Query Received From - Mohan Raj
Can we use aac blocks masonry in 1st floor as load bearing wall @ roof height of 10′ with continued 6″ r.c beam lintel?
Solution by gharpedia
AAC Blocks are a recent invention and are used as an alternative to traditional red bricks. They are made from Aerated Autoclaved Concrete (AAC), which is made up of cement, lime, sand, water, and additives. Sometimes instead of sand, fly ash is used as fine aggregate to manufacture AAC blocks. They are lightweight blocks which are easy to handle and are sustainable. AAC blocks are used for load bearing as well as non-load bearing walls, partition and panel walls, an inner leaf of cavity walls or a backing to brick masonry. Mostly AAC Blocks are used in RCC framed high rise structure. Hence there arises a confusion that can we use AAC blocks in load bearing structure? Here we have given brief information on the use of AAC blocks in load bearing structure.
AAC blocks are prominently used in South-East Asia for a decade. They are widely used in masonry units in a high-rise RCC framed structure. The major advantage of AAC blocks is that they are lightweight and hence contribute less to dead load. This can help in reducing the requirement of structural steel in the RCC framed structure. Hence leading to economical construction.
AAC Blocks which are manufactured in accordance with IS – 2185 (Part – 3), are classified into two grades, Grade 1 and Grade 2. Depending upon the grade of AAC blocks, their compressive strength varies from 1.5 to 7 N/mm2. Generally, for load bearing structure, masonry units should have 3.5 to 4 N/mm2 compressive strength. Hence, AAC blocks of a suitable density must be used in a load bearing structure.
Dry Density of Blocks (kg/m3)
Minimum Compressive Strength (N/mm2)
|451 to 550||2.0||1.5|
|551 to 650||4.0||3.0|
|651 to 750||5.0||4.0|
|751 to 850||6.0||5.0|
|851 to 1000||7.0||6.0|
AAC blocks are available in the following nominal dimensions:
- Length: 400, 500 or 600 mm.
- Height: 200,250 or 300 mm.
- Width: 100, 150, 200, or 250 mm.
The blocks are also available in the corresponding half lengths of 200, 250 or 300 mm.
The major disadvantage of AAC blocks they are very expensive. For small load bearing structure, they can be uneconomical. Also, for small storey structure, which may load bearing or framed structure, you require fewer numbers of AAC blocks as compared to red bricks. The price of fewer numbers of AAC Blocks will be more as compared to the bulk purchase. Hence, from an economical point of view it is not recommended to use AAC blocks for load bearing structure as there is no advantage available in saving of structural steel.
Load bearing is used for low rise structure only. Further, it is the thickness of wall which is important for load bearing walls. Hence availability of different sizes of blocks so that sound wall can be constructed of different thickness such as 300, 450 or 600 mm is crucial. Such walls should be possible in good english bond to impart strength. Hence the walls need to be designed by a structural engineer. As being a new material to construction, contractors, masons, and labourers do not know about its placing methods, techniques, etc.
Theoretically, you can use AAC blocks in load bearing structure provided they are available in the required sizes.