Fracture properties and sustainability assessment of strain-hardening alkali activated composites of up to 100 % rubber aggregate

Abstract

Strain-hardening alkali-activated composites (SHAAC) are eco-friendly materials with ductile fracture characteristics. This study investigates the effects of rubber powder (RP) replacement ratios (0–100 %) on the ductile fracture performance of rubberized SHAAC (R-SHAAC), focusing on the underlying toughening mechanisms. The ductile fracture process was quantified with initiation fracture energy J_IC and failure fracture energy J_IF. The RP toughening mechanism was revealed with matrix-cracking fracture energy J_m, fiber bridging fracture energy J_b, and composite fracture energy J_c. RP enhances R-SHAAC's fracture performance through three mechanisms: reduced matrix toughness, crack bridging, and improved fiber dispersion. R-SHAAC specimens exhibit ductile failure with a primary crack surrounded by dense microcracks. RP extends the steady-state multi-crack propagation phase, increasing J_IF by up to 89.9 % compared to the baseline. For most mixtures, J_m/J_c exceeds 60 %, indicating that matrix cracking is the primary mode of energy dissipation. However, RP replacement ratio above 75 % triggers over-saturated cracking, which shortens the steady-state cracking phase and advancing the onset of instability. In addition, the Technique for Order of Preference by Similarity to Ideal Solution analysis identified the mixture with a 25 % RP replacement ratio as the optimal balance between mechanical performance and sustainability. This study clarifies the influence of RP modification on SHAAC’s ductile fracture behavior, providing insights into toughening mechanisms and enabling the evaluation of R-SHAAC designs for sustainable, high-performance construction applications.