## 5 Applications and Outlook
### Mechanical Properties and Dimensional Effects of Aggregates
Periodic boundary conditions enable the UC model to produce higher elastic moduli. Both the increase in sample size and the increase in UC size reduce the boundary effect. The above studies facilitate the rapid design and optimization of granular materials to increase the aggregate capacity for road use. In the future, multiscale numerical simulations can be performed to investigate more complex material properties. Asphal mixtures are a multi-phase system, and the contact parameters of aggregates and asphalt mortar need to be determined separately. [PERSON] et al. [189] investigated the tracking void fraction and distribution of aggregates and asphalt mortar during compaction by establishing an indoor compaction numerical simulation method considering both the critical aggregate particle size and boundary effects and developed a stacking model with binary particle combinations to determine the size limits of fine particles. [PERSON] et al. [190] conducted a three-point bending test for concrete crack openings with similar geometry but different dimensions, combined with digital image processing techniques to observe crack expansion on the specimen surface. They investigated the effect of size effect on crack expansion. [PERSON] [191] established a three-dimensional mesoscale numerical calculation method. It conducted a splitting tensile damage test study on concrete cubic specimens with different lengths, different aggregate contents and maximum aggregate particle sizes. The static and dynamic uniform size effect law can quantitatively predict the size effect of splitting tensile strength of concrete. The size effect is much more pronounced under dynamic than static loading. The compressive strength of the aggregates under dynamic loading is enhanced as the size of the aggregate increases. Consider that at high-strain-rate, the dynamic size effect is minimally affected by the aggregate content. The splitting tensile strength of the concrete is continuously enhanced due to the increased strain rate. Based on ANOVA and Weibull, [PERSON] [192] analyzed the underlying mechanism of dynamical dimensionality reduction in roller-compacted concrete (RCC) materials under impact loading. The dispersion of the stress-strain curves and dynamic increase factors for aggregates at high-strain-rate is more pronounced. The dynamic compressive intensity variance of the specimen deserves to be focused on in subsequent studies. At high strain rates, there is a correlation between the cracking phenomenon and the morphology of the aggregates. The shape of the aggregate belongs to unnatural angles and flatness. This makes the spherical shape not simulate the irregular morphology of the aggregate and cannot characterize the cracking phenomenon. The existence of interconnected structural features of the angular aggregates in the real specimen model allows for enhanced interlocking effects. This also results in some enhancement of the compressive strength and fracture toughness of the aggregate. The effect of aggregate shape on the strength of the specimens is enhanced at higher strain rates. Under external loading, stress concentration occurs within the aggregate particles, leading to structural damage. Along with the increase in strain rate, microcracks appear inside the specimen and gradually expand the rupture surface where cross-cracking occurs. The interaction between the particles is usually manifested as angular fragmentation, with the coarse particles breaking into a body of smaller particle size and a series of fine particles. Aggregate-crack interaction increases the stress intensity factor and energy release rate of interfacial cracking, making concrete more susceptible to cracking and damage. In addition, factors such as aggregate location, particle size and external loading affect the stress intensity factor and expansion angle. In summary, the characteristic parameters of aggregate shape significantly impact the compressive strength and damage behavior of the concrete.