A kind of high impermeable and crack-resistance chemical admixture ( HICRCA) was prepared , which is a compound chemical admixture composed of an expansion ingredient, density ingredient, and organic hydrophobic poreb...A kind of high impermeable and crack-resistance chemical admixture ( HICRCA) was prepared , which is a compound chemical admixture composed of an expansion ingredient, density ingredient, and organic hydrophobic poreblocking ingredient. The results of the experiments indicate that the addition of HICRCA improves mortar and concrete in the following performances: (1) perfect workability: slump is more than 22cm, theslump afar 3h is about 16cm; (2) high impermeability:for the mortar, the pervious height under a water pressure of 1.5MPa is 1.5cm,for the concrete, the pervious height under a water pressure of 5.0MPa is 2. 2cm;(3) high crack-resistance: there is a micro-expansion at the age of 90d; (4) high compressivestrength: compared with the controlled concrete, the compressive strengths at the age of 3d and 2Sd are improved by 66.4% and 62.0% , respectively. At the same time, the effects of different curing condition on mortar and concrete expansive andshrinkage performance were studied. In addition, the impermeable and crack-resistance mechanism, was investigatedin the present paper.展开更多
A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shr...A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced. The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.展开更多
Construction industries have started to utilize manufactured sand(MS)as an effective alternative for river sand in concrete.High-grade parent rocks are crushed to obtain MS,which also produces a considerable amount of...Construction industries have started to utilize manufactured sand(MS)as an effective alternative for river sand in concrete.High-grade parent rocks are crushed to obtain MS,which also produces a considerable amount of microfine aggregate(MFA).The higher percentage of MFA could lead to both positive and negative effects on the performance of cement-based mixes.This research was done to examine the influence of varying MFA levels,specifically 0%,3%,6%,9%,and 12%(by weight)as the partial replacements of MS on bleeding and plastic shrinkage cracking of concrete.In addition to the varying MFA levels,some concrete mixes also included fly ash(FA)and superplasticizer to investigate the effect of free-water content in the mixes.The bleeding test data were taken as on-site measurements,while the cracks from the plastic shrinkage cracking test were evaluated using an image processing technique.The results concluded that the MFA replacements and the effective water-to-cement ratio have a significant effect on the selected concrete properties.With the increasing replacement levels,cumulative bleeding and crack initiation life gradually decreased,while a progressive increase was observed for crack width,crack length,and crack area.展开更多
基金Funded by Natural Science Foundation of Hubei Province (No.2000J027)
文摘A kind of high impermeable and crack-resistance chemical admixture ( HICRCA) was prepared , which is a compound chemical admixture composed of an expansion ingredient, density ingredient, and organic hydrophobic poreblocking ingredient. The results of the experiments indicate that the addition of HICRCA improves mortar and concrete in the following performances: (1) perfect workability: slump is more than 22cm, theslump afar 3h is about 16cm; (2) high impermeability:for the mortar, the pervious height under a water pressure of 1.5MPa is 1.5cm,for the concrete, the pervious height under a water pressure of 5.0MPa is 2. 2cm;(3) high crack-resistance: there is a micro-expansion at the age of 90d; (4) high compressivestrength: compared with the controlled concrete, the compressive strengths at the age of 3d and 2Sd are improved by 66.4% and 62.0% , respectively. At the same time, the effects of different curing condition on mortar and concrete expansive andshrinkage performance were studied. In addition, the impermeable and crack-resistance mechanism, was investigatedin the present paper.
基金Funded by the National Natural Science Foundation of China (50539010) Nation High Technic R&D Program "863 Program" of China (No. 2005AA332010)
文摘A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced. The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.
基金The authors are grateful to INSEE Siam City,Sri Lanka for providing the necessary binding materials to conduct this study.Furthermore,the authors wish to thank all technical staffs of the Department of Civil Engineering,University of Sri Jayewardenepura for their support on the experimental work.
文摘Construction industries have started to utilize manufactured sand(MS)as an effective alternative for river sand in concrete.High-grade parent rocks are crushed to obtain MS,which also produces a considerable amount of microfine aggregate(MFA).The higher percentage of MFA could lead to both positive and negative effects on the performance of cement-based mixes.This research was done to examine the influence of varying MFA levels,specifically 0%,3%,6%,9%,and 12%(by weight)as the partial replacements of MS on bleeding and plastic shrinkage cracking of concrete.In addition to the varying MFA levels,some concrete mixes also included fly ash(FA)and superplasticizer to investigate the effect of free-water content in the mixes.The bleeding test data were taken as on-site measurements,while the cracks from the plastic shrinkage cracking test were evaluated using an image processing technique.The results concluded that the MFA replacements and the effective water-to-cement ratio have a significant effect on the selected concrete properties.With the increasing replacement levels,cumulative bleeding and crack initiation life gradually decreased,while a progressive increase was observed for crack width,crack length,and crack area.
