AAC panels ... used for partitions.
AAC ‘provides ideal solution’
Germany-based autoclaved aerated concrete (AAC) plant and systems supplier Hess outlines how the versatile, modern-age material can provide an ideal solution in the construction of partitions.
01 September 2010
AS construction costs continue to rise, companies are on the look-out for building materials and systems that help reduce labour, handling and transportation costs, while offering good performance and being kind to the environment.
One such solution is autoclaved aerated concrete (AAC). Also known as pre-cast aerated concrete (PAC), AAC boasts a range of physical properties which are advantageous for today’s market requirements. Available in a wide range of products, AAC comes into its own when it is used as a system – right from the basement to the roof. The material offers a high degree of thermal and sound insulation, is fire resistant, and helps save energy. In addition, costs can be cut down by using AAC during the construction and finishing of building.
In the construction of partition walls, blocks as well as other building material systems are commonly used. However, working with blocks in small thickness of 75 to 100 mm can be time-consuming, while other building materials used as cladding generally need a steel structure frame on which the panel can fixed. AAC, however, offers simple solutions even for such applications.
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For quick and economic installation, AAC panels of standard room height can be produced with a small reinforcement installed in the centre of the panels, enabling them to be easily handled by just two masons equipped with special lifting tools. The partition panels can be easily cut on site in any dimension using an electrical handsaw fitted with a diamond blade.
The small reinforcement at the centre of the panel enables finishing of cable dugs and sockets.
AAC also offers substantial material savings compared to concrete blocks.
To construct a 24-sq-m partition wall, 8 m long and 3 m high, 300 concrete blocks measuring 400 by 200 mm size as well as mortar are required. However, the same wall would require just 13 standard AAC panels measuring 1.8 sq m each as well as one 200-mm-wide section. The rest of the panel that has been cut can be used for another wall, so there is never any wastage.
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Tools for masonry (right) ... stirrer for mixing the thin-bed mortar (1) , angle (2), rubber hammer for driving the blocks together (3), tooth trowels of various breadths for applying thin-bed mortar (4), water level (5), hand saw for cutting pieces (6) and plane board for levelling any unevenness (7). |
Openings for windows or doors can be made using a section of a panel, which is used as non-bearing lintel at the top of the opening.
If a standard room layout is used across a number of buildings, panels can be cut to a specified size at the factory and delivered to the site, resulting in speedier installation more cost savings.
Producing AAC in the state-of-the-art machinery ensures that panels have super-smooth surfaces, and the joints requiring only minor treatment before the wall is finished with wallpaper, paint or any other material. This is a huge advantage for contractors as it saves time and plastering costs. Also, the panels offer clients the opportunity to use their own creativity in finishing such surfaces.
Easy for building
Because of its light weight, larger-sized AAC blocks can be used to greater advantage over traditional concrete blocks.
Let us compare a 400 by 200 mm concrete block with an area of 0.08 sq m to a 600 by 250 mm AAC block with an area of 0.15 sq m.
About 12,500 such concrete blocks would be required to build a 200-mm-thick wall with an area of 1,000 sq m resulting in a total weight of 287,500 kg.
However the same wall could be built using just half as many AAC blocks weighing a third of the total weight of the concrete block wall, with a significant reduction in installation time and the quantity of cement glue or mortar consumed.
AAC systems require just 1 mm of cement glue at horizontal joints only, while the vertical joints are connected using the tongue-and-groove technique.
Similarly, for a 1,000-sq-m wall with AAC blocks of 200 mm (equal to 200 cu m), only 2,200 kg of cement glue is needed; while for an equal volume of concrete blocks with a 10-mm joint, around 10 times more cement mortar is required.
This means a 200-mm-thick AAC wall with a total surface area of 1,000 sq m is around 200,000 kg lighter in comparison to a similar wall made of insulated concrete blocks. When these figures are extrapolated across the entire building from the foundation to the roof, it would show very high savings as well as reduced stress for the mason, due to easier handling of AAC panels on site.
Handling & finishing
Handling, cutting and gluing AAC blocks is also very simple and the tools used for these applications are low in price and simple to operate.
Due to their precise manufacture (+/-1 mm in tolerance), AAC blocks do not require skilled masons for installation. The blocks are also easy to cut with tools used to cut wood.
Tools for masonry include a stirrer for mixing thin-bed mortar, an angle, a rubber hammer for driving the blocks together, tooth trowels of various breadths for applying thin-bed mortar, a water level, a handsaw for cutting desired pieces, and a plane board for leveling any unevenness.
Finishing of AAC buildings is as simple as the masonry work itself, with internal plastering requiring an application of 5 mm to 8 mm of gypsum lime. The surface of this plaster is very smooth, allowing wallpaper to be fixed directly or any desired coating to be applied. Tiles can be fixed directly on to the AAC wall with tile glue – and only a primer has to be used to avoid the rapid drying of the glue.
It has been said that AAC structures cannot support a heavy load because of their light weight. However, as with any building material, it is necessary to use an approved fixing material, such as a dowel, screw or nail for AAC. For example, a load of up to 0.90 kN can be supported using a dowel application. For higher load, other solutions are available.
Buildings made from AAC are generally erected faster and their finishes are cheaper in terms of plaster work, tile application, and air-conditioning, cable or other ducts or opening. Cables, water and gas pipes can be installed within ducts or openings using manual tools and a thin plaster applied after.
Low heat, high profit
AAC systems offer superior thermal insulation with no thermal bridges. Every contracting company is aware of how time-consuming the cladding of ceilings can be and the huge expenses incurred. AAC ceiling panels can be installed without scaffolding as the prefabricated panels can be fixed directly onto the prepared surface. Immediately after fixing the slab, the ring beam can be cast and masonry work can proceed, thus saving time and money.
It takes only 24 working days to erect a 320-sq-m villa, starting with the installation of the concrete slab to the completion of the roof, using around 180 cu m of masonry and 400 sq m of slabs. The trained team for this job comprises a foreman, six masons and a crane operator.
AAC slabs can also provide a suitable solution for stairwells and elevator shafts – or any other openings between the lower and upper floors. For such needs, a steel structure comes prefabricated from the factory and can be fixed during the laying of slabs, and can support the load immediately after installation so that masonry work can continue immediately, thus speeding up erection work.
Conclusion
Working with AAC systems is easy – all that is required is some training in handling a slab gripper, partition handling tools and an insight into AAC construction systems to achieve a major boost in performance on site.
The building material can be delivered on time to the site on trucks, with blocks delivered on wooden pallets and moved by crane onto the concrete slab or the AAC ceilings, thus reducing handling on site while minimizing cost and installation time.
AAC has outstanding physical properties as a thermal insulation and solid building material, while offering savings in terms of time and manpower and hence in total construction costs. This apart, it enhances the living conditions for the occupants, thanks to its excellent thermal isolation properties. Finally, in an increasingly environment-conscious world, AAC also boasts the benefit of saving on natural resources and energy.
