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- ItemTesting the Influence of the Material Bonding System on the Bond Strength of Large-Format Tiles Installed on Concrete Substrate under Mechanical Loading(MDPI, 2020-07-17) Topolář, Libor; Kocáb, Dalibor; Šlanhof, Jiří; Schmid, Pavel; Daněk, Petr; Nováček, JaroslavThe paper describes an experiment focusing on the way the material system influences the bond strength of large-format tiles installed on concrete substrate during mechanical loading under conditions that correspond to real-life application. This involves a controllable mechanical load applied over an area of a test model while observing its condition using non-destructive methods (ultrasonic pulse velocity test, acoustic emission method, strain measurement, and acoustic tracing). The model consisted of a concrete slab onto which were mounted four different systems with large-format tiles with the dimensions of 3 m x 1 m. The combinations differed in the thickness of the tile, the adhesive, and whether or not a fabric membrane was included in the adhesive bed. The experiment showed that the loading caused no damage to the ceramic tile. All the detected failures took place in the adhesive layer or in the concrete slab.
- ItemInfluence of alkali-activated materials placement during curing on their dynamic parameters(EDP Sciences, 2020-04-16) Plšková, Iveta; Matysík, Michal; Topolář, Libor; Bílek, VlastimilThe production of Portland cement has a considerable environmental impact. Its replacement with alkali-activated binders can contribute to reducing the environmental burden of building production. The paper presents partial results from our experimental research carried out on test specimens made of alkali-activated slag mortar (activated by sodium carbonate). The specimens of dimensions 40x40x160 mm differed in the manner of placement after 28 days of curing in water. The samples were tested by non-destructive methods at different ages. We observed the effect of sample storage on ultrasonic pulse velocity, dominant frequency shifts and dynamic modulus of elasticity as well as changes of these parameters over time.
- ItemDatabase 3D Surfaces for Evaluation of Joint Rock Coefficients(Elsevier, 2016-06-13) Ficker, Tomáš; Martišek, DaliborSurfaces of rock joints were classified by means of the computerized procedure utilizing three-dimensional reliefs. These standard reliefs were formed as fractal objects using scaling properties of rock joints. Applicability of the computational scheme was tested and verified.
- ItemEffect of Metallic Inclusions on the Compressive Strength of Cement-Based Materials(Hindawi, 2018-12-26) Ficker, TomášIn the concrete foundations, materials come into contact with bedrocks. The surfaces of bedrocks are often covered by sharp protrusions called asperities. Although geotechnical engineers have developed a reliable theory for assessing the mechanical stability of rocky terrains, the stability of transition zones between concrete and sharp asperities remains unsolved. Due to the large pressures that exist in these transition zones, the invasive influence of sharp asperities on the integrity of the concrete raises a question about possible changes of the mechanical properties of concrete materials used in foundations. These circumstances have inspired experiments in which metallic needles of various lengths have been embedded into cement-based materials to assess the influence of the needles on the compressive strength. This influence has been quantified, and the critical limits identifying the changes of material integrity have been determined. It has been conjectured that sharp rock asperities or needle-like rods of steel reinforcement in concrete may cause similar changes of material integrity as the metallic needles used in the experiments performed.
- ItemMacrodefects and Microdefects within Porous Cement Pastes(IOP Publishing, 2017-11-28) Ficker, TomášIt is shown that the mechanical strength of cement matrix (hydrated cement paste) is a result of competitive interplay between macrodefects and microdefects. The dominance of one of these two kinds of defects depends not only on their sizes but also on their numbers. The cross-over between dominances of macrodefects or microdefects is determined both by a critical number of defects and by their critical size, which depends on the mechanical parameters of the materials.