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What can we tell our contractor-customers who insist on a low water-cement ratio but who then complain the concrete is hard to finish?
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I recently read some papers on the corrosion of concrete in sewer manholes. Apparently, this is not a problem of gasses floating around in the sewer, but an issue of anaerobic bacteria (Thiobacillus) living on the surface of the concrete, creating sulfuric acid, which corrodes the concrete. The...
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I am working on providing material for crane counterweights. What is considered a normal weight loss (in pounds per cubic foot) for concrete from its plastic weight to a normal exposure weight after a month or two? My guess would be in the area of a pound or two per cubic foot.
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As a specialist in industrial floor-hardening products, I am responding to a couple of comments in the "Troubleshooting" column from the October 2002 issue. The comments were in reference to specifying limestone as coarse aggregates in concrete floor slabs. In the last paragraph, the column...
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One question recently posed on Aggregate Research Inc.Æs Industry Forum (www.aggregateresearch.com/forum) drew a number of interesting and important answers that may help you this season. The questioner wrote: ôIÆve noticed that a variation in ambient temperature can have a big effect on the...
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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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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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We were supplying a slab on grade with ordinary 3000-psi concrete when a section of the slab flash set or possibly false set; we are not sure. What is the difference between the two? The contractor asked us if he should retemper the area with water or finish it. What should we have suggested to the...
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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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