Installation of cement concrete pavements on a sandy base

Cement-concrete pavement of highways on a sandy base is constructed using the in-line method using a set of machines on a rail running device. Technological schemes for organizing work are developed taking into account local conditions characteristic of each construction site and category of road under construction.

Sandy bases are used on roads of category III and on certain sections of roads of category II with reduced traffic intensity. The thickness of bases made of coarse or medium sand depends on the type of soil of the subgrade and the road-climatic zone.

Fine sands can be used if the upper part of the base is strengthened by 10-12 cm with binding materials or crushed stone, gravel, or stone castings. In this case, the thickness of the sand base should be increased by 20%.

The composition of the set of linear machines on a rail running device for the installation of a monolithic cement concrete pavement on a sandy base is as follows: rail form laying crane - 1 pc.; base profiler DS-502A(B) - 1 pc.; concrete distributor DS-503A(B) - 1 piece; concrete finishing machine DS-504A(B) - 1 piece; machine for distributing film-forming materials when caring for coatings - 1 pc.; cutters for joints in hardened concrete DS-112 and DS-115-1 pcs.; joint filler DS-67 - 1 pc.

Rice. 147. Schemes for organizing work on the installation of a single-layer cement concrete pavement for a highway of technical category II: a - concreting a strip 3.75 m wide, 6 - concreting a pavement 7.5 m wide; 1 - dump truck MA3-503; 2 - DZ-18 bulldozer, 3 - roller on pneumatic tires, 4 - truck cranes, 5 - two-axle trailers with MT3-5 tractor, 6 - PUM-130 watering machine, 7 - DS-502B base profiler, 8 - MA3- dump truck 503 with side discharge, 9 - concrete distributor DS-503B, 10 - concrete finishing machine DS-504B, 11 - distributor of film-forming materials, 12 - seam cutter, 13 - seam pourer

When constructing cement concrete pavements for category II highways, two options for organizing work are possible.

The first option (Fig. 147, a) provides for concreting the coating in strips 3.75 m wide. When concreting the first half of the coating for installing rail forms, the sand base is arranged 0.5 m larger than the width of the strip on both sides. For the passage of dump trucks with cement concrete mixture or concrete mixer trucks, the second half of the width of the roadbed is used. After the concrete has hardened, the first strip serves to transport the cement-concrete mixture when constructing the second strip. When concreting the second strip, the rail forms are installed only on one side. All machines of the concrete placing and docking set move, resting on one side on

railforms with double-flange rollers, and on the other hand, onto the constructed strip of cement-concrete pavement with flangeless rollers with a wide rim.

The second option (Fig. 147, b) provides for concreting the coating over the entire width of 7.5 m at once. Rail forms are installed along the edges of the roadway in two lines. The cement-concrete mixture is transported along one of the roadsides, the width of which must be at least 4.5 m.

The first option allows you to avoid widening the shoulders and thereby reduce the volume of excavation work, as well as slightly increase the productivity of road transport. However, when concreting the pavement in two strips, the evenness of the pavement deteriorates and the arrangement of pin connections in the compression joint along the axis of the road becomes more complicated. To move a set of machines along the rails, the pins have to be bent and bent back before concreting the second strip, which destroys the coating at the longitudinal seam.

In Fig. 148 shows a diagram of the installation of longitudinal seam pins when concreting the coating in strips 3.75 m wide. Before concreting the first strip, part of the pin is bent so that it touches the wall of the rail form and is buried in the sandy base. The horizontal part of the pin is firmly secured with two clamping clamps on a concrete lining. After removing the rail forms and before concreting the second strip, the bent part of the pin is bent to a horizontal position.

Rice. 148. Scheme for installing longitudinal seam pins when concreting the coating in strips 3.75 m wide on a sandy base:
1 - concrete lining, 2 - part of the pin, bent after concreting, 3 - rail form, 4 - clamping brackets

The disadvantages of the first option for covering with a linear set of machines include the following: the need to return the set of machines to the starting point 15-20 days after completion of work on one half of the coating; a twice as large backlog of subgrade is required; the volume of work on installing rail forms increases by 1.5 times; for concreting the first lane, twice as many rails are required; for concreting the first strip, twice as many rails are required compared to the second option.

When working according to the second option, the productivity of a set of concrete-laying machines increases significantly, but the work of road transport becomes more complicated and the volume of excavation work increases when the roadside is widened. Nevertheless, the cost of additional work is usually small and when constructing highways of categories II-III, the second option for organizing work is usually used.

