## 1 Introduction  
Foam concrete has been used as a construction material for flooring systems in Europe and the United States since the first part of the 20 th century and it was granted a patent in 1934 [1; 2]. In general, foam concrete is a mixture of cement, water and air bubbles produced from a foaming agent. Consequently, foam concrete has a significantly lower density and strength than ordinary concrete [3; 4]. Supplementary cementitious materials, such as fly ash and silica fume, can be used in foam concrete to reduce the percentage of cement usage [5]. Fresh foam concrete mix is highly flowable and self-compacted in nature. Therefore, it can safely and efficiently be placed in some confined or problematic areas, such as tunnels, trenches, pipes, wall backfills [6], road bases [5; 7], soil replacement, concrete flooring, concrete panels, concrete blocks, roadside noise barriers [8; 9; 10; 11; 12; 13], insulating materials [14; 15], and other places where routine soil replacement works are difficult to maintain. Typically, the cast density, thermal conductivity and the modulus of elasticity of foam concrete range from 200 to 1900 kg/m\({}^{3}\), 0.1-0.7 W/mK and 1-8 GPa, respectively [7; 16; 17]. The compressive strength of foam concrete varies substantially depending on the mix design and density requirement. The stability of foam is crucial in manufacturing foam concrete. The instability of air bubbles can lead to a nonhomogeneous mix (segregation of the constituents) and a higher percentage of variation in the unit weight of foam concrete. Foam stability depends on many parameters, e.g., foaming agent type and concentration, \(w/c\) ratio of the mix, foam content, mixing method and duration, curing method and type of binders. As a result, controlling bubble stability remains an active field of research. In foam concrete, a highly influential parameter is the percentage of foam content that directly influences the strength, density and stability of the bubble networks of the product. The higher the rate of foam content, the lower the density and compressive strength of the foam concrete [18; 19]. Therefore, it is important to investigate the effect of foam content and type on the stability of the foam concrete with varied density. In addition, the use of sustainable/recycled materials, such as fly ash, slag and silica fume as supplementary cementitious materials, is becoming important to achieve net-zero targets. Fly ash is a very common supplementary cementitious material that can reduce the permeability of concrete and increase the durability of concrete against elevated temperatures [20]. On the other hand, silica fumes are reported to improve the flexural and thermal behaviour of almost all types of concrete specimens [20; 21]. Moreover, an extensive amount of research on the fresh and hardened state properties of plain foam concrete was conducted in the past [17; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33]; however, research on fibre-reinforced foam concrete with a blend of cementitious materials is limited in the literature [34; 35]. This study aims to reveal foam concrete mixes with various percentages of foam content and their ultimate strength prediction models relating to 3-day compressive strength. Two foam concrete mixes, each containing multiple percentages of foam content, are developed and their physical and mechanical properties are experimentally investigated and compared. This study terms one foam concrete mix as \"Blended\" and another as \"GP cement\". The blended mix contains a blend of Australian general purpose (GP) cement with fly ash and silica fume as the binders. The GP cement mix contains only Australian GP cement as a binder. The blended mix of the foam concrete developed in this study could be suitably used in various civil engineering fields.