Mass production of sand concrete products requires a careful step-by-step organization of the technological process, and compaction is one of these steps.
In the manufacture of heavy concretes according to traditional molding schemes, compaction quality control is usually not carried out. The manufacturer is satisfied with the organoleptic signs of compaction, for example, the appearance of laitance on the surface of the product. Manufacturing practice confirms the sufficiency of these features, primarily due to the workability margins that are included in the design of the composition to simplify the molding step. The price for increasing workability is an increase in cement consumption, however, the management of enterprises willingly agrees to this, believing that high-quality compaction when using aggregates with unstable properties is sufficient compensation for the excessive consumption of cement.
In the manufacture of sand concrete structures, where there is always more cement paste than in heavy concrete, the appearance of cement laitance on the surface of the molded product is already an insufficient sign of high-quality compaction.
The "Recommendations for the manufacture of structures from sand concrete" states that a sufficient sign of high-quality compaction cement-sand mixtures is to obtain a compaction coefficient Ku≥0.97.
The control of the compaction factor should be accompanied by both the design of the composition and the manufacture of structures. This is especially important for sand concretes, where undercompaction is the main defect in the mass production of small-piece products from especially and super-rigid mixtures.

Application of methods for intensive compaction of cement-sand mixtures

In recent years, both in foreign and domestic practice, methods of intensive compaction of concrete mixtures have been increasingly widely used.
With intensive compaction, rigid, extra-rigid and super-rigid mixtures are used, which allows not only to reduce the consumption of cement, but also to fundamentally change the production scheme - to exclude molds from the technological process.
Qualitatively compacted rigid concrete mixtures are able to hold their shape independently, and especially super-rigid ones allow immediate movement of freshly molded products directly or on a pallet.
In world practice, the following main methods of intensive compaction are used: vibrocompression, semi-dry pressing, roller molding, press rolling, extrusion, anti-extrusion, vibroforming with weight, etc.
Vibrocompression
Vibrocompression is the most widely used in Russia; there is both many years of experience in the application of the method, and domestic developments in technology and equipment.
New types of vibropresses are produced and automated lines well-proven in the process of long-term operation. It is shown that vibrocompression can be used to obtain quality products from cement-sand mixtures, and not only to abandon the use of molds and reduce the time of heat and moisture treatment, but also to reduce the requirements for the quality of sand-aggregate imposed by suppliers of foreign equipment. Vibrocompression also provides calibrated dimensions and high quality surface products.
An analysis of the designs of vibropresses from leading world and domestic manufacturers with many years of experience in their manufacture and operation in Russia and abroad showed that in the best equipment options, the matrix is ​​installed on a vibrating platform so that vibration effects are transmitted to the punch, close to the effects on concrete mix in the matrix. This makes it possible to reduce the molding time of products and increase the rigidity of molded mixtures.

