility of preparing geopolymer from GVS lunar regolith simulant and the optimum activator formulation as well as the optimum curing conditions,alkaline activated GVS slurries with different mixing ratios based on an orthogonal test scheme were prepared.The geopolymer products based on GVS were characterized by flexural strength test,compressive strength test,X-ray fluorescence(XRF),X-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy(SEM-EDS),29Si magic angle spinning-nuclear magnetic resonance(29Si MAS-NMR),and 27Al MAS-NMR.The experimental results indicate that changes in the mass ratio of sodium hydroxide and GVS and curing temperature have the most significant influence on the flexural strength and compressive strength,respectively.The GVS-based geopolymer can obtain the highest 28-day compressive strength and 28-day flexural strength up to 75.6 MPa and 6.3 MPa.Microstructural results imply that the changes of Si occurring in a variety of environments that explaining preliminarily about the reaction mechanism of GVS-based geopolymer.This study approves the feasibility of making a geopolymer derived from the GVS lunar regolith simulant and the potential utilization of geopolymer based on lunar regolith for construction of the lunar colony in future space exploration.展开更多
The construction of a lunar base and habitation on the Moon has always been on researchers’minds.Building materials used in in situ lunar resources are of great significance for saving expensive space freight.In this...The construction of a lunar base and habitation on the Moon has always been on researchers’minds.Building materials used in in situ lunar resources are of great significance for saving expensive space freight.In this study,a new type of lunar soil simulant named Beihang(BH)-1 was developed.The chemical mineral composition and microstructure of BH-1 closely resemble those of real lunar soil,as verified by X-ray fluorescence spectroscopy(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM),and reflectance spectra.This research also synthesized a geopolymer based on BH-1 cured at simulated lunar atmospheric conditions.We also investigated the effect of supplementing aluminum(Al)sources on the enhancement of geopolymer strength based on BH-1.The rheological behavior of alkali-activated BH-1 pastes was determined for workability.XRF,XRD,Fourier transform infrared spectroscopy,SEM coupled with energy dispersive spectroscopy,and 27Al magic angle spinningnuclear magnetic resonance were used to characterize resulting geopolymers.Rheological test findings showed that the rheology of BH-1 pastes fits the Herschel–Bulkley model,and they behaved like a shear-thinning fluid.The results showed that the 28-day compressive strength of the BH-1 geopolymer was improved by up to 100.8%.Meanwhile,the weight of additives required to produce per unit strength decreased,significantly reducing the mass of materials transported from the Earth for the construction of lunar infrastructure and saving space transportation costs.Microscopic analyses showed that the mechanism to improve the mechanical properties of the BH-1 geopolymer by adding an additional Al source enhances the replacement of silicon atoms by Al atoms in the silicon–oxygen group and generates a more complete and dense amorphous gel structure.展开更多
To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences...To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.展开更多
In recent years, circulating fluidized bed combustion fly ash （CFA） is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The par...In recent years, circulating fluidized bed combustion fly ash （CFA） is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The particle distribution, mineral composition, and chemical composition of CFA were examined firstly. Geopolymerization products were characterized by mechanical testing, scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, and X-ray fluorescence （XRF）. The CFA-based foam geopolymer was successfully fabri- cated with different contents of hydrogen peroxide and exhibited uncompleted alkali reaction and reasonable strength with relative low atomic ratios of Si/Al and Si/Na. Type-C CFA in this research could be recycled as an akernative source material for geopolymer production.展开更多
The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to...The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to-geopolymer solid （W/Gs） ratio of 0.33 by mass and a constant total binder content of 400 kg/m3. The mass fractions of silica fume that replaced fly ash in this research were 0wt%, 5wt%, 10wt%, and 15wt%. The workability-related fresh properties of SCGC were assessed through slump flow, V-funnel, and L-box test methods. Hardened concrete tests were limited to compressive, splitting tensile and flexural strengths, all of which were measured at the age of 1, 7, and 28 d after 48-h oven curing. The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability; nevertheless, the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume, especially up to 10wt%. Applying this percentage of silica fume results in 4.3% reduction in the slump flow; however, it increases the compressive strength by 6.9%, tensile strength by 12.8% and flexural strength by 11.5%.展开更多
基金supported by the U.S.Department of Energy Office of Science,Office of Basic Energy Sciences,and Office of Biological and Environmental Research under Award Number DE-SC-00012530.
