The response of autoclaved aerated concrete (AAC) confined masonry buildings to seismic ground motion has been studied. Two two-story and on three-story models have been tested on a uni-directional shaking table. Although they were different in height and type of floor structures, the behavior of all models was siilar. Typical storey mechanism, characterised by diagonal shear failure mode of walls in the ground floor in the direction of excitation has been observed in all cases. Taking into consideration the observed behaviour, a numerical model with concentrated masses and storey hysteretic rules has been used to simulate the observed behaviour. Good agreement between the experimentally observed and calculated non-linear behaviour has been obtained.
COBISS.SI-ID: 1837927
The paper presents a new method to determine the transition of different cementitious materials from liquid to solid state, usually defined as a setting period. The method is based on a ratio between maximum amplitudes of two dominant frequency ranges that appear in the frequency spectrum of ultrasonic (US) P-waves, called a TG parameter. Clear and unambiguous correlation between characteristic points in the evolution of TG parameter andpenetration resistance in time is established on samples with different material composition during the early hydration process. The correlation indicates that TG parameter detects the development of rigid bonds between hydrating cement particles. The ability and accuracy of the method to determine setting period is unaffected by the material composition. Non-destructive nature and insensitivity of the method to aggregate size givesit an advantage over penetration methods and other US methods in determining the setting period of cement pastes, mortars, and concretes.
COBISS.SI-ID: 1967207
In the study characterization of steel corrosion in concrete at the macro- andmicro-level was performed. Physical (electrical-resistance probes) and electrochemical techniques (coupled multi-electrode arrays) were implemented in order to upgrade the general information that conventional electrochemical techniques can provide. Measurements were performed in mortar exposed to periodic wetting and drying. Steel corrosion damage was assessed by micro X-ray computer tomography (CT) and SEM. The results were compared and interpreted. By combined use of Micro-CT and electrochemical methods, new insights into the corrosion mechanisms of steel in concrete were obtained.
COBISS.SI-ID: 1966695
Silica, nitrogen, and nitrogen-plus-silica co-doped titania powders were synthesized via sol-gel method. The products of the synthesis were thermally treated in air and under ammonia flow. The determination of Si and/or N into the TiO2 lattice, and the doped samples' crystal structure, was made by means of X-ray powder diffraction, whilst the occurrence of amorphous phase was obtained using the combined Rietveld-RIR method. The optical properties of thepowders were obtained by diffuse reflectance spectroscopy and their energy band gaps were calculated using the differential reflectance method. The photocatalytic activity of the doped samples was assessed in gas phase under UV-light and visible-light irradiation, monitoring the degradation of an organic compound. In addition, the morphology of the samples was further on characterized by means of HRTEM. Nitrogen, silica, and co-doping shifted the anatase-to-rutile (A ? R) phase transition toward higher temperatures. Silica was found to enter the anatase lattice, and nitrogen was presumed to enter thetitania crystal structure as well. Nitrogen doping and SiO2/N-co-doping shifted the light absorption toward the visible region.
COBISS.SI-ID: 1879143
In case of foamed lightweight aggregates (LWA), porosity is introduced by the addition of a foaming agent to the glassy matrix, which degasses at an elevated temperature, so that the resulting gasses remain trapped inside the glassy structure. The efficiency of action of MnO2 as a foaming agent in wasteglass and waste glass / silica mud systems was studied. Samples were fired at different temperatures and with different dwelling times at a certaintemperature, and the development of porosity was investigated by means of X-ray micro-tomography. It was found that, with the prolongation in dwelling times, the number of pores decreased, while, on the other hand, the volume of these pores increased, and that the addition of silica mud increasesthe foaming temperature and slows down the foaming process.
COBISS.SI-ID: 1980007