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Recycling concrete with reinforcement made of basalt fibre polymers: investigations on the composite and tensile load‐bearing behaviour The use of recycling concrete is subject to restrictions in Germany, which prevent its use in environmental conditions containing de‐icing salt of exposure classes XD3 and XS3. To overcome these normative barriers, the Munich UAS is conducting research on the use of alternative reinforcement materials that completely eliminate reinforcement corrosion induced by chlorides. In this regard, non‐corrosive fibre composite bars, made of basalt, are employed, which offer ecological advantages over reinforcements made of stainless steel, glass fibre or carbon. The investigations presented here on the composite and tensile load‐bearing behaviour of basalt fibre‐reinforced polymers have arisen as part of a current research project examining the use of this type of reinforcement in bridge caps made of recycling concrete. In addition to preliminary concrete technology studies on the use of up to 100 % recycled aggregates, composite specimens made of recycled concrete and basalt fibre reinforced polymer were tested to provide insights on the load‐bearing behaviour under static and cyclic conditions. [ABSTRACT FROM AUTHOR]

Influence of recycled aggregate on the bond behaviour of reinforcing steel in concrete The use of recycled aggregates in common structural concretes is considered a promising approach to conserve natural resources. The present study focuses on investigating the bond behaviour of reinforcing steel in concrete with high portions of recycled aggregate from crushed concrete. To clarify a possible influence of the aggregate properties, 5 different aggregates were tested in 12 concretes. The results of the pull‐out tests were evaluated with the help of an analytical bond equation to be able to draw conclusions about the resulting design bond stress. A tendency towards a decrease in the maximum absorbable bond stress with high portions of recycled aggregate was observed. The resulting design values of the bond strength are lower than for the reference concrete, but above the specifications of Eurocode 2. The decrease in the design bond stress appears to correlate with the volume fractions of recycled aggregate and the concrete bulk density. Overall, the study shows that the bond behaviour of concrete with recycled aggregate is similar to that of normal concrete in terms of bond, shear and friction, although the actual effects also depend on the specific properties of the aggregate used. [ABSTRACT FROM AUTHOR]

Investigation on tension and bonding behaviour of basalt fibre reinforced polymers in concrete structures For retrofitting of RC structures, the concrete cover of the renewed reinforcement has to be sufficient to ensure the durability. Alternative reinforcement like rebars of basalt fibre reinforced polymers (BFRP) gives the possibility to minimize the concrete cover ensuring durable structures due to their resistance against carbonation and chlorides. In this paper investigations on load‐bearing behaviour of BFRP reinforced test specimens as an excerpt from a research project on basalt fibre reinforced concrete as repairing material with shotcrete and also basalt rebars as additional strengthening reinforcement for fair faced concrete facades are presented. The tested BFRP rebars show higher tension strength and lower Young's Modulus as comparable steel reinforcement bars. In centrical tension tests on the BFRP reinforced concrete specimen longitudinal cracking due to high tension in the contact zone and a higher number and also higher widths of crosswise cracking appear. The load bearing behaviour can be confirmed by numerical simulation. The results of the investigation with the incident light microscope on prepared specimen after tension tests show an enhanced number of microcracks in the contact zone between BFRP rebar and cement matrix. In pull out tests always the concrete failed, never the BFRP rebars. The results of this investigation confirm the possibility to ensure durable concrete structures using BFRP reinforcement. Further tests have been carried out on the flexural strength behaviour, the fatigue strength and durability. At the moment BFRP rebars of various designs are tested. [ABSTRACT FROM AUTHOR]

Abstract: In recent years several studies presented different parameters and criteria to describe the damage of concrete specimens caused by projectile impact. The parameter used most to characterize damage is the volume of the craters on the front and rear side of the concrete specimen. In this study the damage of concrete specimens is described as a fractured area. In order to describe the whole fractured area it is necessary to consider the crater surfaces and the fractured surface area of the fragments generated by impact. The crater surfaces were analysed using a 3-dimensional laser-scanner system. The fragments were measured with a camera particle analyser. Their surfaces were determined taking into account the following parameters: Feret diameter, length, volume distribution and sphericity. A triaxial ellipsoid model was developed by means of these parameters. The whole fractured surface area is given by the sum of the specimen surface after perforating and the fragments surface minus the specimen surface before perforation. The fragment surface is decisive for the fractured surface and depends on the number of fragments of each size class. This study confirms previously gained results using new parameters: A larger maximum aggregate diameter enhances the impact resistance of concrete against projectiles. [Copyright &y& Elsevier]

Influence of chloride induced pitting corrosion on the mechanical properties of reinforcing bars The durability of chloride‐exposed reinforced concrete components is mainly determined by the corrosion behavior of the reinforcing steel. If an ingress of chlorides in chritical concentration into the component has taken place, pitting corrosion can appear. The occurring, very local loss of material can lead to high cross‐sectional losses of the reinforcement in a short time. For repair planning the planner is faced with the task of specifying the type and scope of the rehabilitation. In doing so, the challenge is to determine the present cross‐sectional losses as accurate as possible. However, an exact determination of the cross‐sectional loss on the site is difficult because of the geometry of the pitting. This is why the loss of cross‐section is often estimated visually. Furthermore, the question arises whether the pittings produce notch stresses that have an influence on the load‐bearing capacity and lead to deviating strength values in comparison to a simple cross‐sectional analysis. In addition, the question of the influence on local damage on the strain behavior of the reinforcing steel is to be answered. To improve the evaluation of damaged reinforcement due to pitting corrosion, tests on reinforcing steel bars with a wide spectrum of damage due to chloride‐induced corrosion have been carried out at the Munich University of Applied Sciences. For this purpose, rebar probes of various diameters were taken both from an underground parking garage of the 1960s, as well as artificial corroded samples produced in the laboratory. The steel samples were examined on the basis of their optical appearance, the measured residual cross section, as well as the residual strain behavior and the residual static load capacity. [ABSTRACT FROM AUTHOR]