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Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Science China(Technological Sciences) 2007年第6期50卷 815-832页

作者： JU Yang JIA YuDan LIU HongBin CHEN Jian State Key Laboratory of Coal Resources and Safe Mining China University of Mining & Technology Beijing 100083 China State Key Laboratory of Coal Resources and Safe Mining China University of Mining & Technology Beijing 100083 China State Key Laboratory of Coal Resources and Safe Mining China University of Mining & Technology Beijing 100083 China State Key Laboratory of Coal Resources and Safe Mining China University of Mining & Technology Beijing 100083 China

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC’s toughness and overcome the disadvantage of high brittle- ness. In this paper, a number of direct uniaxial tension tests have been carried out with ‘8-shape’ RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation tech- niques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the con- tribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρv, opt =1.5% at which the bond performance of a fiber pullout of RPC be- haves best.

关键词： reactive powder concrete, steel fiber, interfacial bond strength, reinforcement and toughening, mesomechanism

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Packing and film thickness theories for the mix design of high-performance concrete

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2016年第10期17卷 759-781页

作者： Pui-Lam NG Albert Kwok-Hung KWAN Leo Gu LI Department of Civil Engineering The University of Hong Kong Pokfulam Hong Kong China Faculty of Civil Engmeering Vilnius Gediminas Technical University Vilnius Lithuania Schoo of Cicil and Transportation Engmeering Guangdong University of Technology Guangzhou 510006 China

A high-performance concrete （HPC） is required to have superior performance in various aspects such as workability,strength, durability, dimensional stability, segregation stability, and passing ability. The mix design of HPC is rather complicatedbecause the number of ingredients in HPC is usually more than those in conventional concrete and some of the required propertiesare conflicting with each other in the sense that improvement in one property would at the same time cause impairment of anotherproperty. However, there is still lack of understanding regarding how the various mix parameters should be optimised forachieving best overall performance. Most practitioners are still conducting mix design primarily through trial concrete mixing,which is laborious, ineffective, and often unable to timely respond to fluctuations in the properties of raw materials. To addressthese issues, the authors have been developing the packing and film thickness theories of concrete materials, in order to revamp themix design philosophy of HPC in terms of the water film thickness （WFT）, paste film thickness （PFT）, and mortar film thickness（MFT） in the concrete. Based on the findings from an extensive experimental programme, suitable ranges ofWFT, PFT, and MFThave been recommended.

关键词： concrete mix design, concrete science, Film thickness, High-performance concrete, Packing density, Sustainability

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