Gradation

Transcription

This video demonstrates the Sieve Analysis of Coarse and Fine Aggregates as modified by the North Dakota DOT. The first part of the video demonstrates the coarse gradation and the second half shows the fine. The material used in this video is from a pit run sample. First, after drying to a constant weight, record your original sample weight. Next, thoroughly hand shake the sample to separate the minus 4 and the plus 4 material. This is done to prevent sieve overload on the number 4 screen. Continue doing this until the entire sample has been separated, taking care not to lose any material. Obtain your nest of sieves as used for the specification being tested. These are the common sieves for a plus 4 sample. Introduce the sample into your nest of sieves, again, making sure you do not lose any material. Next, turn on your shaker and run for the desired period of time, normally 10 minutes. At the end of the 10 minute cycle, take the material retained on each sieve and poor into the pan. If any particles remain, carefully dislodge them. Watch for sieve overload, weigh, and record your first sieve. Next, do the same for each sieve after. The bottom pan will have some residual minus 4 material that will need to be added to the material that was hand shaken before introduced into the next of sieves. Dump the material in the bottom pan into your minus 4 material. Weigh the minus 4 material and record. Next, you reduce the fine aggregate sample to a testing weight. Reduce the sample to approximately 300 to 500 grams. It's important to obtain an approximate weight rather than an exact weight. The sample size needed is determined by your nominal maximum aggregate size. A table in the Wash Test procedure lists the minimum size needed. The splitter shown here is for fine material. And it will have at least 12 shoot openings. Pour the sample into the splitter. Then, discard one half of the sample. Then, again, pour the remaining sample into the splitter and repeat until you have the desired sample. This is approximately 500 grams of minus 4 material. You will perform the Wash Test on this sample. After performing the Wash Test, dry the sample to a constant weight. The next part of the procedure is the fine gradation. Let the sample cool and then weigh it. Make sure you do not lose any material during this process. Brush out the drying container thoroughly. Weigh and record the weight of the sample. Take the material and introduce it into your nest of sieves. Your nest of sieves usually consists of the number 8, 16, 30, 50, 100, and 200 sieves in the bottom pan which is your minus 200 material. Next, cover the nest of sieves and put into the shaker. Shake the sieves for 10 minutes. After the designated time, take the sample out of the shaker and clean the sieves. When cleaning the sieves, make sure to use the appropriate tight brush for each sieve size to avoid damaging the mesh. The coarser sieves need different tools compared to the finer sieves which need more delicate brushes. Take your first sieve off of the nest of sieves and poor the material into a suitable container. Then, tap the side of the sieve to dislodge particles that may be stuck inside the mesh. Use an appropriate tool to push the material through. This is mainly on the coarser sieves. Weigh and record the material retained on each sieve. Repeat the process for the remaining sieves. This is the plus 200 material. Tap the side of your screen and clean from the back side of the sieve with a fine brush, taking care to not damage the fine mesh of the sieve. On the finer sieves, there may be some residual material stuck inside the meshes of the sieve that are close to impossible to remove. This is OK as long as the mesh of the screen allows most material to fall through and is not plugged. Weigh and record the material retained on the number 200 sieve. Be careful to not lose any material. Material in the bottom of the nest of sieves is minus 200 material. This material is weighed and recorded. The minus 200 percentage is derived from both the Wash and Sieve Analysis test. Weigh and record this weight. In this case, it's 1.7 grams.