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Alkali-silica reaction (ASR) is a serious Problem concerning the deterioration of concrete. This leads to significant maintenance and reconstruction costs for concrete infrastructures all over the world. The geographical regions, which play a major role in concrete deterioration, are for example coastal Areas or in general, areas with a high air humidity/salinity due to closeness of rivers or lakes.
These exemplary results show, the application of Raman spectroscopy establishes a valuable approach for characterizing the chemical and structural composition of ASR-products. The results prove the potential to trace the kind of reaction products, developing in dependence on the aggregate and to follow up its local alteration from origin of the gel.
The concrete prism test at 60°C facilitates accelerated testing of alkali-silica reactivity of aggregates within five months. Manual measurement is usually conducted to determine expansion of test specimen every 28 days. This conventional procedure gives only limited insight to expansion behaviour of ASR-affected prisms. Due to the large time intervals, expansion exceeding the critical value of 0.3 mm/m is likely to be noticed late. Continuous recording applied in this work resolves this problem and delivers beneficial information on the shape of the expansion curve.
Different types of aggregate have been tested applying continuous and manual measurement to the concrete specimens.
Models of ASR-induced expansion, available in the open literature, so far are validated with discontinuous data hardly tracing the modelled curve. Continuous measurement improves validation and further model development.
A significant number of German concrete motorway pavements have shown damage only a few years after construction. The alkali-silica-reaction (ASR) is often one of the reasons for this damage. German guidelines and regulations focus on the optimisation of the concrete composition to avoid damage due to ASR. Moreover, diverse research projects have dealt with the development and optimisation of ASR performance test methods with and without external alkali supply. However, the influence of other parameters on the occurrence and intensity of a damaging ASR had not yet been taken into account. Such parameters include, e.g., insufficient curing and the modifications of concrete’s porosity due to the use of slip form pavers. Likewise, the increased traffic loading had not yet been considered. The Federal Institute for Materials Research and Testing (BAM) assesses these parameters and processes in a number of projects. These projects aim primarily to increase the durability of the concrete pavements, in particular by improving preventive measures that may be taken before or after the construction of concrete pavements. This paper gives a short overview of BAM’s projects concerning ASR in concrete pavements. Furthermore, results regarding the influence of the cyclic traffic loading on ASR are presented.
In recent years the German highway network has seen an increase in the occurrence of damage in concrete road surfaces which can be attributed to the alkali-silica reaction (ASR). In view of the often drastic reduction in life expectancy experienced by concrete pavements due to ASR, research activity in this field has notably increased. Until now the main research focus has been, alongside preventative measures in concrete technology, the development of performance-oriented testing procedures for ASR prevention. This included more specifically the accelerated simulation of climatic effects and external alkali supply on concrete pavements. The effects of pre-damage from the additionally interacting cyclic traffic loading had previously not been taken into consideration.
Since 2011, a five-partner research group from the German Research Foundation has been pursuing research on the effects of simultaneous cyclic loading and external alkali supply on the destructive ASR in concrete pavements. The depiction of the myriad degradation and transport processes necessary for an understanding of these effects requires a close interaction between experiments and their multi-scale modelling. This contribution aims to focus on the aforementioned experiments by means of innovative testing techniques. The research is founded on a series of cyclic fatigue tests performed on large-format beams, both with and without previous application of a NaCl solution, with simultaneous tracking of crack development. Thereafter, smaller test specimens were extracted from the pre-damaged beams for further experiments. These included the spatial visualization and quantification of fatigue-induced cracks with X-ray 3D-computed tomography. Additionally, the effects of fatigue-induced cracks on moisture and alkali transport were investigated using 3D-CT and Laser-Induced Breakdown Spectroscopy (LIBS). Subsequent storage of the small-format test specimens, with and without cyclic pre-damage, in an ASR-conducive environment was then able to shed light on the influence of fatigue-induced pre-damage on the ASR.
Die Laser induzierte Breakdown Spektroskopie (LIBS) bietet für die Analyse heterogener, mineralischer Baustoffe, wie z. B. Beton, deutliche Vorteile gegenüber konventionellen Methoden. Sie ermöglicht neben der Quantifizierung von Elementgehalten und -verteilungen im Baustoff auch die Differenzierung von Elementkonzentrationen innerhalb einzelner Phasen im Baustoff. So können beispielsweise die für die Alkali-Kieselsäure-Reaktion (AKR) interessanten Natriumkonzentrationen bestimmt und hinsichtlich ihrer Verteilung aufgelöst werden. Es lassen sich Natriumgehalte, welche sich in der Gesteinskörung befinden, separat von denen der Betonmatrix bestimmen. Der vorliegende Artikel befasst sich mit den Vor- und Nachteilen von LIBS als alternative Methode für die chemische Analyse von Baustoffen. Anhand von Beispielen aus der Praxis wird der derzeitige Stand der Technik dargestellt und ein Vergleich mit etablierten Messmethoden vorgenommen. Compared to conventional methods the Laser Induced Breakdown Spectroscopy (LIBS) provides significant advantages for analysis of heterogeneous, mineral building materials as e.g. concrete. Besides providing the possibility to quantify element concentrations and distributions in building materials, this technique enables also to differentiate concentrations within different phases of the material. It is possible to determine sodium concentrations and distribution directly, which e.g. is important when regarding Alkali-Silica-Reaction (ASR). Sodium contents provided by the aggregates can be distinguished from those provided by the concrete matrix. The present article is concerned with the advantages and disadvantages of LIBS as alternative method for chemical analysis of building materials. On the basis of samples from practice the current state of the art is shown and different measurement techniques will be compared.