Ettringite is a main hydrate of cement,and theSr-bearing ettringite is a main hydrate of Sr-bearing calciumsuplhoaluminate.In this paper the two hydrates are studiedby a quantum chemistry method,the self-consistent-fi...Ettringite is a main hydrate of cement,and theSr-bearing ettringite is a main hydrate of Sr-bearing calciumsuplhoaluminate.In this paper the two hydrates are studiedby a quantum chemistry method,the self-consistent-field dis-crete variation X_α.method (SCC-DV-X_α).The results show:their bond order of Al and covalent bond order of Al-O bondare alike;that the bond order of Sr and the covalent bond or-der of Sr-O in Sr-bearing ettringite are higher than these ofettringite is the main reason,that the strength of Sr-bearingettringite is higher than that of ettringite.展开更多
By employing different forms and amounts of materials , many kinds of ettringite type expansive agents had been prepared. The relationship between the compositions and properties of expansive agents was analyzed . The...By employing different forms and amounts of materials , many kinds of ettringite type expansive agents had been prepared. The relationship between the compositions and properties of expansive agents was analyzed . The design methods of expansive agent have been put forward according to the property requirement of expansive concrete.展开更多
The isothermal absorption properties and kinetic model of Cr (VI) and Cr (III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the ads...The isothermal absorption properties and kinetic model of Cr (VI) and Cr (III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 °C agrees with Langmuir's isothermal model. The ion binding stability was significantly greater than that of Cr (VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich's isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr (7?2>0.994). It can be concluded that the adsorption of Cr (III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr (VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr (III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr (VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr (III) adsorption.展开更多
In part 1 of this two-part series, the formation mechanism of secondary ettringite has been discussed. In this part, the expansive mechanisms of secondary ettringite due to the ettringite form of sulfate attack were r...In part 1 of this two-part series, the formation mechanism of secondary ettringite has been discussed. In this part, the expansive mechanisms of secondary ettringite due to the ettringite form of sulfate attack were reviewed and analyzed. Three theories have been proposed for explaining the expansive mechanism of secondary ettringite, that is, the crystallization pressure theory (or the crystal growth theory), the theory increasing in solid volume and the swelling theory. According to the analysis, swelling theory should be responsible for the expansion of secondary ettringite. The experimental results also verified that the expansion, subsequent the cracking and spalling of concrete can be caused by the swelling of fine ettringite particles formed at the interface zone of coarse aggregate particles.展开更多
Two different mechanisms have been proposed for the formation of ettringite, i.e.through-solution reaction and topochemical reaction. In this paper, the formation mechanism of secondary ettringite in concrete due to s...Two different mechanisms have been proposed for the formation of ettringite, i.e.through-solution reaction and topochemical reaction. In this paper, the formation mechanism of secondary ettringite in concrete due to sulfate attack was reviewed and analyzed. It was deduced that the formation mechanism of secondary ettringite is mainly by topochemical mechanism. The sample made from AFm (4CaO.Al2O3.CaSO4. 12H2O) and Ca (OH)2 was immersed in 5% sodium sulfate at 20 ℃ for 20 days. X-ray diffraction (XRD) was used to analyze the sample. The results verified that the formation mechanism of secondary ettringite should be attributed to topochemical reaction.展开更多
On parabolic flights,the growth of ettringite,[Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O,a major reaction product of cement with water which forms instantaneously,was crystallized under microgravity conditions and...On parabolic flights,the growth of ettringite,[Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O,a major reaction product of cement with water which forms instantaneously,was crystallized under microgravity conditions and studied.In the experiments,Ca(OH)2/Al2(SO4)3 solutions were combined and reacted for 10?s,followed by immediate filtration of the suspension and subsequent quenching with acetone.For the ettringite crystals,the size,aspect ratios,quantity and morphology were determined and the results were compared with those from identical experiments performed under terrestric gravity.Under microgravity,generally smaller crystals (l-2.9 μm) precipitated in larger amount than under normal gravity (l-3.5 μm).The aspect ratios of the crystals grown under terrestric or microgravity condition were comparable at about 5.6.It is assumed that the reason for the smaller ettringite crystals is the absence of convection leading to more initial nuclei,but slower crystal growth which is diffusion limited.Apparently,no preference relative to the ion transport to the different faces of the crystals exists.The results contribute to the understanding of the mineralization of inorganic salts under microgravity conditions for which hitherto only a handful of examples were reported.展开更多
