Pre-cast concrete has an outstanding place in the construction world, offering an easy, affordable, and quick way to construct walls and different structures. This form of concrete is not directly poured on the site, but rather it comes in a pile of pre-cast blocks. Autoclaved Aerated Concrete (AAC) is one of the most common forms of precast-concrete. This particular building material offers many extraordinary benefits others tend to overlook.
This blog will tackle AAC, its benefits, drawbacks, purpose, etc. – serving as a guide for beginners.
Introducing Autoclaved Aerated Concrete (AAC)
AAC is a form of pre-cast concrete comprised of natural raw materials. This concrete has been first developed in Sweden in the early 1920s. Everything started when an architect has mixed the conventional concrete combination of water, cement, lime, sand with a small amount of aluminum powder. The latter serves as an expansion agent, causing the concrete to enlarge massively, somewhat like bread dough.
Today, AAC concrete is commonly made into slabs or blocks and is utilized to build mortared walls. This concrete started with the same process, particularly for standard concrete block construction. Portland cement, water, aggregates are mixed to create a slurry. With the introduction of aluminum as an enlargement agent, air bubbles are used for the entire material. It generates low-density lighter material.
AAC concrete can be utilized on roof panels, walls, floor, lintels, and blocks but take note below:
· Panels are usually available in a standard thickness between 8-12 inches in width. For the lengths, it can be 20 ft.
· Blocks come in different sizes: 24, 32 or 48 inches. For standard thicknesses, 4-16 inches, and the height should be 8 inches
Furthermore, AAC concrete units are highly workable because they can be drilled and cut with conventional woodworking tools like ordinary power drills and band saws. While AAC has relatively low-density and very lightweight, the concrete itself must be tested for bulk density, moisture content, compressive strengths, and shrinkage.
Building with AAC Concrete
AAC concrete is ultimately useful for floors, roofs, and walls because its lightweight has made it much more versatile than standard concrete. The material also offers impressive sound and thermal insulation, aside from being fire resistant and extra durable. Yet, for this concrete to be extra durable, AAC should be covered with one last finish. The applied finished could be siding, natural/engineered stone, or polymer-modified stucco.
If AAC is utilized for basements, contractors should take note of a few things:
· The AAC surface, particularly its outer face, should be coated with a very thick waterproof material layer.
· The surface area of AAC concrete will break down quickly when exposed to weather or soil moisture.
· Interior surfaces can only be finished using plaster pile, drywall, paint or tile. It can also be left exposed.
Benefits and Drawbacks of Autoclaved Aerated Concrete
Below are some of the most extraordinary benefits of AAC:
· Highly termite-and-fire-resistant
· Great material for acoustic insulation and soundproofing material
· Available in various sizes and forms
· The material is recyclable.
· The high thermal mass can store and release energy over time.
· Because it is lightweight, holding and installing it is easier.
· Easier to cut for holes and chases for plumbing and electrical lines
· Economical handling and shipping compared to concrete block or poured concrete.
Like all building materials, autoclaved aerated concrete also has some drawbacks:
· The products can show inconsistencies both in color and quality oftentimes.
· If AAC is installed in high humidity environments, interior finishes will require lower vapor porousness while the exterior finishes might require high porousness.
· R-values are generally lower when compare to energy-sufficient insulated walls construction.
· Costs are higher and tend to increase compared to the conventional wood-frame construction and concrete block.
· The strengths of AAC is 1/6 to 1/3 compared to the traditional concrete block.
AAC: The Ideal Material for Resilient Buildings
AAC is proven to offer several unique advantages in climate change when building more resilient buildings is critical. The vulnerabilities being faced today are incredibly significant and will continuously emerge and increases over the years. Storms and flooding events have become more extreme, wildfires are more very frequent these days, and even termites are more widespread. Oftentimes, standard wood-frame construction will not that useful anymore.
With AAC, the occurring and emerging issues can be reduced. AAC might not solve such issues, but it can certainly help.
