Influence of production parameters on the fiber geometry and the mechanical behavior of ultra high performance fiber‐reinforced concrete

Abstract

In this paper, the relationship between production parameters of ultra high performance fiber‐reinforced concrete (UHPFRC) and the spatial distribution and orientation of the steel fibers is investigated. UHPFRC specimens with varying fiber diameter, fiber volume fraction, and rheology of the mixture are produced. Additionally, casting is performed from the side or the middle of the formwork. Imaging by micro computed tomography allows for a statistical analysis of the spatial arrangement of the fibers in the test specimens. The flexural behavior and the load capacity of the specimens are analyzed by four point bending tests. The results of the bending tests are well explained by characteristics of the fiber systems determined from the image data.

A $K$-function for inhomogeneous random measures with geometric features

“…In this section we apply our K-function to a 3D fiber pattern, shown in Figure 3, of steel fibers in ultra high performance fiber-reinforced concrete. The fiber pattern was extracted from a series of micro computed tomography images kindly provided by the authors of Maryamh et al (2021). The objective in Maryamh et al (2021) is to study the relationship between production parameters of the fiber-reinforced concrete, the spatial distribution and orientation of the steel fibers, and mechanical properties of the concrete (results of bending tests applied to concrete specimens).…”

“…The fiber pattern was extracted from a series of micro computed tomography images kindly provided by the authors of Maryamh et al (2021). The objective in Maryamh et al (2021) is to study the relationship between production parameters of the fiber-reinforced concrete, the spatial distribution and orientation of the steel fibers, and mechanical properties of the concrete (results of bending tests applied to concrete specimens). More specifically, the data set considered here was obtained by imaging a 160 × 40 × 40mm block of con-Figure 2: Left: a simulation of an inhomogeneous fiber pattern with correlated fibers.…”

“…Ideally, for maximal bending strength, the fibers should be aligned with the long axis of the block. Due to sedimentation, spatial inhomogeneity of the fibers is possible although the degree of inhomogeneity depends on the viscosity of the concrete used for casting the concrete block, see Maryamh et al (2021) who considered several blocks produced with varying production parameters. Maryamh et al (2021) studied the spatial variation in fiber density using area fraction profiles obtained from the microscope images.…”

“…Due to sedimentation, spatial inhomogeneity of the fibers is possible although the degree of inhomogeneity depends on the viscosity of the concrete used for casting the concrete block, see Maryamh et al (2021) who considered several blocks produced with varying production parameters. Maryamh et al (2021) studied the spatial variation in fiber density using area fraction profiles obtained from the microscope images. For the directions of fibers they obtained partial derivatives of the gray scale images and considered eigenvectors of the resulting orientation matrices.…”

“…Since fibers are unoriented we, following Section 4, represented tangents by points on be the hemi-sphere S with north pole at (0, 1, 0). Due to strong edge effects in each end of the block, we follow Maryamh et al (2021) and discard data from the first and last (referring to the long axis) 2 cm of the block.…”