Construction and application of a time-dependent surface energy function for self-compacting concrete mixtures

Abstract

[Objective] To address the difficulty in quantitatively characterizing the flowability degradation and interface bonding evolution of concrete during the construction of hydraulic structures such as cutoff walls, a time-dependent modeling method for concrete interface surface energy based on slump evolution is proposed. [Methods] Multi-age slump and spread tests were conducted to obtain the flowability degradation sequence of the concrete mixture. A three-dimensional particle flow model(PFC), consistent with the dimensions of the physical tests, was constructed. The Johnson-Kendall-Roberts(JKR) contact model was used in PFC to characterize the adhesive behavior between particles. Graded surface energy parameters were assigned to different contact interfaces—mortar-mortar, mortar-aggregate, and aggregate-aggregate—to reflect differences in bonding strength. Under the constraint of macroscopic slump result, a three-parameter Logistic function was employed to describe the time-dependent variation of the mortar-mortar interface surface energy with age. The function parameters were inversely calibrated using a sliced/nested orthogonal array(SOA-AR) design. The obtained γ_mm(t) function was then embedded into the PFC model to realize the time-dependent representation of interface bonding parameters. [Results] Numerical simulation result showed that introducing the time-dependent surface energy function could reproduce the observed age-related slump decline. The inflection point of the fitted curve was consistent with the concrete's initial setting time. After applying the γ_mm(t) function in the casting simulation, the height difference of the concrete top surface was approximately 0.26 m, which was below the 0.30 m limit specified in the code. The predicted normal reaction force at the mortar-trench wall interface ranged from approximately 0.02 kPa to 0.05 kPa, consistent with the order of magnitude of the slurry hydrostatic pressure specified in the code. The result indicated that the model could realistically reflect the flow and deposition process of the mixture and the mechanical characteristics of the interfaces. [Conclusion] The proposed time-dependent interface surface energy function effectively captures the evolution of concrete from a fluid to a setting state and establishes a mapping relationship between macroscopic flowability and mesoscopic bonding properties. The findings provide a feasible approach for the numerical simulation of underwater casting and cutoff wall construction processes involving complex interface behavior, offering a reference for related engineering practice and subsequent numerical analysis.

Keywords

interfacial surface energy / slump / JKR contact model / particle flow simulation / SOA-AR inversion / concrete mixture / influencing factors / underwater pouring