To organize work in a complex mechanized team carrying out continuous construction of a cement concrete pavement, the area where work is planned for the upcoming shift is divided into separate segments, moving along with the construction flow.

The flow of construction of a cement concrete pavement using a rail set of concrete laying machines is divided into the following main stages:
1 - removal of sand; 2—installation of rail forms; 3 - laying cement concrete mixture; 4 - arrangement of seams; 5 - removal of rail forms. The estimated length of the main replacement grip for laying the mixture is assigned based on the expected productivity of the leading machine in the flow - the concrete spreader. In turn, the productivity of the concrete spreader depends on the operation of vehicles and the productivity of the cement concrete plant. The length of the remaining grips must correspond to the conditions for performing the shift task, expressed in the length of the finished coating section and equal to the length of the main grip.

Approximate breakdown of a complex team into specialized units:
1 - for installing and removing rail forms; 2- according to the device of the leveling layer; 3 - for laying the mixture; 4 - for cutting joints in hardened concrete; 5 - for filling the grooves of the seams.

In each individual case, the unit composition of the complex team, the composition of each unit, the division of the site into sections and the length of each section are specified depending on the design of the coating, the equipment of the team with machines and mechanisms, the adopted work technology, the productivity of the cement concrete plant and specific construction conditions.

Depending on the project, the organization of work at the first stage works in one or two shifts, but with such an advance in time so as not to delay the flow of work as a whole. The construction of a sand base is allowed to begin only after the construction of the subgrade and its acceptance by the technical inspection.

The sand is transported by dump trucks onto the roadbed and unloaded in stretched heaps within lighthouse pegs installed in advance at a distance of 4.25 m on both sides of the road, every 10-12 m. The unloading locations for each vehicle are indicated by the sand receiving worker. The height of the lighthouse pegs should be greater than the design thickness of the sand base by the amount of sand settlement after compaction.

The sand is evenly distributed along the length and width of the roadbed using a bulldozer with a rotary blade of the DZ-18 type or a D3-31A motor grader. Simultaneously with distribution, the sand is compacted with self-propelled rollers on pneumatic tires DU-29 or DU-31. Before compaction, the sand is moistened with water from a PUM-130 watering machine to a moisture content corresponding to the best compaction mode (11-14%). After completion of the preliminary compaction, the sand base marks should not differ from the design ones by more than 5 cm.

On the second grip, operations for installing rail forms are performed. If the covering is being built in two shifts, then the length of the second grip must be doubled so that the rail forms are installed only during the day shift. Rail forms are allowed to be installed after acceptance of the finished subgrade and base on a section of at least 500 m long from the start of laying the rail forms.

Before installing the railforms, using a theodolite and a template, carefully determine the position of the edges of the future coating and mark them with pegs driven in every 20 m. Then a cord is pulled along these pegs and wooden pads measuring 25X60X8 cm are installed every 4 m to reduce subsidence of the ends of the railforms.

It is prohibited to install rail forms with faulty locking connections and deformed links. Links with rail deformation of more than 2 mm in the vertical plane and more than 5 mm in the horizontal plane should be discarded.

The railform links, brought to the installation site by a truck crane with an extended boom KS-1562 with a lifting capacity of 4 tons, are installed on supports, after which the butt locks are connected. From each crane stop, first place several links of one and then another string of rail forms and use a template to check the quality of their installation in plan - the clear distance between the rail forms should be equal to the width of the coating. After this, the railforms are rolled along the entire length of the grip with a base profiler and the elevation marks of each railform joint are checked using a level. The difference in height of adjacent railform links should not exceed 2 mm. Detected subsidence is eliminated by tamping the base with electric sleeper rammers EShP-3 and manual darning. Correctly installed rail forms are secured with a full set of metal piles driven into the base along the entire length.

At the third stage, all the main operations for constructing a cement concrete pavement are performed: final profiling, moistening and compacting the sand base; laying out waterproof paper or plastic film; installation of edge reinforcement and expansion joint gaskets; distribution of cement concrete mixture, compaction and finishing of the coating surface; care of the laid mixture.

The sandy base is finally profiled and compacted with a base profiler DS-502(B). Before starting work, the profiling blade and compacting vibrating beam of the machine must be installed in the working position using electromechanical mechanisms for raising and lowering the working parts. The cutting edge of the dump must exceed the design elevation of the top of the sand base by the amount of expected sand settlement after compaction. When working with a base profiler, it is necessary to ensure that there is always a roll of sand 7-10 cm high in front of the dump. Otherwise, the density of the sand layer across the width will be uneven. For the same purpose, it is necessary to create an angle of attack of the vibrator by raising its front edge by 10-15 mm relative to the rear edge. With a correctly set angle of attack, a uniform roll of sand 5-7 cm high is formed in front of the vibrating beam.

