# A Detailed Review on Foam Concrete Composites: Ingredients, Properties, and Microstructure
## 4 Physical Properties of Foam Concretes
### Water Absorption  
Foam concretes designed for interiors, such as wall elements inside the building, are generally not exposed to water. In such cases, water absorption is not important, as foam concrete will not be affected by freezing-thawing. In this context, the water absorption is important as freeze-thaw effects posing a threat to foam concrete if it is used as an external element. Foam concretes used as external elements and structural elements are required to have low water absorption values [55]. The water absorption property of concrete is directly related to the spaces and pores in it. The connection of the pores with each other can have an effect of increasing water absorption. However, the presence of capillary voids within the concrete directly increases water absorption [74,89]. Air voids from the foam do not contribute to water absorption [74]. Increasing the paste amount increases the number of capillary pores in the foam concrete content. This allows greater capillary forces to occur [11]. The penetration of water into concrete is not only dependent on the connection of porosity and pores; the pore diameter and distribution of pores also affect water absorption. With the increase in the w/c ratio, the absorption increases [55].  
[PERSON] and [PERSON] [90] reported that water absorption increased significantly with increased foam volume in soil-based foam concrete. This is because the more stable foam increases, the more interconnected pores are formed. They also reported that the use of silica fume reduced water absorption. The time required for water to penetrate the concrete is different from concrete without silica fume. In other words, soil-based foam concrete with silica fume may have more fine and unconnected pores.  
The water absorption of the foam concrete increased by using the RCA as fine aggregate. The reason for this is due to the high water absorption feature of RCA. In other words, the water absorption properties of the aggregates used affect the water absorption of the foam concrete [19].  
In the study performed by [PERSON] et al., FA and quarry dust were used. The quarry dust was used as a fine aggregate partially replaced by sand, and FA replaced cement. As a result of the study, it was seen that the best water absorption performance was achieved in the presence of 30% FA with quarry dust. It was reported that the water absorption was directly related to the density of the foam concrete [91].  
Fibers added to foam concrete can increase water absorption. In connection with the water absorption properties of the fibers, there is an increase in water absorption. As it is  
\begin{table}
\begin{tabular}{c c} \hline \hline
**References** & **Porosity (\%)** \\ \hline
[86] & 48.9–52.8 \\
[87] & 84.78–93.30 \\
[55] & 70.6–89.5 \\
[9] & 35–85 \\
[80] & 50–80 \\
[10] & 50–75 \\
[16] & 17–24 \\
[5] & 31.1–24.4 \\
[81] & 70–81 \\
[88] & 90.7–91.6 \\
[87] & 84.78–93.30 \\ \hline \hline \end{tabular}
\end{table}
Table 7: The porosity percentages of different studies.  
known, natural fibers have water absorption properties. For example, in foam concrete where sugar cane pulp fibers are used, the rate of water absorption is increased for this reason [61].