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I have an answer for the definition of a C-4 mix (ôDesign Specs for a C-4 Wall,ö February 2002. IÆm working with a concrete contractor who is pouring C-4 for his footings in the morning, setting wall forms, and pouring them with C-4 that same day in winter conditions. What is your opinion of this...
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What is the highest percentage of fly ash that can be used in ready-mixed concrete? Is durability the most important issue in determining the limit?
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I have a further question regarding the rounding of compressive strength results (ôHow Precisely Should Labs Round off Compressive Strength Results?ö April, page 26).At our lab, we test 4x8-inch and 6x8-inch concrete cylinders for compressive strength, and we round to the nearest 10 psi according...
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We recently supplied a house slab where the bleedwater had a greenish tint. We discovered that the water retention pond we used for water collection had green algae that had formed on the surface and was used for concrete production. The concrete met and gained strength normally, however. Is there...
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A customer has asked us to include fibers in the mix design for a water retention tank. The idea is that the fibers will reduce the permeability of the concrete. Is that true?
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A testing firm employee says concrete should be rejected if the slump exceeds the maximum allowable value by as little as 1/4 inch. Is there any published information to help us argue our case?
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We're supplying concrete for a parking deck, to be placed by boom pump. The required air content is 4.5% to 7.5%, and, to account for air lost during pumping, specifications require the test lab to perform air-content tests on concrete sampled from the pump discharge hose. We prefer testing for air...
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We have our plants inspected and certified in accordance with the checklist in Section 3 of the National Ready Mixed Concrete Association's Quality Control Manual. This certification includes truck mixer inspection to ensure that there's no appreciable accumulation of hardened concrete in the drum...
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Are there any simple guidelines for use when we get low-strength test results? The low tests seem to make owners especially nervous, and we'd like to have an authoritative document that lays out a course of action following the report of a low test.
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When we change from one cement brand to another, we often need to adjust the dosage of our air-entraining admixture. Sometimes a new shipment of cement from the same source also requires dosage changes. Is this normal, or are we doing something wrong?