During the previous posts , we had a review of the brick masonry ,stone masonry and then also went on to enjoy some basic estimation in brick work.
While speaking of masonry , the name of AAC blocks invariably comes in the picture .Some people also
The C4X blocks were invented in Sweden in the year 1920 and then extensively used in European countries till recent years. For Asian countries, the phase has just begun and we are witnessing a rapid replacement of the traditional red clay bricks to the AAC blocks.
The blocks in brief:
The auto-claved aerated concrete blocks are made from Quartz sand, calcinated gypsum, lime, and/or cement, aluminium powder and water , fly ash and ferrous oxide. Or to simplify , the composition is Cement, Fly Ash Sand & Aeration Compound
Normal dimensions are:
Length: 625 mm. Height: 240 mm.
Thickness: 50 mm. ,75 mm. ,100 mm.,150 mm. , 200 mm. & 300 mm.
Which size to use ?
Many combinations can be worked out depending on specific needs.
Normally, the external walls are made with 150 mm thick blocks whereas for internal walls ,100 mm thick blocks are used. the architectural features such as fins or Cavity walls are made with 50 mm or 75 mm thick walls.
1.Light weight :
The micro structure is porous which makes it lighter (600 Kg/CuM) than the red clay bricks ( 1900 Kg/CuM) and much lighter than conventional concrete ( 2500 Kg/CuM) which directly implies :
1.1 Reduced dead loads due to masonry on beams ,columns and footings. This results in lowered RCC sizes and hence reduced costing.
1.2. For masons the handling is easier .
1.3 Due to its larger size, no of blocks to be handled per CuM of AAC masonry is much smaller than Brick work. [ Only 67 AAC blocks of size 625 mm x 240 mm x 200 mm are needed for 1 CuM whereas for same volume of brick masonry , the mason has to handle 514 bricks.]
It does not need the clay and hence the fertile soil from the green fields is not wasted.
3.3. Lesser piece to piece variation
lower environmental impact as:
Improved thermal efficiency reduces the heating and cooling load in buildings.
Light weight saves cost & energy in transportation, labor expenses, and increases chances of survival during seismic activity.
4. Yes, it does reduce the RCC as well as steel sizes as its density is pretty lower as compared. Requirement of mortar for laying AAC blocks is reduced due to less number of joints. Similarly material required for rendering is also lower due to dimensional accuracy of AAC.
Author’ s note :
Let me put on records my sincere appreciations for Ms.Rakshita who answered to my questions about AAC blocks .You can refer to the question and answer at this link .