Crushed stone - common building material mined by crushing rocks or artificial materials. One of the parameters that determines operational properties material, – compaction coefficient. This is a dimensionless quantity characterizing the degree of reduction in the external volume of a bulk substance during transportation or compaction special tools. Knowing the coefficient will allow you to purchase the required amount of material and avoid destruction of the bulk layer under load due to insufficient compaction.
It is difficult to find any standard value for this case, since it is influenced by many factors:
- the height from which the material was poured;
- length of the route and quality of the road;
- transport feature;
- fraction and flakiness of crushed stone (flaky grains are stacked with a large number voids, compared to cuboid ones).
When delivering large quantities, the difference between the volumes loaded and delivered is quite significant. The compaction factor is specified in the supply contract. According to GOST 8267, this value should not exceed 1.1.
Compaction coefficient of crushed stone at a construction site: value and method of determining it
– bulk material with grains different shapes. When using material for laying the preparatory layer, it is necessary to reduce the number of voids, which reduce the degree of load resistance. Therefore, compaction is a mandatory procedure when constructing road bases and foundations. The compaction coefficient of crushed stone for road construction is regulated by SNiP 3.06.03-85:
- for grades with a strength of 800 or more fractions of 40-70 mm and 70-120 mm, the safety factor for compaction is 1.25-1.3;
- for brands with a strength of 300-600 – 1.3-1.5.
The level of compaction of crushed stone is determined using a density meter - a tool with a tip in the shape of a truncated or regular cone. The choice of tool is determined by the characteristics of the material being tested. Verification process:
- the density meter is brought vertically to the surface;
- immerse with pressure into the compacted mixture;
- the amount of compaction is determined by the deviation of the arrow;
- 3-5 measurements are taken at each point;
- the distance between the measuring points is approximately 15 cm;
- The results obtained are summed up and the average is found.
Attention! If the compaction was carried out in violation of the technology - only on the top layer, and not layer by layer - then the coefficient will not correspond to the actual degree of compaction.
How to compact crushed stone with your own hands?
Manual tamping is relevant when performing small volumes of work, since it requires significant physical effort. Options for the simplest devices:
- The beam is 100x100 mm and the length depends on the height of the person. The best option– length of the beam to the chest. The cross-section size can be increased to 150x150 mm. Handles made of metal rods or wooden blocks are mounted at the top. The lower edge of the beam is lined with a galvanized sheet. The principle of operation is very simple: the beam is raised to the maximum possible height and forcefully lowered onto the rammed surface. The compaction area is not too large, but this compaction option is the most economical and simple.
- More effective option- metal head attached to wooden beam, acting as a handle.
- The most durable design is made entirely of metal. Working with such a tool is effective, but is complicated by vibrations that metal, unlike wood, cannot absorb.
For tamping bulk material on a spacious area where there are no buildings or plantings, a car is used. The brought material is evenly leveled over the surface with a rake or shovel, and then driven around the territory in different directions. The resulting ruts are filled with crushed stone.
Compacting crushed stone with a vibrating plate
Using this equipment, it is possible to perform fairly large volumes of work in places where the use of rollers is difficult or impossible. The plates are distinguished by weight, vibration strength, paw area, and type of engine. By weight, the units are divided into:
- Light - approximately 75 kg. Used for thin sand layers when arranging flower beds and paths.
- Universal – up to 200 kg. Used for compacting soil and asphalt.
- Medium-heavy - up to 400 kg. In demand for working with crushed stone.
Equipment control type: manual or remote. In the first case, the operating speed is low.
By engine type there are:
- Electric stoves. Used in places where there is access to an electrical power source. These are usually small units capable of working on thin layers.
- Gasoline models. Compared to the previous type of equipment, they have greater weight, engine power, performance and cost. A significant advantage is the absence of the need for a power supply.
- Diesel unit. Reliable, high-performance, with a long resource.
Another difference is the number of directions in which the model moves:
- single-pass equipment can only move forward, its plus is a longer working period compared to reverse options;
- The reversible vibrating plate can move both forward and backward.
An effective way to compact crushed stone is declinging
If it is necessary to obtain the most dense base possible, the declinging method is used.
Definition! Clustering is the laying of a base using crushed stone of various fractions. In this case, the voids between large-sized grains are filled with fine-grained crushed stone.
Decluttering stages:
- laying grains of fractions 50-70 or 80-120 mm;
- compaction with a vibrating plate or roller;
- backfilling with fine crushed stone;
- compaction;
- adding material with even finer grains;
- seal
To obtain the most dense base, three splittings are carried out. To reduce friction, the grains are spilled with water. Splintering can be used in road construction, production of reinforced concrete products and structures.
