Strain-hardening alkali-activated fly ash/slag composites with ultra-high compressive strength and ultra-high tensile ductility

This study designed and developed strain-hardening alkali-activated fly ash/slag composites (SH-AAFSC) with both ultra-high compressive strength and ultra-high tensile ductility for the first time. The developed SH-AAFSC showed a compressive strength of 94.4–180.7 MPa and a tensile strain capacity of 8.1–9.9 %, which successfully pushed the performance envelope of alkali-activated materials. A multi-scale investigation was conducted to get an in-depth understanding of the obtained mechanical properties. Results showed that higher GGBS content increased the Ca/Si ratio of C(N)ASH, leading to a further refined microstructure with reduced porosity. As w/p ratio decreased from 0.27 to 0.22, the compressive strength significantly increased but the tensile ductility slightly decreased. Notably, a strong linear relationship was observed between fiber-bridging strength and the average elastic modulus of matrix obtained from nanoindentation. The study provided an avenue to produce SH-AAFSC towards ultra-high compressive strength and tensile ductility, which are promising for resilient and sustainable infrastructures.