Concrete is the bread of construction. Without it, no construction project can be completed; various structures and products are produced, from construction ones - foundations, walls, stairs - to decorative ones - benches, garden paths and small architectural forms. And all this is a simple mixture. True, the proportions of concrete and its characteristics can be very different - to perform different tasks.
Concrete is used to make large multi-storey buildings, paths and small sculptures. For this purpose, concrete of different compositions is used.
Concrete composition: components, their sizes and characteristics
Most concrete consists of three main components:
- The binder is most often cement, sometimes lime.
- Fillers - sand, crushed stone, pebbles.
- Water.
Different quantities of just three components give a wide range of qualities and characteristics. To impart special properties, various additives and additives are also used, which greatly expands the scope of use of this material.
All these brands of concrete are made from the same components, but in different proportions
The main characteristic of concrete is its strength or the load that it can withstand for a long time without losing its strength characteristics. This parameter is the key when choosing the grade of concrete for the foundation. Water permeability and frost resistance may also be important. But these are the characteristics of the “ripened” material, which depend on the recipe. And when kneading, you may be interested in such a characteristic as workability. It reflects the degree of concrete fluidity and depends on the amount of water in the composition. You can increase fluidity without adding water using additives, as well as increase frost resistance and water-repellent properties.
The strength of concrete depends on how accurately the recipe was followed, on the quality of the ingredients and on how thoroughly everything was mixed. Only with a homogeneous composition and high-quality components can design characteristics be achieved. Read more about what components can be used and the requirements for them at the end of the article.
Principle of concrete marking
The main characteristics of concrete are its strength and compressive class. The compression class is indicated by the letter “B”, followed by class numbers from 3 to 40, the strength grade is indicated by the letter “M”, followed by numbers from 50 to 1000. They indicate the maximum load that this type of concrete can withstand. For example, the M300 brand means that the maximum load per 1 square centimeter cannot be higher than 300 kg.
In private construction, the most popular grades are M200-M250; for the foundations of two-story houses, M300-M350 concrete can be used; M400 is much less often poured - for heavy buildings on difficult soils. Higher ones are generally rare. Their area of application is industrial construction and objects with special properties (piers, dams, roads, etc.).
The correspondence between concrete grades in terms of strength and compression is given in the table (used in private construction).
| Concrete class by compressive strength | Compressive strength of concrete kg/cm2 | The closest concrete grade in terms of strength |
| AT 5 | 65.5 | M 75 |
| B 7.5 | 98.2 | M 100 |
| B 10 | 131.0 | M 150 |
| B 12.5 | 163.7 | M 150 |
| B 15 | 196.5 | M 200 |
| B 20 | 261.9 | M 250 |
| B 22.5 | 294.4 | M 300 |
| B 25 | 327.4 | M 350 |
| B 30 | 392.9 | M 400 |
| B 35 | 458.4 | M 450 |
| B 40 | 523.5 | M 500 |
Classification of cement concrete pavements.
Cement concrete is an artificial stone material obtained from a rationally selected mixture of cement, water, aggregates (crushed stone or gravel, sand) and, if necessary, special additives (active, plasticizing, air-entraining, etc.) after its formation and hardening. Special additives are used when it is necessary to impart certain properties to concrete. The mixture of aggregates, cement and water until it hardens is called concrete mix. Concrete that has steel or other types of reinforcement is called reinforced concrete.
