Quaternary blended limestone-calcined clay cement concrete incorporating fly ash

Use of limestone-calcined clay (LC) blends, while eco-friendly, degrades the workability in concrete owing to the water retention in clays. This study proposes a solution by incorporating fly-ash (FA) in a quaternary blended concrete to improve the rheology. Typical LC concrete was prepared by replacing 40% and 60% of cement with 3:1 ratio of clay: limestone. Concurrently, another batch of LC concrete with FA (LCF) was also prepared with 2:1:1 ratio of clay: FA: limestone. Early age effects were monitored using isothermal calorimetry (ITC) and chemical shrinkage. Later age effects were examined using rapid migration test (RMT), water absorption, thermo-gravimetric analysis (TGA), compressive strength and mercury intrusion porosimetry (MIP). Incorporation of FA substantially reduced the dynamic yield stress and plastic viscosity in fresh LCF blends. LCF pastes samples showed slightly lower heat of hydration and comparable chemical shrinkage after 28-days. TGA results after 1-year showed marginally higher CH content in LCF samples, but also with higher degree of hydration. MIP results of 1000 days old samples showed better pore refinement in LCF blend than LC blend. Furthermore, LCF concrete achieved similar strength as the original LC concrete at both 40% and 60% cement replacement levels, while porosity and RMT results showed no statistical differences in LC and LCF mixes. Overall, the use of FA in LC displayed better rheological performance with similar mechanical and durability properties.