Impact of strain rate, free water, and aggregate fragmentation on the dynamic behavior of concrete in compression regime using a unique coupled DEM/CFD technique

This paper examines the simultaneous impact of strain rate, aggregate fragmentation, and free water on the dynamic behavior of concrete in mesoscale uniaxial compression conditions. A concrete specimen measuring 50 × 50 mm² and having a low porosity of 5% was the subject of extensive two-dimensional (2D) dynamic investigations (that is, a research limitation). Its mesostructure was based on laboratory micro-CT images. Concrete’s fracture patterns, strength, brittleness, and fluid pressure distributions were all investigated. A mesoscopic pore-scale hydro-mechanical model based on a unique fully coupled DEM/CFD technique with breakable aggregate particles was utilized to study the behavior of partially or fully saturated concrete. A four-phase material comprising aggregate, mortar, ITZs, and macropores was used to replicate concrete. Groups of small spherical particles were used to simulate the fragmentation of aggregate particles with various shapes and sizes, allowing for intra-granular fracturing among them. A network of fluid channels was assumed in a continuous region between discrete elements. A two-phase laminar compressible fluid flow (air and water) in pores and cracks was suggested for wet concrete. The accurate volumes of pores and cracks were computed for tracking the liquid/gas content. Dynamic numerical compressive tests were performed with strain rates ranging between 1 1/s and 1000 1/s. Strain rate, aggregate fragmentation, and free water flow increased the dynamic compressive strength. Because of free water confinement in pores and cracks, the pore fluid pressures retarded a fracture process, enhancing the concrete dynamic strength.