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Concrete Surfaces (concrete + surface)
Selected AbstractsFixation of heavy contaminants of a dirty bomb attack: Studies with uranium and metal simulantsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2007Thomas L. McGehee Abstract Asphalt emulsions were evaluated as a means to immobilize radiological contaminants deposited on urban surfaces after a dirty bomb attack. Contaminated surfaces would be sprayed with thin coatings of asphalt emulsion to encapsulate the radioactive particles until the site can be safely remediated. This research investigated applications of an asphalt emulsion (Topein C, Encapco Technologies, LLC, Napa, CA) to treat (zero-valent) iron, lead, and uranium powders on various building material surfaces. Initial studies found that some of the building materials (limestone, concrete, and metal) reacted with the emulsion producing gas bubbles, which formed 0.001 to 1 cm vesicles in the cured asphalt emulsion. These vesicles, however, did not expose the building material surface, and the reaction appeared to aid in the setting of the emulsion. Powdered lead did not react with the asphalt emulsion, but iron powder and uranium did. Iron powder and the emulsion formed vesicles up to 0.5 mm (but not exposing the building material surface), while the uranium (U3O8) had a moderate reaction when compared with to the lead and iron powders. Scanning electron micrographs showed that the lead powder formed nonreactive layers adjacent to the concrete surface while iron particles were evenly distributed in the asphalt matrix due to the reaction with the asphalt, indicating that the physical and chemical reactions between the iron metal particles, asphalt, and concrete affected particle distribution in the asphalt matrix. A vertical operation sediment tube was used to determine the flowing shear stress durability of the asphalt/metal/substrate complex. The asphalt treatment with iron had no loss at the shear range tested (0.1,2.5 Pa), while the asphalt stabilized powdered lead lost 8% asphalt and lead at 2.5 Pa mean shear stress applied for 5 h. The chemical reaction between asphalt emulsion and iron increased the resistance of the asphalt/metal/substrate complex to shear when compared with lead. Some hydrogen was formed in reactions with iron, but the amount formed was well below the lower flammability limit. Treatment of uranium indicated that the emulsion was effective at reducing leaching of the uranium 10 fold. These experiments indicate that asphalt emulsions may be a viable means for containing metallic or dense radiological contaminants on common building materials. © 2007 American Institute of Chemical Engineers Environ Prog 26:94,103, 2007 [source] Potential mapping technique for the detection of corrosion in reinforced concrete structures: Investigation of parameters influencing the measurement and determination of the reliability of the methodMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2009Y. Schiegg Abstract The potential distribution around a corrosion site in concrete was modeled by means of a simple mathematical model for a rod-shaped anode. Based on these calculations the influencing parameters and the limits of the potential mapping technique were determined. They demonstrate that the location of anodes depends on the anode length, the concrete coverage, and the measuring grid. Moreover small anodes with less than 1 cm length are virtually impossible to localize. Investigations on concrete elements without reinforcing steel showed that heterogeneous water content and chloride distribution can result in potential differences of up to 150 mV on the concrete surface. This effect was related to the streaming potential and the diffusion overpotential in the concrete. In order to determine the reliability of the potential mapping technique in the field application, the concrete on a tunnel wall was removed after the measurement of the potential distribution and the corrosion loss of the steel was determined. It was found that all corrosion sites with more than 2 mm material loss were detected by the potential mapping technique. Only some smaller corrosion sites were not found. Based on this investigation, the applicability of the potential mapping technique for detecting corrosion sites was confirmed. The observed high reliability of the potential mapping technique can be explained by a combination of the heterogeneous wetting of the concrete, the inhomogeneous contamination with chloride, and the macrocell formation. [source] Acute lethal and behavioral sublethal responses of two stored-product psocids to surface insecticidesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 12 2008Raul Narciso C Guedes Abstract BACKGROUND: The psocids Liposcelis bostrychophila Badonnel and L. entomophila (Enderlein) (Liposcelididae) are emerging pests of stored products. Although their behavior, particularly their high mobility, may contribute to the reported relatively low efficacy of insecticides against them, studies to investigate this have not been conducted. The present study aimed to assess the label rate efficacy of three commercial insecticides (,-cyfluthrin, chlorfenapyr and pyrethrins) applied on concrete surfaces against L. bostrychophila and L. entomophila, and also their sublethal effect on the mobility of these species. RESULTS: The synthetic insecticides ,-cyfluthrin and chlorfenapyr showed high short-term efficacy (LT95,15 h) against both psocid species, unlike the natural pyrethrins (LT95 , 4 days). Liposcelis bostrychophila was slightly more tolerant (,1.2×) than L. entomophila to all three insecticides. Behavioral assays with fully sprayed and half-sprayed concrete arenas indicated that the insecticides reduced the mobility of both species. Pyrethrins seem to elicit weak repellence in L. bostrychophila. CONCLUSION: ,-Cyfluthrin and chlorfenapyr were effective against both psocid species, but not pyrethrins. The mobility of both species does not seem to play a major role in the differential selectivity observed, but the lower mobility of L. bostrychophila may be a contributing factor to its higher insecticide tolerance. Published in 2008 by John Wiley & Sons, Ltd. [source] Betoninstandsetzung , quo vadis?BAUTECHNIK, Issue 4 2007Erich Cziesielski Univ.-Prof. In diesem Beitrag wird der Mechanismus des Korrosionsvorganges für Bewehrungsstähle im nicht chloridbeanspruchten Beton beschrieben. Daraus folgend werden die Schutzprinzipien entsprechend der Richtlinie des Deutschen Ausschusses für Stahlbeton dargestellt. Es wird insbesondere auf das Schutzprinzip W eingegangen, das vereinfachend bedeutet, daß durch wärmedämmende Maßnahmen bzw. Beschichtungen auf den korrosionsgeschädigten Betonoberflächen die Bewehrungsstähle vor weiterer Korrosion geschützt werden. Auf die Grenzen der Wirksamkeit von Beschichtungen wird verwiesen. Concrete restoration , quo vadis? This article describes the mechanism of the corrosion process for reinforcing steel in concrete which is not under strain by chlorides. Concluding from that the principles of protection following the guidelines of the German Committee for Reinforced Concrete will be presented. The protection principle "W" will be addressed in particular which simplistically means that thermal insulating measures resp. coatings on concrete surfaces already damaged by corrosion result in a protection against further corrosion. The limits of efficacy of coatings will be referred to. [source] Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen.BETON- UND STAHLBETONBAU, Issue 7 2006Physikalische Beanspruchungen, Planungsgrundlagen, alternative Beschichtungsvarianten Nach DIN 1045-1 müssen direkt befahrene Parkdecks mit zusätzlichen Maßnahmen ausgeführt werden, zu denen man unter anderem rißüberbrückende Beschichtungen mindestens der Klasse OS 11 nach Instandsetzungsrichtlinie des DAfStb zählt. Die auf dem Markt verfügbaren rißüberbrückenden Beschichtungssysteme mit Allgemeinem bauaufsichtlichem Prüfzeugnis sind für die Beschichtung von Betonoberflächen mit extremen Wassergehalten (Wassersättigungsgrade bis 90 %), wie sie häufig in Bodenplatten Weißer Wannen vorkommen, nicht geeignet. Schadensfälle aus der Baupraxis zeigen, daß gelegentlich an eignungsgeprüften OS-11-Systemen osmotisch induzierte Blasenerscheinungen, vorzugsweise bei rückseitig durchfeuchteten Bodenplatten wasserundurchlässiger Tiefgaragengeschosse, auftreten. Daher werden die physikalischen Beanspruchungen der Beschichtung (osmotische Transportvorgänge, Kapillardrücke, hydrostatische Drücke und Gasdrücke) quantitativ abgeschätzt und dem Leistungsvermögen (Beanspruchbarkeit) der marktüblichen Systeme gegenübergestellt sowie alternative Beschichtungsvarianten vorgestellt. Ferner werden baupraktische Empfehlungen zur Vermeidung von Beschichtungsschäden erläutert. Coatings on directly vehicle-carrying floor slabs of watertight concrete constructions in underground carparks physical stresses , design codes , alternative coating systems According to DIN 1045-1 directly vehicle-carrying park decks have to be realized with additional measures (crack-bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack-bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11-systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given. [source] | ||||||||||