Welcome back to our Fun Fact Friday series on aggregate testing! Today, we discuss the aggregate 200 wash.
Sieve analysis, or gradation testing, is a way to assess the particle size distribution of material. The aggregate material is put through a series of progressively smaller sieves, and the amount “caught” at each sieve size is weighed as a fraction of the material’s whole mass. The aggregate 200 wash is used to remove very fine particles, including salts and other minerals, which are stuck to the larger aggregate pieces, prior to sieving or sorting the entire sample. Washing away the smallest particles also allows the sample to pass through the sieves more readily, without forming clumps or binding up the sieves. This extra weight can skew the results of the sieve analysis by making it seem like there is proportionally more of that particular aggregate size in the mix. When an engineer designs a building, or a roadway, or just about anything using concrete, they specify certain tolerances for the aggregates to be used. Without the aggregate 200 wash, the sample could be rejected as being out of tolerance, when in reality, it just had extra “stuff” stuck to it.
After the aggregate is sampled and the moisture content determined, the sample is weighed. It is then wet washed to remove the “fines” which pass through the number 200 sieve, and weighed again. The difference in weight accounts for the particulate lost during the washing process.
The aggregate remaining in the sieve is transferred to an evaporating dish and dried so that it can be sieved along with the rest of the sample. The entire sample is placed into the top of a stack of ASTM-specified sieves, with the number 200 sieve just above a pan at the bottom of the stack. The tower of sieves is then shaken using a mechanical sieve shaker, moving the aggregate progressively through the sieves. The smallest pieces fall to the bottom, and the largest stay at the top. When the sorting is complete, the mass weight of each sample size increment is measured and recorded, and a grain size distribution curve graph can be created.
Let Encorus sort your aggregate! Call Jeremy Lake at 716.592.3980, ext. 133, or email [email protected].