Polished Aggregate

Polished aggregate is typically due to aggregates that are softer and aren’t resistant to abrasion. River rock is more susceptible to abrasion, especially compared to a quarry or basalt material. 

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

Problem

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 softer or susceptible to abrasion or subject to excessive studded tire wear.

Repair

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.