How to determine the class and brand of concrete?

Anyone working in construction, from professionals to do-it-yourselfers, needs to know the type and brand of concrete. Concrete’s strength, durability, and suitability for different projects are determined by these classifications. You can make sure that your structure will endure over time by learning how to recognize them.

Megapascals (MPa), a unit of measurement for compressive strength, are used to classify concrete. This classification aids in figuring out how much weight the concrete can support. Conversely, the concrete’s brand reveals the quality of the materials used in it as well as the mix proportions. Considering both factors is essential to choosing the best concrete for your particular requirements.

We’ll look at easy ways to identify the class and brand of concrete in this article. We’ll simplify the technical information into clear, actionable steps so you can choose the ideal concrete for your project with assurance. This guide will assist you in making well-informed decisions whether you’re building a driveway, a multi-story building, or a foundation.

Preparation of samples

By testing cast cubic samples, the standard governs how the compressive strength of concrete composition is determined.

The primary property of concrete that is used in structural calculations is its strength class.

Assemble the standards in the subsequent sequence:

• prepare about five special cubic forms from wood, ensuring a side size of 10, 15 or 20 centimeters, depending on the laboratory equipment on which the test will be carried out;
• moisten the inner surface of the wooden box by wetting it with water or applying a special lubricant. This will ensure normal hydration and allow you to easily remove the samples;
• pour the mixture into the group of forms, using the layer-by-layer method of laying the composition;
• remove air pockets by carefully tamping the solution, compacting it. Keep the sample for 28 days.

When selecting the required building solution, pay attention to its brand and class, which define its strength.

Change in strength

Samples from which the composition brand is identified should be kept free from damage and stored at a temperature of at least 20 degrees Celsius with a relative humidity of roughly 90%. One property that varies with the hardening process is strength. Keep in mind that it rises in the following ways over time:

• 7 days after pouring, the strength reaches 70 percent of the design value. An accelerated control method allows you to preliminarily determine the strength of reference samples a week after pouring. For example, the preliminary value of average strength for concrete grade M200 is 140 kg/cm².
• The material acquires performance characteristics after hardening after 4 weeks.
• The process of acquiring final hardness takes years.

Concrete’s compressive strength is characterized by its grade and class.

Classification of concrete compositions

The sample’s compressive strength, expressed in kilograms per square centimeter, is characterized by the concrete grade. Additionally, the standard needs to age for four weeks. The digital index found on the label of the concrete mixture depends on the volume percentage of cement in the composition and describes the average value of the parameter. From M50 to M1000, the composition grade range shifts. The range of applications for concrete differs based on the characteristics that define its strength:

• Works related to concreting, preparation of foundation strips, installation of curbs are performed using composition M100, corresponding to class B7.5.
• Pouring floors, preparing foundations for low-critical objects, making screeds, concreting sites is performed using a commercial solution of class B12.5, corresponding to grade M150.
• Preparation of foundations for objects, concreting stairs, making blind areas, retaining walls is performed using solutions M200 and M250 (classes B15 and B20).
• Individual housing construction, construction of industrial facilities, pouring monolithic structures is performed on the basis of mixtures M300 (B22.5) – M350 (B25), which are the most widely used.
• The construction of hydraulic engineering facilities, special banking facilities, structures to which special requirements are imposed is carried out with durable concrete M 400.
• The construction of special objects requiring a heavy-duty composition is carried out using mixtures marked 500 and higher.

Although the specifications for concrete in regulatory documents are given in grades, construction companies typically order concrete in grades.

Classification into groups can provide a final understanding of a concrete mass’s strength characteristics. The mixture class describes the true hardness of the mass while accounting for the allowable error in the quality of the solution.

The capital letter "B" and a digital index between 3.5 and 80 denote the concrete class. The mixture class range that is most frequently used is B7.5 to B40.

The test results of the reference sample define the composition’s strength indicator. It is decided what the parameter value is:

• volume and brand of binder components in the solution;
• specific gravity of the mixture;
• type of filler used.

Table showing the proportion of grades to classes in concrete

The current construction market provides blends of different grades. A composition designated M150, for instance, is guaranteed to have a compressive strength of 150 kg/cm².

Control methods

The various techniques available for identifying the strength properties of concrete can be categorized into the following categories:

• Control methods based on non-destructive compression testing methods. They are based on the results of indirect measurements of devices that record the value of immersion of the tool striker into the surface of the massif.

When the test results are processed, the strength difference between the concrete’s class and grade is revealed.

• Testing technologies that include an ultrasonic method for monitoring the characteristics. Based on the dependence of the hardness of the composition, the intensity of ultrasonic vibrations in the concrete mass, the technique allows you to determine the strength with high accuracy.
• Destructive testing of parameters, carried out on special presses, deforming reference samples to complete destruction.
• Independent methods for approximate determination of strength characteristics, based on the depth of penetration of the working tool under the influence of impact loads.

Let’s take a closer look at the most popular testing techniques.

