Effect of seashell powder as binder material on the performance and microstructure of low-carbon sustainable alkali-activated concrete

Abstract

This paper proposes using waste seashells as raw materials to partially replace fly ash in alkali-activated concrete (AAC). Fifteen groups of alkali-activated mortar and concrete were designed, with seashell powder (SP) substitution and sodium hydroxide molar concentration as variables. The material's workability, compressive strength, hydration products and micropore structures were examined. The results showed that the 3 days compressive strength of AAC with SP enhanced significantly, exhibiting an increase of nearly 30 % compared to the fly ash control. The 28 days compressive strength showed that the optimal proportion of SP replacing fly ash was 45 %. SEM images showed that micro/nanoparticles of SP filled the pores in the concrete and provided nucleation sites. Nano CT and MIP analyses indicated that the addition of SP could refine the pore structure of concrete, reducing the total porosity by nearly 30 %. Finally, the carbon emission data for 1 m³ of concrete were analyzed using a life cycle assessment approach. The carbon emissions from AAC with 45 % SP were 173.4 kg CO2/m³, compared to the reference ordinary concrete reduction of approximately 60–70 %.