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Journal of Wuhan University of Technology(Materials Science) 2023年第6期38卷 1335-1347页

作者： TIAN Changjin WANG Youzhi QIU Kai YANG Qilin School of Civil Engineering Shandong UniversityJinan 250002China China Construction Infrastructure Co. LtdBeijing 100089China School of Transportation Science and Engineering Harbin Institute of TechnologyHarbin 150090China

To investigate the assumptions proposed in this paper,the evolution law governing the strength and expansion performance of MgO and nano-MgO micro-expansive concrete in the environment of mineral powder was firstly observed in this ***,SEM,XRD,and TG-DSC microscopic tests were conducted to reveal the effects of the active mineral-powder admixture on the hydration degree and expansion performance of MgO and nano-MgO in *** experimental results successfully verified our hypothesis,which indicated that the expansion performance of macro-MgO and nano-MgO was indeed depressed by the addition of active mineral power admixtures,even though the mechanical property of concrete composites was effectively ***,the hydration test also demonstrated the negative interference on the mineral powders,which was induced by the expansion *** is found the amounts of hydrates tend to decrease because the mineral powder ratio reaches and exceeds 40%.Moreover,it is also concluded the effect of expansion agents is governed by the alkalinity cement paste,especially for the *** other words,the expansion performance of nano-MgO will vary more obviously with the hydration process,than *** results of this study provide that effective experimental and theoretical data support the hydration-inhibition mechanism of magnesium expansive agents.

关键词： MgO Nano-MgO mineral powders high-performance concrete expansive agents microstructures

Effect of cavity defect on the triaxial mechanical properties of high-performance concrete

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Frontiers of Structural and Civil Engineering 2022年第5期16卷 600-614页

作者： Yanbin ZHANG Zhe WANG Mingyu FENG School of Civil Engineering Beijing Jiaotong UniversityBeijing100044China

The stress concentration of pipe structure or cavity defect has a great effect on the mechanical properties of the high-performance concrete(HPC)members in deep underground ***,the behaviour of HPC with cavities under triaxial compression is not understood,especially when pressurized liquid flows into the fractures from the *** study aims to investigate the effect of the cavity and the confining pressure on the failure mechanisms,strengths,and deformation properties of HPC with a new experimental *** this experiment,the pressurized liquid can only contact the surface of the sample in the cavity,while the other surfaces are isolated from the pressurized *** further explore the effect of the cavity,the same experiments are also conducted on sealed and unsealed intact samples without a *** failure modes and stress-strain curves of all types of the samples are *** various confining pressures,all the samples with a cavity suffer shear failure,and there are always secondary tensile fractures initiating from the cavity ***,it can be determined from the failure modes and the stress-strain curves that the shear fractures result from the sidewall *** on the different effects of the cavity on the lateral deformations in different directions,the initiation of the sidewall fracture is well *** experimental results show that both the increase of the confining pressure and the decrease of the cavity size are conducive to the initiation of sidewall ***,the cavity weakens the strength of the sample,and this study gives a modified Power-law criterion in which the cavity size is added as an impact factor to predict the strength of the sample.

关键词： high-performance concrete cavity conventional triaxial compression pressurized liquid modified power-law criterion

Self-desiccation mechanism of high-performance concrete

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Journal of Zhejiang University Science 2004年第12期5卷 1517-1523页

作者：杨全兵张树青 ResearchLabofMaterialsEngineering CollegeofMaterialsScienceandEngineeringTongiiUniversityShanghai200433China

Investigations on the effects of W/C ratio and silica fume on the autogenous shrinkage and internal relative humidity of high performance concrete (HPC), and analysis of the self-desiccation mechanisms of HPC showed that the autogenous shrinkage and internal relative humidity of HPC increases and decreases with the reduction of W/C respectively; and that these phenomena were amplified by the addition of silica fume. Theoretical analyses indicated that the reduction of RH in HPC was not due to shortage of water, but due to the fact that the evaporable water in HPC was not evaporated freely. The reduction of internal relative humidity or the so-called self-desiccation of HPC was chiefly caused by the increase in mole concentration of soluble ions in HPC and the reduction of pore size or the increase in the fraction of micro-pore water in the total evaporable water (Tr/Tte ratio).

