DOUBLE MIXING EFFECTS OF FRESH CEMENT PASTE

It was found that bleeding of fresh cement paste mixed with the same final water cement ratio is strikingly changed with divided addition of water each addition being followed by mixing (referred as double mixing: DM). Depending upon the amount of water which is added at the first stage mixing (referred as the primal water: W1), bleeding of the cement paste can be minimized or maximized. In this paper, mechanism of these DM effects and influences of various factors, such as fineness of cement, mixing time, type of mixing water, temperature and chemical components of cement etc., on the DM effects were experimentally investigated. From these experiments it was suggested that the double mixing effect is not only associated with physico chemical interaction between liquid and cement powder but also with chemical reaction of cement particles with water and electrostatic charge of cement particles that might be related to the early stage chemical reaction of cement with water.