Classification of bases and coatings. Prefabricated (disadvantages - high cost, difficult to ensure evenness) are divided into
:1) Not reinforced (used for foundations)
2) Conventional reinforced (PDO slabs)
3) Pre-stressed (PAG, PDN slabs) Monolithic (disadvantages - work is performed only in the summer, complexity of the installation), divided:
1)Continuously reinforced
2) Prestressed (tension of reinforcement) 2.1) Externally compressed (concrete tensions reinforcement). 2) Internally compressed (reverse)
3) Fiber-reinforced concrete (metal, synthetic elements)
Also monolithic according to the method of compaction:
1) Sealed
2) Rolled (up to B30)
3) Cast The basis for the classification of concrete according to structural characteristics is the division of concrete according to its volumetric mass. The following groups are distinguished:
1) especially heavy – with a volumetric mass of more than 2600 kg/m3;
2) heavy – with a volumetric mass of 2100-2600 kg/m3;
3) lightweight - with a volumetric mass of 1800-2000 kg/m3;
lightweight, made using porous aggregates (pumice, tuff, etc.) - with a volumetric mass of 1000-1800 kg/m3 and especially lightweight (thermal insulating) - with a volumetric mass of less than 1000 kg/m3. Based on the type of components, concretes are classified into
- cement,
-lime,
-Gypsum,
-expanded clay,
- thermosite concrete, etc. According to their purpose and conditions of use, concretes are divided into
ordinary - for the manufacture of foundations, columns, building blocks, bridge spans, pipes;
road – for the construction of road and airfield surfaces;
hydraulic engineering – for the construction of dams, sluices and other hydraulic structures;
special - heat-insulating, heat-resistant, acid-resistant, etc. According to technical characteristics -
vibrated,
rammed,
vacuum concrete, etc. By type of binder - cement, silicate, gypsum. Slag. The structure is dense, porous, porous, cellular. According to the hardening condition -
-natural solid, thermal
- processed during natural hardening,
- with increasing temperature and pressure. Requirements for concrete: 1) Compressive strength of 19 classes (B3.5; B5; B7.5...) 2) Tensile strength in bending of 19 classes (Btb0.4; Btb0.8... through 0.4... Btb4) 3) Pine tensile strength 4) Frost resistance (11 grades F25,50,75,100,1500,200 through 100 F1000) 5) Water resistance (10 grades W2, through 2, W20) Requirements for road concrete and concrete mixtures (strength indicators) 1 )Single-layer and top layer of two-layer coating:
a) for tension and bending Btb4, Btb4.5, Btb5, Btb5.5;
b) for compression B30,35,40,45,50 2) Bottom layer of a two-layer coating:
a) Tensile and bending Btb 3.5/4/4.5
b) for compression B25, 30, 35 3) Foundation for improved capital types of coatings
:a) at tension when bending Btb 2/2.5/3/3.5
b) for compression B10,15,20,25
Frost resistance for coatings: F100 for areas with an average monthly temperature of the coldest month of 0-5C;
F150 temperature -5-15C;
F200 temp. -15C and below; Requirements for the components of road concrete: 1) Binders 1.1 Portlandement without additives 1.2 PC with the addition of blast furnace slag (GOST 10178-85) 2) Water (GOST 23732-2011) 3) Fine aggregate (sand) GOST 8736-93 and GOST 26633-2012 ) 4) Coarse aggregate (crushed stone, crushed gravel):
Supplements
1)realistic light TV regulators (increase mobility without reducing the strength characteristics)
2) setting regulators a) slowing down, b) accelerating
3) structure regulators (to increase density or porosity)
4) improving the quality of concrete
5) anti-frost The content of dust and clay particles in crushed stone should not exceed (% by weight): - for single-layer and upper layers of two-layer coatings 2%, for the lower 3% / Brand of crushed stone in terms of strength/abrasion :
| Feature layer name | Fiend. breeds | Sedimentary rocks | Fiend. breeds | Sedimentary rocks |
| strength | abrasion | |||
| Single layer and double layer top coat | I-I | I-II | ||
| Bottom layer double layer | I-III | I-III | ||
| Basis for improved capital types of coverage | I-III | I-IV |
73. Plants for the production of cement concrete mixtures. 1. Stationary 2. Semi-stationary (2-3 years) 3. Mobile. Depending on the layout - parer (arrangement in the horizontal plane) and tower (arrangement vertically). For example, bet.mixes. tower type installation:
Sand and crushed stone belt conveyor 1 through the rotary funnel 2 is fed into the compartments of the supply hopper 3. Each. The bunker compartment is equipped with level indicators that supply impulses to the alarm system and automatic control. Consumables Aggregate hopper 3 is equipped with registers for heating them. Cement from warehouse 10 is supplied to the concrete plant from elevators or pneumatic transport. Cement with air through the cement pipe 11 enters the cyclone 13, from where the screw conveyor 12 is fed into the cement hopper 3. For finishing. The air is purified from cement using a multi-hose fabric filter 14, b/w cat. fan 15 sucks air from the cyclone. For dosing dry ingredients, weighing dispensers 9 with pneumoelectric are used. management. Water is also dosed by weight with dispenser 4. Set retarders, plasticizers or other additives are dosed with dispenser 5. From the distribution hopper 8 with a changeover valve, dry. materials are sent to one of the concrete mixers 6. Prepared. the mixture from/to dispensing hoppers 7 is dispensed into the transport. facilities.
To prevent stratification of the concrete mixture when loading it into dump trucks at the concrete plant, if necessary, intermediate storage bins or trays should be installed. The drop height of the concrete mixture during overload should not be more than 1.5 m.
