Research On Regularity And Control Of Bleeding Of Fresh Concretes

The range of the dormant time of concrete which is defined as t0and the initialbleeding speed which is defined as s in bleeding formula is defined through researches onconcrete bleeding. It made the classification of concrete bleeding more reasonable.Researches of correlation between slump and bleeding of concrete with differentbleeding type show that the bleeding rate and fluidity are of a positive relation, and thebleeding rate will show a sudden increase point as the slump increases.It is concluded from experiments of concrete bleeding that relatively waterconsumption is the key factor which decides the concrete bleeding rate of rapid or slowwhile the other conditions keep the same, and the sand ratio decides when the bleeding ofconcrete will show. It also shows that when high medium w/b is applied in concrete, ifthe w/p is between36%~39%, fresh concrete shows excellent workability and the contentof bleeding is low. It can also reduce the water consumption, initial bleeding rate and thelimited content of bleeding through the application of water-reducing admixture, andmeanwhile improve the workability of concrete.It can also be confirmed from testing results of workability of concrete withdifferent bleeding types that workability of concrete with early-rapid and early-slowbleeding rate is bad, while concrete with late-rapid and late-slow bleeding rate shows thatexcellent workability and fluidity whose pump-ability is good. However workability ofconcrete with late-slow bleeding rate and the fluidity being less than100is somewhatless. Concrete with late-slow bleeding rate shows less plastic shrinkage and settlement,and is less harmful to concrete. The compressive strength of concrete with early-rapid,early-late, and late-rapid bleeding rate is less than designed, while concrete with late-rapid bleeding rate gained higher compressive strength than expected. Analysis on poresin concrete shows that concrete with late-rapid gains the worst property and the propertyof concrete with late-slow bleeding rate is the best.