In order to improve the engineering properties oforganic soil, a new stabilization agent is developed by theaddition of phosphor gypsum and calcium aluminate cement.The artificial organic soil is applied in the study ...In order to improve the engineering properties oforganic soil, a new stabilization agent is developed by theaddition of phosphor gypsum and calcium aluminate cement.The artificial organic soil is applied in the study and a series oflaboratory tests were carried out to explore new stabilizationagents and determine the optimal dosage. Unconfinedcompressive strength （UCS） and the pH value of soil poresolution were measured. The influence of organic content,agent composition and curing time on the UCS of sampleswere also researched. The test results show that the UCS ofstabilized organic soils by a new agent achieves approximately800 and 1 200 kPa at 28 and 90 d curing time, respectively.The pH test results show that a high alkaline environment is anecessary and not a sufficient condition for high strength. Thestrength of stabilized soil is related to the hydration product ofstabilization agent. The mechanism of strength formation wasalso explored by X-ray diffraction （XRD）, mercury intrusionporosimetry （MIP） and scanning electron microscope （SEM）tests. A large amount of ettringite is produced to fill the largepores of organic soils, which contribute to the high UCS valueof stabilized organic soils. The new agent can solidify theorganic soil successfully as well as provide a new approach totreat the organic soil.展开更多
This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and ...This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and 70%)was treated by reconstituted cementitious binders with varying gypsum to clinker(G/C)ratios and added metakaolin to facilitate the formation of ettringite,followed by the measurements of final water contents,dry densities and strengths in accordance with ASTM standards as well as microstructure by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of the CBSC,and there exists a threshold of the G/C ratio,which is 10%and 15%for clays with 50%and 70%initial water contents,respectively.Beyond which adding excessive gypsum cannot improve the strength further,eliminating the beneficial role.At these thresholds of the G/C ratio,the unconfined compressive strength(UCS)values for clays with 50%and 70%initial water contents are 1.74 MPa and 1.53 MPa at 60 d of curing,respectively.Microstructure characterization shows that,besides the common cementation-induced strengthening,newly formed ettringite also acts as significant pore infills,and the associated remarkable volumetric expansion is responsible,and may be the primary factor,for the beneficial strength gain due to the added gypsum.Moreover,pore-filling ettringite also leads to the conversion of relatively large inter-aggregate to smaller intra-aggregate pores,thereby causing a more homogeneous matrix or solid skeleton with higher strength.Overall,added gypsum plays a vital beneficial role in the strength development of the CBSC,especially for very soft clays.展开更多
The influences of different nano-SiO_2(NS) contents on the mechanical properties and rheological behavior of sulfoaluminate cement(SAC) based composite materials were studied.Results show that with increasing content ...The influences of different nano-SiO_2(NS) contents on the mechanical properties and rheological behavior of sulfoaluminate cement(SAC) based composite materials were studied.Results show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity decreases.With a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly improved.Besides,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is accelerated.The forming mechanism of strengths was revealed by scanning electron microscopy(SEM),hydration heat,X-ray diffraction(XRD) and derivative thermogravimetry(DTG).The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.展开更多
The effect of benzene-1,2-diol (pyrocatechol) and benzene-1,3-diol (resorcinol) on the development of sulfate attack in Portland cement mortars containing alkali-free setting accelerator (aluminum sulfate) was studied...The effect of benzene-1,2-diol (pyrocatechol) and benzene-1,3-diol (resorcinol) on the development of sulfate attack in Portland cement mortars containing alkali-free setting accelerator (aluminum sulfate) was studied. It has been found that these compounds (especially pyrocatechol—due to its ability to form chelate complexes with aluminum ions) restrain destructive deformations of Portland cement mortars with aluminum sulfate admixture when under test conditions a constant supply of sulfate ions from external source is provided. According to 27Al-MAS NMR data, pyrocatechol does not influence the amount of ettringite formed in Portland cement paste during its store in sodium sulfate solution. Presumably, in presence of benzenediols, in cement mortars with aluminum sulfate admixture the formation of ettringite crystals with a less pronounced destructive effect takes place.展开更多
