Study on the Influence of Silica Fume (SF) on the Rheology, Fluidity, Stability, Time-Varying Characteristics, and Mechanism of Cement Paste.

Hengrui Liu,Hui Du,Yao Wang,Zhenghong Tian,Xueying Lu,Xiao Sun

doi:10.3390/ma15010090

Hengrui Liu, Hui Du + Show 4 more

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https://doi.org/10.3390/ma15010090

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Abstract

In this study, the rheology, fluidity, stability, and time-varying properties of cement paste with different substitute contents of silica fume (SF) were investigated. The result showed that the effects of SF on macro-fluidity and micro-rheological properties were different under different water–cement ratios. The addition of SF increased the yield stress and plastic viscosity in the range of 2.61–18.44% and 6.66–24.66%, respectively, and reduced the flow expansion in the range of 4.15–18.91%. The effect of SF on cement paste gradually lost its regularity as the w/c ratio increased. The SF can effectively improve the stability of cement paste, and the reduction range of bleeding rate was 0.25–4.3% under different water–cement ratios. The mathematical models of rheological parameters, flow expansion, and time followed the following equations: τ(t) = τ0 + k0t, η(t) = η0eat, and L(t) = L0 − k1t, L(t) = L0 − k1t − a1t2. The SF slowly increased the rheological parameters in the initial time period and reduced the degree of fluidity attenuation, but the effect was significantly enhanced after entering the accelerated hydration period. The mechanism of the above results was that SF mainly affected the fluidity and rheology of the paste through the effect of water film thickness. The small density of SF particles resulted in a low sedimentation rate in the initial suspended paste, which effectively alleviated the internal particle agglomeration effect and enhanced stability. The SF had a dilution effect and nucleation effect during hydration acceleration, and the increase of hydration products effectively increased the plastic viscosity.

Highlights

During the construction of a roller-compacted concrete dam, there is a problem that some areas cannot be compacted, and the application of metamorphic concrete paste injection technology can solve this problem [1]
While there was no direct relationship between the fluidity and the substitute contents of silica fume (SF) at a w/c ratio equal to 0.7
The results showed that the changing regularity with the increasing substitution of SF under different w/c ratios was not the same

Summary

Introduction

During the construction of a roller-compacted concrete dam, there is a problem that some areas cannot be compacted, and the application of metamorphic concrete paste injection technology can solve this problem [1]. The stability, fluidity, rheology, and timevarying properties of metamorphic concrete paste are all important properties that need to be considered [2,3]. The fluidity and rheology of the paste directly influence the effect of grouting or infiltration, which in turn affects the construction quality of metamorphic concrete [5,6]. The timevarying characteristics can significantly affect the diffusion effect of paste [7,8]. Traditional metamorphic pastes often have problems such as poor rheology, insufficient strength, and poor stability. Considering the grouting performance, resources, environment, and cost of the metamorphic paste, it is a challenging task to improve grouting with new additives

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