Checking the strength of concrete: basic methods of determination and measurement

Concrete is a vital building material that is renowned for its durability and strength. Any structure’s longevity and safety depend on it meeting the necessary strength requirements. This article examines the various techniques for determining the strength of concrete to assist you in properly assessing its performance.

The strength of concrete can be determined using a variety of methods, from simple tests you can do on your own to more involved lab processes. Every approach has benefits and uses, based on the particular requirements of a given project.

As a homeowner, builder, or contractor, you can make sure that your projects are dependable and safe by learning how to test the strength of concrete. Let’s examine the fundamental approaches for calculating and measuring concrete strength and how you can use them in your work.

Method Description
Compression Test Measures the concrete"s ability to withstand axial loads. Concrete samples are compressed until they fail, and the force required to break them is recorded.
Tensile Test Assesses the concrete"s ability to resist tension forces. This test involves pulling the concrete sample until it fractures, helping to understand its tensile strength.
Flexural Test Determines the concrete"s ability to resist bending. A sample is supported at two points and loaded at the center until it breaks, providing insight into its flexural strength.
Ultrasonic Pulse Velocity Uses sound waves to measure the speed of a pulse passing through the concrete. Faster speeds indicate higher strength and quality of the concrete.
Rebound Hammer Test Measures the hardness of the concrete surface by using a spring-loaded hammer. The rebound distance of the hammer indicates the surface strength.

In order to guarantee concrete’s longevity and safety during construction projects, its strength must be ascertained. The basic procedures for evaluating the strength of concrete will be discussed in this article, along with more contemporary methods as well as more conventional ones like compressive strength tests. By being aware of these techniques, you can make sure your concrete structures are long-lasting and select the best testing strategy for your requirements.

What affects strength

Prior to delving into the techniques for assessing concrete strength, it is imperative to comprehend the variables that impact this measure and the factors that may negatively impact frozen stone properties. It’s important to keep in mind that, under laboratory conditions, concrete mix that has solidified on a building site can exhibit flawless qualities.

Concrete can be affected by external factors as long as it is mixed with fillers that have the same technical qualities and cement of the same quality.

  • The conditions and duration of the transportation of the mixture (if the solution is prepared not at the construction site, but at the factory).
  • Concrete laying method in formwork.
  • Form and dimensions of the structure.
  • The environment is the level of humidity, the air temperature throughout the time of hardening of the solution.
  • Type of stressful state.
  • The correctness of the solidifying monolith after pouring.

When the conventions and guidelines for working with concrete are not followed, the mixture’s quality usually deteriorates significantly and its characteristics are diminished.

  • Delivery of the mixed mixture not in a mixer.
  • Exceeding the permissible value of the travel time.
  • Lack of compaction with rammers/vibrators when pouring the solution.
  • Very low/high air temperature during the work, wind or rain.
  • Lack of optimal curing conditions after pouring into the formwork.

Improper transportation or noncompliance with work requirements may cause the concrete mixture to set, delaminate, or lose its mobility. Lack of compaction causes air bubbles to stay in the stone’s thickness, which lowers the quality. Seven to fifteen days after pouring, the concrete reaches seventy-five percent of its design strength at an ambient temperature of +10 to 25 degrees and high humidity. If not, the terms arrive later, the monolith may deteriorate, and its strength may be reduced.

Steaming or autoclaving of structures is a common practice at reinforced concrete product plants to shorten the concrete’s strength-curing time. Normally, this process takes eight to twelve hours, but it is not possible to use such a method on a construction site.

A variety of methods and techniques are used to test concrete for strength and compliance with design characteristics. These include laboratory testing of samples, indirect and non-destructive direct methods, etc.d.

  • Stone surface defects.
  • Uneven composition of the solution.
  • Moisture content of the material.
  • Reinforcement of the concrete monolith.
  • Oiling, corrosion, carbonization of the outer layer.
  • Malfunctions in the operation of research devices – weak battery charge, failure of parts, etc.d.

Testing concrete by taking samples out of the monolith’s thickness and analyzing them is the most illuminating technique. Errors can be excluded in this instance, but the method’s high cost and labor intensity make it less popular.

The most common method for testing the strength of concrete is to use instruments that measure properties such as hardness, wavelength, shear/tear force, etc. that are directly related to strength. After that, calculations are made using unique formulas.

Testing requirements

The majority of clients favor non-destructive techniques when assessing the strength of concrete. With the use of specialized tools, you can quickly and accurately identify the necessary indicators without boring, drilling, or chopping samples.

Three primary indicators are involved in any measurement of concrete strength: equipment cost, result accuracy, and labor intensity. The most costly are tear-off tests with a chip and core tests performed with a laboratory press. less costly techniques for impact pulse, plastic deformation, elastic rebound, and ultrasound. It is recommended that they be used only after the calibration dependence between the selected indirect characteristics and the actual strength has been established.

