For the sphere of construction services, such a thing as building mortars is typical and familiar. GOST 28013 (approved and put into effect by the Decree of the State Construction Committee of the USSR No. 7 in 1989; it was replaced by a similar GOST, approved by the Decree of the Gosstroy of Russia No. 30 of 1998 and put into effect in July 1999) interprets the concept as a set of terms "mortar mixture", "dry mortar mixture", "mortar" and defines uniform requirements for general technical characteristics regarding their preparation, acceptance and transportation and quality indicators.
As a note: these standards do not apply to heat and chemical resistant mortars.
What is mortar?
The composition of the solution is correctly arranged and thoroughly mixed to a homogeneous mass of components: a binder, fine aggregates and a sealer. If necessary, special additives can be added to the solution. Traditionally, cement, gypsum or lime acts as a binder that gives the solution elasticity. The aggregate is usually sand, the aggregator is water.
Notrequiring hardening, completely ready for use after connecting the necessary components, the mortar is called the mortar mixture. The mortar mixture may consist of dry components mixed at the factory. This is the so-called dry mortar mixture. It is closed with water before use.
A hardened mass, resembling an artificial stone, in which an astringent binds sand particles together, thereby reducing friction, is called a mortar.
Construction mortars: general specifications
Mortars are classified as follows.
Depending on the binder used in the composition, they distinguish:
1. Simple one-component - cement, lime or gypsum. As a rule, they are indicated by the ratio 1:2, 1:3, in which 1 is a 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, multicomponent. These are, for example, cement and limestone, limestone and gypsum, clay and straw, limestone and ash, and others. They are indicated by three numbers: knitting main, knitting additional, filler.
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 an excess of binder, give a large shrinkage during laying, cracks (when applied in a thick layer). Are determinedby dipping the stick into the solution - the greasy mixture envelops it in 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, building mortars 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 (dry density from 1500 kg / m3) and light (up to 1500 kg / m3) mortars. The quality of the aggregate directly affects the strength of the final product. So, in comparison with slag, mixing a binder with building sand without impurities (mineral s alts, 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 a lack of it, the solution is characterized by rigidity, with an excess - 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 itsworkability. The mobile, plastic composition is able to fill all the voids, it is well compacted, rammed, does not crumble, does not crumble, does not slip along the walls. With a slight addition of a binder and a mortar, the mortar becomes more plastic, but this leads to greater shrinkage of the building material during hardening and, accordingly, to the formation of cracks.
Let's dwell in more detail on the technical features of mortar mixtures and solutions, all parameters of which are controlled by the current standards.
Quality characteristics of mortar mixes
Important quality indicators of mortar mixtures are the average density, the ability to retain water, mobility and stratification. The lower the binder consumption for the requirements for mixtures, the better. If the mixture has had time to seize or it has thawed, it is strictly forbidden to add a sealer to it. To achieve the desired properties, it is important to properly prepare mortar mixtures, dose, and adjust the substances in them. These should be mixers of cyclic (continuous type), gravitational (forced) action. At the same time, an error of up to 2% is permissible with respect to binders, a mixing agent, dry additives, up to 2.5 - with respect to aggregate. For winter conditions, the solution temperature should be equal to or greater than 5 °C. The optimum water temperature for mixing is up to 80 ° С.
Depending on the norm of mobility, several brands of mortar mixtures are distinguished:
1. Pk4 - characterized by a mobility rate of 1-4 cm. Used in vibrated rubble masonry.
2. Pk8 - a fork of mobility variations is based in the range from 4 to 8 cm. It is relevant for ordinary rubble (from hollow stones and bricks) masonry, facing works, wall installation (large-block, large-panel).
3. Pk12 - mobility over 8 and up to 12 cm. Used when laying ordinary bricks, plastering, cladding, filling voids.
The ability of freshly prepared mortar mixes to retain water is also one of the significant indicators. The quality indicator in laboratory conditions is 90% in winter, 95% in 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. For factory dry mortars, moisture content up to 0.1% by weight is acceptable.
As for stratification and average density, for 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 one established by the project.
Quality standards for mortars
Average density, frost resistance, compressive strength are the main quality indicators of mortars. So, there are several grades that determine the axial compressive strength: M4, M10, M25, M50, M75, M100, M150, M200.
F10, F15, F25, F35, F50, F75, F100 - grades characterizing the indicatorfrost resistance of the solution, which is subjected to alternate freezing - thawing. The frost resistance index is one of the paramount values for concrete, masonry, plaster mortars, when it comes to external plaster. All brands of solutions are controlled.
