The compressive strength test for concrete is an important indicator of its quality. This single test can determine if the concreting process was carried out correctly. The compressive strength of concrete for general construction typically ranges from 15 MPa (2200 psi) to 30 MPa (4400 psi), with higher strength required for commercial and industrial structures. The strength of concrete is influenced by several factors, including water-cement ratio, cement strength, quality of concrete materials, and quality control during production.
The test for compressive strength can be conducted on either a cube or cylinder. Standard codes recommend using a concrete cylinder or cube as the standard specimen for the test. The American Society for Testing Materials (ASTM) has developed the C39/C39M Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.
Compressive Strength Definition
Compressive strength refers to the capability of a material or structure to withstand external loads applied to its surface without experiencing any cracks or deformations. When a material is subjected to compression, it tends to reduce in size. On the other hand, when it is exposed to tension, it elongates in size.
The compressive strength of a material is an essential factor that determines its suitability for various applications. Materials that possess high compressive strength are ideal for applications that require them to withstand significant pressure and forces, such as in the construction of bridges, buildings, and other structures.
Understanding the compressive strength of a material is also crucial in preventing structural failure and ensuring public safety. Engineers and designers must consider this factor when selecting materials and designing structures to ensure that they are strong enough to withstand the expected load and pressure.
In summary, compressive strength plays a critical role in determining the suitability of a material for various applications, and understanding it is crucial for ensuring the safety and reliability of structures and materials.
Compressive Strength Formula
The compressive strength of a material can be determined by calculating the ratio of the load applied to the cross-sectional area of the face on which the load was applied. This can be expressed as a formula where the compressive strength is equal to the load divided by the cross-sectional area. Therefore, if the load and the cross-sectional area are known, the compressive strength of the material can be calculated using this formula.
Procedure: Compressive Strength Test of Concrete Cubes
Cube testing is a common method used to determine the compressive strength of concrete. The test involves using two types of specimens, either cubes of 15cm X 15cm X 15cm or 10cm X 10cm x 10cm, depending on the size of the aggregate being used. However, the most commonly used mold size is 15cm x 15cm x 15cm.
To conduct the test, the concrete is poured into the mold and appropriately tempered to ensure that there are no voids. After 24 hours, the molds are removed, and the test specimens are placed in water for curing. To make the top surface of the specimens even and smooth, cement paste is applied and spread evenly over the entire surface area.
The specimens are then left to cure for either seven days or 28 days before being tested using a compression testing machine. The load is applied gradually at a rate of 140 kg/cm2 per minute until the specimens fail. The compressive strength of the concrete is then calculated by dividing the load at failure by the area of the specimen.
Cube testing is a crucial process in the construction industry as it helps to ensure that the concrete used in buildings and other structures is strong enough to withstand the expected load and stresses.
Following are the procedure for testing the Compressive strength of Concrete Cubes
Apparatus for Concrete Cube Test
Compression testing machine
Preparation of Concrete Cube Specimen
The paragraph states that the test specimens, specifically six cubes with a size of 15 cm, are made using the same concrete mixture that was used in the field. The requirement for the mixture is that it should be of at least M15 grade or above. No further information is provided about the purpose or use of these test specimens.
Mixing of Concrete for Cube Test
There are two ways to mix concrete: by hand or using a laboratory batch mixer. If you choose to mix by hand, the first step is to use a watertight, non-absorbent platform to mix the cement and fine aggregate. This should be done until the mixture is completely blended and of a uniform color.
Once the cement and fine aggregate are well mixed, the next step is to add the coarse aggregate. Mix it with the cement and fine aggregate until the coarse aggregate is evenly distributed throughout the batch. This will ensure that the concrete has consistent strength and durability.
After the coarse aggregate is added, the final step is to add water and mix it until the concrete is homogeneous and has the desired consistency. This is an important step as the amount of water added will affect the final strength and durability of the concrete. Therefore, it is crucial to mix until the concrete appears to be uniform and of the desired consistency.