On fig. 5.7 shows a diagram of a molding complex, including a vibropress with a lifting matrix. The vibropress consists of three main units: the forming unit, the pallet feeder and the concrete feeder. The forming unit includes bearing columns 1, upper beam 2, lower base plate 3. Brackets with shock absorbers are installed on the columns, on which a vibration platform 4 with vibrators 5 is located. Matrix 6, consisting of a frame and an insert, moves along the columns using hydraulic or pneumatic cylinders.
The cylinder 7 of the punch 8 is mounted on the upper traverse, to which the stamps are attached.
The concrete dosing mechanism is a welded frame 9, on which the hopper 10 is mounted.
A measuring box 13 with a pusher moves along the guides by a system of levers 11 and a drive 12. On the front wall of the box there is a device for cleaning punch dies from concrete residues.
The pallet feeding mechanism includes an accumulator 14 mounted on a frame 15, along which a trolley with folding stops reciprocates with a hydraulic cylinder. The vibropress is equipped with a receiving table 16, a hydraulic pump station 17 and a control system 18.
Vibropress operation procedure:
- the pallet at the next step of the conveyor is installed on the vibration platform;
- the matrix goes down and presses the liner to the pallet, then its upper plane coincides with the reference base for the movement of the measuring box. The punch is in the up position;
- concrete is fed into the hopper of the dosing mechanism. The pusher is in its original position, i.e. pressed against back wall measuring box;
- the measuring box is installed above the matrix, the vibrators are turned on, the concrete mixture from the measuring box is distributed over all the matrix sockets;
- after the vibration stops, the measuring box returns to its original position;
- a punch is lowered onto the concrete mixture in the matrix cell, the vibrators are turned on. The concrete mixture is compacted by the combined effect of vibration and weight;
- after the end of the compaction process, the matrix lifting cylinders are switched on. The punch continues to remain in the lower position, keeping the products from lifting together with the matrix until they are completely released. Further rise of the matrix occurs together with the punch;
- the pallet with freshly molded products is pushed out from under the forming device, and the next pallet comes in its place;
- the matrix together with the punch is lowered, the matrix presses the pallet against the vibration platform, the punch rises to its original position. The forming unit is ready for the next cycle.
The process of bulk vibrocompression itself can be divided into 3 stages:
Pre-compacting.
The stage is usually combined with volumetric vibrodosing: the concrete mixture is placed in a matrix under the action of vibration. In this case, the mixture is distributed over the area of ​​the matrix, partial removal of air and preliminary compaction of the mixture due to the convergence of particles.
Aggregate particles covered with cement paste automatically occupy the optimal position during vibration - small particles are placed between large ones, reducing the voidness of the mixture.
Since in the process of pre-compaction the mixture is dosed “per product”, it is essential to ensure the uniformity of filling the matrix with the concrete mixture, for which a number of techniques have been developed by vibrocompression practice:
- vibrodosing. Dosing of the mixture is carried out with the vibrating platform turned on, which leads to partial removal of air from the concrete mixture and, consequently, to greater uniformity of the backfill;
- multivibration. When the measuring box moves along the matrix, it abruptly stops at the beginning and end of the movement, which causes the system to oscillate with low frequency and high amplitude (during vibration dosing, high frequency and low amplitude). This movement of the measuring box is made 3-5 times;
- "entry" of the measuring box. The stop of the front face of the measuring box occurs behind the front face of the matrix;
- an increase in the volume of the measuring box. The volume of the measuring box is 1.5-2 times greater than the volume of the vibropress matrix, which ensures the constant presence of a column of concrete mixture above the matrix;
- installation of "turner". The agitator in the process of multivibration provides additional directional mixing of the mixture. The configuration of the agitator usually depends on the type of product to be molded. Moving the measuring box causes the agitator to make low-frequency vibrations, on the one hand, preventing the compaction of the concrete mixture in the measuring box, and on the other hand, improving the filling of the matrix cells. A number of foreign firms began to supply vibropressing equipment with active (having their own drive) turners.
The positive effect of an active agitator on the quality of filling the matrix cells, especially for products with high thin walls, has been experimentally confirmed.
Among the activities that ensure high-quality filling of the vibropress matrix, also include:
- regulation of the moisture content of the mixture as a factor that significantly affects its rheological characteristics;
- thorough mixing of the mixture, ensuring its uniformity in accordance with the standard;
- with the overall dimensions of the matrix, in terms of close to a square and exceeding 1.0 m, - the use of two hoppers and two measuring boxes, each filling its own half of the matrix;
- supply of aggregates and cement from one manufacturer, including sand with a stable granulometric composition and fixed activity cement without additives with a constant normal density of the cement paste.
All these problems also occur in foreign practice, although to a lesser extent, in connection with the use of washed, dry, graded aggregates and pure clinker cements in the technology.
Usually, the cement-sand mixture entering the matrix contains up to 60% air. As a result of the preliminary compaction measures, its amount is reduced to 20-25%, and this air is fairly evenly distributed throughout the volume of the mixture.
Formation.
With the right composition of concrete, the parameters of vibration effects and the amount of pressure from the side of the punch, the liquefaction of the cement paste is ensured, i.e., the aggregate particles approach each other, thin structured shells of the cement paste are formed around them. As a result, the cement-sand mixture acquires fluidity properties, which ensures the almost complete removal of trapped air.
This stage of molding in the best samples of vibrocompression equipment is characterized by the pulsating nature of the interaction between the mixture and the punch. In the process of vibration, the punch periodically breaks away from the concrete mixture, followed by impact on the molded product.
The total impact from the punch (own weight, hydraulic (pneumatic) pressure) and the nature of the vibration effects are assigned so that the inertial forces of separation can create conditions for a pulsating mode in the interaction "vibration platform - compacted product - punch".
Final seal.
The compaction obtained at the preliminary stages can be considered close to the required one - at this stage, there is practically no visible movement of the punch, and only the removal (partially more uniform distribution over the volume) of the trapped air residues is carried out.
In order to exclude destructive processes in a freshly molded product and air leakage, an additional force is applied to the punch at this stage of compaction, which ensures the vibrating system "punch - product - vibrating platform" is closed.
It is expedient to simultaneously increase the vibration frequency of the vibrating platform, for example, up to 100 Hz, which brings into resonance small particles aggregate, contributing to the compaction of the concrete mixture.
The above mechanism for forming hard and especially hard mixtures is the result of many years of research and is the basis for the operation algorithm of the vast majority of foreign and domestic brick making machines.
However, vibrocompression existing models equipment is successfully implemented in the manufacture of structures either in the form of thick flat plates, or products having a constant height and section in the direction of molding.
In the manufacture of structures of variable thickness or uneven height in the direction of molding or thin plates, the above molding scheme does not provide high-quality compaction.
The deterioration in the quality of compaction not only affects the strength characteristics of concrete products, but also makes poorly predictable characteristics that depend on the structure of the material - frost resistance, water absorption, water resistance.
The following are ways to obtain products of variable thickness and products of fixed height by vibrocompression.
Vibrocompression, as a technology in its classical version, involves the manufacture of products of constant height in the direction of molding. Usually these are slabs or blocks, solid or including vertical channels. These products are classic version molding on a flat pallet.
The production of products of variable thickness on pallets of complex configuration is, as a rule, recognized as inexpedient due to their excessively high cost, which, even with flat pallets, is close to the cost of molding equipment.
Giving the product a different configuration using a punch is a much more widely used technique.
This is how trays, gutters, well covers, covering stones for plinths, etc. are made.
However, the practice of forming products of variable thickness by methods used for products of constant thickness lead to underconsolidation of individual sections in them. Indeed, when forming on a flat pallet, the measuring box fills the entire volume of the matrix with a mixture of constant height. As a result, only the thinnest section of the product is compacted under the figured punch. When forming “uneven height” products from mixtures with high workability, the latter moves under weight, but this does not happen in hard, extra-hard and super-hard mixtures, so the product turns out to be uncompacted.
A technological technique has been developed that includes an additional operation before vibrocompression: after pouring the concrete mixture with a measuring box under continuous vibration effects, the mixture is loaded with a punch with a force of -20% of the molding force. Thus, the concrete mixture, moving under the influence of vibration in a closed space, acquires in its upper part a shape corresponding to the configuration of the punch.
The next stage of molding is traditional vibrocompression, however, compaction in a product containing sections of different heights, in this case, will be of better quality.
Many years of experience with especially and super-rigid concrete mixes, molded using intensive compaction methods, showed that with Ku≥0.97 it turns out quality concrete with high physical and mechanical characteristics, and that obtaining a higher Ku, as a rule, is not economically justified due to an increase in the cost of compacting concrete mixtures and a decrease in equipment productivity.
Thus, despite the established practice, it becomes obvious that undercompacting of concrete in products with low strength, for example, in wall blocks, is unacceptable.
Another way to obtain the required compaction in products of variable thickness is to increase the workability of the mixture to a level that allows, on a specific equipment, to transfer it to a vibro-liquefied state by vibration effects on the concrete mixture. This will ensure its free movement in the matrix, and the pressure from the punch should not interfere with this.
However, with an increase in the workability of the concrete mixture during compaction, laitance appears on the surface of the freshly molded product. Cement milk can also appear as a result of poor-quality mixing, when individual volumes of the mixture have an increased water content, or from the uneven amplitude field of the vibrating platform or punch. Then the cement laitance can protrude not on the entire surface of the molded product, but at its individual points. As a result, the concrete mixture sticks to the punch, forming holes on the surface of the products after it is lifted.
When the workability of the mixture is increased to a level that leads to the appearance of cement laitance on the entire molding surface, the product sticks to the punch, and the van der Waals forces of adhesion are so great that the freshly molded product, even freed from the matrix, rises with the punch when it returns to the starting position.
Technical solutions that exclude sticking to the punch were obtained during the development of vibrocompression technology cement-sand tiles- a thin plate of variable (10-25 mm) thickness.
Accommodation polymer film between the product and the punch completely eliminated sticking, the molded surface was perfectly smooth. A mechanism has been developed for continuously pulling the film after each molding.
An even better result was achieved when the tiles were molded with a punch heated to 110-120 °C. In this case, a vapor layer formed between it and the molded product. As a result, the tile did not stick to the punch, and its surface after molding was mirror-like. In addition, the tile after vibrocompression turned out to be hot. It was shown that the heat accumulated by the product is sufficient for the mixture to pass through the period of structure formation, which corresponds to the pre-exposure time in the heat-moisture treatment mode.
Equally important is the development of a method for obtaining products of a fixed height by vibrocompression and, first of all, wall blocks - one of the most mass-produced structures produced using vibrocompression technology.
Calibration of blocks in height allows not only applying the laying scheme “on glue”, but also improving the heat-shielding properties of the walls by reducing the thickness of horizontal cold bridges.
The scheme of compaction of cement-sand mixtures in vibrocompression technology provides for the lowering of rigidly interconnected punch elements into the matrix cells, which implies uniform filling of the concrete mixture into each of the cells.
The filling of the mixture into the matrix is ​​​​made by a measuring box, i.e. a volumetric dosage of the mixture is produced, and in its worst case. As a result, even with the implementation of measures to improve the filling, as a rule, the amount of the mixture in each cell turns out to be different and, therefore, differently compacted. In fact, only one of the products or one of the walls of the product is qualitatively compacted, all the rest are, to one degree or another, undercompacted.
What is the measure of this underconsolidation, and how significant is it for the properties of concrete? According to the data, each percentage of undercompaction leads to a decrease in strength by 5-7%. In general, this assessment can be considered correct. However, this is an integral estimate. The essence of undercompaction is the unformed structure of concrete: the presence of spontaneously located air not removed from the concrete product. This air may, for example, be in the zone of main tensile stresses, and then we are no longer talking about percentage reduction in strength - the breaking load can decrease several times. Air can be close to the edges of the product (this is often the case in the manufacture of paving slabs), and then these edges are painted, broken off already in the process of transport operations or packaging, which worsens the durability and presentation of the products.
But this is not the worst result of undercompaction. For products that require frost resistance, the presence of "unorganized" air caverns in them leads to their filling with water. Freezing-thawing of this water destroys products within 1-2 seasons.
An analysis of the practice of manufacturing small-piece concrete products shows that the compaction coefficient Ku = 0.97 is sufficient (including in terms of durability), i.e., about 3% of the air phase is allowed in freshly molded concrete. The accuracy of the dosage of the cement-sand mixture per product is estimated at 4-6%, i.e. the total volume of the air phase can reach 9%. This also means the appearance of unevenly high products in parallel moldings, which is unacceptable, first of all, for wall and finishing materials.
In the practice of vibrocompression, to obtain products of constant height, the method of stopping the vibropress punch at a fixed height is used. It could be mechanical fixation- stop, or the movement of the punch stops under the influence of a signal from the position sensor.
Obviously, in this case, all products are undercompacted. The way out of the contradiction is the proposed method of using concrete with air entrainment. The essence of the method is the introduction of an air-entraining additive into the concrete mixture in an amount that provides up to 10% air entrainment.
When vibrocompressing products with a fixed punch lowering height, this will mean that the entrained air in different quantities will be in each product. However, this air is already not randomly distributed in the form of large pores, but evenly distributed over the mass in the form of small air entrainment pores throughout the entire volume of the product. It is known that such air for concretes made from especially hard cement-sand mixtures, in the amount of 5-6%, practically does not reduce the bearing capacity of products, significantly increasing their frost resistance.
In addition, air entrainment plasticizes the concrete mixture, and, given this circumstance, the strength of concrete may even increase.
Thus, the mechanism for implementing the method of molding products with a calibrated height is the use of an air-entraining additive in especially rigid concrete mixtures of a continuous structure (i.e., with an excess of cement paste), which provides air entrainment up to 10% and fixing the vibropress punch at the level required by the product height standard.
Then, with a properly selected concrete composition, one of the products to be compacted will have Ku≥0.97, and the rest Ku = 0.97-0.93, and the variation in the strength characteristics of concrete will not exceed the regulatory requirements.
Roll molding
The production of small-piece concrete products in domestic and world practice is carried out mainly by vibrocompression. The advantages of the method are so significant that the development of other compaction mechanisms is clearly not enough.
However, vibrocompression also has serious drawbacks: a very “noisy” and “vibratory” technology, the dimensions of products manufactured by vibrocompression are limited.
With matrix dimensions over 1.0 m, the equipment becomes bulky and metal-intensive. The load on the equipment increases many times over. No experience in mass production by vibrocompression reinforced concrete structures.
To a large extent, to avoid these deficiencies a vibration-free method of compacting concrete (primarily cement-sand) mixtures was developed - roller molding.
The essence of the method is the layer-by-layer compaction of the cement-sand mixture with rollers that create the pressure necessary for compaction by reaction in the roller bearings.
A prototype unit was developed and research work was carried out on an experimental line for the manufacture of large-sized unreinforced paving slabs 1000x1000x100 mm.