The hydrating products and microstructure of permeablity resisting portland cement have been studied by x-ray diffraction (XRD) and electron microscopy(EM). The hydrates such as calcium silicates hydrate and calcium s...The hydrating products and microstructure of permeablity resisting portland cement have been studied by x-ray diffraction (XRD) and electron microscopy(EM). The hydrates such as calcium silicates hydrate and calcium sulphaluminate hydrate, ettringite crystal of needles can be observed under the EM, most of which were filled into pores of hardened cement paste.展开更多
The addition of cement for stabilization of expansive soils is one of the most commonly used methods.As with every calcium-based stabilizer,the time delay between the physical mixing of the stabilizer and compaction p...The addition of cement for stabilization of expansive soils is one of the most commonly used methods.As with every calcium-based stabilizer,the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization.However,a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established.Furthermore,the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay.The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite,which deteriorates the stabilized soil matrix.In view of this,the present study is aimed at using the sulfate resistant cement(SRC)as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil.To bring out the above effects,three periods of time delays(0 h,6 h and 24 h)and three sulfate concentrations of 5000 parts per million(ppm),10,000 ppm and 20,000 ppm were adopted.The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil.Upon sulfate addition to SRC-stabilized expansive soil,the formation clogs was not curtailed and resulted in the formation of ettringite clusters.These formations were captured with the help of scanning electron microscope(SEM)images and validated with electron dispersive X-ray spectroscopy(EDAX)analysis.Further,an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry(MIP)studies.展开更多
Herein,micro iron ore tailings(micro-IOTs)were prepared by wet-grinding and applied to improve sulphoaluminate cement(SAC)performance.The physicochemical properties of micro-IOTs were investigated by particle size ana...Herein,micro iron ore tailings(micro-IOTs)were prepared by wet-grinding and applied to improve sulphoaluminate cement(SAC)performance.The physicochemical properties of micro-IOTs were investigated by particle size analysis,XRD,and XPS.The hydrates trait and the hydration mechanism of micro-IOTs-SAC composite were studied by XRD,TGA,MIP,and SEM.The results demonstrated that micro-IOTs with an average grain diameter of 517 nm could be obtained by wet-grinding.The setting time of SAC gradually decreased with increasing micro-IOTs content.By adding 2%micro-IOTs,the compressive strengths of SAC pastes were enhanced about 22%and 10%at 4 h and 28 d,respectively.Moreover,the addition of micro-IOTs accelerated ettringite precipitation and changed its morphology,resulting in early strength improvement of the binary system.And increased later strength by micro-IOTs was closely related to the high content of AH_(3),fine pore structure,and high hydration degree of SAC.The findings suggested one new approach to utilize iron ore tailings in cementbased materials.展开更多
Shrinkage-compensating concrete can enhance the permeability and strength. In addition,expansive admixture can densify concrete to advance the carbonation resistance ability. Due to special quality of ettringite,the r...Shrinkage-compensating concrete can enhance the permeability and strength. In addition,expansive admixture can densify concrete to advance the carbonation resistance ability. Due to special quality of ettringite,the relative humidity of curing environment has significant effect on the carbonation rate of concrete. This paper discusses the influence of environmental humidity on carbonation rate of shrinkage-compensating concrete. Four different curing conditions were set up,namely the natural environment (RH 60%),standard environment (RH 90%),early age water curing environment for 3 d and 7 d. After curing in these four environments for 28 d,an accelerated carbonation test was performed. Micro-hardness analysis was used to evaluate surface hardness,which depends on,to a great degree,the carbonation depth. TG-DSC analysis was used to study Ca(OH)2 content gradient in the surface layer of concrete in different environment. The results show that natural condition lead to a relatively worse carbonation degree,curing in water for 3 d is harmful to the carbonation resistance,while curing in water for 7 d lead to an equivalent carbonation degree with standard condition,which show the most improvement to carbonation resistance ability.展开更多
文摘Ettringite is a main hydrate of cement,and theSr-bearing ettringite is a main hydrate of Sr-bearing calciumsuplhoaluminate.In this paper the two hydrates are studiedby a quantum chemistry method,the self-consistent-field dis-crete variation X_α.method (SCC-DV-X_α).The results show:their bond order of Al and covalent bond order of Al-O bondare alike;that the bond order of Sr and the covalent bond or-der of Sr-O in Sr-bearing ettringite are higher than these ofettringite is the main reason,that the strength of Sr-bearingettringite is higher than that of ettringite.
