Bioactive Polyoxymethylene Composites: Mechanical and Antibacterial Characterization.

The aim of this study is to analyze the strength and antibacterial properties of composites based on structural polyoxymethylene. The base material was modified with the most used antibacterial additives, such as silver nanoparticles, copper oxide, zinc oxide, and titanium oxide. Basic strength and low-cycle fatigue tests were conducted to determine the dissipation energy of the material. The composites were also tested for antibacterial properties against two strains of bacteria: Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 6538. Strength properties showed no significant changes in the mechanical behavior of the tested composites against the matrix material. The best antibacterial additive was the addition of titanium oxide nanoparticles, providing 100% efficacy against Escherichia coli and almost 100% biocidal efficacy against Staphylococcus aureus. The other antibacterial additives showed biocidal efficacy of about 30-40% against the unmodified material. The added value of the work is the consistency in the methodology of testing materials modified with antibacterial additives, as well as the same compactness of the introduced additives. This study makes it clear which of the introduced additives has the highest biocidal activity.

Accuracy Assessment of Semi-Automatic Measuring Techniques Applied to Displacement Control in Self-Balanced Pile Capacity Testing Appliance.

Static load tests of foundation piles are the basic method for the designing or verification of adopted design solutions which concern the foundation of a building structure. Preparation of a typical test station using the so-called inverted beam method is very expensive and labor-intensive. The settlement values of the loaded pile are usually recorded using accurate dial gauges. These gauges are attached to a reference beam located in close proximity to the pile under test, which may cause systematic errors (difficult to detect) caused by the displacement of the adopted reference beam. The application of geodetic methods makes it possible to maintain an independent, external reference system, and to verify the readouts from dial gauges. The article presents an innovative instrumentation for a self-balanced stand for the static load test made from a closed-end, double steel pipe. Instead of typical, precise geometric leveling, the semi-automatic measuring techniques were used: motorized total station measurement and terrestrial laser scanning controlled by a computer. The processing of the acquired data made it possible to determine the vertical displacements of both parts of the examined pile and compare displacements with the results from the dial gauges. On the basis of the excess of the collected observations, it was possible to assess the accuracy, which confirmed the usefulness of measuring techniques under study.