EFFECTS OF CONSTRUCTION WORKS AND MIX PROPORTION ON QUALITY OF COVER-CONCRETE

Abstract

 The quality of structural concrete, which is affected by the execution conditions of construction works such as casting and consolidation method, is different from test specimens. Durability of concrete structures depends on the mass transfer resistance of cover concrete. Therefore, the quality of the cover concrete is very important for ensuring the concrete structures' durability. Currently, effects of concrete types and construction for the mass transfer resistance is not understood quantitatively.
 This study investigates the influence of bleeding of concrete, re-vibration, arrangement of steel bar, and change of mix proportions on quality of cover-concrete. As a result, it was clearly shown that the surface air permeability at the upper layers was larger than the lower layers, and the variation in height could be explained by the bleeding quantity of concrete. When examining the effect of reinforcement, it was found that the presence of reinforcement reduced the amount of coarse aggregate of cover concrete which caused an increase in air permeability. However, there was less vertical variation in the air permeability when using reinforcement than without reinforcement. This may be due to the reduction of consolidation by self weight as a driving force for bleeding due to the resistance of reinforcement and formwork. In addition, the improvement of surface air permeability by re-vibration after casting was quantitatively shown, as the effective time of re-vibration after casting depends on the properties of concrete such as slump.