Advances in Science and Technology Vol. 145

Abstract: The conducted research program was focused on the creation steel fiber reinforced concrete (SFRC) dedicated for casting columns with fractal based cross-sections. The columns in question were planned to be cast using 3D printed plastic formworks. Harnessing 3D printing of plastic enables easy creation of cross-sections which are not possible to be achieved using traditional formwork techniques. The mix had to be characterized by consistency enabling almost self-compacting behavior, reasonably high volume of fiber (volumes of fiber ranging from 0.5% to 2.0% were considered) and the maximum diameter of used aggregate of 2mm. Due to very complicated cross-sections of planned columns the mix had to be able to effortlessly penetrate very elaborate shapes of fractal formwork. All desired properties were achieved during the research program using two admixtures and micro steel fiber. The mix was tested using column specimens with circular, square and pentagon cross-sections.

Abstract: During the research study focused on 100-year-old concrete bridges, a couple of them were found with a very low carbonation depth under an ordinary cement-based protective render coat (PRC). Phenolphthalein test showed at this place carbonation depth up to 2 mm. Bridge concrete was carbonated up to 80 mm, when a PRC spalled up. Close correlation between the surface permeability of a PRC estimated by the Torrent method and the carbonation depth of the base concrete beneath it, was observed. Most of the PRCs appeared to be almost impermeable showing the coefficient of permeability below 0.01 × 10^-16 m². The field experiments were replaced by those of laboratory-made aiming to a PRC development from currently available materials. For this purpose, material composition and rheological optimization of the PRCs were suggested and relevant tests performed. The PRCs applied to a surface of concrete panel were tested for permeability (Torrent method), adhesion (target) and crack propagation. The resistance to carbonation of the plain concrete C8/10 strength class according to EN 206 + A2 and those of PRC-protected were verified by an accelerated carbonation in 20 °C/60 % R.H./20 % vol. CO₂-exposure. By contrast, dry-air cure served as a reference cure. This article is mainly focused on the laboratory tests evaluation and explanation of the observed low carbonation of the base concrete covered by a PRC.

Abstract: Abstract. Additive manufacturing of concrete structures is a novel and emerging technology. Freecontouring in civil engineering, which allows for entirely new designs, is a significant advantage. Inthe future, lower construction costs are expected with increased construction speeds and decreasingrequired materials and workers. However, architects and civil engineers rely on a certain quality ofexecution to fulfil construction standards. Although several techniques and approaches demonstratethe advantages, quality control during printing is highly challenging and rarely applied. Due to thecontinuous mixing process commonly used in 3D concrete printing, it is impossible to exclude varia-tions in the dry mixture or water content, and a test sample cannot be taken as a representative samplefor the whole structure. Although mortar properties vary only locally, a defect in one layer duringprinting could affect the entire integrity of the whole structure . Therefore, real-time process monitor-ing is required to record and document the printing process.At the Bundesanstalt für Materialforschung und -prüfung (BAM) a new test rig for the additive man-ufacturing of concrete is built. The primary purpose is measuring and monitoring the properties of amortar during the printing process.The following study investigates an approach for calculating yield stress and plastic viscosity based onexperimentally recorded pressure data. The calculations assume that fresh mortar behaves as a Bing-ham fluid and that the Buckingham-Reiner-equation is applicable. A test setup consisting of rigid pipeswith integrated pressure sensors at different positions is utilized.Monitoring the printing process with different sensors is crucial for the quality control of an ongoingprocess.

Abstract: Building industry is an important player that consumes a significant part of raw materials and energy. With regard to construction industry sustainable development and design requirements there is a space for innovative solutions, where one of the possibility include the use of high-strength concrete. The paper deals with the substantial description and detailed evaluation of the testing of reinforced high strength concrete beam which was exposed to three point loading test. Large scale experiment was complemented with material diagnosis of selected mechanical properties using destructive and non-destructive methods. Non-destructive methods were used to verify compressive strength and dynamic modulus of elasticity. Destructive compressive strength testing was applied on cylinder samples prepared with core drilling and determined values were compared with non- destructive testing. Measured data will be used for future advanced non-linear modelling.