INFLUENCE OF PUMPING ON THE AIR-VOID SYSTEM OF HIGH-PERFORMANCE CONCRETES

摘要

This paper presents the results of an experimental study aiming to assess the influence of pumping on the air-void system of high-performance concretes. In a first series of laboratory tests, concrete mixtures having different water to cement ratios (0.45, 0.35, and 0.25) were placed in a pressurized vessel and subjected to a water pressure ranging from 1.4 to 5.5 MPa. In a second series of tests, an ordinary concrete (W/C = 0.43) and a high-performance concrete (W/C = 0.30) were both pumped at a job site using different pumping set-ups. For both series of tests, the characteristics of the air-void system were recorded before and after the pressurization, or the pumping. The results of the laboratory tests clearly indicate that the value of the spacing factor increases linearly with the pressure irrespective of the water to cement ratio. However, the results obtained at the job site reveal that pumping was much more detrimental to the high-performance concrete than to the ordinary concrete. This is most probably due to the poorer initial air-void system of the high-performance concrete. The test results also suggest that the stirring of concrete, during and after pumping, helps to reduce the detrimental influence of pumping by subdividing the remaining larger air voids.