Alternative Design of Guardrail Posts in Asphalt or Concrete Mowing Pads (405160-14-1)

The objective of this project was to identify alternative backfill materials for the low strength two-sack grout mix currently used to fill the voids around posts in guardrail mow strips. In order to maintain impact performance, a candidate material should have a compressive strength comparable to the grout that was successfully crash tested in a mow strip application. The material should be able to retard vegetation growth around the guardrail posts without restricting its motion in an event. Static laboratory and dynamic bogie impact testing was conducted to evaluate several products for use around guardrail posts encased in a pavement mow strip. A two-sack grout mixture that had been successfully crash tested under a previous research study was used as a baseline reference for acceptable impact performance. The basic of the evaluation was that if a candidate product offered resistance to post movement in the leave out section that was equal to or less than that of the two-sack grout, it could be considered an acceptable alternative without the need for further crash testing. The products that were investigated include a two-part urethane foam, a molded rubber product that has an insert fabricated to match the size of the leave out, a flat recycled rubber mat that rests on top of a leave out backfilled with soil, and a new pop-out wedge conceived under this project.