To ensure the proper mix for your construction needs, you must ascertain the class and brand of concrete. This procedure entails determining the concrete’s strength, longevity, and project-suitability. You can ensure the longevity and safety of your structures by making informed decisions by learning to identify the class and brand.

Non-destructive methods

The integrity of the sample can be preserved during mechanical testing of concrete parameters utilizing non-destructive techniques and specialized laboratory equipment that records:

• rebound value;
• impact pulse value;
• tearing;
• chipping;
• soft deformation value;
• result of combined tearing action simultaneously with chipping.

Strength varies with time as the solution hardens and becomes stronger; it takes 28 days for the solution to reach its normal (design) strength.

A determination is made regarding the strength characteristics based on the variation in the striker’s immersion depth into the massif. To perform plastic deformation of the concrete surface, specialized laboratory hammers are used. The impact causes the formation of a hole, the diameter of which is used to compute the strength parameters. Use this method for measuring, and complete the tasks in the following order:

• Clean the surface from paint, plaster, putty layer.
• Perform about 10 blows of medium force on the controlled area, observing an interval between prints of about 5 centimeters.
• Check, using a caliper, the dimensions of the holes, observing an accuracy of up to one tenth of a millimeter.
• Determine the arithmetic mean of the diameter of the print.
• Use a calibration curve constructed on the results of measuring reference samples, and in accordance with the obtained average diameter, determine the strength parameter.

Other non-destructive testing techniques create two prints: one on the controlled surface and the other on the standard. The process of calculating strength parameters entails contrasting print sizes with a calibration diagram.

Sclerometers, specialized instruments that rely on the elastic rebound principle, are used in non-destructive testing when samples are not available and information on percentage characteristics is required. There are also pistols in use, the mechanism of which is a rod striker. The device’s scale displays a digital value in response to the striker’s action.

The true values of the concrete class approach a manufacturer’s brand more closely the higher its production culture.

To test using a combined method that allows chipping and tearing to occur at the same time, the concrete mass is attached to a unique pre-installed anchor device. The gadget displays its power and has an impact on the designated area.

Ultrasonic technique

Because they enable the preservation of the concrete mass’s integrity, ultrasonic testing techniques are also in demand. Reliable acoustic contact is provided by the method’s application of an ultrasonic transducer to the regulated structure. The rate at which ultrasonic vibrations spread throughout the mass determines its strength.

The following sounding types are utilized by the technology:

• through, used for columns, beams, in which the sensors are installed on opposite sides of the structure;
• transverse, used for panels, floor slabs, in which the wave transducer is located on the side of the control zone.

Ultrasonic control equipment consists of an electronic module and specific sensors.

The class of concrete is an indication of guaranteed strength, and the grade of concrete by strength is an indication of average strength.

The following factors influence how quickly ultrasonic waves move:

• Mass density.
• Homogeneity of composition.
• Elasticity.
• Presence of cavities, cracks, local defects.

The apparatus transforms ultrasonic oscillations into digital representations of attributes.

Destructive testing methods

Traditionally, a specialized hydraulic machine that compresses standards is used to determine the concrete grade in a laboratory setting. Testing any kind of concrete composition is possible with a considerable force, up to several tons. Pressure is applied to a concrete cube continuously, reaching a maximum pressure at which the sample is destroyed. The concrete grade is indicated by this pressure gauge.

Methods of independent testing

The concrete grade can be ascertained on its own. After all, using an independent laboratory’s services isn’t always feasible. By using a sharpened chisel and an ordinary hammer weighing between 0.3 and 0.4 kg, you can make an approximate estimate of the concrete grade by striking the chisel.

It is feasible to determine the strength of the concrete composition, which corresponds to M100–M150, when the chisel is submerged under impact into the concrete massif to a depth of 5 mm. The material is softer and has a strength of less than 75 (class B5) with a higher immersion value. In the event that tiny pieces break or the chisel is not completely submerged in the massif, a determination of the hardness can be made at the M200–250 kg/sq cm level, which corresponds to classes B15–B25.

There are no expenses involved in using this method. However, we advise utilizing the services of specialized laboratories if necessary to obtain accurate values.

Any construction project’s success and longevity depend on knowing the type and brand of concrete being used. Whether you’re choosing concrete for a straightforward sidewalk or a sophisticated structural element, you can select the best kind for your project by being aware of the various classifications.

Concrete’s strength should always be taken into account when evaluating it; this is usually indicated by its class and brand. These indicators aid in determining the concrete’s ability to support weight and suitability for a range of environmental circumstances. Selecting the appropriate class and brand increases your structure’s longevity and safety.

Recall that identifying and attaining the intended concrete class and brand requires precise testing and appropriate mixing. By maintaining standards and conducting routine quality checks, concrete is guaranteed to function as intended, preventing possible problems later on.

You can make well-informed decisions and help your construction projects be completed successfully by keeping an eye on these factors. The concrete you use will endure the test of time with the correct preparation and knowledge, giving your work a solid and dependable foundation.

Video on the topic

Testing CONCRETE for strength | Checking the class and grade of concrete

Pouring a 535 m2 slab. What kind of concrete do we use. What is the class and grade of concrete.