By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing pr...By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm 3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na 2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.展开更多
The dielectric performance of alkali activated slag (AAS) cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste wer...The dielectric performance of alkali activated slag (AAS) cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste were mostly influenced by the fraction of free water in paste or absorbed water from ambient, but not including hydration water and microstructure. The free water was completely eliminated by heat treatment at 105 ℃ about 4 hours, and then its dielectric loss was depressed; but with the exposure time in air increasing, the free water adsorption in ambient air made the dielectric property of harden cement paste to be bad. The temperature and relative humidity of environment was the key factors of free water adsorption; hence, if the influence of free water on dielectric constant was measured or eliminated, the cement-based materials may be applied in humidity sensitive materials or dielectric materials domains.展开更多
An appropriate proportion of alkali activated slag cement, abbreviated as AASC later, was determined based on strength test of paste specimens. Results showed that AASC prepared from 14% low modulus water glass and bl...An appropriate proportion of alkali activated slag cement, abbreviated as AASC later, was determined based on strength test of paste specimens. Results showed that AASC prepared from 14% low modulus water glass and blast furnace slag presented its compressive strength of hardened cement paste of 69.6, 84.0 and 91.8 MPa at 3, 7, and 28 d curing ages respectively. Flowability of the fresh railings-cement pastes and the strength development of hardened tailings-cement paste were also tested both in the cases with addition of AASC and Portland cement. The fresh tailings-cemant paste added with AASC presented much better flowability and the corresponding hardened paste presented higher compressive strength, especially the long term strength, than those added with Portland cement. Therefore, tallings paste added with AASC allowed lager solid content than that of Portland cement in order to keep the similar flowability. SEM observation on the microstructure of the hardened tailings-AASC mixture pastes showed obvious cementation effect. MIP measurements also showed that the total porosity of the hardened tailings-cement pastes decreased, and the portion of larger pore also decreased when the dosage of AASC increased. It is believed that AASC is more suitable to be used as a binder for the stabilization of zinc-lead railings and for its backfilling operation than Portland cement.展开更多
High-alkali species in coal are notorious for causing ash slagging and fouling incidents.In this paper,four high-alkali coals were individually subject to hydrothermal pretreatment(HTP),within a batch-type autoclave a...High-alkali species in coal are notorious for causing ash slagging and fouling incidents.In this paper,four high-alkali coals were individually subject to hydrothermal pretreatment(HTP),within a batch-type autoclave at 300 -C for 1 h,and the treated coals were analyzed,along with the oxygen-containing functional groups determined by Fourier transform infrared spectrometer(FT-IR).Then the alkali species and other components in the coal ash were quantified by X-ray fluorescence(XRF)for evaluating the ash slagging and fouling tendency.Apart from this,FactSage was adopted to simulate the occurrence and transformation of alkali species during coal thermal conversion ending at various temperatures.The findings indicate that the treated coals are superior to the parent ones in terms of certain remarkable changes via HTP.The moisture,oxygen and sulfur of the hydrothermally treated coals decline obviously,while the calorific value rises sharply.HTP could reduce the alkali species to less than 2%(%,by weight,equivalent to Na2O in dry ash),with a maximum removal ratio of 88.9%,lowering the ash slagging and fouling tendency.The proposed mechanism of HTP was that the alkali species in coal matrix became released due to the breakage of the coal functional groups and micropores during HTP.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
The effect of magnesia bumt at 800-950℃ on the properties, especially the shrinkage, of alkali-activated slag cement (AASC.) was experimentally studied. Experimental results show that, although adding 4%-8% lightly...The effect of magnesia bumt at 800-950℃ on the properties, especially the shrinkage, of alkali-activated slag cement (AASC.) was experimentally studied. Experimental results show that, although adding 4%-8% lightly-burnt magnesia may shorten the setting time and slightly reduce the compressive strength of AASC, it c, an remarkably reduce the shrinkage of AASC. The results also show that the setting time of AASC with a certain amount of magnesia increases with the buming temperature, and that the flexural and compressive strengths of AASC decrease with the increase of the additive amount of magnesia. Generally, the adverse effect of magnesia decreases with the increase of the burning temperature:, and the shrinkage-reducing effect of magnesia increases with the additive amount of magnesia. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses show that some magnesia particles in the hardened AASC paste at a 28-d age remained unhydrated, and that the compactness decreased a little as magnesia was added. We can also conclude that magnesia bumt at 850-950℃ can be used to reduce the shrinkage of AASC only when its additive amount does not exceed 8%; otherwise, the setting time may be too short, and the flexural and compressive strengths may severely decrease.展开更多