The quality of compaction of the sand base is determined using the Kovalev device using the standard compaction method. The density of the sand must be at least 0.98 standard. To achieve such a density, the sand must be moistened to optimal humidity with a PUM-130 watering machine before the profiler passes. The deviation of the thickness of the sand base layer from the design value should not exceed ±5%, and the deviation of the transverse slope should not exceed ±0.5% of the design value.

Before laying the mixture on a sandy base, rolls of bitumen paper or plastic film are rolled out along the axis of the road. To prevent the mixture from sticking, the inner surface of the rail molds is lubricated with used oil or lime-clay solution. Then the edge reinforcement rods are placed on supports made of reinforcing steel with a diameter of 10-12 mm, which are installed every 1.2 m. The edge reinforcement rods are not brought to the expansion seam by 10 cm, but are passed through the compression seams without breaking. In places where expansion joints are installed, pre-assembled pin connections are placed along the cord.

The reception of cement concrete mixture from dump trucks and its distribution along the width of the laid strip in a layer of a given thickness is carried out with a concrete spreader DS-503A(B). Before starting work, the machine's hopper is installed using a screw mechanism so that the lower edge of the distribution frame is 10-15% above the rails of the coating thickness. This allowance is necessary to take into account the settlement of the concrete mixture during its compaction and is 2-3 cm for a mixture with a cone settlement of 1-2 cm or a hardness according to a standard viscometer of 25-15 s. When using mixtures with a different hardness, the amount of allowance for compaction must be carefully selected experimentally, adjusting the installation of the working parts of the concrete finishing machine and concrete spreader, since a lack of mixture leads to insufficient compaction and a decrease in the strength of the coating, and an excess leads to the formation of unevenness and losses of the mixture.

The distribution of the mixture should be carried out in such a way that during the transverse movement of the distribution hopper, the discharge hole in the longitudinal direction overlaps the already distributed layer of the mixture by approximately one-tenth of its length. The remainder of the mixture in the hopper after its transverse movement is placed in the coating while moving the entire machine forward.

When working on the DS-503A(B) concrete spreader, you must adhere to the following basic rules: – distribute the mixture with transverse movements of the hopper across the entire width of the base without skipping or multiple passes of the hopper in one place; – to maintain the design position of the edge reinforcement and gaskets in the expansion joints, cover them with the mixture during the first passes of the machine; – adjust the stops of the limit switches for the transverse movement of the bunker so that the mixture does not fall outside the rails during operation of the machine.

After distributing the mixture in the places where the compression joints are installed, using a template, place the pins on the surface and immerse them in a horizontal position to the designed depth using a vibratory driver.

Following the concrete spreader with a gap of no more than 8-Yum, the concrete finishing machine DS-504A(B) moves along the rails.

Before starting to distribute the mixture and compact it, the working parts of the concrete finishing machine are adjusted. The lower edges of the leveling blades of the concrete finishing machine DS-504A(B) are set using two adjusting screws at the surface level of the distributed mixture layer, taking into account the compaction allowance strictly parallel to the surface of the coating.

The rear edge of the compacting beam of the concrete finishing machine must be installed at the level of the rail heads or when laying the mixture into the coating with a cone draft of 0.5-1.5 cm - 3-5 mm below the rail heads.

The screed beam of the concrete finishing machine must also be positioned at a certain angle of attack. To do this, the beam is lowered to its lowest position until the suspension rope is completely weakened, then using eccentric clips on the suspension carriages moving along the rails, the amount of lifting of the leading edge of the lower plane of the leveling beam is adjusted.

During the work process, the formation of a uniform roller of cement-concrete mixture with a height of 8-10 cm in front of the compacting vibrator beam and a solution roller with a height of 2-4 ohms in front of the smoothing vibrator beam indicates the correct adjustment of the working parts of the concrete finishing machine. During normal operation, the concrete finishing machine compacts a layer of mixture up to 24 cm thick in one pass.

While the concrete finishing machine is operating, the workers servicing it must clear the rails from the influx of mixture, and the assistant driver must monitor the action of the working parts. If too large a bead of mixture forms in front of the screed bar and it increases as the machine moves, it is necessary to lower the compaction bar slightly. In case of excess mixture formation in front of the compacting vibrator, it is also necessary to lower the blade shaft of the DS-504A(B) machine and reduce the compaction allowance on the concrete spreader.

