The unit measures the mobility of the concrete mixture. Determination of mobility of concrete mixture. The scope of application of the concrete mixture depending on the mobility. Dense and light consistency

The most complete answers to questions on the topic: “tests to determine mobility in joints.”

When controlling flexibility in mass exercises physical exercise and especially during self-control, it is more convenient to use a qualitative assessment.

Tests that determine a qualitative assessment of the mobility of certain departments

Mobility of the cervical spine.

• Tilt your head forward. The chin should touch the chest.

  Tilt your head back (keep your torso vertical). The gaze should be directed straight up or slightly forward.

  Tilt your head to the left (right). The upper edge of the right (left) ear should be on the same vertical line with bottom edge another.

  Attach a mark to the wall at nose level. Stand on your left (right) side. Turn your head towards the mark (do not turn your body after your head!). Your nose should be pointing exactly at the mark.

  If the exercises are easy, mobility is cervical spine spine excellent , if with difficulty - good

Mobility in the wrist joints.

Stand up straight, arms forward, palms facing in. Bend your hands inward so that your fingers face each other (fingers and palm should be on the same straight line, do not bend your elbows).

If the hands are perpendicular to the arm (90 degrees), then mobility excellent , if 80 degrees – good , less - bad .

Stand straight on the palm of your left hand near the pad thumb place a paperclip or button and clasp your palms in front of chest so that your fingers point up. Gradually move your elbows out to the sides until your forearms form a straight line with each other.

If an object is held freely, then flexibility excellent , with difficulties - good , if an object falls - bad .

Mobility in the elbow joints.

Stand straight, arms at your sides, bend your elbows.

If the hand touches the shoulder, then flexibility excellent , if only with your fingers - good , if not concerned at all - bad .

Mobility in shoulder joints.

Stand straight with your legs slightly apart. IN left hand take a small object (soap dish or box of matches). Raise your left arm up and bend it behind your head. Lower the right one down and bend it behind your back. Try to pass the object from your left hand to your right. Then change hands and do the same exercise.

If the exercise is easy, then mobility in the shoulder joints excellent , if with difficulty - good , does not work - bad .

Stand with your back to the wall, feet apart, arms at your sides (palms forward). Slowly move your arms back as far as possible (without lowering them down or raising them up). Try to touch the wall with your fingers and hold this position for 2-3 seconds. (do not tilt your body).

If you can do it easily - flexibility excellent , with difficulties - good , does not work - bad .

Spinal mobility.

Attach a marker to the wall at shoulder level. Stand with your back to the wall one step away. Lean back so that you can see the mark.

Then stand against the wall with your right (left) side at a distance of one step, raise your left (right) hand up and try to reach the mark fixed on the wall with your straight hand.

Concrete is simply an irreplaceable material for construction, which is used everywhere. But in order to choose the right type of solution, it is necessary to take into account the main characteristics of the mass, such as workability, cone settlement and mass mobility. And exactly what the mobility of concrete is is what this article will discuss.

Basic terms and definitions

Before defining the main characteristics of the solution, it is necessary to clearly understand what this construction material.

Concrete is a composition consisting of four main components:

1. Cement;
2. Sand;
3. Water;
4. Crushed stone.

Note! If in , then it's just cement.

The main task . Achieving this goal is only possible if you comply correct proportions two main components such as water and cement.

Sand and crushed stone are referred to as fillers of the composition, and are used to impart strength to the mass and reduce possible deformations of the monolithic product after hardening. It is these fillers that make up the structural frame of a monolithic product, which makes it possible to increase the elasticity of the structure and reduce deformation under severe loads.

Mobility

Mobility or elasticity of the solution – important property, which can influence the choice of material for the construction of buildings and structures for various purposes. Mobility is the ability of a mass to fill the shape in which it is placed.

Note! The ability of a mass to fill a shape can manifest itself both under the influence of external forces and under the influence of its own mass.

Mobility concrete mixture According to GOST, it is divided into 4 categories from p2 to p5 depending on the amount of added liquid. The less liquid, the thicker the solution, the thickest has the index p2, the most liquid, respectively, p5.

Based on plasticity indicators, building materials are divided into 2 groups:

1. Slow or hard mixtures. They contain a small amount of water and are not able to fill the form in which they are placed under the weight of their own weight without the influence of external forces. Such compositions have indicators p2 or p3. Laying of the sedentary mass is carried out using vibrating and compacting equipment, which makes it possible to remove voids from the monolith;

Advice. If construction work using hard concrete is carried out in winter, the solution must first be heated.

