Reuse of biomass ash in cement based materials

Abstract

U ovome radu istražena je zamjena cementa i pijeska s otpadnim letećim pepelom od spaljivanja drvnog otpada u Hrvatskoj. Ovaj pepeo ima relativno veliki udio slobodnog CaO i MgO, ali i povoljne minerale Ca2SiO4, Ca2AlFeO5 i Ca2Al2SiO7, karakteristične za cement, čime je opravdana njegova primjena u svrhu zamjene dijela cementa. Već i sam leteći pepeo, te u smjesi sa cementom, pokazuje znatnu hidratnu i pucolansku aktivnost. Glavni utjecaj na kemiju hidratacije cementa je u nastanku C4AHx. Dodatak pepela do 20% smanjuje: gustoću slagaline čestica, kapilarno upijanje, tlačnu i savojnu čvrstoću (10-15% nakon 28. dana), ali povećava ekspanziju (unutar norme) i poroznost. Optimalni sastav novih cementnih materijala je 15-20%-tni dodatak letećeg pepela biomase (po masi cementa) za zamjenu cementa i pijeska pri čemu se čestice koje su veće od 80 μm uzimaju za zamjenu pijeska, a manje čestice za zamjenu cementa.This work investigates replacement of cement and sand with fly ash waste generated from combustion of wood waste in Croatia. The ash has a relatively high fraction of CaO and MgO, but also Ca2SiO4, Ca2AlFeO5, Ca2Al2SiO7 minerals characteristic to cement thus justifying it's application as cement replacement. Even the hydration of the ash alone, as well as blended with cement, exhibits large hydraulic and pucolanic activity. The main effect on cement hydration chemistry is in formation of C4AHx product. Addition of up to 20% (per cement mass) decreases: particle packing density, capillary absorption, compressive and flexural strength (10-15% at 28 days), and increases volume expansion (within norm limit), and porosity. Optimal mixture design of the novel cementitious materials would be a 15-20% of biomass fly ash loading (per cement mass) for both cement and sand replacement, in which the particles larger than 80 μm are considered as replacement of sand, while smaller of cement