Even a person far from the construction industry will give the right answer to the question about the most popular building material. It’s about cement. It was thanks to him that the construction of strong and stable houses, bridges, factories, poles and even fences became possible. Cement is the basis of concrete and mortars. True, their quality depends not only on cement, but also on other components. We are talking about sand that can both provide the expected strength and negate all the efforts associated with choosing a good cement. Let’s try to figure out which sand for cement is better to choose, well, but high-quality cement is much easier to find. Cement wholesale and retail in Moscow is sold by the CEM-Cement plant. The company offers a mixture of different brands and with modifying additives. The plant has a full production cycle, so the quality of products is controlled at all stages. Wholesale buyers receive decent discounts and fast delivery, as the manufacturer has its own vehicle fleet.
# 1. The role of sand for concrete and masonry mortar
A huge part of all cement produced is used for concrete production. In addition to the cement itself, crushed stone, water and, of course, sand are also used. The latter plays the role of a placeholder. It closes the voids that form between the rubble, and when the concrete hardens and deforms, it prevents the formation of cracks and allows the internal stress to be evenly distributed. As a result, the quality of concrete increases and the service life of the facility being built increases.
When preparing mortar for brickwork, sand takes on slightly different functions. Here it is necessary to fill the voids that can form due to irregularities on the surface of the brick. Also, sand regulates the volume of the resulting solution and can significantly reduce shrinkage. In addition, it can give the mortar the desired shade, which is important when it comes to cladding.
No other placeholder was found or created. However, there are no problems yet: sand is very common, it is inexpensive and at the same time chemically inert, strong enough and represented by various fractions. It remains only to understand which sand for cement is better to choose, which fraction to give preference to, and figure out how important the type of sand origin is.
# 2. Sand particle size
According to GOST 8736-93, sand is divided into several fractions by particle size (fineness modulus). Sand with particles larger than 3.5 mm is called very coarse, with particles 3-3.5 mm of increased size, etc. The distribution by fractions can be seen from the table, but in reality, sand is often divided into only three types: fine, medium and coarse.
Depending on the particle size, sand is usually divided into two classes:
Class I. The composition does not contain fractions with a particle size of up to 1.5 mm, which are undesirable in the preparation of solutions. With an increase in their content, the connection between larger particles deteriorates, the quality of the solution decreases, and its cost increases;
Class II also contains the smallest particles of sand. Such sand is not suitable for preparing concrete for a foundation, but it can be useful for a masonry mortar. When it comes to decorative finishes, the solution is kneaded using sufficiently small particles.
If it is necessary to prepare concrete for further pouring the foundation, it is better to use sand with a particle size of 2-2.5 mm. To prepare high-quality concrete, take a fraction of 2.5-3 mm. If you need concrete with a low grade (up to M200), it is allowed to use sand with a fraction of 1-1.5 mm. The logic should be clear: the more stable the solution is needed, the larger the fraction is used. Sand of increased size and very coarse is sometimes used in private construction to create a sand cushion.
When choosing sand for preparing concrete for a foundation, it is allowed to contain particles of 5-10 mm in size (gravel), but their part should not exceed 10%. Dusty and silty fractions (particle size less than 0.05 mm) should not exceed 3%, otherwise it will not be possible to achieve the design strength of concrete.
Some experts advise to choose “different-sized” sand, where in addition to the medium / coarse fraction, contains slightly smaller particles. The thing is that sand with a high modulus of fineness is characterized by an increased voidage index. To fill the space between grains of sand, more cement will be needed, which will affect the final cost. Therefore, in some cases (when we are not talking about critical objects) it makes sense to use a little fine sand, which will perfectly fill the voids.
It is important that the sand is clean and free of clay (which will cause lumps to form) and foreign particles such as branches and other debris. Much depends on the origin of the sand.
No. 3. Sand extraction site
There is a lot of sand on the planet. All the deposits are united by the fact that the extraction is carried out in an open way, but the peculiarities of the natural formation of sand leave an imprint on its properties.