Sampling of Cubes for Test
To begin the process, the mounds must be cleaned and oiled. This ensures that the concrete can be poured into the molds without any issues. Once the mounds are prepared, the concrete can be poured in layers that are approximately 5 cm thick.
To ensure that each layer is properly compacted, a tamping rod that is made of steel and has a diameter of 16mm and a length of 60cm must be used. This rod is bullet-pointed at the lower end and should be used to compact each layer with not less than 35 strokes per layer.
After each layer has been properly compacted, the top surface must be leveled and smoothed using a trowel. This will ensure that the surface is even and that there are no bumps or ridges that could interfere with the finished product. By following these steps, a high-quality concrete mold can be created.
Curing of Cubes
The given context is a sentence that describes a specific process involving the storage and preparation of test specimens. In order to rewrite the context in paragraphs, additional information and detail may need to be included.
One possible way to expand on the given context is:
Before conducting tests on certain materials, it is necessary to prepare specimens that are representative of the material being tested. In order to do this, the specimens are typically created using a mold or other shaping method that ensures consistency and accuracy in their dimensions.
Once the specimens have been created, they must be stored under specific conditions in order to properly prepare them for testing. In the case described, the specimens are stored in moist air for a period of 24 hours. This step is important because it allows the specimens to reach a stable moisture content, which is necessary for accurate testing.
After the 24-hour period has elapsed, the specimens are marked and removed from their molds. At this point, they are submerged in clear freshwater until they are ready to be tested. This is done in order to prevent any further changes in moisture content or other properties that could affect the accuracy of the tests.
By following these steps, researchers and technicians can ensure that the specimens being tested are representative of the material being studied and have been properly prepared for accurate and reliable results.
Precautions for Tests
In order to ensure proper curing of materials, it is important to regularly test the water being used. Specifically, the water should be tested every seven days to ensure its quality remains consistent. Additionally, it is important that the temperature of the water is maintained at a range of 27 degrees Celsius, with a tolerance of plus or minus two degrees Celsius. By following these guidelines, the curing process can be optimized and the materials can reach their maximum strength and durability.
Procedure for Concrete Cube Test
In order to test the strength of concrete, certain steps must be taken. First, the specimen should be removed from the water after a specified curing time and excess water should be wiped off from its surface. Next, the dimensions of the specimen should be measured to the nearest 0.2m. It is important to clean the bearing surface of the testing machine before placing the specimen in the machine. The specimen should be placed in such a way that the load is applied to opposite sides of the cube cast, and should be aligned centrally on the base plate of the machine.
Once the specimen is in place, the movable portion of the machine should be rotated gently by hand so that it touches the top surface of the specimen. The load should then be applied gradually, without any shock, at a continuous rate of 140 kg/cm2/minute until the specimen fails. It is important to record the maximum load and note any unusual features in the type of failure.
It is recommended that a minimum of three specimens be tested at each selected age. If the strength of any specimen varies by more than 15 percent of the average strength, the results of such specimens should be rejected. The crushing strength of concrete can be determined by taking the average of three specimens. It is important to note that the strength requirements of concrete must be met.
Calculations of Compressive Strength
The given information includes the size of a cube, which is 15cm x 15cm x 15cm, and the calculated area of a specimen, which is 225 cm2 based on the mean size. Additionally, the characteristic compressive strength (f ck) at 7 days is also provided.
To determine the expected maximum load, the range must be selected by multiplying the f ck, area, and factor of safety (f.s). However, the range to be selected is not given and needs to be determined based on the specific requirements of the project or experiment.
A similar calculation must also be done for the 28-day compressive strength. The maximum load applied can be determined by multiplying the f ck at 28 days, the area, and the factor of safety. The maximum load will be given in tones and can be converted to Newtons (N) using appropriate conversion factors.
Finally, the compressive strength can be calculated by dividing the maximum load in N by the area in mm2. This will give the compressive strength in N/mm2, which is a common unit used in construction and engineering applications.
Reports of Cube Test
When testing concrete specimens, there are several key pieces of information that should be recorded for accurate analysis. Firstly, it is important to note the identification mark of the specimen, as this will ensure that the correct sample is being evaluated. Additionally, the date of the test should be recorded to provide context for any changes in the properties of the concrete over time.
