Study on clinker ash recycling in geopolymer materials

Clinker ash (CA) is a granular waste from thermal power plants besides fly ash (FA). When used as fine aggregate e, CA’s porous nature reduces mechanical properties and durability of concrete. This study explores CA recycling in concrete by geopolymer (GP) technique, modifying CA with alkali activator solution (AS). We investigated the effects of CA substitution of partial FA and sea sand on fluidity, strength, and durability of slag/FA-based GP concrete and mortar. We also examined the changes of CA particles after immersed in AS to clarify CA’s compatibility with GP binder. The results indicated that CA particles react with AS, densifying CA and refining the interfacial transition zone (ITZ) between the GP matrix and CA particles. Although FA replacement with CA reduced strength of GP concrete, replacing sand with CA (up to 20%) minimally affected GP concrete’s flowability, while enhancing compressive and flexural strengths. A surface modifier, composed of sodium aluminate solution (AN) and ablendof silica fume and caustic soda (SN), greatly improved the carbonation resistance of GP with CA. XRD analysis identified components in CA and reaction products between CA and AS in GP materials. These results confirmed CA’s potential as fine aggregate of geopolymer concrete.