concrete - Executive Summary TO: Grace Hsuan FROM: SUBJECT:...

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Executive Summary TO: Grace Hsuan FROM: SUBJECT: Portland Cement Concrete DATE: March 7, 2008 Per your request, I have analyzed the data for various concrete mix designs. The concrete has a unit weight around 150 psi and about a 3% air content. The design with Type III cement, w/c value of 0.34, round aggregate, and HRWR addition had the highest strengths in compression, splitting and flexure (7523.43, 541.834, and 43051 psi respectively). However, on average, the concretes with the Type I cement performed better than the Type III cement concretes, with exception of the flexure test. This is more likely a result of human error, since some of the type III cement concretes had very low strength values that did not make sense. In all cases the flexure test resulted in the greatest strengths and splitting test were most brittle. This is a result of concrete being brittle in tension. Type I cement concrete performed better in 21-days. Type III cement concrete performed better in the 7 and 14-day test because of its early strength. Depending on the amount of time you have, I would recommend Type III cement with a lower w/c ratio, round aggregate, and the use of HRWR. If you have more time for the concrete to set I would use Type I cement as well as curing in a dry room.
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Description of Test Procedures: #Co-1 Mixing 1. Pre-moisten all concrete mixing tools and pans. Remove any excess moisture. 2. Using the pre-prepared mix designs, weigh out enough components to make 0.35 cubic feet of concrete for each mix type. See attachment for mix designs. 3. Place cement and fine aggregate in the mixing pan. Dry mix by hand until a uniform mixture is achieved. Add the coarse aggregate and dry mix again until a uniform mixture is achieved. Form a well in the center of the dry mixture and pour half of the water into the formed well. Mix by hand until the moisture is uniformly distributed throughout the mix. Add the remaining water and thoroughly mix until the fresh concrete has reached a uniform consistency (3 to 5 minutes). Occasionally scrape the sides and bottom of the pan with a trowel to mix in segregated fines. If necessary, add HRWR and remix. Manufacturing Cylinders 1. Moisten tamping rod. Remove excess moisture. 2. Fill the mold with concrete to a third of the volume and stroke through the fresh mix with 25 strokes of the tamping rod, distributing the strokes across the cross-section of the layer. Fill the mold to two thirds of the volume and rod 25 times through the depth of the second layer. Fill the mold to overflowing and rod the layer 25 times. 3. Strike off any excess concrete from the top with a screening motion of the tamping rod. Add extra concrete if necessary to fill the mold. Label each mold with the mix design and date of cast. 4. For each mix place nine of the filled molds in the moist room and keep the remaining
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concrete - Executive Summary TO: Grace Hsuan FROM: SUBJECT:...

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