The evenness of the cement concrete pavement can be achieved with non-stop operation of the concrete finishing machine - with an uninterrupted supply of the mixture to the laying site and with a sufficient backlog of preparatory work. When the vehicle is forced to stop, vibrators should be turned off. If, after the first pass of the concrete finishing machine, a small (up to 5% of the area) amount of unevenness and cavities remains on the surface of the coating, they are removed manually. If there are more defects, a second pass of the machine is necessary, for which the machine is stopped, the vibrators are turned off, and the vibrating bars are raised by 5-10 cm and only then are they reversed.

If, after finishing the coating surface, cement laitance appears, it must be removed with trowels with handles 3-3.5 m long. The trowels should be moved from the axis of the coating to the side with smooth movements, without pressure, with sequential overlap of the treated strips, without disturbing the transverse slope and evenness of the coating.

When creating artificial roughness of a cement concrete coating to increase its coefficient of adhesion to the wheels of a car, immediately after the passage of the concrete finishing machine, transverse strokes 2-3 mm deep are applied to the entire coating area with special brushes.

The film-forming material is applied to the surface of the freshly laid mixture using distributors. The first layer is applied after finishing the concrete coating and removing cement laitance from it, when the surface of the coating becomes dull and damp. The second layer is applied 30-60 minutes after the first. The total thickness of the moisture-retaining film should be 0.4-0.7 mm.

The quality of application of film-forming materials is checked once per shift on a coating area measuring 20X20 cm. The surface of the area is washed with water, wiped with a rag and a 10% solution of hydrochloric acid or a 1% solution of phenolphthalein is poured. Foaming of hydrochloric acid or reddening of phenolphthalein is allowed at no more than two points per 100 cm2 of surface. Otherwise, an additional layer of film-forming material must be applied to the coating surface.

To avoid overheating of the surface by the sun's rays, after applying the second layer of bitumen emulsion, the coating is covered with sand 2-4 cm thick or covered with a layer of lime milk, which is located in a special container on the distributor of film-forming materials.

If there are no film-forming materials or equipment for their distribution, then the surface of the coating must be covered with sand with a layer thickness of at least 5 cm. Immediately after finishing the coating, its surface is first covered with damp burlap or waterproof paper, which is removed before filling the coating with sand. This protects the coating surface from the formation of shrinkage cracks. The sand layer is moistened for 20 days using a PUM-130 watering machine.

At the final stage of concrete care, after completing the period of keeping it in optimal temperature and humidity conditions, before starting temporary or permanent operation of the cement concrete coating, it is necessary to clean its surface from sand with brushes and rinse it.

Expansion joints are cut in hardened concrete using DS-112 and DS-115 cutters on average 10-20 hours after it is laid. At lower air temperatures, this interval increases. The places for cutting transverse seams are indicated by marks, which are applied on both sides of the rail forms at the beginning of concrete hardening in order to avoid their swimming.

First of all, the control seams are cut, dividing the concrete coating between the expansion seams in half, then the transverse compression and expansion seams are cut, and lastly, the longitudinal seam. The longitudinal seam must be cut exactly in the middle of the covering, and the transverse seams - perpendicular to the axis of the covering,

The work design can provide for the combination in one flow of two methods of cutting expansion joints - transverse joints in hardened concrete and longitudinal joints in freshly laid concrete. This reduces the number of joints cut in hardened concrete by almost half.

Correct and timely cutting of joints in hardened concrete requires clear organization and high labor discipline. Cutters must always be in working order, provided with a sufficient number of cutting discs, water to cool them during the cutting process and other means of operation and repair. The marking of seams must be done accurately and in a timely manner, the places of future seams must be clearly marked and fixed on the ground.

Expansion joints are filled with insulating materials within a month after cutting and before the opening of traffic on the constructed section of the coating. Work on filling joints can only be carried out in dry, preferably cool, weather.

The operator of the DS-67 joint filler cleans them with a metal hook while simultaneously blowing them with compressed air from the compressor. The adhesion of the mastic to the seam walls and, thereby, the quality and durability of the seam structure as a whole depends on this operation.

The walls of the joint are primed immediately after cleaning it with liquefied or liquid bitumen. When filling joints with thiokol sealant, instead of using a primer, the joint walls are cleaned with acetone immediately before filling.

Before filling the seam with bitumen-polymer mastic BPM-1 or thiokol sealant, a rope is placed in the seam, and strips of coating 5-10 cm wide adjacent to the cleaned seam are lightly sprinkled with mineral powder. Then the rope is removed and the seam is filled using fillers with mastic heated to a temperature of 120'-130 ° C, or with cold thiokol sealant. The formation of the mastic in the seam lasts 2-4 weeks, and the thiokol sealant turns into a rubber-like elastic mass after 7-15 days.

