# A Detailed Review on Foam Concrete Composites: Ingredients, Properties, and Microstructure
## 3 Properties of Fresh Foam Concrete
### Stability  
It was reported that there is a 45% spread as the appropriate workability value of foam concretes with the use of typical materials [1]. The foam used can have different effects on stability. [PERSON] et al. [20] established a test system to evaluate the stability of foam produced using protein and synthetic foaming agents. Both foams were placed in beakers with a capacity of 1000 mL, and balls of equal weight and diameter were placed on them. The contact times of the balls to the bottom base of the beaker were recorded. In this way, the sinking time of the ball and the stability of the foam could be evaluated. At the end of the test, the ball sinking in protein-based foam took 19 min, while it dipped in synthetic foam for 13 min, and it was concluded that the stability of the protein-based foam was better. The reason for the better stability performance of the protein-based foam is that the protein adsorbed at the interface forms a viscoelastic layer with high surface shear viscosities, resulting in stable air bubbles in the Plateau Limits. It made it more stable [20].  
The use of nanoparticles can be used to improve the stability of foams. [PERSON] et al. [36] used synthetic surfactant (SS), plant surfactant (PS), and animal surfactant/blood-based surfactant (AS), and the mean disappearance rates of SS, PS and AS foam were respectively 0.25%/min, 0.6%/min and 0.5%/min. SS showed the best foam stability performance. The reason for this is that the SS foam is stabilized with nanoparticles.  
The increased foam content increases the water-to-solid ratio requirement of the main mix. The adhesion between the bubbles and the solid particles in the mixture increases the stiffness, which affects the stability of the mixture, causing the bubbles to segregate during mixing [76]. In the study using NAC as a foaming agent, it was reported that if the NAC content is more than 5%, it segregated in the foamed concrete samples. It was reported that the probable reason for this may be the excessive amount of gas that cannot remain constant due to the excessive expansion of the bubbles by heat dissipation [41].  
The use of magnetic water significantly increased the stability of foam concretes produced with synthetic foam. However, it had a negative effect on protein-based foams. The reason for the positive effect of the tap water passing through the magnetic field on the stability of the foaming agents is the strengthening of the hydrogen bonding of the water passing through the magnetic field [77].  
The type of aggregate used also may affect the foam stability. With the use of recycled concrete aggregate in geopolymer foam concrete instead of fine sand, the depth of defoaming decreased and the stability increased. Additionally, the use of RCA improved the yield strength. In this way, a more stable and uniform air void system is obtained [19].  
It was reported that adding 1-2% of the setting accelerator causes segregation, but more stable results are obtained with the use of dosages of 2%. The set accelerator improves the degree of clumping of hydration products and increases the resistance of the foam to changes. In this way, the stability of the foam is increased, and the coalescence and crushing of the preformed foam can be prevented. From a thermodynamic perspective, as the amount of hydration products formed on the surface of the bubbles increases, the gas-liquid interface energy of the air bubbles decreases and the stability of the foam increases [15]. Superplasticizers were reported to allow the w/c ratio to drop below 0.3 and provide 43% increase in stability. The increase in w/c causes difficulties due to overlapping of hydration products and a decrease in torque associated with the slurry. It was reported that the low torque achieved at w/c = 0.1 caused a decrease in stability and segregate [15].