Study shows Crack Sealing as Pretreatment Improves other Surface Treatments
By Ade Craig
Simply put, crack sealing works.
Few resources impact society more than roads. Roads supply access to the world and are the arteries through which economies pulse. And like arteries transporting oxygenated blood to the body; roads do not last forever but have a time from original construction to terminal condition, or design life. “For a typical highway, we generally design an asphalt pavement for 20 years,” said ADOT Pavement Design Group Manager Paul Burch. “It does not mean the road’s going to fall apart in 20 years.”
Roads are designed to serve for a specific length of time and once constructed deterioration begins. Preventive maintenance requires an early adoption of routine measures to ensure road systems continue to perform to their design life and beyond.
Preventive Treatment Is Not a One and Done Application
Preventive pavement treatments are low-cost maintenance treatments designed to preserve or improve functional condition. Pavement preservation is not a one and done application. Rather, much like preventive healthcare, pavement preservation is a series of treatments applied continually across a pavement’s service life. Multiple pavement preservation treatments are far more cost effective than the “built it and forget it” cost of total reconstruction or rehabilitation.
Pavement preservation treatments include chip seal, slurry seal, micro surfacing, thin hot mix overlays, fog seal, and crack seal. Pavement preservation treatments are generally used to restore pavement surface characteristics. However, the performance and effectiveness of any preservation treatment is dependent on the condition of the existing pavement. Studies show preservation treatments are most effective when applied earlier in a structure’s service life. While there is benefit to preserving older, further degraded roads, preserving early and continually throughout a pavement’s service life is the most cost-effective way to maintain.
First Step, Crack Seal
Cracking is a primary mode of distress in asphalt pavements with approximately 75% of cracks developing into potholes within 3 years if not sealed. According to the National Center for Asphalt Technology (NCAT), “if left untreated, cracks can lead to accelerated deterioration and potholing, further reducing pavement serviceability.” When the right preventive treatment is applied to the right road at the right time, roads can be kept in good condition eliminating the need for costly rehabilitation alternatives later in the pavement’s life when the structure has deteriorated,” NCAT adds.
As soon as the first crack appears, water and debris permeate the pavement structure. Crack sealing should begin early after the first formation of cracks on a road surface.
Cracks are Inevitable, but Not Potholes
Crack sealing is the process of installing crack sealant (specialized material) into a crack for the purpose of preventing the intrusion of water and incompressible materials into the pavement. Crack sealing is the most common pavement preservation approach with the highest-benefit-to-cost ratio. Research demonstrates a dollar spent on early preventive maintenance, such as crack sealing; can delay, or altogether eliminate spending $6 to $14 in future rehabilitation costs. Compared to 75% of unsealed cracks becoming potholes in 3 years, when cracks are sealed early, only 1% will develop into potholes within the same length of time.
Cracks are going to develop as asphalt pavement naturally oxidizes and deteriorates. Before initiating a preventive preservation treatment, it is important to ensure all cracks in the existing pavement are properly sealed. Sealing cracks promptly as part of a pavement preservation program prevents water infiltration, loss of load-carrying capacity and is the most important step in preventing potholes, ultimately ensuring a smooth ride for motorists.
Crack Sealing Provides Immediate Value to Other Surface Treatments
Pavement preservation study proves crack sealing improves performance of other surface treatments.
To answer the question of how much life-extending benefit can be gained from crack sealing-and other preservation treatments, the Minnesota DOT Road Research Project (MNROAD) and NCAT evaluated 25 treatments from 2012-2015 using field performance data of test sections on Lee Road 159, a two-lane road near NCAT.
As shown in the table, sections were divided into three categories (stand alone crack seal/fill, chip seal, and micro surfacing) to allow direct comparisons among pairs of treatment. The control in this study is defined as normal cracking as if no treatment were applied. The results generated in the following sections (L5, L6, L7, L11, and L12) were from the changes in pavement vs. the control.
Beginning with Section L5 where only a crack sealing treatment was applied to the pavement, results showed 100% less cracking than the control group at year one. At year two, this same section developed 75% fewer cracks compared to the control section, which again received no treatment.
Section L6 received a chip seal treatment only. At year one, the pavement experienced 100% less cracking. After the first seasonal cycle as winter turned to spring at approximately 18 months post-treatment, the chip seal had more cracking than the control section. These types of treatments and materials are not able to withstand the anticipated movement of the pavement from summer to winter. In a short time, the treatment lost all value as compared to having done no work at all.
Section L7 reported the amount of cracking after a chip seal with a crack seal pretreatment. At years one and two, 100% less cracking was reported compared to the control. In comparison, the test section that had crack sealing applied as a pretreatment to chip seal surface treatment, performed with 100% effectiveness and had no cracking over the same period and seasonal change. Crack sealing can move with the pavement, preserving the performance of the surface treatment.
By crack sealing as a pretreatment before advancing to a chip seal, the pavement went from 25% more cracking with a chip seal alone to 100% less cracking with the application of a chip seal over a crack seal pretreatment. A small investment in crack sealing yields a large return.
Section L11 reported the amount of cracking after a micro surfacing with a crack sealing pretreatment. At year one, 50% less cracking than the control was reported. At year two, there was 15% less cracking than the control.
Like the previous section, Section L12 reported the amount of cracking after a micro surface course that included a crack sealing pretreatment. At year one, 90% less cracking was reported. At year two, there was 60% less cracking than the control. Crack sealing alone has a significant, immediate, and sustained benefit.
Effects over the study revealed crack sealing reduces the development of interconnected cracking, reduces subgrade moisture levels, and improves surface treatment results when used as a pretreatment.
Crack Seal Early and Often.
It begins as a crack, and an unsealed crack is a problem waiting to happen. Pavement is always moving, expanding, and contracting with temperature changes and traffic loads, and no pavement is immune to cracking. What is proved through numerous studies is that crack sealing is the lowest-cost-with-the-highest-benefit preservation treatment and provides life-extending benefits as either a stand-alone treatment or in combination with other preservation activities like chip sealing and micro surfacing.
Simply put, crack sealing works. Do you have an annual crack sealing program for your pavement?
Ade Craig is a Content Development Writer with Crafco, Inc. For more information, please visit Crafco.com or call (800) 528-8242.