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As a producer, how can I use the recent changes in ASTM standards to use process water in my concrete? Promoting using process water in concrete is a tedious effort. We turned to three experts to answer this important question. The answer below is supplied by Richard S. Szecsy, PhD, PE, vice...
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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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One of our customers wants to cut construction time on a job that will include several concrete retaining walls. They’ve asked us how quickly they can backfill these walls and how much sooner they can do that if they use a high early-strength mix. What should we tell them?
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What are the most effective products to clean and to seal the older type slump block. I’m working on a 1977 vintage slump block home.
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What is the R-value of normal weight concrete made with limestone aggregate? Is it expressed per inch of concrete thickness?
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We are a ready-mixed producer in northern Wisconsin. Several contractors we supply have placed in-floor heating in garage or basement floors. Two of these floors have cracked after turning on the heat. We have been told that this may be due to thermal cracking or shocking. We would like information...
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How thick should concrete be to withstand four hours of temperatures of 2000 degree F without degrading or failing? The concrete barrier likely will be exposed to more than 2000 degrees F. The barrier would be more than 30 feet tall and more than 30 feet long. It will be outdoors and subject to...
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How long must concrete be protected from freezing temperatures, with and without accelerators or admixtures? ASTM’s ready-mixed concrete specification says, “air content of air-entrained concrete when sampled from the transportation unit at the point of discharge” is to be within 1.5% of the...
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We are continually running up against structural engineers who push the limits of the cover for rebar and post-tensioning cables for suspended slabs in concrete structures. We normally never like to work with rebar cover less than 1/4 inch above the aggregate size. We are finishing an underground...
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A local contractor we supply is doing after some renovation work in an upscale area and has asked us about exposed aggregate. Specifically, he wants to know the best way to install the exposed aggregate finish and if there are durability and maintenance issues to be concerned about. What can we can...
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How long must concrete be protected from freezing temperatures, with and without accelerators or admixtures?
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I have a ready-mix customer who is supplying concrete for caissons. The mix design is an ordinary caisson mix (similar to CDOT Class BZ) designed for 6- to 8-inch slump placements. The caissons range from 30 to 60 inches in diameter and are 20 to 25 feet deep. They have not encountered any water...
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I’m a mason working in an area devoid of building codes and cannot afford an engineer. I’m building a 16-foot diameter circular gazebo that will have a concrete floor. I will lay 12-inch half blocks side by side in a circle beginning 9 feet below grade and would like to use this space under the...
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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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A patio looked great on the day we finished installing it. But within two weeks, it had deteriorated into a gray/white color instead of the terracotta/charcoal patio that was visible on the day it was installed. The concrete sealant was applied 24 to 48 hours after the concrete was first laid, and...
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A contractor we supply asked for help in meeting the new energy code requirements for a residential project.
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I've heard a lot about integral water repellents for block. What are they and what is their purpose? Do I need to specify them in the mortar as well as the block?
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We are working with two water sources. One is treated soft water. The other is hard water from a well with a hardness of about 450. Using the same mix, we have to add 6 to 7 liters more of hard water per cubic meter of concrete to obtain the same workability we get with the lesser amount of soft...
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