For the construction services industry, a concept such as mortars is characteristic and familiar. GOST 28013 (approved and enforced by resolution of the USSR State Construction Committee No. 7 in 1989; it was replaced by a similar GOST, approved by Gosstroy of Russia No. 30 of 1998 and entered into force in July 1999) interprets the concept as a combination of terms "mortar mixture", "dry mortar mixture", "solution" and determines the uniform requirements for the general technical characteristics regarding their preparation, acceptance and transportation and quality indicators.
As a note: these standards do not apply to heat and chemically resistant mortars.
What is mortar?
The composition of the solution is composed of components that are correctly arranged and thoroughly mixed to a homogeneous mass: an astringent, a fine aggregate and a grout. If necessary, special additives can be added to the solution. Traditionally, cement, gypsum or lime acts as an astringent that gives the solution elasticity. The aggregate, as a rule, is sand, the filling agent is water.
Not requiring hardening, completely ready for use after connecting the necessary components, the mortar is called the mortar. The mortar mixture may consist of dry components mixed at the factory. This is the so-called dry mortar mixture. It is shut with water before use.
The hardened mass, resembling an artificial stone, in which an astringent binds sand particles together, thereby reducing friction, is called a solution.
Building solutions: general specifications
Mortars are classified as follows.
Depending on the astringent used in the composition, they distinguish:
1. Simple one-component - cement, lime or gypsum. As a rule, they are denoted by a ratio of 1: 2, 1: 3, in which 1 is the part (share) of the binder, the second number is how many parts of the aggregate are added to the part of the binder.
2. Complex, mixed, multi-component. This, for example, cement and limestone, limestone and gypsum, clay and straw, limestone and ash and others. They are indicated by three digits: core cement, secondary cement, aggregate.
A lot also depends on the quantitative ratio of binder and sand. There are mortars:
1. Normal . They are characterized by an optimal ratio of binder and aggregate.
2. Fatty . They are characterized by excess binder, give greater shrinkage during installation, cracks (when applied in a thick layer). They are determined by immersing a stick in a solution - a greasy mixture envelops it with a thick layer.
3. Skinny . They are characterized by a disadvantage, a small amount of binder, practically do not shrink, are optimal for facing. They are defined as follows: when the stick is immersed in the solution, the mixture does not stick to it.
According to the properties of the binder, construction solutions are divided into:
- air - their hardening occurs in air in dry conditions (gypsum);
- hydraulic - hardening processes begin in air and continue in a humid environment, for example, in water (cement).
Depending on the sand used, whether it is ordinary natural, mountain, river or light porous (expanded clay, pumice, tuff), there are heavy (in the dry state density from 1500 kg / m3) and light (up to 1500 kg / m3) mortars. The quality of the aggregate directly affects the increase in strength of the final product. So, in comparison with slag, mixing the binder with building sand without impurities (mineral salts, inclusions of clay rocks) increases the strength of the solution up to 40%.
The quantitative ratio of water also plays an important role in the preparation of solutions: with its lack, the solution is characterized by stiffness, with excess - by delamination, as a result of which the qualitative characteristics of strength are reduced.
Confirmation that the mortar (GOST 28013-98) is prepared correctly, according to quality standards and the correct ratio of the required components, is its workability. The mobile, plastic composition is able to fill all the voids, it is well compacted, rammed, does not crumble, does not crumble, does not slide along the walls. With a slight addition of a binder and a hardener, the solution becomes more plastic, but this leads to greater shrinkage of the building material during hardening and, accordingly, to the formation of cracks.
Let us dwell in more detail on the technical features of mortar mixtures and solutions, all of whose parameters are controlled by current standards.
