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Curb Construction Testing for Quality
Concrete used in curbs should be tested for quality according to the requirements in ASTM C-94 at least once per day or once every 150 cubic yards of concrete delivered to a job site. Since curbs and curb and gutter sections may require less than one cubic foot per foot of length, 150 cubic yards can represent a very long length of curb, and more frequent testing may be desired, especially in hot weather. Tests may include checking for entrained air (ASTM C 231 or C 173), slump (ASTM C 143), temperature (ASTM C 1064), unit weight (ASTM C 138), and compressive strength (ASTM C 39). Concrete should be sampled according to ASTM C 172. The flexural strength tests should not be used for quality control. Slump tests are irrelevant for concrete that is successfully passing through a slipform curb machine. Assuming an approved mixture design produces concrete of a satisfactory quality, the main purpose for performing quality control tests during construction is to confirm uniformity of production. If the consistency of the delivered concrete is satisfactory for efficient placement, the most useful quality control test is the unit weight test. This test is relatively easy and quick to perform and it will quickly detect changes in entrained air content and other variations in quality. Changes in unit weight should be investigated by testing for entrained air. ACI Certified Testing Technicians should perform the field sampling and testing.
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