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The influence of the curing methods on the flexural performances of the milling steel fiber reinforced ultra-high-performance concrete (UHPC) with a high fiber content was systematically evaluated in this study, alongside the flowability and compressive strength. The UHPC specimens were subjected to standard curing and steam curing, employing three steel fiber reinforcing schedules: single milling fiber, single straight fiber, and a combination of both. The flowability of the UHPC was found to be less affected by the milling fiber compared to the straight fiber. Steam curing significantly enhanced the compressive strength but had a slight negative effect on the flexural behavior. However, this adverse effect could be mitigated as the fiber content increased. The flexural strength and toughness of the UHPC with milling fiber were minimally influenced by steam curing, suggesting that standard curing was sufficient for the milling fiber-reinforced UHPC. Conversely, steam curing exhibited an improvement in the flexural behavior of the UHPC containing a hybrid combination of milling and straight fibers. In addition to developing an empirical model for compressive and flexural strengths, we proposed a data-driven model called Gaussian process regression (GPR) to predict the flexural behaviors of the UHPC with varying fiber content, types, and curing methods. The data-driven model demonstrated high accuracy, with an R2 value of 1.0 when compared to the experimental data. [ABSTRACT FROM AUTHOR]

• Develop a new algorithm for rapid aggregate placement based on optimal positions identified by skeleton theory. • A three-dimensional real aggregate model is established by means of voxelization. • Accurately simulate the mechanical damage of natural and recycled aggregate concrete. A new aggregate placement algorithm has been developed that can automatically identify the remaining space after the aggregate is placed, and only new aggregates are placed in these spaces. This results in a reduction in the number of overlaps with existing aggregates, and the more aggregates placed, the higher the efficiency. This method is suitable for various types of concrete, such as ordinary aggregate concrete, recycled aggregate concrete (RAC), and fiber-reinforced concrete. Finite element analysis is applied to simulate stress and damage evolution in mesoscale models of concrete, taking into account the effects of actual aggregate slenderness ratio, concavity, flatness, asymmetry ratio, and compaction degree. The study reveals that tensile damage is the primary factor in concrete damage evolution up to peak stress, with both tensile and compressive damages influencing the post-peak behavior. In RAC, older Interfacial Transition Zones (ITZs) are found to be more susceptible to early damage than newer ones. Moreover, the model effectively illustrates the influence of recycled aggregate content and concavity on concrete's mechanical properties. This mesoscale concrete modeling method, as developed in this study, holds potential for future research on various types of concrete. [ABSTRACT FROM AUTHOR]