文摘Development of sustainable construction materials has been the focus of research efforts worldwide in recent years.Concrete is a major construction material;hence,finding alternatives to ordinary Portland cement is of extreme importance due to the high levels of carbon dioxide emissions associated with its manufacturing process.This study investigates the geopolymerization process.Specimens with,two different water/binder weight ratios,0.30 and 0.35,were monitored using acoustic emission.Results show that there is a significant difference in the acquisition data between the two different water/binder weight ratios.In addition,acoustic emission can be used to beneficially monitor and investigate the early geopolymerization process.The acoustic emission data were processed through pattern recognition.Two clusters were identified,assigned to a specific mechanism depending on their characteristics.SEM observations were coincided with pattern recognition findings.
基金Funded by the National Natural Science Foundation of China(Nos.U23A20672,52171270,51879168)the PI Project of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML20240001,GML2024009)。
文摘We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.
基金Funded by the Natural Science Foundation of China(No.52109168)。
文摘In order to study the characteristics of pure fly ash-based geopolymer concrete(PFGC)conveniently,we used a machine learning method that can quantify the perception of characteristics to predict its compressive strength.In this study,505 groups of data were collected,and a new database of compressive strength of PFGC was constructed.In order to establish an accurate prediction model of compressive strength,five different types of machine learning networks were used for comparative analysis.The five machine learning models all showed good compressive strength prediction performance on PFGC.Among them,R2,MSE,RMSE and MAE of decision tree model(DT)are 0.99,1.58,1.25,and 0.25,respectively.While R2,MSE,RMSE and MAE of random forest model(RF)are 0.97,5.17,2.27 and 1.38,respectively.The two models have high prediction accuracy and outstanding generalization ability.In order to enhance the interpretability of model decision-making,we used importance ranking to obtain the perception of machine learning model to 13 variables.These 13 variables include chemical composition of fly ash(SiO_(2)/Al_(2)O_(3),Si/Al),the ratio of alkaline liquid to the binder,curing temperature,curing durations inside oven,fly ash dosage,fine aggregate dosage,coarse aggregate dosage,extra water dosage and sodium hydroxide dosage.Curing temperature,specimen ages and curing durations inside oven have the greatest influence on the prediction results,indicating that curing conditions have more prominent influence on the compressive strength of PFGC than ordinary Portland cement concrete.The importance of curing conditions of PFGC even exceeds that of the concrete mix proportion,due to the low reactivity of pure fly ash.
文摘This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes.To this end,binders including lime alone,LG(slag-based geopolymer),LGNM(nano-modified LG with NM)and LGNMF(LGNM/fiber)mixture were separately added to soft soil samples.The fabricated composites were then subjected to a set of macro and micro level tests.The results indicated that,adding LG binary with a 20%NM replacement can lead to a significant increase(by nearly 21 times)in soil strength and a remarkable decline(about 70%)in the compression index.In fact,NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric,which staggeringly improve the soil hydromechanical attributes.It was also observed that raising the curing temperature will effectively augment the polymerization kinetics,leading to a substantial increase(~2 times)in the soil solidification process.However,the stabilized composites containing NM may reveal a brittle nature under more intense stress.Such a potential drawback seems to be resolved by the integration of fibers within the matrix.LGNM combined with fiber would boost(≥10 times)the energy absorption capacity of the soil,notably enhancing its residual strength.Overall,LGNMF may not only feature a broader range of benefits(inc.economic,technical,environmental)compared to traditional binders but also promote the ductility of the GP materials.
