Aircrete and foamcrete and are both types of lightweight concrete. By definition, lightweight concrete is a type of concrete that has incorporated an expanding agent, increasing the volume of the mixture, giving it more desirable qualities like a low physical weight, but which is better?
Note that aircrete and foamcrete are used for specific structural purposes. Where aircrete is ideal, foamcrete may be lacking in some aspects and vice versa.
With many similar physical characteristics, the major difference between aircrete and foamcrete is in how the air bubbles in the cement mixture are generated. In this article, we have shed some light on how each is made, what it’s used for, advantages and disadvantages as well. Let’s have a look.
The Fundamental Difference Between Foamcrete and AirCrete
Foamcrete is ideal for backfilling voids that are no longer in use, particularly in inaccessible places, such as pipes and sewage systems, culverts, and road trenches. It is also used to fill voids under floors, sub-screeds, and flat concrete roofs.
Foamcrete is a construction material that is made using a cement-based mortar with at least 20% volume of air within. It is made by introducing gases or foam into a mixture of cement slurry and fine sand. Therefore, it has no coarse aggregates.
Aircrete is popular for its use in constructing housing systems from foundations, soundproof wall and floor slabs, shock-absorbent surfaces, ceilings, and even roofs. It is also effective in replacing unstable soil and covering underground structures that are sensitive to weight.
For industrial purposes, pulverized fuel ash is used instead of sand and lime instead of cement.
How Foamcrete Is Made
Foamcrete is made in two major ways. Air or gas can be injected during the mixing process via chemical reaction, or a stable, pre-formed foam can be introduced into the cement slurry.To generate the foam, a surfactant is diluted in water at a ratio of 1:30 and passed through a foam generating machine to produce stable foam, then mixed into the cement slurry.
The foaming agent used should be very stable. A quick test is just to pour it into a glass. The foam should hold without shrinking or forming liquid at the bottom of the glass. Small bubbles are ideal, as they are stronger than the bigger ones.
Foaming agents can be synthetic or protein-based. Protein-based foaming agents produce more stable bubbles, making it possible to use more air, while synthetic foaming agents tend to expand more, resulting in a lower density.
In terms of volume, the foam is about 40-80%. Foamcrete is cured in the same way as normal concrete since it has a higher cement content. The air bubbles in foamcrete are smaller in size than those found in aircrete, making them more durable.
The density of foamcrete depends on the amount of foam introduced into the mixture, while the strength depends on the sand quantity used. More foam means less weight and, consequently, less strength. However, with less weight comes better thermal insulation.
A more detailed explanation of how it’s made is available here.
Applications of Foamcrete
- Bridging embarkments
- Insulated floors, roofs and roof decks with 2-hour fire ratings
- Permeable pavements
- Lining underground conduits
- Culvert installation
- Backfilling trenches
- Pre-cast blocks and filling hollow blocks
- Seasonal decorations like Halloween (it can be painted and is considerably weather resistant)
Advantages of Foamcrete
- Foamcrete flows easily from an outlet and requires no compaction as it does not settle once poured. For this reason, it is possible to pump it to higher ground, or over a distance.
- It has very little dead weight due to its lightweight.
- Due to its free-flowing nature, it is convenient when filling voids in foundations since it can conform to the sub-grade contours.
- It absorbs approximately half the amount of water absorbed by aircrete and has low permeability, as the air bubbles do not allow water to pass through.
- It has no lateral load and imposes very little vertical stress.
- The air present makes foamcrete fire-resistant. A load-bearing wall of about 15 cm thickness can withstand fire up to 7 hours. Tem wall remains below the flashpoint.
- The dense cell structure gives foamcrete high energy absorbing capabilities and can stop moving objects. This reason, in particular, makes it suitable for military training purposes to stop bullets. In areas prone to earthquakes, foamcrete is a perfect building material.
- It has an outstanding capability of load distribution.
- It has great freeze and thaw resistance hence does not get frozen in cold weather.
- It allows speedy construction processes and is very cost-effective.
- It has low thermal conductivity.
- It has good sound insulation as it absorbs more sound instead of reflecting it or letting it pass through.
