Bernhard Freytag

Glass-Concrete Composite Technology

This paper deals with a new method of construction with highly transparent building elements. Glass is connected with ultra-high-performance concrete by direct contact. The specific structural behaviour as well as failure mechanisms are demonstrated by means of large scale experiments. A first analytical approach tries to consider all the complex phenomena with simple models. Verifications of the models are given by the comparison of calculation and experiment.

The three-dimensional morphometry of the odontoid peg and its impact on ventral screw osteosynthesis

Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis. Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability. The mean length of the odontoid peg was 39.76 mm (SD 2.68). The mean screw entry angle α was 59.45° (SD 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (SD 2.70), the maximum possible mean converging angle of two screws was 20.35° (SD 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (SD 0.84) for the inner diameter in the sagittal plane and 7.35 mm (SD 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (SD 0.91) in the sagittal plane and 11.77 mm (SD 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (SD 1.14) for the sagittal inner diameter and 5.50 mm (SD 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (SD 1.0) in the sagittal plane and 10.00 mm (SD 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible. The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.

Adhesive Power of Ultra High Performance Concrete from a Thermodynamic Point of View

Ultra high performance concrete (UHPC) is well suited to provide adhesive connections with other materials. Here, not only does mechanical interlocking provide adhesion, but also intermolecular forces that are closely related to the surface energy of the used materials. The determination of intermolecular forces for UHPC connected to glass and steel is presented in this work. First, the theoretical relation between intermolecular forces and the surface energy is shown. The main part deals with experiments on the determination of the surface energies. Contact angle measurements are used to determine surface energies of steel, glass, and hardened UHPC. Some ideas on estimation of the surface energy of fresh UHPC using conventional testing methods are presented. Finally, the calculated specific adhesion is compared to the technical adhesion determined by direct tension tests.