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Real bridge structures are affected by environmental conditions. The environmental loads in time cause the degradation of concrete and reinforcement. The diagnostics of real state of existing bridges are very important due to actual degradation and corrosion. In the frame of research activities of Department of Structures and Bridges, Civil Engineering Faculty, University of Žilina, the real bridge structure was observed for a few years. It is girder reinforced concrete bridge near town of Žilina in Slovakia. The results of diagnostics which focused on reinforcement corrosion are presented. The paper deals with reinforcement corrosion and its influence on the moment resistance of the existing concrete structures.

The article presents experimental analysis of concretes mixed by using natural and low quality recycled concrete aggregate (RCA) Roman JaskulskiWarsaw University of Technology Branch in Płock, Poland e-mail: romanjas@pw.plock.pl Miroslav BrodnanUniversity ofZilina, Slovakia e-mail: brodnan@fstav.uniza.sk IntroductionIncreasing the use of recycled concrete aggregate (RCA) and supplementary cementitious materials (SCM) in concrete industry can considerably enhance the environmental friendliness of concrete production. The availability of natural sources of aggregates, which makes up about 60%-70% of concrete volume, is becoming more limited due to restrictions on quarrying operations and longer hauling distances. The disposal of old concrete, which remains from demolished structures, is still a problem and frequently it is deposited in the landfills [1]. So a growing trend to replace the traditional concrete constituents with more sustainable materials is increasingly present in concrete technology. Using RCA as a substitute for natural aggregates and SCM as a partial cement replacement in concrete mixtures is a way to potentially address the economic and environmental concerns. Dosho 2007 [2] wrote about papers on recycled aggregate concrete that has been published just after World War II: physical properties by Glruzhge in 1946, Russia, and the influence of mixture impurities by Graf in 1948, Germany. First detailed test results on application of the RCA in concrete technology were published by Nixon in 1978 [3]. He suggested that the main field in which more information about the behaviour of the recycled concrete is required is its durability. The studies on the application of RCA into concrete mixture have mainly concerned mix design [4,5], mechanical properties [6][7][8], structural performance [9,10] and the final purpose [11,12]. Until now many of the durability parameters have been investigated and technological recommendation and detailed requirements according to quality of RCA has been drawn [13]. It has been stated that is possible to design and prepare durable concretes by using adequately good quality RCA. The aggregate characteristics of density, porosity and water absorption are a primary focus in determining the proper concrete mixture and the required concrete properties. These characteristics should be known to limit water absorption capacity of aggregates to no more than 5% for structural concrete, and thus the proportion of RCA is often limited in concrete mixes [13,14].Most of the research concerning RCA quality and the durability of concrete mixed by using RCA has been performed in

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