Effects of Calcium Carbonate and Fly Ash as Supplementary Cementitious Materials in Quaternary Binder for Foam Concrete Mixes

T his study is about the Production of a sustainable and high - performance foamed concrete by using a quaternary binder system to substitute a part of ordinary Portland cement (OPC). The research investigates the replacement of cement by Class F fly ash (FA) as the main replacement material and ground granulated blast-furnace slag (GGBFS) and limestone powder (CaCO 3 ) as secondary replacement materials at replacement levels of 20%, 30% ,and 40% .All investigated mixes were designed mix proportion 1:1.2:0.45 with the fresh target density of 1350 ± 50 kg/m³ for semi-structural applications. An extensive assessment was conducted in terms of fresh density, compressive strength, splitting tensile strength, carbonation depth, and microstructural characterization using scanning electron microscopy (SEM). SEM analysis observed that the 40% replacement level resulted in a dense microstructure with secondary C–S–H and C–A–S–H gels and refined pore structure. The results showed that the 40% quaternary substitution level provided a 28-day compressive strength of 9.00 MPa, exceeding that of the control mixture, with a good fresh density of 1345 kg/m³ and improved foam stability. In contrast, it had higher splitting tensile strength but also had higher carbonation depth than control. Finally, these findings confirm 40% of quaternary binder as systematically sustainable and balanced alternative for the production of stable foamed concrete for semi-structural applications.