Chip and scrub seals are main components of some common combination treatments because they address a major distress that plagues roadways worldwide — cracking. Cracks are like mold. If you don’t take care of the root of the problem, they will come back. Addressing cracks is an important step in restoring and preserving roadways.
The Original Cape Seal: Slurry Seal + Chip Seal
One of the more popular combination treatments is a cape seal. Cape seals have historically included the application of a chip seal followed by a slurry seal. The slurry seal application provides a stronger seal as the emulsion latches onto the chip seal cover aggregate. This keeps the aggregate intact for a longer period of time, allowing for greater protection of the underlying layers. This technique also reduces tire noise — an important feature in urban areas.
Cape Seal 2.0: Scrub Seal + Micro Surfacing
Recently, the term cape seal has expanded to include other combinations such as a scrub seal followed by a micro surfacing treatment. Scrub seals have been proven to provide exceptional benefits both as stand-alone treatments and as part of a combination. The scrub seal is similar to a chip seal except the emulsion contains a rejuvenator, and the addition of a scrub broom pulled behind the emulsion distributor makes it a more suitable application for addressing mass cracking. The mechanical force of the broom heads forces emulsion deeper into cracks and voids for an even longer-lasting seal. The magic of the scrub seal is the broom. It’s like caramel on a sundae; it just seals the deal!
The micro surfacing treatment that follows the scrub seal is suitable for use on surfaces with larger traffic volumes that require greater durability than the slurry seal. Micro surfacing is typically applied using Type II and/or Type III aggregate. The increased durability micro surfacing provides, coupled with the mass crack sealing properties of a scrub seal, allows for increased protection and make for a stronger roadway with exceptional performance.
Want more technical information on cape seals? Visit https://savemyroad.com/treatment-resource-center/cape-seal/.
Can You Really Tell the Difference?
In 2012, the National Center for Asphalt Technology (NCAT) began a study with the goal of informing state agencies on how they can objectively consider the use of pavement preservation treatments. Scrub seals and scrub seal combination treatments were included in their selection of pavement preservation alternatives. During this study, the scrub seal was applied to a few sections of pavement that were part of the half-mile project located on Lee Road 159, a low-traffic area in Alabama. The scrub seals were applied as a stand-alone treatment in some sections and as the first course of a cape seal treatment (scrub seal and micro surfacing) in others. Thus far, results from cracking and subgrade moisture data show the scrub seal and scrub cape seal provide excellent performance when compared to the conventional chip seal and the conventional cape seal. (See Figure 1.)
Figure 1. Latest data on 2012 NCAT study on Lee Road 159 shows percentage of cracking over time of road sections with different treatments applied during the study — single layer chip seal, single layer chip seal with crack sealing, scrub seal and scrub cape seal. Data shows yearly effects of treated vs. untreated roadways in good, fair and poor condition.
In 2015, NCAT took these same treatments and tested them on a section of U.S. 280, a high-traffic roadway. They also added other combinations to be tested in this section including a scrub seal + thinlay combination. So far, there is a similar trend in the resulting road performance (regarding cracking) when compared to the results from the Lee Road 159 project. The benefit of a scrub seal was observed when used in combination with both a micro surface and a thinlay. Both the 2012 and 2015 studies used emulsion supplied by Ergon A&E.
In 2016, NCAT engaged in a research partnership with the Minnesota DOT to expand the scope of preservation research to include cold climates. As part of this effort, it was decided to test the effectiveness of scrub seal as a stand-alone and as a scrub cape treatment on low- and high-traffic roadways in Minnesota (with another company supplying the emulsion). The goal was to compare performance in a colder climate versus the previous tests conducted in hot-weather climates. Aside from some damage from snowplowing, which is prevalent in the area, NCAT noted similar trends in data regarding performance.
When asked about the additional benefits of combination treatments, NCAT’s Assistant Director/Senior Research Engineer Buzz Powell notes that with research the organization has done on combination treatments in general, not just with scrub seal, “We’re seeing that combination treatments tend to perform better than stand-alone emulsion treatments.”
Extra Value in Combos
There is proven benefit in combination treatments that allow agencies to take already remarkable components and bring them together to create one super-performing solution to provide maximum benefit to their roadways. The best part about these types of treatments is that agencies can use more than one tool in the pavement preservation toolbox without spending a lot of money. It’s just a matter of knowing which products best complement each other.
Contact your local salesperson for more information on how cape seals can save your roads and extend their service lives for up to 6-10 years.