Another crucial factor to consider is the age of the specimen, as this can impact its strength and other properties. Therefore, it is important to document the age of the concrete at the time of testing. Curing conditions are also a significant factor, as the way in which the concrete was cured can impact its properties. This includes the date of manufacture of the specimen, which can help to identify any issues related to the manufacturing process.
Finally, it is important to examine the appearance of fractured faces of concrete, paying particular attention to any unusual types of fractures. This information can provide valuable insights into the quality and strength of the concrete, and can help to identify any issues that may need to be addressed. Overall, by documenting all of these key factors, concrete testing can be conducted more accurately and effectively, leading to better outcomes for all involved.
Results of Concrete Cube Test
The context provided states two pieces of information related to the compressive strength of concrete cubes. Firstly, it mentions the average compressive strength of the concrete cube at 7 days, measured in N/mm2. Secondly, it provides the average compressive strength of the concrete cube at 28 days, also measured in N/mm2. These are the only pieces of information provided in the context, and therefore, they are rewritten as two separate paragraphs.
Compressive Strength of Concrete at Various Ages
Concrete is a widely used construction material known for its strength and durability. It is composed of cement, aggregates, water, and various additives. One of the unique properties of concrete is that its strength increases with age. The strength of concrete is typically measured in terms of its compressive strength, which is the amount of pressure that it can withstand before it cracks or breaks.
To measure the strength of concrete, it is necessary to wait for a certain period after casting. Typically, the strength of concrete is measured 28 days after casting. This period is known as the standard curing period, and it allows the concrete to gain its full strength. After this period, the strength of concrete continues to increase, albeit at a slower rate.
The strength of concrete at different ages is typically expressed as a percentage of the strength at 28 days after casting. For example, if the strength of concrete at 7 days after casting is 60% of the strength at 28 days after casting, it means that the concrete has achieved 60% of its full strength. This information is important for engineers and builders, as it helps them determine the appropriate time to remove formwork and apply loads to the concrete structure.
In summary, the strength of concrete is an essential factor to consider in construction projects, and it increases with age. The strength is typically measured in terms of compressive strength, and the standard curing period is 28 days after casting. The strength of concrete at different ages is expressed as a percentage of the strength at 28 days after casting, and this information is important for determining the appropriate time to apply loads to the concrete structure.
| Age | Strength percent |
| 1 day | 16% |
| 3 days | 40% |
| 7 days | 65% |
| 14 days | 90% |
| 28 days | 99% |
Compressive Strength of Different Grades of Concrete at 7 and 28 Days
| Grade of Concrete | Minimum compressive strength N/mm2 at 7 days | Specified characteristic compressive strength (N/mm2) at 28 days |
| M15 | 10 | 15 |
| M20 | 13.5 | 20 |
| M25 | 17 | 25 |
| M30 | 20 | 30 |
| M35 | 23.5 | 35 |
| M40 | 27 | 40 |
| M45 | 30 | 45 |
Some Facts on Concrete Strength Test
Why Compressive Strength Test of Concrete is Important?
The concrete cube test is a crucial method to assess the strength of concrete. It provides valuable insight into various characteristics of concrete and enables one to determine whether the concreting process has been executed correctly or not.
The compressive strength of concrete, which is evaluated through this test, is a fundamental property that affects the durability and performance of concrete structures. It reflects the capacity of concrete to resist compressive loads and plays a significant role in determining the design and construction of buildings, bridges, and other infrastructure.
The concrete cube test is considered a reliable method to measure the compressive strength of concrete. It involves casting concrete cubes of standard size and shape, and subjecting them to a compressive force using a hydraulic press. The test results provide a clear picture of the strength of concrete, and enable engineers and construction professionals to make informed decisions regarding the suitability of the concrete for its intended use.
Overall, the concrete cube test is an essential tool for evaluating the quality and strength of concrete. Its results are vital in ensuring the safety and longevity of structures, and in preventing costly and potentially dangerous structural failures.
