The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested wit...The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.展开更多
A kinetic model of the pozzolanic reaction for the preparation of flue gas desulfurizers from fly ash and Ca(OH)_(2) was deduced on the basis of solid phase reaction kinetic theory.Kinetic expressions and parameters w...A kinetic model of the pozzolanic reaction for the preparation of flue gas desulfurizers from fly ash and Ca(OH)_(2) was deduced on the basis of solid phase reaction kinetic theory.Kinetic expressions and parameters were obtained and verified by experiment.A comparison of calculated results with experimental results showed that precision in kinetic expressions was good.The apparent reaction rate constants of the pozzolanic reaction could be raised by increasing the specific surface area of fly ash and the hydration temperature,and by using a suitable additive.展开更多
For some years it has been possible to control the particle size of fly ashes, by-products of thermal power stations. Incorporating these very fine particles （obtained by grinding and/or pneumatic selection） improve...For some years it has been possible to control the particle size of fly ashes, by-products of thermal power stations. Incorporating these very fine particles （obtained by grinding and/or pneumatic selection） improves the physical-mechanical characteristics of mortars and concretes. In this study, we measured the lime consumption of the various fractions （granulometric and densimetric） and identified by X-ray diffraction the neoformed phases by the pozzolanic reaction, to show that it is not sufficient to simply define the pozzolanicity of products based on lime consumption since it does not take into account the nature of the phases formed. The size of the particles used in the test samples also has a determining effect on the quantity of lime consumed. Before comparing results, it is necessary to ensure that the size of the particles （of the global ash and its constituents） be the same. Two distinct neoformed ohases appear： CSH in the largest granular fractions （d〉 40 μm） and C3AH6 in the smaller fractions.展开更多
Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance...Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.展开更多
基金Funded by the “13th Five-Year” National Science and Technology Support Program of China(No.2016YFC0701003–05)the Science and Technology Support Program of Hubei Province(No.2015BAA084)the National Natural Science Foundation of China(No.51378408)
文摘The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.
文摘A kinetic model of the pozzolanic reaction for the preparation of flue gas desulfurizers from fly ash and Ca(OH)_(2) was deduced on the basis of solid phase reaction kinetic theory.Kinetic expressions and parameters were obtained and verified by experiment.A comparison of calculated results with experimental results showed that precision in kinetic expressions was good.The apparent reaction rate constants of the pozzolanic reaction could be raised by increasing the specific surface area of fly ash and the hydration temperature,and by using a suitable additive.
文摘For some years it has been possible to control the particle size of fly ashes, by-products of thermal power stations. Incorporating these very fine particles （obtained by grinding and/or pneumatic selection） improves the physical-mechanical characteristics of mortars and concretes. In this study, we measured the lime consumption of the various fractions （granulometric and densimetric） and identified by X-ray diffraction the neoformed phases by the pozzolanic reaction, to show that it is not sufficient to simply define the pozzolanicity of products based on lime consumption since it does not take into account the nature of the phases formed. The size of the particles used in the test samples also has a determining effect on the quantity of lime consumed. Before comparing results, it is necessary to ensure that the size of the particles （of the global ash and its constituents） be the same. Two distinct neoformed ohases appear： CSH in the largest granular fractions （d〉 40 μm） and C3AH6 in the smaller fractions.
文摘Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.
