Thermally cured high-strength engineered geopolymer composites containing carbon nanotubes

This study investigates the mechanical, shrinkage, thermal, and microstructural behaviour of thermally cured high-strength engineered geopolymer composites reinforced with multiwalled carbon nanotubes (MWCNTs) and polypropylene (PP) fibres. Fly ash and ground granulated blast furnace slag served as binders, while fine and coarse MWCNTs were incorporated at dosages up to 0.4%. Specimens were subjected to a two-stage thermal curing regime and later exposed to temperatures between 60°C and 600°C. Fresh properties, compressive and tensile performance, drying shrinkage, and residual properties after thermal exposure were evaluated. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared, and thermogravimetric analysis analyses were conducted alongside economic and statistical assessments using one-way analysis of variance and Tukey’s honestly significant difference tests. MWCNT incorporation significantly enhanced composite performance. At 90 days, compressive strength increased from 90.0 MPa for the control mix to 104.0 MPa with 0.4% coarse MWCNTs, while comparable strength was achieved using only 0.2% fine MWCNTs. Tensile strength increased from 6.09 to 7.78 MPa, while tensile strain capacity reached 11.01%. Drying shrinkage decreased by 26.0%. Moderate thermal exposure improved residual strength by 15.9%, whereas limited reductions occurred at 140°C because of PP fibre softening. Microstructural analyses confirmed enhanced gel formation and crack-bridging effects. Statistical results confirmed the significant synergistic influence of MWCNTs and thermal exposure on performance.