The effect of hydrate microcrystals such as calcium silicate hydrates ( CSH) and ettringite on the early strength of slag cements was studied. The authors explored the possibility of improving the early strength of th...The effect of hydrate microcrystals such as calcium silicate hydrates ( CSH) and ettringite on the early strength of slag cements was studied. The authors explored the possibility of improving the early strength of the slag cement by applying crystal seed technology. It is shown that slag crystal seeds make the early strength of the cement increased due to the action of hydrate crystal seeds , which speed up the hydration of clinker minerals in the nucleation of ettringite. Therefore, the early strength of the slag cement is obviously improved.展开更多
To accelerate the early strength of lime-flyush stabilized soil for extending its further uses in highway and shortening highway constraction time, five kinds of chemical odditives were chosen on the basis of mechanis...To accelerate the early strength of lime-flyush stabilized soil for extending its further uses in highway and shortening highway constraction time, five kinds of chemical odditives were chosen on the basis of mechanism analysis of accelerating early strength in highway as a semi-rigid base materhd, and a series of experiments about the effect of differeat kinds of additives and quantity on the early strength of the stabilized soll were tested. The results show that chemical additives can efftciently improve the early strength of lime-flyush stabilized soil both the 7 d and 28d, and the optimum quantity for above chemical additive is 1.5%-2.5% approximately. Some suggestions for the practical construction were also proposed.展开更多
The effect of fly ash and early strength agent on resistance of concrete to the cyclic sulfate environment was studied.Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fl...The effect of fly ash and early strength agent on resistance of concrete to the cyclic sulfate environment was studied.Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%,or 1% early strength agent and fly ash with the replacement of 20%,were made and subjected to 250 cycles of exposure to the cyclic sulfate environment.Concrete properties including loss of mass,chloride ion diffusion coefficient,compressive strength and flexural strength were measured.Microstructure and chemical component of samples were determined by means of X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The experimental results indicated that effect of fly ash on the cyclic sulfate resistance of concretes was mostly dependent on the amount of fly ash.Early strength agent improved performances of concrete with 20% fly ash exposed to cyclic sulfate environment.展开更多
The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with dif...The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with different functional additives have been studied through compressive strength, flexural strength, volume stability at early age and porosity characterization tests. The results show that the addition of silica fume and aluminum sulfate reduces the fluidity and shortens the setting time of sulfoaluminate cement paste, promoting hydration process and increasing hydration products at early age. In the case of appropriate proportion of mortar, the inclusion of hydroxy propyl methyl cellulose, dispersible polypropylene fiber arid organic silicon kind of defoamer can control segregation and bleeding, improve mechanical strength and volume stability at early age, and modify the pore distribution of sulfoaluminate cement mortar, respectively. The sulfoaluminate cement mortar can carry out gravitational grouting in the absence of outside force, the compressive strength of 2 hours and 24 hours have reached 26 and 58 MPa respectively, and have good micro- expansion and tiny.pore distribution characterization.展开更多
The primary objective of this research was to determine optimum dosage of mixing concrete containing plasticizers and fly ash, consistent with desirable structural grade concrete properties. Factorial tests were also ...The primary objective of this research was to determine optimum dosage of mixing concrete containing plasticizers and fly ash, consistent with desirable structural grade concrete properties. Factorial tests were also conducted to investigate the four main factors: water-cementing materials ratio, water content, content of superplasticizers (SP) and fly ash content. It was found that the requirement for setting time played the dominant role in shrinkage and anti-cracking, and fly ash played a critical role in workability and reducing heat of hydration but showed insignificant effects on slump, early strength and initial setting time of concrete.展开更多
High early strength(HES)concrete pavements are commonly opened to traffic within the first 24 h after construction,making early-opening decisions critical for pavement quality and traffic operations.Currently,most sta...High early strength(HES)concrete pavements are commonly opened to traffic within the first 24 h after construction,making early-opening decisions critical for pavement quality and traffic operations.Currently,most state departments of transportation rely on compressive strength testing for early-opening decision making.However,there laboratory tests are labor intensive,costly and not always representative of field strength development.In this study,non-destructive testing(maturity and ultrasonic tomography)was explored for faster and reliable in-situ strength estimations.An experimental section constructed using HES concrete was routinely monitored using compressive testing,maturity,and ultrasonic tomography in the first 24 h after construction.The shear wave velocity,measured using ultrasonic tomography,was able to capture the strength-gain variability within a single slab and between different slabs due to the ability to monitor several locations in a short period of time.Maturity results were consistently conservative in the first 24 h of monitoring.Results show that both maturity testing and ultrasonic tomography are able to replace or add to conventional strength testing for HES concrete pavements to facilitate making the opening decision within the first 24 h.Ultrasonic tomography proved more beneficial as a result of the device's portability,increased speed of testing,and accurate estimations of HES concrete strength for the entire pavement length.展开更多
