Analysis of Failure Modes in Fiber Reinforced Concrete Using X-ray Tomography and Digital Volume Correlation

Mathias Flansbjer,Stephen Hall,Jonas Engqvist,Natalie Williams Portal

doi:10.3390/icem18-05238

Mathias Flansbjer, Stephen Hall + Show 2 more

Open Access

https://doi.org/10.3390/icem18-05238

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Publication Date: May 19, 2018
Citations: 3	License type: CC BY 4.0

Affiliation: RISE Research Institutes of Sweden, Lund University

Abstract

Pull-out mechanisms for different common steel fibers were investigated using adapted pull-out tests performed in-situ in an X-ray micro tomograph (µXRT). High-resolution volume images from the µXRT scans enable clear visualization of aggregates, pores, the fiber and the fiber-matrix interface. Furthermore, the natural density speckle pattern from aggregate distribution and pores was found suitable for Digital Volume Correlation (DVC) analysis. From the DVC results it was possible to visualize and quantify the strain distribution in the matrix around the fiber at the different load levels up to final failure, being marked by either pull-out or fiber rupture. This study demonstrates that strain measurements within the concrete matrix can be obtained successfully using µXRT imaging and DVC analysis, which leads to an increased understanding of the interaction mechanisms in fibre reinforced concrete under mechanical loading.

Highlights

Fiber pull-out is generally considered to be the dominating failure mechanism in fiber reinforced concrete (FRC) to mitigate brittle failure
The natural grey-scale speckle in the images due to the chosen aggregate distribution and pores was found to be suitable for Digital Volume Correlation (DVC) analysis
Each specimen was imaged by μXRT at different load levels selected based on the load-displacement relations obtained in the reference pull-out tests

Summary

Introduction

Fiber pull-out is generally considered to be the dominating failure mechanism in fiber reinforced concrete (FRC) to mitigate brittle failure. Pull-out tests are typically performed on FRC to characterize the fiber-matrix behavior and estimate average tensile stresses near a crack opening. Little direct insight can be gained on the actual mechanisms of the pull-out from such test, whereas, a deeper understanding of the underlying interaction mechanisms between discrete fibers and the surrounding concrete matrix could clearly lead to optimized FRC. Such deeper understanding could be gained through the addition of non-destructive techniques to pull-out tests to enable the visualization and quantification of the mechanical interaction between the fibers and the concrete matrix.

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