These studies made it possible to determine the main parameters of the installation (the diameter of the rollers, their length, the number of double passes), which make it possible to obtain high-quality compaction and eliminate such specific disadvantages of roller molding as lamination, rupture cracks, etc. The scheme of the roller molding unit is shown in Fig. 5.8, where 1 is a form, 2 is a beam, 3 is pressure rollers, 4 is support rollers, 5 is a product.
At the Kretinga plant building structures this technology is organized industrial production road products of a wide range.
On fig. 5.9 shows a diagram of a production line that includes 2 horizontal transport streams with a molding unit 1 and a transfer machine 2. Molding is carried out on pallets 3, the molding space is formed by the transverse partitions of the pallet and the longitudinal sides of the installation.
The process of heat treatment of products is divided into 3 stages:
- preliminary exposure in chamber 7 at a temperature of 25-30 °C for 4-5 hours (products are on pallets);
- isothermal heating in chamber 9 at a temperature of 70 °C for 4-5 hours (products are on pallets);
- exposure of products in chamber 7 without pallets with their transportation on freshly molded products located on pallets.
Hardened products during transportation cool down to 25-30 ° C for 4-5 hours.

This scheme of heat and moisture treatment made it possible to create a compact high-performance line.
Line operation order: the tray with freshly molded products 4 by the pusher 5 is installed on the roller table 6 of the chamber 7, in which the first stage of heat treatment takes place. Then the pallet with the products is transferred by the translator 2 to the roller table 8 of the chamber 9 for the second stage of the HME. The pallets are moved by the pusher 10. After passing through the chamber 9, the hardened products are removed from the pallet by the formworker 11 and installed on the freshly molded products located on the roller table 6 to undergo the third stage of heat treatment. The pallets released from the products are sent through the cleaning and lubrication mechanism 12 to the molding table 13.
The conveyor performs two functions: it packs products that have passed a full cycle of heat treatment, and transfers pallets from roller table 6 to roller table 8.
Roll molding allows you to simultaneously produce a different range of products. So, on the specified line, out of 87 pallets available in the technological stream, 40% are intended for the manufacture of main side stones, 11% - lawn stones, 49% - paving slabs.
A single molding cycle is 3 minutes. The proposed technology, in comparison with vibrocompression, expands the possibilities for the production of products with a finished surface, including when using embossed sheets for pallets. industrial production, the use of a hardening retarder instead of lubricating pallets, etc.
The hardening retarder makes it possible to obtain a decorative surface of the "shagreen" type, formed after the "washing" of the surface layer of concrete in products that have undergone heat and moisture treatment.
The principal possibility of manufacturing large-sized reinforced concrete structures from sand concrete by roller molding, including road slabs 3.0x1.75 m.
Press rolling, semi-dry pressing
Press rolling is a very limited technology used in Russia almost exclusively for the manufacture of cement-sand tiles.
The tile is made on figured cast pallets, which are fed under the forming device as a continuous tape.
From the hopper of the forming unit, a portion of a particularly hard cement-sand mixture is poured onto the pallet, which is then rolled (compacted) with profiled rollers. The lower (profile, with irregular protrusions) surface of the tile is formed according to the profile of the pallet, the upper (longitudinal waves, interlock elements) - with a roller device.
Advantages of the method: low noise, high productivity, good geometry of products, the possibility of using especially hard mixtures.
Disadvantages: high cost of pallets, poor redistribution of the cement-sand mixture under the forming roller, the need to use high-quality, mainly prepared aggregates, the possibility of manufacturing a limited number of structural forms of products.
The domestic practice of the production of tiles by press rolling faces serious problems in ensuring the waterproofness of products.
The absence of clear requirements for the quality of aggregate sand, the use of quarry, river sands without processing leads to constantly changing rheological characteristics of the cement-sand mixture. As a result, the mixture is unevenly distributed over the plane of the pallet and, therefore, differently compacted in various parts products. With the adopted molding scheme, the mixture does not have the ability, as it happens, for example, during vibrocompression, to move along the pallet under the influence of vibration. The uneven backfilling and the associated heterogeneity of the compacted material leads not only to a decrease in strength, but also to the impossibility of guaranteeing the waterproofness of the tiles. It is not possible to test every tile - water resistance must be ensured by technology. A number of firms that have been aiming to enter the Russian market for several years roofing materials, despite significant investments, have not been able to complete the solution of this problem.
Attempts to stabilize the characteristics of raw materials by supplying sand from certain quarries also did not lead to the necessary results, and attempts to use dry mixes for the production of tiles increased the cost of products so much that it approached the cost of metal tiles.
As a result, manufacturers began to apply on the surface of the hardened tiles polymer layer, which not only eliminated leaks in the roof, fio and decorated it. In the brochure, however, the consumer is offered not only colored coated tiles, but also uncoated tiles. It would be expedient to apply a colored colloid-cement glue to the freshly molded tiles (the result of joint grinding of cement with pigment), which provides clogging of the pores of the surface layer. In addition, this would save the dye and eliminate the possibility of delamination of the polymer layer.
There is information about the use of press-roll technological lines for the manufacture of paving slabs - products that are in much higher demand than tiles. Paving slabs are thick flat plates of constant thickness, and their molding by press rolling is more simple task than making tiles.
The molding of paving slabs takes place on a flat pallet, which is a metal sheet 4 mm thick, which makes the production of pallets a very simple task.
The height of the paving slabs (usually 70-80 mm) allows the movement of the mixture under the compacting roller and, consequently, their better molding.
The disadvantages of the technology include the possibility of obtaining relief in paving slabs only in the form of longitudinal strips and chamfers only in the direction of movement of the slabs along the conveyor.
It is not clear from the literature whether a chamfer was obtained in the direction perpendicular to the movement when cutting a continuous strip of formed board into products. It was assumed that the formation of the transverse chamfer can be organized simultaneously with the cutting.
Semi-dry pressing is a technology that provides for a one-time intense force effect of a pressing body on a concrete mixture without vibration. Both the disadvantages of the method and its advantages are obvious.
The latter include low noise, the possibility of using mixtures of higher mobility than in vibrocompression, primarily due to the absence of vibration, which leads to sticking of the punch to the product. Semi-dry pressing technology makes it possible to increase the productivity of forming equipment, to expand the range of workability of molded mixtures, and to obtain products with decorative surface. With semi-dry pressing of cement-sand mixtures, a surface of the "shagreen" type is obtained, because the cement milk does not protrude onto the surface of the product, "covering" the filler.
The main disadvantage of semi-dry pressing is that it is difficult to compact the concrete mix with high quality only by pressure without vibration. Therefore, as a rule, the technology is used in the production of thin non-bearing or lightly loaded products, for example, finishing materials.