关键词： high-performance concrete Autogenous shrinkage Self-desiccation Relative humidity

INFLUENCE OF MINERAL ADMIXTURES ON MECHANICAL PROPERTIES OF high-performance concrete

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Journal of Wuhan University of Technology(Materials Science) 1999年第2期14卷 1-7页

作者： Ma, Baoguo Li, Jinzong Peng, Jun Wuhan Univ Technol Coll Mat Sci & Technol Wuhan 430070 Peoples R China Hong Kong Univ Sci & Technol Hong Kong Hong Kong

The improvements of the mechanical properties, including bulk density of fresh mixtures, elastic modulus, and compressive strengths of four high-performance concrete mixtures, made with the addition of fly ash, refined ground blast - furnace microslag (microslag) and silica fume are studied. The concrete mixtures were determined based on the dispersion testing results. The study indicates that the elastic modulus at 28 and 91 days, and compressive strengths of the concretes are improved a lot when fly ash and microslag by 25 percent by weight of cement are added into the mixtures individually. The improvement is especially evident when silica fume by 5 percent and fly ash by 25 percent by weight of cement are added together into the mixture, while the fresh concrete mixture keeps a good workability. Through the analysis of chemically combined water ratios of the four mixtures at various hydration ages, it is found that the addition of all these mineral mixtures are beneficial to the hydration process, especially, at later stages, which might be one of the reasons for the improvement of mechanical properties. (Author abstract) 4 Refs.

关键词： high-performance concrete mineral admixture mechanical properties

SULFATE RESISTANCE MECHANISM OF high- performance concrete CONTAINING NCI

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Journal of Wuhan University of Technology(Materials Science) 1999年第1期14卷 6-15页

作者： MA Baoguo Wuhan University of Technology Wuhan University of Technology China Coll. of Mat. Sci. and Engineering Wuhan University of Technology Wuhan 430070 China

It is found that the incorporation of Nitrite Corrosion Inhibitor (NCI) greatly weakens the resistance of mixtures to sulfate attack. To study the mechanism of this phenomenon, in this paper, the influence of NCI addition on the cement paste and microstructure change of high performance concrete specimens is studied by means of quantitative XRD, SEM tests. The results demonstrate that the incorporation of NCI accelerates the formation of calcium hydroxide and ettringite crystals, and weakens the pore refinement effect caused by the secondary hydration reaction of fly ash and microsilica. At the age up to one year, the relative crystal quantity in mixture containing NCI is always higher than that in control mixture. The reasons for the degradation in sulfate resistance of mixtures may be attributed to the increase and stability of the calcium hydroxide and ettringite crystals formed and the weakening of secondary hydration reaction. Based on the results, conclusion can be drawn that NCI should be used cautiously in practical engineering where high resistance to sulfate attack is required. (Author abstract) 7 Refs.

关键词： nitrite corrosion inhibitor high-performance concrete microstructure sulfate resistance

Assessment of early-age cracking of high-performance concrete in restrained ring specimens

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Water Science and Engineering 2010年第1期3卷 113-120页

作者： Quang-phu NGUYEN Lin-hua JIANG Qiao ZHU College of Mechanics and Materials Hohai University Nanjing 210098 P R. China Faculty of Civil Engineering Water Resources University Hanoi Vietnam

high-performance concrete （HPC） is stronger and more durable than conventional concrete. However, shrinkage and shrinkage cracking are common phenomena in HPC, especially early-age cracking. This study assessed early-age cracking of HPC for two mixtures using restrained ring tests. The two mixtures were produced with water/binder mass ratio （mw/mB） of 0.22 and 0.40, respectively. The results show that, with greater steel thickness, the higher degree of restraint resulted in a higher interface pressure and earlier cracking. With steel thickness of 6 mm, 19 mm, and 30 mm, the age of cracking were, respectively, 12 days, 8 days, and 5.4 days with the mw/mB = 0.22 mixture; and 22.5 days, 12.6 days, and 7.1 days with the mw/mB= 0.40 mixture. Cases of the same steel thickness show that the ring specimens with a thicker concrete wall crack later. With the mw/mB = 0.22 mixture, concrete walls with thicknesses of 37.5 mm, 75 mm, and 112.5 mm cracked at 3.4 days, 8.0 days, and 9.8 days, respectively; with the mw/mB = 0.40 mixture, the ages of cracking were 7.1 days, 12.6 days, and 16.0 days, respectively.

关键词： high-performance concrete shrinkage early-age cracking restrained ring test

INITIAL BINDING CAPACTIES OF CHLORIDE ION OF COMPONENTS IN high-performance concrete

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Journal of Wuhan University of Technology(Materials Science) 1998年第4期13卷 16-24页

作者：马保国 Wuhan University of Technology China Hongkong Univ. of Sci. and Technol. Coll. of Mat. Science and Technology Wuhan University of Technology Wuhan 430070 China

An investigation is reported on the influence of different components of high performance concrete (HPC) on the initial binding capacities (IBC) of chloride ion. The testing results demonstrate that cement has the largest IBC, and the relative binding ratio is as high as 30% of total ion amount. Among the mineral admixtures, fly ash has the largest IBC of chloride ion. The IBC of silica fume is about 14.4%, which is smaller than that of fly ash. The IBC of refined ground blast-furnace slag (microslag) is abnormal due to the influence of sulfate ion contained. The addition of superplasticizer and corrosion inhibitor containing calcium nitrite weakens the IBC of mixtures. The fluidity and pore-filling effect of mineral admixtures are studied with paste samples with WIC ratio of 0.3. The influence mechanism of various components in high-performance concrete in IBC is studied further through SEM and Mercury Instrusion Porosimetry tests with paste samples at the age of 3 days.