基金Funded by the State "the Nineth Five-Plan"of Communica-tion Ministry(95 - 05 - 02 - 25)
文摘By employing different forms and amounts of materials , many kinds of ettringite type expansive agents had been prepared. The relationship between the compositions and properties of expansive agents was analyzed . The design methods of expansive agent have been put forward according to the property requirement of expansive concrete.
基金Supported by the National Natural Science Foundation of China(No.2010CB735803)
文摘The isothermal absorption properties and kinetic model of Cr (VI) and Cr (III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 °C agrees with Langmuir's isothermal model. The ion binding stability was significantly greater than that of Cr (VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich's isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr (7?2>0.994). It can be concluded that the adsorption of Cr (III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr (VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr (III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr (VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr (III) adsorption.
基金Funded by the National Natural Science Foundation of China(No. 0378092)
文摘In part 1 of this two-part series, the formation mechanism of secondary ettringite has been discussed. In this part, the expansive mechanisms of secondary ettringite due to the ettringite form of sulfate attack were reviewed and analyzed. Three theories have been proposed for explaining the expansive mechanism of secondary ettringite, that is, the crystallization pressure theory (or the crystal growth theory), the theory increasing in solid volume and the swelling theory. According to the analysis, swelling theory should be responsible for the expansion of secondary ettringite. The experimental results also verified that the expansion, subsequent the cracking and spalling of concrete can be caused by the swelling of fine ettringite particles formed at the interface zone of coarse aggregate particles.
基金Funded by the National Natural Science Foundation of China (No. 50378092)
文摘Two different mechanisms have been proposed for the formation of ettringite, i.e.through-solution reaction and topochemical reaction. In this paper, the formation mechanism of secondary ettringite in concrete due to sulfate attack was reviewed and analyzed. It was deduced that the formation mechanism of secondary ettringite is mainly by topochemical mechanism. The sample made from AFm (4CaO.Al2O3.CaSO4. 12H2O) and Ca (OH)2 was immersed in 5% sodium sulfate at 20 ℃ for 20 days. X-ray diffraction (XRD) was used to analyze the sample. The results verified that the formation mechanism of secondary ettringite should be attributed to topochemical reaction.
文摘On parabolic flights,the growth of ettringite,[Ca3Al(OH)6·12H2O]2·(SO4)3·2H2O,a major reaction product of cement with water which forms instantaneously,was crystallized under microgravity conditions and studied.In the experiments,Ca(OH)2/Al2(SO4)3 solutions were combined and reacted for 10?s,followed by immediate filtration of the suspension and subsequent quenching with acetone.For the ettringite crystals,the size,aspect ratios,quantity and morphology were determined and the results were compared with those from identical experiments performed under terrestric gravity.Under microgravity,generally smaller crystals (l-2.9 μm) precipitated in larger amount than under normal gravity (l-3.5 μm).The aspect ratios of the crystals grown under terrestric or microgravity condition were comparable at about 5.6.It is assumed that the reason for the smaller ettringite crystals is the absence of convection leading to more initial nuclei,but slower crystal growth which is diffusion limited.Apparently,no preference relative to the ion transport to the different faces of the crystals exists.The results contribute to the understanding of the mineralization of inorganic salts under microgravity conditions for which hitherto only a handful of examples were reported.