Inert building materials include a large number of names, brands and varieties of materials that are used in various industries construction. Inert building materials include: sand, gravel, sand and gravel, crushed stone different varieties and other types of products.

Sand is a fine-clastic loose sedimentary rock, consisting of at least 50% quartz grains, feldspars and other minerals and rocks sizes of 0.052.0 mm and more. Sand is river, mountain, ravine, sea. The sand may contain impurities of dust and clay particles, fragments of rocks. River sand is the cleanest, sea sand is polluted with salts and requires clean washing. fresh water. Mountain and ravine are often contaminated with clay, which reduces strength mortars. AT river sand, mined in the bed of dried rivers, combines two properties rarely found together: fineness up to 2.6 mm and high purification from foreign inclusions, clay impurities, organic residues - this makes it universal building material. The granulometric composition includes four groups of sand depending on the size of individual particles: dust-like sand with particles up to 0.05 mm in size; fine from 0.05 to 0.25 mm; average 0.250.5 mm; large 0.52.0 mm and more. The flowability of sand depends on the humidity. Highest values the angle of repose (about 40°) reaches 510% sand moisture content. A further increase in humidity reduces the angle of repose to 2025°. The moisture content of sand layers of different heights is not the same and increases with a decrease in the level of the layer from the surface. The resistance to chemical action of cement alkalis must be taken into account for sand intended as an aggregate in the production of concrete. The resistance of sand is determined by the mineral and petrographic composition and the content of harmful components and impurities. Natural building sand is intended for use as a filler for heavy, fine-grained, cellular and other types of concrete, mortars, preparation of dry mixes for road and airfield pavement devices.

Sand from screenings of crushing rocks, having a true grain density of more than 2.8 t / m 3 or containing grains of rocks and minerals classified as harmful components in an amount exceeding their permissible content, or containing several different harmful components, is produced for specific types construction work on technical documents developed in accordance with the established procedure and coordinated with laboratories specialized in the field of corrosion. Sand is transported in bulk on an open rolling stock.

Natural gravel is a loose mixture of grains of various materials (5150 mm in size) formed as a result of weathering of rocks, which are part of igneous (rarely sedimentary) rocks. There is a specially made artificial gravel obtained by crushing hard rocks. According to the condition of occurrence, gravel is divided into river, sea and mountain (ravine). Grains of river and sea gravel are abraded when carried by water and have a rounded shape. Grains of mountain gravel are acute-angled. River and sea gravel is usually cleaner, contains less clay and organic impurities than ravine gravel. Sea gravel contains admixtures of limestone grains and shell fragments. Gravel with a size of 20-40 mm is called a pebble.

To special properties gravel include strength and frost resistance. Strength is characterized by a grade determined by the crushability of gravel during compression (crushing) during special tests and is characterized by a weight loss of grains in percent (dust is screened out). The frost resistance of gravel is characterized by the number of freezing and thawing cycles, at which the loss in percentage by weight of gravel or crushed stone does not exceed the established values. Gravel must be resistant to environmental influences. The resistance of gravel is determined by the mineral-petrographic composition of the original rock and the content of harmful components and impurities that reduce the durability of concrete and cause corrosion of the reinforcement of reinforced concrete products and structures. Gravel is transported on open rolling stock (in gondola cars), with the obligatory application of measures to prevent the loss of these goods from blowing and spilling into cracks and defects in the car body or in hopper dispensers. Crushed stone is used in construction both in its pure form (for example, for filling roadbed), and as a filler in the production of concrete and asphalt concrete. Crushed stone from rocks - inorganic granular bulk material with grains larger than 5 mm, obtained by crushing rocks, gravel and boulders, incidentally mined overburden and host rocks or substandard waste from mining enterprises for the processing of ores (ferrous, non-ferrous and rare metals of the metallurgical industry) and non-metallic minerals from other industries and subsequent screening of crushed products.

Crushed stone is one of the main materials used for the construction, reconstruction, repair and maintenance of automobile and railways. From quality characteristics crushed stone are largely dependent consumer properties(evenness, friction coefficient, etc.) and durability of roads. This is especially true for the crushed stone used for the device. upper layers road pavement (cubic crushed stone) that directly perceive high mechanical loads from moving vehicles and are under the influence natural factors(variable temperature and humidity regime, multiple freezing - thawing, the effect of solar radiation, etc.) and anti-icing chemicals. The main properties of crushed stone. like all mineral building materials discussed above are: strength, frost resistance, abrasion, grain shape, water absorption, radioactivity, adhesion, contaminant and chemical content harmful impurities. The strength of crushed stone is characterized by the compressive strength of the original rock, crushability of crushed stone during compression (crushing) in the cylinder, and wear in the shelf drum. These figures mimic the resistance stone material under the influence of vehicles passing on the road and mechanical impacts during the construction process road structures(laying and compaction with rollers). Depending on the strength brand, crushed stone is divided into groups: high-strength Ml, strong M, medium strength M600800, weak strength M300600, very weak strength M200. Granite crushed stone with M1200 strength is in the greatest demand, as well as high-strength crushed stone from hard rocks (consisting of other structural minerals), including basalt crushed stone with a strength grade M. It is mainly used in the production of heavy high-strength concrete, in load-bearing bridge structures, responsible foundations. The frost resistance of crushed stone is characterized by the number of freeze and thaw cycles. It is allowed to evaluate the frost resistance of crushed stone by the number of saturation cycles in a solution of sodium sulfate and drying. Flakiness. In crushed stone, the content of grains of lamellar (the term comes from the breed of fish bream, i.e. "flaky gravel" means "flat like a bream") and needle-like forms are normalized. Grains of lamellar and acicular shapes include such grains, the thickness or width of which is three times or more less than the length. According to the shape of the grains, crushed stone is divided into four groups (the content of grains of lamellar and acicular shapes,% by weight): cuboid up to 15%; improved from 15% to 25%; ordinary from 25% to 35%; normal from 35% to 50%. The presence of lamellar and needle-shaped grains in crushed stone leads to an increase in intergranular voidness in the mixture. This, in turn, leads to an increase in binder component, which entails additional material costs. In addition, cube-shaped grains have greater strength than lamellar and needle-shaped grains. Therefore, the use of cube-shaped crushed stone in production is more economically feasible, for example, in the production of concrete, it can significantly reduce the consumption of cement, and in road construction it can reduce the time and labor costs for laying by 50%. asphalt concrete pavement; approximates the compaction factor asphalt mix to unit, which ensures not only the durability of the road surface, but also increases its frost resistance. Rubble radioactivity. In the production of crushed stone and gravel, a radiation-hygienic assessment should be carried out, the results of which determine the class of crushed stone by radioactivity and the types of work for which it can be used. The first class of radioactivity is used for newly built residential and industrial buildings and structures. Second class for road construction within the territory of settlements and zones of promising development. Third class for road construction outside built-up areas.