- Has a long life since it does not decompose with time
- The foaming agent in the cement continues to absorb water from the atmosphere, ensuring a continued increase in strength over time.
- Easy to handle and transport
Disadvantages of Foamcrete
- It has low compressive and flexural strength due to the high density of the foam. Flexural strength measures elasticity of the material or how much the foamcrete deforms and moves when broken, like in an earthquake.
- The absence of coarse aggregates makes it prone to shrinking.
- The ratio of connected pores and total pores present affects its durability.
- It takes more time during the mixing stage.
- It makes finishing difficult due to the smooth outer surface.
How Aircrete Is Made
Aircrete is made by mixing cement, lime, pulverized fuel ash, aluminum powder, and water. The chemical reaction catalyzed by the aluminum forms multiple air bubbles then dissolves, resulting in a very lightweight block.
In aerated concrete, the foam is generated from a chemical reaction between aluminum powder and calcium hydroxide, an alkaline element formed when the cement is mixed with water. This reaction forms hydrogen bubbles that remain in the cement slurry. After setting, the aerated concrete is cut into blocks and autoclaved for extra strength. It has the strength and durability of traditional concrete, without the physical weight. For a more compressive procedure on how it’s made, you can have a quick look here.
Applications of Aircrete
- Pre-cast blocks and panels
- Floors slabs, decks, and insulated roofs
- Underground piping systems
- Shock absorbent floors
- Acoustic buildings
- Lightweight filling over underground structures
- Backfilling mines and pipelines
- Replacing unstable soil in foundations
Advantages of Aircrete
- It is easy to handle, transport, and use.
- It is cost-effective in the aspect of the cost of materials required to make it, and the
- Overall construction costs.
- It has low thermal conductivity and low density.
- It has good acoustic properties, due to its porous nature.
- Aircrete does not combust and is fire resistant; hence can be used to construct furnaces.
- It is permeable to water vapor, which is effective in keeping indoor spaces cool.
- Materials used are Eco-friendly, and the final product does not emit any harmful gases during construction.
- It’s water-resistant and very durable as it doesn’t rust, rot or decompose over time.
- It is pest and rodent proof.
- It permits the use of coloring agents for aesthetic purposes.
Disadvantages of Aircrete
- In low quantities, the cost of production is high due to the need for expensive equipment, which results in high power consumption.
- Aircrete absorbs water over time hence the need to add cover using materials like plaster. Expansion of the absorbed water makes the aircrete prone to cracking over time.
- The resulting structures have a smooth surface, making it difficult to apply the finish.
- It absorbs water, which means an outside cover is required, like plaster.
- When exposed to water continuously over some time, the strength of aircrete may reduce.
From these advantages and disadvantages, here is a quick comparison of some aspects of both aircrete and foamcrete:
|Cost||Reduction in the use, and consequently cost of concrete and steel in high rise buildings||Reduction in the use, and consequently cost of concrete and steel in high rise buildings|
|Quality||Final quality varies depending on the foaming agent used.||The quality of the final product is consistent, as it is available ready for use.|
|Acoustic properties||Sound absorption or insulation is great.||Sound absorption or insulation is great.|
|Thermal conductivity||Low thermal conductivity of about 0.24 Kw-M/C||Low thermal conductivity of about 0.32 Kw-M/C|
Aircrete is better than Foamcrete in some applications, while foamcrete is better in others. The similarities in both include low density, reduced dead weight in construction, and easy to nail, saw, or cut.
Both are self-compacting and free-flowing; therefore, they can fill cavities and voids even when pumped over a distance. When it comes to cost-effectiveness, they both save on materials used, and time is taken to complete the project and manual labor as well. They pose a minimal threat to the environment and are fire-resistant.
There are common disadvantages such as sensitivity due to the use of water during production, and they have a smooth, porous exterior, which makes applying finish difficult.The key is to remember that each has different applications specific to its properties. Before settling on either, be sure to check if it applies to the project you have in mind.
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- The Constructor: Foam Concrete -Materials, Properties, Advantages and Production Methods
- Understanding Cement: Autoclaved aerated concrete (AAC, Aircrete)