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Influence of cyclic compressive loading induced degradation of road pavement concrete on harmful AAR In recent years the German motorway network has seen an increase in the occurrence of damage to concrete road surfaces built before 2005, which can be attributed to the alkali‐silica reaction (ASR). In addition to exposure to ASR‐stimulating alkali‐rich deicing‐agents, road surfaces are also subjected to cyclical mechanical loading resulting from traffic and induced stresses due to climatic impact. Such mechanical loadings are not considered in any of the previously developed ASR testing procedures. This cyclical loading could, however, lead to a degradation of the concrete microstructure and, in turn, stimulate the ASR‐process. This article presents investigations that contribute to answering the question of whether a mechanically induced degradation influences the ASR‐process. The hypothesis that the mechanically induced degradation leads to an increase in mass transport is examined. The mass transport is important for the ASR process because the reactants need to be transported to the reaction location before the reaction can take place. Therefore, it is assumed that increased mass transport also leads to increased ASR damage. Concrete specimens made of typical pavement concretes are subjected to a pre‐damaging cyclic compressive loading. The degradation is characterized simultaneously during the pre‐damaging process using non‐destructive testing (NDT) techniques. Then the effects of the cyclical pre‐damage on the mass transport as well as on the ASR are determined by comparing results from test specimens with and without pre‐damage. The results lead to the conclusion that the cyclical pre‐damage increases both the mass transport and the ASR. [ABSTRACT FROM AUTHOR]

Methods for evaluating concrete pavements for a damaging alkali‐silica reaction It is very difficult to plan the maintenance requirements of concrete pavements with alkali‐silica reaction. Up to now, the necessary assessment has been carried out via visual appearance, AKR‐provoking concrete investigations as well as polarization microscopic investigations on thin sections. With these investigations a forecast for the damage development is not possible. It is only possible to assess whether damage is no longer to be expected or whether there is still further potential for residual damage. The often significant deterioration of concrete pavement can be traced back to an undetected horizontal crack formation. In the context of an alkali‐silica reaction (ASR), horizontal cracks can be found in the area of the joint crosses, the transverse joints and the longitudinal joints, which then extend several centimeters into the carriageway slab. The article illustrates the consequences of a damaging ASR and other loads in a carriageway slab. For the first time, it establishes a systematic relationship between a damaging ASR in a carriageway slab and the horizontal cracks in the area of the joints. [ABSTRACT FROM AUTHOR]

Automated ASR Concrete Prism Testing at 60 °C The Concrete Prism Test at 60 °C (60 °C‐CPT) is a common method to evaluate the susceptibility of concrete and aggregates to the Alkali‐Silica Reaction (ASR). This paper presents a new device for an automated version of the 60 °C‐CPT. The system monitors the expansion of concrete prisms automatically. Compared to the conventional test method, effort and time consumption are notably reduced. The nearly continuous recording of expansion signals allows for studying of ASR‐mechanisms in more detail than the conventional test. In addition, the interruptions of ASR‐provoking storage, necessary for manual measurements, are avoided. The presented study compares results of conventional and automated testing of two types of aggregate. In accordance with previous findings, continuously stored prisms generally expand less than the conventionally tested prisms. To find a possible explanation, differences in leaching of alkali from the concrete prisms were quantified. For verifying the alkali‐reactivity of the two aggregates, they were also classified in the fog chamber test at 40 °C, the German reference method. [ABSTRACT FROM AUTHOR]

Creep and mechanical properties of pavement concretes after ASR‐provocative storage Four pavement concretes were subjected to ASR‐provoking storage with the FIB climate simulation concrete prism test which has been developed on F.A. Finger‐Institute for Building Materials Science of Bauhaus University Weimar. Strains, compressive strength, elastic modulus, creep and shrinkage have been determined. The results show, that the ASR‐induced damage process can be described as follows: ASR‐induced micro‐cracking in the cement matrix is rather negligible for compressive strength of concrete. Dissolution processes and cracking in the aggregate reduce the stiffness of the concrete (modulus of elasticity), but not the compressive strength of concrete. The cracks that originate in the rock grain of slow‐reacting aggregates continue into the matrix. With a larger matrix volume and thus increased crack formation, creep is increased. Undamaged concrete shows marginally larger creep under the influence of salt solution (NaCl solution). This indicates a chemical influence of the matrix. [ABSTRACT FROM AUTHOR]

