Analysis of the relationship between the L-Box test and the yield stress of fresh concrete: an analytical approach

The objective of this paper is to study the fresh concrete flow in the L-box test, predict the final shape deposit after the flow stoppage, and estimate the yield stress. This is very useful in controlling the concrete casting in real structures, detecting problems and preparing solutions on time. Concrete rheometers, used for concrete rheological parameters measurement, are expensive, not always available and resulting in measurements disparity. To overcome this difficulty, the effective method was to analyze the concrete flow phenomena physically and solve the problem analytically based on L-box measurements. In the first part, fresh concrete is considered as a homogeneous yield stress fluid moving under the effect of its self-weight. By developing the momentum equations for an incompressible fluid, a theoretical approach is proposed to study three probable final shapes depending on concrete rheology. Expressions are established for the final shape and yield stress prediction. In the second part, the obtained results were compared to previous models, and a good agreement was observed giving a good validity. This study can be a consolidation of the rheometers' results, allowing an evaluation and perhaps a calibration to reinforce their validity.