By Steven Hoard, Southwest Region Sales Manager, Arcosa Lightweight
During a recent visit to an asphalt chip seal project in Bryan, TX, I was able to witness first-hand the superior retention value of expanded shale, clay, and slate (ESCS) lightweight aggregate versus normal weight sandstone aggregate.
On this county road project, the county used both the ESCS aggregate, and sandstone aggregate on different portions of the road. Immediately after the contractor rolled the road it was open to traffic. It was visually apparent that the ESCS aggregate held in place while the sandstone aggregate lifted immediately under the tire tracks. It was even more apparent as I drove over the road as the ESCS aggregate made little to no noise on the under carriage of the vehicle but, when I hit the normal weight sandstone portion of the road, the rocks hitting the under carriage of the vehicle were extremely loud indicating that that material was not being held in place. The lack of hold demonstrated by the sandstone aggregate can contribute to broken windshields, which can be dangerous for drivers. In addition to broken windshields, the loose aggregates create issues with vehicle traction and stopping.
So, the question is why are ESCS lightweight aggregates superior to normal weight aggregates with retention value? The primary reason for the superior retention value is related to the exposed voids on the surface of ESCS aggregates. These voids enable emulsion to enter these areas, thus creating exceptional bonding to the road surface. The voids also reduce road noise as compared to normal weight aggregates. The almost cubical shape of ESCSI aggregate enables it to lock into the stone matrix for better performance.
ESCS lightweight aggregates are also uniform in size and free of dirt and dust, so when Departments of Transportation or contractors specify ESCS lightweight in contracts, reducing the need for sometimes inferior normal weight aggregates. These can range from dirty, too wet, flat and angular stone as well as gradations on the high and/or low side of a specification.
