Effect of Curing Regime on the Mechanical Strength, Hydration, and Microstructure of Ecological Ultrahigh-Performance Concrete (EUHPC).

Zhiwu Zuo,Xiao Chen,Gongfeng Xin,Jiachen Zhang,Beixing Li,Chuqi Shen

doi:10.3390/ma15051668

Zhiwu Zuo, Xiao Chen + Show 4 more

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https://doi.org/10.3390/ma15051668

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Abstract

This paper investigates the effect of curing regimes (standard and steam curing) on the mechanical strength, hydration, and microstructure of ecological ultrahigh-performance concrete (EUHPC). The flowability, compressive strength, flexural strength, hydration, porosity, pore size distribution, and microstructure of UHPC with different contents of supplementary materials (silica fume, fly ash, and ground granulated blast furnace slag) were assessed. The test results showed that the compressive strength of EUHPC under steam curing was increased considerably compared to that under standard curing, while the flexural strength was mildly decreased. The steam curing could decrease the porosity of EUHPC, which ranged between 7% and 9% for standard curing, and between 3.5% and 5% for steam curing. The aperture of EUHPC was below 20 nm, mainly located in the range of 10 nm to 20 nm under standard curing, while it was less than 10 nm for steam curing. C–S–H gel was produced under steam curing, while unhydrated fly ash, mineral powder, and Ca(OH)2 crystal were observed in the amorphous C–S–H gel. The microstructure of EUHPC under steam curing was denser than that under standard curing, and the interfacial transition zones under both curing regimes were compact.

Highlights

Ultrahigh-performance concrete (UHPC) is a novel cement-based composite material, which is characterized by ultrahigh compressive and tensile strength, good ductility due to the addition of steel fiber, and superior durability because of the compact microstructure [1].To the authors’ knowledge, UHPC was first mentioned in the publication by De Larrard and Sedran [2]
The excellent properties of UHPC are due to the meticulous design of the mix proportion, such as high binder content, low water/binder ratio, and a large dosage of superplasticizer, supplementary materials, fine quartz powder, and steel fiber
The coarse aggregate is usually excluded in most mixtures to increase the homogeneity of matrix, as well as reduce the micro-cracks existing in the interfacial transition zone between the paste matrix and coarse aggregate [4,5,6]

Summary

Introduction

Ultrahigh-performance concrete (UHPC) is a novel cement-based composite material, which is characterized by ultrahigh compressive and tensile strength, good ductility due to the addition of steel fiber, and superior durability because of the compact microstructure [1].To the authors’ knowledge, UHPC was first mentioned in the publication by De Larrard and Sedran [2]. Ultrahigh-performance concrete (UHPC) is a novel cement-based composite material, which is characterized by ultrahigh compressive and tensile strength, good ductility due to the addition of steel fiber, and superior durability because of the compact microstructure [1]. Depending on the mix proportion and the preparation method, the compressive strength of UHPC usually exceeds 150 MPa, with a tensile strength of 6.2 MPa [3,4]. The excellent properties of UHPC are due to the meticulous design of the mix proportion, such as high binder content, low water/binder ratio, and a large dosage of superplasticizer, supplementary materials (silica fume, fly ash, granulated blast furnace slag, etc.), fine quartz powder, and steel fiber. The coarse aggregate is usually excluded in most mixtures to increase the homogeneity of matrix, as well as reduce the micro-cracks existing in the interfacial transition zone between the paste matrix and coarse aggregate [4,5,6].

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