Polymaterial Lattice Discrete Particle Model for the Optimization of Lightweight Aggregate Concrete: Intragranular Fracture and Compression Behavior

Lightweight aggregate concrete (LWAC) offers clear advantages for sustainable construction, including reduced density and improved thermal insulation. However, its mechanical and fracture behavior is difficult to characterize due to the heterogeneity and brittle crushing of porous lightweight aggregates. This study examines the mechanical response and fracture behavior of ultra-high-performance concrete with foam glass aggregates (UHPC–FGAs) as a representative LWAC system by combining targeted experiments with mesostructure-resolved numerical simulations. Experimental investigations included single-particle crushing tests on FGAs, uniaxial compression tests on the UHPC matrix, and three-point bending (TPB) tests on the UHPC matrix. These data informed parameter identification for the Polymaterial Lattice Discrete Particle Model. Aggregate-related parameters were calibrated under joint constraints to reproduce both FGA crushing behavior and the compressive response of UHPC–FGA composites. Realistic mesostructures were generated from voxel-based microstructures produced by the Virtual Cement and Concrete Testing Laboratory and mapped into the numerical model. TPB simulations of UHPC–FGA composites were then performed to quantify fracture energy. Results show that cracking initiates within porous FGAs and propagates transgranularly into the UHPC matrix, rather than along interfaces as in normal-weight concrete. The fracture energy of UHPC–FGAs is approximately 50% lower than that of plain UHPC, reflecting limited crack deflection and bridging. Parametric analyses indicate that aggregate stiffness and tensile strength primarily govern fracture energy and post-peak ductility, while the shear-to-tensile strength ratio controls compressive strength and peak strain. The proposed experimental–numerical framework offers practical guidance for optimizing lightweight concrete systems by balancing strength and ductility.