1. High fluidity mixtures, liquid or castable. Solutions of this type have indicators equal to n4 or n5. Such masses are used in the process of pouring formwork, densely reinforced products and do-it-yourself columns.

Dilution with water

Low elasticity of the material can significantly increase production time construction work subject to absence at the construction site necessary equipment. And in order to decide this problem many resort to the dilution method, making mixtures p2-p3 into mixtures p4-p5.

If the compaction is done correctly and the dilution method is eliminated, you will get a strong, reliable design, mechanical restoration which can be produced by such methods as cutting reinforced concrete with diamond wheels and diamond drilling holes in concrete.

Mobility indicators

In the case where the grade of concrete in terms of mobility has been chosen correctly, but it is ordered from a supplier and you have doubts about the compliance of the delivered product with the declared characteristics, and the price of the mixture is not so low, then you can check it at the construction site.

The mobility of a concrete mixture can be determined directly during unloading in 2 ways:

• Determination by monolith analysis;
• Cone for determining the mobility of a concrete mixture.

Determination of elasticity by monolith analysis

The instructions for such a test stipulate the possibility of determining any indicator of the plasticity of the mixture:

1. Before starting the test, you should build from wooden planks several cube-shaped boxes with sides measuring 10-15 cm;
2. Before pouring concrete into prepared forms, the wood should be slightly moistened to prevent moisture from being absorbed from the solution;
3. We pour the solution into the boxes, after which the mass must be pierced with a sharp rod of reinforcement, thus compacting the monolith and releasing the air;

Advice. Additional compaction can be achieved by tapping the walls of the drawers with a hammer.

1. The cubes must dry for 28-30 days at a temperature of at least 20 0 C and a humidity of at least 90%;
2. After the created samples have dried, they should be sent to the laboratory, where the mixture will be checked for compliance with the declared indicators.

The obvious disadvantage of this method is its duration, therefore the method of determining plasticity using a cone is more often used.

Determination of elasticity by cone

The photo shows a diagram of a cone

To use this method, you will need a cone to test the mobility of concrete with a height of about 30 cm. This form should not contain more than 6 liters of material.

This check is carried out as follows:

1. The cone is filled with solution;
2. Concrete is pierced to compact and remove voids;
3. The cone is removed and placed next to the solution;
4. We test for elasticity:
   • If the concrete settlement is 5 cm, then you have hard concrete;
   • If the settlement is more than 5 cm, then you have moving concrete.

Finally

When working with concrete, it is necessary to choose the right grade of material in accordance with the elasticity of the mass and the purpose for which it will be used. Well, if you doubt that, for example, the mobility of P3 concrete is easy to check using the described methods.

The video in this article will tell you even more about how important it is to correctly select concrete in accordance with the elasticity parameters of the mass.

Bacterial motility is important specific character and carried out during diagnostic studies: the result is taken into account when identifying microorganisms. In mobile species, the ability of independent translational (and rotational) movement is due to the presence flagella- special thin thread-like formations. Flagella come in different lengths.

Their diameter is so small that they are invisible in a light microscope (less than 0.2 microns). U different groups bacteria, the number and location of flagella are not the same. Flagella do not accept dyes well. Complex coloring methods distort authentic look flagella, therefore in laboratories flagella are not stained, but bacteria are examined in a living state. Depending on the location and number of flagella, microbes are divided (Fig. 3):

A) monotrichs- microorganisms that have one flagellum at one of the poles, active, translational movements (pseudomonas);

Rice. 3. Types of arrangement of flagella in bacteria

b) lophotrichs- microbes that have a bundle of flagella at one of the poles (Listeria);

V) amphitrichs- microbes that have flagella at both poles of the microbial cell;

G) peritrichous- microbes in which flagella are located over the entire surface of the cell (E. coli).

There are types of microorganisms that have mobility, but do not have flagella (spirochetes, leptospira). Their movement is caused by impulsive contractions of the fibrillar motor apparatus of the microbial cell. Flagella come in different lengths.

To determine the mobility of bacteria, it is necessary to use a culture no older than one day old, since old cultures lose the ability to move.

Determination of bacterial motility using the hanging drop method. A drop of a young (18-20 hour) broth culture of bacteria is applied to a cover glass using a bacteriological loop. A drop of culture is covered with a special glass slide with a recess (well) so that the cover glass with the drop is in the center of the well and sticks to the slide (the edges of the well are first lightly greased with Vaseline). The drug is turned upside down, and the drop “hangs” over the hole (Fig. 8). The specimen is examined microscopically under a darkened field of view, first at low, then at medium or high magnification. On a light background, microbes are dark gray. Shukevich's method. To do this, a drop of microbial suspension is applied to the condensate of a slanted dense nutrient medium in a test tube. Mobile microorganisms, moving from the condensate, grow on the surface of the medium; non-motile species reproduce only in the condensate of the medium (“without going” to the surface of the agar).