基金The National Natural Science Foundation of Chin(No.51578148)the Project of China Communications Construction(No.2015-ZJKJ-26)the Fundamental Research Funds for the Centra Universities,the Scientific Innovation Research of College Graduates in Jiangsu Province(No.SJLX15_0062)
文摘In order to improve the engineering properties oforganic soil, a new stabilization agent is developed by theaddition of phosphor gypsum and calcium aluminate cement.The artificial organic soil is applied in the study and a series oflaboratory tests were carried out to explore new stabilizationagents and determine the optimal dosage. Unconfinedcompressive strength （UCS） and the pH value of soil poresolution were measured. The influence of organic content,agent composition and curing time on the UCS of sampleswere also researched. The test results show that the UCS ofstabilized organic soils by a new agent achieves approximately800 and 1 200 kPa at 28 and 90 d curing time, respectively.The pH test results show that a high alkaline environment is anecessary and not a sufficient condition for high strength. Thestrength of stabilized soil is related to the hydration product ofstabilization agent. The mechanism of strength formation wasalso explored by X-ray diffraction （XRD）, mercury intrusionporosimetry （MIP） and scanning electron microscope （SEM）tests. A large amount of ettringite is produced to fill the largepores of organic soils, which contribute to the high UCS valueof stabilized organic soils. The new agent can solidify theorganic soil successfully as well as provide a new approach totreat the organic soil.
基金supported by the National Key R&D Program of China (Grant No. 2019YFC1806004)National Natural Science Foundation of China (Grant Nos. 51878159 and 41572280)
文摘This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay(CBSC).A soft marine clay at two initial water contents(i.e.50%and 70%)was treated by reconstituted cementitious binders with varying gypsum to clinker(G/C)ratios and added metakaolin to facilitate the formation of ettringite,followed by the measurements of final water contents,dry densities and strengths in accordance with ASTM standards as well as microstructure by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of the CBSC,and there exists a threshold of the G/C ratio,which is 10%and 15%for clays with 50%and 70%initial water contents,respectively.Beyond which adding excessive gypsum cannot improve the strength further,eliminating the beneficial role.At these thresholds of the G/C ratio,the unconfined compressive strength(UCS)values for clays with 50%and 70%initial water contents are 1.74 MPa and 1.53 MPa at 60 d of curing,respectively.Microstructure characterization shows that,besides the common cementation-induced strengthening,newly formed ettringite also acts as significant pore infills,and the associated remarkable volumetric expansion is responsible,and may be the primary factor,for the beneficial strength gain due to the added gypsum.Moreover,pore-filling ettringite also leads to the conversion of relatively large inter-aggregate to smaller intra-aggregate pores,thereby causing a more homogeneous matrix or solid skeleton with higher strength.Overall,added gypsum plays a vital beneficial role in the strength development of the CBSC,especially for very soft clays.
基金Funded by the Fundamental Research Funds for the Central Universities(No.2013-YB-25)the National Natural Science Foundation of China(No.51378408)
文摘The influences of different nano-SiO_2(NS) contents on the mechanical properties and rheological behavior of sulfoaluminate cement(SAC) based composite materials were studied.Results show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity decreases.With a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly improved.Besides,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is accelerated.The forming mechanism of strengths was revealed by scanning electron microscopy(SEM),hydration heat,X-ray diffraction(XRD) and derivative thermogravimetry(DTG).The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.
