Martin Vavro

Granodiorite aggregates from East Bohemia for high-performance and high-strength concretes

This paper describes the petrological characteristics of biotite granodiorites from the Litice nad Orlici Quarry in East Bohemia (Czech Republic). Physical, chemical and mechanical parameters of extracted rocks and crushed aggregates are presented, together with the results of a study of rock fabric influence on the shape parameters of aggregate grains as a principal component of high-performance and high-strength concretes.

Utilization of X-ray computed micro-tomography to evaluate iron sulphide distribution in roofing slates

Slate is a traditional stone product that has long been used for roofing widely around the world. The presence of iron sulphides is one of the most significant factors affecting roofing slate resistance to weathering and, therefore, the quality of slates and their use in construction. Iron sulphide oxidation is the main process of roofing slate degradation. Qualitative and quantitative analyses to determine iron sulphides in roofing slates are usually conducted using transmitted and reflected light microscopy, and X-ray diffraction techniques. However, this paper presents X-ray computed micro-tomography as a new laboratory method in this field, which also allows for 3D visualization and analysis of iron sulphide distribution in roofing slates. It also discusses some technical limits of this technique and tomographic scan interpretation pitfalls. The results obtained by tomographic observations were subsequently verified by optical microscopy, X-ray powder diffraction and scanning electron microscopy, as well as energy-dispersive X-ray spectroscopy analyses. Spanish slate from the Ordovician Luarca Formation and Culm slate from the Moravice Formation in the Czech Republic are both characterized by low to extremely low iron sulphide content, and for this reason were selected for this study.

Novel Device for 4-Point Flexural Testing of Quasi-Brittle Materials During 4D Computed Tomography

This paper deals with development and validation of a novel device for investigation of the crack behavior in quasi-brittle materials using radiographically observed flexural testing. Instead of standard horizontal arrangement of three-point bending devices, a novel approach consisting in a vertically oriented four-point bending setup is proposed. In the paper, technical description of the proposed device together with its advantages over existing methods and results of validation experiments with natural rocks are presented. The validation experiments were concentrated on the ability of the device to capture the fracture behavior of the samples using X-ray transmission radiography and 4D X-ray micro-tomography. Particular attention was paid to evaluate the ability to perform tomographic scans during post-peak softening, i.e. on intermittent loading of samples after formation of the crack. The acquired results showed very good performance in terms of both the mechanical characteristics of the device (stiffness and loading precision) and the X-ray imaging properties.