Alkali-activated waste seashell binder material: mechanical properties, reaction mechanism and life cycle assessment

The reactivity of binder materials and the hydration process are critical factors in the development of concrete properties. This paper utilizes discarded seashells as an assisted binder material to investigate the hydration reaction mechanism of seashell powder (SP) in an alkali-activated system, and to examine the mechanical properties of SP in different alkali activators. The experimental results show that the addition of shell powder increased the calcium ion concentration in the solution by nearly 50 %, effectively promoting the hydration reaction process of the alkali-activated system. Combined thermogravimetric (TG) test results indicate that nearly 40 % of SP participated in the hydration reaction. The mechanical properties of the mortar improved with the increase of SP content, and when the mortar containing 40 % SP was activated with a 1:2 mixture of activator, the maximum compressive strength at 28 days was 83.6 MPa and the maximum flexural strength was 8.9 MPa. Life cycle studies show that by optimizing the selection of alkali activators, alkali-activated concrete containing SP can not only reduce carbon dioxide emissions by 60 %, but also save 40 % in production costs.