Dynamic tensile properties of geopolymer aggregates engineered cementitious composites (GPA-ECC) with varying GPA replacement ratios

Abstract

To investigate the dynamic tensile properties of geopolymer aggregates engineered cementitious composites (GPA-ECC), this study conducted direct tensile tests at strain rates ($\dot{\epsilon }$) of 10⁻⁵ s⁻¹, 10⁻⁴ s⁻¹, 10⁻³ s⁻¹, and 10⁻² s⁻¹ on GPA-ECC with varying GPA replacement ratios (0 %, 25 %, 50 %, 75 %, and 100 %). Tensile properties, including tensile strength, tensile strain, strain energy density, and the strength index for pseudo-strain hardening (${\text{PSH}}_{\text{strength}}$), were derived from the stress-strain curves. The dynamic increase factor (DIF) was introduced to characterise the relationship between dynamic tensile properties and strain rates. Fracture morphology, scanning electron microscopy (SEM), backscattered electron (BSE) imaging, and energy-dispersive spectroscopy (EDS) analyses were combined to examine crack behaviour and microstructural characteristics, elucidating the mechanisms by which strain rate and GPA influence the dynamic tensile properties of GPA-ECC. Macroscopic tensile results revealed that, under quasi-static conditions (10⁻⁵ s⁻¹), the incorporation of GPA reduced tensile strength by up to 46.8 % but significantly enhanced ductility, energy absorption capacity, and strain-hardening ability, with maximum improvements of 125.2 %, 20.8 %, and 40.9 %, respectively. A comparison with other aggregate types of ECC reveals that the GPA-ECC with full replacement (F0G100) still maintains excellent strength levels. Under dynamic conditions with increasing strain rates (10⁻⁵ s⁻¹ to 10⁻² s⁻¹), tensile strength increased, while tensile strain, strain energy density, and ${\text{PSH}}_{\text{strength}}$ decreased. Additionally, GPA increased the strain rate sensitivity of the tensile properties, with more pronounced DIF variations observed at higher GPA replacement ratios. BSE-EDS analysis demonstrated that GPA interacted with the matrix, forming additional chemical bonds at the interfacial transition zone. SEM characterization of both fibre fracture morphology and fibre/matrix interfacial morphology revealed that the enhanced interfacial bonding was primarily responsible for the fracture failure of PE fibres under high-strain-rate loading.