Proportions of concrete of different grades
This entire range and range of qualities is obtained by using the same materials, just in different quantities. To achieve the required characteristics, the recommended proportions must be strictly observed.
When building your house, you want to do everything as best as possible, and therefore, when making concrete, you want to add more cement to make it stronger. This should not be done. It's unlikely to get better, but it could easily get worse. To gain strength, concrete needs a certain amount of water and other components. If there is little water, there is a lot of cement, bonds between particles are formed in insufficient quantities, which is why the concrete can crack and crumble. The same applies to the number of fillers. Both their too high and insufficient content negatively affects the qualities of concrete stone.
Concrete proportions are usually displayed in fractions. The amount of cement is taken as a unit, and the remaining components are prescribed in relation to it. The data is presented in the form of tables for the corresponding brands; the units of measurement must be indicated. You can see such a table of concrete components below.
Proportions of concrete of different grades from Portland cement M400 and M500
How to determine the required proportions of concrete using this table? In the second column, find the required grade of concrete. For example, you need an M250. Depending on which Portland cement you will use M 400 or M 500, choose one of two lines. The third column shows the proportions for concrete in kilograms: for 400 cement it is 1/2.1/3.9. This means this: to obtain concrete grade M 250, for 1 kg of Portland cement M400 you need to add 2.1 kg of sand and 3.9 kg of crushed stone. Similarly, determine the proportions for concrete M200 - the data for it in the table is slightly higher, or concrete M 300 - slightly lower.
The fourth column presents volume fractions: all components are given per 10 liters. They are selected in the same way.
Such tables do not indicate the amount of water. It depends on how thick the solution is needed. The water-cement ratio is given in separate tables. For example, below are data on the number of inputs in relation to a kilogram of cement, provided that medium-sized aggregates are used.
The amount of water to obtain concrete of the required grade when using medium-sized crushed stone and sand
For example, to obtain concrete grade M 300, the proportions of cement M 500 and water are defined as 0.61. This means that for 1 kg of cement, 0.61 liters of water (610 ml) are added to the solution. This produces a medium-plastic solution, which is used most often. But when pouring foundations or other structures with dense reinforcement, a plastic solution may be needed. Then, when determining the amount of water, in addition to the brand of cement, it is also necessary to take into account the size of the aggregates and how fluid the solution should be. These data are presented in the table below.
The amount of water in concrete depending on the size of crushed stone/gravel and the fluidity of the solution
Sometimes it is necessary to determine how much cement you will need for a particular task. To do this, you need to know how much cement is contained in a cubic meter of concrete. Data on concrete and cement grades can be found in the table below.
Amount of cement per cube of concrete
We build it ourselves
If you have the opportunity to purchase a ready-made cement concrete mixture at a price of approximately 4,500 rubles per 1 cubic meter and the mixer has the ability to drive up to the unloading site, then please do so. This method will significantly speed up the construction process and lighten your wallet at a corresponding speed. When purchasing a cement concrete mixture, take into account the delivery distance; it should not exceed 3 hours. Since the beginning of setting of the cement concrete mixture is 4 hours, during this time it is necessary to deliver it, lay it and compact it.
the quality of cement concrete visually and using the batch passport, which the driver who delivered the mixture must have. Also, the factory where it was prepared must have a certificate authorizing the preparation of the mixture. Visually, the mixture should be gray in color, evenly mixed without particles larger than 20mm. If the mixture has a yellowish tint, then this may be the result of using sand with a high clay content, which is absolutely unacceptable. In such a situation, it is better to refuse to lay the mixture and immediately call the organization where you purchased the mixture and report that they brought you a low-quality mixture. In turn, they should send their specialist to you and solve this problem. To avoid getting into such a situation, carefully select a supplier, checking the availability of a license and quality certificates for materials.
If you do not have a large budget and decide that you will prepare cement concrete yourself, then I strongly recommend buying a mixer with a ready-mix output volume of 80 liters - it will pay for itself very quickly and save a lot of your time.
We will assume that you have bought a mixer, purchased crushed stone, sand, cement, have clean water at your construction site without foreign impurities and are ready to get to work.
