Concrete undergoes various tests to ensure that the material delivered to the job site matches the specifications and quality standards. These tests include both freshly mixed and hardened concrete, with additional tests based on specific organizational requirements such as the Army Corps of Engineers, the Federal Highway Administration, and State departments of transportation.
Tests on the Fresh Concrete
One common test is the slump test, which measures the consistency or flowability of concrete. A low slump may indicate issues with consolidation, while a high slump may result in problems such as mortar loss, formwork pressure, finishing delays, and segregation.
Air content is another important test, which measures the total air content in fresh concrete. However, it does not necessarily reflect the final in-place air content as some air may be lost during transportation, consolidation, placement, and finishing. Common field tests for air content include the pressure meter and volumetric method as per ASTM standards, and the Chace Indicator as per AASHTO procedure.
Unit weight is a measure of the weight of a known volume of fresh concrete, providing insights into its density and compactness.
Compressive strength is tested by pouring concrete cubes and measuring the force required to break them at specified intervals during the hardening process. According to the Building Code Requirements for reinforced concrete (ACI 318), as long as no single test result falls more than 500 psi below the design strength, and the average of three consecutive tests meets or exceeds the design strength, the concrete is considered acceptable. If the strength tests do not meet these criteria, steps must be taken to improve the average strength.
Fresh Concrete Testing
Fresh concrete testing is an important process used to evaluate the workability, consistency, and other properties of freshly mixed concrete before it sets and hardens. The purpose of this testing is to ensure that the concrete will meet the requirements of the job and perform as intended.
Some common tests that are performed on fresh concrete include:
1. Slump Test: This test measures the consistency of the concrete and is used to determine the workability of the mixture.
2. Flow Test: This test is similar to the slump test but is used for very fluid concrete mixes, such as those used in self-leveling floors or pumped concrete.
3. Air Content Test: This test measures the amount of air that is entrained in the concrete, which is important for freeze-thaw durability and workability.
4. Unit Weight Test: This test determines the density of the concrete and is used to calculate the yield of the mix.
5. Temperature Test: This test measures the temperature of the concrete, which is important for predicting the setting time and curing process.
6. Bleeding Test: This test measures the amount of water that rises to the surface of the concrete, which can affect the strength and durability of the finished product.
It is important to perform these tests in accordance with established standards and procedures to ensure accurate and consistent results. The results of these tests can be used to adjust the concrete mix design or to determine if the concrete is suitable for use in the desired application.