Masterbuilder in collaboration with Baton Consultants is starting a series for students. The articles in this series are for students. They are written towards improving the thought process & making the students ready for the real world.



    The real world, what is so different about the real world?

    At the college level, many students do not get enough exposure to material, equipment & projects. There are several gaps between the curriculum and the actual working. In fact, I will not mince my words in calling the real world a cruel person, who expects civil engineers & architects to be well prepared & knowledgeable from day one.

    What is it that I need to know about AAC Blocks?

    The thirst for better building material is never ending. Scientists globally are doing research on how improvements can be made in areas of energy saving, material saving & pollution control. Our topic for this article is an invention which is exactly pertaining to these areas.

    Since the last five or more decades, AAC blocks or Autoclaved Aerated Concrete blocks have been giving us the following significant advantages.

    a) Insulating properties giving lower electricity bills for relatively lesser usage of air conditioning
    b) Will have better Fire resistance due to its porous structure
    c) Easy to cut, reducing the wastage while in application
    d) Lesser energy in transportation due lightweight
    e) Easy for labour to handle
    f) Large size increases speed of work
    g) Lighter structures & lesser steel

    AAC blocks are factory made. This revolution has or will eventually stop the brick usage & reduce the pollution plus child labour issues.



    Unlike most other concrete applications, AAC is produced using fine aggregates. Quartz sand, calcined gypsum, lime (mineral) and/or cement and water are used as a binding agent. Aluminum powder is used at a rate of 0.05%0.08% by volume (depending on the pre-specified density). In some countries, like India and China, fly ash generated from coal fire power plants and having 50-65% silica content is used as an aggregate.

    The process of manufacturing the blocks involves the following steps.

    Materials like sand, water, quicklime, Aluminium powder, Gypsum, cement and fly ash are collected in various bins. Sand is well grounded by grinders and oversize is removed.

    Each item is then weighed & mixed in a mixer. The slurry is poured into moulds to form green cakes. The green cakes are cut into the required size before autoclaving. Rough edges are also removed at this stage.

    The steam cures the green cakes under pressure. The cooling also happens in the chamber. Autoclaving is a process involving a pressure chamber used to carry out the manufacturing at an elevated temperature and pressure different from ambient air pressure.



    When AAC is mixed and cast in forms, several chemical reactions take place that gives AAC its light weight (20% of the weight of concrete) and thermal properties. Aluminum powder reacts with calcium hydroxide and water to form hydrogen. The hydrogen gas foams and doubles the volume of the raw mix creating gas bubbles up to 3mm (? inch) in diameter. At the end of the foaming process, the hydrogen escapes into the atmosphere and is replaced by air.

    Because of the relatively low temperature used AAC blocks are not considered as fired brick but a lightweight concrete masonry unit. After the autoclaving process, the material is ready for immediate use on the construction site. Depending on its density, up to 80% of the volume of an AAC block is air.

    Laying these Blocks is also very easy & fast. Regular cement mortar can be used but most of the buildings erected with AAC materials use thin bed mortar. Thin bed mortar is basically polymer modified to increase properties like adhesion. The thickness required is about 3 mm, depen-ding on the national building codes. AAC materials can be coated with a stucco or plaster compound to guard against the elements, or covered with siding materials such as brick or vinyl.

    In some buildings, Gypsum plaster is directly applied over AAC blocks. This can be done for internal walls which are then directly painted. Thus saving time & construction cost.



    A few side effects of AAC blocks have been observed. The dry shrinkage test needs to be done by ACC block makers & users. Each block has the tendency to shrink during actual usage. If this shrinkage happens beyond permissible limits, the block cracks which is extended in the walls. Such cracks can cause leakages & spoil the finish of the walls.

    The blocks are also brittle in nature & can break during application. They need to be handled more carefully than clay bricks to avoid breakages.

    The Open Book Contest

    This contest allows you to read books or search the internet for answers. What we are looking for is the writing style specially the explanation part which needs to be crisp & smart. Please take part in this contest. It will give you a chance to interact with the author as well as help brush up your knowledge for that special interview & get your dream job.


    Mandar Chitre, Consultant, Trainer & Writer


    Mandar Chitre is a Consultant, Trainer & Writer. He comes with a 20 years of ex-perience in the construction & building material industry. Mandar is an engineering graduate with masters in marketing. He also holds a diploma in business management & indirect tax. He is one of the very few marketing professionals who also holds a diploma in corporate laws. Mandar has a completely diversified portfolio ranging from multinational to owner driven companies & sales to supply chain. As a writer, he has won a few national prizes.


    1. Very good.
      We are manufacturing aac with fly ash in India.
      We are facing crack problem in dried cake.
      The carbon content in fly ash is @10%.
      We had done lot of trials but still the problem is present.
      Please guide in this matter, if possible.
      Mahaveer chougule


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