“Crushed drop” method. A drop of bacterial suspension is applied to a regular glass slide, carefully covered with a coverslip and pressed lightly with a finger. Microscopy is carried out in the same way as in the hanging drop method.

Method of sowing by injection into semi-liquid agar. To do this, a bacteriological loop is used to inoculate the culture under study by injecting it to the bottom of a test tube with a semi-liquid nutrient medium. The mobile culture grows throughout the nutrient medium, forming a uniform turbidity, and the stationary culture grows only along the prick in the form of a rod, maintaining the transparency of the uninoculated area of ​​the medium.

The mobility of a concrete mixture is determined using a standard cone. This method is used for mobile concrete mixtures. To determine mobility, the following equipment is required.

1. Standard cone shape, made of sheet steel or galvanized iron. The inner surface of the cone should be smooth. WITH outside cone has 2 handles and lower base cones 2 stops. The height of the cone is 300 mm, the diameter of the lower base is 20 cm, the upper one is 10 cm.
2. Feeding funnel inserted into the upper hole of the cone.
3. A platform measuring 700×700 mm made of boards covered with sheet steel or linoleum.
4. Steel rod with a diameter of 16 mm, a length of 650 mm with a rounded end.
5. Steel or wooden ruler without divisions, 500-700 mm long and 40 mm wide.
6. Steel ruler without divisions, 500-700 mm long and 40 mm wide.
7. Trowel.

The test is carried out as follows. Inner surface The molds and platform are moistened with water. The platform is installed horizontally, the cone shape is placed in the middle of the platform and pressed with the feet through the stops.
The mold is filled with concrete mixture through a loading funnel mounted on a cone. Filling is carried out in three layers of equal height and each layer is compacted by bayoneting with a metal rod 25 times. The bottom layer of the concrete mixture is bayoneted to its entire thickness, and the top two layers - to the bottom.
Then the funnel is removed and the excess mixture is cut off with a trowel flush with the edges of the mold. After this, the concrete mixture is released from the mold, carefully lifting the latter into vertical position. The cone mold is placed on the platform next to the concrete mixture cone. The concrete mixture, freed from the mold, begins to settle under the influence of its own mass.
A metal or wooden ruler is placed on the upper base of the cone form, from the lower edge of which the cone slump (DC) of the concrete mixture is measured with an accuracy of 1 cm. The cone slump is determined twice and the arithmetic mean is taken from two determinations that differ from each other by no more than 2 cm. If the results differ more, the test is repeated.

The amount of cone draft (OC), expressed in cm, characterizes mobility concrete mixture. If the mobility of the concrete mixture is lower than the established one, then water and cement are added to it in an amount of 10% of the initially taken materials, maintaining the water-cement ratio. Then the mass is mixed again, after which the mobility of the concrete mixture is determined. If the mobility of the concrete mixture turns out to be higher than the specified one, then add, maintaining the specified ratio, sand and coarse aggregate in an amount of 10% of the originally taken. The addition of portions of sand and coarse aggregate is continued until the mobility of the concrete mixture is brought to the specified level. The amount of added materials is recorded and summed up with the estimated costs of materials.

Depending on the amount of mobility, concrete mixtures are conventionally divided into:
1) fluid (cast), having a cone draft (DC) of 17-20 cm;
2) mobile with OK 10-16 cm;
3) moderately mobile with OK 6-9 cm;
4) sedentary with OK 1-5 cm;
5) moderately hard, hard, highly hard and especially hard concrete mixtures with OK equal to zero.

Cast (flowing) concrete mixtures have high mobility, move by gravity along gutters with a slope of more than 50° or are supplied by pumps. Cast concrete without any compaction under the influence of its own weight is placed into a mold or formwork. Movable concrete mixtures are also capable of being easily placed into the mold. Moderate and low-slump concrete mixtures are placed mainly mechanically or manually for light pouring of concrete mixture

Concrete is very complex system, in which many chemical processes occur inside throughout its entire service life.

Mobility of concrete mixture - how to determine?

Nowadays, there are many types of concrete, with different properties for specific structures and operating conditions. When organizing concreting work, it is important to know such properties of concrete as workability.

Workability of concrete mixture- this is the ability of concrete, when concreting, to fill a form, formwork under the influence of its own weight or applied external force (vibration, compaction).

