Posted by Graniterock on Mar 18, 2015
A tender or slow-setting asphalt pavement is defined as one that scuffs under horizontally applied shearing loads after compaction has been completed, such as when power steering turns are made by a stationary vehicle. There are several causes of “tender pavements” including a faulty mix design, low compaction, and liquid asphalt saturation. Although each of these causes contributes to tender pavement, the most common root cause of a tender asphalt pavement is premature application of a preventive maintenance surface treatment (i.e. sealcoat, slurry seal, chip seal).
Most preventive maintenance applications are designed to be applied between the first 18—36 months of a pavements life. By waiting 18—36 months, the new pavement surface can properly cure or “age”, allowing the pavement to harden. Contractors often find themselves in a position of needing to sealcoat their work to satisfy customer demands for a “smooth” pavement. Premature application of a surface treatment is a short-term solution. Although the sealcoat or other surface treatment will help “sell” the project at completion, more often than not, the contractor is called back to the project 6—12 months later to address tender pavement issues.
Factors such as ambient temperature, time of year and type of mix used will all affect the length of the mat cure time. As a rule, most paving is done during the hot months of the year when asphalt pavements soften during the day and stiffen at night. This is an important element in the curing process of the fresh mat. The problem with surface treating a fresh pavement is that the pavement is not allowed to go through its curing process before additional liquid asphalt is applied. The nature of the surface treatment is that it “seals” the top of the pavement. Since (in most cases) the coating is made with emulsified asphalt, applying the surface treatment early essentially saturates the mat with liquid asphalt and then seals it in. Therefore a pavement that may have not been tender at the time the surface application was applied has the potential of becoming a tender pavement. If this happens during the hot time of the year, the pavement gets soft and static loads such as radial tires will mar the surface of the pavement.
When a cosmetic problem occurs on a paving job, it is best to deal with it up front. First, explain to the owner that the pavement investment is in the whole mat and not just the top 1/8”. Second, it is important to explain that pavements go through a curing stage where they may actually soften before they finish curing. Third, never apply a surface treatment to a fresh pavement even if the customer insists. In fact, it is best to wait 18—36 months before applying a surface treatment. Finally, there is a terrific booklet available, entitled “Your New Driveway” from Asphalt Press Industries (800-728-3778; asphaltpress.com) that can be left with the customer and helps to explain curing and maintenance of a Hot Mix Asphalt pavement.
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