Early in the semester you created two sets of concrete cylinders. You tested one of those sets the following week for ultimate strength. The second set will be tested during this period. The results of the tests for each set will allow you to make qualitative conclusions concerning the role that curing plays in concrete strength. The procedural instructions are duplicated below. Be certain that the spacing between the supports is identical to that of the first set of cylinders. An outline for the report is also provided at the end.
Time appointments for each group have been given. Please be on time! The group after you will want to begin promptly.
Procedure:
Place the two 3-prong extension clamps on laboratory stands using the adjustable chucks, about 40 cm above the surface of the table. Open the jaws of the clamps completely and rotate them such that the single prong of the jaw is down. Place the stands such that the prongs are 10.0 cm apart and at the same height. The jaws will provide the end supports for the concrete cylinders. Place a foam mat below the apparatus. This will minimize secondary fracturing when the cylinders fall.
Choose one set of the four cylinders of varying mixture ratios and carefully unwrapped one of the cylinders. Find the mass of the cylinder, measure the length, and measure the diameter at 5 locations along its length. Record this data along with the mixture ratio information and a brief description of the cylinder. The description should include observations about the texture and uniformity, as well as notations of any voids or other imperfections.
Place the cylinder symmetrically on the jaws and mark the center with a pencil. Place a string loop around the cylinder at the center and hang the mass hanger from the loop. Gently add masses to the hanger in 20 gm intervals until the cylinder fractures. Record the total mass (including the hanger mass) at which the cylinder fractured. Inspect the cylinder at the break. Record your observations, including information as to where along the cylinder the fractured occurred and whether or not there were voids along the fracture cross section.
Repeat the procedure with the remaining three cylinders. Keep all data in a neat table format. You must keep this information until the experiment is completed later in the semester, when the same tests will be performed on the second set of cylinders.
Final Report
Create a table for the data. Organize the rows of the table such that the same-mixture cylinders are next to one another. The columns of the table should be as follows:
In the report, state the distance between the supports used for the test. State your qualitative conclusions about the effect that the mixture ratios and the curing time had upon the stength of the cylinders. Be sure to take into account the descriptions you have recorded and justify your conclusions.
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