基金supported by the National Key R&D Projects of China(No.2018YFC1801706-01)the National Natural Science Foundation of China(No.22162007)+2 种基金the Science and Technology Supporting Project of Guizhou Province(No.[2021]480,[2023]379)the Wengfu(Group)Co.,Ltd.Technology Development Project(No.WH-220787(YF))the Project from Guizhou Institute of Innovation and Development of Dual-carbon and New Energy Technologies(No.DCRE-2023-05)。
文摘This study used steel slag,fly ash,and metakaolin as raw materials(SFM materials)to create silica-alumina-based geopolymers that can solidify Hg^(2+)when activated with sodiumbased water glass.The experiments began with a triangular lattice point mixing design experiment,and the results were fitted,analyzed,and predicted.The optimum SFM material mass ratio was found to be 70%steel slag,25%fly ash,and 5%metakaolin.The optimum modulus of the activator was identified by comparing the unconfined compressive strength and solidifying impact on Hg^(2+)of geosynthetics with different modulus.The SFM geopolymer was then applied in the form of potting to cure the granulated mercury tailings.The inclusion of 50%SFM material generated a geosynthetic that reduced mercury transport to the surface soil by roughly 90%.The mercury concentration of herbaceous plant samples was also reduced by 78%.It indicates that the SFM material can effectively attenuate the migration transformation of mercury.Finally,characterization methods such as XPS and FTIR were used to investigate the mechanism of Hg^(2+)solidification by geopolymers generated by SFM materials.The possible solidification mechanisms were proposed as alkaline environment-induced mercury precipitation,chemical bonding s,surface adsorption of Hg^(2+)and its precipitates by the geopolymer,and physical encapsulation.
基金supported by the Fundamental Research Funds for the Central Universities,China(No.104972025RSCrc0005)the Science and Technology Project of Shaanxi Yanchang Petroleum(Group)Co.,LTD,China(No.yc-whlg-2023ky-03)。
文摘The escalating production of industrial solid waste,combined with the dwindling availability of natural resources,has intensified the focus on waste recycling.However,the heterogeneity and complexity of waste pose significant challenges to determining process parameters.In this study,burnt coal cinder(BCC),granite powder(GP),and high-calcium fly ash(Class-C FA)were used as raw materials,and the response surface methodology(RSM)and single-factor experiments were applied to optimize the process parameters for geopolymer preparation.The optimized precursor powder composition was determined to be a mass ratio of 1.6:0.9:7.3 for BCC,GP,and Class-C FA.The NaOH-precursor powder ratio and liquid-solid ratio were adjusted to 0.084 and 0.222,respectively.The curing condition was set at 80℃ for 24 h.The resulting 28 d-aged multi-solid wastes-based geopolymer exhibited a high compressive strength of61.34 MPa.The microstructure,mineral phase,and atomic bonding of geopolymers were investigated using X-ray diffraction(XRD),thermal analysis(TA),Fourier transform infrared spectroscopy(FTIR),and scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS).Findings indicate that the compressive strength of geopolymer is most significantly influenced by the Class-C FA,followed by BCC.Furthermore,a minor addition of GP can optimize the structural density of the geopolymer.The Ca present in the Class-C FA participates in the geopolymerization,forming a hybrid N-(C)-A-S-H gel.RSM optimization facilitates the synergistic utilization of multi-solid wastes,ensuring an even distribution of gel and filler.This research establishes a theoretical framework for optimizing the preparation parameters of multi-solid wastes-based geopolymer and its subsequent applications;it holds significant scientific implications for the circular economy,resource transformation,and environmental conservation.
