Cellular concrete, in comparison with conventional heavy concrete, has a number of positive properties and characteristics, due to which they are increasingly used in low-rise cottage construction. The high popularity of cellular concrete, including gas and foam concrete, is constantly growing, which gave an incentive to real competition among manufacturers. Everyone is trying to prove that it is their products that have undeniable advantages, and consumers are lost in the choice.
Let’s look at the similarities and differences in their operational properties and characteristics in more detail. What is cellular concrete?
This is an artificial stone-like material, which consists of a hardened binder having a uniformly distributed structure in the form of air cells, which, as a rule, occupy up to 80-85% of the total volume. Due to the high porosity, this material is referred to as especially light varieties of concrete. A wall built from cellular concrete, having sufficient strength, is several times lighter than a wall built from brick and concrete.
Over the long years of using concrete in multi-storey monolithic concrete construction, due to its strength, wear resistance and durability, it has become, along with wood and brick, a “traditional” building material. In terms of its structure, cellular concrete inherited only the name from traditional concrete, since its strength is ensured only by the walls between the pores, while the role of the filler in the bearing capacity of the material is very small. From “heavy” concrete, he “inherited” received durability, good resistance to external weathering, as well as fire resistance. In addition, cellular concrete also has its own properties that are not inherent in “heavy” concrete, such as high thermal insulation capacity, lightness and ease of processing, excellent soundproofing characteristics.
Heat-shielding characteristics are provided due to the high degree of filling of the internal structure with air, which by its nature is an excellent heat insulator. The thermal insulation characteristics of cellular concrete are 3 times higher than those of ceramic bricks, and 8 times higher than those of “heavy” concrete. When building walls from ordinary bricks without additional insulation, their thickness should be 3-4 times greater than from cellular concrete in order to provide the same level of thermal conductivity. Using “lightweight” concrete, you not only save on insulation and heating, but also on the arrangement of the foundation, which will bear less load, and, therefore, will be much cheaper in construction.
Depending on the type of binder component and production technology, cellular concrete is divided into two types: aerated concrete and foam concrete.
The composition of aerated concrete includes quartz sand, lime, water, a small amount of cement and a blowing agent – aluminum powder. The foaming and curing process takes place in an autoclave oven in a steam environment at high pressure and temperature. In the course of a chemical reaction between alkali and aluminum, hydrogen is formed, which gives porosity to the structure of the material.
In the production of foam concrete, a cement mixture is used, into which special foaming additives of organic or synthetic origin are introduced under high pressure. In this case, the air bubbles formed in the solution are evenly distributed throughout the mold and create a porous mixture with closed cells. Depending on the production technology, aerated concrete is also called “autoclaved”, and foam concrete – “non-autoclaved” cellular concrete. The advantages of the technology for the production of non-autoclaved cellular concrete (foam concrete) is that it can be produced in small batches in the immediate vicinity of the facility under construction, as well as the possibility of using both in the form of packaged products (foam block) and in the form of a concrete mix for pouring directly into the formwork on the object under construction (monolithic structure).
When performing masonry work, laying gas and foam blocks can be done using a conventional cement-sand mortar, but experts recommend using special adhesives or mortars. Their use will significantly reduce the thickness of the seams, get rid of the “bridges” of cold, and also give a more attractive aesthetic appearance. Special glue has a high cost, but due to its low consumption compared to the usual mortar, in the end you only win. Cellular concrete of both types is produced with different densities, which can vary from 300 to 1200 kg / m3 (density grade is indicated by the Latin letter D). If we compare foam concrete and aerated concrete blocks of the same brand, then aerated concrete has a higher strength, which is 2-3 times higher than that of foam concrete.
For the construction of private houses and cottages, you can use aerated concrete blocks of the D400 – D500 brands, while foam concrete blocks starting from the D600 brands, and for more reliable construction of the D700 – D800 brand. When using blocks of higher density during construction, you will need to equip a more powerful foundation, since the weight of the wall will have a large mass, and therefore these are additional costs for building the foundation (foundation) of the house. It is also important that the thermal insulation characteristics of “light” (cellular) concrete have an inverse relationship with its strength.
