Advancing carbon sequestration in engineered cementitious composites: Incorporating slag and pyrolysis-enhanced biochar for net-zero emissions

This study explores the impact of adding biochar (BC) on various engineering properties of GGBS-incorporated engineered cementitious composites (ECC). This study investigates the effects of biochar (BC) on the performance of engineered cementitious composites (ECC) incorporating ground granulated blast furnace slag (GGBS). Key properties assessed include workability, density, strength, shrinkage, durability, carbon mineralization, and microstructural characteristics (SEM, XRD, TGA/DTG). Incorporating 5 % BC enhanced compressive strength by 24 % at 7 days and 20 % at 28 days, attributed to improved calcium silicate hydrate (C-S-H) gel formation. However, higher BC contents (>5 %) led to reduced strength—up to 66.7 %—due to increased porosity and hindered hydration. Flexural strength declined more sharply, influenced by BC's porous structure. Drying shrinkage remained similar to the control at 5 % BC but increased at higher levels. CO₂ uptake more than doubled in mixes with 15–20 % BC under both air and CO₂-curing, driven by BC's high surface area and reactive functional groups. XRD confirmed calcite formation as a nucleation site for C-S-H, promoting early strength, while SEM revealed improved hydration at low BC levels but unfilled pores at higher dosages. TGA/DTG identified the thermal decomposition of C-S-H, portlandite, and calcite. Optimizing BC at 5 % balances strength, shrinkage control, and carbon sequestration, supporting sustainable ECC development.