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Recently we supplied an integrally colored pea-gravel mix for a job that used textured vertical formwork. The contractor insisted on adding the dissolvable color bags at the jobsite just prior to placement. We dispatched 8-cubic-yard loads in standard 10-cubic-yard rear-discharge mixers. The driver...
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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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Five years ago we supplied the concrete for an elevated slab that was later covered with vinyl composition floor tiles. We recently got a letter from the building owner telling us that the floor tiles were coming loose and that the flooring installer had inspected the problem, measured the pH at...
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We supplied 4x24-foot hollowcore slabs for a building floor that received a 2-inch-thick concrete topping placed by the concrete contractor. Part of the building was left unfinished for later use, and, when it was built out, the owner noticed a crack that was visible on the topping surface but not...
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Of the three methods for measuring air content--pressure, volumetric, and gravimetric--which one is the most reliable?
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At our precast plant, we put the air-entraining agent on the fine aggregates during batching. I've heard that it should be added with the mixing water. Is our procedure incorrect?
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We're thinking of developing a 6-inch-thick precast concrete residential wall system made with lightweight aggregates.
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We were asked by a concrete contractor to add calcium chloride to the concrete we supplied but not show it on the batch ticket. We refused and lost the order. Are there producers who will supply concrete this way?
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I've heard that the two-cone fracture pattern is typical when compressive-strength cylinders are tested. Does that mean any other fracture pattern indicates a testing or concrete problem?
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Last winter our company was asked by the city street department to supply concrete for temporarily patching some large sections of failed pavement during breaks in the cold weather. When the weather warmed up, the city permanently repaired the patches with hot-mix asphalt. We'd like to show that a...
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One of our architectural precast customers wants to remove a thin skin from the surface of narrow bands on cladding panels. He wants a surface effect that's similar to that achieved by light abrasive blasting, but masking off the larger areas that won't lose the skin will be time-consuming. Is...
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We're supplying the concrete for bridge piers on a state DOT project. The specifications set a maximum allowable concrete temperature difference between the center of the piers and their exterior faces. The state requires use of the Schmidt formula to show the calculated temperature difference...
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Our precast plant recently received a shipment of galvanized rebar for a state project. While examining the rebar, our inspector noticed that some bars had a gray coating, a king of mottled appearance. Is the presence of this coating a possible cause for rejection?
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We're supplying integrally colored concrete for a large architectural concrete project. We've supplied similar concrete previously but have always had trouble maintaining color uniformity. What steps can we take at the plant to minimize color variation?
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We supply ready-mixed concrete to residential contractors in the Northeast. During cold weather, our customers order concrete with 2% calcium chloride but then add more flake calcium chloride at the jobsite. Are there any harmful effects of this practice? For instance, if the chloride dosage is too...
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We supplied concrete for a wastewater treatment plant for which the specifications required an entrained air content of 6% ± 1%. An elevated exterior walkway required 12 cubic yards which were delivered in two loads. The testing laboratory inspector performed an air test on the first load and told...
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What can cause an occasional load of concrete to exhibit a retarded set? We may batch out three loads of concrete with good setting times, then have a load that's severely retarded, and go the rest of the day without any other bad loads. The next day, the same thing may happen or a few days may go...
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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?
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