Factors Affecting the Efficiency of Fibers in Concrete on Crack Reduction

Christian O. Sorensen, Egil A. Berge, Petter E. Saga, Andreas Østvold

Civil Engineering and Architectural Section, Institute of Technology, The Norwegian University of Life Sciences, ?s, Norway.
Multiconsult AS, Skien, Norway.
Sweco Norge AS, Hamar, Norway.

DOI: 10.4236/ojce.2013.32008                

Abstract

The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed into the samples, layer by layer, by applying a drill-mounted mortar mixing device. For each amount of fiber content, 4 rings were cast, and of the plain concrete control samples, 5 rings were cast. After removing the outer steel casting, strain gages were installed on the exposed outer concrete surface. Strain values were continuously logged, and crack developments and crack widths were measured daily. Sufficient data with statistically high significance were obtained to indicate that: A synthetic fiber content of 3 kg/m³ did not decrease crack-widths as compared to the non-fiber concrete samples. Synthetic fiber contents of 5 kg/m³ and higher, did reduce crack widths on par with hooked-end steel fibers in the amounts of 25 kg/m³ and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with regards to crack width reduction, yielding 33% narrower cracks, than hooked-end steel fibers, at equal weight-contents, with aspect ratio 45.

Keywords

Concrete; Shrinkage; Fibers; Cracks

Conflicts of Interest

The authors declare no conflicts of interest.

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