Bleeding of Fresh Concrete Containing Cement Supplementary Materials

Plastic cracking of concrete such as plastic settlement and plastic shrinkage cracking is directly related to the bleeding of concrete, which is a natural time-dependent process in a fresh concrete mix. A portion of the mixing water together with very fine materials finds its way to the surface of the concrete during this process. The rapid rate of initial bleeding slows down with the elapsed time and the bleeding process may continue to occur for a period up to 2 hours. When the concrete is placed by pumping it is become necessary to have control over the bleeding capacity to achieve stable concrete mixes under pressure. Both the bleeding rate and bleeding capacity of concrete are affected by the amount of very fine materials in concrete as well as the mix compositions. This paper reports the results of an extensive study on the effects of binder materials and the mix compositions on the rate of bleeding and the bleeding capacity of freshly mixed concrete. The parameters used in this study were the water content, superplasticer dosage, granulated blast-furnace slag as fine aggregate replacement, fly ash for cement replacement, and fly ash as an addition material. The results obtained with a number of fresh concrete mixes indicated the existence of a direct correlation between the bleeding capacity and the initial bleeding rate. The empirical expression developed will be useful to predict the bleeding capacity based on the initial bleeding rate.