When using non-prene gaskets of a special shaped profile as joint fillers, it is necessary to strictly maintain the parallelism and evenness of the edges of the seam; the deviation from the designed seam width should not exceed 1-1.5 mm. The inner surface of the cleaned seam is lubricated with diluted thiokol sealant, which makes the gasket adhere well to the concrete, and the gasket is inserted into the groove using a press tool. The use of neoprene gaskets makes it possible to completely ensure the waterproofness of the seam, simplify the process of sealing the seams and almost double the shift productivity compared to filling the seams with mastic or thiokol sealant.

Rail forms are removed no earlier than 18 hours after the end of laying the cement concrete mixture at an air temperature above 15 ° C and after 24 hours at a lower temperature. Before removing the rail forms, you should use claw crowbars to remove all the pins attaching the rail forms to the base, and also knock out all the wedges from the locking joints. Each link is then carefully separated from the concrete, using only a crowbar and not driving the metal wedges between the slab and the rail.

The railforms must be cleared of any remaining concrete and sand and numbered so that the order of their arrangement remains constant when rearranged. The cleaned rail forms are loaded using a truck crane onto a car or tractor trolley and transported to a new installation site. Immediately after removing the rails, the side faces of the coating are covered in two layers with film-forming material and sprinkled with sand.

When constructing a cement concrete pavement, it is necessary to constantly monitor the quality of work at individual stages. The preparation of concreting sites for receiving the mixture is controlled before the start of each shift and continues continuously throughout the shift: the quality of installation of reinforcement and gaskets for seams is checked by external inspection and measurements; The installation of rail forms is checked by leveling and running a base profiler along them.

The quality of the coating is determined by external inspection and control measurements of the gap under a three-meter strip laid on a freshly laid coating. During all shifts, a sample is taken from each batch of cement concrete mixture with a total volume of 250 m3 for the manufacture of six beams and six cubes. Samples are stored under conditions similar to coating care conditions. Half of the samples are tested on the seventh day after their manufacture, and the other half on the 28th day. Cement concrete is considered to meet technical requirements if, after curing for 28 days, the strength of 90% of the samples in bending is not lower than 95% and in compression - not lower than 90% of the design grade.

To check the strength of concrete in the coating, along with drilling and subsequent testing of cores, non-destructive testing methods are used. The quality of concrete in terms of strength in the road surface can be assessed using the ultrasonic electronic-acoustic device “Beton-ZM-Transistor”. The operation of the device is based on the relationship between the strength of concrete and the speed of propagation of ultrasound in it.

The cement concrete coating is approved by a commission of representatives of the customer, contractor and higher organizations. At the same time, the external ocmqtp of the coating is carried out, control measurements of the work performed are carried out, their compliance with the technical design is checked, the longitudinal and transverse profiles, evenness and thickness of the coating are measured. Permissible deviations from the design values: transverse slope - 2.5%, when the actual slope is steeper than the design one, and 5% when it is lower than the design one; coating thickness - no more than 5% downwards; coating width ±5 cm; the gap between a three-meter lath and the surface of the coating should not exceed 5 mm, and the edges of adjacent slabs should rise above each other by more than 3 mm.

TO category: - Machines for the construction of cement concrete road surfaces

The biggest problem and at the same time a headache for constructing a foundation is the geological structure of the soil on the construction site. Preparing the foundation for a foundation on weak peat soils can consume half the budget allocated for the arrangement of the entire foundation system. A competent analysis of the geology and bearing capacity of the soil makes it possible to avoid serious problems, but even with positive results, experienced builders carefully prepare the base for the foundation, remove weak soil and prepare the cushion, without skimping on materials and volume of work. Moreover, the work done and the results obtained are necessarily recorded in the act of acceptance of the base for the foundations.

Proper preparation of the base for the foundation

Any professional builder knows that the first half meter of soil has the lowest load-bearing capacity and is often not taken into account when designing foundations. To obtain the most stable and reliable position of the building box, it is necessary to get to the most stable and dense layers of rock, the condition of which and bearing capacity do not depend on air temperature and amount of precipitation. Therefore, preparing the base for the arrangement of the foundation requires a significant and materially costly amount of work:

• Planning the site of the future foundation, removing surface soil, and in the case of thick deposits of peat, loam, and water-logged clays, during preparation it is necessary to remove the surface layer by a meter or more;
• Arrangement of drainage systems with planning of future drainage slopes and storm sewers;
• Compacting the soil with vibratory rollers, filling cushions of crushed stone and sand;
• If necessary, laying concrete preparation under the base of the foundation and waterproofing.

