00:00This video will demonstrate the proper procedures for making grout cubes for compression strength testing on NCDOT projects.
00:19AASHTO T106 is a specification that governs how grout samples are made.
00:24Grout cube specimens are made in 2-inch cube molds.
00:28With each mold fixture having no more than three compartments.
00:32Molds are preferably constructed of hard metal that does not react with the cement grout and are rigid to resist deflection while the cubes are formed.
00:40At NCDOT, plastic molds are commonly used for field sampling.
00:45However, they are more prone to deflection and thus require careful use to ensure quality cubes are made.
00:51Prepare the molds correctly to ensure leak thickness.
00:55If not, samples will lose moisture and may affect the compressive strength results.
00:59To prepare the molds, seal mold walls to the base plate by applying petroleum jelly or light cup grease to the entire contact surface of the base.
01:14Seal the mold halves by applying the sealant to both contact surfaces.
01:18Use sufficient grease to ensure a small amount is extruded from the joint when the halves are pressed together.
01:23Be sure to remove the excess grease.
01:25Then clamp the base to the molds and wipe off the excess jelly.
01:29This is especially critical for the plastic molds as the base can bow, creating a significant gap for moisture to escape between the mold halves and the base.
01:42Complete the assembly of the mold and tighten all screws.
01:51Wipe the inside walls and corners, being careful to remove any excess grease.
02:01Next, spray the mold surfaces with a release agent or apply oil or grease using an impregnated cloth.
02:08Wipe away excess material with a cloth, leaving only a slight residue that would leave a fingerprint if touched.
02:15If using brass molds after cleaning sufficiently, follow the same steps of sealing, assembling, and lubricating prior to making the grout cubes.
02:34Molding of the specimen should begin within two and a half minutes of completion of mixing the grout.
02:39The grout should be added to the molds in two separate layers.
02:42Apply the first layer approximately half full in each of the cube compartments.
02:46For plastic grout, tamp the grout in each compartment eight times over four rounds, following the pattern shown for a total of 32 times.
02:54Enough pressure should be applied while tamping to ensure consolidation of the first layer.
03:08Once the first layer of grout has been tamped in each mold compartment, fill each mold with the top layer of grout and tamp as performed in the first layer.
03:25While tamping, grout will be forced out onto the top of the mold.
03:29Reincorporate this grout into the second layer using the tamper or a glove finger after each round of tamping.
03:35Once tamping has been completed, the grout should slightly overfill the molds.
03:40Strike off the top of each mold with the flat side of a trowel at 90 degrees to the length of the mold.
03:58Next, draw the flat side of the trowel lightly over the cubes and along the length of the mold to level and smooth the surfaces.
04:05Cut off the grout to create a plain surface plushed with the top of the mold by drawing the straight edge of the trowel in a sawing motion over the top of the mold.
04:13Using a wet rag, wipe off any excess grout from the top of the mold.
04:17When making samples for flowable or fluid grout, follow the same procedures as for plastic grout, but instead of using the tamper, use a glove finger to puddle each layer a minimum of five times to consolidate the grout.
04:39Cover the crout.
05:08Cover the freshly molded grout with a cover plate if provided with the mold, or carefully place the mold in a plastic bag.
05:15A wet paper towel or rag should be placed in the bag to create a moist, curing environment.
05:20A wet rag can also be placed directly over the sample.
05:25Tie the bag to help retain moisture and place the samples in a level and secure location that includes protection from direct sunlight and freezing or excessive hot temperatures, such as a cooler.
05:38When placed in the field, ensure that it is placed on a level surface and away from all construction activity.
05:49Carefully demold the samples after a period of 24 plus or minus four hours.
05:55Once removed from the mold, inspect the cubes for any damage.
06:16If the HICAM's number is known, write it directly on the cubes.
06:23The cubes can then be placed in a watertight container and a wet rag or paper towel placed with the cubes to create a moist environment.
06:38Prior to delivering the sample to the lab, the HICAM's number should be written on the outside of the container.
06:44If storing the cubes in a plastic bag do not fill with water as this can burst and leak.
06:49The 2018 specifications created five categories of grout.
06:53It is critical that the type of grout being sampled be noted on the sample card.
06:58The sample requirements can also be found on this chart.
07:02Please remember that any early break cubes should be in addition to these sample requirements.
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