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Empirically, summarizing many years of experience in the construction of crushed stone layers, the optimal parameters of rollers (weight, type) that ensure maximum compaction of the layer, as well as their operating modes (static, vibration, high-speed) have been established, depending on the type, strength and grain composition of crushed stone, as well as layer thickness. It has been established that a sign of complete compaction of the layer is the absence of a trace from the passage of a heavy smooth drum roller in static mode. Crushed stone thrown under the drum is crushed. The above control method is today the only one standardized by the relevant technical documents. It should be noted that this method is of a qualitative nature, so over the years attempts have been made to find quantitative method assessing the degree of compaction of the layer.
Previously, the so-called “hole method” was proposed to control the density of the constructed crushed stone layer. The essence of the method is to measure the mass and volume of crushed stone removed from a hole in the constructed layer. From the measured values, the density is calculated, which can be compared with the density of the first constructed layer section of the same material using the same rollers. The lack of a standard density, as well as the labor intensity of the method, did not allow it to be used in construction practice.
There are known attempts to equip skating rinks various sensors, which were supposed to record the degree of compaction of the rolled layer. Until now practical use Such methods were not found in the construction of crushed stone layers.
There are proposals for assessing the quality of compaction of the crushed stone layer by determining its bearing capacity. It should be said that the methods for determining the load-bearing capacity are standardized by BSN 46-83 and described in this instruction and involve two methods: measuring the deflection of the constructed structure under the wheel truck deflection meter or measuring the deflection of a constructed structure loaded through a stamp of standard diameter from the pressure of a truck. Based on the measured deflection, the overall modulus of elasticity of the constructed structure (crushed stone + sand + earth bed) is calculated. If you ask or also measure the deflection of the underlying sand layer and roadbed, then you can use VSN 46-83 to calculate the actual modulus of elasticity of the crushed stone layer and compare it with the calculated (normative) one. As can be seen from the above, these proposals for quality control of compaction are labor-intensive and in their pure form do not show the density of the controlled crushed stone layer.
IN recent years developed and are increasingly found wide application dynamic deflection meters that record the deflection of a constructed structure loaded by the impact of a falling weight on a stamp mounted on the structure being tested. This method is more efficient compared to the above-described methods for determining deflection according to VSN 46-83. However, the device is very expensive, and when calculating the elastic modulus of the tested layer, it has the same disadvantages as those described above. Therefore, its most appropriate area of application is assessing the quality of the entire constructed structure (crushed stone-sand-soil). Analysis of the known proposed methods for assessing the quality of the crushed stone layer made it possible to develop a reliable, simple, lightweight and cheap device for quantitative control of the degree of compaction of the crushed stone layer under construction. The above mentioned it distinctive features allow us to say about the possibility of its use in all field road construction laboratories. Below are its parameters and test results.
The device was developed by the Federal State Unitary Enterprise Soyuzdor Research Institute in collaboration with JSC Dorstroypribor and is intended to control the density (compaction quality) of crushed stone layers of road pavement.
The operation of the device is based on a loaded and flat stamp installed on the surface of the test layer of material, with impacts from a freely falling load.
The value of the rebound of the falling load from the surface of the compacted layer is taken as a controlled parameter characterizing the degree of compaction of the material layer.
When working with the device, it is necessary to install the stamp 8 of the device on a crushed stone base. Having moved the load to its uppermost position, secure it with the load-locking handle 2. Then, using the vertical handle 1, press the stamp to the crushed stone base being tested and release the load-locking handle. The weight falls freely onto the anvil. The weight on the rebound of the load is fixed with a rebound locking tongue.
All the main parameters of the device (diameter of the stamp, weight of the load, lifting height of the load, spring stiffness, system for recording the height of the rebound of the load) were established experimentally. The criterion for choosing the parameters of the device was to ensure the required sensitivity of the device to the measured parameter (degree of compaction - rigidity of the crushed stone layer), reliability of measurements and the creation of a device with minimal weight and the simplest design.
The diameter of the device stamp, equal to 150 mm, was chosen based on the need to fulfill two conditions: first, the stamp diameter exceeds maximum size crushed stones by 2-3 times, which allows us to consider the well-known condition that the device measures the elasticity of the layer, and not of individual crushed stone, to be fulfilled; the second is based on the well-known theoretical principles that the dynamic load is transmitted through the stamp to a depth of 1.5-3.0 diameters, which in our case is 22.5-45 cm and corresponds to the actual thickness of the crushed stone layers being arranged.