关键词： high-performance concrete super-plasticizer corrosion inhibitor initial binding capacity permeability

Effects of submicron-MgO and nano-MgO on the expansion and microscopic properties of high-performance concrete

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Journal of Central South University 2022年第9期29卷 3186-3200页

作者： TIAN Chang-jin WANG You-zhi QIU Kai YANG Qi-lin School of Civil Engineering Shandong UniversityJinan 250061China School of Transportation Science and Engineering Harbin Institute of TechnologyHarbin 150090China

MgO-series expansive agents can effectively compensate for the shrinkage and deformation of concrete ***,few experimental studies have been conducted on MgO expansive agents,particularly concerning the difference between and effects of submicron-MgO and nano-MgO in high-performance concrete(HPC)with a low water-cement ratio,thereby limiting their application in practical *** clarify the expansion effect and expansion mechanism of MgO expansive agents in HPC,the effects of submicron-MgO and nano-MgO on the strength,toughness,and expansion characteristics of HPC were *** test results showed that submicron-MgO and nano-MgO continued to hydrate in the cement environment to produce Mg(OH)_(2),thus improving the structural compactness and structural strength of ***-MgO concrete was found to have more stable mechanical properties and better structural deformability than submicron-MgO *** study provides effective data support and theoretical reference concerning the hydration expansion mechanisms and engineering applications of nano-expanded materials.

关键词： submicron-MgO nano-MgO high-performance concrete strength toughness expansion characteristics microstructure

Measurement and analysis of defects in high-performance concrete with three-dimensional micro-computer tomography

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Journal of Southeast University(English Edition) 2009年第1期25卷 83-88页

作者：郭丽萍 Andrea Carpinteri 孙伟秦文超东南大学材料科学与工程学院南京211189 东南大学江苏省土木工程材料重点实验室南京211189 帕尔马大学土木工程系意大利帕尔马43100 德国依科视朗国际射线有限公司上海代表处上海200041

In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomography）is employed to quantitatively analyze the initial defects in four series of highperformance concrete （HPC）specimens with additions of different mineral admixtures. The nigh-resolution 3D images of microstructures and filtered defects are reconstructed by micro- CT software. The size distribution and volume fractions of initial defects are analyzed based on 3D and 2D micro-CT images. The analysis results are verified by experimental results of watersuction tests. The results show that the additions of mineral admixtures in concrete as cementitious materials greatly change the geometrical properties of the microstructures and the spatial features of defects by physical-chemistry actions of these mineral admixtures. This is the major cause of the differences between the mechanical behaviors of HPC with and without mineral admixtures when the water-to-binder ratio and the size distribution of aggregates are constant.

关键词： high-performance concrete defect microstructure X- ray micro-focus computer tomography mineral admixtures

Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

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Water Science and Engineering 2008年第4期1卷 67-74页

作者： Nguyen Quangphu Jiang Linhua Liu Jiaping Tian Qian Do Tienquan College of Material Science and Engineering Hohai University Nanjing 210098 P. R. China Faculty of Hydraulic Engineering Water Resources University Hanoi Vietnam Jiangsu Institute of Building Science Nanjing 210008 P. R. China International College for Chinese Studies Nanjing Normal University Nanjing 210097 P. R. China

high-performance concrete （HPC） has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios （mW/mB） in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and cracking of HPC. This study used a shrinkage-reducing admixture （SRA） for that purpose. concrete was prepared with two different mW/mB （0.22 and 0.40） and four different mass fractions of SRA to binder （w（SRA） = 0%, 1%, 2%, and 4%）. The mineral admixtures used for concrete mixes were： 25% fly ash （FA） and 25% slag by mass of binder for the mixture with mW/mB = 0.40, and 15% silica fume （SF） and 25% FA for the mixture with mW/mB = 0.22. Tests were conducted on 24 prismatic specimens, and shrinkage strains were measured through 120 days of drying. Compressive strength, splitting strength, and static modulus of elasticity were also determined. The results show that the SRA effectively reduces some mechanical properties of HPC. The reductions in compressive strength, splitting tensile strength, and elastic modulus of the concrete were 7%-24%, 9%-19%, and 5%-12%, respectively, after 90 days, compared to concrete mixtures without SRA. SRA can also help reduce drying shrinkage of concrete. The shrinkage strains of HPC with SRA were only as high as 41% of the average free shrinkage of concrete without SRA after 120 days of drying.

关键词： high-performance concrete shrinkage-reducing admixture compressive strength elastic modulus splitting tensile strength drying shrinkage