Testing concrete samples (cubes) for strength, laboratory research

Modern construction relies heavily on concrete, and any structure’s longevity and safety depend on its strength. Testing samples—typically in the shape of cubes—is one of the most dependable ways to determine the strength of concrete. These tests offer insightful information about the material’s quality and performance in varied settings.

Concrete cubes are carefully prepared and put through rigorous testing procedures in laboratory settings. To guarantee consistency, the concrete must first be carefully mixed. Next, cubes must be cast into molds. The cubes are cured for a predetermined amount of time after the concrete hardens to provide the appropriate level of maturity for testing.

Concrete cubes are tested for strength by applying pressure to the sample until it breaks. The maximum load that the concrete can bear is determined by this process, which is called a compression test. In order to ascertain whether the concrete satisfies the standards and specifications necessary for its intended use, the outcomes of these tests are essential.

Engineers and builders can use these tests to find any possible weaknesses in the concrete mix and make the necessary corrections. By taking a proactive stance, structural failures can be avoided and the long-term safety and durability of buildings, bridges, and other infrastructure are guaranteed. The construction industry can keep creating stronger, more resilient structures by comprehending and putting into practice efficient testing techniques.

What does concrete strength depend on and what does it affect

The most significant property of concrete that is considered during the design and calculation stages as well as during work is its strength indicator. Class B (measured in MPa) or M (kg / cm2), which denotes the maximum compression pressure that the material can readily withstand without deforming, is the grade that determines the strength of concrete.

The laboratory or construction organization (possibly the master himself) follows the guidelines in the main regulatory documents (GOSTs 10180-2012, 22690-88, 18105-2010, 28570) when testing concrete for strength.

The type of cement used and the ingredients added to the mixture have a direct impact on how well concrete resists external forces as a result of internal stress. When examining a concrete sample to determine whether it adheres to the designated brand, it must be free of any cracks, chips, delamination, deformations, or destruction.

Concrete strength tests in laboratories are necessary, particularly when pouring significant structures, load-bearing components, etc. Ultimately, even a small difference (which frequently arises from cutting costs on cement and other materials) can quickly demolish a structure or structural component.

The composition’s strength is contingent upon several factors, including the type of cement used, the proportion of fillers to cement, the percentage of fillers, the caliber of each component, the water’s purity, and the addition of plasticizers and additives. Concrete is reinforced with steel rods, wire, or mesh if it is intended to fill a structure that will support heavy loads.

The external conditions under which the concrete is poured and dries have a significant impact on the strength of the concrete being tested. Vibration also makes the monolith denser by eliminating air bubbles, which greatly increases strength.

Concrete must be heated or combined with specific anti-freeze additives if it is to be poured in below-freezing temperatures. Heat-insulating materials, sawdust, etc., can be used to cover the base and install electrodes. The monolith needs to be moistened after pouring to keep moisture from evaporating too quickly and causing cracks on its surface.

Even though there are many variables that affect how strong concrete is, conducting accurate and prompt solution testing can help rule out the chance of creating a subpar mixture and reduce the chance that the entire structure will be destroyed.

Other influences on the quality of the solution can be minimized or neutralized as long as the concrete satisfies the required strength indicators.

Classification of testing methods

Concrete tests are conducted using a variety of techniques, the selection of which is based on the capacities that are available, the operating environment, the age of the monolith, the possibility of modifying the mixture’s composition, the initial data, and the desired outcomes.

1. Testing concrete samples that are cast in laboratory conditions – cylinders and cubes, cones are created from the mixture, then tested using a press.
2. Testing samples that were cut out / sawed out of an already finished monolith – usually drilled with diamond crowns, cores are sent to the laboratory, where the strength is determined using a press.
3. Non-destructive methods – using devices/tools that allow you to study the properties of a monolith without the need to place them in certain devices and conditions. Ultrasound, shock-pulse method, etc. are used.d.

Even with the advent of numerous contemporary tools and techniques, pressing concrete samples is still the most common and efficient method (compression testing).

Two techniques are employed: pressure testing and weight measurement both before and after concrete is mixed or shaken in a special apparatus.

• Color – high-quality concrete should be greenish-gray in color, and the greener the better (a yellow tint is a sign of poor quality).
• The appearance of cement milk on the surface of poured concrete – the thicker, the better.
• Filler fractions not covered by the mixture – there should be none.
• When struck, the hammer should bounce off the hardened monolith with a ringing sound, leaving a small dent.

