Alkali activated foams (known also as "geopolymer foams") are formed by the adding of a foaming agent, such as Al powder or H2O2, to an alkali activated matrix which can be based on, for example, fly ash, slag or meta-kaolin. The foaming agent decomposes and reacts inside the matrix, resulting in the release of gasses which form pores within the structure. Such pores have to be created before the alkali activated foams harden. In order to prevent the escape of these gasses from the foam, a stabilizing agent can be added to the foam mixture. This paper presents the results of tests involving the pore-foaming process in the case of highly porous, alkali activated, fly-ash based foams. Between 0.5 and 1.5 mass % of H2O2 was added to the fly ash precursor as a foaming agent, as well as different amounts (varying from 0.1 to 4.0 mass %) of the selected stabilizing agent, which is known as SDS - sodium dodecyl sulfate. The physical, mechanical, and microstructural properties of the hardened alkali-activated foams were determined. Their pore structures were characterized by SEM, as well as by a three-dimensional (3D) technique, X-ray computed micro-tomography. The advantage of the latter method is that a better insight can be obtained into the characteristics of the hardened pore structure, including information about its homogeneity and the pore size distribution. The influence of the amount of the added foaming agent, as well as that of the amount of the stabilization agent, was evaluated, and optimal addition mass percentages were determined. In the case of the best mixtures, the investigated hardened pore structures showed relatively good mechanical properties, and could therefore be used for various applications in the building industry.
COBISS.SI-ID: 2276455
Nanoremediation procedures are usually designed so that only one contaminant or similar class of contaminants is being considered. In the present work, a holistic approach was applied towards processes which simultaneously occur after the treatment of real effluent water from a small biological wastewater treatment plant (SBWTP) with different nanoscale zero-valent iron (nZVI) particles. Three different types of nZVI particles were tested: in-house nZVI, commercially available Nanofer STAR and Nanofer25 slurry, which differ in reactivity and their methods of synthesis. In order to optimise the conditions for the efficient removal of selected elements, nitrogen species, and pathogenic bacteria (Coliform bacteria, Escherichia coli, Intestinal Enterococci and Clostridium perfringens), effluent water samples were treated with different iron loads from each of the investigated nZVI at various mixing and settling times. The results demonstrated that in-house nZVI, which is the most reactive of the nanoparticles tested, most effectively removed metals and inactivated pathogenic bacteria. However, the application of in-house nZVI is restricted, as it contaminates the remediated water with B, which originated from the reagents used in its synthesis. To a certain extent, all of the investigated types of nZVI reduced nitrates and nitrites to ammonium cations. The additional formation of ammonium nitrogen was the result of the interactions of the nZVI with the organic nitrogen present in the effluent water. At an optimised iron load, mixing time, and settling time, the most efficient removal of elements and disinfection of pathogens was achieved when Nanofer25 slurry was applied.
COBISS.SI-ID: 30391847
Photocatalytic TiO2 degrades organic matter unselectively. However, in certain applications, such as degradation of pollutants, selectivity towards pollutants is beneficial. We synthesized core@shell TiO2@SiO2 nanoparticles with photocatalytic activity featuring a significantly faster preferential degradation of model pollutant (rhodamine B) in presence of abundant concentration of natural organic matter compared to pure TiO2 (P25). The material%s photocatalytic activity was tested in aqueous medium. The selectivity of prepared effect of core@shell materials is explained based on transmission electron microscopy, nitrogen adsorption, X-ray powder diffraction and zeta potential measurements.
COBISS.SI-ID: 2268519
Anticorrosive coatings are commonly used to protect metal structures from corrosion and thus assure constancy of the metal profile area, and consequently the mechanical stability of the metal structure. Due to environmental factors, corrosion of metal structures is inevitable and is considered during the design process; however, it is very difficult to predict the corrosion rate a priori, and the designer usually relies on empirical data to make an assessment. In an attempt to address this issue, various types of sensors that monitor the state of metallic coatings have been developed. In this study, the abilities of two systems, one based on electrochemical impedance and one using electrical resistance, developed by the authors to allow remote real-time monitoring of bridges are described. A laboratory study is presented in which three different sensor coating configurations were evaluated in three simulated environments: a salt spray chamber, a humid chamber, and an industrial chamber. The corrosion rates were monitored over a 9-month study period. Periodic measurements were made of the sensor output signals, and visual inspections (close-up photographs) were made to compare the visual and monitored response of the sensors. The sensitivity of the sensors is described, and the advantages and disadvantages concerning their deployment for field operations are discussed.
COBISS.SI-ID: 2299495
In this paper an extensive experimental study is presented in which the efficiency of seismic strengthening of brick masonry walls, typical in Slovenia and wider region, is analyzed. The results of cyclic shear tests of 24 walls are presented. The walls were strengthened using different materials and different layouts of the reinforcement. Externally bonded glass and carbon composites were used for strengthening and were applied to the wall by either cementitious mortar or epoxy resin. 12 walls were first tested up to the point where repair was still feasible and then strengthened and retested until collapse to study the efficiency of repair/strengthening. The rest were strengthened in the undamaged state. In addition to cyclic shear tests, the tests of the composite-masonry bond in double shear lap configuration were also performed. Results of cyclic shear tests show significant differences between different types of strengthening with shear strength resistance improvements of up to 130%. The displacement capacity was barely increased, except for one type of strengthening, thus confirming the importance of correct strengthening layout and anchoring. The observed failure mechanisms were characterized by debonding of coating which resulted in sudden resistance and stiffness degradation, leading to brittle collapse of the walls. The performance of composite-to-masonry bond in double shear lap test was significantly better than in cyclic shear tests. Finally, the resistance of strengthened walls is estimated using simple numerical models based on measured bond strength.
COBISS.SI-ID: 2292327