00:11This 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.
00:27With each mold fixture having no more than 3 compartments.
00:31Molds are preferably constructed of hard metal that does not react with the cement grout and are rigid to resist
00:37deflection while the cubes are formed.
00:40At NCDOT, plastic molds are commonly used for field sampling.
00:44However, 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.
00:54If not, samples will lose moisture and may affect the compressive strength results.
00:58To prepare the molds, seal mold walls to the base plate by applying petroleum jelly or light cup grease to
01:04the entire contact surface of the base.
01:13Seal the mold halves by applying the sealant to both contact surfaces.
01:17Use sufficient grease to ensure a small amount is extruded from the joint when the halves are pressed together.
01:22Be sure to remove the excess grease.
01:24Then clamp the base to the molds and wipe off the excess jelly.
01:28This is especially critical for the plastic molds as the base can bow, creating a significant gap for moisture to
01:34escape between the mold halves and the base.
01:42Complete the assembly of the mold and tighten all screws.
01:50Wipe 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.
02:07Wipe away excess material with a cloth, leaving only a slight residue that would leave a fingerprint if touched.
02:21If using brass molds after cleaning sufficiently, follow the same steps of sealing, assembling, and lubricating prior to making the
02:30grout cubes.
02:33Molding of the specimen should begin within two and a half minutes of completion of mixing the grout.
02:38The grout should be added to the molds in two separate layers.
02:41Apply 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
02:51total of 32 times.
02:53Enough 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
03:14of grout and tamp as performed in the first layer.
03:24While tamping, grout will be forced out onto the top of the mold.
03:30Reincorporate 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.
03:53Strike off the top of each mold with the flat side of a trowel at 90 degrees to the length
03:58of the mold.
03:59Next, draw the flat side of the trowel lightly over the cubes and along the length of the mold to
04:04level and smooth the surfaces.
04:05Cut off the grout to create a plain surface flush with the top of the mold by drawing the straight
04:10edge of the trowel in a sawing motion over the top of the mold.
04:14Using a wet rag, wipe off any excess grout from the top of the mold.
04:26When making samples for flowable or fluid grout, follow the same procedures as for plastic grout,
04:32but instead of using the tamper, use a glove finger to puddle each layer a minimum of five times to
04:38consolidate the grout.
05:08Cover the freshly removed.
05:09molded grout with a cover plate if provided with the mold,
05:12or carefully place the mold in a plastic bag.
05:15A wet paper towel or rag should be placed in the bag
05:18to 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
05:27and place the samples in a level and secure location
05:29that includes protection from direct sunlight and freezing
05:32or excessive hot temperatures, such as a cooler,
05:41when placed in the field, ensure that it is placed on a level
05:44surface and away from all construction activity.
05:49Carefully demold the samples after a period of 24 plus or minus 4
05:53hours.
05:55Once removed from the mold, inspect the cubes for any damage.
06:15If the HI-CAM's number is known, write it directly on the cubes.
06:24The cubes can then be placed in a watertight container
06:27and a wet rag or paper towel placed with the cubes
06:30to create a moist environment.
06:38Prior to delivering the sample to the lab,
06:41the HI-CAM's number should be written
06:42on the outside of the container.
06:44If storing the cubes in a plastic bag
06:46did 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
06:56be noted on the sample card.
06:58The sample requirements can also be found on this chart.
07:01Please remember that any early break cubes
07:03should be in addition to these sample requirements.
