- №1. The role of sand for concrete and masonry mortar
- №2. The size of the sand particles
- No. 3. Place of extraction of sand
- №4. Basic characteristics of sand
- №5. Preferred sand for concrete and masonry
Even a person far from the sphere of construction will answer the question about the most popular building material. It's about cement. It was thanks to him that it became possible to build strong and stable houses, bridges, factories, poles and even fences. Cement is the basis of concrete and mortar. True, their quality depends not only on cement, but also on other components. It's about sand that can both provide the expected strength, and negate all the efforts associated with the selection of good cement. Let's try to figure out which sand for cement is better to choose, well, and quality cement is much easier to find. Cement in bulk and in retail in Moscow is sold by the plant "CEM-Cement". The company offers a mixture of different brands and with modifying additives. The plant has a full cycle of production, so that the quality of the products is controlled at all stages. Wholesale buyers receive decent discounts and quick delivery, as the manufacturer has at his disposal a fleet of vehicles.
№1. The role of sand for concrete and masonry mortar
A huge part of all cement produced goes exactly to productionconcrete. In addition to the cement itself, gravel, water and, of course, sand are also used. The last one playsrole of filler. It closes the voids that are formed between the rubble, and when the concrete hardens and deforms it prevents the formation of cracks and allows even distribution of internal stress. As a result, the quality of concrete increases and the service life of the erected object increases.
When preparingmortar for masonryBrick sand takes on a slightly different function. Here it is necessary to fill the voids, which can be formed due to unevenness on the surface of the brick. Also, the sand regulates the volume of the solution obtained and allows to significantly reduce the shrinkage. In addition, it can give the mortar solution the necessary shade, which is important when it comes to facing.
No other placeholder was found and created. However, there are no problems yet: the sand is very common, it is inexpensive and at the same time chemically inert, quite durable and represented by various fractions. It remains only to understand what sand for cement is better to choose which fraction to give preference, and to understand how important the type of origin of sand.
№2. The size of the sand particles
According to GOST 8736-93, sand is divided into several fractions according to the particle size (the size modulus). Sand with particles larger than, mm is called very coarse, with particles of 3 mm - increased size, etc. The distribution according to the fractions is evident from the table, but in reality, sand is often divided into only three types: small, medium and large.
Depending on the particle size, the sand is divided intotwo classes:
- I class.There are no fractions with a particle size of up to, mm, which are undesirable in the preparation of solutions. As their content increases, the connection between larger particles deteriorates, the quality of the solution decreases, and its cost increases;
- Grade IIcontains the smallest particles of sand. For the preparation of concrete for the foundation, such sand is not suitable, but for masonry mortar it can be useful. When it comes to decorative finishing, the solution is kneaded using small enough particles.
If it is necessary to prepare concrete forfurther foundation pouring, it is better to use sand withparticle size 2 mm. For preparationhigh-quality concretetakefraction, -3 mm. If necessaryconcrete low mark(up to M200), it is allowed to use sand of fraction 1 mm. Logic should be clear: the more durable solution is needed, the more large a fraction is used. Sand of increased size and very large sometimes used in private construction to create a sand cushion.
When sand is chosen for the preparation of concrete for the foundation, it is allowed to have particles of 5-10 mm in size (gravel), but part of them should not exceed 10%. Dust and silt fractions (particle size less than 5 mm) should not be more than 3%, otherwise it will not be possible to achieve the design strength of concrete.
Some experts advise choosing"Different" sand, where, besides the middle / coarse fraction, there are a few smaller particles. The thing is that sand with a high modulus of size is characterized by an elevated void index. To fill the space between grains of sand, more cement will be required, which will affect the final cost. Therefore, in some cases (when it is not a question of responsible objects), it makes sense to use a bit of fine sand, which will perfectly fill the voids.
It is important that the sand is clean, does not contain clay (it will cause the formation of lumps) and foreign particles, such as branches and other debris. Much depends on the origin of sand.
No. 3. Place of extraction of sand
There is a lot of sand on the planet. Combines all deposits that are extracted by the open method, but the features of the natural formation of sand impose an imprint on its properties.