What is compressive strength of commonly used concrete?
The compressive strength required for general construction typically ranges from 15 megapascals (MPa), equivalent to 2200 pounds per square inch (psi), to 30 MPa, equivalent to 4400 psi. In commercial and industrial structures, higher compressive strengths may be necessary
What is compressive strength after 7 days and 14 days?
Concrete is a widely used construction material known for its strength and durability. The strength of concrete is an essential characteristic that determines its ability to withstand the stresses and loads it will encounter during its lifespan. Typically, the strength of concrete is measured in terms of its compressive strength, which is the maximum compressive load that it can bear without failing.
According to industry standards, the compressive strength of concrete increases with time as it cures and hardens. Generally, the compressive strength achieved by concrete at 7 days is about 65% of the target strength, while at 14 days, it increases to about 90% of the target strength. This means that concrete gains strength rapidly in the first week after being poured, and its strength continues to increase at a slower rate over the next week.
Understanding the compressive strength of concrete is crucial in determining the right time for removing the formwork and applying loads to the structure. Additionally, the compressive strength of concrete is used to ensure that the mix design meets the required strength specifications for the intended application. Therefore, it is essential to monitor the strength gain of concrete over time to ensure that it achieves the desired level of strength for its intended use.
Which test is most suitable for concrete strength?
To evaluate the strength of concrete after a certain amount of time has passed since casting, it is common practice to conduct either a concrete cube test or a concrete cylinder test. These tests are used to determine the compressive strength of the concrete, which is an important factor in determining its overall quality and suitability for a given application. Typically, the tests are carried out at set intervals after the concrete has been cast, such as 7 days, 14 days, or 28 days. By measuring the strength of the concrete at these intervals, engineers and builders can gain a better understanding of how well it will perform over time and in various conditions.
What is the size of concrete cubes used for testing?
The cube test is a commonly used method for determining the compressive strength of concrete. Two types of specimens are used for this test, either cubes of 15cm X 15cm X 15cm or 10cm X 10cm x 10cm. The choice of specimen size depends on the size of aggregate being used in the concrete mix.
In most cases, cubical molds of size 15cm x 15cm x 15cm are used for the cube test. These molds are widely used in various construction projects and provide a reliable and accurate means of measuring the compressive strength of concrete.
The cube test is an important test in the construction industry as it helps ensure that the concrete used in a construction project meets the required standards for strength and durability. The results of the cube test are used to determine the quality of the concrete and to make any necessary adjustments to the concrete mix to improve its strength and durability.
Which machine is used for concrete strength test?
A machine called the compression testing machine is utilized specifically for testing the compressive strength of concrete. This machine is designed to apply a compressive force to a concrete sample until the sample fails, allowing for the determination of the maximum amount of pressure that the concrete can withstand before breaking or crushing. It is an important tool in the construction industry as it helps ensure that the concrete used in structures is of the required strength and durability. By conducting these tests, builders can determine the structural integrity of the concrete and make necessary adjustments to ensure the safety and stability of the overall structure. Therefore, the compression testing machine plays a crucial role in ensuring the quality and safety of concrete-based structures.
What is the rate of loading on compression testing machine?
When conducting a test on a specimen to determine its strength, it is important to apply the load gradually. The recommended rate of loading for this particular test is 140 kg/cm2 per minute. Applying the load at this steady pace ensures that the specimen is not subjected to sudden, extreme forces that could skew the results or damage the equipment.
It is also important to continue applying the load until the specimen fails. This ensures that the full strength of the specimen is accurately determined, allowing for more precise analysis and comparison with other materials.
In summary, when testing the strength of a specimen, a gradual and steady application of load at a rate of 140 kg/cm2 per minute is recommended until the specimen fails. This approach helps ensure accurate results and protects the equipment being used in the testing process.
.
Which ACI Code is use for Concrete Strength Test?
The ASTM C39/C39M is a standard test method provided by the American Society for Testing Materials. This method is used for determining the compressive strength of cylindrical concrete specimens.