Elsevier

Cement and Concrete Research

Volume 36, Issue 9, September 2006, Pages 1653-1660
Cement and Concrete Research

Non-destructive monitoring of fiber orientation using AC-IS: An industrial-scale application

https://doi.org/10.1016/j.cemconres.2006.05.026Get rights and content

Abstract

A comprehensive study has been undertaken to investigate the ability of AC-impedance spectroscopy (AC-IS) to non-destructively monitor the fiber dispersion of conductive fiber-reinforced cement-based materials. Previous work showed that AC-IS effectively monitors various fiber dispersion issues in lab-scale steel fiber-reinforced specimens. In this part of the study, AC-IS was used to study fiber orientation in an industrial-scale pre-cast concrete beam. A conventional method–image analysis (IA)–was used to verify the results of AC-IS measurements. The results of AC-IS and IA were found to match very well in experimental uncertainty. Splitting tensile tests and bending tests were conducted on the parts of the beam to study the effects of fiber orientation on the mechanical performance. The results of the mechanical tests also confirmed the results of AC-IS with splitting tensile strengths increasing as the alignment of fibers increased.

Introduction

The use of fibers for reinforcing cement-based materials has been widely studied in the last four decades. The advantages and effectiveness of fiber use is known and well documented. Better understanding of fiber-reinforced composite (FRC) systems has led to the extension of fiber use from non-structural to semi-structural applications such as pavements, industrial floors, wall panels, bridge decks, tunnels, pre-cast roof elements, etc. [1], [2]. However, the use of FRC is still limited in spite of the advantageous features of fiber reinforcement [3], [4].

Undoubtedly, the use of fiber-reinforced cement composites for structural components will be more common in the future with increasing understanding of material behavior and development of new technologies such as engineered fibers [5]. Some structural applications of FRC have already been made possible using special high-performance fiber-reinforced composite materials such as DUCTAL® [6].

However, further research is required for a comprehensive understanding and a more widespread use of fiber-reinforced cement-based materials. Quality assurance and quality control systems are needed to be able to further commercialize these composites. Fresh and hardened state properties should be well monitored. Good fiber dispersion, as well as good concrete quality, should be assured. This study is focused on non-destructive fiber dispersion monitoring for quality control purposes. A non-destructive electrical method (AC-IS) was used to study fiber orientation on a portion of an industrial-scale FRC beam which was supplied by a pre-cast concrete company. Experiments were conducted at Northwestern University (NU).

Alternating current-impedance spectroscopy (AC-IS) is an electrical characterization method that can be used to study various aspects of cement-based materials such as hydration development, pore structure [7], cracking (damage evolution) [8] and chloride ion diffusivity [9]. Recently, the use of AC-IS was extended to fiber dispersion monitoring, which is possible due to the dual-arc behavior that occurs with the inclusion of conductive fibers [10], [11]. Previous work of the authors showed that AC-IS can be used to monitor various fiber dispersion issues, including clumping, orientation and segregation in lab-scale specimens [12], [13], [14]. In this study, similar experiments were conducted on an industry-scale specimen to study the ability and potential of AC-IS to detect fiber orientation in structural components. The results show promise, suggesting that AC-IS can be developed as a non-destructive quality control technique in the near future. It should be noted that AC-IS can only be used for fiber dispersion monitoring when the fibers are conductive and the experimental configuration may vary depending on the size/geometry of the fibers and specimen under consideration.

Section snippets

Experimental study

A pre-cast fiber-reinforced concrete beam was used to study preferred orientation of fibers using AC-IS. CON/SPAN® Bridge Systems supplied a FRC beam that had been manufactured at their plant. The beam was cast and tested under four point bending by the company prior to be sent to NU. (Only a part of the whole beam was used for convenience of transportation and experimental study.) CON/SPAN® Bridge Systems provided the information regarding the materials and their properties. The dimensions of

Conclusions

The use of AC-IS as a non-destructive technique to monitor fiber orientation was studied in an industrial-scale self-compacting steel fiber-reinforced concrete beam. The fiber orientation in the beam was described by means of matrix-normalized conductivity profiles in two directions. Results suggested a preferred orientation of fibers in the XY plane. This was expected based on previous results from other researchers. Image analysis was conducted to understand the extent to which AC-IS predicts

Acknowledgements

The authors gratefully acknowledge CON/SPAN® Bridge Systems and Dave Brodowski for their support and contribution to this work. The first author also would like to acknowledge the financial support of TUBITAK (The Scientific and Technical Research Council of Turkey) and ITU (Istanbul Technical University). The authors are grateful to Dr. Leta Woo for helpful discussions.

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