Dynamic fracture mechanism and damage constitutive model of LF-LAMOC under water-to-binder ratio regulation

Abstract

Limestone powder-lightweight aggregate magnesium oxychloride concrete (LF-LAMOC) is a novel green building material. To investigate its dynamic mechanical properties, electromagnetic-driven split Hopkinson pressure bar techniques were employed to test LF-LAMOC specimens with varying water-to-binder ratios under impact loading. High-speed photography and digital image correlation methods were utilized to reveal the dynamic compressive and tensile fracture behaviors of LF-LAMOC. Scanning electron microscopy was applied to observe the thickness variation of the interfacial transition zone (ITZ) between magnesium oxychloride cement paste and lightweight aggregates as a function of water-to-binder ratio. Results show that LF-LAMOC exhibits significant strain-rate sensitivity in dynamic compressive/tensile strength and energy dissipation. At low impact velocities, energy dissipation is dominated by plastic and inertial energy, while energy consumed by inter-particle fracture damage is relatively minor. Under low strain rates, dynamic compressive failure of LF-LAMOC specimens manifests as splitting failure primarily caused by tensile stress. For dynamic tensile loading, cracking in disk specimens originates from the center. At high strain rates, failure transitions to pulverization, driven by combined tensile and shear stresses, with cracking initiating from both ends of the disk. Limestone powder effectively enhances the bond strength between aggregates and paste, while ITZ thickness increases with rising water-to-binder ratio. A modified Zhu-Wang-Tang dynamic constitutive model incorporating material damage was developed to derive the dynamic constitutive equation for LF-LAMOC, which demonstrates favorable predictive capability for the material’s dynamic stress-strain relationships. The conclusions obtained in this study provide valuable references for the engineering applications of LF-LAMOC.