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Title: Testing and Modeling of Reinforcement Cage Penetration Capacity from Concrete Rheometer Results

Author(s): Yannick Vanhove, Chafika Djelal, and Albert Magnin

Publication: Materials Journal

Volume: 118

Issue: 6

Appears on pages(s): 407-419

Keywords: continuous flight auger (CFA) piles; deep foundation; rheology; structural buildup; yield stress

Date: 11/1/2021

Abstract:
Workability after concrete placement is important in continuous flight auger (CFA) piles construction because the reinforcement cage needs to be placed within the concrete at the end of casting. During the rest phase, which can last 30 minutes, the restructuring of the concrete affects the penetration capacity of the reinforcement cage. An experimental investigation was carried out over a period of 30 minutes to compare the static and dynamic yield stress, measured using a rotational rheometer, with the shear stress interaction between the reinforcement cage and the concrete. Tests were performed using 10 mixtures in the laboratory. A viscosity-modifying admixture was used to promote the thixotropy effect. The study was completed with four mixtures on site. The results showed a good correlation between the concrete rheological properties and the capacity to sink the reinforcement cage into the concrete. A simple model is proposed to estimate the shear stress applied to the reinforcement cage. The time needed to reach the final depth was correlated with the plastic viscosity, while the shear stress of the cage and the final depth were connected to the concrete yield stress. The penetration cage test is an effective tool to optimize concrete mixture proportions for the construction of CFA piles.


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