The weight of the weight is 2.5 kg, the lifting height is 45 cm and the applied spring stiffness is established experimentally, based on ensuring the conditions for the necessary sensitivity of the device from the dynamic - kinetic energy it creates when the weight hits the stamp through the spring and the elastic characteristics of the measured crushed stone layer.
Several systems for recording the height of a load's rebound have been tested. The most reliable and simple one was chosen.
The use of the device makes it possible to establish a quantitative assessment of the degree of compaction of the layer and its relationship with the requirements of SNiP 3.06.03-85. The results of assessing the degree of compaction in accordance with the requirements of SNiP are shown in the table.
At each measurement location, five determinations of the height of the rebound of the striker (weight) of the device are carried out without displacing the device stamp. The first two dimensions in the calculation average size rebound are not applied, because at the first blows
there is a change in the contact of the lower surface of the device stamp with the tested surface of the crushed stone
grounds. Based on the last three measurements, the arithmetic mean value of the rebound value of the falling load of the device is determined, which characterizes the compaction quality of the tested layer.
Due to the fact that the rebound value of the density meter weight for different materials is not the same, it is necessary to determine the required rebound value of a particular material on the first experimental section of the foundation before starting construction. This a certain amount rebound will further characterize the compliance of the compaction of the base sections with the requirements of SNiP 3.06.03-85.
To assess the quality of compaction of the constructed section of the crushed stone layer, at each diameter of the section, measurements are taken of the rebound value of the device load at three points: on the axis of the road and 1 m from each edge.
Along the length of the road, measurements are taken every 100 m. If the length of the road section is less than 300 m, the number of cross-sections should not be less than 3.
The quality of compaction of the constructed section is assessed by calculating the arithmetic mean value of the value of the rebound of the load at all measured points, based on the arithmetic mean value of the value of the rebound of the load at each point.
If the arithmetic mean value of the rebound value in the constructed area deviates from the required value downwards by more than 5%, it is necessary to carry out additional compaction of the constructed layer with smooth roller rollers.
Crushed stone is a popular building material, thanks to which it is possible to solve many problems in the field of construction. The process of obtaining the material is carried out by crushing rock solids. Extraction of raw materials is carried out by blasting during quarrying. After this, the rock is crushed to required size factions. In addition, crushed stone is assigned a certain compaction coefficient. Let's take a closer look at what this parameter is for and how to determine it.
Factions
Sheben is an extremely popular material. Thanks to him, it is possible to build very strong and reliable structures. But due to their inexperience, many people do not take into account such a parameter as the compaction coefficient during construction.
It is he who plays a special role during the shrinkage of the house. If the process of measuring this parameter was incorrect, this will affect the durability of the building being constructed. As a result, shrinkage will occur and cracks will appear on the surface of the house.
You can learn about the difference between crushed stone and gravel from this
The compaction coefficient is an immeasurable number that indicates the degree to which the external volume of a bulk component is reduced during transportation or compaction. Apply the compaction factor to sand and gravel mixtures, sand and crushed stone.
What crushed stone is needed in different cases
Soil compaction with crushed stone is used when it is necessary to build a specific house. Thanks to this technological process it is possible to complete all the assigned tasks without causing subsidence of subsequent layers. If the compaction process is not carried out correctly, then over time the layer of crushed stone and compacted soil will form a cage. As a result, cracks will form on the surface.
What is the significant difference between gravel and crushed stone is indicated in this
Tamping material
Compacting crushed stone is a mandatory activity for those who want to get a strong and high-quality foundation when constructing roads and buildings. To perform compaction it is necessary to use special equipment. Most often, a roller or vibrating plate is used. If the volumes are small, the material can be compacted manually.
It is necessary to check the quality of the installation using a special device. These measures are considered mandatory, otherwise poor-quality compaction will lead to a lot of trouble. During the measurement, it is necessary to determine the degree of compaction. This is done using the dynamic sensing method.
It is very difficult to carry out the weight of the event to determine the coefficient on your own. As a rule, people turn to a special laboratory for help. The use of static equipment is necessary in cases where it is necessary operational control for all values of compaction of mortars.
This method can be used not only when determining the coefficient for crushed stone, but also for sand and other bulk materials. But at the same time, the test mixture should not contain particles with a particle size larger than 10 mm. The percentage of their content cannot exceed 15%. The equipment can show reliable results with an error of 0.9-1 from the density standards of GOST 22733.
