Mechanical strength and heat tolerance of 3D printed rubberised concrete at elevated temperatures

This study investigates the impact of recycled crumb rubber (CR) content on the mechanical strength, thermal performance, and anisotropic behaviour of 3D-printed concrete (3DPC) at elevated temperatures (100 °C, 300 °C, and 600 °C) to optimise material composition and print orientation for enhanced structural performance. Recycled CR from used tyres is explored as a sustainable alternative in 3DPC to address tyre waste accumulation. Using the control mix design, four mix designs containing 5 %, 10 %, 15 %, and 20 % CR aggregates, replacing ground-granulated blast-furnace slag (GGBFS) by volume, were prepared to assess the effect of CR on the mechanical performance of cementitious composites in terms of compressive and flexural testing, as well as mass loss assessments. These samples were subjected to temperatures of 100 °C, 300 °C, and 600 °C. Results show that CR reduces compressive strength by up to 30 % at ambient conditions compared to traditional concrete. At 600 °C, the compressive strength further declined by approximately 43 %–70 %, with values ranging from 13 to 25 MPa, depending on the rubber content. Flexural strength peaked at 9.73 MPa at 300 °C but dropped sharply to 3.99 MPa at 600 °C due to rubber degradation. Anisotropy influenced performance significantly, with compressive strength in Direction An up to 105.7 % higher than Direction B and flexural strength in Direction C outperforming Direction D. Mass loss at 600 °C ranged from 13 % to 16 %, correlating with rubber content and thermal stress (R 2 = 0.9849). While rubber improved post-crack toughness at moderate heat, it compromised stiffness and strength at extreme temperatures. These findings highlight CR's potential for eco-friendly construction and, for the first time, reveal how optimising both material composition and print orientation can enhance anisotropic performance under elevated thermal stress. • 3D print direction causes up to 105.7 % variation in compressive strength. • CR content alters thermal response and anisotropy in 3D-printed concrete. • Flexural strength in 3DPC peaks at 300 °C, then degrades with higher heat. • Elevated temperatures reveal print-orientation impact on structural behaviour. • Optimising mix and print path enhances 3DPC performance under heat stress.