Resistance of ternary cement-based and alkali-activated concretes against silage effluent attack

This paper reports the performance of ternary blends of a Portland cement-based system, alkali-activated blast furnace slag system, and fly ash and calcined clay based geopolymer systems against silage effluent attack. The binder blends were carefully to selected to have lower quantities of Ca compounds, with a view to reduce the formation of calcium-based hydrate minerals, that undergoes decalcification in acidic environments. The concrete specimens were exposed to silage effluent in two ways: (1) in laboratory conditions where silage effluent was changed every week for the first six months and not replenished for three years, and (2) in situ exposure in a gully of a silage clamp with a constant flow of raw silage effluent for 3 years. The performance of the specimens was evaluated by recording visual damage, mass loss, and compressive strength loss against reference specimens stored in water. In addition, paste specimens exposed to laboratory conditions as above were used to study the evolution of microstructural properties using XRD, TGA, FTIR, and SEM-EDS. The findings show that decalcification and carbonation are the significant changes occurring to the ternary and activated GGBS systems due to effluent exposure. The activated fly ash and calcined clay systems, although of lower strength grade, were not affected by the exposure and gained strength, whereas the other binder systems recorded a loss in strength of 6–32 %. Fly ash and calcined clay systems showed changes to aluminium and iron minerals, respectively, closer to the exposure surface. However, the depth to which these metals were removed from are nominal in comparison to Ca dissolution/leaching in other blends.