Simulation of U-box test for fresh self-compacting concrete based on lattice Boltzmann method

Abstract

• The 3-D model of the U-box test is successfully established based on H-B model and LBM with an average error of 7%. • The yield stress is the key rheological parameter that determines the passing performance of fresh SCC. • The increase of rheological parameters all reduce the flow ability of fresh SCC. • The rheological features made a greater impact on the average surface pressure of the steel bars at the start of U-box test. • The speed of pulling up the partition gate only had an influence on the early period of U-box test. In this research, the numerical model of fresh self-compacting concrete (SCC) U-box test was established by combining lattice Boltzmann method (LBM) and Herschel-Bulkley (H–B) model. The flow behavior of fresh SCC in U-box was studied and its rheological mechanism was analyzed. The test results showed that the simulation model established based on U-box test had high simulation accuracy, and the average error was about 7 %. The effects of rheological parameters (power-law index n , consistency index k and yield stress σ 0 ) on the U-box test were explored. The numerical results demonstrated that σ 0 was the crucial rheological parameter that determined the passing ability of fresh SCC, and its increase resulted in weaker passing ability . n and k had less effect on the passing ability. At the early stage of U-box test ( t < 1.0 s), the increase of n , k and σ 0 all reduced the velocity of flow and the pressure exerted on the fresh SCC, with n bringing the most significant effect. The peak velocity and pressure of shear-thinning ( n = 0.6) SCC could reach 0.74 m/s and 4200 Pa at t = 0.1 s. The peak velocity of shear-thickening ( n = 1.4) SCC was less than half of the former, and a larger negative pressure appeared, up to about −1600 Pa. The speed of pulling up the partition gate ( u g ) only had an effect, which gradually diminished with the increase of u g , on the initial phase of U-box test ( t < 5.0 s). The cross-sectional area corresponding to the obstacles that could be passed by the SCC was the main factor affecting the early velocity and pressure of the concrete.