Mortar for aerated concrete blocks: components, selection and preparation

When building aerated concrete block structures, mortar is an essential element that helps to ensure durability and stability. The quality of your building project can be greatly affected by choosing the appropriate mortar to use with aerated concrete blocks, regardless of whether you are a professional builder or a do-it-yourself enthusiast.

The special qualities of these lightweight blocks are enhanced by the thoughtful selection of mortar ingredients for aerated concrete blocks. Common components include water, cement, sand, and lime; however, depending on the needs and the surrounding environment, the amounts and extra additives may change. A solid bond and the best possible thermal insulation can only be achieved by carefully selecting the components.

When choosing the right mortar, it’s important to take into account things like the structure’s intended finish, exposure to weather, and load-bearing requirements. A range of mortar formulations are available to meet different requirements. Structural walls require mortar with high strength, while non-load-bearing partitions require a more flexible mixture.

Making the mortar ready is just as crucial. The performance of the mortar depends on a consistent blend, which is ensured by using the right mixing techniques. Common problems like poor adhesion and cracking can be avoided with careful attention to the mixing process, which includes blending the material thoroughly and using the proper water-to-cement ratio.

This post will cover the ins and outs of mortar composition, help you make the right choice, and provide you step-by-step instructions on how to make the ideal mortar for your aerated concrete block projects. With this understanding, you’ll be ready to build long-lasting, sturdy structures that withstand the test of time.

Topic	Details
Components	Mortar for aerated concrete blocks typically includes cement, sand, lime, and water.
Selection	Choose a mortar with good adhesion, flexibility, and durability to ensure a strong bond with the blocks.
Preparation	Mix the dry ingredients thoroughly, then gradually add water until the desired consistency is achieved.
Proportions	Common mix ratios are 1 part cement, 3 parts sand, and a small amount of lime.
Application	Apply a thin, even layer of mortar to the blocks to avoid gaps and ensure stability.

To avoid confusion

Non-specialists won’t comprehend terms like foam concrete, autoclaved and non-autoclaved, or aerated concrete. Thus, we will give explanations at the outset of the article.

Foam and aerated concrete

The GOST requirements for these cellular concretes are identical, indicating their high degree of similarity. They have a porous structure with numerous air-filled cells throughout the volume, in contrast to heavy, dense concrete. As a result, they serve as heat-insulating material in addition to structural ones. variations in the pore formation process.

• Foam concrete — pores are formed by introducing a foaming agent into the solution, usually a surfactant (surfactant).

In other words, while being washed, the mixture foams like water mixed with soap and then solidifies in this form.

• Aerated concrete — pores are formed by introducing a foaming agent, most often based on aluminum powder. A reaction occurs with the release of gases (mostly hydrogen), which form pores.

Because aluminum reacts so well with alkalis in its finely dispersed state (powder form), an alkaline reaction can also be produced by a cement-based solution, which shields the reinforcement from corrosion.

This is very similar to how the carbon dioxide that results from quenching baking soda in yeast-free baking makes buns loose (see the picture below).

The manner in which pores form is also related to the differences between the materials:

1. Foam concrete has closed pores and can vary significantly in size.
2. Aerated concrete has smaller pores (about a millimeter) in size, some of them are connected to each other. They are more uniform in size.

Because of this, foam concrete’s pores are closed, making it less uniform in its properties throughout the volume than aerated concrete, but it also absorbs water less well.

Autoclaved and non-autoclaved

Let’s now investigate the distinction between concrete that has been autoclaved and that has not.

Autoclaved

The first is more typical and is discussed the most. Lime binder is the foundation for its creation. Products made from this material are subjected to high pressure steam treatment in autoclaves to make it waterproof. The process for making sand-lime brick is the same, but a porous structure is not formed.

Therefore, it cannot be used directly on the construction site to create monolithic structures. Making things by hand is also challenging (unless you are lucky enough to have an industrial autoclave and a strong steam boiler on your property).

The primary benefit of autoclaved aerated concrete is its low cost, which comes from the solution’s 92%–95% sand content and reasonably priced lime remainder.

