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C0191_18a_14

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Quickly form the cement paste-- prepared as described in the section on preparation of cement paste-- into a ball with gloved hands, and toss six times, from one hand to the other, maintaining the hands about 150 millimeters-- or 6 inches-- apart. Press the ball, resting in the palm of the hand, into the larger end of the conical ring-- as shown in Figure A1.1 of the written standard-- held in the other hand, completely filling the ring with paste. Remove the excess at the larger end by a single movement of the palm of the hand. Place the ring on its larger end onto the non-absorptive plate, and slice off the excess paste at the smaller end of the top of the ring by a single oblique stroke of the trowel, held at a slight angle with the top of the ring. Smooth the top of the specimen, if necessary, with one or two light touches of the pointed end of the trowel. During the operation of cutting and smoothing, take care not to compress the paste. Immediately after molding, place the test specimen in the moist cabinet or moist room, and allow it to remain there, except when penetration measurements are being made. The specimen shall remain in the conical mold, supported by the non-absorptive plate, throughout the test period. Allow the time of setting specimen to remain in the moist cabinet or moist room for 30 minutes after molding without being disturbed. Determine the penetration of the 1-millimeter needle at this time, and every 15 minutes thereafter, every 10 minutes for Type III cements, until a penetration of 25 millimeters or less is obtained. Perform the test by lowering the needle of the rod until it rests on the surface of the cement paste. Tighten the set screw, and set the indicator at the upper end of the scale, or take an initial reading. Release the rod by quickly releasing the set screw, and allow the needle to settle for 30 seconds. Then take the reading to determine the penetration. At the option of the tester, if the paste is obviously quite soft on the early readings, retard the fall of the rod to avoid bending the 1-millimeter needle. But when the actual penetration measurements to determine time of setting are made, release the rod only by the set screw. Make each penetration test at least 5 millimeters away from any previous penetration, and at least 10 millimeters away from the inner side of the mold. Record the results of all penetration tests, and, by interpolation, determine the time when a penetration of 25 millimeters is obtained. The elapsed time between the initial contact of cement and water and the penetration of 25 millimeters is the Vicat time of setting, or Vicat initial time of setting. Determine the Vicat final time of setting endpoint to be the first penetration measurement that does not mark the specimen surface with a complete circular impression. Verify final set by performing two additional penetration measurements on different areas of the specimen surface. Obtain verification measurements within 90 seconds of the first final set measurement. The elapsed time between the initial contact of cement and water, and the endpoint determination above is the Vicat final time of setting. Keep all the apparatus free from vibration during the penetration test. Keep the 1-millimeter needle straight and clean. The needle must be kept clean to prevent cement from adhering to the sides of the needle and decreasing penetration, and to prevent the cement from adhering to the point and increasing penetration.

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Duration: 3 minutes and 45 seconds
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Language: English
License: Dotsub - Standard License
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Views: 5
Posted by: abuckmaster on Aug 7, 2019

C0191_18a_14

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