Q: I have a question regarding the testing procedures in ASTM 109. It specifies that the load rate will be between 12xxx and 22xxx lbs/min. Could you specify an exact load rate that will be used in the competition?
A: Not exactly. The judges will try to maintain a loading rate in the middle of the ASTM specified range. However, throughout the loading history, the rate will fluctuate some within the prescribed range as the specimen "softens" due to microstructure crack development and propagation.
Q: Will there be neoprene padding used in the competition to reduce point loading?
A: No neoprene pads will be used. When producing the cubes, the competition teams should try to produce cubes that have a flat surface to avoid any effects due to an uneven loading of the specimen's surface.
Q: What is the rate of applying the load (inkN/sec) to the samples?
A: See ASTM C109 for the loading rate and testing method. To determine the appropriate testing time, take the ultimate strength in labs and divide by loading rate (lbs/sec) specified in ASTM C109.
Q: Are we allowed to have random metallic particles such as iron fillings in our aggregate?
A: Iron fillings are not allowed. See Section 2b in the rules for allowable materials.
Q: I don't understand at all if the cubes are able to have some entrapped air or entrained air?
A: All concrete or mortar has some entrapped air that is caused naturally during the batching or mixing process so entrapped air will occur naturally and is ok within the framework of this competition. However, the use of any entraining air admixtures is NOT allowed in this competition. If it is determined that an air-entraining admixture has been used, the cube and team will be disqualified.
Q: Does the air content have a maximum or minimum for this competition?
A: There is no air content maximum or minimum, but again, no air-entraining admixtures may be used in this competition.
Q: In the compression test, do you use any cushion or something similar? Or is it that the cube will just be in contact with the compression tester metal? Or will it have any special complement to unify the charge applied over the cube's area?
A: The compression test should conform to ASTM C109. In this test method the cube will be tested directly against the steel platen of the testing machine. To have uniform loading against the platen, it is advisable for the cube to naturally have a uniform smooth flat surface.
Q: I have a question concerning failure rates for the cubes. If they have to totally fail or if a chip on the side is considered a failure?
A: The concrete cubes are tested in accordance with ASTM C109 as indicated in the rules. This ASTM dictates the loading rate for the machine and indicates that the total maximum load shall be used in calculating the compressive strength. This generally means the cubes are tested to total failure beyond yield where they do not resist additional load, and a chip on one side or something similar would not define failure if the cube is able to resist additional load. The judges do have some latitude on this in rare cases such as a safety concern or equipment limitations. For the target strength of this competition, these situations should not occur.
Q: Will the cubes be weighed very closely after being submitted, or will they sit out on a table for some time before being weighed?
A: This is at the judge's discretion and depends on several set up-related factors. Generally, the cubes are weighed and measured after the cubes are submitted and prior to the start of the testing portion of the competition.
Q: Are we allowed to keep the cubes in a curing bath with calcium hydroxide until the time of the break at competition?
A: No. Once they are submitted they cannot still be in a water bath.
Q: Are we allowed to oven dry/cure the cubes after taking them off the casting?
A: Per the rules, curing is to be in accordance with ACI 308, which does not prohibit curing under elevated temperatures.