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In the middle of the last century the carbonation of concrete was an important issue. The damages then occurred, caused by the corrosion of the reinforcement, led to corresponding improvements of the standards. Due to changes in the cement and concrete market the durability of concrete is now again in the centre of attention. Thereby the performance of concrete has to be assured increasingly by testing. The present paper deals with the testing of the carbonation resistance of concrete. It is shown that the test with 4 % CO 2 is feasible and allows evaluating various factors. Furthermore, results on the influence of curing, preconditioning (pre-treatment) as well as of the relative humidity are presented. Copyright © 2012 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

Bisschop J.,ETH Zurich | Bisschop J.,TFB AG | Kurlov A.,ETH Zurich
Cement and Concrete Research

A flow-through method for measuring dissolution rates of cement minerals is described. The quantity of dissolved material is measured after the dissolution experiment from SEM-BSE images. This makes it possible to measure dissolution rates of individual phases in multiphase cements. The SEM images also directly show if precipitation (hydration) occurred and how the surface roughness changed during dissolution. Furthermore, the method is designed for the purpose of determining if dissolution rate is reaction- or diffusion-controlled, by changing water flow rate or by calculating expected diffusion fluxes. Dissolution rates of flat-ground Portland cement clinker and synthesized alite in deionized water were measured to demonstrate the potential of the method. Initial dissolution rates at lower flow rates were transport-controlled as indicated by the flow rate dependency and predicted diffusion fluxes. The highest alite dissolution rate measured in this study was 93 μmol/m 2/s. © 2013 Elsevier Ltd. Source

Torrent R.,Materials Advanced Services Ltd | Denarie E.,Ecole Polytechnique Federale de Lausanne | Jacobs F.,TFB AG | Leemann A.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Teruzzi T.,University of Applied Sciences and Arts Southern Switzerland
Materials and Corrosion

It is recognized that most damage to reinforced concrete structures is caused by insufficient durability rather than by low strength. In most cases, the quality and thickness of the cover concrete (covercrete) determine the service life of the structure. Since the quality of the covercrete is influenced, not only by the mix composition, but also by the placing and curing conditions, it is appropriate to measure the achieved properties on the structure rather than just on separately cast specimens. Swiss Standard SIA 262 on Concrete Construction recommends checking the impermeability of the cover concrete on site. With that aim, a non-destructive method to measure the air-permeability on site has been standardized (SIA 262/1 Annex E). A team of Swiss experts was appointed by the Swiss Federal Highway Administration (ASTRA) to prepare recommendations for specifying, measuring, and assessing the conformity of the air-permeability kT. This paper describes these recommendations covering: (a) specification of limiting values of kT as function of the exposure class; (b) sampling of the measurement points; (c) testing (including suitable temperature and moisture conditions); (d) evaluation of conformity with specified values; (e) expected impact on service life. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Hunkeler F.,TFB AG | Muhlan B.,Tiefbauamt Kanton Graubunden | Ungricht H.,Tiefbauamt Kanton Graubunden
Beton- und Stahlbetonbau

The use of inhibitors is considered worldwide as a technically and economically interesting alternative to the conventional repair of reinforced concrete structures since the removal of concrete can be considerably reduced or completely omitted. In this contribution the results of practical laboratory investigations are presented (active, e.g. ongoing corrosion, different concrete cover depths and chloride contents of the substrate or "old concrete", macroelement effect). None of the three tested systems was able to reduce the corrosion rate or to stop the corrosion. © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

In order to achieve the goals for a sustainable development, concrete with recycled aggregates (concrete and mixtures from concrete and masonry, e.g. clay bricks and calcium silicate blocks etc.) is going to be used more and more in the future. Due to its thermal insulating properties, the demand for concrete with light-weight aggregates (e.g. foam glass) will also increase. As an essential element of this development, an increasing amount of cements with a reduced clinker factor as well as of mineral additions such as fly ash and ground granulated blast furnace slag is used for concrete production. Therefore, as a general tendency, the carbonation resistance of concrete mixes decreases while the risk of corrosion damages increases. The goal of the investigations described in this paper was to evaluate and to assess the corrosion resistance of a stainless rebar (Top12, composition corresponds approx. to steel grade 1.4003) in various carbonated concrete mixes and to compare the results with common rebars. The results lead to the conclusion that, in contrast to common rebars, Top12 is durable in all investigated concrete mixes, including strongly carbonated recycling concretes. Copyright © 2010 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

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