Cons: Because it absorbs moisture well, the material is sensitive to high temperatures and prolonged exposure to moisture.

Non-autoclaved concrete

Created using regular Portland cement as a base. In other words, the lack of a substantial filler and the presence of pores set it apart from heavy concrete. One can mold products and structures made of this kind of material at home or on a building site.

One of the benefits is that, provided subzero temperatures are not combined with its effect on the material, it is not afraid of moisture. It actually gets stronger with time instead of getting weaker.

A gray surface and a high cost are among the drawbacks. Nevertheless, white cement can be used to address the latter issue.

Let’s get straight to the block-making solutions now. First, we will examine the aerated concrete block mixture, which is based on Portland cement and can be made on its own. Next, we will examine its autoclaved sibling in more detail.

Mixture for non-autoclaved concrete

Let’s go over the components required to make the solution, how to determine its composition, and how to prepare it step-by-step.

Materials for the mixture

There are just a few ingredients needed to make an aerated concrete mixture:

• water;
• Portland cement grade not less than 500;
• sand;
• plasticizer;
• gas generator – aluminum powder or paste.

Because the walls separating the pores are so thin, we require high-grade cement to give them the strength they require.

Polypropylene fiber, which reinforces the material throughout the volume, can also be added to the composition of aerated concrete to increase its strength. In order to use less cement, a plasticizer is added. To promote gas formation, alkali is occasionally added in addition (the concrete mixture itself has an alkaline reaction with a pH of roughly 13, but it might not be sufficient).

With the exception of sand, the specifications are the same as those for the heavy concrete component parts (no impurities, standard compliance). We won’t use the one that is brought in from the quarry, even though it is regarded as premium for other building mixtures. We require very fine sand—that is, sand with a fineness modulus of less than 1.

How to determine the fineness modulus

Finding a set of sieves with a mile of 2.5, 1.25, 0.63, 0.315, and 0.16 mm will make it simple to determine the size module on your own. The steps are as follows.

1. We put the sieve on each other in order below with the smallest cells at the top – the largest.
2. We measure out sand, for example 1 kg and begin to sift it. The operation can be considered complete if, when shaking any of the sieves above the sheet of paper, there is no sifting.
3. Then we weigh the remains on each sieve and determine how many percent of the hitch they make up.
4. Determine the full residues that are indicated by A2.5, A1,25, and so on, the index after the letter is the size of the corresponding sieve. Full residues are equal to the balance on this sieve plus the sum of the remains on the sits above it (that is, the amount of sand that would not have been on it from above).
5. The fineness modulus of sand is calculated using the formula: Mk = (A2.5 + A1.25 + A0.63 + A0.315 + A0.16) / 100.

It is evident that sand is finer the lower its fineness modulus; in accordance with GOST 8736-2014 "Sand for construction work," they are categorized as follows.

Sand group	Fineness modulus (MK)
Very coarse	sv. 3.5
Increased fineness	sv. 3.0 to 3.5
Large	sv. 2.5 to 3.0
Medium	sv. 2.0 to 2.5
Small	sv. 1.5 to 2.0
Very fine	sv. 1.0 to 1.5
Fine	sv. 0.7 to 1.0
Very fine	up to 0.7

Sand that is fine, fine, or very fine must be ordered. It is referred to as dispersed filler in the composition of aerated concrete.

Suggestions. The use of dolomite flour is not prohibited by the standards in the event that obtaining the necessary sand presents difficulties. You may find it easier at times because this substance is widely used in agriculture to deoxidize soil.

What kind of aerated concrete will we prepare

The type of aerated concrete we will prepare needs to be decided next. Non-autoclaved concretes are required to meet the following density grades, which match the strength classes and frost resistance grades, as per GOST 25485-89.

Density grade	Concrete type	Strength class	Frost resistance grade
D400	Heat-insulating	B0.75; B0.5	Not standardized
D500		B1; B0.75
D600	Structural and heat-insulating	B2; B1	From F15 to F35
D700		B2.5; B2;

1. In the density grade, after the letter D, the density in kg/m3 of the material is indicated in numbers.
2. The concrete class is the strength guaranteed for 95% of samples in MPa.
3. In the frost resistance grade, after the letter F, the number of thawing and freezing cycles the material can withstand without losing more than 5% of its strength in a state completely saturated with water is indicated in numbers.