Adhesion is one of the specific characteristics of crushed stone. It reflects the assessment of the quality of adhesion of bituminous binders to the surface of crushed stone. Crushed stone is transported in specialized open dump cars, hopper-dispensers or gondola cars.

MINISTRY OF TRANSPORT CONSTRUCTION
STATE ALL-UNION ROAD SCIENTIFIC RESEARCH INSTITUTE

soyuzdornii

Approved by the Director of Soyuzdornia, Candidate of Technical Sciences E.M. Dobrov

Approved by Glavdorstroy
(Letter No. 5603/501 of 08/01/83)

Moscow 1985

Designs of crushed stone bases treated with sand-cement mixture developed by Soyuzdornia, Giprodornia and Gosdornia, a method for determining the calculated modulus of elasticity of the layer are given; requirements for sand-cement mixture and crushed stone treated with sand-cement mixture.

Recommendations are given on the selection of mixture compositions that provide the required strength and frost resistance of the base layer; according to the technology of building a crushed stone base, treated in the upper part with a sand-cement mixture by two methods: the mixing method using a profiler and the indentation method using a vibratory roller, a cam roller and a roller on pneumatic tires.

The need to control the quality of construction is indicated.

Layer Height Ratio h 1 / h	Modulus of elasticity of the raw part E 2, MPa	The value of the average modulus of elasticity of the base E cp, MPa, equal to E 1, MPA, equal to
0,25
0,50
0,75

The value of the average modulus of elasticity of the base layer E cf when calculating according to the "Instructions for the design of non-rigid type pavements" VSN 46-83 (M. one.

2.2. The calculated modulus of elasticity of the lower, untreated part of the base, depending on the properties of the materials used, must be taken according to the "Instructions" VSN 46-83 with the additions given in Table. 2 of these Guidelines.

2.3. The calculated modulus of elasticity of the upper, treated part of the base, depending on the grade for the strength of the sand cement used and its amount in the crushed stone layer, providing different grades for the strength of the treated material that meets the requirements of GOST 23558-79, should be taken according to.

Grade for the strength of crushed rock			Estimated modulus of elasticity of the raw part, MPa, with crushed stone size, mm
carbonate	igneous	sandstone	5-40	40-70	70-120
600-800
	800-1000	800-1000
	> 1000

Resistance of sand cement to compression, MPa, at a ratio of W: PC, % ( To section)			Indices of the properties of the processed material
80:20 (0,8)	65:35 (1,35)	50:50 (2,45)	Modulus of elasticity, MPa	Brand	Bending tensile strength, MPa

2.4. The minimum total thickness of the base layer should be at least 10 cm, the maximum - no more than 25 cm. The maximum grain size of crushed stone should not exceed 2/3 of the base thickness.

The maximum depth of processing crushed stone with sand cement when laying the foundation by mixing using a profiler and impregnating using a cam roller should be no more than 15 cm, and using rollers on pneumatic tires and vibration - no more than 7 cm.

The surface layer of sand cement in the construction of a crushed stone base treated with a sand-cement mixture should not exceed 1-2 cm.

3. Requirements for the materials used

3.1. The stone materials used for the device of the proposed design should be subject to requirements for strength, frost resistance and grain composition.

A mixture of sand with cement or other inorganic binder should be subject to requirements for composition, strength and frost resistance,

3.2. The strength of crushed stone from natural rocks must meet the requirements of GOST 8267-82, the strength of slag crushed stone - GOST 3344-73.

3.3. Frost resistance of crushed stone must meet the requirements given in table. 4 of these "Guidelines".

Table 4

	Climatic conditions	Grade of crushed stone in terms of frost resistance, not less, for
		grounds	coatings
I, II, III	severe		Do not apply
	Moderate
	Soft
I V, V	severe
	Moderate
	Soft

3.4. When constructing the foundation by mixing, it is advisable to use crushed stone of a fraction of 5 - 40 (70) mm, by impregnation-indentation using rollers on pneumatic tires - crushed stone of a fraction of 40 - 70 or 70 - 120 mm. When using cam and vibratory rollers, it is also advisable to use crushed stone with a fraction of 20 - 40 mm.

3.6. Losses in mass during testing of crushed slag for structure stability should not be more than 7%.

3.7. For processing crushed stone, you can use sand-cement, sand-slag (based on crushed ferrous metallurgy slag and cement activator) and sand-ash mixtures (based on ashes and slags from thermal power plants), as well as non-crushed granulated blast-furnace slag and belite sludge.

3.8. The mixtures listed in clause 3.7 must meet the requirements of GOST 23558-79. Compression resistance of sand cement at the age of 28 days, and slag and sludge at the age of 90 days. must be at least 3 MPa. In each specific case, the grade of samples from the mixture should be assigned so as to obtain the required strength (calculated modulus of elasticity) of the treated part of the layer and the entire base structure as a whole according to.

The composition of the sand-cement mixture is determined in each case by laboratory selection.

3.9. The frost resistance of sand cement, determined in accordance with GOST 23558-79, must meet the requirements given in.

3.10. Cement for sand-cement mixture must meet the requirements of GOST 10178-76. The beginning of cement setting is not earlier than 2 hours after mixing.

	Climatic conditions	Grade of sand cement in terms of frost resistance, not less, for
		the bottom layer of the base	the top layer of the base	coatings
I - II	severe			Do not apply
	Moderate
	Soft
	severe
	Moderate
	Soft
I V-V	severe
	Moderate
	Soft

3.11. Granulated blast-furnace slags or slag fines with an activity of more than 5 MPa according to GOST 3344-73 and a maximum particle size of 5 mm can be used as a wedging and binding material in the proposed design.

3.12. Instead of a sand-cement mixture, alumina production waste can be used for processing crushed stone - belite (nepheline or bauxite) sludge with the following characteristics:

Maximum grain size, mm, no more than 5

Fineness modulus according to GOST 8736-771 - 2.5

Bulk density, kg/m 3 900 - 1200

Natural humidity,% 15 - 30

Optimum humidity, %20 - 25

Compressive strength of sludge at the age of 90 days, MPa, not less than3

3.13. Sand must meet the requirements of GOST 8736-77 with the following additions.

The plasticity number of sand fractions finer than 0.63 mm should not exceed 2.