Next, we are faced with the question - how much of what to put in the mixture? The question is from the field of construction laboratory and not everyone can do it. There is no need to get lost, everything is much simpler than you think. For work we will need: a shovel, a 15 liter bucket, a 10 liter bucket, a concrete mixer (mixer), and materials accordingly. Next, I describe the process of preparing cement concrete with the most optimal sequence:
Pour approximately 7-8 liters of water into the concrete mixer (depending on the moisture content of the source materials), then fill in two ten-liter buckets of sand and wait 10 seconds until the sand is mixed with water. Next, fill one ten-liter bucket of cement and wait 20-30 seconds for the water, sand and cement to mix until a homogeneous mass is similar in consistency to sour cream. Then we add two fifteen-liter buckets of crushed stone, or three of 10 each. We give the concrete mixer a slightly greater slope and leave the materials to mix. At this time, you can collect everything else in buckets. The amount of water is adjusted individually, and after 2-3 batches you will find the ideal amount of water. The mixture is usually mixed for 2 - 3 minutes after adding crushed stone and unloaded. The cement-concrete mixture can be unloaded directly into the formwork, into buckets, into a stretcher, into a wheelbarrow - it all depends on you, whichever is more convenient for you. Personally, I always tried to reduce labor costs and installed the concrete mixer so that the unloading was carried out directly into the formwork. It’s much easier to work this way, and faster.
To ensure the quality of the concrete mixture, pay special attention to the original stone materials and cement, since the quality directly depends on their quality.
Areas of use
We have decided what materials are required for concrete in what proportions, but what brand is needed? This depends on the purpose of the structure and its operating conditions. It will be easier to navigate if you know which grades of concrete can be used for what (let’s name only those that are used in the construction of a private house, its renovation or landscaping).
M100 (B7.5). This is the so-called lean concrete. It is used to prepare sites for critical structures. For example, when building a strip foundation, a layer of lean concrete is laid on a gravel-sand backfill, and then reinforcement work begins. The same composition is used when laying curb stones, for example, when making paths or blind areas around the house.
M150 (B12.5). This composition is used in preparation for slab foundations, for screeds, pouring concrete floors or garden paths. This type of concrete can be used to make foundations for small lightweight buildings such as a wooden bathhouse or a small guest house made of timber or logs.
M200 (B15). One of the most popular brands of concrete. It is used to make foundations of any type for light houses on normal soils, screeds, stairs, blind areas, paths. Cement blocks are made from this brand of concrete at home, and it is also used in factories for the production of foundation and building blocks.
Read about how to build your own foundation from FBS blocks here.
The ratio of cement and sand for concrete affects the strength characteristics
M250 (B20). The scope of application is almost the same, but in more difficult conditions. They make any foundations on difficult soils, or on normal ones, but for houses built from heavy materials. They make blind areas that will be used as paths, external stairs, concrete porches, fences, etc. It is also used to make floor slabs for light loads.
M300 (B22.5). Also suitable for all areas listed above, but under even more severe operating conditions. They make foundations for heavy houses on heaving soils, make monolithic walls, paths, waterproof blind areas, etc. This brand of concrete is mainly used to make floor slabs and grillages for pile-grillage foundations.
M350 (B25). The strength of this brand for private construction is generally excessive. This concrete is used for the construction of monolithic pool bowls or for the manufacture of foundations at high groundwater levels, for other structures that require high water resistance. This brand is already more often used in industrial construction.
M400 (B30). This is already an expensive brand of concrete, which is used in facilities with special requirements: for large swimming pools, dams, bank storage facilities, etc.
Question 1. Cement concrete mixture and cement concrete
Lesson plan No. 43
Discipline : Technology and organization of construction of city streets and roads
Topic of the lesson: “Construction of monolithic cement concrete pavements”
Purpose of the lesson: to study the general characteristics and technology of constructing cement concrete road surfaces
Planned results:
— educational –
formation of knowledge about the technology of constructing cement concrete road pavements
— developing — memory development, mastery of linguistic means: the ability to logically and accurately express one’s point of view, use adequate linguistic means
- educational –
development of logical thinking, spatial imagination necessary for future professional activities, for continuing education and self-education
Type of lesson : lecture
Lesson plan:
1. Cement concrete mixture and cement concrete
2. Requirements for cement concrete pavements
3. Advantages and disadvantages of cement concrete pavements
Equipment: board, multimedia complex, presentation
Literature: Literature: “Construction of highways. Road surfaces" edited by: Podolsky V.P., Level of education: Higher professional education, 2015, 304 pp.
Teacher: Malyarenko N.V.