Using the most popular aerated concrete, D400, as an example, we will calculate the output to ensure that it complies with GOST.

Calculation

The most fascinating part of our article is this one. The truth is that the author, a construction engineer-technologist with a focus on monolithic concrete, was unable to recall or locate the calculation methods in his student notes; they were just never taught.

Additionally, you won’t find an online calculator (the only thing available online is a tool for calculating the quantity of building blocks needed; a mixture for making aerated concrete cannot be chosen). I had to research the literature and found multiple reliable sources.

Let’s make a reservation right away. The recipe is not only calculated but also experimentally verified in every production of aerated concrete. The majority of calculation techniques need to be adjusted through prototype testing.

Going off subject a bit, we can say that the cook engineer-technologist determines the quality composition of the mixture for aerated concrete, just like they do when creating a delicious pilaf recipe. The owner has a role to play when starting a business at home; experiment.

Calculation methods that were abandoned

There were several approaches found; we dropped four of them:

1. According to the publication: Sazhnev N. P. "Production of cellular concrete products: theory and practice", the formula is given: C = Rs x Kc / 100, where C is the amount of cement, Rs is the amount of dry components in the mixture in kg, Kc is the amount of cement in percent.
2. According to the book: Portik A. A. "All about foam concrete" the formula is similar: Rc = Rvyaz x n, here Rvyaz is the mass of the binder in kg, n is the proportion of cement in the mixed binder.

As you can see, the amount of cement is specified rather than actually calculated in these two methods:

1. Next edition: Makhambetova U. K. “A refined method for selecting the composition of foam concrete” offers a calculation using the formula: P = Pdry / (Ksx (1 + Spc), where Pdry is the mass of dry materials, Ks is the coefficient of chemically bound water, it is taken as 1.1 for preliminary calculations, Spc is the ratio of the mass of sand to the mass of cement.
2. According to the book: Kudyakov A. I. "Design of non-autoclaved concrete" the formula looks like this: Ц= ρб/(1.15-Снц), where ρб is the density of concrete, Снц is the ratio of filler and binder.

Upon examination of these two formulas, it becomes evident that the quantity of water that is chemically bound is established by a fixed coefficient. Furthermore, these formulas fail to consider the characteristics of cement, the circumstances surrounding the creation of the concrete structure, or the strength of the structure. Furthermore, the addition of fiber and plasticizer to the mixture is not taken into account by the aforementioned methods. It was decided to give up on them as a result.

Selected method

The publication of 2010 BelNIIS employees contained the most accurate calculation method (it should be noted that the author of this article completed his pre-graduation practicum there, albeit prior to the development of the calculation method presented below). It was decided to cite and apply it as a result. Here are the detailed instructions for carrying out the calculations.

• First of all, we find a rational ratio of the mass of the filler to the mass of solids: n = Gdn / (Gvyaz + Gdn), where Gdn is the mass of the dispersed filler (sand), Gvyaz is the mass of the binder. To do this, we use graphs obtained as a result of laboratory tests of various proportions of compositions. They are given below.

The graph indicates that n = 0.4 is the most appropriate value for our example, which has a density of 400 kg/m3, to fit into the strength normalized by GOST between classes B 0.5 and B 0.75.

• Strength can be adjusted if fiber is introduced. To do this, we find out the strength growth coefficient when introducing Kv fiber fiber from the table below.

Amount of introduced fiber fiber in kg per m3 of aerated concrete	1	1.5	2.5
Strength increase coefficient Kv	1	1.2	1.3

After determining the coefficient, you can compute the anticipated strength of concrete at 28 days by using the formula R28 = (5.3×10 -3x ρb-2.1xn-0.49)xKv. Taking 1.5 kg/m3 of fiber as our starting point for our example, we find that Kv = 1.2 and that R28 = (0.0053×400 – 2.1×0.4 – 0.49) x 1.2 = 0.94 MPa. This is marginally greater than the GOST-adopted class B 0.75.

