In the world construction practice, autoclaved aerated concrete has strongly occupied one of the leading places as a versatile material that allows solving a wide range of engineering tasks and providing modern quality and competitiveness of construction products. The physical and technical properties of autoclaved cellular concrete allow it to be used for the construction of bearing and enclosing structures in various areas of construction. Due to its qualities, this type of concrete is most widely used in civil engineering. Moreover it is used in buildings of different floor number for both frame and wall-bearing construction systems.
One of the most common areas of mass application of cellular concrete is its use in high-rise buildings of monolithic frame construction, as well as in individual one- and two-storey residential buildings. In such buildings, the external and internal walls and partitions are made of cellular concrete.
The technology of artificial stone was invented by the Swedish engineer A. Eriksson. In 1924, this material received an international patent and recognition. The beginning of industrial production of autoclaved cellular concrete was put by SIPOREX (Sweden) in 1929. Since that time, the use of aerated concrete in construction has begun.
So what is Aerated Concrete? Aerated concrete is an artificial stone with spherical pores of 1-3 mm in diameter, which are uniformly distributed throughout the volume. The quality of aerated concrete is determined by the uniformity of pores’ distribution, the equality of their volumes and the closeness of pores. Autoclaved aerated concrete consists of such components as: quartz sand, cement, and lime, where lime plays a key role. The thing is that active quicklime interacts with ball milled sand in special mixers, thereout on a chemical level at high pressure and temperature in autoclaves is synthesized a new mineral called tobermorite. Tobermorite is a crystal having a high strength of the crystal latitude. Where high-strength concrete has maximum strength grades of 500-700 kg/ m2, a dense tobermorite (silicate concrete) can reach strength of 2500 kg/cm2.
Due to the large range of blocks' sizes, a customer has the opportunity to build a wall of almost any required thickness. High accuracy of linear dimensions makes it possible to lay blocks using not common masonry mortar, but glue. And thickness of the adhesive layer will be 2-3 mm. Autoclaved aerocrete is also easily processed. With the help of cutting tools, aerated concrete blocks can be easily cut, drilled, grooved, make slots and openings for electrical, water and sewerage systems. Aerated concrete's fire resistance is much higher than that of conventional building material.
Aerated concrete is the ideal material for protecting metal structures from direct fire exposure.
Nowadays this is the only material that allows you to make a single-layered wall without additional insulation. There are a number of factors stimulating the construction using gas concrete. These include:
- a great need of the population for housing located next to big cities, in small towns, villages and in rural areas;
- more rigorous requirements for thermal protection of buildings and structures;
- low-rise construction, where the construction using aerated concrete is recognized as a modern and efficient technology for housing erection. Today this construction type is one of the most promising sectors of the economics;
- a lower cost of construction in comparison with the construction using wood and brick;;
- reduction of construction time;
- high thermal insulation properties of aerated concrete, which allow comparing the climate in a gas-concrete house with that in a wooden house.
Along with low-rise construction, cellular concrete blocks have found wide application also in frame-monolithic housing construction as a material for external and internal walls. There is no need to build thick internal partitions in monolithic buildings, where the load is transferred to the supporting frame, and the outer walls perform only the role of a cladding and heat-insulating structure. In the future, demand for aerated concrete blocks in the market of monolithic residential construction will develop due to:
- overall increase of frame-monolithic structures usage during housing construction;
- some gradual replacement of fully brick walls with aerated concrete blocks.
The use of aerated concrete in non-residential construction is still poorly developed. Meanwhile, in the future we should expect growth in demand in this sector. In this case, the situation will develop similarly to residential housing construction.
Basic physical and technical properties of aerated concrete:
- The average density (kg / m3) is characterized by a mass of 1 m3 of material in a dry state. The density of cellular concrete is determined by the volume of voids (pores): the lower the density of concrete, the greater its voidness, and vice versa. The strength of cellular concrete is related to its average density by direct dependence: with an increase in the density of the material its strength parameters increase.
- Strength (kgf/cm2) is the ability of a material to withstand destruction under the action of deforming external forces. The method for strength determination is measuring the minimum forces that destroy specially manufactured control samples with their static load applied at a constant load growth. Further there is made a calculation of stress under these loads with the assumption for material's elastic behavior.
- Modulus of elasticity which distinguishes deformation properties of the material is its ability to change its volume under the impact of external load. Numerically elastic modulus is equal to the ratio of the stresses arising in concrete under the axial load application, and the relative deformations appeared from these stresses (in the direction of loading action).
- Freeze-thaw resistance of cellular concrete is an indicator of concrete's quality, which defines its ability to maintain physical and mechanical properties under repeated influence of alternating processes of freezing on air and thawing over water. Such resistance is assessed by the freeze-thaw resistance mark, which is established according to the set number of alternate freezing and thawing cycles. Concrete freeze-thaw resistance mark (F) is a set number of cycles of alternate freezing and thawing at which the compressive strength of concrete does not decrease by more than 15%, and the weight loss does not exceed 5%.
- Shrinkage is a cellular concrete deformation without any influence of external loads that occurs due to moisture exchange processes between concrete and environment and influence of carbon dioxide contained in the air. Shrinkage upon drying is evaluated by measuring the change in the length of aerated concrete sample associated with a change in its humidity from 35 to 5% by weight.
- Specific heat capacity is a measure that determines the amount of heat that should be applied to 1 kg of material in order to increase its entire mass temperature by 1 °C. Specific heat capacity describes the ability of a material to accumulate thermal energy, and depends on humidity and temperature.
- Thermal conductivity coefficient W / (m ∙ °C) is a physical parameter that characterizes the ability to conduct heat. The value of thermal conductivity coefficient determines the amount of heat that passes through a surface unit per time unit with a temperature drop of 1 °C per length unit.
Consumer properties of cellular concrete products:
- Thermal properties of cellular concrete are 2-3 times higher than those of bricks.
- Due to the absorption and return of moisture, cellular aerated concrete maintains a constant air humidity inside the room, creating an ideal room microclimate.
- Environmentally friendly (does not evolve toxic substances).
- The cellular concrete has a high fire resistance.
- Cellular concrete's freeze-thaw resistance is equal to or greater than that of most brands of bricks and heavy concretes.
- Cellular concrete is a soundproof material, which significantly increases the comfort and safety of the housing.
Operational properties of cellular concrete products
- Cellular concrete structures are much lighter than solid ones having the same volume..
- The use of cellular blocks (instead of bricks and conventional heavy concrete with a heater) reduces construction costs of all types of structures as well as their construction time by several times.
- Reducing wall thickness while maintaining thermal insulation properties;
- Reduction of labor costs for masonry, decoration, finishing of walls;
- Saving mortar, plaster, and underpaint putty;
- Simplicity of processing: the products can be easily sawed, drilled, covered with wallpapers and painted.
- High labor productivity in setting.
Based on the listed consumer and operational properties of cellular concrete it can be concluded that it is a deserving and practically non-alternative replacement for traditional building materials.