Pressure-dependent friction behavior governing concrete pumping resistance

Concrete pumping resistance has traditionally been treated as a purely hydrodynamic interaction, with frictional effects largely neglected. This study develops a pressure-adjustable coaxial cylinder tribometer (PACCT) to systematically investigate the effects of pressure, flow velocity, particle characteristics, and surface roughness on the frictional behavior of concrete. Results show that pressure increases boundary flow resistance while promoting lubrication layer formation, whereas stable layers formed at realistic pumping velocities significantly reduce the frictional coefficient. Higher coarse aggregate contents and rougher surfaces intensify frictional effects, with temperature rise confirming the role of friction under pressure. Furthermore, within the experimentally accessible pressure range, a power-law correlation between the maximum applied pressure and the apparent friction coefficient was identified. Although direct prediction under full-scale pumping pressures requires further validation, this correlation indicates that pressure-dependent interfacial friction may contribute to nonlinear pumping resistance and provides experimental support for the feasibility of a pressure-dependent frictional framework. This study provides new insights into assessing concrete pumpability from a frictional perspective, supporting further development of pressure-dependent pumpability assessment models.