Wall products made of cellular concrete have long occupied the first positions on the market of construction materials. The very name of the material makes it clear that it consists of cells filled with air. The walls of the cells are as firm as stone. Currently, there are two options for obtaining air cells – it is gassing and foaming. Therefore, a distinction is made between aerated concrete and foamed concrete. Stone-like firmness can be achieved in two ways:

- the first method – due to hardening of a special binder made of cement, lime and sand during autoclave treatment (in same way as in the production of silicate bricks);

- the second way – due to natural hardening of cement.

Therefore, according to curing method, autoclaved and non-autoclaved cellular concrete are distinguished.

Among different types of autoclaved cellular concrete, the technology of wall materials production from autoclaved aerated concrete has become the most widespread in the world, and no wonder, as it has been improving for about 100 years since its invention. It should be noted that the production of such aerated concrete requires high energy and operating costs related to obtaining superheated steam, which is formed in a boiler room for high-temperature heat treatment under high pressure in special autoclaves.

Non-autoclaved cellular concrete is mainly represented by such material as foam concrete, which was invented almost simultaneously with aerated concrete. Foam concrete technology has also gone through a certain development path. Due to its simplicity, the technology of wall materials production  from non-autoclaved foam concrete resulted in mass production of foam concrete blocks, which was carried out in makeshift conditions throughout the whole period starting from the early 90s to about 2010s.
Despite the fact that non-autoclaved foam concrete is much inferior to autoclaved aerated concrete in its physical, mechanical and geometric characteristics, and that sometimes it simply did not meet the requirements of state standards, this material was in demand in the context of shortage of building materials.
After commissioning of new autoclaved aerated concrete plants, the production of non-autoclaved wall foam concrete blocks became irrelevant.
Nowadays, non-autoclaved foam concrete has its practical area of application as monolithic thermal insulation produced right at the construction site. In addition, the production of wall materials from non-autoclaved foam concrete with standard characteristics is associated with increased consumption of high-grade cement.

The course of technical progress led to the emergence of a new building material – non-autoclaved aerated concrete.
The technology of high-grade cement production improved, a new class of concrete additives and admixtures appeared, numerous research works were carried out in order to improve physical and mechanical characteristics of non-autoclaved aerated concrete. Considering regulatory provisions, including certain requirements to the geometry of products, automated production lines were developed and designed to fabricate wall products in a closed loop production cycle. Competent scientific approach in the selection and preparation of raw components, upgrading of the equipment for preparation of a raw mixture, as well as the development of control algorithm based on modern industrial controllers, made it possible to obtain non-autoclaved aerated concrete with new, improved characteristics, by far exceeding the properties of non-autoclaved foam concrete. Cement consumption, compared to foam concrete, was considerably reduced. The newly developed cutting complexes employing new principles of moulded mass cutting allow fabrication of wall products distinguished by top-quality geometric parameters.

Non-autoclaved aerated concrete produced from new materials, according to new technologies is already coming close to its autoclaved counterpart in many technical parameters.

It should be noted that modern autoclaved aerated concrete is a high-quality wall construction material, which is used in many climatic zones. The range of autoclaved aerated concrete products is quite wide.
Nowadays, wall blocks, reinforced roof and slab panels, link beams are produced.
However, due to constant growth of prices for energy resources, the production of autoclaved aerated concrete calls for significant investments in working capital. Initial capital construction costs and expenditures related to obtaining high metal intensity equipment are very high.

The production of non-autoclaved aerated concrete with improved characteristics requires neither large capital investments in the autoclave fleet, nor significant working capital for purchasing energy resources.

Main advantages of production and application of non-autoclaved aerated concrete wall blocks using vibration impact technology at new-generation plants

Contemporary mass production of cellular concrete wall blocks is based on autoclaved aerated concrete and non-autoclaved foam concrete technology. It is widely known that the physical and technical characteristics of foam concrete, especially in the highly demanded D500 - D600 grades, are much inferior to similar properties of autoclaved aerated concrete, no matter that their densities are the same. There are a lot of complaints to foam concrete blocks regarding their compliance with geometric dimensions. However, it is obvious that the technology of cellular concrete production by non-autoclaved method requires lower initial and production capital investments. Therefore, starting to develop a new technology, our company saw its task in combining all the best achievements and scientific developments, both implemented and promising ones, in the field of cellular concrete technology by autoclaved and non-autoclaved production method. The goal was to obtain non-autoclaved cellular concrete, which would not be inferior to autoclaved aerated concrete in its main operational and consumer properties.

Today, after reviewing the results achieved at the existing production facilities, it is safe to say that basically, the goal has been achieved. Such technology, as well as the whole complex of the respective equipment have been developed. For a couple of years, our company has been searching for new technologies in the field of non-autoclaved cellular concrete production. As a result, we have made a gradual transition from the traditional foam concrete technology and production of appropriate equipment to a fundamentally new trend - the production of non-autoclaved aerated concrete by impact technology.

