采用硅酸和纯CaO人工合成不同n(Ca)/n(Si)值的水化硅酸钙,利用合成的CSH与Na2CrO4溶液进行一系列的吸附反应.实验结果表明:所有n(Ca)/n(Si)值的CSH对CrO42-的俘获量都不大,因此在利用水泥固化处理含Cr(Ⅵ)污染物过程中,CSH对Cr(VI)的固...采用硅酸和纯CaO人工合成不同n(Ca)/n(Si)值的水化硅酸钙,利用合成的CSH与Na2CrO4溶液进行一系列的吸附反应.实验结果表明:所有n(Ca)/n(Si)值的CSH对CrO42-的俘获量都不大,因此在利用水泥固化处理含Cr(Ⅵ)污染物过程中,CSH对Cr(VI)的固化作用很有限;2 0℃时低n(Ca)/n(Si)值的CSH对CrO42-的吸附量比8 0℃时的略高,但温度对高n(Ca)/n(Si)值的CSH的吸附性几乎不产生影响.n(Ca)/n(Si)值为1.6的CSH在含Cr(VI)液相中形成时,对液相中的Cr(Ⅵ)有一定的吸附作用,但已形成的CSH对液相中的Cr(Ⅵ)吸附量比较小;n(Ca)/n(Si)为1.6的CSH对CrO42-的吸附在10 m in内可达到平衡,且所吸附的CrO42-全被石灰水中浓度不高的OH-所置换,故该吸附为晶格外吸附.展开更多
This study investigated the nature of hydration products of white portland cement (WPC) containing 20 mM malic acid or 1 M calcium chloride hydrated for 11 years. The study identified the hydration products and char...This study investigated the nature of hydration products of white portland cement (WPC) containing 20 mM malic acid or 1 M calcium chloride hydrated for 11 years. The study identified the hydration products and characterized the chemical composition, morphology, micro/nano structure of C-S-H and the main binding phase in cementitious materials. Calcium hydroxide (CH), ettringite and C-S-H were identified in WPC with 20 mM malic acid paste hydrated for 11 years. WPC with 1 M calcium chloride paste hydrated for 11 years contained the same phases, but with less CH, and the presence of Friedel's salt (Ca2AI(OH)6CI2H2O). There were still small amount of anhydrous cement particles remaining in both pastes after 11 years hydration according to the SEM and 29Si MAS NMR results. The hydration products of paste containing malic acid had a lower porosity than those prepared with calcium chloride upon visual inspection under SEM. The morphology of the outer product (Op) C-S-H was coarse fibrillar and the inner product (Ip) C-S-H had a very fine microstructure in both pastes under TEM. Both Ip and Op C-S-H formed in paste containing malic acid had lower Ca/Si and higher A1/Si than those in paste containing calcium chloride. C-S-H in paste containing calcium chloride had longer MCL and less percentage of bridging tetrahedra occupied by aluminum in silicon/ aluminum chains due to relatively less Qp and more Q2. A new type of silicon tetrahedra, Q28, was introduced during deconvolution of 29Si MAS NMR results. Ip and Op C-S-H in both pastes had aluminum substituted tobermorite-type and jennite-type structure, and all the charges caused by aluminum substituting silicon bridging tetrahedra were balanced by Ca2+.展开更多
In the present work, silica nanoparticles (30-70nm) were supplemented into cement paste to study their influence on degree of hydration, porosity and formation of different type of calcium-silicate-hydrate (C-S-H)...In the present work, silica nanoparticles (30-70nm) were supplemented into cement paste to study their influence on degree of hydration, porosity and formation of different type of calcium-silicate-hydrate (C-S-H) gel. As the hydration time proceeds, the degree of hydration reach to 76% in nano-modified cement paste whereas plain cement achieve up to 63% at 28 days. An influence of degree of hydration on the porosity was also determined. In plain cement paste, the capillary porosity at lhr is ~48%, whereas in silica nanoparticles added cement is -35 % only, it revealed that silica nanoparticles refines the pore structure due to accelerated hydration mechanism leading