Valorization of co-combustion fly ash in concrete production

• Co-combustion and coal fly ashes partially replace cement (substitution ratio 20%).
• CCFA has a higher unburned carbon content and slightly lower fineness than CFA.
• CCFA and CFA have a beneficial effect on concrete workability when used as SCM.
• CCFA use decreases slightly concrete compressive strength and durability.

The purpose of this paper is to compare the effects of two different Supplementary Cementing Materials (SCMs) on mechanical and durability-related properties of structural concrete. Three mixes were produced, where coal and co-combustion fly ashes were used as partial substitute of cement (20% in volume) and compared with a control/reference concrete. Performances investigated included fresh concrete properties, compressive and tensile strength, elastic modulus, permeability, capillarity and drying/wetting resistance. Results indicate that both the SCMs can be classified as low-carbon fly ashes, and their use in concrete improves the workability of the mixes. A slight reduction of mechanical strength was observed for the concretes including both the SCMs. In addition, concrete transport properties were also slightly reduced when co-combustion fly ash was used. Wetting-drying cycles affected significantly the durability of all the mixes: compressive strength after these cycles was significantly lowered, and the cracks occurred due to the thermal stress applied, appeared to be filled by needle-shape crystals of ettringite.

Figure optionsDownload as PowerPoint slide