Concrete Pumping Blockages in CFA Piling-PPT Presentation

PPT Presentation
Pdf Summary
The presentation examines concrete pumping blockages in continuous flight auger (CFA) piling, focusing on how concrete properties, aggregate grading and air in delivery lines may contribute.<br /><br />Concrete rheology describes how fresh concrete flows, particularly its yield stress and plastic viscosity. Aggregate size, shape and total surface area influence workability and pumping friction. James Blackwell’s modelling suggests that workable mixes may have around 8,000–9,000 m² of aggregate surface area per cubic metre. More fluid concrete can reduce friction, but may also increase segregation risk. The presentation notes differences between UK and Australian aggregates, including typical particle size and shape.<br /><br />A proposed blockage mechanism involves particles settling in the line while air rises and travels through the concrete. Air may displace lighter material, form pockets and move heavier aggregate, contributing to blockage. Swansea University laboratory work used a 1:30 scale model to investigate line clearing. Preliminary observations indicate that a sponge ball may not form an effective air barrier: air can pass around or through it and flush out the fluid’s upper layer. Results may also be affected by delays during cleaning and static segregation.<br /><br />Site incident reports describe highly compressed air trapped between blocked sections of concrete, with air having penetrated the concrete and the sponge ball failing to contain it. Possible causes include air entering the concrete and concrete itself blocking the line. Contributing factors may include hose length and friction, concrete head pressure, fluidity and ineffective cleaning.<br /><br />The presentation also highlights mix-design challenges: highly fluid concrete can become thixotropic when stationary, while low cement content and finely ground slag may increase viscosity. The speakers identify aggregate grading, paste volume and concrete fluidity as important considerations, and propose a UK aggregate sieve as a potential response.
Keywords
concrete pumping
blockage
continuous flight auger
CFA piling
rheology
aggregate grading
air entrainment
segregation
thixotropy
mix design