The higher the heat-shielding properties of concrete, the lower its thermal conductivity and lower strength. In addition, for foam concrete blocks, this dependence is more pronounced.
Low-density foam blocks are an excellent heat-insulating material, but they are not strong enough to be used as load-bearing walls. Structural foam concrete has lower thermal insulation characteristics in comparison with aerated concrete. So, for example, if you build a wall that meets the standards for thermal protection from foam concrete blocks of the D600 brand, then its thickness will be 45-50 cm, from D800 – about 70 cm, at the same time, when building this wall from aerated concrete blocks of the D400 brand – D500 its thickness will be only 35-45 cm.
From this it can be seen that the walls built from aerated concrete blocks will have a sufficient level of strength and thermal conductivity with smaller values of the width and mass of the structure than foam concrete. It is also worth noting that, due to the production technology used, aerated concrete blocks have a stable density and strength that do not change over time. The material has a homogeneous, uniform and constant structure, which has the same properties, both in the horizontal and vertical planes. In addition, aerated concrete blocks have a much greater accuracy of geometric shapes and overall dimensions. The maximum allowable deviation in size is only 1 mm. The surface of aerated concrete blocks has the best adhesive properties during finishing and plastering work.
If we talk about these properties of foam blocks, then they usually have large deviations from the specified dimensions (complicates the masonry process, increases the consumption of masonry mortar), have unstable physical and technical characteristics (which differ at different points and planes of the block). In the manufacture of foam blocks, a special requirement is placed on the quality of the foam concentrate and strict adherence to production technology, which not all manufacturers can afford. Another serious advantage of aerated concrete is its minimal shrinkage (0.5-0.7 mm per 1 meter), in contrast to foam concrete (up to 3 mm per 1 meter). This is due to the fact that foam concrete blocks dry out gradually and independently, while aerated concrete blocks dry out even during the production process in autoclave ovens. This feature of foam concrete increases the likelihood of cracks in the walls during construction and its uneven drying. An interesting fact is that foam concrete blocks gain additional hardness over time.
So, you can easily drive nails into foam and aerated concrete blocks, saw with an ordinary hand saw, install engineering systems and electrical wiring, etc. After 2-3 years, the foam concrete wall will become an order of magnitude harder, and the aerated concrete wall will remain at the same level. Foam and aerated concrete has a porous structure, and, therefore, it absorbs moisture. Foam concrete blocks, unlike aerated concrete ones, have closed pores, which causes its greater moisture resistance. Foam concrete manufacturers claim that it can be used in wet areas, but in practice, foam and aerated concrete are best waterproofed. Regarding frost resistance, according to this indicator, aerated concrete blocks are comparable to ceramic bricks, and for foam concrete blocks it is even higher.
Foam concrete can be safely used for construction in places with low temperatures and high humidity (in the lowlands). Regardless of the type, houses built of cellular concrete have the reliability of stone and the microclimate of a wooden structure. Walls made of cellular concrete “breathe”, there is no accumulation of excessive moisture inside the room, dampness, fungal formations and mold do not form, it does not rot and does not accumulate harmful impurities. Foam concrete and aerated concrete are environmentally friendly building materials; during operation they do not emit harmful substances or toxins. Any of the types of cellular concrete have high refractory properties. Aerated concrete wall materials are classified as fireproof materials, and foam concrete is characterized as a material with an increased level of fire safety.
Based on the above, we see that, in general, the performance characteristics of aerated concrete and foam concrete are almost the same. In some ways, one material is inferior, and in some ways – another. Moreover, modern technologies for the production of building materials do not stand still, but are constantly evolving, while improving the physical and technical characteristics of materials, their reliability, strength and durability.
Currently, blocks of any type of cellular concrete are suitable for building a house, but it is preferable to use aerated concrete for the construction of new houses (bearing walls, partitions), and foam concrete blocks for the reconstruction of existing buildings, arranging curtain walls and partitions. In any case, cellular concrete walls will be light, durable and warm enough, largely outperforming brick counterparts.
Successful construction to you!