The Influence of Graded Concrete Strength on Concrete Element

The integrated use of concrete in combination with reinforcement has been acknowledged as a versatile material for structures. The resulting concrete components, whatever their size and shape, are customary assumed to have uniform compression strength and identical mechanical properties over the entire structural component. This contradicts the reality, since in practice the mixing and casting of fresh concrete creates disparities in the mixture and the material composition. The relatively heavier components, i.e. the coarse aggregates, tend to sink to the bottom of the cast, while on the upper surface, however the attempt, bleeding will occur. Further, the concrete surface exposed to the air will undergo a higher evaporation rate when compared to the layers not in direct contact with the air. Also, a relative low surface-area-to-volume ratio will experience a slower evaporation rate when compared to the areas with a higher ratio, the more intense the evaporation, the greater the risk for micro crack formations, and propagation. This research work is aimed to evaluate the actual condition of a relatively deep concrete element, and look into the presence of a gradation in terms of the concrete compression strength. Further, the study was conducted to describe the influence of compression strength gradation as function of element dimensions. For this purpose; two specimen‘s panels sized 60×60×20 cm casted, cured and tested to obtain their compression strength at a variation of layers. The panels were tested at the age 28 days. The testing method involved the rebound hammer readings, the UPV measurement and the direct cylindrical compression tests, performed on specimen's, core drilled from the test panel.