文摘The effect of benzene-1,2-diol (pyrocatechol) and benzene-1,3-diol (resorcinol) on the development of sulfate attack in Portland cement mortars containing alkali-free setting accelerator (aluminum sulfate) was studied. It has been found that these compounds (especially pyrocatechol—due to its ability to form chelate complexes with aluminum ions) restrain destructive deformations of Portland cement mortars with aluminum sulfate admixture when under test conditions a constant supply of sulfate ions from external source is provided. According to 27Al-MAS NMR data, pyrocatechol does not influence the amount of ettringite formed in Portland cement paste during its store in sodium sulfate solution. Presumably, in presence of benzenediols, in cement mortars with aluminum sulfate admixture the formation of ettringite crystals with a less pronounced destructive effect takes place.
文摘The hydrating products and microstructure of permeablity resisting portland cement have been studied by x-ray diffraction (XRD) and electron microscopy(EM). The hydrates such as calcium silicates hydrate and calcium sulphaluminate hydrate, ettringite crystal of needles can be observed under the EM, most of which were filled into pores of hardened cement paste.
文摘The addition of cement for stabilization of expansive soils is one of the most commonly used methods.As with every calcium-based stabilizer,the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization.However,a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established.Furthermore,the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay.The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite,which deteriorates the stabilized soil matrix.In view of this,the present study is aimed at using the sulfate resistant cement(SRC)as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil.To bring out the above effects,three periods of time delays(0 h,6 h and 24 h)and three sulfate concentrations of 5000 parts per million(ppm),10,000 ppm and 20,000 ppm were adopted.The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil.Upon sulfate addition to SRC-stabilized expansive soil,the formation clogs was not curtailed and resulted in the formation of ettringite clusters.These formations were captured with the help of scanning electron microscope(SEM)images and validated with electron dispersive X-ray spectroscopy(EDAX)analysis.Further,an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry(MIP)studies.
基金This work was supported by University Natural Science Research Project of Anhui Province(KJ2019A0171)National Natural Science Foundation of China(Grant No.52005009)+1 种基金Anhui Province Natural Science Funds for Youth Fund Project(2008085QE273)Anhui Province Key Research and Development Project(202004e11020003).
文摘Herein,micro iron ore tailings(micro-IOTs)were prepared by wet-grinding and applied to improve sulphoaluminate cement(SAC)performance.The physicochemical properties of micro-IOTs were investigated by particle size analysis,XRD,and XPS.The hydrates trait and the hydration mechanism of micro-IOTs-SAC composite were studied by XRD,TGA,MIP,and SEM.The results demonstrated that micro-IOTs with an average grain diameter of 517 nm could be obtained by wet-grinding.The setting time of SAC gradually decreased with increasing micro-IOTs content.By adding 2%micro-IOTs,the compressive strengths of SAC pastes were enhanced about 22%and 10%at 4 h and 28 d,respectively.Moreover,the addition of micro-IOTs accelerated ettringite precipitation and changed its morphology,resulting in early strength improvement of the binary system.And increased later strength by micro-IOTs was closely related to the high content of AH_(3),fine pore structure,and high hydration degree of SAC.The findings suggested one new approach to utilize iron ore tailings in cementbased materials.
基金supported by the National Fundamental Scientific Research Project(PR China),relevant to"Basic research in Environmentally Friendly Concrete (2009CB623201)"
文摘Shrinkage-compensating concrete can enhance the permeability and strength. In addition,expansive admixture can densify concrete to advance the carbonation resistance ability. Due to special quality of ettringite,the relative humidity of curing environment has significant effect on the carbonation rate of concrete. This paper discusses the influence of environmental humidity on carbonation rate of shrinkage-compensating concrete. Four different curing conditions were set up,namely the natural environment (RH 60%),standard environment (RH 90%),early age water curing environment for 3 d and 7 d. After curing in these four environments for 28 d,an accelerated carbonation test was performed. Micro-hardness analysis was used to evaluate surface hardness,which depends on,to a great degree,the carbonation depth. TG-DSC analysis was used to study Ca(OH)2 content gradient in the surface layer of concrete in different environment. The results show that natural condition lead to a relatively worse carbonation degree,curing in water for 3 d is harmful to the carbonation resistance,while curing in water for 7 d lead to an equivalent carbonation degree with standard condition,which show the most improvement to carbonation resistance ability.
