Concrete cylinder testing, also known as compressive strength testing, is a standard method used to determine the strength of concrete specimens. The American Association of State Highway and Transportation Officials (AASHTO) is an organization that develops standards and specifications for transportation materials and testing.
In the context of AASHTO, concrete cylinder testing refers to the procedure outlined in the AASHTO T 22 standard, titled "Compressive Strength of Cylindrical Concrete Specimens." This standard provides guidelines for testing the compressive strength of concrete cylinders, an important parameter used in assessing the quality and durability of concrete.
Here are the critical steps involved in concrete cylinder testing according to AASHTO:
- Specimen Preparation: Cylindrical concrete specimens are typically cast from fresh concrete samples obtained from the field or laboratory. The AASHTO standard specifies the dimensions of the cylinders, such as diameter and height, which are typically 6 inches by 12 inches (150 mm by 300 mm).
- Curing: After casting, the specimens are cured under specific conditions, usually moist or water-submerged, to promote hydration and develop proper strength. The curing period is typically 28 days, but other durations can also be specified based on project requirements.
- Testing Procedure: At the end of the curing period, the concrete cylinders are subjected to a compressive strength test using a hydraulic testing machine. The AASHTO standard specifies the testing machine requirements, including the capacity and accuracy.
- Load Application: The testing machine applies a gradually increasing load to the concrete cylinder until failure occurs. The load is usually applied at a specified rate, such as 20 to 50 pounds per square inch (psi) per second.
- Failure Criteria: Failure of the concrete cylinder occurs when the applied load causes the specimen to deform significantly or fracture. The failure is usually identified when there is a sudden drop in the load capacity or a visible cracking of the specimen.
- Compressive Strength Calculation: The maximum load sustained by the concrete cylinder is recorded, and the compressive strength is calculated using the cross-sectional area of the specimen. The AASHTO standard provides equations and formulas to calculate the compressive strength based on the dimensions and type of specimen.
Concrete cylinder testing allows engineers and contractors to assess the strength characteristics of concrete, verify compliance with design requirements, and ensure the quality of construction materials. The results obtained from these tests are used for quality control, acceptance of concrete batches, and structural design calculations.
The concrete cylinder testing conducted according to AASHTO standards provides valuable information about the strength of the poured concrete. Here are some key insights that can be obtained from the test:
- Compressive Strength: The primary purpose of concrete cylinder testing is to determine the compressive strength of the concrete. Compressive strength measures the concrete's ability to withstand applied loads or pressure. It indicates how well the concrete will perform under compression and bear the weight and stresses it will encounter in its intended application.
- Quality Assessment: The test helps assess the overall quality of the concrete. It indicates whether the concrete meets the specified strength requirements for its intended use. The compressive strength results are compared against the project specifications or industry standards to evaluate the quality and acceptability of the concrete.
- Structural Performance: The compressive strength of concrete is an essential factor in determining the structural performance of a building or infrastructure element. It influences the load-bearing capacity, durability, and resistance to cracking or failure under various loads. The test results help ensure the concrete has sufficient strength to support the intended structural loads safely.
- Construction Verification: Concrete cylinder testing allows for verification of the concrete placed on-site or in the laboratory. Testing samples from the actual concrete poured ensures that the concrete used in construction meets the required strength standards. This helps in controlling the quality of construction and mitigating potential risks.
- Quality Control: The test results are used for quality control during the construction process. By regularly testing concrete cylinders, contractors and engineers can monitor the strength development of the concrete over time and make adjustments as necessary. This helps identify any issues or deficiencies in the concrete mix or curing procedures and enables timely corrective actions.
- Design Verification: The compressive strength results obtained from the test can be used to validate the design assumptions and calculations. Engineers can compare the actual strength values with the design requirements to ensure that the structural design is appropriate and that the concrete will perform as intended.
Overall, concrete cylinder testing provides crucial information about the strength and quality of the poured concrete. It helps ensure that the concrete meets the necessary standards, performs well under expected loads, and contributes to the safety and durability of the structure.
Concrete cylinder testing specifications vary depending on the specific testing standards or guidelines. In the case of AASHTO, the testing specifications are outlined in the AASHTO T 22 standard, titled "Compressive Strength of Cylindrical Concrete Specimens." Here are some of the key specifications used for testing concrete cylinders according to AASHTO:
- Specimen Dimensions: The AASHTO standard specifies the dimensions of the concrete cylinders. The most commonly used sizes are 6 inches (150 mm) in diameter and 12 inches (300 mm) in height. However, other dimensions may be used based on project requirements or specific standards.
- Sample Preparation: The standard provides guidelines for sampling fresh concrete from the field or laboratory and casting the concrete cylinders. It outlines the procedures for proper compaction, removal of voids, and finishing of the cylinder surfaces.
- Curing Conditions: The AASHTO standard specifies the curing conditions for the concrete cylinders. Typically, moist curing or water submersion is employed to maintain proper moisture levels and promote hydration during the curing period. The standard may specify the duration of curing, such as 28 days or other durations, as required.
- Testing Machine Requirements: The AASHTO standard outlines the requirements for the hydraulic testing machine used for compressive strength testing. It specifies the machine's capacity, accuracy, and compliance with specific criteria, such as ASTM E4, for testing machine verification.
- Loading Rate: The standard may specify the rate at which the load is applied to the concrete cylinder during testing. Commonly, the loading rate ranges from 20 to 50 pounds per square inch (psi) per second.
- Failure Criteria: The AASHTO standard guides on identifying the failure criteria during the test. It describes the signs of failure, such as a sudden drop in load capacity or visible cracking, indicating the test's end.
- Compressive Strength Calculation: The standard provides formulas or equations for calculating the compressive strength of the concrete based on the maximum load sustained by the cylinder and its cross-sectional area.
It's important to note that specific testing specifications may vary depending on regional or project-specific requirements. Therefore, it is advisable to refer to the relevant standards or guidelines, such as the AASHTO T 22 standard, for detailed and accurate information regarding concrete cylinder testing specifications.