1. AAC is fireproof
Wildfire has been a growing concern today. There have been several destructive wildfires in some states, and it is very devastating. Over 10,000 homes and 18,000 structures are destroyed because of the wildfire. That is why there is a desperate need to find better building materials for houses and infrastructures today. Good thing that AAC is introduced to the market. It is one of the commonly suggested concrete materials of many contractors.
AAC is proven to be a non-combustible material. The exterior finishes of it can either be fiber-cement siding or cement stucco that can help avoid a structure fire. According to AERCON, a unique property of this concrete is that it fully contains crystalline-formed water. When this kind of water is heated, it produces steam that will escape through the entire porous structure without making the surface spalled.
2. AAC serves as a building system for flood-prone areas
It is no denial that the flood risk is intensifying as the climate becomes increasingly warm. For instance, in coastal areas, the sea level is rising, increasing the frequency of flooding events. There has been more intense rainfall in the U.S. in most places, leading to more flooding occasions. With that being state, it is a very great idea to build using materials that can be wet and dry out at the same time.
AAC is more than capable of moistening and drying out. The material itself can absorb moisture. While following the manufacturer’s suggestions for surface treatments, AAC can dry out without any lasting damage. As a matter of fact, this monolithic material can function well as it serves as a seasonal moisture buffer. Thus, it absorbs moisture during the summer season with high humidity, and it will release that stored moisture during the winter months.
· AAC is purely organic; hence, no part of it can decay.
· There is no food source of mildew and mold in ACC, although when it gets wet, ensure to dry it out.
· Use a damp proofing layer or waterproofing in the exteriors in some cases.
· Gypsum plasters or minerals are suggested as interior finishes for this concrete.
· Use either rain screen detail or inorganic stucco with applied siding and strapping.
3. AAC and wind loading
Autoclaved Aerated concrete can absolutely provide a higher degree of wind resistance if proper reinforcing is implemented. Tons of strength is going to be provided with the grout-filled cores, reinforced-vertical, and bond beams. When AAC is ordered, the cored block needs to be specified to identify the advanced structure requirements. Manufacturers and contractors often provide assistance.
Interlocking AAC walls, floor panels, roofs are determined at proper measurements and thicknesses. Concrete contractors can work collaboratively together to achieve any level of structural requirements quickly. With many predictions of intense storms today, it makes sense to go further with the minimal suggested structural designs with AAC or in any building systems for this matter.
4. AAC and passive survivability
A design criterion labeled as passive survivability has emerged right after some of the strongest hurricanes. The storm has caused extended power outages. The idea is strongly suggesting that the buildings must be designed with passive design features and high insulated exterior membranes. By doing so, it will maintain habitable settings despite losing power during intense storms.
To satisfy passive requirements, attaching additional exterior insulation is highly suggested. AAC with insulation in the outer surface provides tons of thermal mass inside the insulated membranes. It helps in maintaining livable temperatures during the loss of heating fuels and power outages. With the combination of passive solar designs such as natural ventilation and shading, the thermal mass will keep buildings extra safe in the long run. No supplemental energy is also needed within the process.
Plumbing and Electrical Installations in AAC
Installations both for plumbing and electrical in AAC are typically placed in routed chases. It is important to take care of it meticulously, especially when laying out the chases. It is a way of ensuring that the structural integrity of AAC elements is well-maintained.
· Do not reduce the structural thickness or cut the reinforcing steel of the AAC elements unless if permitted by the designers.
· In spanning AAC elements vertically, horizontal routing must be allowed only in areas with compressive stresses and lower flexural.
· In spanning AAC elements horizontally, vertical routing must be considerably reduced.
· If possible, it might be beneficial to offer designated chases for enormous quantities of plumbing.
From an environmental viewpoint, AAC is a mixed bag, and this material works well for people with chemical sensitivities. Along with the benefits mentioned above of this concrete, it also provides excellent assemblies. With expanding interests in resilience today, particularly for buildings, the prospects for AAC will get brighter. It will finally emerge one day as one of the best building materials.