Topic of the lesson: “Construction of monolithic cement concrete pavements”
Lesson plan:
1. Cement concrete mixture and cement concrete
2. Requirements for cement concrete pavements
3. Advantages and disadvantages of cement concrete pavements
Question 1. Cement concrete mixture and cement concrete
Link to video materials:
https://www.youtube.com/watch?v=ZvCLUqKsjNU&t=20s
Cement concrete is one of the most common construction materials, which is used for the production of reinforced concrete products, as well as for housing and road construction. Cement concrete roads are superior to asphalt roads in many respects, which has become the reason for increased attention to this material on the part of engineers and transport route designers.
Cement concrete road surfaces can replace traditional asphalt. Cement-based concrete Properties and characteristics The photo shows the process of laying concrete from an automatic mixer. Concrete is a stone material of artificial origin, which is used in construction and production of reinforced concrete products.
Rice. 1. Cement concrete produces a light gray canvas that is better visible at night
It is obtained by forming and subsequent hardening of a specially selected mixture of components, including a binder (cement, gypsum, bitumen, etc.), small and large n fillers, water and special targeted additives.
Classification of concrete is carried out according to GOST 25192-2012, GOST 25192-82 and GOST 747З-2010 according to various indicators: volumetric mass, main purpose, type of binder substances, type of fillers, hardening conditions and structure. Here are the main types of concrete: By volumetric mass - especially heavy (with a density of more than 2500 kg/cubic m), heavy (from 2200 to 2500 kg/cubic m), lightweight (1800 - 2200 kg/cubic m), lightweight cue (500 – 1800 kg/cubic m) and particularly light (density less than 500 kg/cubic m);
By type of binder component – silicate, gypsum, cement, slag-alkali, polymer, asphalt;
According to the main purpose - ordinary, used for the construction of industrial and civil objects, special, including hydrotechnical, heat-insulating, road, decorative, heat-resistant , acid-resistant, radiation-protective;
Based on the type of fillers, concrete is divided into mortars with dense, porous and special fillers;
According to the hardening conditions, there are materials of natural hardening, hardening under conditions of heat and moisture treatment at atmospheric pressure and autoclave hardening;
Based on their structure, products of cellular, large-porous, porous and dense structure are distinguished.
After hardening, the cement-concrete mixture for road surfaces produces heavy, dense cement concrete of natural hardening, for special purposes on dense fillers.
The construction of cement-concrete roads can improve the quality of transport routes in our country. Cement-concrete road surfaces differ from traditional asphalt in a number of ways. Moreover, these qualities are very significant, on which not only the beauty and comfort of the road surface depends, but also its reliability, safety and durability.
Compared to asphalt concrete, cement concrete has the following advantages:
Higher strength.
Cement mixtures produce stone that can withstand higher loads of compression, tension and bending during tension, which has a positive effect on the operational characteristics of the surface opogs;
Resistance to elevated and high temperatures resulting from infrared radiation from the Sun, as well as from tire friction and the effects of hot exhaust gases, and in the case of airport runways ov - the impact of the reactive flame of engines.
Rice. 2. Construction of a road surface made of cement concrete
Unlike asphalt, cement concrete does not melt or burn; Resistance to abrasion as a result of traffic. It has been established that in a year the cement sheet wears off by about 1 mm, which is relatively little; Durability. The design service life of roads made of this material is about 30 years, but the real one can easily reach 50 or more; Resistance to aggressive chemical environments and petroleum products.
This is the case of the case for the derivatives of the same, to the same, they will have a ponds and diesel, and the sides of the pacifies and sides of the Ximikatami.
Concrete is laid using special road construction equipment. Of course, there are also disadvantages of using cement concrete in road construction. This is a higher price of the material, the likelihood of swelling and cracking of the top layer, and also the need to install longitudinal and transverse expansion joints in the cement etone, where labor-intensive cutting of reinforced concrete with diamond wheels and diamond drilling of holes in the concrete, which is produced by special machines, are involved. The work is carried out under the constant supervision of engineers and builders.
Concrete road surfaces are exposed to many wear factors, so the instructions set quite strict requirements for the quality of components and the composition of the mixture. your mixture, as well as the conditions of preparation, storage and transportation of the solution.
Making a quality product with your own hands is quite difficult. Taking into account the special operating conditions and increased specific wear of the material, cement concrete for road surfaces must be produced in accordance with a number of requirements. These are, first of all, the requirements for the component composition of the mixture.
