Non-destructive testing of concrete strength: measurement methods, testing

Ensuring the strength and durability of concrete structures is imperative when working with them. An effective method for evaluating the integrity of concrete without causing any damage is non-destructive testing. By using this technique, we can precisely measure the strength of the concrete while maintaining the overall condition of the structure.

Non-destructive testing uses a variety of methods, each with its own benefits. These techniques, which range from basic tools to sophisticated instruments, assist engineers and builders in assessing concrete quality in a useful and effective way. Having a thorough understanding of these tests’ operation can help you make wise maintenance and safety decisions.

This post will examine the various non-destructive concrete strength testing techniques. We’ll go over the procedures used in these tests, the parameters they look for, and the reasons they are crucial to guaranteeing the durability of concrete constructions. This guide will offer insightful information about the field of concrete testing, regardless of whether you’re an interested homeowner or a construction professional.

Non-destructive technologies for testing concrete strength

Non-destructive testing of concrete entails evaluating the state of concrete structures by examining a number of variables that impact the material’s strength, adhesion, protective layer thickness, thermal conductivity, humidity, and other characteristics. When there are significant volumes of control but no known characteristics of the reinforcement and concrete monolith, this kind of research is particularly pertinent.

This set of techniques enables you to conduct research in a lab, right on the construction site, and even while the machine is in use.

• Preservation of the integrity of the structure being tested.
• Possibility to avoid the need to organize laboratory assessment directly at the construction site.
• Full preservation of the operational properties of buildings and structures.
• Quite a wide scope of application.

Although there are many techniques and approaches for researching both liquid and hardened concrete, as well as numerous features, strength is the primary attribute and indicator. Strength determines the structure’s range of applications, operating circumstances, dependability, and durability. Therefore, the building will simply collapse if, for example, the concrete is plastic when poured, frost-resistant, and has the best versatile characteristics but is not strong enough to withstand the design loads.

Concrete’s strength is what counts and needs to be examined closely. GOSTs 22690-2015, 17624-2012 (inspection procedure), and 18105-2010 (general inspection rules are described) serve as the foundation for all tests. The application of mechanical techniques (impact, tearing, chipping, and indentation) and ultrasonic inspection are examples of non-destructive methods.

Concrete undergoes non-destructive testing in accordance with the schedule, if and when required, and at the age determined by the project. The research has made it feasible to compare the real material property indicators obtained with the passport ones and assess the release/stripping strength.

Conventionally, methods that cause local destruction are considered non-destructive. Their primary benefit is the accuracy and dependability of the outcomes. Tests are subject to GOST 22690-2015 regulation.

The necessity to determine the depth of the reinforcement, the high labor intensity, and the partial damage to the monolith’s surface, which may (though not significantly) alter its operational properties, are the primary drawbacks of using local destruction to measure the strength of concrete.

Although impact-pulse impact methods yield higher productivity, their applicability is restricted because they are only capable of testing the uppermost 25–30 millimeter layer of concrete. According to test results in the press of control batches, the surface needs to be cleaned, the damaged layer needs to be removed, and the graduated dependencies of the devices need to be brought into full compliance with the actual strength of the monolith.

The most popular method for determining the class of concrete by conducting studies at various angles to the surface while accounting for the material’s elasticity and plasticity is the impact pulse method, which is frequently used to measure the strength of concrete.

Thanks to a spring, when a spherical striker strikes the concrete, the impact energy causes the surface to deform, resulting in the appearance of a dimple (plastic deformations) and a reactive force (elastic deformations).

The impact’s mechanical energy is transformed into an electrical impulse by the electromechanical converter, and the compressive strength is actually measured in these units. For research, a Schmidt hammer is employed.

The method’s benefits include its ease of use, small equipment requirements, and capacity to identify the material class. Its drawbacks include its poor accuracy stemming from its ability to measure layer strengths as thin as five centimeters.

• Sclerometers are used in tests – special spring hammers with spherical stamps. A free rebound after impact is realized due to the spring system. The path of the striker during rebound is fixed on a scale with an arrow.
• The strength of the material is determined by graduated curves that take into account the position of the hammer, because the rebound value directly depends on the direction.
• The average research indicator is calculated based on 5-10 measurements taken, the distance between the impact points should be at least 3 centimeters.
• The measurement range of the methods is 5-50 MPa, special devices are used.
• Main advantages: simplicity/speed of research, the ability to assess the strength of densely reinforced products. Disadvantages: determination of concrete strength is carried out in the surface layer with a depth of 2-3 centimeters, checks need to be done often and a lot.

