Waste olivine and silica sands boost geopolymers’ performances: experimental investigation

The present research deals with the production and characterisation of geopolymers prepared by mixing metakaolin (MK), a commercial sodium silicate solution, a sodium hydroxide solution and two types of industrial by-products: one olivine (OS) and one silica sand (SS) both of them in form of loose powders. Different specimens were prepared by mixing different quantities of OS or SS to the blank geopolymeric matrix. Specimens containing MK, a commercial sodium silicate solution and a sodium hydroxide solution were also prepared as blank composition for comparison. All specimens were characterised by their compressive strength, water absorption, pore size distribution, specific surface area and microstructure. The addition of olivine or silica powders improves the performances of the resulting materials in all the compositions examined, but those containing 50 wt% of added sand (relative to the amount of MK) displayed the best mechanical behaviour.