# Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete +
## 2 Materials and Methods  
### Sample Material  
In the framework of the investigations presented herein, five samples with varying fiber alignments were produced and tested. For the sample examinations, it was required to create samples with randomly distributed fibers, and with fibers aligned parallel and transversely to the sample main axis. Depending on the test type and configuration, different sample dimensions were required: the samples used for ultrasound testing were prismatic with dimensions of 80 \(\times\) 80 \(\times\) 300 mm, while the SIP- and CT-based evaluations used smaller cylindrical samples with a diameter of 50 mm and a length of 150 mm. The prismatic samples were initially cast as described below. Following ultrasonic measurement, the cylindrical samples were extracted from these prisms through diamond core drilling along their longitudinal axis. The material used was identical for all samples: a concrete of class C35/45 having a target mean compressive strength of 50 MPa. The mix included CEM I 42.5 R cement from the producer Phoenix Zementwerke Krogbeumker Holding GmbH & Co. KG at 344 kg/m\({}^{3}\), added water at 147 kg/m\({}^{3}\) (w/c = 0.43), aggregates from the Rhine river plant of Hulskens GmbH & Co. KG with grading of 0/2, 2/8 and 8/16 mm at 779, 574, and 571 kg/m\({}^{3}\) (or 40%, 30%, and 30%), respectively, and no further admixtures. Furthermore, hooked-ended 5D Dramix(r) fibers 5D 65/60 BG (with 62 mm length and 0.9 mm diameter ([24]) and fy = 2300 N/mm\({}^{2}\)) were used. Fiber dosages of 80 kg/m\({}^{3}\) (or 1 vol.%) and 40 kg/m\({}^{3}\) (or 0.5 vol.%) were realised in the samples (Figure 2, right). One sample was cast without any fibers for reference. The air void content in all samples was estimated as ca. 1.5% per mix volume. In order to produce the samples, the concrete material was mechanically mixed in a small laboratory concreting barrel without fibers. A portion was separated and kept without fibers, then fibers were added in the rest of the mix and it was further mixed in order to obtain a homogeneous spatial and orientational distribution of the fibers. This latter material was then directly cast in prismatic moulds. In order to produce the samples with orthotropically aligned fibers, the withheld plain concrete portion was cast sequentially in layers, followed by a manual placement of the fibers in the desired alignment (Figure 2, right). At intervals, the samples were compacted on a vibrating plate. A photo of all prepared samples is shown in Figure 3. However, in this paper, we will investigate and explain in detail the potential of the NDT methods using five selected specimens as examples. These are three specimens with 40 kg/m\({}^{3}\) fiber content, where the fibers are distributed longitudinally, transversely as well as randomly. Furthermore, the results of a sample with 80 kg/m\({}^{3}\) fibers arranged longitudinally to the sample axis and a sample without fibers are discussed. The samples with random fiber distribution, and with fibers aligned parallel and transversely to the longitudinal sample axis are denoted throughout the paper using the specifications *, \(\mid\mid\mid\), and --, respectively. The fiber dosage is stated in the sample name as either 40 or 80 according to their amount of fibers in kg/m\({}^{3}\). The specimen preparation was performed in the concreting facilities of the Building Research Lab at the TU Dortmund. All samples discussed in the following are colour coded in Figure 3. This colour coding will be further used throughout the paper consistently in the presentation of results. Ultrasonic (US) measurements generally have to be performed on relatively large specimens in order to allow undisturbed wave propagation. Hence, the US tests were performed first on the largest available test specimens, which in our case where the prisms with 300 mm length and 40 mm edge length.