3.14. When processing crushed stone with a fraction of 70 - 120 mm, it is allowed to use a sand-gravel mixture and crushing screenings with a maximum fineness of 20 mm. When processing crushed stone of a fraction of 40 - 70 mm, there should not be grains larger than 10 mm in the sand, when processing crushed stone of fractions of 20 - 40 mm - larger than 3 (5) mm.

3.15. For the preparation of mixtures and watering gravel, it is recommended to use water suitable for drinking.

3.16. To reduce cement consumption by 10 - 15% and improve the technological properties of sand cement (increase mobility), SDB should be introduced into the mixing water in an amount of 0.5 - 1% of the mass of cement.

SDB consumption is specified in the laboratory selection of the composition of the sand-cement mixture from specific materials.

4. Technical and economic choice of the pavement base

4.1. Depending on the depth of impregnation, as well as the required average modulus of elasticity of the base layer, the base designs shown on.

4.2. The design of the base must be chosen on the basis of a technical and economic comparison of options, taking into account the cost of materials and the composition of the mixture.

The cost per unit area of ​​the base structure with pincer consists of the cost of rubble With u sand-cement mixture With hc spent on the construction of this structure:

with pincer = With u + With hc

Rice.2. Examples of structures of crushed stone bases treated with inorganic binders to different depths, E cf- average modulus of elasticity of the base layer, MPa; h - total base thickness, cm; h 1 - thickness of the upper, processed part of the layer, see Figures for structures - moduli of elasticity, MPa.

The cost of crushed stone is determined by the formula:

where - the cost of 1 m 3 crushed stone, rub.;

l, in- length and width of the site, respectively, m;

h2- the thickness of the lower, raw part of the layer,

To ysh- crushed stone compaction coefficient;

K p- loss factor, K p = 1,03;

h1- the thickness of the upper, processed part of the layer. m;

Method for pressing sand cement into crushed stone	Thickness of the monolithic base layer, cm	The number of passes of the rink on one track
Successive passes of the cam roller	8-10
	11-13	7-13
Alternating passes of the cam and pneumatic or smooth rollers	14-20	8-12

Indentation into the crushed stone layer of sand-cement mixture or belite slurry with a cam roller starts from the shoulders with the movement of subsequent passages to the longitudinal axis highway and overlapping the trace of each previous pass by at least 20 cm.

7.8. For processing a layer of crushed stone by the method surface pressure rollers on pneumatic tires should be used, pressing sand cement with two or three passes of the roller along one track.

7.9. The final compaction of the layer after processing the crushed stone by one of the previously mentioned methods should be done with rollers on pneumatic tires of the type DU-29, DU-16V, DU-31 in 12 - 16 passes along one track and in accordance with paragraphs. 5.42 - 5.46 "Technical instructions" VSN 184-75.

When using the indentation method by alternating passes of the cam and pneumatic or smooth-roller rollers, the number of passes of the pneumatic roller can be reduced to five to eight due to the fact that the base is partially compacted simultaneously with the indentation.

The compacted base should be trimmed with the passages of a smooth-roller roller.

7.10. At the end of the compaction of the base, it is necessary to take care of it (see these "Methodological recommendations").

7.11. The movement of construction vehicles on the base can be opened after they have gained 70% of the design strength when processing crushed stone with a sand-cement mixture or slag binders with an activator-cement.

On a base of crushed stone treated with belite slurry, traffic can be opened immediately after the device. If on the next day after the installation of such a base it is not planned to lay the overlying layer, then the base must be maintained by watering it daily (in dry weather) with water in the amount of 1.5 - 2 liters per 1 m 2 during the entire warm period before laying the overlying pavement layer.

8. Construction quality control

8.1. All foundation materials should be checked for compliance with their standards for those materials.

8.2. The composition of the sand-cement or sand-slag mixture and its quantity per 1 m 2 of the base, which ensure the design strength of the mixture of crushed stone with sand cement, the laboratory must determine before construction begins by selecting materials.

8.3. The design composition of the sand-cement or sand-slag mixture should be controlled in accordance with SNiP III-40-78 using batchers at the mixing plant.

8.4. The quality of the prepared sand-cement (sand-slag) mixture should be controlled by making three samples in each shift and testing them for compressive strength at the age of 28 days. in accordance with the requirements and methods of GOST 23558-79 with the addition of an activator-cement to the slag, and at the age of 90 days. when using slag and sludge without additives.

Bending strength (split), as well as frost resistance, should be determined on samples taken from every 5 thousand m 3 of the prepared mixture, in accordance with the requirements of GOST 23558-79.

8.5. When spreading crushed stone and sand-cement or sand-slag mixture, as well as slag and sludge, the thickness and width of the layer of distributed materials should be controlled with measuring rulers and tapes for every 100 m of the base. The thickness of the layer in each diameter must be measured along the axis of the base and at a distance of 1 - 1.5 m from the edges.

8.6. The quality of mixing crushed stone with sand-cement. or sand and slag mixture, as well as with slag and sludge, or the quality of impregnation should be assessed by the depth of impregnation or by the amount of binder used.

The depth of impregnation must be measured with a measuring ruler every 100 m in each diameter along the axis of the base and at a distance of 1 - 1.5 m from the edges.

The amount of sand-cement (sand-slag) mixture in a layer of crushed stone is recommended to be determined at least once per shift by taking a sample weighing 10 kg and then sieving it on a sieve with a hole diameter of 5 mm.

8.7. The technological gap between the preparation of the sand-cement mixture and the end of the compaction of the base, as well as the quality of the compaction, should be controlled in accordance with SNiP III-40-78.

8.8. Compliance with the strength of the arranged base of the design one can be assessed by determining the modulus of elasticity with a deflection meter or other device. The modulus of elasticity must not be less than the calculated (design).

8.9. After completion of compaction and finishing, for every 100 m of the base, the evenness and transverse slopes of the three-meter metal rail and a template with a level.

8.10. After compaction of the base, it is necessary to monitor the timely pouring of film-forming material or water. Lack of care reduces the strength of the base by 50%. Reducing the care time (when watering) up to 21 days. from the moment of compaction of the base, it reduces the strength by 8 - 10%, up to 14 days. - by 20 - 25% and up to 7 days. - by 25 - 30%.

When using cement grades 300 and 500 indicated in table. 8, the quantity should be changed using the coefficients 1.2 and 0.9, respectively.

When using slag and ash binders according to strength grades of 50, 100, 150, their number must be increased by 3; 2; 1.5 times compared with the data in Table. 6.

Slags, ash and sludge with an activity of at least 5 MPa at the age of 80 days can be used as an independent binder.

To increase the strength of the treated part of the layer by 10–30% or reduce the consumption of cement by 10–20%, it is advisable to introduce SDB into the mixture in an amount of 0.5–1% of the mass of cement.

5.8. Sand cement of the highest strength at a given cement content can be obtained with the optimal amount of water in the mixture (approximately 7–10% of the mass of the dry mixture), which is established experimentally when selecting the composition of the mixture.

The amount of water (t) for the preparation of sand cement when laying the foundation by mixing or pressing with a cam roller should be calculated using the formulas:

where l, b - length and width of the section, respectively, m;

h1 - thickness of the upper, treated part of the layer, m;

ρpc - density of sand-cement mixture, t/m3;

Optimal water content in the sand-cement mixture, fractions of a unit;

Qpc - the amount of sand-cement mixture, t.

When arranging the foundation with vibratory rollers or rollers on pneumatic tires, the amount of water in the sand-cement mixture for its good penetration into crushed stone should be 3–5% less or more than the optimal one calculated by formulas (9).

