Credit: Phil Vandermost
Scrub/sand sealing. Emulsion is applied with a computer rate-controlled distributor truck that drags a hydraulic broom. The broom works the liquid asphalt into cracks, sealing them and allowing a bond to form with the material that’s placed on top (in this case, sand and fine aggregate). The surface is then rolled and compacted and can be returned to traffic in a few hours.
Counties are dealing with rising costs and declining budgets, but the population of New Mexico’s Luna County also rose 200% since 1980. Incredibly, only one of 1,900 center lane miles of road has had to be rehabilitated since then.
Even more incredibly, the road department has saved $15 million to $30 million over 15 years and has the lowest per-lane-mile costs in the state. Using rejuvenating emulsions to extend asset life has worked so well, that for several years up to 25% of maintenance funding can be allocated to converting dirt roads into paved roads.
By 1995 the New Mexico DOT had transferred maintenance on many state routes to the counties. Instead of taking a “worst-first” approach, road superintendent Martin Miller used that new state funding to launch a preservation program that has virtually eliminated the need for rehabilitation and reconstruction. Rather than relying on existing specifications, the department researched and tested a variety of products and strategies, and then designed a program and related specs around those that proved most cost-effective.
The department’s toolbox for managing wear and tear now includes sand seals, chip seals, and rejuvenating fog seals.
Chip-sealing unpaved roads
When Miller joined the department nearly two decades ago, the county’s roads, most of which are unpaved farm-to-market, were five to 15 years old.
Miller’s team learned the Arizona DOT was using Western Emulsions Inc.’s PASS CR (chip retention) emulsion, a polymer-modified asphalt rejuvenating agent and surface sealer designed and formulated for scrub seal and chip seal applications, to perform scrub seal treatments.
Miller’s team found the product to be equally effective for chip sealing directly on dirt roads.
It could be applied directly to the natural base without first requiring a prime coat of cutback emulsion, lowering costs by nearly 50% through reduced staff time and material costs. Constructing an effective wearing course on natural base also lessens the need to blade and recompact after storms while improving both safety and air quality.