Rice. 3. Laying is carried out using special road equipment
The cement for such a solution should be of the Portland cement type. The grade is allowed no lower than M400, and for bases of multi-layer coatings – no lower than M300. Concrete production plant. At the same time, the brand must be standardized for frost resistance, it should be no lower than F 150, and for the base – no lower than F 50. These numbers show the number of freezing/thawing cycles tion in the presence of chloride salts. Another important characteristic that affects the mobility and strength of concrete is the water-cement ratio or W/C. Theoretically, for mixing concrete, B/C = 0.2 is sufficient, but in practice such a solution is too rigid and immobile, and laying it is impossible. For road mortar, B/C is standardized within the following limits: no more than 0.5 for the top layers, no more than 0.6 for the bottom layers and no more than 0.75 for the bases. Mobile concrete plant. The composition of fillers must also comply with the standards and regulations.
Natural coarse-, medium- and fine-grained sand is allowed, crushed stone is of optimal granulometric composition with an amount of impurities of no more than 1%. The fractional composition is accepted up to 40 mm - for a single-layer coating or the bottom layer of a double-layer coating, up to 20 mm - for the top layer of a double-layer coating. Concrete is prepared using cyclic concrete mixers or continuous mobile installations, and is laid using a set of concrete and concrete paving machines finishing machines, as well as machines for cutting shrink seams.
Cement concrete is an excellent raw material for the construction of modern highways, runways and highways. The material is superior to traditional asphalt in a number of important indicators, and the video in this article demonstrates the process of laying the solution on the road.
Preparation of concrete
For large volumes of work, it is better to order concrete from the factory. Making large quantities of mortar by hand or even using concrete mixers is a difficult task, and laying it in batches requires additional effort to ensure that the layers adhere well. However, you can prepare concrete manually. In this case, there are two sequences of actions:
- First, concrete and sand are mixed dry. It is mixed until the color becomes uniform. Then crushed stone is poured in, everything is mixed again, and water is added last.
- First, water is poured into it and cement is poured into it. When everything is mixed, add sand and then coarse aggregate.
The order of adding components for concrete during mixing may be different.
In the first option, there is a possibility that during manual mixing, unmixed composition will remain at the bottom, near the walls of the container, which will lead to a decrease in the strength of the concrete. The solution is to mix everything well and thoroughly. But you can’t spend too much time on this: the solution will begin to set.
The second option has its disadvantages: obtaining a homogeneous cement laitance (a mixture of water and cement) sometimes takes a lot of time. As a result, there is simply not enough of it to form bonds with the backfill: the cement “seizes” and the strength of the concrete also decreases.
All this is not so critical when using concrete mixers, but it is also not ideal. There is another difficulty here. Concrete is usually delivered to the construction site in carts. The entire volume does not fit into one, and the remainder is left to spin in a concrete mixer. This is better than leaving it just standing, but if you mix it too long, the solution may begin to delaminate, resulting in lower concrete strength. The solution is two carts and two people to carry them. The filling method - first or second - choose for yourself.
For small volumes, concrete can be mixed by hand
So after all, how to prepare concrete. The choice is yours. If the volumes are small, you can knead by hand. Just do it carefully. To pour the foundation, it is better to order a mixer, but you can also use a concrete mixer (or two, depending on the volume). And to solve problems with the heterogeneity of the mixture (although it is better that it is good), treat the concrete being laid with a vibrator. Most of the problems will go away.
Next, we’ll talk about the requirements for concrete components, their sizes and qualities.
Cement based concrete
Properties and characteristics
The photo shows the process of laying concrete from an automixer.
Concrete is a stone material of artificial origin, which is used in construction and the production of reinforced concrete products. It is obtained by forming and subsequent hardening of a specially selected mixture of components, including a binder (cement, gypsum, bitumen, etc.), small and large fillers, water and special targeted additives.
Classification of concrete is carried out in accordance with GOST 25192-2012, GOST 25192-82 and GOST 7473-2010 according to various indicators: volumetric mass, main purpose, type of binder, type of fillers, hardening conditions and structure.
Here are the main types of concrete:
- By volumetric mass - especially heavy (density more than 2500 kg/cubic m), heavy (from 2200 to 2500 kg/cubic m), lightweight (1800 - 2200 kg/cubic m), light (500 - 1800 kg/cubic m m) and especially light (density less than 500 kg/cubic m);
- By type of binder component - silicate, gypsum, cement, slag-alkaline, polymer, asphalt;
- According to the main purpose - ordinary, used for the construction of industrial and civil facilities, special, including hydraulic engineering, thermal insulation, road, decorative, heat-resistant, acid-resistant, radiation protective;
- Based on the type of fillers, concretes are divided into solutions with dense, porous and special fillers;
- According to the hardening conditions, there are materials of natural hardening, hardening under conditions of heat and humidity treatment at atmospheric pressure and autoclave hardening;
- Based on their structure, products have a cellular, large-porous, porous and dense structure.