How much crushed stone is included in lightweight concrete is indicated
The process of determining the compaction level is carried out taking into account the depth of the tip of the equipment, as well as taking into account resistivity. Depending on what mixture is used during construction, a truncated or regular cone can act as a tip. The compaction coefficient can be determined by the level of deviation of the indicator needle when the ring is deformed.
You can find out what it is in this article.
The procedure itself for determining the compaction coefficient of crushed stone is short and simple. It is necessary to take the density meter in your hands and bring it vertically to the surface. After this, lower the tip into the pressure mixture. As a result of the described actions, remove the device and note the obtained indicators. For a certain point you need to take measurements 5 times. And the step between the points should be equal to 15 cm. After such experiments, the indicators are compared and a certain graph is built, according to which the required coefficient is determined.
What it is is indicated in the description of the article.
The density coefficient is very important indicator, thanks to which you can build houses, roads and not worry that shrinkage will occur after a while. The process of determining this parameter does not involve anything complicated. If you can handle the density meter, then no problems should arise.
The compaction coefficient of crushed stone is an important indicator that is required both for generating a supply order required quantity materials (consumption of crushed stone per 1 m3), and to predict further shrinkage of a layer of a certain fraction after its loading building structures, as well as the sustainability of objects built using them. This parameter allows you to determine whether it is possible to reduce the volume of material and, if so, by how many times (this is required, for example, to find out the compaction coefficient of crushed stone of 20-40 during compaction).
It is important to understand the difference between the bulk density of crushed stone (kg per m3) and how much this material will be compacted during compaction.
Each type of crushed stone has its own marking, which is specified in the SNiP standard and GOST 8267-93. There you can also find methods for determining the compaction coefficient. The compaction of crushed stone is directly dependent on many factors, including its characteristics. Therefore, it is important to consider:
- density;
- flakiness;
- grain size (fraction);
- frost resistance;
- radioactivity.
Based on these characteristics, a decision is made in favor of which material is more suitable for a particular type of work. It is also noteworthy that, according to construction technologies, it is customary to distinguish by several types of density: average, true and bulk density of crushed stone.
Why is crushed stone compacted?
Quite different high performance strength and when creating a foundation, for example, for highway or the foundation of a building, it is enough to simply level it. However, this is not at all true. The grains of the material obtained as a result of crushing rocks are distinguished by a completely arbitrary shape. That is why, in the process of filling any space between adjacent elements, air voids are formed, which contribute to a significant reduction in the level of resistance of the material to loads. Thanks to compaction, the grains lose mobility, which contributes to a significant reduction in the size of voids and an increase in the strength of the crushed stone base.
At a construction site, the compaction coefficient of crushed stone 20-40, 40-70 and other fractions is quite easy to find out. To do this, measure the height of the sides vehicle and the total volume of material delivered. The resulting number is multiplied by the compaction percentage. Also, knowing the compaction coefficient, it does not amount to a lot of work determine the required amount of crushed stone materials to carry out a particular specification construction work. To make an independent calculation, it is enough to know the following parameters:
- thickness of the base after compaction;
- specific gravity of crushed stone (must be indicated in the quality certificate);
According to current standards, the values of the crushed stone compaction coefficient can be as follows:
- sand and gravel mixture - 1.2;
- construction sand - 1.15;
- expanded clay - 1.15;
- crushed gravel - 1.1;
- soil - 1.1 (1.4);
- etc.
The unit of measurement for the compaction coefficient of crushed stone is ton/cubic meter (t/m3).
The compaction coefficient of any bulk material shows how much its volume can be reduced with the same mass due to compaction or natural shrinkage. This indicator is used to determine the amount of filler both during purchase and during the construction process itself. Since the bulk weight of crushed stone of any fraction will increase after compaction, it is necessary to immediately lay down a supply of material. And in order not to purchase too much, a correction factor will come in handy.
The compaction coefficient (K y) is an important indicator that is needed not only for correct formation ordering materials. Knowing this parameter for the selected fraction, it is possible to predict further shrinkage of the gravel layer after loading it with building structures, as well as the stability of the objects themselves.
Since the compaction ratio represents the degree of volume reduction, it varies under the influence of several factors:
1. Loading method and parameters (for example, from what height is backfilling performed).
2. Features of transport and the duration of the journey - after all, even in a stationary mass, gradual compaction occurs when it sags under its own weight.
3. Fractions of crushed stone and grain contents of smaller size than the lower limit of a specific class.
4. Flakiness - needle-shaped stones do not give as much sediment as cuboid ones.
The strength subsequently depends on how accurately the degree of compaction was determined. concrete structures, building foundations and road surfaces.
