Mastering AAC Blocks

AAC chemistry, like a Twenty20 cricket game, has two batsmen. They bat and score runs individually, and give strength to the AAC product. These two batsmen are Cement and Lime. They undergo their own hydration reactions – independent of each other. And they both contribute to the strength of the product.

Let's look at this twin hydration system closely...

In 2013, I was possessed by the idea of setting up an AAC plant. It was the "in-thing". I wanted to become a first-generation entrepreneur – with no business background in the family. You may say that a mid-life bug had bitten me. And I took the plunge. Describing how we sailed through the ups and downs of the business is a long story, but all I can say here is that the journey was worthwhile.

I have a book on setting up and running an AAC block plant, "How To Run Your AAC Block Plant". It will discuss many finer points like finalizing the plant layout, controlling the process parameters, maximising production, and ensuring top product quality. The above book is written for readers who want to either set up a plant or for those facing challenges in running a plant. Both these topics – setting up a plant and running it – contain an ocean of information and merit a separate book.

In this chapter, we will look at the production process of AAC blocks.

"Show me the proof", my client shouted at me. I had no clue what to say. It was one of those hard days when I did not know how to speak to my client. He was furious about the weight of the blocks. The truck had reached the client's site, and his unloading workmen informed him that these blocks were heavier than the last truck they received.

The client immediately took two samples to the laboratory – one from the last truck and one from the current truck. And yes indeed, there was a substantial difference in the weight of both the blocks. The client was on the phone with me, "What kind of consistency do you have in your production?"

After I understood the issue, I explained the concept of dry density and IS code requirements to my client – but he thought I was trying to fool him by using technical terminology Finally, he asked me the above question, "Show me the proof – that what you are saying is the truth."

This chapter is for those who will need proof to show your client.This chapter is also for those who genuinely want to understand how to test AAC blocks.

As much as the taste of a biryani depends on the cook, so do the test results of an AAC block depend on the technician. Not Good. Sorry for the unscientific comparison with Biryani, but one slip from the lab technician and the results are distorted. Therefore, this chapter alerts us to the pitfalls, even though the IS codes give step-by-step procedures for all five parameters.

The IS code 2185 (part 3) has specified five properties for the AAC blocks. We have seen them in detail in the previous chapter. Interestingly, test procedures are not given for these parameters in the IS code 2185 part (3). The following list shows the test parameters and the corresponding IS code numbers specified for its test procedure

We will briefly discuss the test procedures to be followed for these tests. The first one is the dimensional tolerance which can be easily checked with an accurate measuring scale. The rest of the four tests need detailed procedures ...

At the end of World War 1, Europe wanted a building material that would keep the cold from coming inside. This material had to be cheap, readily available and easy to work with. What else would fulfil these three criteria than some form of concrete? The AAC blocks were invented to keep the building thermally insulated – to keep the cold out in Europe and the heat out for us in India.

We measure heat by a simple unit of degree Celsius. But this unit doesn't tell us directly about the property of building material. We need to know the flow of heat through a surface in a building material to check its suitability. The terms U value and R value inform us about this unique property of every building material – the flow of heat through a wall surface. Both these terms are opposite to each other

A high R-value means a low U-value, but their real difference is much more complex.U-value is more of an engineering term as it describes thermal performance. When looking for a building material for your structure, you usually look for a high R-value because you want the heat (or cold) to stop coming inside.

The unit of R-value is m2K/W whereas the unit of U value is precisely the opposite of W/m2K.

Imagine you want to construct a house for the wealthiest person in the world. You want to use quality building materials for the construction. Cost no concern. What will you use for masonry?

A customer has enormous choices today – each material offers some unique perspective to the customer. But how does a customer evaluate the suitability of these products in his construction? Not every customer is going to value environmental protection. Few may want faster speed and lower cost of construction. Others may need safety features like earthquake resistance and fire resistance. And few others will value comfort factors like high thermal insulation and low lifetime cost of the structure.

And what about ease of construction – like that famous TV commercial "Fill it, Shut it and Forget it?" Since you want to construct a house for the richest person in the world, you may need all the above benefits in a single product. You may want the house to have high fire resistance and earthquake resistance; you may want lifetime comfort for its occupants, or you would need high product consistency and possibly a faster speed of construction

Is it even possible to get all this in a single product?

Go and ask any site engineer. What is the one thing he is most worried about the AAC blocks? His answer will always be cracking in the wall. The problem is compounded due to a lot of misinformation on this subject. In this chapter, we will see various causes of masonry wall cracking and how to eliminate these causes at the root level. There are three secrets to superior AAC masonry construction. Once you learn these secrets, you will master AAC wall construction. But first, let us look at the four causes that lead to cracking in AAC block wall:

8.1 Cracking Cause No 1: Drying Shrinkage of AAC blocks
8.2 Cracking Cause No 2: Deflection of beam above the wall

1. The AAC block has cracked at some places in the wall. What is the reason?
2. The Chakravyuha of Compressive Strength Test