Cement concrete produces a light gray surface that is better visible at night.
Important! After hardening, the cement-concrete mixture for road surfaces produces heavy, dense cement concrete of natural hardening, for special purposes on dense fillers.
Benefits for road construction
The construction of cement concrete roads can improve the quality of our country’s transport routes.
Cement concrete road surfaces differ from traditional asphalt in a number of qualities. Moreover, these qualities are very significant, on which not only the beauty and comfort of the road surface depends, but also its reliability, safety and durability.
Compared to asphalt concrete, cement concrete has the following advantages:
- Higher strength . Cement mixtures produce stone that can withstand higher loads in compression, tension and tensile bending, which has a positive effect on the operational characteristics of the road surface;
- Resistance to elevated and high temperatures arising from infrared radiation from the Sun, as well as from tire friction and exposure to hot exhaust gases, and in the case of airfield runways, exposure to engine jet flame. Unlike asphalt, cement concrete does not melt or burn;
- Resistance to abrasion due to traffic . It has been established that the cement sheet wears off by about 1 mm per year, which is relatively little;
- Durability . The design life of roads made of this material is about 30 years, but the actual life can easily reach 50 or more;
- Resistance to aggressive chemical environments and petroleum products . This is also an important quality indicator for road surfaces that are constantly in contact with combustion products of gasoline and diesel fuel, water, salts and their solutions, and other chemicals.
Concrete is laid using special road construction equipment.
Of course, there are also disadvantages to using cement concrete in road construction. This is a higher price of the material, the likelihood of swelling and cracking of the top layer, as well as the need to install longitudinal and transverse expansion joints in cement concrete, which involves labor-intensive cutting of reinforced concrete with diamond wheels and diamond drilling of holes in concrete, which is produced by special machines.
The work is carried out under the constant supervision of engineers and builders.
Important! Concrete road surfaces are exposed to many wear factors, so the instructions impose fairly strict requirements on the quality of the components and the formulation of the mixture, as well as on the conditions for preparing, storing and transporting the solution.
Requirements
Making a quality product with your own hands is quite difficult.
Taking into account the special operating conditions and the increased specific wear of the material, cement concrete for road surfaces must be produced in accordance with a number of requirements. These are, first of all, the requirements for the component composition of the mixture (also find out how the joists are attached to the concrete floor).
The cement for such a solution should be of the Portland cement type. The grade is allowed no lower than M400, and for bases of multilayer coatings – no lower than M300.
Concrete production plant.
In this case, the brand must be standardized for frost resistance; it must be no lower than F 150, and for bases – no lower than F 50. These numbers show the number of freezing/thawing cycles in the presence of chloride salts.
Another important characteristic that affects the workability and strength of concrete is the water-cement ratio or W/C. Theoretically, W/C = 0.2 is sufficient for mixing concrete, but in practice such a solution is too hard and immobile, and its laying is impossible.
For road mortar, W/C is standardized within the following limits: no more than 0.5 for top layers, no more than 0.6 for bottom layers and no more than 0.75 for bases.
Mobile concrete plant.
The composition of the aggregates must also comply with the norms and regulations. Natural coarse-, medium- and fine-grained sand is allowed, crushed stone is of optimal granulometric composition with the amount of impurities not exceeding 1%. The fractional composition is accepted up to 40 mm - for a single-layer coating or the bottom layer of a two-layer coating, up to 20 mm - for the top layer of a two-layer coating.
Concrete is prepared using cyclic concrete mixers or mobile continuous installations, and is placed using a set of concrete placing and finishing machines, as well as machines for cutting shrinkage joints.
Requirements for cements for concrete
For most construction work, cement concrete is used, where Portland cement is used as a binding component. There is also limestone, but its scope of application is limited mainly to finishing work, which is done “the old fashioned way.”
Types of Portland cement and their storage
There are several types of Portland cement: Portland slag cement, aluminous cement and pozzolanic cement. They all differ slightly in characteristics, but any are suitable for private construction. The difference can only affect the setting time: slag Portland cement takes the longest to harden - up to 12 hours, followed by standard Portland cement - up to 10 hours, and aluminous binder hardens the fastest - no more than 8 hours.
