Geometric characterization of polymeric macrofibers

Abstract

The geometric characteristics of synthetic macrofibers are important because they affect the behavior of fiber-reinforced concrete (FRC). Because there is a lack of specific, relevant publications in Brazil, the European standard EN14889-2:2006 was adopted as a reference to perform the characterization. Thus, an experimental plan was developed to assess the adequacy of testing procedures for the qualification of synthetic macrofibers for use in FRC. Two types of macrofibers were evaluated. The length measurement was performed using two methods: the caliper method, which is a manual measurement, and the digital image analysis method using the ImageJ software for image processing. These aforementioned methods were used to determine the diameter together with the density method, which is an indirect method that uses the developed length obtained by one of the previous methods. The statistical analyses revealed that the length results are similar regardless of the method used. However, the macrofibers must be pre-stretched to maximize the accuracy of caliper measurements. The caliper method for diameter determination has the disadvantage of underestimating the macrofiber cross-section because of the pressure applied by the load claws. In contrast, the digital image analysis method obtains the projected diameter in a single plane, which overestimate the diameter because the macrofibers are oriented with the pressure of the scanner cover. Thus, these techniques may result in false projections of the diameters that will depend on the level of torsion in the macrofibers. It was concluded that both the caliper method using previously stretched macrofibers and the digital imaging method can be used to measure length. The density method presented the best results for the diameter determination because these results were not affected by the method chosen to determine the length.

Mechanical Characterization of Synthetic Macrofibres

“…As described in Cáceres et al 17 , previously to the test, a sample of macrofibres was taken in order to determine their density (ρ) by means of the picnometer test. This test requires a quantity of 30 g of cut macrofibres and provide an average value.…”

“…Table 2 presents the results of cross-sectional areas (S) of a total of 10 macrofibres under normal and mixed conditions. The determinations were made measuring the diameter according to the density method as indicated in the study of Cáceres et al, 17 . It is noteworthy that were measured exactly the same macrofibres that were tested to direct tensile strength.…”

“…In case of mixed macrofibres it was not possible to make any comparison; since the tensile stress of a blended macrofibre is generally not provided. It is also necessary to highlight that the scatter of the mechanical results depends on the approach of measuring the cross-sectional area of the macrofibres as observed in Cáceres et al 17 . This study considered three methods to determine the cross-sectional area: caliper, images analysis and density method.…”

Mechanical Characterization of Concrete Reinforced With Composite Glass Macrofibre

“…The result is an average equivalent diameter. This difference could be justified by the fact that the diameter was calculated by the density method which is not affected by the pressure employed by the calliper load claws or the position of the fibre [15] as regularly used for this kind of determination.…”