Qualitative characteristics of mortar mixtures
Important quality indicators of mortar mixtures are the average density, the ability to retain water, mobility and delamination. The lower the binder consumption for the requirements for mixtures, the better. If the mixture had time to set or it defrosted, it is strictly forbidden to add a coffering agent. To achieve the desired properties, it is important to properly prepare mortar mixtures, dose, adjust substances in them. These should be mixers of cyclic (continuous type), gravitational (forced) action. In this case, an error of up to 2% with respect to binders, grout, dry additives is permissible, up to 2.5 with respect to aggregate. For winter conditions, the temperature of the solution should be equal to or exceed 5 ° C. The optimum temperature for mixing water is up to 80 ° .
Depending on the mobility rate, several grades of mortar mixtures are distinguished:
1. Pk4 - characterized by a mobility rate of 1-4 cm. It is used in vibrated rubble masonry.
2. Pk8 - a plug of mobility variations is based on from 4 to 8 cm. It is relevant for ordinary rubble (from hollow stones and bricks) masonry, cladding, wall installation (large-block, large-panel).
3. Pk12 - mobility over 8 and up to 12 cm. It is used when laying from ordinary brick, plastering, cladding, pouring voids.
The ability of freshly prepared mortar mixtures to retain water is also one of the significant indicators. An indicator of quality in the laboratory is the mark of 90% in the winter, 95% in the summer. At the place of production, it must exceed 75% of the water-holding capacity determined by laboratory data. The higher the density, the higher the water resistance rating. For factory dry mortar mixtures, humidity up to 0.1% by weight is acceptable.
As for stratification and average density, in relation to both indicators an error is allowed within 10%, not higher. If air-entraining additives are added to the mortar mixture, relative to the average density, the indicator decreases to 6% of the set by the project.
Quality Standards for Solutions
Average density, resistance to frost, compressive strength are the main quality indicators of solutions. So, there are several brands that determine the index of axial compression strength: M4, M10, M25, M50, M75, M100, M150, M200.
F10, F15, F25, F35, F50, F75, F100 are brands that characterize the frost resistance of a solution that undergoes one-time freezing - defrosting. The frost resistance index is one of the paramount values for concrete, masonry, plaster mortars, if we are talking about external plaster. All brands of solutions are controlled.
According to the density construction solutions (GOST 28013) are divided into heavy and light, the plug deviations in the indicators can not be higher than 10% of the set by the project. The most difficult is the concrete mixture. It is used when laying the foundations, the construction of basement floors. The higher the density, the stronger, harder the solution.
Quality Standards for Substances in Solutions
As the substances used for the preparation of solutions, cement, lime, gypsum raw materials, sand, including from slags of thermal power plants, blast furnace slag are used. All these components, as well as water for mortar, must meet certain requirements imposed by both GOST 28013 and quality standards for each component.
Aggregate
For each individual mortar, depending on the purpose, a certain aggregate of the required humidity is needed. So, for finishing works building sand with grains of sand up to 1.25 mm is suitable, for soil up to 2.5 mm, when plastering, sand grains can reach 1-2 mm, when plastering the finishing layer - not more than 1.25 mm (possible deviations up to 0.5% by mass, but the solution should not contain sand with grains over 2.5 mm). If sand with ash is used, then there should not be ice, frozen lumps in the mass. In the preheated state, the temperature of building sand cannot exceed 60 ° C. Lightweight mortars involve mixing a binder with porous sand (shungite, vermiculite, expanded clay, perlite, slag pumice, aglonirite, fly ash and others). Decorative solutions are made of washed quartz sand, crumbs of rocks with grains of sand up to 2.5 mm (granite, marble, ceramics, coal, plastic). Color plastering of the facades involves the use of 2-5 mm granite, glass, ceramic, coal, shale, plastic chips. Colored cement-sand plastering is carried out by adding colored cement, natural or artificial pigments of the relevant standards to the composition of the solution.
Chemical additives
The preparation of mortars often involves the addition of various chemical additives that improve product quality , which prevent delamination, contribute to greater mobility, strength, and increase the frost resistance of the mixture. These are the so-called superplasticizing, plasticizing, stabilizing, water-retaining, air-entraining, accelerating hardening, retardation of setting, antifreeze, compacting, hydrophobilizing, bactericidal, gas-generating complexes. The last four are intended for use in special cases.
