Concrete is a popular material in building construction due to its strength and durability. However, before being used, concrete must undergo a series of tests to ensure its quality. One of the most crucial tests is the concrete compressive strength test.
The concrete compressive strength test is a measurement to determine the ability of concrete to withstand compressive loads.
This is important because concrete in building structures will be subjected to significant compressive loads.
So, what exactly is concrete compressive strength? Why is this test so important? Let's find the answers in this article.
What Is the Concrete Compressive Strength Test?
In the construction industry, concrete is a crucial building material. There are several structures that affect its strength and durability, including foundations, columns, beams, and floors.
However, before concrete is deemed suitable for use, its quality must be tested, one of which is through the compressive strength test.
The compressive strength test is a process to determine the level of concrete's ability to withstand compressive loads.
In this test, concrete samples shaped as cubes or cylinders are subjected to pressure from a concrete compressive testing machine to determine the maximum load they can bear before failing.
The amount of compressive force required to break the concrete is what is referred to as the concrete compressive strength.
Why is this test so important? Concrete with high compressive strength can withstand larger loads, making building structures more robust and safe. Concrete compressive strength is one of the primary indicators in assessing the quality of concrete.
This is because various physical and mechanical properties of concrete, such as tensile strength, durability, modulus of elasticity, water resistance, and shear strength, can be determined based on the compressive strength value obtained from this test.
In short, the concrete compressive strength test is a crucial process to ensure that the concrete used in building construction has the best quality, resulting in strong, safe, and durable structures.
Factors Affecting Concrete Compressive Strength
Several factors affect the compressive strength of concrete, and understanding them is essential in construction. Here are some of the key factors that influence concrete compressive strength:
1. Concrete Mix
The concrete mix is one of the essential factors affecting concrete compressive strength. The initial step in making concrete is to pay attention to the properties and proportions of the concrete mix.
Several factors significantly impact the concrete mix, including the type of cement, water-cement ratio, type of aggregate, moisture content, and other additives.
Read also: Advantages and Functions of Reinforced Concrete in Construction
2. Curing Conditions
The next factor affecting concrete compressive strength is curing conditions. Proper curing conditions are vital for maintaining the durability of concrete, even though concrete is known as a very strong construction material.
After the manufacturing process, concrete requires regular maintenance to keep its durability optimal.
3. Cement Quality
The quality of cement is crucial in concrete because it acts as an adhesive and determines compressive strength. Choosing cement that meets the requirements will result in concrete with optimal compressive strength.
How to Test Concrete Compressive Strength
How is the compressive strength of cylindrical concrete calculated? Before contractors market and deliver the concrete to customers, each batch must undergo a testing process known as the concrete compressive strength test. This test ensures that the concrete's strength meets the needs of the planned building structure.
This test is usually performed on fresh concrete shaped as cubes or cylinders representing the concrete mix.
Firstly, contractors should record the weight and size of the concrete to be tested. Next, prepare the concrete compressive strength testing machine. This machine is specifically designed to test concrete strength, so using improper methods or tools is not allowed.
Once the machine is ready, place the concrete in the center of the testing machine. Operate the machine with a constant load increase between 2 kg/cm² and 4 kg/cm² per second.
Conduct the compressive test until the tested concrete fails, and ensure to record all results, including the maximum load, the condition of the concrete during testing, and a picture of the fracture pattern.
This test usually takes place when the concrete is 3 days, 7 days, and 28 days old, with at least two samples tested each time.
Why is the compressive strength test often conducted at 28 days old? The following table shows the increase in concrete compressive strength at various ages and its relationship to the classification of concrete usage:
|
Concrete Age |
Percentage of Concrete Strength |
|
1 day |
16% |
|
3 days |
40% |
|
7 days |
65% |
|
14 days |
90% |
|
28 days |
99% |
Concrete experiences rapid strength gain in the first 2 weeks after casting, reaching 90% in 14 days. At 28 days, the concrete strength reaches 99% and continues to increase during its use.
However, the strength gain after 28 days is not as fast or as significant as the gain during the first 28 days.
Since concrete strength reaches 99% at 28 days, this result is very close to the final strength that will be achieved in 1 or 2 years. Therefore, engineers use the 28-day test results for planning and other design calculations.
Read also: 5 Effective Tips for Concrete Casting
Procedures for Conducting a Concrete Compressive Strength Test
Ensuring the strength of concrete is a critical step in construction. Here is a brief overview of the concrete compressive strength test process:
- Creating a mold: Prepare a cylindrical mold measuring 30 cm (height) and 15 cm (diameter). Coat the mold with a lubricant so the concrete can be easily released.
- Preparing the concrete: Place the concrete mixture into the mold in 3 layers, compacting each layer with 25 strokes. Level the concrete surface and cover the mold. Label the mold with the date and time of manufacture.
- Hardening process: Allow the concrete to dry and harden for 24 hours.
- Testing: Take the concrete cylinder to the laboratory. Place it in the compressor machine and turn it on. The machine will gradually press the concrete until it fails. Record the maximum pressure the concrete withstands.
- Calculation: Calculate the concrete strength using the standard compressive strength formula. Repeat the test on another cylinder from the same batch on different days. Record all test results.
That is the comprehensive review of concrete compressive strength, which is one of the crucial factors in determining the quality and reliability of building structures.
Understanding concrete compressive strength and its influencing factors is essential in selecting the right concrete materials for construction.
Besides compressive strength, choosing high-quality building materials is equally important. Semen Merah Putih offers a solution by providing ready-mix concrete and precast concrete produced using selected and premium-quality raw materials.
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