You can take a smaller number n, decrease the amount of fiber, or leave everything as it is (extra strength does not interfere). Using 1 kg/m3 of fiber in our example, we obtain a strength of 0.79, which is comparable to class B 0.75.

• Next, we find out the amount of binder using the formula: Gbinder=ρb/(1+αмхмхсв+n/(1-n)), where αм is the degree of hydration of the binder (for most cements 0.7), mхв is the amount of chemically bound water (assumed 0.227).

For our example, let’s calculate: Gknit=400/(1+0.7×0.227+0.4/(1-0.4))=219 kg.

• Find out the amount of dispersed filler: Gdn=nxGknit/(1-n). For our example Gdn=0.4×219/(1-0.4)=146 kg.
• Next, the volume of gas is calculated using the formula:

Where ρ knit and ρ dn are the true densities of the binder and dispersed filler (on average for cement 3100 kg/m3 and sand 2400 kg/m3), Vg=Vb-((αxGknit)/ρ knit+Gdn/ρ dn+(αxGvyazhmkhsv)/1000). We use one cubic meter of aerated concrete in the computation.

Vg = 1-((0.7×219)/3100 + 146/2400 + (0.7x219x0.227)/1000) = 0.86 m3 is the formula we used in our example.

• Next, we calculate the pressure inside the gas bubble: Рп = ρбсх9.8хhф + Ратм, where ρбс is the density of the concrete mixture, hф is the height of the form, Ратм is the atmospheric pressure (for the calculation, we assume 101325 Pa).

Using aerated concrete, fill forms 0.5 meters high. In this scenario, the pressure inside the gas bubble will be ο = 400̅9.8̅0.5 + 101325 = 103285 Pa.

• Next, we calculate the amount of blowing agent (aluminum powder or paste) using the formula: Gg=((0.018xVgxPn)/(RxTxCal))x100, where R is the universal gas constant equal to 8.31 J/(mol x kg), T is the temperature in kelvins at which gas formation occurs, Sal is the content of active metal in the blowing agent in percent.

Sal = 85% and T=293 K (absolute zero, or -273 o C plus 20 degrees, is what we use for our example). Gg = ((0.018 × 0.86×101325) / (8.31 × 293×85)) x 100 = 7.57 kg is the formula we use.

• Next, the amount of water required to prepare the suspension of the blowing agent is calculated: Bsus = Ggx5, in our example Bsus = 7.57×5 = 37.85 kg.
• If it is necessary to enhance gas formation by adding alkali, then its amount is calculated using the formula: Gsh = Gvyaz х0.05. For us, Gsh = 219×0.05 = 10.95 kg.
• When adding a plasticizer, we calculate its amount: Gd = (Gvyaz x Dd) / Cd, where Dd is the dosage of the plasticizer in the ratio by weight, Cd is the concentration of the plasticizer solution. For our example, we take Dd = 0.005, Cd = 0.4. We calculate Gd = (219×0.005) / 0.4 = 2.73 kg.
• This is the most interesting part of this technique. If for calculating the amount of water in a solution of heavy concrete, tables or graphs are most often offered that take into account the required mobility and maximum the particle size of the coarse aggregate, then in the case of aerated concrete these characteristics are not important. The authors (as well as in almost all other recommendations) write that the mass of water should be determined experimentally.

We’ll use W/C=0.44, the ideal water-to-cement ratio, for our example. By using the binder consumption and the formula Βо= (W/C)̅Gвязь, we can calculate the water content. In this case, Βо=0.44̅219=96.33 kg.

Furthermore. As the volume of water is established empirically, you can reject any additional computations. However, once you’ve discovered the ideal mixture, you can simply modify the recipe—for instance, by substituting powdered aluminum for paste or sand with a different humidity.

