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Asphalt 101

Producing quality asphalt pavement is much more involved than it looks.  You may not be a paving expert, but being aware of the following information will help a long way toward a successful project.

Key Terms

  •  Hot mix asphalt (HMA): hot asphalt used for permanent paving.
  • Cold mix asphalt: cold asphalt. Used for temporary fixes when hot asphalt is not available (in the winter).
  • Seal coat/seal: thin, sprayed layer(s) of liquid. Think of it as a coat of paint ap­plied to the top of your existing asphalt.
  • Resurface/overlay/top/surface: final sur­face layer placed over existing or a base course of asphalt.   This is hot mix asphalt.
  • Mill: grinding or scraping off the sur­face of the existing asphalt. This is most­ly done to resolve grade problems or to make tie-ins.
  • Crack fill: hot rubberized tar that is used to fill cracks in the existing asphalt to help prevent moisture from penetrating to the subgrade.

Installation of asphalt paving requires many important steps.  Not all bids are the same.  Including these elements in your project are important.• Compaction and Thickness—A general rule of thumb is 4 inches for driveways and 6 inches for car parking lots (after compaction).  To ensure consistent as­phalt thickness, the sub-grade must be fine-graded and compacted prior to plac­ing the asphalt.  Specifications should al­ways refer to

  • Compaction and Thickness—A general rule of thumb is 4 inches for driveways and 6 inches for car parking lots (after compaction).  To ensure consistent as­phalt thickness, the sub-grade must be fine-graded and compacted prior to plac­ing the asphalt.  Specifications should al­ways refer to thickness after compaction because pavement loses approximately 25% of its thickness during compaction.
  • Patching—Broken asphalt should be re­moved and replaced before overlaying with new asphalt.  The best way to repair a weak area is to excavate the old asphalt down to the subgrade, check for solid subgrade (excavate deeper if necessary), and replace with new base asphalt.
  • Overlay—A tack coat should be applied first to bond new asphalt to existing sur­faces and to prevent slippage cracks.

In paving, there is a right way and a wrong way to do a job and an entire spectrum of tradeoffs in between.  The differences among contractors’ prices are frequently due to a judgment about where your budget falls on the spectrum.  A standardized scope of work based on clear goals will help ensure crucial elements are included, the right tradeoffs are made, and you can compare bids “ap­ples-to-apples.”   As you develop the scope of work consider the following:

  • Determine the amount of patching need­ed (square feet or square yards) and the recommended depth of patching and/or overlay.
  • Ask for a square yard price to compare unit prices.
  • Determine if you need milling, and how much is necessary (full surface mill or edge mill).  This affects the grade, which will determine the potential for creating water drainage problems after the job is done.
  • Plan project logistics.  Accomplishing the work in one phase during the day is much less expensive than several phases at night.  Establish traffic control needs.
  • Do not assume that all numbers are presented equally across all propos­als.  For example, the phrases “machine lay 2 inches and then compact” versus “machine lay then roll to a compact­ed thickness of 2 inches.”  Both phrases communicate thickness, but the finished product thickness for the first one will be 1.5 inches after compaction, and 2 inches for the second.

Before making a contractor selection, you should be clear on the following issues:

  • Request references from an industry in­sider or past customers.
  • Scheduling— how long will it take and when will it be started.
  • What change orders may be typical for your type of job.  Change orders should only arise when a customer requests a change in scope or an unforeseen issue is uncovered such as unsuitable subgrade.
  • What weather conditions do they pave in?  A contractor should be willing to delay a project if the weather or tempera­ture is not ideal.

Having a project meet your expectations is often related to the amount of detailed com­munication and thoughtful planning per­formed coupled with a concise scope of work developed before the job begins.  Pav­ing projects are no different, but now that you know the basics, you will be able to be better equipped to achieve your goals.

Simply asking each contractor to bid on what they think needs to be done will set you up for a suboptimal outcome.

 

By Kim Viers Uffner
Kim is the third generation at her family-owned company, A.B. Veirs and Sons, Inc. Her work involves asphalt estimations, marketing, and human resources. Kim is an active member of WMCCAI’s Quorum Editorial Committee.

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