Durable concrete pavements using different binders in top and bottom lift It is a matter of common knowledge that ground granulated blast furnace slag and siliceous fly ash can be used to mitigate alkali-silica-reaction (ASR) in concrete. Nonetheless such materials are seldom used for the construction of concrete pavements in Germany, as their application can impair the deicer-scaling resistance of the concrete. In two-lift concrete pavements a possible approach to avoid this problem is to use cements with a higher proportion of blast furnace slag only in the thick bottom lift, thus minimizing its susceptibility to ASR. The thin top lift, which is subjected to a high level of mechanical and freeze-thaw stress, is still produced with Ordinary Portland Cement, hence ensuring a sufficient deicer-scaling resistance. However, this approach is currently hindered by the German technical standards for concrete pavements, which require the use of the same cement in the top and bottom lift. Furthermore the standards do not permit the application of siliceous fly ash to partly substitute cement in concrete pavements. It was therefore the aim of a research project to obtain the necessary knowledge for assessing potential benefits and risks of a more flexible use of binders in concrete pavements. [ABSTRACT FROM AUTHOR]

Zur Beurteilung der Alkaliempfindlichkeit der Gesteinskörnung finden normativ der Betonversuch mit Nebelkammerlagerung bei 40 °C und alternativ der 60 °C-Betonversuch Anwendung. Als Beurteilungskriterium für den Schädigungsprozess wird bei beiden Verfahren die an Betonprismen diskontinuierlich ermittelte Dehnung herangezogen. Auch bei den zusätzlich in der Nebelkammer gelagerten Würfeln beschränkt sich die Schadensanalyse auf eine diskontinuierliche Verfolgung der maximalen Breite der Oberflächenrisse. Im Rahmen des Beitrags wird eine neuartige, bereits erfolgreich erprobte zerstörungsfreie Prüfmethodik vorgestellt. Diese ermöglicht durch eine gleichzeitige kontinuierliche Dehnungs-, Schallemissions- und Ultraschallmessung eine kontinuierliche Verfolgung der inneren Gefügeveränderungen in den Betonprüfkörpern während der AKR-provozierenden Lagerung. Dabei wurden drei zeitlich aufeinanderfolgende Phasen der inneren Gefügeveränderung mit einer Dominanz von Hydratation, Rissbildung sowie vermutlicher Rissverfüllung mit Reaktionsprodukten identifiziert. Die ablaufenden Rissbildungsprozesse wurden zusätzlich mit diskontinuierlich durchgeführten röntgentomografischen Untersuchungen zeitlich und räumlich visualisiert. Die CT-Befunde wurden durch mikroskopische Untersuchungen bestätigt. Analysis of ASR-induced damage processes in concrete Application of innovative measurement techniques The alkali-reactive potential of aggregates is assessed according to the German guidelines by two different test methods. These are the 40 °C fog chamber storage and as an alternative method the 60 °C concrete prism test. In both tests, the discontinuously measured expansion of ASR-generating stored concrete prisms is used as criterion for the internal damage process. The damage analysis of the cubes additionally stored in the 40 °C fog chamber is also restricted to the discontinuous measurement of the crack width on the cubes surfaces. This paper describes an innovative, already successfully applied, non-destructive measurement methodology. This methodology enables a continuous monitoring of the internal damage processes in ASR-generating stored concrete specimens due to a continuous recording of expansion, acoustic emission and ultrasonic velocity. Thereby, three sequent phases of internal structural changes dominated by hydration, crack formation and filling of the cracks with ASR-gel and/or other reaction products can be detected. The crack formation was temporally and spatially visualised by discontinuously applied X-ray computed tomography measurements. Microscopic analyses confirm the findings of the X-ray 3D-CT. [ABSTRACT FROM AUTHOR]