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Carbon-based conductive coatings are complex composites, consisting of an organic or inorganic binder and conductive carbon components, for application as anodes in impressed current cathodic protection systems of reinforced concrete structures. The electrochemical properties of three coatings at different humidity and in saturated calcium hydroxide solution were studied by electrochemical methods, such as electrochemical impedance measurement, measuring of open circuit potential over time and galvanostatic polarization.
In the last decades, numerical simulations of fresh concrete flow have gained importance in concrete industry. They showed a potential to become a tool for prediction of concrete casting and to help engineers to avoid expensive mistakes on site. A promising field for application of numerical modelling is casting of Self-Compacting Concrete (SCC), since the main area of application of SCC are complex and highly-reinforced building elements. Simulations of fresh concrete flow involve complex mathematical models and time-consuming computations. In case of casting simulations, the simulation time is additionally significantly increased because each reinforcement bar occurring in succession has to be considered one by one. This is particularly problematic in case of SCC casting, since this type of concrete is typically used for heavily-reinforced structural members. With the aim to decrease simulation time and to come closer to a practical simulation tool, we proposed an innovative modelling approach that models a zone with arrays of the reinforcement bars as a porous medium (PM). By defining characteristic parameters of the PM, its influence on the flow can be defined. This approach simplifies the geometry to be modelled and significantly decreases the computational time. The present contribution provides a brief description the proposed numerical model and of the conducted validation studies. The applicability of the model on fresh concrete is verified through the comparison between experimental measurements and numerical simulations.
Rubbers are usually reinforced with a high content (> 40 phr) of carbon black (CB) and silica. In recent years several nanofillers have been proposed, including expanded graphite/graphene. Extremely low loading of nanoparticles can considerably improve the properties. In this contribution multilayer graphene (MLG) is investigated as efficient nanofiller for rubbers. MLG has a BET specific surface area of 250 m2/g. Compared to a single graphene sheet, the MLG used constitutes only approximately 10 graphene sheets.
When homogenously dispersed, it works at low loadings enabling the replacement of CB, increase in efficiency, or reduction in filler concentration. Actually the appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing and mechanical properties of different rubbers, as shown for Chlorine-Isobutylene-Isoprene Rubber (CIIR), Nitrile-Butadiene Rubber (NBR), Natural Rubber (NR), and Styrene-Butadiene Rubber (SBR).
A mere 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of carbon black. Similar equivalents are observed for MLG/CB mixtures. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards fire behavior. The higher the nanofiller concentration is (3 phr, 5 phr, and 10 phr was investigated), the greater the improvement in the properties of the nanocomposites. Moreover, the MLG nanocomposites improve stability of mechanical properties against weathering. An increase in UV-absorption as well as a pronounced radical scavenging are proposed and were proved experimentally. To sum up, MLG is interesting as multifunctional nanofiller and seems to be quite ready for rubber development.
Large scale reinforced concrete test specimen for potential mapping under practical conditions
(2017)
Electrochemical potential mapping according to guideline B3 of DGZfP (German Society for Non-Destructive Testing) is a recognized technique for the localization of corroding reinforcing steels. In reinforced concrete structures the measured potentials are not necessarily directly linked to the corrosion likelihood of the reinforcing steel. The measured values may be significantly affected, different from e.g. stress measurement, by different influences on the potential formation at the phase boundary metal/concrete itself as well as the acquisition procedure. Due to the complexity of influencing factors there is a risk that the results are misinterpreted. To investigate these influencing factors under practical conditions it requires a specimen with similar damage patterns, dimensions and more factors e.g. metallic mounting parts. Recently the BAM realized such a large scale test specimen for this purpose.
Corrosion of galvanized steel in chloride containing mortar is different from the corrosion of reinforcement made of carbon steel. This is based on the corrosion behavior of galvanized steel in chloride containing mortar. To describe the influence of a chloride containing zinc-hydroxide layer at the phase boundary against a zinc-hydroxide layer in chloride free mortar, different electrochemical measurements were made. The anodic and cathodic partial reaction were investigated by galvanostatic pulse measurements and potentiodynamic measurements. Especially the galvanostatic pulse measurements can describe the influence of the chloride content by the polarization resistance with pt = 20 sec. (polarization time). Additionally, corrosion current measurements were performed, coupled with potential measurements, between galvanized steel in chloride containing and chloride free concrete. Normally, the potential measurements are an indicator to localize the anodic and cathodic parts of a macro system. In this case the results show that there is no formation of a significant macro element cell between chloride containing and chloride free mortar. After 1500 h of potential and current measurement the results show a more positive corrosion potential with increasing chloride content. The results of the potential/current curves show a significant different free corrosion current depending on the chloride content, the free corrosion current increase with increasing chloride contents; reasons for this behavior are discussed.
Imaging of results in NDT-CE: Strength and limitations in the use of Radar vs. Ultrasonic Echo
(2022)
Presentation on behalf of the co-author specified in BAM-Publica.
Study on capabilities of volume methods (GPR, Ultrasonic Echo) regarding lateral and depth localisation of reinforcement and tendons in concrete components. Varied boundary conditions: spacing and diameter of both the near surface rebars of the mesh, and the reflectors of interest, as well as component thickness and concrete cover. Please find corresponding references on slide 2.
A few layer/multilayer graphene (MLG) with a specific surface area of BET ≥ 250 m2/g is proposed as an efficient multifunctional nanofiller for rubbers. The preparation method, i.e., ultrasonically-assisted solution or latex premixing of master batches followed by conventional two-roll milling, strongly influences the dispersion in the elastomeric matrix and is fundamental for the final properties. When homogenously dispersed, single stacks of only approximately 10 graphene sheets, with an aspect ratio of ca. 35, work at low loadings, enabling the replacement of large amounts of carbon black (CB), an increase in efficiency, and a reduction in filler load. The appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing, gas barrier properties, electrical and thermal conductivity, as well as mechanical properties of different rubbers, as shown for chlorine-Isobutylene-Isoprene rubber (CIIR), nitrile-butadiene rubber (NBR), natural rubber (NR), and styrene-butadiene rubber (SBR).[1-5] 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of CB. The stronger interactions between MLG and NR or SBR also resulted in a reduction in the elongation at break by 20% and 50%, respectively, while the same parameter was hardly changed for CIIR/MLG and NBR/MLG. CIIR/MLG and NBR/MLG were stiffer but just as defomable than CIIR and NBR. The strong reinforcing effect of 3 phr MLG was confirmed by the increase of greater than 10 Shore A in hardness. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards flammability. We investigated MLG also as a synergist for reducing the aluminium trihydrate loading in flame retardant hydrogenated acrylonitrile-butadiene (HNBR), polybutadiene chloroprene (BR/CR), and chlorosulfonated polyethylene rubber(CSM).[6-8] The higher the nanofiller concentration is, the greater the improvement in the properties. For instance, the permeability decreased by 30% at 3 phr of MLG, 50% at 5 phr and 60% at 10 phr, respectively. Moreover, the MLG nanocomposites improve stability of mechanical properties against the effects of weathering. In key experiments an increase in UV-absorption and a pronounced radical scavenging were proved as stabilizing mechanisms. In a nutshell, MLG is an efficient multifunctional nanofiller ready to be used for innovative rubber development.