to denser microstructure. Similarly, increasing gel porosity reveals the formation of more C-S-H gel. Furthermore, C-S-H gel of different CaJSi ratio in hydrated cement paste was quantified using X-ray diffractometer and thermogravimetry. The results show that in presence of silica nanoparticles, -24% C-S-H (Ca/Si 〈 1.0) forms, leading to the formation ofpolymerised and compact C-S-H. In case of plain cement this type of C-S-H was completely absent at 28 days. These studies reveal that the hydration mechanism of the cement can be tuned with the incorporation of silica nanoparticles and thus, producing more durable cementitious materials.展开更多
The nanostructure and chloride binding capacity evolution of C-A-S-H gel exposed to aggressive solutions were investigated,utilizing 29Si NMR,27Al NMR,SEM-EDS,and XRD techniques.The experimental results show that whil...The nanostructure and chloride binding capacity evolution of C-A-S-H gel exposed to aggressive solutions were investigated,utilizing 29Si NMR,27Al NMR,SEM-EDS,and XRD techniques.The experimental results show that while Cl-ions show a smaller effect on the microstructure of C-A-S-H sample,and SO4^2-ions can react with C-A-S-H,resulting in decreasing Ca/Si and Al[4]/Si for the C-A-S-H gel (i e,decalcification and dealuminization).The presence of Mg^2+ ions can aggravate the decalcifying and dealuminizing effects of SO4^2-ions on the C-A-S-H.With decreasing Ca/Si ratio and aluminum substitution for the original C-A-S-H gel,the depolymerization degree of silicate tetrahedra increases and the calcium aluminosilicate skeleton strengthens.C-A-S-H gel with lower Ca/Si ratio and higher Al[4]/Si ratio shows gentler nanostructure evolution under chemical attack,i e,improving thermodynamic stability under chemical attack.Furthermore,the chloride binding capacity of C-A-S-H gel is decreased after the sulfate attack.Aluminum substitution can also help C-A-S-H gel resist the degraded chloride binding capacity induced by sulfate attack.展开更多
The nanostructure of cementitious materials has important effects on concrete properties. The effects of rice husk ash(RHA) on cement hydration product phases and interfacial transition zone(ITZ) in mortar were in...The nanostructure of cementitious materials has important effects on concrete properties. The effects of rice husk ash(RHA) on cement hydration product phases and interfacial transition zone(ITZ) in mortar were investigated from the nano-scale structure perspective. The experimental results indicate that, with the increase of RHA dosages of samples, the volume fraction of high-density calcium-silicate-hydrate(HD C-S-H) in porosity and hydration product phases increases. The volume fractions of HD C-S-H in C-S-H of samples show an increasing trend with the increase of RHA dosages. RHA decreases the thickness of ITZ and increases the matrix elastic moduli of samples, however, the RHA dosoges hardly affect the thickness and elastic moduli.展开更多
文摘采用硅酸和纯CaO人工合成不同n(Ca)/n(Si)值的水化硅酸钙,利用合成的CSH与Na2CrO4溶液进行一系列的吸附反应.实验结果表明:所有n(Ca)/n(Si)值的CSH对CrO42-的俘获量都不大,因此在利用水泥固化处理含Cr(Ⅵ)污染物过程中,CSH对Cr(VI)的固化作用很有限;2 0℃时低n(Ca)/n(Si)值的CSH对CrO42-的吸附量比8 0℃时的略高,但温度对高n(Ca)/n(Si)值的CSH的吸附性几乎不产生影响.n(Ca)/n(Si)值为1.6的CSH在含Cr(VI)液相中形成时,对液相中的Cr(Ⅵ)有一定的吸附作用,但已形成的CSH对液相中的Cr(Ⅵ)吸附量比较小;n(Ca)/n(Si)为1.6的CSH对CrO42-的吸附在10 m in内可达到平衡,且所吸附的CrO42-全被石灰水中浓度不高的OH-所置换,故该吸附为晶格外吸附.