5.9. To obtain the maximum strength of the layer of crushed stone treated with sand cement, before spreading the sand cement, the crushed stone should be moistened to create a mixture of optimal moisture content (approximately 7 - 9% of the mass of the mixture).

The approximate amount of water for irrigation of crushed stone (t) when arranging the base by mixing and pressing with cam rollers should be calculated by the formula

where is the optimal water content in a mixture of crushed stone with sand cement, t,

and when arranging the base by impregnation using vibratory rollers or rollers on pneumatic tires - according to the formula

5.10. The amount of sand-cement mixture Qpc or other binders introduced into the crushed stone can be determined by the voidness of the crushed stone and the specified processing depth (thickness of the treated base layer) approximately according to the formulas

where ρ1 is the density (bulk mass) of crushed stone grains, t/m3;

ρ2 - bulk density (bulk bulk mass) of crushed stone in a compacted state, t/m3;

Кр - coefficient of separation of crushed stone grains, Кр = 1 ÷ 1.15;

vpsh - voidness of crushed stone, fractions of a unit;

Kp - loss factor, Kp = 1.03.

The value of ρ2 can be determined by compacting 10 kg of crushed stone in a steel cylinder with a diameter and height of 234 mm with a load of 10 kg on a vibrating table at a vibration frequency of 3000 rpm, an amplitude of 0.4 mm for 30 s.

5.11. When constructing the foundation by the impregnation-indentation method, taking into account the depth of processing, fractionated crushed stone should be treated with 35 - 40% of the sand-cement mixture, which corresponds to the voidness of the laid material.

Crushed stone with a fraction of 5–40 mm during the construction of the base by mixing, taking into account the depth of processing, it is advisable to treat with a sand-cement mixture in an amount of 20%, which also corresponds to the voidness of the mixture. It is allowed during a feasibility study to process crushed stone 35 - 40 and 50% of the sand-cement mixture.

Before starting work, to clarify the consumption of the sand-cement mixture, it is necessary to determine the voidness of the materials used and use formulas (12).

The approximate consumption of the sand-cement mixture for the device of 100 m2 of base at different depths of crushed stone processing, taking into account the surface layer of sand cement with a thickness of 1.5 cm, is given in Table. 7 of these "Guidelines".

Table 7

5.12. After establishing the laboratory composition of sand cement, the need for materials per unit area of ​​​​the base should be calculated.

The required amount of crushed stone (m3) can be determined by the formulas:

where Kusch - crushed stone compaction coefficient.

5.18. The amount of sand (m3) for the preparation of a sand-cement mixture should be determined by the formulas:

ρnp - bulk density of sand, t/m3.

5.14. The amount of cement Qc (t) for the preparation of sand cement can be determined by the formulas:

5.15. In the course of work, the calculated composition of materials must be amended to take into account the actual moisture content of the materials, according to the formulas:

where Wp, Wsh - moisture content of sand and crushed stone, respectively, fractions of a unit;

The amount of water required to prepare a sand-cement mixture on wet sand, t;

Optimum water content in the sand-cement mixture, t;

The amount of water required to prepare the mixture on wet gravel, i.e.

6. The technology of building foundations by mixing

6.1. During the construction of foundations by mixing, crushed stone is taken out onto the prepared underlying layer, the amount of which should be determined taking into account the design thickness of the foundation and the compaction coefficient.

In winter, crushed stone can be taken to intermediate roadside warehouses in the area of ​​the planned construction.

6.2. Crushed stone is preliminarily distributed by a bulldozer or motor grader, and finally to the design thickness of the base, taking into account the compaction coefficient, by a profiler of the DS-108 type or other distributors in one pass.

When crushed stone is distributed by a profiler, the cutter and cutter blade are raised. The screw blade is set to the design mark with a margin for compaction. The auger is raised 2 - 2.5 cm higher cutting edge dump.

6.3. After distribution, crushed stone, if necessary, before processing with sand cement, should be moistened to obtain the subsequent mixture of crushed stone with sand cement of optimal moisture content (approximate water consumption - up to 10 liters per 1 m2) and rolled for construction transport (two or three passes of the skating rink along one track).

8.4. The sand-cement mixture intended for processing the upper part of the crushed stone layer must be prepared in mixing plants such as SB-78 or DS-50A. To provide qualitative composition mixture, the required accuracy of sand supply is at least ± 5%, cement and water ± 2% of the mass of the supplied material.

8.5. The mixture should be transported by dump trucks or other vehicles with an appropriate feasibility study.

8.6. The sand-cement mixture must be pre-distributed with a motor grader, and finally laid on the surface of the distributed crushed stone with a profiler or other distributors. The consumption of sand cement is determined taking into account the given depth of processing of the crushed stone layer and the ratio between crushed stone and sand cement in the processed part of the layer.

The sand-cement mixture is planned by a profiler in one pass at a working speed of 10 - 15 m / min. When planning, the auger and blade are raised by the thickness of the layer of the distributed mixture, and the cutter and blade of the cutter are raised to the transport position.

8.7. At the end of the distribution, the sand-cement mixture must be mixed with the laid crushed stone to the calculated (required) depth. The maximum mixing depth for the profiler should not exceed 15 cm. at the same time, the blades are raised to the transport position, and the cutter and auger are set to the mark of the processing depth.

If necessary, the resulting mixture is additionally moistened so that the mixture has an optimal moisture content, and mixed again with one or two passes of the profiler.

At the end of mixing, the base is planned in one pass of the profiler. Working bodies are installed in the same way as when planning crushed stone. Working speed 7 - 8 m/min.

6.8. The base immediately after mixing should be compacted in 12 - 16 passes of the roller on pneumatic tires in one track. In this case, the compaction coefficient at a depth of 5 - 20 cm should be at least 0.98. Seal starts from the edges of the base to the middle.

6.9. Compaction must be completed within 3 hours from the moment of preparation of the sand-cement mixture, including the time for transporting the finished sand-cement mixture to the road section under construction, its distribution and compaction.

The technological gap between the preparation and compaction of a sand and slag mixture based on crushed slag or non-crushed slag with the addition of an activator - cement should not exceed 4-5 hours. 6 - 8 o'clock

6.10. Upon completion of the compaction, the base should be finely finished with a profiler and the surface layer should be finally compacted with a heavy smooth-roller roller in one or two passes along one track.

When finishing planning, the cutter and blade of the cutter are raised; the screw blade is set to the design mark; the auger is raised 1 - 2 cm above the cutting edge of the blade.

6.11. Upon completion of the final layout, it is necessary to care for the base by one of the generally accepted methods used in the care of cement concrete, in accordance with SNiP III-40-78. It is allowed to lay the coating on the day of the foundation; in this case, maintenance of the base is excluded.

6.12. Opening traffic on the base, arranged with the use of cement, should be after gaining 70% of the design strength of the base, but not earlier than 7 days after the completion of work.

7. Technology of foundation construction by impregnation-indentation

7.1. The essence of processing a layer of crushed stone with a sand-cement mixture is to fill the voids of the crushed stone layer with a mixture under the action of its own weight and indentation during rolling (mechanical action), in several ways:

vibration using vibrating plates of laying machines;

vibration and pressure - vibration rollers;

deep pressure - cam rollers;

surface pressure - rollers on pneumatic tires.

7.2. Crushed stone before processing with sand cement should be carefully planned with a motor grader and poured with water in the amount of 3 - 10 liters per 1 m2.

If it is necessary to ensure the passage of construction vehicles, crushed stone is rolled with a light roller in two to four passes along one track in accordance with SNiP III-40-78.

