Examination of Air Entrainment Stability Factors of Pumped Concrete (1254-3F)

Pumping of concrete can be an economical and versatile method of placement. However, the mix design process of a pumpable concrete should account for factors construction site, such as difficulty in pumping, blockages, air loss, and changes in the air void system of the concrete. These problems are addressed on a fundamental level to provide a basis for construction guidelines to avoid or minimize such problems during pumping operations.|The air entraining mechanism and the instability of the air void system in the fresh concrete is detailed. The various factors such as resistance to flow, flow velocity of concrete, and pressure on concrete are examined in terms of workability, pumpability and the air loss mechanism. The mechanical and pressure aspects of air loss and changes in the air void system are discussed in detail.|Factorial designs are used to formulate an empirically based prediction model for air loss based on the factors, such as, Coarse Aggregate Factor (CAF), Intermediate Aggregate (IA), type of Air Entraining Admixture (surface tension), and the pumping boom angle. The effect of surface texture and shape of the aggregate in terms of workability and pumpability is examined. Linear traverse results are analyzed to study the effect of pumping on the air void characteristics.|Optimized mix design concepts lead to reduced flow resistance, reduced pumping pressures by improving workability characteristics, avoid or minimize pumping difficulties and improve construction productivity.