Mechanical and Carbonation Performance of Alkali-Activated Mortars Incorporating GGBS and Recycled Construction Spoil

This study evaluates the mechanical properties and carbonation resistance of alkali-activated mortars (AAMs) formulated with ground granulated blast-furnace slag (GGBS) and recycled construction spoil (CS). The experimental variables included the water-to-solid ratio, alkali content, activator type (NaOH vs. Na2SiO3), and GGBS/CS mass ratio. The effects of these parameters on workability, flexural strength, and compressive strength were analyzed, along with the influence of accelerated carbonation curing. Results indicate that CS incorporation reduces flowability, with NaOH-activated mortars displaying marginally better workability than the Na2SiO3-activated counterparts. At an alkali content of 6.5% and a water-to-solid ratio of 0.45–0.5, a 30% CS replacement significantly improved the 7-day flexural strength in Na2SiO3-activated systems. Compressive strength generally increased with higher alkali content, though this effect diminished at elevated CS substitution levels. Under supercritical carbonation, NaOH-activated GGBS exhibited a ~20% strength increase, whereas Na2SiO3-activated GGBS showed negligible change or a slight reduction. Blends containing 50% CS demonstrated minimal carbonation-induced alterations. These findings provide insights into optimizing industrial byproduct utilization in AAMs while improving their carbonation durability, supporting sustainable construction material development.