Engineers have often speculated whether prime coats are a cost-effective element of pavement construction, because some pavements constructed without a prime coat have provided satisfactory performance. However, there have also been failures due to the omission of the prime coat. Undoubtedly, the application of a prime coat reduces the risk of premature failure resulting from imperfections that may occur in the base, which are very costly to repair.
After a large study of Texas DOT projects, Vignarajah and Senadheera (2007) concluded that priming the base is one of the most critical elements in surface treatment construction.
The South Carolina Division of the FHWA sponsored a research program for improving the design and construction specifications of surface treatments for secondary roads in South Carolina. Field trial sections were constructed to evaluate surface treatment design as well as several variations in materials and construction procedures. The construction variables were selected to determine the effect of prime coats. The investigators concluded that a prime should be applied prior to all surface treatments to avoid delamination.
The primary driver of cost will be priming method chosen. Using a SS or CSS emulsion will be less expensive per gallon but will have some offsetting manpower requirements to blade the top layer, spay and, re-compact. If the spray method is chosen, cutbacks and specialty prime emulsions will be more expensive per gallon but will be less manpower intensive.
Prime coats are often deleted if no wet weather is anticipated and the base can be covered within seven days.
Prime coat may also not be necessary if the HMA is greater than 100mm or 4 inches thick.