基金supported by the National Natural Science Foundation of China(Nos.52101328 and 52171277)the National Key Research and Development Program of China(No.2022YFE0109200)+1 种基金the Foundation of the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(No.2022SZ-TD006)the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(CPSF)(No.GZB20230653)。
文摘The waterproof performance,mechanical properties,chemical composition,microstructure,and pore structure of hydrophobically-modified geopolymer concrete are investigated before and after dry-wet cycles,to determine the long-term feasibility of using hydrophobically-modified geopolymer concrete in wet environments.We use two types of organic modifying agents:polydimethylsiloxane(PDMS)and sodium methyl siliconate(SMS).The experimental results show that incorporating 2%–6%PDMS or 5%–15%SMS can make the concrete hydrophobic,with water absorption and chloride transport rates decreasing by up to 94.3%.We also analyze the bonding modes of organic molecules and geopolymer gels,as well as their evolution mechanisms during dry-wet cycles.PDMS-modified geopolymer concrete is found to exhibit long-term waterproof performance that is not weakened by dry-wet cycles.This is attributed to the robust combination of organic components and the geopolymer gel skeleton formed through phase cross-linking.Meanwhile,PDMS-modified geopolymer concrete’s hydrophobicity,strength,and microstructure are essentially unaffected.In contrast,SMS-modified geopolymer concrete shows higher water sensitivity,although it does maintain efficient waterproof performance.Due to relatively low binding energy,the dry-wet cycles may lead to the detachment of some SMS molecules from the gel network,which results in a decrease of 18.6%in compressive strength and an increase of 37.6%in total porosity.This work confirms the utility of hydrophobically-modified geopolymer concrete as a building material for long-term service in wet environments,for instance,areas with frequent precipitation,or splash and tidal zones.
基金the Natural Science Foundation of Shandong Province(No.ZR2022QE153)the Doctoral Startup Fund of Shandong University of Aeronautics(No.2024Y13)。
文摘Metakaolin(MK)and sodium alginate(SA)were employed as raw materials to prepare SA-MK geopolymers,which were inorganic/organic composites.The microscopic morphologies,mineral phases,and chemical bonds of these composites were examined using mercury intrusion porosimetry,X-ray diffraction,Fourier-transform infrared spectroscopy,and scanning electron microscopy.And low-field nuclear magnetic resonance(LF-NMR)experiments were conducted to study the water forms at different curing ages.In addition,fluidity,bond strength,and compressive strength measurements were conducted to determine their macroscopic mechanical properties.The obtained results revealed that SA addition improved the viscosity and adhesion of the geopolymer slurry and increased the adhesion strength and density of the geopolymers with low Si/Al ratios.Nevertheless,it also reduced the fluidity of the mixed slurry and shortened the operation time.Adding the optimal amount of SA increased the compressive strength of the MK-based geopolymers.At a SA content of 1.5 wt%,the 7-day strength of the geopolymer reached its maximum value of 28.3 MPa,which was 74.6%higher than that achieved without the addition of SA.Furthermore,the presence of SA changed the water distribution and the pore structure of the MK-based geopolymers,which strongly affected their mechanical properties.
基金supported by the National Natural Science Foundation of China(No.U22A20151)Taiyuan Major Science and Technology Project in 2021.
文摘Phenolic foam(PF)has attracted growing attention in plugging areas due to its lightweight,flame retardancy and high fillability,yet its friable character and high reaction temperature severely weaken its potentials toward practical coal mining applications.Herein,a novel phenolic composite material filled with modified fly ash(MFA)geopolymer has been proposed to address the above issues.By modifying fly ash(FA)particles with siloxanes,robust interfacial bonding between the organic PF polymer and inorganic geopolymer network has been established,which enables modulation of their micro-morphologies to optimize their macro performances.The foam structure of PF evolves from an open-cell to a closed-cell morphology with the incorporation of MFA,leading to a decreased pulverization ratio(41%)while enhanced mechanical properties(15%).Compared with neat PF,the composite exhibits faster gelation dynamics during curing,with a maximum reaction temperature as low as only 40°C.PF/MFA composite show high reliability against gas leakage during a laboratory designed coal mine plugging test.Furthermore,the formation of a silica hybrid char layer with higher graphitization degree and a multiple continuous closed-cell structure following the combustion of PF/MFA effectively inhibits the release of combustible volatiles and toxic gases.It is provided that this strategy of geopolymer filled polymer cross-linking networks with tunable morphology opens up an avenue for advanced mining phenolic filling materials.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52378401,12202494)the Fundamental Research Funds for the Central Universities(Grant No.30922010918)。
文摘The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts,reducing the vibration effect on the structure.Explosion tests were conducted using several composite structure models,including a concrete lining structure(CLS)without foam geopolymer and six foam geopolymer composite structures(FGCS)with different backfill parameters,to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading.Pressure,strain,and vibration responses at different locations were synchronously tested.The damage modes and dynamic responses of different models were compared,and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed.The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading,reducing the strain in the liner structure by 52%and increasing the pressure attenuation rate by 28%.Additionally,the foam geopolymer backfill reduced structural vibration and liner deformation,with the FGCS structure showing 35%less displacement and 70%less acceleration compared to the CLS.The FGCS model with thicker,less dense foam geopolymer backfill,having more pores and higher porosity,demonstrated better compression and energy absorption under dynamic impact,increasing stress wave attenuation efficiency.By analyzing the stress wave propagation and the compression characteristics of the porous medium,it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77%lower than that of CLS,and the transmitted wave energy was 90%lower.The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.