In this paper,C50 ultra-high-early-strength concrete was prepared with rapid-harden sulphoaluminate cement,alkali carbonate early strength agent,inorganic tribasic acid retarder and polycarboxylate water reducing agen...In this paper,C50 ultra-high-early-strength concrete was prepared with rapid-harden sulphoaluminate cement,alkali carbonate early strength agent,inorganic tribasic acid retarder and polycarboxylate water reducing agent. The properties testing results of C50 ultra-high-early-strength concrete indicated that the compressive strength at 12 h exceeded 37 MPa and at 3 d exceeded 59 MPa. Compared to the C50 ordinary reference concrete,the durability of C50 ultra-high-early strength concrete was investigated. The results indicated that C50 ultra-high-early-strength concrete had the same chloride ion permeability resistance,carbonization resistance and abrasion resistance to the C50 ordinary concrete. As to the sulfate resistance,the ultra-high-early-strength concrete was much better than the ordinary concrete.展开更多
As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen t...As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.展开更多
The technology of activation by adding few activators ( less than 1%) to increase the amount of blends in cement was investigated. The results show that outer activation has a remarkable effect on improving the physi...The technology of activation by adding few activators ( less than 1%) to increase the amount of blends in cement was investigated. The results show that outer activation has a remarkable effect on improving the physical properties of slag cement, flyash cement and volcanic cement. For example, the compressive strength was increased by 5-10 MPa. Morever, the application of activation is beneficial to grind-aiding, early strength and water-reducing etc. (Author abstract) 4 Refs.展开更多
In recent building practice,rapid construction is one of the principal requisites.Furthermore,in designing concrete structures,compressive strength is the most significant of all parameters.While 3-d and 7-d compressi...In recent building practice,rapid construction is one of the principal requisites.Furthermore,in designing concrete structures,compressive strength is the most significant of all parameters.While 3-d and 7-d compressive strength reflects the strengths at early phases,the ultimate strength is paramount.An effort has been made in this study to develop mathematical models for predicting compressive strength of concrete incorporating ethylene vinyl acetate(EVA)at the later phases.Kolmogorov-Smirnov(KS)goodness-of-fit test was used to examine distribution of the data.The compressive strength of EVA-modified concrete was studied by incorporating various concentrations of EVA as an admixture and by testing at ages of 28,56,90,120,210,and 365 d.An accelerated compressive strength at 3.5 hours was considered as a reference strength on the basis of which all the specified strengths were predicted by means of linear regression fit.Based on the results of KS goodness-of-fit test,it was concluded that KS test statistics value(D)in each case was lower than the critical value 0.521 for a significance level of 0.05,which demonstrated that the data was normally distributed.Based on the results of compressive strength test,it was concluded that the strength of EVA-modified specimens increased at all ages and the optimum dosage of EVA was achieved at 16%concentration.Furthermore,it was concluded that predicted compressive strength values lies within a 6%difference from the actual strength values for all the mixes,which indicates the practicability of the regression equations.This research work may help in understanding the role of EVA as a viable material in polymer-based cement composites.展开更多
文摘The effect of hydrate microcrystals such as calcium silicate hydrates ( CSH) and ettringite on the early strength of slag cements was studied. The authors explored the possibility of improving the early strength of the slag cement by applying crystal seed technology. It is shown that slag crystal seeds make the early strength of the cement increased due to the action of hydrate crystal seeds , which speed up the hydration of clinker minerals in the nucleation of ettringite. Therefore, the early strength of the slag cement is obviously improved.
文摘To accelerate the early strength of lime-flyush stabilized soil for extending its further uses in highway and shortening highway constraction time, five kinds of chemical odditives were chosen on the basis of mechanism analysis of accelerating early strength in highway as a semi-rigid base materhd, and a series of experiments about the effect of differeat kinds of additives and quantity on the early strength of the stabilized soll were tested. The results show that chemical additives can efftciently improve the early strength of lime-flyush stabilized soil both the 7 d and 28d, and the optimum quantity for above chemical additive is 1.5%-2.5% approximately. Some suggestions for the practical construction were also proposed.
基金Funded by the Western Communication Construction Science and Technology Item (No. 200631822302-08)
文摘The effect of fly ash and early strength agent on resistance of concrete to the cyclic sulfate environment was studied.Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%,or 1% early strength agent and fly ash with the replacement of 20%,were made and subjected to 250 cycles of exposure to the cyclic sulfate environment.Concrete properties including loss of mass,chloride ion diffusion coefficient,compressive strength and flexural strength were measured.Microstructure and chemical component of samples were determined by means of X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The experimental results indicated that effect of fly ash on the cyclic sulfate resistance of concretes was mostly dependent on the amount of fly ash.Early strength agent improved performances of concrete with 20% fly ash exposed to cyclic sulfate environment.
基金Funded by the National Natural Science Foundation of China(No.51178363)the Major State Basic Research Development Program of China("973" Program)(No.2009CB23201-1)
文摘The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with different functional additives have been studied through compressive strength, flexural strength, volume stability at early age and porosity characterization tests. The results show that the addition of silica fume and aluminum sulfate reduces the fluidity and shortens the setting time of sulfoaluminate cement paste, promoting hydration process and increasing hydration products at early age. In the case of appropriate proportion of mortar, the inclusion of hydroxy propyl methyl cellulose, dispersible polypropylene fiber arid organic silicon kind of defoamer can control segregation and bleeding, improve mechanical strength and volume stability at early age, and modify the pore distribution of sulfoaluminate cement mortar, respectively. The sulfoaluminate cement mortar can carry out gravitational grouting in the absence of outside force, the compressive strength of 2 hours and 24 hours have reached 26 and 58 MPa respectively, and have good micro- expansion and tiny.pore distribution characterization.
