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To date, only 1 746 bridges have been reported to collapse due to various effects. Of these accidents, 1 001 are due to hydraulic causes (friction, leaching), 520 collisions or overloads, 52 fires and only 19 times an earthquake caused the damage. Currently, there is no standard specifically developed for the fire behaviour of bridges. Therefore the designer can decide what methodology he wants to use during the design process. Two bridge fires have occurred in Hungary over the past three years. In this paper, the authors present the experiences of the fire investigation and the suggestions for the restoration.

The porosity of concrete affects the durability of reinforced concrete structures, wherein high levels of porosity are linked to a shorter service life. Recent works have noted that high porosity levels naturally exist in the aftermath of a fire exposure - especially when concrete is classified as high strength concrete (HSC). To shed more light into this phenomenon, this paper showcases a method for measuring the porosity of HSC under elevated temperatures through scanning electron microscopy (SEM). In this method, SEMbased images were examined to quantify the surface porosity of fire-affected HSC. Detailed image analysis was performed for HSC exposed to various heating durations. The study concludes that the surface porosity obtained via the SEM processing method is in good agreement with that from the SEM-based method (with a minor average difference of 3.8%). As such, the proposed method is expected to be reliable for the porosity analysis of fire-damaged concrete. [ABSTRACT FROM AUTHOR]

The strength properties of concrete are significantly influenced by the type of binder used. In the case of cement, the use of cement-containing admixtures (CEM II) is becoming increasingly popular from a durability and environmental point of view. The first question was how cements containing different admixtures behave and how their compressive strength changes under high temperatures (fire). First, the experiments were carried out with the cement tests, and then the concrete specimens were checked for the extent to which the addition of admixtures modifies the favourable effect measured for cement. Under thermal loading, the value of the residual compressive strength of the cement paste increased with the addition of the admixture content. The results of the compressive strength test and the developed crack patterns were consistent with each other. The most severe cracking was observed in the Portland cement specimens, and the decrease in strength was also the most significant. Based on the results of the cement tests, several types of cement were used for the concrete tests. The second research question was: Which concrete recipe has the lowest specific ecological footprint? Therefore, for each formulation, the specific ecological footprint is crucially influenced by the type and amount of substitute used, as their specific CO2 emissions are typically lower than those of Portland cement. Based on our previous studies, a reduction in the specific ecological footprint of up to 10 % can be achieved by using substitutes. The novelty of our research lies in the combined use of fire resistance and ecological aspects, which helps to select a formulation with better technical properties and, at the same time, more sustainable. [ABSTRACT FROM AUTHOR]

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