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1

Study on stability of self-compacting concrete applied for filling layer structure from paste, mortar and concrete

Liu He, Zhang Jingyi, Yang Yanhai

Archives of Civil Engineering

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2022

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Vol. 68, nr 3

501--522

EN

Self compacting concrete (SCC) filling layer is core structure of China rail track system (CRTS) ? type ballastless track. Construction quality, service performance and durability of CRTS ? ballastless structure are affected by stability of SCC for filling layer. In this study, the stability of SCC of filling layer is researched at three levels as paste, mortar and concrete by theory and experiment. Evaluation indices including bleeding (B), surface bubble rate (θ), thickness of paste (𝜎paste) and thickness of surface mortar (L) are proposed based on the theoretical calculation and analysis. The threshold viscosity of paste 0.394 Pa·s and mixture satisfied area are obtained at paste level based on the relationship between viscosity and B, θ of paste. The mixture satisfied area was defined at mortar level under criterions of maximum value of 𝜎paste and slump flow. Optimal range of gap between neighboring aggregates (λca) 12.4 mm-14.1 mm is chosen by flow ability, passing ability, stable ability of SCC. These research results will help to further understand the stability of SCC.

2

Rheological properties of paste for self-compacting concrete with admixtures

Liu He, Duan Guangchao, Zhang Jingyi, Yang Yanhai

Archives of Civil Engineering

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2022

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Vol. 68, nr 3

585--599

EN

The paste content in the self-compacting concrete is about 40% in unit volume. The rheological properties of paste directly determine the properties of self-compacting concrete. In this paper, the effect of silica fume (2, 3, 4, and 5%), limestone powder (5, 10 and 15%), and the viscosity modified admixture (2, 3, 4, 5, 6, and 7%) on the rheological properties were investigated. The effect of admixtures on shear thickening response was discussed based on the modified Bingham model. The results indicate that yield stress and plastic viscosity increased with increased silica fume and viscosity modified admixture replacement. The paste’s yield stress increases and then decreases with limestone powder replacement. The critical shear stress and minimum plastic viscosity are improved by silica fume and viscosity modifying admixture. The critical shear stress first increases and decreases as the limestone powder replacement increases. A reduction in the shear thickening response of paste was observed with silica fume and viscosity modified admixture replacement increase.

3

Drying shrinkage and creep properties of self-compacting concrete with expansive agent and viscosity modified admixture

Liu He, Duan Guangchao, Zhang Jingyi

Archives of Civil Engineering

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2022

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Vol. 68, nr 3

539--551

EN

Self-Compacting Concrete (SCC) has been widely used in the filling layer of high-speed railways. The quality of the filling layer directly affects the durability, comfort, and safety of the track system. In this study, shrinkage characteristics and the creep behavior of SCC were investigated by compressive creep tests and shrinkage tests. They were performed on specimens with different loading levels with a calcium sulfoaluminate-based expansive agent (UEA) and viscosity modified admixture (VMA). Furthermore, based on the scanning electron microscope (SEM) morphology of hydration products and X-ray diffraction (XRD) analysis, the influence of admixtures on microstructure and mineral phases of SCC was analyzed. The results show that when concretes were loaded with the same stress level, the main factor influencing creep of SCC was the quantity and microstructure of amorphism and hydration crystal. The XRD and SEM result showed that UEA and VMA make the creep and shrinkage of SCC reduce obviously as the cementitious system grow many crystals in hydration products. The creep of NC was less than SCC with identical compressive strength. At the same time, the addition of UEA can improve the ability to resist drying shrinkage.