基金Funded by the National Natural Science Foundation of China(51409202)the Fundamental Research Funds for the Central Universities(2013-IV-36)the Jiangxi Provincial Project of Science and Technology(20132GGB70107)
文摘The primary objective of this research was to determine optimum dosage of mixing concrete containing plasticizers and fly ash, consistent with desirable structural grade concrete properties. Factorial tests were also conducted to investigate the four main factors: water-cementing materials ratio, water content, content of superplasticizers (SP) and fly ash content. It was found that the requirement for setting time played the dominant role in shrinkage and anti-cracking, and fly ash played a critical role in workability and reducing heat of hydration but showed insignificant effects on slump, early strength and initial setting time of concrete.
基金supported by the by the University of Pittsburgh Center for Impactful Resilient Infrastructure Science and Engineering(IRISE)the University of Pittsburgh Anthony Gill Chair。
文摘High early strength(HES)concrete pavements are commonly opened to traffic within the first 24 h after construction,making early-opening decisions critical for pavement quality and traffic operations.Currently,most state departments of transportation rely on compressive strength testing for early-opening decision making.However,there laboratory tests are labor intensive,costly and not always representative of field strength development.In this study,non-destructive testing(maturity and ultrasonic tomography)was explored for faster and reliable in-situ strength estimations.An experimental section constructed using HES concrete was routinely monitored using compressive testing,maturity,and ultrasonic tomography in the first 24 h after construction.The shear wave velocity,measured using ultrasonic tomography,was able to capture the strength-gain variability within a single slab and between different slabs due to the ability to monitor several locations in a short period of time.Maturity results were consistently conservative in the first 24 h of monitoring.Results show that both maturity testing and ultrasonic tomography are able to replace or add to conventional strength testing for HES concrete pavements to facilitate making the opening decision within the first 24 h.Ultrasonic tomography proved more beneficial as a result of the device's portability,increased speed of testing,and accurate estimations of HES concrete strength for the entire pavement length.
基金the financial support from China Communications Construction Company Limited.
文摘In this paper,C50 ultra-high-early-strength concrete was prepared with rapid-harden sulphoaluminate cement,alkali carbonate early strength agent,inorganic tribasic acid retarder and polycarboxylate water reducing agent. The properties testing results of C50 ultra-high-early-strength concrete indicated that the compressive strength at 12 h exceeded 37 MPa and at 3 d exceeded 59 MPa. Compared to the C50 ordinary reference concrete,the durability of C50 ultra-high-early strength concrete was investigated. The results indicated that C50 ultra-high-early-strength concrete had the same chloride ion permeability resistance,carbonization resistance and abrasion resistance to the C50 ordinary concrete. As to the sulfate resistance,the ultra-high-early-strength concrete was much better than the ordinary concrete.
基金financial support of the National Natural Science Foundation of China (No. 51474017)the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (No. 2014211B013)
文摘As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.
文摘The technology of activation by adding few activators ( less than 1%) to increase the amount of blends in cement was investigated. The results show that outer activation has a remarkable effect on improving the physical properties of slag cement, flyash cement and volcanic cement. For example, the compressive strength was increased by 5-10 MPa. Morever, the application of activation is beneficial to grind-aiding, early strength and water-reducing etc. (Author abstract) 4 Refs.
文摘In recent building practice,rapid construction is one of the principal requisites.Furthermore,in designing concrete structures,compressive strength is the most significant of all parameters.While 3-d and 7-d compressive strength reflects the strengths at early phases,the ultimate strength is paramount.An effort has been made in this study to develop mathematical models for predicting compressive strength of concrete incorporating ethylene vinyl acetate(EVA)at the later phases.Kolmogorov-Smirnov(KS)goodness-of-fit test was used to examine distribution of the data.The compressive strength of EVA-modified concrete was studied by incorporating various concentrations of EVA as an admixture and by testing at ages of 28,56,90,120,210,and 365 d.An accelerated compressive strength at 3.5 hours was considered as a reference strength on the basis of which all the specified strengths were predicted by means of linear regression fit.Based on the results of KS goodness-of-fit test,it was concluded that KS test statistics value(D)in each case was lower than the critical value 0.521 for a significance level of 0.05,which demonstrated that the data was normally distributed.Based on the results of compressive strength test,it was concluded that the strength of EVA-modified specimens increased at all ages and the optimum dosage of EVA was achieved at 16%concentration.Furthermore,it was concluded that predicted compressive strength values lies within a 6%difference from the actual strength values for all the mixes,which indicates the practicability of the regression equations.This research work may help in understanding the role of EVA as a viable material in polymer-based cement composites.