According to the type of origin, sand is usually divided into the following types:
quarry sand lies at a shallow depth under the ground. Quarries are created for its extraction. This sand contains a significant amount of clay, soil and dust, which is clear from the peculiarities of its occurrence. In its raw form, it can be used for filling under a screed or foundation. Washed sand (washed at the site of production) is suitable for preparing concrete. Quarry sand is finer than river sand, excellent for preparing mortars for plastering walls, as well as masonry mortars for bricks. Also, washed sand is used in the manufacture of paving slabs;
river sand due to constant exposure to water is clean of impurities, and the grains of sand themselves have a very smooth surface. With its help, it is much easier to obtain a high-quality solution, but it also costs more. On the other hand, the surface of the grains of sand is absolutely smooth, their adhesion is slightly lower than that of quarry grains of sand, and the weaker the connection of the individual components, the less strong the solution comes out. The difference, in fact, is not that significant, but in some cases it makes sense to play it safe. River sand is excellent for pouring concrete foundations and creating reinforced structures. It is used for the preparation of masonry mortars when working with large building blocks, as well as in the production of paving slabs;
sea sand actually repeats the properties of river sand. It is fairly clean and homogeneous in fractional composition, but it may contain shell particles, requiring additional cleaning;
- so called artificial sand obtained by crushing rock. It will definitely not contain impurities, but too small particles can come across it, so sieving is often indispensable.
If you are not sure about the purity of the sand, and laboratory tests cannot be carried out for any reason, do a simple analysis. It is enough to take a transparent container, fill it 1/3 with sand and add half of the water, shake everything well, ensuring that the sand is completely moistened, and leave the container alone for 10-15 minutes. If the water turns out to be dirty, or a layer of foreign substance is present on the sand, then sand is not suitable for creating concrete and mortar.
No. 4. Main characteristics of sand
The quality of concrete and mortars is strictly regulated by the relevant regulations, including the requirements for sand are also spelled out. Some parameters can be checked directly on the construction site, others – only in the laboratory, but when a responsible project is being built, quality control for all characteristics should not be neglected.
The most important characteristics of sand include:
volume weight. A cubic meter of wet sand weighs about 1500-1800 kg, but the lower the value, the better;
humidity is usually around 5%. It is very important to determine the moisture content of the sand, as the amount of added water will depend on this. It is clear that less water will need to be added to the solution to which sand with a moisture content of 10% was added than to the solution for the preparation of which sand with a moisture content of 1% was used. To determine this indicator, you can ignite a small amount of sand. The difference in weight between wet and fully dried sand will make it easy to calculate moisture content. You can simply squeeze the sand in the palm of your hand, and if after unclenching it does not crumble, then the humidity is more than 5%, but this is not a particularly accurate method;
the mineral composition is determined only in the laboratory. The sand can include limestone, quartz, dolomite, feldspar, granite, mica and other rocks. Sand with a predominance of quartz will be the most durable and stable. The presence of oxidized metals will be indicated by a reddish and orange tint, and the presence of aluminum salts – by green and blue shades;
the granulometric composition can be determined by eye, but laboratory studies will be more accurate, the conclusion of which will be a full report on how much and what fraction is contained in the sand. On its basis, you can decide where it is best to use the material, or how it is better to process it (sifting, washing, etc.) in order to apply where planned;
the chemical composition is necessary in order to determine the area of use of the sand. Important in the construction of critical facilities;
bulk density should be about 1.5 t / m3, but may fluctuate between 1.3-1.9 t / m3. A too low value indicates the presence of impurities, and a high value indicates waterlogging;
the coefficient of porosity shows the ability of the sand itself and the solution prepared on its basis to pass moisture.
No. 5. Preferred sand for concrete and masonry
For the preparation of concrete, river sand will still be preferable. Even though its grains are smooth and have a lower degree of adhesion, it is much cleaner than quarry. In the latter, even when washing, it is not possible to completely remove all the clay. Mixing of river and quarry sand is allowed. The grain size is 2-3 mm.
For masonry, you can take cheaper quarry sand. The fraction depends on how large the blocks are stacked: for a slok block, you can take sand with larger particles, and for facing bricks, on the contrary, with small ones.
When buying sand, you need to study all accompanying documentation. This will allow you to be sure that the object being erected will turn out to be durable and strong.