文摘The performance of roller compacted concrete(RCC)was greatly influenced by variations in material proportion,optimum moisture content,density of mixes and methodology adopted making it different from conventional concrete mixes.Even though RCC has gained popularity,the complex phenomenon involved in developing the RCC mixes limits it from large-scale applications.In this study,reclaimed asphalt pavement(RAP)incorporated roller-compacted geopolymer concrete(RGC)mixes were developed herein with different compaction techniques such as vibratory hammer(VH),modified proctor(MP),vibration table(VT)and compression machine(CM)are studied and compared with control mixes of natural aggregates.Initially,the effect of alkali solutions such as sodium hydroxide(SH)and sodium silicate(SS)on the physical properties.During,the second phase mechanical properties such as dry density,compressive,flexural and split-tensile strength,modulus of elasticity and microstructure properties will be investigated.The test results revealed that compaction efforts were greatly influenced by the alkali solution.Furthermore,the poor bond characteristics between RAP and the binder matrix had a significant effect on strength properties.Also,the various compaction techniques affected the mechanical properties of mixes developed herein.In Comparison with various compaction efforts,VH and MP produced comparable results,whereas the VT method underestimated and overestimated the various strength properties.Although,the CM method reports comparable results but difficult to maintain consistency in strength aspects.Therefore,optimization of various parameters influencing the concrete properties needs to be achieved for field density.
基金Funded by the National Natural Science Foundation of China(No.52008046)the Natural Science Foundation of Jiangsu Higher Education Institutions of China(No.19KJB560007)+1 种基金the Innovation Project of the Jiangsu Postgraduate Research of China(No.KYCX19_1788)the Research Start-up Funding of Changzhou University(No.ZMF18020307)。
文摘The strength and microstructural analysis of recycled geopolymer are presented in this paper.Five kinds of geopolymers containing 0%,20%,50%,80%and 100%of recycled geopolymer powder were prepared using metakaolin as the source material.The alkali activator solution was a mixture of sodium silicate(Na_(2)SiO_(3))and 12 M sodium hydroxide(NaOH).The change laws of compressive and flexural strength of recycled geopolymer specimens were investigated.And the microscopic characteristics were carried out by SEM,XRD and FTIR to observe the internal morphology and analyze changes in components of recycled geopolymers at different substitution rates.The results show that,with the increase of substitution rate of recycled geopolymer powder,the mechanical properties of recycled geopolymers degenerate and the looser structure are formed.When the substitution rate is less than 50%,the recycled geopolymer specimen meets the use requirements of heavy traffic load class.And the specimen with 80%of substitution rate satisfies the requirements of plastering mortar.