It is important to keep in mind that the solution parameters and the ones that the calibration dependence is based on might differ significantly. Concrete stone’s dependable compressive strength must be ascertained by measuring the pull-off force with chipping or by inspecting the cubes on a press. There could be serious mistakes in the control and strength level assessment (from 15% to 75%) if this operation is abandoned.

For evaluating a structure’s technical state, indirect methods work best when identifying regions of material heterogeneity. In this instance, using an imprecise relative indicator is permitted by the control rules.

How to determine the strength of concrete

Three primary test methods are used to determine the strength of concrete: destructive, non-destructive indirect, and direct. They all enable control and assessment of the concrete stone’s true strength in a lab, on building sites, or in prefabricated designs.

Destructive methods

This process requires a lot of labor: samples are sawed or cut from a completed structure that has already been poured and fully strengthened, and they are subsequently destroyed in a press. Following every test, the maximum compressive force values are obtained, recorded, and statistical processing is applied.

Although the method ensures the objectivity of the results, it is frequently unsuitable for certain conditions because of labor intensity, high cost, or localized building/structural defects. Concrete is tested under production conditions using a number of samples that were made using a working concrete mixture in accordance with GOST 10180-2012. After being maintained in conditions that closely resemble actual ones, cylinders or cubes are tested in a press.

Non-destructive direct

This category of techniques includes material testing without causing structural damage. While riding the rib, the mechanical interaction between the device and surfaces passes at a simple separation when divided with a chip.

An epoxy composition is used to adhere a steel disk to the stone’s surface during the tear-off test. Next, a portion of the structure and it are ripped off using a specialized tool (the PIV, GPNV-5, and POS-50MG4 devices are used for this). Using specific formulas, the resulting force is transformed into the desired indicator.

The tool is affixed straight into the concrete cavity rather than to the disk when tearing off with a chip. Drilling is done, petal anchors are inserted, and a portion of the material is removed while the destructive force is recorded. Special conversion factors are used to calculate the brand indicator.

When working with structures that have external angles, such as ceilings, beams, columns, and others, rib chipping is utilized. The device, which is typically GPNS-4, is smoothly loaded after being fastened to one of the projecting segments using an anchor and a dowel. The chip’s depth and force are measured when destruction happens. Next, the strength is ascertained using the formula’s values, which inevitably account for the solution’s filler content.

Non-destructive indirect methods

These techniques omit the need for labor-intensive procedures like installing anchors or introducing devices inside the concrete block itself. This set of techniques consists of the plastic deformation method, ultrasound research, impact pulse methods, and elastic rebound methods.

By comparing the longitudinal wave speed in the completed monolith with a reference sample, the ultrasonic method of measuring the strength of concrete can be determined. The UGV-1 measuring apparatus is set up on a level, non-deformable surface, and the sections are rung strictly in compliance with the test protocol. Outlier values are not taken into consideration during the processing of any collected data.

Electronic databases are available on all modern devices for basic computations. As long as GOST 17624-2012’s guidelines are followed, there shouldn’t be more than 5% error in this kind of study.

Determining the strength of concrete by the impact impulse method involves using the impact energy of a metal striker in the form of a sphere on the surface of a concrete monolith. A magnetostrictive or piezoelectric device converts impact energy into an electrical impulse, the time and amplitude of which have a functional relationship with the strength level of concrete.

You need to buy a testing equipment before you can use this method to check the class and grade of concrete. It produces results in a ready-made format, is compact, and uses the desired indicator’s measurement units. It is also very simple to use.

You will need a sclerometer, a specialized tool for recording the striker’s reverse movement after striking a concrete surface or a metal plate pressed against it, in order to use reverse rebound to measure the strength of concrete. This is the process of figuring out a material’s hardness, which is correlated with its strength.

The plastic deformation method uses a metal ball to strike concrete and measure the size of the mark. The reference sample and the obtained values are contrasted. This long-standing technique is most commonly applied with a Kashkarov hammer, in which a replaceable steel rod with documented properties is inserted into the hammer’s body.

The surface of the monolith is struck repeatedly. The strength is then calculated using the diameter ratio of the resulting prints on the rod and concrete.

For construction projects to be long-lasting and safe, it is essential to know how to test the strength of concrete. You can accurately ascertain whether your concrete satisfies the necessary standards and specifications by using the appropriate techniques.

The three main techniques used to evaluate the strength of concrete are non-destructive testing, curing condition monitoring, and compressive testing. Every technique has benefits and works with various concrete types and construction phases.

Testing concrete frequently during construction helps identify possible problems early and guarantees that the finished structure will be sturdy and dependable. Whether you opt for more modern, non-destructive methods or more traditional ones, conducting thorough checks will increase the project’s overall success and lifespan.

Video on the topic

Technical inspection of buildings: shock-pulse method for determining the strength of concrete in Hectare Group

Checking the strength of concrete . How to know if concrete is good or not? #housebuilding #concrete #construction

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Dmitry Sokolov

Chief engineer in a large construction company. I have extensive experience in managing construction projects and implementing modern technologies.

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