Why is concrete air content important?
The principal reason for entraining air in concrete is to increase resistance to the destructive effects of freezing and thawing and deicing salts. The entrainment of air also increases the workability of the concrete for placement purposes and permits a reduction in the sand and water contents of the mix.
How does air content affect concrete strength?
They increase the freeze-thaw durability of concrete, increase resistance to scaling caused by deicing chemicals, and improve workability. Air entrainment will reduce concrete strength. As a general rule, a 1% increase in the concrete air content will decrease the 28-day compressive strength by about 3 to 5%.
What is the purpose of concrete testing?
Firstly, it’s important to know why: concrete is tested to ensure that the material that was specified and bought is the same material that was delivered to you or the job site.
What is air content of fresh concrete?
Testing tip: A typical air content for concrete with a ¾-inch maximum-size aggregate is about 6%, and specified ranges in air content are typically minus 1 ½% and plus 1 ½% of the target value.
Is air entrained concrete weaker?
Air entrained concrete of the same workability and strength was found to have 5% less solid materials hence of lower weight. This will result in an economy of about 5% in the cost of cement and aggregate.
What are the strengths of concrete?
Usually, the compressive strength of concrete varies from 2500 psi (17 MPa) to 4000 psi (28 MPa) and higher in residential and commercial structures. Several applications also utilize strengths greater than 10,000 psi (70 MPa).
How do you reduce the air content of concrete?
Adding a pumping aid along with an AEA increases air c o n t e n t . Dust on the aggregate decreases air content. Crushed-stone concrete entrains less air than gravel concrete. Diluting AEA with hard water prior to batching decreases air content.
How do you test the strength of concrete?
One of the most common new methods is what is called Rebound Hammer Test. This method required a tool that uses a spring release to drive a plunger-tipped hammer down into the concrete that is being tested. The distance the hammer is rebounded is measured and assigned a score between 10 and 100.