Three different methods were applied to study the alkali content of gelpores in cement. In the closed system, the concentration of K+, Na+ and OH - have not reduced with the increase of age. In the open system, the ...Three different methods were applied to study the alkali content of gelpores in cement. In the closed system, the concentration of K+, Na+ and OH - have not reduced with the increase of age. In the open system, the diffusion and transferring of K+ and Na+ towards free space leads to the de-crease of total alkali content. In the micro-analysis system, the contents of K+ and Na+ in the first hy- drated layer of ground granulated blastfurnace slag (GBFS) are very low, while the contents of calcium and magnesium are relatively high. This phenomenon shows that the mechanism of GBFS preventing alkali aggregate reaction (AAR) is: when GBFS is dissolved by alkali medium, SiO2 and Al2O3 are dissolved into the cement matrix, then around GBFS particles form reaction rings rich in Ca2+ and Mg^2+, and the C-S-H gel of positive charges formed in the area repulses K+ and Na+, which are forced to transfer to the mortar's matrix, pore or mortar sample surface. The transferred K ^+ and Na^+ form alkali gel products with other dissolved ions, then become evenly distributed in the mortar sample and react with Ca(OH)2 in pore solutions to form (Na,K)x-2z·zCa·(SiO2)y·(OH)x gel products; and thus changes the AAR gel products' structure. The gel products will not expand, and so they can delay expansion destruction.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 effect of the ground granulated blast-furnace slag ( GGBFS ) addition, the modulus n ( mole rutio of SiO2 to Na2O ) and the concentrution of sodium silicate solution on the compressive strength of the materi...The effect of the ground granulated blast-furnace slag ( GGBFS ) addition, the modulus n ( mole rutio of SiO2 to Na2O ) and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material ( AACCM for short ) was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% ( by mass ) ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.展开更多
文摘By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm 3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na 2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.
文摘The dielectric performance of alkali activated slag (AAS) cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste were mostly influenced by the fraction of free water in paste or absorbed water from ambient, but not including hydration water and microstructure. The free water was completely eliminated by heat treatment at 105 ℃ about 4 hours, and then its dielectric loss was depressed; but with the exposure time in air increasing, the free water adsorption in ambient air made the dielectric property of harden cement paste to be bad. The temperature and relative humidity of environment was the key factors of free water adsorption; hence, if the influence of free water on dielectric constant was measured or eliminated, the cement-based materials may be applied in humidity sensitive materials or dielectric materials domains.
基金Funded by the Major State Basic Research Development Program of China(973 Program)(No.2011CB013800)
文摘An appropriate proportion of alkali activated slag cement, abbreviated as AASC later, was determined based on strength test of paste specimens. Results showed that AASC prepared from 14% low modulus water glass and blast furnace slag presented its compressive strength of hardened cement paste of 69.6, 84.0 and 91.8 MPa at 3, 7, and 28 d curing ages respectively. Flowability of the fresh railings-cement pastes and the strength development of hardened tailings-cement paste were also tested both in the cases with addition of AASC and Portland cement. The fresh tailings-cemant paste added with AASC presented much better flowability and the corresponding hardened paste presented higher compressive strength, especially the long term strength, than those added with Portland cement. Therefore, tallings paste added with AASC allowed lager solid content than that of Portland cement in order to keep the similar flowability. SEM observation on the microstructure of the hardened tailings-AASC mixture pastes showed obvious cementation effect. MIP measurements also showed that the total porosity of the hardened tailings-cement pastes decreased, and the portion of larger pore also decreased when the dosage of AASC increased. It is believed that AASC is more suitable to be used as a binder for the stabilization of zinc-lead railings and for its backfilling operation than Portland cement.
