# A Detailed Review on Foam Concrete Composites: Ingredients, Properties, and Microstructure
## 2 Compositions of Foam Concrete  
### Cements  
In addition to OPC, magnesium phosphate cement (MPC), sulfoaluminate cement (SAC), and fast-setting Portland cement are used in foam concrete production. Different cement types of foam concrete have an effect on setting time, strength, thermal conductivity [37; 38; 39]. For example, [PERSON] et al. [12] concluded that for a certain dry density or a certain thermal conductivity, MPC foam concrete has a higher compressive strength compared to OPC foam concrete [40]. The strength of OPC develops slowly, while for SAC-based foam concrete, the strength develops early, but in the future, the phenomenon of retraction will occur in the strength development. MPC, on the other hand, has the characteristics of rapid development of strength and no retraction in strength [40]. In the study conducted by [PERSON] and [PERSON] [41], the thermal conductivity of foam concrete prepared using 10% fly ash and MPC increased the compressive strength and thermal conductivity by 25% and 9.1%, respectively, compared to those without fly ash. The reason for this can be shown as the participation of fly ash in the hydration mechanism and improving the pore structure. However, with the increase in the amount of fly ash, a decrease in the compressive strength occurred. This situation may be due to the decrease in the amount of cement. In the study, the effect of silica fume was also investigated, and it was reported that silica fume reduced the compressive strength and thermal conductivity. As reported in the literature, silica fume may decrease the mechanical properties of the MPC mortar because amorphous silica of SF (silicon dioxide) does not contribute to the hydration products of MPC [41]. In this manner, the reason also can be that the decrease in the MAP (MgNH\({}_{4}\)PO\({}_{4}\)-6H\({}_{2}\)O) (hydration product of MPC) amount causes a decrease in the compressive strength [41]. It is also reported that geochemical and alkaline Portland cement can be used to increase the fire resistance of foamed concrete [7]. The use of supplementary binder components contributes to the reduction in cement consumption [42]. In addition, mineral additives are used to increase the consistency, adjust the hydration temperature and change the compressive strength values. The strength development of foam concretes prepared using fly ash is slow [21; 43]. The spherical shape of the fly ash increases the fluidity [11; 21]. They also reported that the use of coarse fly ash in foam concrete has a positive effect on increasing workability, mechanical properties and freeze-thaw resistance, and has a negative effect on drying shrinkage and water absorption. However, in different studies, it was reported that the strength increase at early ages is slow and that the strength increases in the long term [21; 43]. Temperature development during hydration is reduced by the use of fly ash [44]. In order to reduce the hydration heat of foam concrete, SF, GGBFS and FA up to 10% to 75% of the cement weight is used instead of cement [45]. [PERSON] et al. used granulated blast furnace slag for adjusting the rate and the amount of hydration heat of foam concrete. It was also used for controlling the temperature rise to prevent the newly placed foam concrete from deforming and cracking in an uneven volume [46]. The use of silica fume was reported to improve strength by 20-30% [47]. At the same time, in the study of [PERSON] et al. [48], the use of silica fume increased the density, compressive strength and thermal conductivity in constant foam content. [PERSON] et al. [49] reported that silica fume increased the compressive strength and splitting tensile strength. SAs improve the hydration reaction and lead to fine hydration products that affect the air void structure and reduce the rheological properties [15].