文摘In this study,the feasibility of producing eco-friendly bricks by using geopolymer technology and a waste grinding wheel(WGW)from the grinding wheel industries was investigated.Nowadays,in order to meet industrial needs,for instance,in Taiwan,approximately 500,000 grinding wheels are used annually.That is,a large number of“waste”grinding wheels are produced.Furthermore,few studies have been conducted on the use of WGWs as raw materials in geopolymer applications.The use of geopolymer technology to form bricks can avoid the utilization of clay and cement and even prevent the use of a high-temperature process in kilns.Moreover,it can decrease CO_(2) emission and energy consumption and thus,protect the environment.In this study,the following three major factors were considered:press-forming pressure(70 and 100 kgf/cm2),NaOH molar concentration(2 and 4M),and the ratio of binder fineaggregate(1:3,1:4,and 1:5).Under these conditions,the specimens were tested using the compressive strength test,water absorption test,microstructure analysis,a freezing–thawing test and toxicity characteristic leaching procedure test.The optimal formulation was composed of 1:4 binder fine-aggregate ratio,4M NaOH concentration,and 100-kgf/cm2 pressure.Furthermore,we used a WGW and achieved a compressive strength of 50.6 MPa after 28 days,which was greater than 32 MPa and conformed to the Grade A brick standard of National Standards of the Republic of China(13295).In conclusion,this brick fabrication method based on geopolymer technology was not only beneficial to the environment but also improved the efficiency of reutilizing WGW.
文摘The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations.One example is the use of coal ashes from thermalelectrical plants in the production of geopolymer–a green cement made by mixing aluminosilicate with alkaline activator.In this study,fly and bottom ashes from a thermal-electrical unit were used as sources of aluminosilicate in the synthesis of geopolymers.A mixture of sodium hydroxide(10 mol/L)and sodium silicate(SiO_(2)/Na_(2)O ratio of 2.2)was used as the alkaline activator.The type(fly or bottom ash)and content of the ash were the variables in the synthesis.The ashes were characterized by X-ray fluorescence(XRF),X-ray diffraction(DRX),particle size distribution(PSD),specific surface area(BET),and thermal analysis(DTA/TGA).The ash-based geopolymer samples were measured to obtain their compressive strength after curing.The evolution of the geopolymerization process was also assessed based on final alkali concentration measurements.The results show that it is possible to obtain geopolymers using coal ashes as raw materials with high solid content.The compressive strength for the bottom ash geopolymer after 90 days of curing is 35 MPa.The low concentration of unreacted alkalis after curing(1.5×10^(-3)e 3.5×10^(-3)M)corresponds to high efficiency of the geopolymerization reaction.
基金Project(51878322)supported by the National Natural Science Foundation of ChinaProject(18YF1FA112)supported by Key Research and Development Program of Gansu Province,China。
文摘The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content.A series of tests including X-ray diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,physical adsorption and unconfined compressive strength were used to investigate this effect.The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer,so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a“peak shifting”phenomenon,i.e.,the higher the water-to-binder ratio,the higher the optimum mass ratio.Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems;higher addition of sodium sulfate,however,could cause the symmetrical stretching vibration of Si—O and the symmetrical stretching vibration of Si—O—Si and Al—O—Si,and promote the formation of N-A-S-H gels.Furthermore,the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously.The maximum strength of geopolymer curing at ambient temperature was 52 MPa.This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content.The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated,and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.
基金supported by the National Natural Science Foundation of China(No.51978029,51622805)the Department of Transportation of Shandong Province of China(No.2018BZ4).
文摘In this study,a new GVS(Ground Volcanic Scoria)lunar regolith simulant was produced.The similarity between GVS and lunar soil was proved by comparison with Apollo lunar soil samples and other commercial lunar soil simulants.Then,GVS lunar regolith simulant was investigated as the source material for preparing geopolymer to produce building material for lunar colony construction.To study the possibility of preparing geopolymer from GVS lunar regolith simulant and the optimum activator formulation as well as the optimum curing conditions,alkaline activated GVS slurries with different mixing ratios based on an orthogonal test scheme were prepared.The geopolymer products based on GVS were characterized by flexural strength test,compressive strength test,X-ray fluorescence(XRF),X-ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy(SEM-EDS),29Si magic angle spinning-nuclear magnetic resonance(29Si MAS-NMR),and 27Al MAS-NMR.The experimental results indicate that changes in the mass ratio of sodium hydroxide and GVS and curing temperature have the most significant influence on the flexural strength and compressive strength,respectively.The GVS-based geopolymer can obtain the highest 28-day compressive strength and 28-day flexural strength up to 75.6 MPa and 6.3 MPa.Microstructural results imply that the changes of Si occurring in a variety of environments that explaining preliminarily about the reaction mechanism of GVS-based geopolymer.This study approves the feasibility of making a geopolymer derived from the GVS lunar regolith simulant and the potential utilization of geopolymer based on lunar regolith for construction of the lunar colony in future space exploration.