文摘This study investigated the nature of hydration products of white portland cement (WPC) containing 20 mM malic acid or 1 M calcium chloride hydrated for 11 years. The study identified the hydration products and characterized the chemical composition, morphology, micro/nano structure of C-S-H and the main binding phase in cementitious materials. Calcium hydroxide (CH), ettringite and C-S-H were identified in WPC with 20 mM malic acid paste hydrated for 11 years. WPC with 1 M calcium chloride paste hydrated for 11 years contained the same phases, but with less CH, and the presence of Friedel's salt (Ca2AI(OH)6CI2H2O). There were still small amount of anhydrous cement particles remaining in both pastes after 11 years hydration according to the SEM and 29Si MAS NMR results. The hydration products of paste containing malic acid had a lower porosity than those prepared with calcium chloride upon visual inspection under SEM. The morphology of the outer product (Op) C-S-H was coarse fibrillar and the inner product (Ip) C-S-H had a very fine microstructure in both pastes under TEM. Both Ip and Op C-S-H formed in paste containing malic acid had lower Ca/Si and higher A1/Si than those in paste containing calcium chloride. C-S-H in paste containing calcium chloride had longer MCL and less percentage of bridging tetrahedra occupied by aluminum in silicon/ aluminum chains due to relatively less Qp and more Q2. A new type of silicon tetrahedra, Q28, was introduced during deconvolution of 29Si MAS NMR results. Ip and Op C-S-H in both pastes had aluminum substituted tobermorite-type and jennite-type structure, and all the charges caused by aluminum substituting silicon bridging tetrahedra were balanced by Ca2+.
文摘In the present work, silica nanoparticles (30-70nm) were supplemented into cement paste to study their influence on degree of hydration, porosity and formation of different type of calcium-silicate-hydrate (C-S-H) gel. As the hydration time proceeds, the degree of hydration reach to 76% in nano-modified cement paste whereas plain cement achieve up to 63% at 28 days. An influence of degree of hydration on the porosity was also determined. In plain cement paste, the capillary porosity at lhr is ~48%, whereas in silica nanoparticles added cement is -35 % only, it revealed that silica nanoparticles refines the pore structure due to accelerated hydration mechanism leading to denser microstructure. Similarly, increasing gel porosity reveals the formation of more C-S-H gel. Furthermore, C-S-H gel of different CaJSi ratio in hydrated cement paste was quantified using X-ray diffractometer and thermogravimetry. The results show that in presence of silica nanoparticles, -24% C-S-H (Ca/Si 〈 1.0) forms, leading to the formation ofpolymerised and compact C-S-H. In case of plain cement this type of C-S-H was completely absent at 28 days. These studies reveal that the hydration mechanism of the cement can be tuned with the incorporation of silica nanoparticles and thus, producing more durable cementitious materials.
基金Funded by the Key Science and Technology Project of Heilongjiang Transport Department(No.2017HLJ0029)the National Natural Science Foundation of China(Nos.51778513 and 51878003)the Key Projects of Anhui Province Outstanding Young Talents Support Plan(gxyqZD2019055)。
文摘The nanostructure and chloride binding capacity evolution of C-A-S-H gel exposed to aggressive solutions were investigated,utilizing 29Si NMR,27Al NMR,SEM-EDS,and XRD techniques.The experimental results show that while Cl-ions show a smaller effect on the microstructure of C-A-S-H sample,and SO4^2-ions can react with C-A-S-H,resulting in decreasing Ca/Si and Al[4]/Si for the C-A-S-H gel (i e,decalcification and dealuminization).The presence of Mg^2+ ions can aggravate the decalcifying and dealuminizing effects of SO4^2-ions on the C-A-S-H.With decreasing Ca/Si ratio and aluminum substitution for the original C-A-S-H gel,the depolymerization degree of silicate tetrahedra increases and the calcium aluminosilicate skeleton strengthens.C-A-S-H gel with lower Ca/Si ratio and higher Al[4]/Si ratio shows gentler nanostructure evolution under chemical attack,i e,improving thermodynamic stability under chemical attack.Furthermore,the chloride binding capacity of C-A-S-H gel is decreased after the sulfate attack.Aluminum substitution can also help C-A-S-H gel resist the degraded chloride binding capacity induced by sulfate attack.
基金Funded by the National Natural Science Foundation of China(Nos.51602198,41427802 and 41302257)the Zhejiang Provincial Natural Science Foundation of China(No.LQ13D020001)the Shaoxing University Scientific Research Project(No.20145030)
文摘The nanostructure of cementitious materials has important effects on concrete properties. The effects of rice husk ash(RHA) on cement hydration product phases and interfacial transition zone(ITZ) in mortar were investigated from the nano-scale structure perspective. The experimental results indicate that, with the increase of RHA dosages of samples, the volume fraction of high-density calcium-silicate-hydrate(HD C-S-H) in porosity and hydration product phases increases. The volume fractions of HD C-S-H in C-S-H of samples show an increasing trend with the increase of RHA dosages. RHA decreases the thickness of ITZ and increases the matrix elastic moduli of samples, however, the RHA dosoges hardly affect the thickness and elastic moduli.