Eco-efficient ternary cements with limestone powder, metakaolin and recycled waste glass: Characterization and sustainability assessment

Reducing the CO 2 emissions is a major concern for the modern cement industry . Using locally available wastes and natural materials offers a viable solution for creating eco-efficient cements. This study explores ternary alkali-activated pastes and mortars incorporating, limestone powder (LSP), metakaolin (MK) and high loads of waste glass (WG) as precursors. The effects of liquid sodium silicate (LSS) with modulus (Ms) of SiO 2 /Na 2 O ratios of 0.8, 1.0, 1.2, and 1.4, and Na 2 O concentrations of 4–10 wt%, were evaluated for compressive strength and microstructural evolution for up to 360 days. Mixtures with 30 % LSP, 10 % MK and 60 % WG, achieved 360-day compressive strength up to 71 MPa, while mortar formulations showed strengths between 20 and 46 MPa, depending on curing conditions. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and 29 Si Nuclear Magnetic Resonance (NMR) revealed the formation of (C,N)-A-S-H-type gels intermixed with silica gel . LSP and WG exhibited a dual role as reactive components and fillers reinforcing the matrix, while MK underwent higher extent of reaction , forming N-A-S-H- type gels, gradually incorporating Ca. The use of LSP and WG in ternary binders reduced CO 2 emissions by 10–61 % and energy demand up to 47 % compared to Portland cement . The findings support the development of eco-friendly, high-performance cements that align with global sustainability goals. Processing route, mechanical performance, and environmental benefits of ternary alkali activated binders • Ternary cements with LSP, MK, and WG reduce CO 2 by up to 60 %. • Mortars with 30 % LSP, 30 % MK, and 40 % WG reach 46 MPa in 90 days. • Activated pastes yields up to 71 MPa at 360 days. • LSP acts as both a filler and reinforcement in the cement matrix. • Replacing PC with AAC lowers costs and energy demand.