The workability of a concrete mixture is determined by the mobility of the concrete mixture (P) or the settlement of the cone (OK, S). The mobility of the concrete mixture is determined according to the DSTU B V.2.7-114-2002 method, where the cone settlement OK (S) is determined, cm. To test the concrete mixture, standard cones are used ( photo 2) depending on the coarse aggregate fraction:

• with a crushed stone fraction of no more than 70 mm - 300×200×100 mm (H×D×d);
• with a crushed stone fraction of more than 70 mm - 450×300×150 mm (H×D×d),

Where H – cone height; D – lower diameter of the cone; d – upper diameter of the cone.

The essence of determining the cone slump comes down to the fact that the prepared concrete mixture is poured into a truncated standard cone in three stages and compacted with a bayonet (usually a piece of smooth rod reinforcement). Level the upper surface of the cone, removing the remaining concrete mixture, and then lift the form vertically and place it near the formed cone. The height difference between the shape and the mixture is the value of the cone settlement.

Based on DSTU B V.2.7-176:2008, all concrete mixtures, depending on consistency, are divided into the following grades ( table 1)

Table 1. Brand of concrete mixture by consistency

Also, the consistency of a concrete mixture can be defined by the following terms:

• rigid concrete mixture: OK from 0...1 cm;
• slow-moving concrete mixture: OK from 1...5 cm;
• mobile concrete mixture: OK from 6...14 cm;
• cast concrete mixture: OK more than 15 cm.

By table 1 it can be seen that the thickest concrete mixture has the following indicators: S1, V0. The most liquid concrete mixture has the following grades: S4 or S5, V4. Rigid mixtures S2, S3 are used for concreting construction sites using vibration and compaction.

If compactors and vibrators are not used, then voids will form in rigid mixtures, violating the integrity and solidity of the structure and thereby reducing strength, photo 4.

The mobility of a concrete mixture depends on many factors:

• type of cement;
• amount of water;
• water-cement ratio (W/C);
• absence or presence of additives;
• type of additives used;
• quality and shape of aggregates;
• size of aggregates (fine and coarse).

How to choose the desired mobility of a concrete mixture?

The most important factor responsible for the properties of concrete is the water-cement ratio (W/C). Therefore, it is strictly unacceptable to dilute the concrete mixture with water to give it increased mobility. The strength of concrete directly depends on the water-cement ratio W/C. If the W/C is violated by adding water to the concrete mixture, the basic characteristics of concrete are violated. In this case, the strength of concrete may decrease by several classes, for example, from strength class C40 it can become C30.

There is an opinion that concrete with high mobility has better strength. Concrete grades S4 and S5 will be more expensive in consistency than concrete grade S1, but this does not mean that it is stronger. The strength class of concrete with cone slump S1, S2, S3, S4, S5 will be the same, but the cement consumption will be different, which determines the price of concrete. For more mobile concrete mixtures, it is necessary to use more cement than for less mobile ones in order to ensure the same strength of concrete. Thus, you should not order concrete with mobility S5 for concreting an open area or slab, where it is possible to compact the concrete mixture using vibrators - this is an unnecessary and unreasonable expenditure of money.

If it suddenly happens that a concrete mixture below the required mobility is brought to the construction site, it can be increased with the help of plasticizer additives. Adding plasticizers will not significantly reduce the strength of concrete. When concreting in winter at negative temperatures nessesary to use antifreeze additives, which can provide the necessary mobility for up to 6 hours.

IN table 2 The rational scope of application of concrete mixtures of different mobility for different construction needs is given.

Table 2. Scope of application of concrete mixture depending on mobility

When calculating the composition of concrete to determine required quantity water at a given mobility, you can use the following graphs: rice. 1.

Rice. 1. Graph of water demand for plastic (a) and rigid (b) concrete mixture made using Portland cement and sand medium size(water requirement 7%) and gravel of the largest size: 1 – 70 mm; 2 – 40 mm; 3 – 20 mm; 4 – 10 mm

Most often in construction, cone slump is used to describe the consistency of a concrete mixture. But in some cases they use such a characteristic as hardness of the concrete mixture.

Concrete mix hardness (W) defined as the vibration time in seconds required to measure and compact a pre-formed cone of concrete using a hardness tester (Vebe type) – rice. 2. This characteristic more accurately reflects the properties of rigid or low-flow mixtures and is found in construction.

Rice. 2. Determination of the hardness of a concrete mixture: І – Vebe type device; II – concrete mixture on the device before vibration; II – concrete mixture on the device after vibration; 1 – cylindrical ring, 2 – truncated cone, 3 – funnel, 4 – tripod, 5 – disk with 6 holes, 6 – rod, 7 – vibrating table

Konev Alexander Anatolievich