Testing the strength of concrete samples—especially cubes—is essential to guaranteeing the material’s dependability and sturdiness in building projects. Concrete cubes are made in this manner, cured under particular circumstances, and then compressed until they fracture. The outcomes give crucial information regarding the concrete’s compressive strength, assisting engineers and builders in determining whether the mixture satisfies requirements and is safe to use to support structures. The integrity and safety of buildings, bridges, and other infrastructures depend on this simple but essential testing procedure.

Stages of testing

Concrete can be tested using two major categories of techniques that are currently in widespread use to assess the material’s quality and compliance with requirements.

Destructive methods

Testing is done with a press on cubes, cylinders of concrete that are taken from a completed monolith or obtained in the laboratory (which can affect the strength of the entire structure). Concrete fragments are subjected to increasing pressure until the control sample is completely destroyed, which is then recorded.

When building significant structures, concrete must be tested using this effect, which is the most precise way to determine its strength.

Non-destructive methods

In this instance, the study under consideration does not entail any detrimental effects on the sample or structural damage. The tool uses mechanical means to interact with the monolith’s surface, including tearing, tearing along with chipping, and chipping the edge.

Should a tear-off test be employed, a steel disk is affixed to the monolith using epoxy adhesive and subsequently detached using a specialized tool containing a piece of the structure. The formula is used to convert the resultant force indicator to the desired value.

The device is fixed to the concrete cavity during tear-off with chipping. Petal anchors are placed into holes that have been drilled, after which some material is removed and the breaking force is noted. Conversion factors are used to determine brand attributes.

Where there are exterior corners (ceilings, columns, beams), rib chipping is used. The device, which is typically the GPNS-4, is loaded smoothly and fastened to any projecting segment using an anchor and dowel. When the force and depth of the chip are measured at the point of destruction, a formula that inherently considers the filler fraction is used to calculate the strength.

Procedure for testing workability

In a laboratory, a viscometer is a specialized instrument used to study this property of concrete. It lets you calculate how long it takes to lay the mixture in seconds. The viscometer is started simultaneously with the laying process, and the resulting indicators are then recorded. The quality of the material increases with decreasing work time.

Procedure for conducting tensile tests

A destructive load is first applied to the center of the sample in an increasing manner while the concrete cone is first prepared and horizontally positioned in a special apparatus. The effect has a step of 0.5 MPa/s. Once the concrete structure has crumbled in the sample’s center, the outcome is noted.

Procedure for conducting compression tests

Concrete grade can be ascertained using this technique. Firstly, cubes with edges measuring between 100 and 300 millimeters are cast from the material (or cut out of a previously poured mixture).

Cylinders and prisms can also be employed in testing. Samples are poured into a vibration table in the lab, and tests are run on the third, seventh, and 28th days (main test) following pouring.

The sample is subjected to a press that applies pressure in increments of 3.5 kgf/m2 to the cube at a power of 140 kgf/m2. The force vector needs to be exactly perpendicular to the concrete’s base. The grade is noted in the test protocol and the concrete’s resistance to compression is calculated based on the data collected.

A crucial step in guaranteeing the excellence and longevity of any concrete construction is testing concrete samples for strength. Through the examination of these samples, which are usually cubes, we are able to determine with accuracy how well the concrete will function in different scenarios. This procedure guarantees that the concrete satisfies all requirements and standards for the purpose for which it is intended and aids in the identification of any potential weaknesses.

Concrete cubes are put through strict testing procedures and controlled conditions in a laboratory setting. The stresses and strains that concrete will encounter in practical applications are replicated in these tests. By doing this, scientists and engineers can learn a great deal about the properties of the material and use that knowledge to help them decide on the best mix design, curing techniques, and project scheduling strategies.

Testing concrete samples on a regular basis adds years to the life of structures while also ensuring safety. Early detection of problems that may eventually result in expensive repairs or even structural failures is made possible by it. Therefore, no matter how big or small the construction project, it is imperative to invest in appropriate laboratory research and testing.

To sum up, the process of evaluating concrete samples in a laboratory setting is essential to the building sector. It offers a dependable way to guarantee that the concrete used in construction projects meets the necessary requirements. We can construct structures that are longer-lasting, safer, and more robust by following these testing procedures.

Video on the topic

Testing a concrete core sample

Testing concrete for strength using destructive testing methods (testing concrete cubes and cores).

Testing concrete cubes for strength on the 7th day // Improvement.rf

Determining the strength of concrete using control samples