For your information! The most common reason for violating the bearing capacity of the foundation is the use of fill building materials that do not meet the requirements of the project.

The completed acceptance document, protocol or act confirms the scope of work completed, the thickness of the laid crushed stone and sand, the presence of a geotextile base, but does not reflect the quality of the sand, which plays a major role in ensuring the bearing capacity of the foundation base.

To ensure the necessary strength of the surface layer of the rock, the soil is prepared, compacted and filled with crushed stone of different fractions, first coarse, then screenings and, finally, sand. A layer of crushed stone sealed into the ground dramatically increases the stability of the foundation, but due to its high rigidity and hardness, it is not able to evenly transfer the load from the weight of the building to the base of the foundation and to the surface of the earthen layer.

Construction of the base for the foundation

If you try to install a concrete foundation directly on crushed stone, without adding sand, part of the foundation strip or slab will be overloaded, and part will remain unloaded. In such a situation, the concrete casting of the foundation will quickly become unstable and cracks and deformations will form.

Functions of sand filling

Sand plays the role of glue and elastic cushion, which allows you to compensate and distribute all forces, including when the soil swells or the foundation settles.

The sand material used in preparing and filling the base must meet certain requirements and criteria:

• Gravel sand, very coarse and clean, is considered the best; fills made from such material have the lowest specific gravity, but at the same time easily allow water to pass through;
• Minimum amount of inclusions of clay, earth, lime and salt contaminants;
• Sand should not contain any forms of organic matter, silt, peat, plant remains - everything that natural bodies of water are rich in. When such material is used in preparing the base, after a certain period of time the sand cushion turns into a dense waterproof layer of mud, saturated with organic decomposition products.

Advice! The quality of sand can be easily checked using available tools. For example, if you pour 5-6 liters of water into a hole dug in the ground, covered with sand, then if the quality is good, the water will go away in a few minutes; in dirty sand, a puddle will remain on the surface.

Classic foundation design for foundations made of crushed stone material

In the classic version, the technology for preparing a cushion under a concrete slab or tape uses crushed stone as a material that provides drainage and a rigid base. Therefore, the base is covered with at least one layer of crushed stone. The use of crushed stone material requires considerable costs associated with the purchase of building materials, delivery and planning work. Despite the high cost and scarcity of high-quality crushed stone, it is impossible to refuse its use in preparing the base for the foundation.

In cases where, in the process of surface leveling, large volumes of soil are removed and moved by bulldozers or excavators, crushed stone embankments are used to level the slope of the base. It is not always possible to perfectly level a gravel bed, so builders often use intermediate concreting or concrete preparation. Essentially, this is a thin layer of concrete laid on a sand-crushed stone base of the pillow and perfectly leveled with the horizon. After such preparation, it is enough to simply lay the waterproofing and insulation layer.

If the soil has high load-bearing characteristics, the preparation technology can be significantly simplified. In this case, the construction of the base for sand foundations is carried out in a simplified manner. A polyethylene film is laid on the leveled and compacted layer of sand, a layer of fine gravel or screenings is poured, and after compaction, a layer of waterproofing and insulation is laid. At the next stage, the reinforcement is laid and the concrete solution is poured.

Conclusion

It is generally accepted that the widespread use of polyethylene films as lining material under crushed stone layers to prepare the base is dictated by the fear of “concrete milk” leaving through crushed stone and sand into the soil layer. In reality, such incidents occur when the quality of the concrete is poor or its delamination is severe. Liquid saturated with cement leaves the base of the foundation in an amount of no more than 2-3% of the total volume. The film, like waterproofing, is necessary to prevent sand saturation and screening out with silty deposits and salts, which can over time reduce the efficiency of drainage to almost zero.

In preparation for construction of the road base remove the top layer of soil with a bulldozer, and then strengthen the base with a soil vibratory roller. The base of the roadway can be sand, crushed stone, crushed stone-sand, cement concrete, and can also be made of black crushed stone and mixtures reinforced with binders. This or that type of foundation has its advantages and disadvantages in terms of operational characteristics and capital costs. The underlying layer of sand serves to reduce the load on the earthen base from vehicle traffic, accumulates moisture, and performs a drainage function on clay soils. Compaction of the sandy base is carried out with rollers weighing 5-6 tons, vibratory compactors or pneumatic rollers. When constructing a sandy base, in order to add moisture to the sand, it is watered.