According to the density, building mortars (GOST 28013) are divided into heavy and light ones, the fork of deviations in indicators cannot be higher than 10% of the one established by the project. The heaviest is the concrete mixture. It is used when laying foundations, building basement floors. The higher the density, the stronger, harder the mortar.
Quality standards for substances that make up solutions
Cement, lime, gypsum raw materials, sand, including from slags from thermal power plants, blast-furnace slag are used as substances used for the preparation of mortars. All these components, as well as water for mortars, must meet certain requirements, both given by GOST 28013 and quality standards for each component.
Filler
For each individual mortar, depending on the purpose, a certain aggregate of the required moisture content is needed. So, for finishing work, building sand with a grain size of 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 - no more than 1.25 mm (possible deviations up to 0.5% by weight, but the solution should not contain sand with grains over 2.5 mm). If sand is usedash, then there should be no ice, frozen lumps in the mass. In a heated state, the temperature of building sand cannot exceed 60 ° C. Light mortars involve mixing a binder with porous sand (shungite, vermiculite, expanded clay, perlite, slag pumice, aglonirite, fly ash, and others). Decorative solutions are made from washed quartz sands, rock crumbs with grain sizes up to 2.5 mm (granite, marble, ceramics, coal, plastic). Color plastering of facades involves the use of 2-5 mm granite, glass, ceramic, coal, slate, plastic chips. Color cement-sand plastering is carried out by adding colored cement, natural or artificial pigments of the appropriate standards to the composition of the mortar.
Chemical additives
Preparation of mortars often involves adding to their composition various chemical additives that improve the quality of products, 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, retarding setting, antifreeze, sealing, water-repellent, bactericidal, gas-forming complexes. The last four are for special occasions.
The required amount of chemical additives is determined by mixing in laboratoryconditions. Produced in accordance with standards, they do not cause destruction of materials, corrosive effects on buildings and structures in use. Classified by type, brand, they all have symbols, as well as designations of standard and technical conditions. Thus, sodium sulfate (SN, GOST 6318, TU 38-10742) can be attributed to accelerating hardening additives, urea (urea) (M, GOST 2081) to antifreeze additives, carboxymethylcellulose (CMC, TU 6-05-386) to water-retaining additives.. A complete list of additives is specified in the appendix to GOST 28013. Cement mortar is produced with the addition of organic (microfoam formers) and inorganic (clay, lime, cement dust, fly ash and others) plasticizers.
Technical quality control
An enterprise that is engaged in the manufacture of mortar mixtures, without fail, carries out technical control over the dosing of the necessary components and the preparation of the mortar mixture itself. 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 (taken according to GOST 5802) to determine all technical characteristics.
If the consumer sets indicators different from those specified in GOST 28013, product quality is subject to control by agreement between the manufacturer and 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 andsolutions. The mortar mixture is dispensed by volume, the dry mortar mixture is dispensed by mass.
Regarding the characteristics of the mortar mixture for the ability to delamination and retention of liquid, and the mortar for frost resistance, a check is carried out when selecting or changing the composition or characteristics of the mortar components. Further, the products are subject to inspection every six months. If, in the event of verification, non-compliance with the current standard is found, the entire batch is rejected.
What should be contained in the documents for the goods?
The following information should be written in documents serving as confirmation of product quality and endorsed by the representative of the manufacturer responsible for technical control:
- 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 quantity 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 recorded. For a dry mixture, the volume of the mixer is prescribed so that the mixture acquires the desired mobility. Also, the documents must contain a guarantee period for the storage of the mixture in dry form, which is calculated from the date of preparation until the expiration of six months.
Transportation of mortar mixes
When transporting mortar mixtures, it is important to exclude the loss of laitance. Permissibletransportation of products by road, as well as in tubs (bunkers) by cars and on railway platforms. At the same time, the temperature of the transported mortar mixture should be checked, which is recorded when the technical thermometer is immersed to a depth of 5 cm.
In dry form, mortar mixes are transported in cement trucks, containers or packaged up to 40 kg (paper packaging) and up to 8 kg (polyethylene packaging). At the same time, in paper bags, transportation is carried out on wooden pallets, in polyethylene - by placing bags with a 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 a mixer or other containers.
Using Mortars
The scope of application of mortars is diverse. Construction concretes and mortars based on cement binder as a structural material are widely popular both in private and industrial construction in the construction of strong load-bearing foundations, horizontal, vertical, inclined structures, structures, ceilings, during major and current repairs, reconstructions, restorations.
It is generally accepted that during the construction of stone buildings, the consumption of mortar 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-calledfinishing compositions). Also, someone had to purchase masonry mortars for installation work, cladding, masonry, refractory. In the construction market, you can now find building mortars (GOST 28013), which have superior properties of thermal insulation, sound absorption, heat and fire resistance.