As it was already mentioned, we have chosen the way of synthesis of the best achievements of autoclaved and non-autoclaved production methods. Let us dwell on this in more detail.

At present, the most promising trend in autoclave production technology is the so-called impact moulding method.
Thanks to it, the physical and technical characteristics of aerated concrete improved dramatically.
These developments were recognized worldwide.
Currently, the equipment for impact technology of aerated concrete production is used in plant construction by several western companies that manufacture equipment for autoclaved aerated concrete by impact technology.

The method of moulding masses from viscous aerated concrete mixtures under dynamic impact was successfully applied by us in course of development of non-autoclaved aerated concrete technology.

The second most significant trend is the technology of cellular concrete production by autoclaved and non-autoclaved technology with the use of microfillers (fly ash, slag dust, carbonate flour, etc.).
 For this purpose, various modifier additives were widely used: plasticizers, setting and hardening accelerators, etc. By using microfillers and modifier additives as raw materials at the plants installed by us allowed to arrange immediate release of products that successfully passed certification tests for compliance with the regulatory requirements to non-autoclaved cellular concrete blocks.

As for modern achievements in the field of non-autoclaved foam concrete production, positive results from the experience of dispersed reinforcement with microfibre were taken into account. Microfibre can be made of mineral (basalt, glass fibre) and synthetic (propylene, lavsan) raw materials. Thanks to the use of microfibre, non-dissolvable aerated concrete mixtures were obtained. The density of aerated concrete in the upper and lower parts of the mass is practically the same, which is unattainable in the moulding technology of autoclaved aerated concrete. In addition, microfibre significantly increases crack resistance of the products.

Table 1

In the framework of the non-autoclave curing aerated concrete technology, a low-energy method of heat treatment of products has been recently developed – the method of ‘thermos-like’ self-steaming. In these conditions, heat treatment costs will be twice as low. All this was taken into account in our developments.

Table 2

One of the main arguments in favour of autoclave production technology is the fact that the geometric dimensions of the products are accurate.
Thanks to such precision, it is possible to lay wall blocks on thin seam adhesive mortars, which increases thermal protection properties of such walls.
That is why our specialists have developed a set of equipment including a new-generation cutting machine.
To date, it is the world’s only technology of programmable cutting of aerated concrete masses, which makes it possible to obtain the specified geometric dimensions of blocks with an accuracy of ±1mm.
Notably, this factors in the requirement to produce wall blocks of any dimensions (except length) as ordered by the customer.
This machine makes it is possible to produce blocks whose width and thickness can be varied with an increment of 1 mm, i.e. practically of any size.

Different types of blocks, both wall and partition ones, can be cut out of the same mass. Reprogramming takes minutes. Currently, modern autoclaved aerated concrete plants do not provide such an opportunity.

Table 3

Owing to this comprehensive approach, our plants using aerated concrete impact technology in the serial production of wall blocks have achieved results that are close to autoclaved aerated concrete in terms of their basic performance properties.
The results obtained by far exceed the technical and economic performance of non-autoclaved foam concrete production.

Table 4

At present, the issue of autoclaved aerated concrete durability is among the most debatable ones. As known, the main carrier of firmness in autoclaved concrete is tobermorite.
Studies have convincingly shown that autoclaved aerated concrete, unlike non-autoclaved, is subject to the process of aging associated with carbonate destruction of tobermorite bond. The decrease in firmness of autoclaved aerated concrete and gas silicate with a D500 density grade can reach 20 to 50% after the end of carbonization.
During carbonization, the density of aerated concrete can increase by 20%, which will consequently lead to a deterioration in the thermal protection properties of such concrete. Manufacturers of autoclaved aerated concrete excuse themselves by giving examples of buildings made of autoclaved aerated concrete that were constructed 60-80 years ago. However, it should be noted that the plants at that time used to produce wall blocks of a much higher density, not sparing cement and lime. In pursuit of low production costs and selling price, manufacturers of autoclaved aerated concrete can resort to reduced consumption of expensive cement and lime, deteriorating its durability even more.

Table 5

To date, the technology of production of low-water consumption binder is a very promising trend. The application of this very technology in our research helped us obtain materials similar to autoclaved aerated concrete in their basic operational properties, and even superior to it in terms of durability. We are successfully working in this direction and intend to implement this technology at newly designed production facilities.

Table 6

All the above leads to this conclusion: when choosing a production method, one should have a clear idea that at the present stage, the technology of non-autoclaved cellular concrete is not standing still and has gone far ahead from the first primitive installations, which actually produced material that can only provisionally be called cellular concrete wall blocks.
As for compliance with the regulatory requirements related to products, it is unthinkable in such hapless production plants.
And even now, if such plants still exist, no one sticks to standards there.
Proponents of the autoclaved production method give examples and photos of such ‘products’ and talk about their low quality.
And we absolutely agree with them, as far as this is concerned.
Such production facilities should simply be closed down.