Cleanliness

In California there are two tests to check the cleanliness of your aggregate materials.  The Sand Equivalent (SE)  test is used on fine aggregates (smaller than #4 sieve) and the Cleanliness Value (CV) test is used on coarse aggregates. 

As I've mentioned before, the SE test determines the ratio of sand vs. clay and silty materials.  The simple way for me to explain the test is: the test material finer than the #4 sieve is placed in a cylinder with a flocculent and agitated to remove the clay-like coatings from the sand particles.  More flocculent solution is added to the cylinder in order to suspend the clay and silts above the sand.  After a time period, the height of the sand and the height of the "clays" are measured and compared to each other as a proportion to each other creating the SE result.  A higher SE value means that there is more sand than clay and silty material and is typically preferable.  A lower SE value means that there is more clay and silty material than sand.  So that you have a frame of reference, the Caltrans concrete sand specification requires a minimum SE value of 71 which means that 71% of the material is made up of sand and 29% is made up of potentially detrimental clays and silts.  Hot Mix Asphalts typically require a minimum SE of 47. 

So why does the SE test matter?  In hot mix asphalt, clay-like and silty fines can coat aggregate particles and prevent proper asphalt binder to aggregate bonding.  That means that your mix could have problems with moisture damage and stripping.  Excess dust or fines, as shown with the SE test can also lead to a lake of stability with rutting or shoving in the mix.  In non-hot mix asphalt products, fines can reduce permeability and drainage.  If the materials are of a clay like material and are of an expansive nature, the material can actually expand when it encounters water.  This can lead to a load of problems but it all differs on what you are using the material for.  If you are using it for pipe bedding, the expansion might put too much pressure on the pipe and burst it.  If you are using it as a subbase, the expansion can push up the road above it and cause cracking in the concrete or asphalt above.

The CV test is a Caltrans test method and there is not an equivalent ASTM test.  It determines the amount of clay-sized material clinging to the coarse aggregate.  The simple way for me to explain the test is: the coarse aggregates are placed in a bucket with water and shaken to knock off any fine material from the rocks.  The water/fines are then filtered through a #200 sieve and then poured into a graduated cylinder with a flocculent.  After 20 min the height of the material in the cylinder is measured and multiplied by 100.  This is the Cleanliness Value.  High values are desirable in a CV test.  A CV of 100 means that there was no coating on the coarse aggregates.  Typically you will see the CV of hot mix asphalt aggregates to range between 80 and 100.

So why does the CV test matter?  Dirty coatings on aggregate surfaces can prevent the asphalt binder from properly adhering to the aggregates, leading to an increased potential for moisture damage.  This is especially true when clayey fines coat the aggregates.  Fine coatings also will degrade faster than the rock itself and cause a loss of structural support and prevents binder-aggregate binder which causes raveling.  In addition to all of that, excess dust can also absorb the asphalt binder making the binder requirement for a mix higher than it needs to be. 

There are times when fines can be desirable in your product but many of the uses for aggregates now adays specify a clean product.  The SE and CV tests are fast and easy ways of determining that.