Standard Test on Fresh Concrete: Concrete is tested to ensure that the material that was specified and bought is the same material delivered to the job site. There are a dozen different test methods for freshly mixed concrete and at least another dozen tests for hardened concrete, not including test method unique to organization like the Army Corps of Engineers, the Federal Highway Administration, and State department of transportation.
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Slump, air content, unit weight and compressive strength tests are most common tests.
Slump is a measure of consistency, or relative ability of the concrete to flow. If the concrete can’t flow because the consistency or slump is too low, there are potential problems with proper consolidation. If the concrete won’t stop flowing because the slump is too high, there are potential problems with mortar loss through the formwork, excessive formwork pressure, finishing delays and segregation.
Air content measure the total air content in a sample of fresh concrete, but does not indicate what the final in-place air content will be, because a certain amount of air is lost in transportation Consolidating, placement and finishing. Three field tests are widely specified: the pressure meter and volumetric method are ASTM standards and the Chace Indicator is an AASHTO procedure.
Unit weight measures the weight of a known volume of the fresh concrete.
Compressive strength is testes by pouring cubes of fresh concrete and measuring the force needed to break the concrete cubes at prescribed interval as they harden. According to Building Code Requirements for reinforced concrete (ACI 318) as long as no single test more than 500 psi below the design strength and the average of three consecutive tests equals or exceed the design strength then the concrete is acceptable. If the strength tests don’t meet these criteria, steps must be taken to raise the average.
Standard Test on Fresh Concrete
There are a number of standard tests that can be performed on fresh concrete to assess its properties. These tests include:
- Slump test:Â The slump test is a measure of the workability of concrete. It is performed by filling a standard slump cone with concrete and then lifting the cone vertically. The amount of slump, or the decrease in height of the concrete, is measured. A slump of 20 to 40 mm is considered to be ideal for most concrete applications.
- Air content test:Â The air content test is a measure of the amount of air entrapped in the concrete. Air is intentionally added to concrete to improve its workability and durability. However, too much air can reduce the strength of the concrete. The air content test is performed by injecting a known volume of air into a sample of concrete and then measuring the volume of the air bubbles.
- Unit weight test:Â The unit weight test is a measure of the density of the concrete. It is performed by weighing a known volume of concrete. The unit weight of concrete is important for calculating the amount of concrete required for a project.
- Flow table test:Â The flow table test is a measure of the workability of high- or very high-workability concrete. It is performed by pouring a sample of concrete onto a flat surface and then measuring the distance that the concrete flows under its own weight.
- Vebe test:Â The Vebe test is a measure of the cohesiveness of concrete. It is performed by inserting a needle into a sample of concrete and measuring the time it takes for the needle to penetrate a certain depth. A longer penetration time indicates a more cohesive concrete.
- Temperature test:Â The temperature test is a measure of the temperature of the concrete. The temperature of the concrete is important for ensuring that it cures properly.
These are just a few of the standard tests that can be performed on fresh concrete. The specific tests that are performed will depend on the type of concrete and the application.
The results of these tests can be used to assess the quality of the concrete and to ensure that it meets the requirements of the project.