by Russell V. Timmerman
When an owner decides to construct a new parking lot/roadway or rehabilitate an existing one, it usually requires a significant capital investment. Many important decisions are required along the way for this investment to have its greatest long-term impact. Following are some of the most common mistakes owners make, possibly due to lack of knowledge and experience, budget restrictions, bad advice, or lack of due diligence.
We have asked hundreds of facility managers the question, “Which factor (design, materials, installation, quality control, or maintenance) has the greatest influence on pavement or roof performance?” By a large percentage, design is rated the most important factor. Yet more often than not, we are finding a quality pavement design is being overlooked. Too many people assume a pavement installation is pretty simple and straightforward.
Obtaining pavement construction bids without an in-depth analysis and testing of existing conditions so a quality, site-specific design specification can be provided often results in a significant compromise in the pavement’s service life. Accepting bids based on a generic scope of work may provide a lower initial cost but will result in long-term problems and short-term pavement life. Leaving out seemingly minor items from the design (underdrain, pavement thickness, undercut requirements, etc.) may have a significant impact on the service life of the pavement. Generally, the low bid is low due to omitting one or more critical design factors, and sometimes these omissions lead to costly change orders too.
It does cost money to hire a professional to develop a quality design for bid purposes. When considering all of the factors mentioned above, design is by far the least costly. Since design is considered the most important and least costly component, that makes it the most cost-effective component of any of the factors mentioned.
A high-quality design should result in a new asphalt pavement serviceable for up to 15 years or a new concrete pavement serviceable for up to 25 years, and more if they are properly maintained. Asphalt overlays of existing pavements should be expected to last approximately 10 or more years with preventive maintenance.
Pavement criteria differ with each and every facility; therefore, design parameters will also differ. For example, freeze-thaw cycles and salt applications are a concern in the northern climates. Soil types, traffic loading, drainage, and weather will vary from northern to southern climates. Every design should be site specific, including performing tests such as soil borings when necessary.
Construction Project Management
As mentioned above, a proper design is considered the most cost-effective factor due to its relatively low cost and high importance. However, no matter how good the design, it will not perform properly if it is not installed properly. Therefore, some level of construction oversight provides value to ensure all design parameters are met. One of the benefits of having someone on site full time is that they can be the eyes and ears for protecting the owner’s best interests.
- Amount of undercut required to remove unsuitable base soils.
- Proper mix design and gradation testing.
- Acceptable densities of stone and asphalt.
- Acceptable asphalt content and temperature readings.
- Documentation of material quantities. (Being shorted only 1/4″ of asphalt can reduce the pavement’s life expectancy dramatically. This more than offsets the cost for a dedicated, full-time, on-site professional to protect your best interests.)
- Acceptable air, slump, and compression readings of concrete.
Ensuring a proper pavement design and installation will more than pay for itself in long-term performance and reduce potential problems in the future.