Effects of Aggregate Content on Rheological Properties of Lubrication Layer and Pumping Concrete

The lubrication layer plays a governing role in predicting the pumpability of fresh concrete. The effects of aggregate content on the rheological properties and formation of the lubrication layer were determined from the measurements of the sliding pipe rheometer, tribometer, and mortar rheology. The performance indexes of fresh concrete, including its rheological properties and workability, were investigated in parallel to fully characterize the impact of aggregate content on the pumpability of concrete. The results show that there is an optimal sand-to-total aggregate ratio (sand ratio) that yields the best rheological properties of the lubrication layer and pumpability of concrete. They also improve with the increase in paste-aggregate (PA) ratio. The shearing degree of bulk concrete is affected by the aggregate content, which leads to different formation processes of the lubrication layer. The rheological properties and workability of concrete are improved with a moderate sand ratio and an increased PA ratio due to the change in thickness of the paste layer on the surface of aggregate particles. The thixotropy of concrete is affected by the aggregate content. Moreover, the formation of the lubrication layer and its rheological property evolution depend on the measurement systems.