Skip to main content

Cracks in AAC Block Walls

Why there are more complaints of Cracks in Walls made with AAC Blocks :
Drying Shrinkage
During the manufacturing, when AAC blocks come out after autoclaving, they have high amount of residual moisture from 24 to 28%.
(This is the reason most of the manufacturers do not despatch the blocks to the market as the strength of the blocks is less and they tend to chip or crack during loading and unloading of the blocks.)
This residual moisture leaves the blocks predominantly in the first 48 hours. As the moisture leaves the blocks they shrink. Imagine we have got installed these blocks during a masonry wall within the primary 48 hours then the shrinkage happens inside the wall. The shrinkage may be a massive force which tears the wall vertically resulting into a crack at the centre of the length of the wall.
On the other hand if the blocks are allowed to “dry down” for a period of 48 hours to 96 hours before they go in a masonry wall, then you will find that the cracks in your building would be reduced by 80%.
Now what about the remaining 20% of the cracks?
There may be two reasons for the remaining 20% of cracks in the walls made with AAC Blocks. The first one is workmanship.
We need to pack the wall with the upper beam before we set any mortar therein gap. We can use 10 mm size aggregates for the same. Our RCC beam is not in ‘line and level’. This leaves variable gaps between the top of the wall and the bottom of the beam. This gap creates a point load on the wall due to deflection in the upper beam. Once the wall is full of the aggregates then the purpose load from beam gets converted into a udl and stress concentration within the wall is reduced eliminating the cracking in the wall.
Compressive strength or Tensile strength
The other reason for cracking is the strength of the blocks which needs to be minimum 4Mpa which brings down the drying shrinkage value to less than 0.05%.
Another cause is using strong mortar. Use of higher grade of cement to make mortar. Use of rich cement mortar i.e. the cement content is higher than specified in the design mix.
Jointing Mortar Compressive Strength is higher than AAC block.
Now if block compressive strength is less than its joint mortar strength with less construction joint, the surface tension of mortar will be very high. And it will be crack because of very less tolerance limit in AAC block.
After knowing all these things, a person named Mr. Ramakrishna has come out from the company and started his own dry mix unit. He is selling more than 600 tons of dry mix products in Hyderabad whereas the company he was working earlier, is not able to sell the same throughout India.
Expansion Joints
The main cause is that the lack of expansion joints, we should never run blockwork longer than 6m without joints.
Even for every 1200 mm height, we should have bed reinforcement.
Plant Rejections
If the plant rejections are more, it will also reflect in loading, unloading and in the site (after construction). For example, Ascolite, ecolite, shreeshakthi plants have fewer rejections (below 3%) whereas in corporate companies rejection levels are more than 5% and the cracks after construction are more. Big corporate company which uses dry fly ash in their batch, have more complaints of cracks in the market. In the enquiry it was found that their rejection levels are more than 10%.


  1. This article provided me with a wealth of information about Concrete contractors San Antonio. The article is incredibly helpful and offers some of the most useful information. Thank you for sharing it with us.

  2. I generally want quality content and this thing I found in your article. It is beneficial and significant for us. Keep sharing these kinds of articles, Thank you. Christopher Contracting


Post a Comment

Popular posts from this blog

Recipe Calculation for AAC Blocks

Recipe is nothing but knowing the dry weight (batch weight) of one batch or one cake. To find out dry weight, we should know the desired dry density of final block. Let us work on the density of 600 kg/m³. Batch Weight = Density x Mould volume Density = 600 kg/m3 Dimensions of the mould : Length = 4840 mm = 4.84 M Width = 1250 mm = 1.25 M Height = 670 mm = 0.67 M Volume of the mould: 4.84 M x 1.25 M x 0.67 M = 4.0535 M³ Batch Weight = 600 x 4.0535 = 2432 kg (We have taken mould height 670 mm, which is actually depth of the mould. Generally we maintain the cake height equal to mould level. But in some AAC factories, cake height may be 650 mm or 680 mm depending on the parameters like quantity of returns required, sinking of cake, uneven surface of the cake, etc., In this case cake height should be taken to calculate the volume.) Batch weight or Dry weight consists of binders (Cement and Quicklime), Fly ash or Sand, returns and anhydrite. Usually th

What is Aluminium Powder? Why it is used in AAC Plants?

  Aluminium Metal powder or paste Aluminium powder, which is commonly used as a reaction agent in AAC Plants, is a fine granular powder made up of Aluminium Metal. Process of Manufacture: The aluminium powder is usually manufactured in many forms such as flaky particles, granulated powder (atomised aluminium) etc. There are different processes one can use for the production of aluminium powder. The metal is melted in furnaces, and the temperature is maintained around 720 to 760 C. Atomised Aluminium is produced by blasting the stream of molten Aluminium into small articles by air jet. For this purpose, an atomiser is employed which consists of a straight tube with lower end dipped in molten metal and upper end terminating as a little orifice. A jet of hot air under pressure is passed through armular opening near the top which impinges on a stream of molten Aluminium drawn by suction through the orifice. This results in the formation of small particles of Aluminium. Th

What is AAC? What are the properties of AAC? How AAC blocks are produced?

  Definition of AAC Blocks   AAC Blocks   A - Autoclaved A - Aerated C - Concrete   Autoclaved aerated concrete is a lightweight concrete containing uniformly distributed voids that is subjected to high-pressure steam curing.   Production of AAC Blocks   This is a light- weight building material produced by autoclaving a set mix of fine siliceous materials such as ground silica sand or flyash and the binders like Portland cement and lime. Lightness is achieved by incorporating a large proportion of closed microscopic pores in the slurry with the help of entraining or foaming agent. The basic raw materials are fine-ground sand or fly ash, cement, quicklime, anhydrite or gypsum, water, and aluminum  powder or paste as a rising component. A suitable mixture of these raw materials is poured into a mould, and the rising process starts due to the development of hydrogen gas formed by the reaction of aluminium in the alkaline suspension. After 20 to 40 minutes the maximum rising