Experimental investigation of flow of fresh self-compacting concrete in improved L-box

• Flow observations by both improved L-box and image processing technique are operated.
• The stable flow surge profile is assumed to be divided into six flow zones.
• A stable laminar flow zone is highlighted for further rheological solving.
• An empirical fitting model of stable flow depth profile with distance is developed.
• The improved L-box test is also available to test workability parameters.

To approach the rheological testing method based on L-box test for obtaining internal rheological parameters of fresh self-compacting concrete (SCC), an improved L-box without fiber bars and end wall is developed, and a flow investigation utilizing an image processing technique is operated. Specifically, the improved L-box test method is able to accurately reconstruct the process of free-surface evolution of fresh SCC when it is suddenly released in an open channel. The process involves the dam-break problem and open channel flow problem. In addition, by applying the image processing technique, the flow of fresh SCC in improved L-box (i.e. the front position of time-dependent and surge profile evolution), is easily observed and analyzed. By analyzing the experimental results, we conclude the time-dependent flow front position is governed by two regimes: an inertial regime and a pseudo-equilibrium regime. The flow surge plane is assumed to be divided into six flow zones (at the surge profile during the stable flow in pseudo-equilibrium regime). Simultaneously, a stable laminar flow zone is highlighted for further rheological solving. Additionally, by considering the fact of the most of the depth profiles in stable flow are convex curves in the experiment, a crude empirical fitting model is developed, and then the process of physical interpretation and verification is given. The comparison of results among improved L-box test and other tests shows that the improved L-box test is also available to test the workability parameters (i.e. penetrability, fillibility, et al.). Hence, this work is of significance for the further theoretical analysis and numerical simulation on the flow behaviors of the fresh SCC. The work may also interest the researchers who try to develop a convenient testing method in order to determine the rheological parameters of fresh SCC.