Cement for concrete must be dry, free-flowing and fresh
Cement is demanding on storage conditions, and especially humidity. For the manufacture of important structures - foundations, floors, etc. It is advisable to use fresh one, recently released from the factory. Within a month it loses up to 10% of its properties, and after 6 months they deteriorate by 30-35%. Therefore, for example, when pouring a foundation, it is better to take it a maximum of two weeks ago and purchase it shortly before use.
Store in a dry, ventilated area. If there is no room, they are stored under a roof or wrapped in several layers of film to protect them from moisture. Please note - wrapped, not covered. And preferably not on the ground, but on a wooden floor. The thing is that when moisture gets in, even in a vapor state, the cement becomes lumpy, which greatly worsens the characteristics of concrete. If there is an abundance of moisture, it simply becomes a stone and there is no way to use it. Therefore, take care of a place to store cement in advance.
Cement marking
What brand of cement should be used is usually indicated in the concrete recipe. It is designated by the letter M and numbers that indicate the maximum concrete strength that can be achieved with this binder. For example, with M400 grade cement you can get maximum concrete grade M400, as well as lower ones.
Next comes the letter “D” and numbers indicating the amount of impurities. M400 D15, means that there are 15% impurities in the binder. For construction work, this figure should not be more than 20%.
Fillers - crushed stone and sand
The composition of concrete is determined by the functions and characteristics of concrete that are necessary during its operation. The most common are sand and crushed stone. They are subject to no less stringent requirements than the quality of cement. Sometimes pebbles are used, but only if they have sharp edges and not round ones. In the presence of broken lines, the adhesion of the aggregate to the solution is better, as a result, the strength of the concrete is much higher.
Sand
Construction sand can be river or quarry sand. River water is more expensive, but it is usually cleaner and has a more uniform structure. It is best used when preparing concrete for pouring foundations and screeds. For masonry or plastering, it is appropriate to use cheaper quarry sand.
In addition to its origin, sand is distinguished by fractions. For construction work, large or medium ones are used. Small and dusty ones are not suitable. The normal size of sand grains is from 1.5 mm to 5 mm. But optimally in solution it should be more homogeneous, with a difference in grain size of 1-2 mm.
The sand must be clean, preferably with the same grain sizes
The cleanliness of the sand is also important. It should definitely not contain any foreign organic inclusions - roots, stones, pieces of clay, etc. Even the dust content is standardized. For example, when mixing concrete for a foundation, the amount of contamination should not exceed 5%. This is determined empirically. 300 ml of sand is poured into a half-liter container, everything is filled with water. After a minute, when the grains of sand settle, the water is drained and refilled. This is repeated until it is transparent. After this, determine how much sand is left. If the difference is no more than 5%, the sand is clean and can be used when mixing concrete for the foundation.
For those jobs where the presence of clay or lime is only a plus - when laying or plastering - there is no need to take special care of the cleanliness of the sand. There should be no organic matter or stones, and the presence of clay or lime dust will only make the solution more plastic.
Crushed stone
For critical structures - floors and foundations - crushed crushed stone is used. It has sharp edges that adhere better to the mortar, giving the structure greater strength.
Crushed stone fractions are standard:
- extra small 3-10 mm;
- small 10-12 mm;
- average 20-40 mm;
- large 40-70 mm.
In the batch, crushed stone is used in several fractions - from small to coarse
Several different fractions are used simultaneously in concrete. The largest fragment should not exceed 1/3 the size of the smallest element of the structure being poured. Let me explain. If a reinforced foundation is being poured, then the structural element that is taken into account is the reinforcement. Find the two elements closest to each other. The largest stone should not be more than 1/3 of this distance. In the case of pouring a blind area, the smallest size is the thickness of the concrete layer. Choose crushed stone so that it is no more than a third of its thickness.
Fine crushed stone should be about 30%. The remaining volume is divided between medium and large in arbitrary proportions. Pay attention to the dustiness of the crushed stone. Lime dust is especially undesirable. If there is a lot of it, the crushed stone is washed, then dried, and only then poured into concrete.
Aggregate storage
It is clear that a construction site is not the cleanest and most organized place, and sand and crushed stone are often dumped directly onto the ground. In this case, when loading, you must ensure that no soil gets into the mix. Even a small amount will negatively affect the quality. Therefore, it is advisable to pour aggregates onto solid areas.
It is also necessary to protect them from precipitation. In concrete formulations, the number of components is given based on dry components. You learn to take into account the moisture content of components with experience. If you don’t have one, you have to take care of the condition and cover the sand and gravel from rain and dew.
