CGN 3501 Lab 2(Lab Manual)

CGN 3501 Lab 2(Lab Manual) - Laboratory Exercise #2...

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18 Laboratory Exercise #2 Preparation and Evaluation of a Concrete Mixture Introduction: When making Portland cement concrete, there are two sets of criteria that must be considered: i) Short-term requirements while the concrete is still in the plastic state ( fresh concrete), generally lumped together under the term workability . ii) Long-term requirements of the hardened concrete such as strength, durability and volume stability. The most important parameters for both sets of requirements are the total water content of the mix and the water/cement (W/C) ratio. The workability of the concrete is primarily a function of the total water content, increasing as the water content increases. If, as is commonly (though incorrectly) done, the water content is increased to improve workability without a proportional increase in the cement content, the W/C ratio will also increase, resulting in a decrease in both strength and durability. The ultimate strength of properly cured concrete is almost entirely a function of the W/C ratio since it is the W/C ratio that determines the porosity of the concrete. Purpose: This laboratory exercise will be broken into two separate components. The first part involves concrete mixing and subsequent evaluation of the fresh concrete properties. The second part will examine hardened concrete properties. The purpose of this laboratory exercise is to introduce the student to proper concrete mixing procedures, the evaluation of fresh concrete properties and the determination of hardened concrete properties. An emphasis will be placed on the W/C ratio and its effect on concrete strength.
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19 Part A : Fresh Concrete Properties Concrete Mixing 1) Prepare 20 - 4" x 8" cylinders molds by placing a small piece of tape over the hole in the bottom and applying a light coating of form release agent. (Hint: though only the inside surface actually requires form oil, cleaning of the molds is much easier if the outer surface is oiled as well) 2) Weigh out the following quantities of materials for the mix: Cement 24.9 kg Water 9.9 kg (W/C = 0.40) Fine Aggregate 49.7 kg Coarse Aggregate 74.6 kg 3) Rinse the mixer with water. Drain excessive water from the mixer after rinsing. Place all of the coarse aggregate and cement in the mixer and run for 30 seconds. Stop the mixer and add the fine aggregate. Run the mixer for another 30 seconds. Stop the mixer and add the water. Turn the mixer on and allow it to run for 3 minutes, followed by a 3 minute rest period. Turn the mixer back on for a final 2 minute mixing period. 4) After mixing is complete, shut the mixer off. Measure the slump, unit weight and air content of the
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This note was uploaded on 05/26/2011 for the course CGN 3501 taught by Professor Mang during the Fall '10 term at University of Florida.

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CGN 3501 Lab 2(Lab Manual) - Laboratory Exercise #2...

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