基金the National Key Basic Research Program of China (No. 2014CB238905)
文摘High-alkali species in coal are notorious for causing ash slagging and fouling incidents.In this paper,four high-alkali coals were individually subject to hydrothermal pretreatment(HTP),within a batch-type autoclave at 300 -C for 1 h,and the treated coals were analyzed,along with the oxygen-containing functional groups determined by Fourier transform infrared spectrometer(FT-IR).Then the alkali species and other components in the coal ash were quantified by X-ray fluorescence(XRF)for evaluating the ash slagging and fouling tendency.Apart from this,FactSage was adopted to simulate the occurrence and transformation of alkali species during coal thermal conversion ending at various temperatures.The findings indicate that the treated coals are superior to the parent ones in terms of certain remarkable changes via HTP.The moisture,oxygen and sulfur of the hydrothermally treated coals decline obviously,while the calorific value rises sharply.HTP could reduce the alkali species to less than 2%(%,by weight,equivalent to Na2O in dry ash),with a maximum removal ratio of 88.9%,lowering the ash slagging and fouling tendency.The proposed mechanism of HTP was that the alkali species in coal matrix became released due to the breakage of the coal functional groups and micropores during HTP.
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.
基金supported by the National Natural Science Foundation of China (Grant No. 51139001)the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2009345)the Fundamental Research Funds for the Central Universities from the Ministry of Education of China (Grant No.2010B19914)
文摘The effect of magnesia bumt at 800-950℃ on the properties, especially the shrinkage, of alkali-activated slag cement (AASC.) was experimentally studied. Experimental results show that, although adding 4%-8% lightly-burnt magnesia may shorten the setting time and slightly reduce the compressive strength of AASC, it c, an remarkably reduce the shrinkage of AASC. The results also show that the setting time of AASC with a certain amount of magnesia increases with the buming temperature, and that the flexural and compressive strengths of AASC decrease with the increase of the additive amount of magnesia. Generally, the adverse effect of magnesia decreases with the increase of the burning temperature:, and the shrinkage-reducing effect of magnesia increases with the additive amount of magnesia. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses show that some magnesia particles in the hardened AASC paste at a 28-d age remained unhydrated, and that the compactness decreased a little as magnesia was added. We can also conclude that magnesia bumt at 850-950℃ can be used to reduce the shrinkage of AASC only when its additive amount does not exceed 8%; otherwise, the setting time may be too short, and the flexural and compressive strengths may severely decrease.
基金Funded by the German Academic Exchange Service (DAAD) for the Project A/09/00743the Science and Technology Project of Wuhan City(No.200860423208)
文摘Three different methods were applied to study the alkali content of gelpores in cement. In the closed system, the concentration of K+, Na+ and OH - have not reduced with the increase of age. In the open system, the diffusion and transferring of K+ and Na+ towards free space leads to the de-crease of total alkali content. In the micro-analysis system, the contents of K+ and Na+ in the first hy- drated layer of ground granulated blastfurnace slag (GBFS) are very low, while the contents of calcium and magnesium are relatively high. This phenomenon shows that the mechanism of GBFS preventing alkali aggregate reaction (AAR) is: when GBFS is dissolved by alkali medium, SiO2 and Al2O3 are dissolved into the cement matrix, then around GBFS particles form reaction rings rich in Ca2+ and Mg^2+, and the C-S-H gel of positive charges formed in the area repulses K+ and Na+, which are forced to transfer to the mortar's matrix, pore or mortar sample surface. The transferred K ^+ and Na^+ form alkali gel products with other dissolved ions, then become evenly distributed in the mortar sample and react with Ca(OH)2 in pore solutions to form (Na,K)x-2z·zCa·(SiO2)y·(OH)x gel products; and thus changes the AAR gel products' structure. The gel products will not expand, and so they can delay expansion destruction.
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Supported by the National "863"Research Project of China(No.2002AA335050) ,the National Natural Science Foundation ofChina( No.50409011) and the High-level University ConstructionProject of South China University of Technology (No.B09-224)
文摘The effect of the ground granulated blast-furnace slag ( GGBFS ) addition, the modulus n ( mole rutio of SiO2 to Na2O ) and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material ( AACCM for short ) was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% ( by mass ) ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.