For Quality Hot mix, Start Early
For quality mix, there are many items that should be evaluated/completed before any mix ever hits the ground. Below are a number of best practices that, if utilized, will ensure that the hot mix placed has the best opportunity to achieve the desired quality.
For overlays, the plans should address any type of surface preparation that is needed. Large cracks, for example, may need to be cleaned and sealed before mix placement; assurance that these crack seals are sufficiently cured before mix is placed is of the utmost importance to prevent reflection into the surface. Major rutting in the existing roadway—which should be addressed prior to mix placement—could present a problem and could mirror through the surface mat. Minor rutting in existing surfaces could affect quantities on the project (such as thicknesses and yields) and should be factored in ahead of time. Edges are another area where minor work before the mix is laid could yield major benefits; this could be as minor as blading off grass, or could potentially include placing some material (one-foot wide or so) ahead of the mix placement in order to provide a consistent section to overlay. This practice will keep the mix from breaking off prematurely at these locations.
Ensuring that all parties involved are on the same page from day one is an additional method that helps to secure a quality hot mix pavement. There will probably be some discussion regarding hot mix placement during the pre-construction meeting, but, as the expression goes, “the devil's in the details,” and those details should be resolved during the pre-pave meeting. This meeting, held before hot mix operations begin, should include all of the day-to-day team members (owner, contractor, hot mix provider, CEI firm, and testing firm). During this meeting the contractor should provide their Quality Control Plan and hot mix designs, along with material test results, including Hamburg results. Items that should be discussed include target discharge temperature, warm mix (if allowed), and discharge temperature. Plans should be reviewed to ensure everyone is familiar with the typical section as well as cross slopes in the contract. Pavement thickness, targets for yields, and joint placements should also be reviewed. Because a good bond between the hot mix layer and the underlying layer is critical, a discussion on whether a tack coat will be applied, the rate, and the type to be used will determine how this bond will be established. Adverse weather on a hot mix project will typically happen when least expected, and a plan to address how this will be handled ahead of time will simplify those decisions. Testing protocols such as binder sampling, longitudinal joint testing, test reporting for production and placement, and pay factors will need to be discussed and planned for. Determining lot sizes and personnel who will be adjusting and approving JMF changes, along with a time and date for the trial batch, will also need to be determined. Finally, ensure everyone involved in the production, placement, and acceptance share their contact information; this will help establish good lines of communication once the hot mix placement begins.
For a great hot mix project, planning is essential. A successful project is the result of a lot of little things getting daily attention and a team following through with action on items discussed in the planning stages.