Device crushed stone foundations has a number of advantages compared to bases made of other materials. The crushed stone base can be laid in any weather, without blocking traffic. Also, crushed stone can be stored for a long time on the road or in the highway area. The quality of the crushed stone base determines the strength of the road pavement, which is influenced by the rigidity of the crushed stone base layer and the compressive stress during compaction that occurs under the influence of automobile traffic. The crushed stone base is compacted using heavy pneumatic and vibratory rollers. The rigidity of the base is increased by using easily compacted crushed stone. It is very important to choose crushed stone of a certain shape, since the shape of the grains affects the bearing capacity of the crushed stone layer. Compaction of the crushed stone base occurs due to the filling of pores with proppant materials, due to the spatial reorientation of grains, and also due to the fine-grained fractions of the main placer.

Device crushed stone-sand base optimal for the construction of road foundations. Laying a crushed stone-sand base eliminates the possibility of “reflected” cracks appearing on the road surface. The possibility of long-term preservation in the open air under any weather conditions characterizes the crushed stone-sand mixture as a high-tech raw material for laying the foundation. The base of the roadway made of crushed stone-sand, gravel-sand, crushed stone-gravel-sand, ash and slag mixtures can be strengthened with binding materials. Binders fill voids, increase adhesion between particles of mineral material, while increasing the density and water resistance of the mixture. When compacting mixtures with binders, choose a binder that could bind the loose material into a monolith and, at the same time, lay as a thin film over the surface of the material.

When constructing bases from black crushed stone, the crushed stone is prepared in mixers with forced mixing. Depending on the laying temperature and the type of binder used, black crushed stone is divided into hot, warm and cold. Accordingly, the temperature for laying a mixture of black crushed stone varies from 150 ° C to sub-zero temperatures. Binders can be used from viscous and liquid bitumen and bitumen emulsions. Compaction of the base of black crushed stone occurs first with medium rollers and then with heavy rollers (combined vibratory roller or soil roller for rent).

Road bases made of cold black crushed stone are usually compacted with self-propelled pneumatic rollers. If you want to learn in detail about the design and compaction of cement concrete foundations and other types of foundations, contact our specialists.

In order for a building to stand unshakably and reliably, it will need to be provided with good support. The foundation, which is the foundation of the building, will serve as such a support. This structure is the part of the house that is responsible for transferring loads to the ground from elements that are located above.

The basis of any foundation is a high-quality sand cushion, which must be at least 10 cm thick and well compacted.

To install a sand cushion and a strip or other foundation you will need:

• fittings;
• gravelly sand of coarse fraction or clean river sand of medium fraction;
• heavy tamping;
• water;
• excavator;
• cement;
• lime or clay;
• gravel;
• crushed stone;
• sand;
• roofing felt;
• geotextiles;
• bitumen;
• building level;
• roulette.

Return to contents

Reasons why you should install a sand cushion under the foundation of a country house

1. It is possible to replace problematic soil under sand with sand. For example, there may be clay underneath. Heaving soil does not perform well during thawing and freezing.
2. Even a small layer of sand makes it possible to level the bottom of a trench or pit, which is quite important for the subsequent stages of constructing any.
3. The sand cushion will resist compression. It is an intermediate link between the base soil and the foundation. Despite the fact that the soil becomes stronger with increasing depth (due to natural compaction under the influence of the mass of the overlying layers), replacing its surface layers with sand will help reduce the settlement of a private house. The cushion will break the capillary bridge and additionally protect the reinforced concrete from moisture.

Return to contents

What kind of sand should be used to create a base pad?

A sand foundation is the simplest and relatively cheapest type of foundation. There are several types of such structures, each of which has its own disadvantages and advantages. A sand base is a gravel-sand or sand bedding for the underground part of a house that does not have a basement. They are most often arranged for one-story single-apartment houses. These foundations are not suitable for buildings that are heavy. The cost of this design is much lower than that of any other type of foundation, which is why it is often used in the construction of small houses in the private sector.

First of all, to lay foundations on a sand bed, you need to dig a trench. Its depth should be such that the bottom is located on a dense base, which you will definitely need to reach. The resulting swarm must first be covered with coarse sand. This should be done in small layers 15 cm thick. Each layer will need to be well watered and thoroughly compacted using a heavy tamper.

The width of the sand backfill is most often made so that it exceeds the width of the wall by 10 cm. If necessary, this parameter can be increased. The foundation ends on a sand cushion 15 cm below the earth's surface. From this moment the construction of the basement begins. In order to increase the bearing capacity of the foundation, it should be poured with cement-lime, cement-clay or cement mortar.