基金This research was supported by the National Key Research and Development(R&D)Program of China(2018YFB1600100)National Natural Science Foundation of China(51978029 and 51622805)Shanghai Pujiang Program.The authors also acknowledge NASA/Lunar and Planetary Institute for permission of the figures in"Lunar sourcebook:a user’s guide to the moon"to be reused in this study。
文摘The construction of a lunar base and habitation on the Moon has always been on researchers’minds.Building materials used in in situ lunar resources are of great significance for saving expensive space freight.In this study,a new type of lunar soil simulant named Beihang(BH)-1 was developed.The chemical mineral composition and microstructure of BH-1 closely resemble those of real lunar soil,as verified by X-ray fluorescence spectroscopy(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM),and reflectance spectra.This research also synthesized a geopolymer based on BH-1 cured at simulated lunar atmospheric conditions.We also investigated the effect of supplementing aluminum(Al)sources on the enhancement of geopolymer strength based on BH-1.The rheological behavior of alkali-activated BH-1 pastes was determined for workability.XRF,XRD,Fourier transform infrared spectroscopy,SEM coupled with energy dispersive spectroscopy,and 27Al magic angle spinningnuclear magnetic resonance were used to characterize resulting geopolymers.Rheological test findings showed that the rheology of BH-1 pastes fits the Herschel–Bulkley model,and they behaved like a shear-thinning fluid.The results showed that the 28-day compressive strength of the BH-1 geopolymer was improved by up to 100.8%.Meanwhile,the weight of additives required to produce per unit strength decreased,significantly reducing the mass of materials transported from the Earth for the construction of lunar infrastructure and saving space transportation costs.Microscopic analyses showed that the mechanism to improve the mechanical properties of the BH-1 geopolymer by adding an additional Al source enhances the replacement of silicon atoms by Al atoms in the silicon–oxygen group and generates a more complete and dense amorphous gel structure.
基金Project(2006AA06Z225) supported by the National High-Tech Research and Development Program of China
文摘To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.
基金financially supported by the National Natural Science Foundation of China(No.50872151)the National Key Technology Support Project(No.2009BAB48B02)+1 种基金the Fundamental Research Funds for Central Universities(Nos.2009KH09 and 2009QH02)the Specialized Research Fund for Doctoral Program of Higher Education of China(No.20120023110011)
文摘In recent years, circulating fluidized bed combustion fly ash （CFA） is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The particle distribution, mineral composition, and chemical composition of CFA were examined firstly. Geopolymerization products were characterized by mechanical testing, scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, and X-ray fluorescence （XRF）. The CFA-based foam geopolymer was successfully fabri- cated with different contents of hydrogen peroxide and exhibited uncompleted alkali reaction and reasonable strength with relative low atomic ratios of Si/Al and Si/Na. Type-C CFA in this research could be recycled as an akernative source material for geopolymer production.
基金Universiti Teknologi PETRONAS and the Ministry of Science,Technology,and Innovation,Malaysia (Research grant 06-02-02-SF0052) for providing the financial support and research facilities
文摘The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete （SCGC） was investigated in this paper. The work focused on the concrete mixes with a fixed water-to-geopolymer solid （W/Gs） ratio of 0.33 by mass and a constant total binder content of 400 kg/m3. The mass fractions of silica fume that replaced fly ash in this research were 0wt%, 5wt%, 10wt%, and 15wt%. The workability-related fresh properties of SCGC were assessed through slump flow, V-funnel, and L-box test methods. Hardened concrete tests were limited to compressive, splitting tensile and flexural strengths, all of which were measured at the age of 1, 7, and 28 d after 48-h oven curing. The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability; nevertheless, the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume, especially up to 10wt%. Applying this percentage of silica fume results in 4.3% reduction in the slump flow; however, it increases the compressive strength by 6.9%, tensile strength by 12.8% and flexural strength by 11.5%.
