The paper presents an overview of modern Non-Destructive Testing methods that can be applied for concrete integrity evaluation, with particular attention paid to bridges. Assessment of "in-situ" quality of concrete and its integrity is primarily concerned with the current adequacy of the existing structures and their future performance. Routine maintenance needs of concrete structures are now well established and increasingly utilize "in-situ" NDT-testing to assist lifetime predictions. Such approach allows evaluating the basic concrete composite properties and makes possible to answer several questions, which seem to be crucial for engineering practice. Among other things, "Impact-Echo" and "Impulse Response" seem to be one of more promising diagnostic techniques for structural integrity testing of concrete structures. The general principles of these advanced testing methods are discussed. Among other things, it has been shown that Impulse-Response can be used for fast screening of large areas of concrete structures with the purpose to control their structural integrity and to determine local areas with possible flaws for subsequent detailed analysis, e.g. by the impact-echo, ultrasound shear waves or by invasive inspection with drilled cores. Main evaluation parameters have been discussed and general recommendations for proper interpretation of obtained results were proposed. Practical applications of these methods have been discussed as well.
The influence of two types of silica fume (SF) on the rheological properties of cement pastes with water-cement ratios typical of very high performance concrete was investigated. The sensitivity of cement to the sulphonated naphthalene formaldehyde type of superplasticizer (SP) and its optimum content was determined from apparent viscosity as afunction of three parameters. It was found that the values characterizing apparent viscosity of the pastes depend non-linearly on the amount of C3A, and that the relation is linked to the content of free CaO in cement. Values of pH for the cement suspensions are also highly correlated with the content of free CaO, and may be regarded as an indicator for selection of cements that have good workability with SP. The quality of SF had no significant influence on the rheological behaviour of the cement pastes with SP that had the lowest content of C3A, free CaO and alkalis. For all the cements with higher contents of these components, a decrease in viscosity was observed only after the addition of the lower reactivity SF. It has been proved that SF can improve the efficiency of the SP and may reduce the water content provided that its reactivity is limited. The chemical processes at the beginning of hydration are restrained by the same phenomenon.
The subject of the paper is north dome of the Four Domes Pavilion in Wroclaw, which was erected according to the project by architect Hans Poelzig in 1913. The geometry of the dome (plan, rise, thickness) has an essential influence on the stress distribution in the structure and may be a crucial factor determining the cracking pattern. The results of the study of archival documents and numerical analysis indicate that there is a need for increasing the bearing capacity of the structure. After carrying out 3D FEM analysis, it was decided to apply strengthening technology based on the FRCM system with carbon and P.B.O. fibers on the surface and on the external ring of the dome.
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