1. Next, we calculate the amount of chemically bound water: Вхсв=Gвязьхαхmхсв, for our example Вхсв=219х0.7х0.227=34.8 kg.
2. We calculate the amount of water in the dispersed filler (sand): Вдн=Wдн х(Gдн/100). We take the sand humidity of 5% for our example, we calculate: Вдн=5(146/100)=7.3 kg.
3. Next, you need to find out how much water the plasticizer contains: Вд =(1-Сд)хГд. For our example: Вд=(1-0.4)х2.73=1.64 kg.
4. In the same way, we calculate the amount of water in the paste (if we use dry aluminum powder, then naturally there is no need to do this): Bg = (1 – Sal) x Gg. We calculate Вг=(1-0.85)х7.57=1.13 kg.
5. It remains to calculate how much water is needed to prepare the mixture without taking into account the moisture already contained in the components: В=Во-(Всус+Вхсв+Вдн+Вд+Вг). For our example, В=96.33-(37.85+34.8+7.3+1.64+1.13)=13.6 kg.

The computation is complete, and for ease of reference, the outcomes of our example are listed below:

1. Cement – 219 kg.
2. Sand (fine filler) – 146 kg.
3. Fiber – 1 kg.
4. Plasticizer – 2.73 kg.
5. Gazing paste – 7.57 kg.
6. Alkali for intensifying gas formation – 10.95 kg.
7. Water for preparing the paste suspension – 37.85 kg.
8. Water in the solution – 13.6 kg.

Preparation of solution for aerated concrete

We will now briefly discuss the technology used to prepare the non-autoclaved aerated concrete solution. The following operations are part of the process.

• We immediately measure out the water, from which we select a part for preparing a suspension based on powder or paste, and a solution plasticizer.

Suggestions. Heating the water is preferable because it will hasten the gas formation reaction.

• Make a suspension of the gas former by thoroughly mixing the paste or powder in water.
• Then prepare the plasticizer solution in exactly the same way.
• Mix the rest of the water, cement, sand and fiber, weighing them accurately. Add the plasticizer solution to the mixture. If alkali is used to activate gas formation (usually caustic soda), then we also add it to the mixture.
• Start mixing, for aerated concrete that does not have large filler (its particles additionally mix the other components when falling), it is better to use not the usual gravity concrete mixers, but forced action (with blades).

• After all the components except the suspension are well mixed, we add it. Gas formation begins, and the mixture significantly increases in volume. We continue mixing for a few more minutes until the entire composition reacts.
• Place the finished aerated concrete in molds or formwork and level the surface. No need to vibrate.

Pay heed. Even when the mixture is laid, pores are still being formed. As a result, the products have a hump that resembles a "brick" of bread. The mixture can be severed once it has solidified.

In this post, we can also provide a video that demonstrates how to prepare aerated concrete.

For aerated concrete blocks to be constructed with strength and durability, the proper mortar must be used. Cement, sand, lime, and water are the ingredients of mortar, and they must be properly chosen and combined in the right amounts. This improves the building’s overall thermal and acoustic qualities in addition to ensuring the stability of the blocks.

Take into account the particular requirements of your project when selecting the mortar. The kind of cement used and the proportion of lime to sand can have a big effect on how well the mortar works. Additionally, it is essential to modify the mixture according to the specific qualities of the aerated concrete blocks you are using as well as the local climate.

Precision and attention to detail are necessary when preparing the mortar. Cracks and weak joints can be avoided by regularly combining the ingredients into a homogenous paste. The proper consistency and workability of the mortar are ensured by using clean, uncontaminated water and accurately measuring the amount added.

You can create a high-quality mortar that will improve the durability and performance of your aerated concrete block structures by adhering to these guidelines. Successful construction outcomes depend heavily on the components, selection, and preparation process. Your construction projects will endure and provide years of comfort and safety if you take the proper approach.

Selecting an appropriate mortar for aerated concrete blocks is essential to guarantee robust and long-lasting construction. This post will walk you through the necessary elements, selection standards, and mortar preparation techniques to help you accomplish the best possible bonding and performance in your construction projects. Whether you’re a skilled builder or a do-it-yourselfer, knowing these essentials will guarantee that your aerated concrete blocks are joined effectively and securely, producing a sturdy and long-lasting structure.

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