Return to contents

Do-it-yourself foundation on a sand cushion using crushed stone

The construction of this type of sand foundation begins in the same way: the sand is laid in layers and compacted. Crushed stone is placed on top of the compacted sand. It is poured in a layer of 5-10 cm, which is first compacted and then poured with cement-lime or cement-clay mortar. Next, the next layer is poured and the procedure is repeated. Approximately 4 rows of bricks are laid above ground level. Waterproofing from several layers of roofing material is installed on top, after which the base is placed.

A sand and gravel foundation can be arranged in a similar way. In this case, you will need to fill up the sand not in its pure form, but together with crushed gravel. This mixture is prepared in a 1 to 1 ratio. Most often, small stones made from durable gravel, broken bricks, and cobblestones are used. When backfilling, you should carefully ensure that the voids between pieces of broken brick or individual elements of gravel are completely filled with sand.

Return to contents

Strip foundation on a sand bed

Recently, the construction of strip foundations with a sand cushion has begun. The sand cushion plays a significant role in the design of the strip base: it will drain water from under the base and also reduce the effects of frost heaving forces.

The sand cushion will evenly transfer the load from the foundation to the underlying soil, increase the design resistance of the foundation and serve to level it. It is imperative to lay geotextiles before backfilling the sand-gravel mixture or sand. Geotextiles can protect the cushion material from siltation by heaving soil at high groundwater levels.

If there are basement premises, it is necessary to provide a connection between the concrete cushion and the body of the foundation strip using a profiled tongue-and-groove connection. Another option is to perform vertical reinforcement.

The upper surface of the strip foundation on a sand cushion will need to be waterproofed. When installing a prefabricated strip foundation on excessively heaving and highly heaving soils on top of foundation blocks, it will be necessary to reinforce the structure with a reinforced concrete or reinforced belt.

If you plan to build a frame wall, anchors must be cast into the body of the base strip during concreting. This must be done in order to frame the walls. The presence of threaded anchors to secure the vertical reinforcement that connects the foundation to the interfloor reinforced belt may be necessary for some technologies for constructing walls made of cellular concrete. Bent reinforcement outlets from the base body will be needed in order to connect the foundation with monolithic walls and monolithic floors.

On top of the sand cushion you will need to lay a layer of waterproofing (bitumen-polymer roll material or thick plastic film). After the reinforcement has been completed, it is necessary to cast it in the formwork.

It is worth paying attention to the thickness of the protective layer of the concrete tape on the side of the sand cushion. The requirements of American and domestic standards are almost identical: the thickness of the protective layer of concrete on the side of the sand cushion must be 70 mm. If you plan to use concrete preparation, the thickness of the protective layer will be reduced to 35-40 mm.

font size

STATE ELEMENTAL ESTIMATED STANDARDS FOR CONSTRUCTION WORKS - COLLECTION 31 - AERODROMS - GESN-2001-31 (approved by the State Construction Committee of the Russian Federation... Relevant in 2018

Table GESN 31-01-039 Construction of a sand base

Scope of work:

01. Leveling sand with a bulldozer (standard 1).

02. Leveling and leveling sand with a motor grader (standard 2).

03. Installation and removal of tracer strings (standard 1).

04. Construction of a sand layer using a high-performance kit profiler (standard 1).

05. Rolling the sand layer with rollers on pneumatic wheels with watering.

Meter: 100 m3 base

Sand base construction:

31-01-039-1 high-performance kit profiler

31-01-039-2 motor grader

Resource code	Cost element name	Unit measured	31-01-039-1	31-01-039-2
1	Labor costs of construction workers	person-hour	7,18	8,21
1.1	Average job level		2	2,3
	Driver labor costs	person-hour	4,4	2,51
3	MACHINES AND MECHANISMS
070149	Bulldozers when working on other types of construction (except water) 79 (108) kW (hp)	mach.-h	1,04	-
120910	Self-propelled road rollers with pneumatic wheels 16 t	mach.-h	1,37	1,04
121309	Base profilers with sliding forms	mach.-h	0,67	-
121601	Watering machines 6000 l	mach.-h	0,65	0,66
120202	Medium motor graders 99 (135) kW (hp)	mach.-h	-	0,81
4	MATERIALS
101-1682	Polyamide twisted cord, diameter 2 mm	T	0,0001	-
408-9040	Natural sand for construction work	m3	110	110
411-0001	Water	m3	5	5