Viscoelastic Characterization of Equivalent Lubrication Layer for High Shear Applications

Pumping is a high shear process used in the placement of concrete. The lubrication layer (LL), a thin layer of micromortar, forms at the inner periphery of the pipe during the pumping of concrete, facilitating its movement inside the pipe. Although this process is essential for effective concrete placement, challenges arise during interruptions, prompting a shift in focus toward understanding the behavior of concrete at rest in the pipe. This shift led to the exploration of the structural buildup properties of the equivalent LL during concrete pumping operations. The investigation systematically considers the influence of various factors, including supplementary cementitious materials [fly ash, ground granulated blast-furnace slag, and limestone calcined clay (${\mathrm{LC}}^2$)], the water-to-binder ratio ($\mathrm{w}/\mathrm{b}$), and the addition of superplasticizer (SP) on the LL’s structural buildup properties (percolation time and structuration rate). The research highlights a significant finding: a higher deformation ratio in the lubrication layer benefits concrete at rest during pumping interruptions. For instance, the optimized superplasticizer dosage in slag-based LL mixtures offers a handling time of 30 min, whereas ${\mathrm{LC}}^2$-based mixtures provide an extended 45 min for managing potential pumping interruptions. Intermittent shearing tests revealed negligible formation of hydration products, confirming the dominant role of colloidal interactions in the structural buildup of the LL. The study also addresses potential anomalies in investigations and analyzes the evolution of the structuration rate, providing a comprehensive understanding of the viscoelastic properties of cementitious suspensions. In a broader context, this work significantly contributes to our fundamental understanding of the lubrication layer’s behavior in high shear applications like concrete pumping. Beyond academic insights, the findings hold practical implications for optimizing concrete pumping operations and ensuring smoother resumption after interruptions by providing an informed time for managing potential interruptions, thereby enhancing the overall efficiency of construction processes.