Polished Aggregate

Two adjacent SMA pavements at the NCAT Test Track near Auburn, AL.  The pavement on the right uses river rock, which is more susceptible to abrasion, as its aggregate and is showing some signs of aggregate polishing. 

Areas of HMA pavement where the portion of aggregate extending above the asphalt binder is either very small or there are no rough or angular aggregate particles.

This close-up picture of a road surface shows aggregate wear after about 5 years of wear.  Washington generally has high quality aggregate that rarely suffers from excessive polishing.  Notice the aggregate still appears rough.


Decreased skid resistance

Possible Causes

Repeated traffic applications.  Generally, as a pavement ages the protruding rough, angular particles become polished.  This can occur quicker if the aggregate is susceptible to abrasion or subject to excessive studded tire wear.


Micro-milling of the pavement can restore or enhance skid resistance.  A thin lift overlay with a 3/8″ minus hot mix asphalt or a thicker overlay with 1/2″ minus HMA will provide a new, highly skid resistant surface, while also adding strength to the pavement structure.  Some improvement may also be achieved via application of a skid-resistant/ aggregate embedded slurry seal or by applying a bituminous surface treatment (BST) to the existing surface.