According to the type of origin, sand is divided into the following types:
- quarry sandlies at a shallow depth below the ground. For his prey create a career. This sand contains a significant amount of clay, soil and dust, which is understandable from the peculiarities of its occurrence. In untreated form it can be used for padding under screed or foundation. Washed sand (flushing at the place of extraction) is suitable for the preparation of concrete. Quarry sand is smaller than river sand, excellent for making mortar for plaster walls, as well as masonry solutions for bricks. Also washed sand is used in the manufacture of paving slabs;
- river sandbecause of the constant effect of water is pure of impurities, and the grains themselves have a very smooth surface. With its help it is much easier to get a quality solution, but it also costs more. On the other hand, the surface of the sand is absolutely smooth, their adhesion is slightly lower than that of quartz grains, and the weaker the bonding of individual constituents, the less strong the solution goes. The difference, in fact, is not that great, but in some cases it makes sense to be safe. River sand is excellent for pouring concrete foundations and creating reinforced structures. It is used for the preparation of mortar, when working with large building blocks, as well as in the manufacture of paving slabs;
- sea sandactually repeats the properties of the river. It is sufficiently pure and uniform in its fractional composition, but it can contain particles of shells, requiring additional purification;
- so-called.artificial sand, obtained as a result of crushing rock. It will not contain impurities exactly, but it can contain too small particles, so it is often necessary to do without sieving.
If you are not sure about the purity of sand, and laboratory tests can not be carried out for any reason, do a simple analysis. It is enough to take a transparent container, fill it with 1/3 of sand and add up to half the water, shake well, to achieve complete moisture of the sand, and leave the tank alone for 10-15 minutes. If the water turns out to be dirty, or there is a layer of foreign substance on the sand, then sand does not fit to create concrete and mortar.
№4. Basic characteristics of sand
The quality of concrete and mortar is strictly regulated by the relevant regulatory enactments, in which, among others. and the requirements for sand are also prescribed. Some parameters can be checked directly on the construction site, others - only in the laboratory, but When a responsible project is built, a quality check for all characteristics is better than neglect.
To the most important characteristicssand include:
- volume weight. The cubic meter of wet sand weighs about 1500-1800 kg, but the lower the value, the better;
- humidity, as a rule, is about 5%. Determine the moisture content of sand is very important, since this will determine the amount of water added. It is clear that in the solution, where sand was added with a moisture content of 10%, it will be necessary to pour less water than in the solution, for the preparation of which sand was used with a moisture content of 1%. To determine this indicator, you can burn a small amount of sand. The difference in the weight of wet and completely dried sand will make it easy to calculate the moisture content. You can just squeeze the sand in your palm, and if after decompression it does not crumble, then humidity is more than 5%, but this is not a particularly accurate method;
- mineral compositionis determined only in the laboratory. The composition of sand may include limestone, quartz, dolomite, feldspar, granite, mica and other rocks. The most stable and stable is sand with a predominance of quartz. The presence of oxidized metals will prompt a reddish and orange shade, and the presence of aluminum salts - green and blue shades;
- gradingcan be determined by eye, but more accurate will be laboratory studies, the conclusion of which will be a full report, how much and what fraction is contained in the sand. On its basis, you can decide where to use the material, or how to better process it (sieving, washing, etc.) to apply where it was planned;
- chemical compositionIt is necessary to determine the area of use of sand. Important for the construction of critical facilities;
- bulk densityshould be about, t / m3, but can fluctuate within, t / m3. Too low the value indicates the presence of impurities, and high - about waterlogging;
- coefficient of porosityshows the ability of the sand itself and a solution prepared on its basis to pass moisture.
№5. Preferred sand for concrete and masonry
For the preparation of concrete, river sand will be the preferred one. Even though its grains are smooth and have a lower degree of adhesion, it is much cleaner than a quarry. In the latter, even during washing, it is not possible to completely remove all clay. Mixing of river and quarry sand is allowed. The size of the grains is 2-3 mm.
For masonry it is possible to take cheaper career sand. The fraction depends on how large the blocks are stacked: for the sloka block you can take sand with larger particles, and for facing brick - on the contrary, with small ones.
When buying sand, it is necessary to study all accompanying documentation. This will make sure that the constructed object will be durable and durable.