However, do not forget that compaction on the site is sometimes performed only on the top layer, and in this case the calculated coefficient does not fully correspond to the actual shrinkage of the pillow. Home craftsmen and semi-professional construction crews from neighboring countries are especially guilty of this. Although, according to technology requirements, each layer of backfill must be rolled and checked separately.
Another nuance - the degree of compaction is calculated for a mass that is compressed without lateral expansion, that is, it is limited by the walls and cannot spread out. At the site, such conditions for backfilling any fraction of crushed stone are not always created, so a small error will remain. Take this into account when calculating the settlement of large structures.
Sealing during transport
Find some standard value compressibility is not so simple - too many factors influence it, as we discussed above. The crushed stone compaction coefficient can be indicated by the supplier in the accompanying documents, although GOST 8267-93 does not directly require this. But transporting gravel, especially large quantities, reveals a significant difference in volumes when loading and at the final point of delivery of the material. Therefore, an adjustment factor that takes into account its compaction must be included in the contract and monitored at the collection point.
The only mention from outside current GOST– the declared indicator, regardless of the faction, should not exceed 1.1. Suppliers, of course, know this and try to keep a small supply so that there are no returns.
The measurement method is often used during acceptance, when crushed stone for construction is brought to the site, because it is ordered not in tons, but in cubic meters. When the transport arrives, the loaded body must be measured from the inside with a tape measure to calculate the volume of gravel delivered, and then multiply it by a factor of 1.1. This will allow you to roughly determine how many cubes were put into the machine before shipping. If the figure obtained taking into account the compaction is less than that indicated in the accompanying documents, it means that the car was underloaded. Equal or greater - you can command unloading.
Compaction on site
The above figure is taken into account only for transportation. Under construction site conditions, where crushed stone is compacted artificially and using heavy machines (vibrating plate, roller), this coefficient can increase to 1.52. And performers need to know shrinkage gravel backfill for sure.
Typically the required parameter is specified in project documentation. But when exact value no need, use average indicators from SNiP 3.06.03-85:
- For durable crushed stone of fraction 40-70, a compaction of 1.25-1.3 is given (if its grade is not lower than M800).
- For rocks with a strength of up to M600 - from 1.3 to 1.5.
For small and medium size classes of 5-20 and 20-40 mm, these indicators have not been established, since they are more often used only when clinching the upper load-bearing layer of grains 40-70.
Laboratory research
The compaction factor is calculated based on laboratory test data, where the mass is compacted and tested for various devices. There are methods here:
1. Substitution of volumes (GOST 28514-90).
2. Standard layer-by-layer compaction of crushed stone (GOST 22733-2002).
3. Express methods using one of three types of density meters: static, water balloon or dynamic.
Results can be obtained immediately or after 1-4 days, depending on the study chosen. One sample for standard test will cost 2500 rubles, in total you will need at least five of them. If data is needed during the day, express methods are used based on the results of selecting at least 10 points (850 rubles for each). Plus you will have to pay for the departure of a laboratory assistant - about 3 thousand more. But during the construction of large projects it is impossible to do without accurate data, and even more so without official documents confirming the contractor’s compliance with the project requirements.
How to find out the degree of compaction yourself?
IN field conditions and for the needs of private construction, it will also be possible to determine the required coefficient for each size: 5-20, 20-40, 40-70. But to do this, you first need to know their bulk density. It varies depending on the mineralogical composition, although slightly. Much greater impact on volumetric weight crushed stone fractions provide. For calculations, you can use averaged data:
| Fractions, mm | Bulk density, kg/m3 | |
| Granite | Gravel | |
| 0-5 | 1500 | — |
| 5-10 | 1430 | 1410 |
| 5-20 | 1400 | 1390 |
| 20-40 | 1380 | 1370 |
| 40-70 | 1350 | 1340 |
More accurate density data for a specific fraction is determined in the laboratory. Or by weighing a known volume of building rubble, followed by a simple calculation:
- Bulk weight = mass/volume.
After this, the mixture is rolled to the state in which it will be used on site and measured with a tape measure. The calculation is made again using the above formula, and as a result, two different densities are obtained - before and after compaction. By dividing both numbers, we find out the compaction coefficient specifically for this material. If the sample weights are the same, you can simply find the ratio of the two volumes - the result will be the same.
Please note: if the indicator after compaction is divided by the initial density, the answer will be greater than one - in fact, this is the material reserve factor for compaction. It is used in construction if the final parameters of the gravel bed are known and it is necessary to determine how much crushed stone of the selected fraction to order. When calculated inversely, the value is less than one. But these numbers are equivalent and when making calculations it is only important not to get confused which one to take.
