Pressure Meter Test Pdf4/20/2021
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Pressure Meter Test Upgrade Your BrowserSignificance and Use of ASTM C231 This tests purpose is to get the air content of a sample of concrete using a pressure meter. In the meter you have a known volume of air at a known pressure in a sealed air pot with an unknown volume of air being contained inside the sample of wet concrete. You set it to the percentage of air (your initial pressure) where the pressure is equalized inside the chamber, fill it with concrete and water so that the only air left is the air inside the concrete, and then release the pressure inside of the air chamber to get your apparent air content. The actual air content is found by subtracting the aggregate correction factor, which you can calculate using batch information and a test that is expanded on below, from the apparent air content. The amount of air can increase or decrease the strength of the concrete, can determine whether the concrete is protected from freeze-thaw conditions or is prone to weathering, and can affect the finish and cosmetic look of the concrete (if you spend months planning out a building, you want it to look good). For every percent of entrained air (air that is added to the mix and does not occur naturally in the concrete), the strength of the concrete goes down about 200-300 psi. Check with whoevers in charge at the site to see the air content they need in their specifications and notify them if the results come out unusually high or low. This method is only used for regular weight concrete that has relatively dense aggregate. Lightweight concrete is typically done with the volumetric method (the infamous rollermeter) because the aggregate is too porous and the test results will be thrown off with so much entrapped air. Also, this test should not be performed on any concrete with aggregate larger than 2. Air Content Test Equipment A clean, working pressure meter, complete with gauge and bowl (see calibration for more specifics). Must have a smooth hemispherical tip and be between 4 and 24 inches longer than the measuring bowl. Fun fact: its typically the same thing you would use to suck snot out of a babys nose. Note that concrete stuck to the inside of the chamber can be dissolved with vinegar or a special liquid called backset if you come back from the field and there is some concrete you couldnt remove. The gauge must be pumped to an initial pressure, which is beyond the zero mark. ASTM C231 Procedure Wipe down the inside and rim of the measuring bowl and the cover with a wet rag to ensure that the pressure meter seals correctly when it is closed. Make sure you are doing the test on a level surface away from moving vehicles. You will put in 3 layers of equal volume, and use your tamping rod to strike 25 blows through each layer of concrete. Space out your blows over the surface of each layer, and know that each blow should penetrate the previous layer by about an inch. On the third layer you will want the concrete to be slightly above the rim of the bowl. After each layer is done, strike it 10-15 times with a mallet to get rid of air bubbles that could overinflate your air content value. Move it towards you while doing the sawing motion, then away, until there is a smooth surface on top of the bowl at the level of the rim. Make sure you have an air tight seal or the results of your test will be invalid.
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