7.3. The sand-cement mixture prepared in the installation must be spread over the surface of the crushed stone layer by a profiler or motor grader.

The consumption of sand cement is determined depending on the voidness of the crushed stone and the depth of the layer processing. The time of the technological gap between the preparation of the mixture and the end of the compaction is recommended to be taken in accordance with paragraph 6.9 of these "Guidelines".

7.4. For processing crushed stone by vibration, it is recommended to distribute the sand-cement mixture with DS-97, DS-108, D-345 pavers equipped with vibration compacting bodies. In this case, at the same time, in one pass of the paver, the distribution and penetration of the sand-cement mixture into the crushed stone layer occurs.

7.5. To treat the crushed stone layer with vibration and pressure, a DU-54 vibratory roller should be used, the vibrating roller of which contributes to the penetration of the distributed sand-cement mixture into the voids of the crushed stone layer in three to four passes along one track.

7.6. For processing the crushed stone layer by the method of deep pressure, it is advisable to use a cam roller, which in the process increases the gaps between the individual crushed stones, providing an increase in the depth of penetration of the sand-cement mixture into the crushed stone layer.

7.7. Depending on the required thickness of the treated monolithic base layer, indentation can be carried out in two ways. With the required thickness of the monolithic layer of not more than 13 cm, it is recommended to press the sand-cement mixture or other binder into the crushed stone in successive passes of the cam roller, and with a thickness of more than 13 cm - alternating the passages of the cam and pneumatic or smooth-roller rollers through each pass. The approximate number of passes of the cam roller can be assigned in accordance with Table. 8 of these "Guidelines" and updated based on the results of a test indentation at the beginning of work.

The minimum budget for finishing terraces and landscaping is provided by laying paving slabs on sand with mandatory compaction with a vibrating plate. There is a paving technique for carving - a sand-cement dry mix of PCS, the composition of which can vary over a wide range of 1/4 - 1/8 (cement / sand, respectively).

For an individual developer, the budget for landscaping is extremely important. Therefore, when laying paving slabs, the following questions are relevant:

• proportions of sand / cement in the mixture;
• Is it possible to replace the carving with clean sand.

Adherents of the paving technology for carving make the following arguments:

• when adding cement to a dry mix with your own hands after heavy rainfall, moisture penetrates through the seams into the layer of carving, hydration of the cement stone occurs;
• in the presence of clay under the underlying layer of crushed stone, the concrete crust formed from the carving prevents the penetration of water into this swelling rock.

On the other side:

• dry carving without mixing inside the concrete mixer cannot turn into either mortar or concrete with any amount of water that has penetrated to the cement;
• when facing surfaces with clinker and ceramics, dry DSP is strictly prohibited, since hydration damages materials that are made from similar raw materials, but using different technologies, therefore, some experts do not recommend laying concrete paving slabs on the carving.

• sand volume - obtained by multiplying the area of ​​\u200b\u200bthe track (parking, recreation areas) by the thickness of the standing (usually 3 - 5 cm);
• the amount of cement is 3-5 times less than sand;
• compaction coefficient - when using an areal vibrator (vibrating plate) for tamping, it is 1.18.

Preparing a garnish.

The volume of crushed stone is calculated in a similar way, but the compaction factor for this inert material is 1.3.

Advice! It is very difficult to calculate on your own what consumption of carving or sand is necessary to fill the seams due to the variety of sizes and configurations of tiles. Therefore, experts recommend focusing on an average of 4 - 5 kg / m 2 with standard seams of 3 mm, which are usually obtained using paving slabs with a thickness of 6 cm.

Paving technology

Due to the variety of configurations and sizes of paving slabs, professionals call it FEM (curly paving elements). In principle, the laying technology is identical, both when using carving and sand:

• do-it-yourself tamping of the underlying layer of crushed stone to ensure rigidity and stable geometry of the base;
• installation of a curb stone on mortar or sand concrete to provide a spatial "trough";
• installation of storm water inlets and storm drains;
• after which, it remains to properly lay the tiles inside the curbs.

Step-by-step scheme for laying paving slabs.

Paving can be done on a dry mixture of cement and sand in a ratio of 1/3 - 1/6, respectively, or on clean sand. To save the budget for the improvement of the territory, the thickness of the dry mixture is taken less (3 - 5 cm) than pure sand (5 - 10 cm).

markup

Straight sections to be paving can be marked with your own hands according to the classical technology:

• cast-offs - made from two wooden pegs with horizontal strips nailed to them;
• installation - cast-offs are installed along the edges of the path or parking lot, the cords are pulled with a slope along the length of 2 - 4 degrees for a natural drain.

To reduce the laying time of paving slabs, you should adjust the width of the track depending on the dimensions of the solid tile. It will not be possible to completely avoid cutting, but the labor costs of the master will be significantly reduced.

Advice! On radius and curved sections, marking is carried out with paint or lime mortar on the ground after preliminary planning of the territory.

Soil preparation

With a dry paving method, it is necessary to ensure the maximum possible rigidity of the base and take part of the measures to eliminate swelling. clay soils under him. Soil preparation technology is as follows:

Important! The height of the curbs and storm trays is greater than the thickness of the tiles. Therefore, deeper trenches must be created along the outer perimeter.

In this case, it is necessary to take into account what material will be used when laying the tiles:

• a mixture of cement and sand - 3 - 5 cm;
• clean sand - 5 - 10 cm.

Crushed stone should be compacted hand tool(rammer with handle) or vibrating plate.

Installation of curbs

You can mount the curbs with your own hands, as if on a mortar. The proportions of cement / sand will be 1/3. The curb stone installation technology is as follows:

If paving slabs are laid as a blind area without a concrete base, the removal of roof drains is carried out in several ways:

The seams between the curb and the storm drain are filled with mortar, dry mix or sand.

Sand laying

The technology for applying the mounting layer has several options:

To calculate what consumption of sand or carving is necessary for a particular area, you should take into account the nuances:

• clean sand is moistened before laying from a watering can for better compaction;
• gartsovka keeps within in a dry form without moistening.

In any case, paving is carried out in the direction "away from you", so the mounting layer can be applied on large plots with considering weather conditions. Carving consumption is 7 - 8 kg/m 2 with a layer thickness of 5 cm.

paving tiles

If there are helpers, you can immediately lay both solid tiles and trimmings on curved sections, at the junction of paving slabs with a curb, a storm drain, and storm water inlets. However, productivity increases if you first lay the entire solid tile on the mixture with your own hands, and then cut and install the pieces. The main nuances of paving are:

After laying the last trimming, the entire surface is compacted with a vibrating plate, regardless of whether clean sand or carving was used. achieve High Quality flatness of the front surface with a manual rammer is impossible in principle.

Seam sealing

Unlike clinker or porcelain stoneware, colored decorative grouts for paving slabs are not used, even when laying on mortar (very expensive). Therefore, when choosing a “dry” paving technology, you can fill the seams with your own hands with the same materials on which the tiles are laid - pure sand or its mixture with cement according to the technology:

• the material is distributed by hand on the surface in piles;
• swept away with a broom or a stiff brush, penetrates into the seams, fills them completely.

Seam sealing.

Advice! Instead of sand-cement carving or simple sand, professionals recommend for filling joints quartz sand. It does not contain organics and clay, the particles of the material have a diamond-shaped configuration. Therefore, they wedged under their own weight inside the seam, do not weather and are not washed out by rain, and prevent the germination of grass.

Thus, you can really save on paving slabs if you do the work yourself, use sand without adding a binder.

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