The least expensive way to test the strength of concrete is to use the plastic deformation method, which measures the hardness of the concrete surface by measuring the mark left by a steel rod or ball that is integrated into the hammer. After positioning the hammer in the monolith surface’s perpendicular plane, a few blows are delivered. Measurements are made of the striker’s and the concrete’s imprints. The obtained ratio of the imprint sizes is used to determine the characteristics of the concrete surface. The obtained data are recorded, and the average value is sought.

The plastic deformation research device operates by applying static or impact pressure to the stamp. Impact devices (spring/hand hammers, pendulum devices with a disk/ball stamp) are more frequently used than static pressure devices. Static pressure devices are rarely used.

The specifications state that the disk must be at least one millimeter thick, the ball must have a diameter of one centimeter, the impact energy must be 125 N or greater, and the steel used in the dies must have a minimum hardness of HRC60. The technique is straightforward, quick, and appropriate for heavily reinforced structures; however, it is only meant to ascertain the maximum M500 concrete grade strength.

Other non-destructive testing techniques include vibration, acoustic, infrared, electric potential, etc. Shock impulse, tear-off with chipping, and ultrasound are regarded as basic, but they are used less frequently.

Controlling structures exposed to aggressive environments, such as those that are chemically affected by acids, salts, and oils, thermally affected by high and low temperatures, and atmospherically affected by carbonization of the upper layer, is thought to be the most challenging.

Using a phenolphthalein solution to wet the area and tap to conduct an examination, they look for a layer with a disturbed structure, remove it, and clean the area with sandpaper for control. Next, local destruction or sampling are used to determine the strength. When employing shock-pulse and ultrasonic devices, the monolith’s surface roughness should not exceed Ra 25.

Non-destructive testing of concrete GOST 17624-2024

The ultrasonic method of concrete strength testing involves measuring the wave speed as it travels through the monolith. There are two methods for ultrasonic sounding: one involves attaching sensors to one side of a surface, and the other involves installing sensors on various sides in relation to the tested sample. Controlling the strength of the structure’s deep layers as well as its surface is made feasible by the through method.

Ultrasonic testing equipment is used to find flaws, assess the quality of the concreting, and determine the concrete’s and the monolith’s depth of reinforcement. These devices allow for continuous control of the strength increase/decrease and for the examination of various shapes on a regular basis.

The type and volume of the filler, the amount of binder used, how the concrete solution is prepared, and how compacted it is all have an impact on the relationship between the grade strength of concrete and the ultrasound speed. The primary drawback of the approach is a sizable inaccuracy in the study’s findings.

Given the high ultrasound speed (roughly 4500 m/s) in the material monolith, the calibration dependence of the wave speed and concrete strength is computed ahead of time for every test composition. For a particular concrete and an ambiguous composition, using two graduated dependencies can result in a significant error.

The capacity to repeatedly perform mass studies of products of any shape and efficiently carry out continuous monitoring of the increase / decrease in the strength of the structure in online mode are the key advantages of testing the strength of concrete using a non-destructive ultrasonic method.

Types of tests: table of values

Every non-destructive concrete strength testing technology has recommended compressive strength values as well as its own ranges of values. The maximum measurement values are determined by the manufacturers of the instruments used and by empirical findings. Tables provide a more convenient way to interpret research data by summarizing ranges and errors.

Sections of the required area’s monolith surface where there are no obvious damages and amorphous delaminations are typically used to measure the strength of the concrete. Additionally, the ambient air temperature should be positive.

To guarantee the longevity and safety of constructions, it is essential to comprehend the strength of concrete without causing any harm. Without compromising the integrity of the concrete, non-destructive testing techniques offer insightful information about its quality. These methods are crucial for assessing current buildings and directing upkeep or repairs.

Every technique that is available has benefits of its own and best applications. For example, ultrasonic pulse velocity can identify internal defects, and rebound hammer tests provide rapid surface hardness evaluations. Accurate and trustworthy results are ensured by knowing when and how to apply these techniques.

In conclusion, non-destructive testing is an essential instrument for assessing concrete. Professionals can obtain a clear picture of the strength and quality of concrete by selecting the appropriate method and applying it correctly, which will result in structures that are safer and more resilient.

For the purpose of evaluating the longevity and integrity of structures without causing any harm, non-destructive testing of concrete strength is essential. This article examines several techniques for determining the strength of concrete, including ultrasonic pulse velocity, core sampling, and rebound hammer tests. The advantages and disadvantages of each technique vary, so it’s critical to select the best one for the job based on the particular requirements as well as the state of the concrete.

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