ABSTRACT
This chapter discusses the behaviour of the concrete during each of these stages and how they affect construction practice. The constituent materials of the concrete are of differing relative particle density and therefore while the concrete is in its semi-fluid, plastic state, the aggregate and cement particles tend to settle and the mix water has a tendency to migrate upwards. Segregation involves the larger aggregate particles falling towards the lower parts of the pour, and bleeding is the process of the upward migration or upward displacement of water. Overall settlement of the concrete will result in greater movement in the fresh concrete near the top surface of a deep pour. Bleed water arriving at an unprotected concrete surface will be subject to evaporation. Any tendency to plastic shrinkage cracking will be encouraged by greater evaporation rates of the surface water, which occurs, for example, with higher concrete or ambient temperatures, or if the concrete is exposed to wind.
