Long term mechanical performance of nano-engineered high volume fly ash concrete

High Volume Fly Ash (HVFA) concrete is a sustainable construction material which can act as a viable alternative to Portland cement (PC) concrete. This study investigates the long-term mechanical performance of two unique HVFA concrete mixes, 65% and 80% cement replacements, incorporating hydrated lime, up to 18%, and 3% nano silica. HVFA-65 concrete achieved compressive strength values increasing from 32 to 73 MPa, from 7 to 450 day while HVFA-80 displayed a strength increase from 22 to 71 MPa in the same period. The flexural strength of HVFA-65 concrete increased from 3.6 to 8.7 MPa while the splitting tensile strength and elastic modulus gave values of 2.7-5.8 MPa and 30.3-40.5 GPa, respectively. Meanwhile, HVFA-80 concrete achieved flexural strengths of 2.7-8.7 MPa, splitting tensile strengths of 1.6-5.0 MPa and an elastic modulus of 28.9-37.0 GPa. Analysis of paste samples identified the presence of 11%, 3.2%, 5.3% and 2.1% higher concentrations of Por-tlandite within the HVFA-65 system at 7, 28, 90 and 450 days respectively, indicating a high availability of portlandite for the pozzolanic reaction of the fly ash. In microstructural investigation, HVFA-65 concrete dis -played a denser gel matrix and stronger bond within the interfacial transition zone (ITZ) boundary compared to HVFA-80 at all ages. In addition, a statistical regression analysis conducted to predict relationships between long term mechanical properties of HVFA concrete are compared with existing design equations available in Australian Standards and ACI codes.

Automated summary

The study found that different cement replacement levels and additives in HVFA concrete significantly influence the mechanical properties of concrete, with HVFA-65 concrete exhibiting higher compressive strength and flexural strength, and a denser microstructure with stronger bonding in the immature age, demonstrating better long-term mechanical performance.