During operation, depending on the intended purpose, a number of technical requirements are imposed on the floors of buildings and structures. These are strength, evenness, the maximum value of the specific load, the degree of thermal insulation, and so on.
General description of expanded clay concrete
An excellent option in terms of price, quality and speed of installation of the floor surface is the laying of a concrete screed, which provides perfect evenness and high wear resistance. However, this type of floor has a number of disadvantages - this is a high specific gravity per unit area and a low degree of thermal insulation throughout the depth of the surface. Expanded clay screed, which is a lightweight concrete, retains the advantages of a conventional concrete screed, but is devoid of its disadvantages.
The method of obtaining expanded clay concrete for floor screed is simple and differs from the classic concrete mortar, consisting of cement, sand, water and crushed stone, only in that expanded clay is used instead of crushed stone. It has the form of gravel with a porous structure in the form of an oval of various fractions from 5 to 40 mm, it is produced industrially, by firing clay or its derivatives. The variability of expanded clay fractions is determined by the type ofconstruction works. The smallest one is used for the production of expanded clay concrete screed and the production of blocks, the middle one is used for bulk insulation of floors and ceilings, the large one is used for thermal insulation of outbuildings and heating mains.
Types and scope of expanded clay concrete
Classification of expanded clay concrete is quite extensive and depends on the requirements for the type of product produced, the density of the granules, the application and solidity. All these signs are standardized by the brand (for example, expanded clay concrete M100), which determines the class of its application and varies from 35 to 100 kg / cm²:
| Grade of expanded clay concrete | Scope of application |
| M50 | Arrangement of load-bearing structures, construction of indoor partitions |
| M75 | erection of load-bearing structures in the construction of residential and industrial buildings |
| M100 | floor tie |
| M150 |
production of expanded clay concrete blocks |
| M200 | expanded concrete blocks and floor slabs |
| M300 | installation of engineering structures with heavy periodic load |
Taking into account the scope, the density of expanded clay concrete is an important characteristic, which is determined by the ratio of mass to volume of the materialand has limits from 700 to 1400 kg/cm². Often in buildings of old and not very old construction, for a number of reasons (foundation subsidence, unskilled installation), there are significant differences in the floor level of adjacent rooms, and sometimes even within the same room. Leveling to a single level using a conventional cement-sand screed can seriously increase the load on the bearing elements of the building, which is highly undesirable, especially when it comes to multi-storey buildings.
Due to the porosity of expanded clay, the density of expanded clay concrete screed is much less than the density of heavy concrete, which determines the unconditional priority of its use in such a situation. Increasing the percentage of cement in expanded clay concrete increases the strength of the structure, however, there is a significant increase (up to 1.5 times) in the weight of concrete. Accordingly, the maximum possible reduction of the cement component of the material allows to reduce its volumetric weight. In this regard, the grade of Portland cement used in its production must be at least 400.
Advantages of using expanded clay concrete
And it does not sink in water, and does not burn in fire. Low thermal conductivity determines the high heat resistance of expanded clay concrete, which means long-term resistance of the material to high temperatures. Even at temperatures above 1000 °C, expanded clay concrete retains its mechanical properties. The material shows itself very well when exposed to moisture. Unlike stones, which, having been soaked with water during frost, are destroyed, expanded clay concrete has high frost resistance, that is, the ability tofreeze and thaw repeatedly without loss of strength.
Another important factor determining the priority choice of expanded clay as a filler for concrete is its environmental friendliness. It does not emit harmful substances either when exposed to an aggressive environment, or over time, or when completely destroyed. This explains the choice of it as a building material and insulation in residential premises.
Preparation of the base for pouring the floor with expanded clay concrete
If the screed is made over an existing even and dense coating, then this stage of work can be skipped. However, most often pouring is performed directly on the ground, in which case additional preparation of the base is required. The surface is leveled and carefully compacted, the pits are covered with sand, the protrusions are knocked down for uniform laying of the pillow. The pillow is a layer of sand about 2-3 cm and a layer of expanded clay or crushed stone 3-5 cm thick, or more, up to the level of the draft base. Next, a plastic film or roofing material is laid to waterproof the future screed, a masonry mesh is mounted and beacons are installed.
Types and methods of using expanded clay screeds
Having de alt with the basic properties and technical characteristics of expanded clay concrete, its pros and cons, let's try to understand how to properly fill the floor using this material. The choice of the type of expanded clay concrete screed depends on the type of base on which it isis produced, in connection with which floor screeds can be of three types. Let's take a look at each one.
Dry screed
Expanded clay gravel is evenly and without cement-sand mixture distributed over a pre-prepared, cleaned and compacted base surface, not reaching 2 cm to the lower level of the lighthouse. The thickness of the floor screed in this case is determined by the required degree of thermal insulation. Next, the entire area is poured with cement milk, which is made by mixing cement with a large amount of water without adding sand. This procedure will fix the expanded clay and cover the gravel with a thin protective layer that prevents moisture from being drawn out of the finishing screed, which will give additional strength to the floor. After that, the usual thin screed is performed. The advantages of this method are the speed of installation, the disadvantages are low surface strength.
Wet screed
With this option, so much water is added to the solution so that light and porous expanded clay floats to the surface after pouring the screed. The hardening of concrete takes a little longer, all the filler is concentrated at the top of the screed. The advantages include self-leveling of the mixture. The disadvantages are long drying, the need for special preparation of the surface to be coated in order to avoid leaks, as well as the subsequent surface screed, if necessary, to obtain a smooth surface. Attics and outbuildings are usually insulated in this way.
Semi-dry screed
The mosta common type of expanded clay concrete pavement, which is identical to conventional concrete in terms of the manufacturing method. For the correct filling of the floor in this way, expanded clay concrete M100 is used. In its manufacture, expanded clay of the first fraction with a diameter of 5-10 mm is taken. The proportions of the mixture are as follows: 1 part of Portland cement grade 400 - 3 parts of sand - 4 parts of expanded clay. As for the amount of water, this parameter must be selected individually, depending on the moisture content of the sand. It is necessary to achieve a consistency in which the granules of the material would not float to the surface, which makes smoothing difficult, at the same time, the mortar should not be too dry, as this complicates its installation and can lead to the formation of voids and cracks in the mass of the screed.
The mortar is mixed in a concrete mixer or in a large container. The use of a mixer nozzle is extremely problematic due to small portions in one batch, and this makes laying long, the solution turns out to be of different consistency, and expanded clay is distributed unevenly in the mass of concrete. The sequence of mixing the ingredients in different sources is described in different ways, but in practice this is of no fundamental importance. The main thing is that the solution is uniform and the expanded clay granules are completely covered with a binder.
Thickness of floor screed
The solution is applied evenly over the entire surface to be covered, while the condition must be met - the thickness of the expanded clay concrete floor screed must be at least 3 cm, usually it is 4-6 cm. If selectedthe correct consistency of the solution, then the surface will turn out to be perfectly even and all that remains is to grout it a day after laying. The advantages of this coating method are obvious - the possibility of using it for any type of floor and ceiling. The disadvantage is the high labor intensity, pouring using beacons and the need for finishing grout.