The required amount of chemical additives is determined by mixing in the laboratory. Produced in accordance with the standards, they do not cause destruction of materials, corrosive effects on operating buildings and buildings. Classified by type, brand, they all have symbols, as well as the designation of standard and technical conditions. So, sodium sulfate (SN, GOST 6318, TU 38-10742) can be attributed to hardening additives, urea (urea) (M, GOST 2081) to antifreeze additives, and carboxylmethyl cellulose (KMTS, TU 6-05-386) to water-retaining ones. . A full list of additives is given in the appendix to GOST 28013. Cement mortar is produced with the addition of organic (microfoam) and inorganic (clay, lime, cement dust, fly ash and others) plasticizers.
Technical quality control
An enterprise engaged in the manufacture of mortar mixtures, is subject to mandatory technical control for dosing the necessary components and preparing the actual mortar mixture. Control is carried out once per shift. Mortar mixtures of the same composition produced per shift are delivered in batches. At the same time, control samples are sent to the laboratory (selected in accordance with GOST 5802) to determine all technical characteristics.
If the consumer sets indicators other than those specified in GOST 28013 , product quality is subject to control by agreement of the manufacturer with the consumer.
Testing mortars is carried out in laboratory conditions by the manufacturer, from which the consumer has the right to request control samples of the mortar mixture and mortars. The mortar mixture is dispensed by volume, the dry mortar mixture is dispensed by weight.
Regarding the characteristics of the mortar mixture for the ability to delaminate and retain the liquid, and the solution for frost resistance, it is checked when selecting or changing the composition or characteristics of the components of the solution. Further products are subject to inspection every six months. If in the event of verification inconsistencies are found to be in force with the current standard, the entire batch will be rejected.
What should be contained in the documents for the goods?
The documents that serve as confirmation of product quality and endorsed by the representative of the manufacturer responsible for technical control should include the following information:
- name and address of the manufacturer, the exact date and time of preparation of the mixture;
- brand of solution;
- type of binder;
- quantity, mobility of goods;
- name and amount of chemical additives;
- an indication of this standard, which is a guarantee of compliance of ready-to-use products with technical data.
If porous aggregates are used, the average density in the dried state is additionally fixed. For the dry mixture, the volume of the curing agent is prescribed so that the mixture acquires the necessary mobility. The documents must also contain a warranty period for storing the mixture in dry form, which is calculated from the date of preparation until the expiration of six months.
Mortar Transportation
When transporting mortar mixtures, it is important to eliminate the loss of cement milk. It is permissible to transport products by road, as well as in tubs (bins) by cars and on railway platforms. In this case, the temperature of the transported mortar mixture, which is recorded when the technical thermometer is immersed to a depth of 5 cm, should be checked.
Dry mortar mixtures are transported in cement trucks, containers or packaged up to 40 kg (paper packaging) and up to 8 kg (plastic packaging). At the same time, in paper bags, transportation is carried out on wooden pallets, in polyethylene - by packing bags with the mixture in special containers. Storage of the mixture in bags is allowed at a temperature of 5 ° C in closed, dry rooms. After transportation, the mortar mixture is unloaded into the mixer or other containers.
Mortar application
The scope of mortars is diverse. Building concretes and mortars on cement binder as a structural material are widely popular in both private and industrial construction for the construction of strong bearing foundations, horizontal, vertical, inclined structures, structures, ceilings, during overhaul and current repairs, reconstructions, and restoration .
It is generally accepted that during the construction of stone buildings, the consumption of mortars reaches a quarter of the total volume of the structure. Many of us have ever purchased lime, gypsum, mixed mortars for plastering walls in apartments or private households (these are the so-called finishing compounds). Also, someone had to purchase masonry mortars for installation work, cladding, masonry, stone, refractory. In the construction market, construction solutions (GOST 28013) can now be found that have superior properties in thermal insulation, sound absorption, heat and fire resistance.