16.5 SPECIFICATIONS
Specifications include description of construction materials, methods, and/or end product. There are
primarily three types of specifications: performance-based or end product–based method specification
and proprietary specification.
There are advantages and disadvantages of different kinds of specifications. For example, a performance-
or end result–based specification could be shorter, but relatively difficult to prepare, and
while it is easy to write a method specification, the results may not correlate well with performance,
and while writing a proprietary specification is relatively easy, it does not allow the use of equal or
better materials, and does not encourage innovations and competition.
An example of method-based specification, for compaction of an HMA pavement, is as follows:
Use two passes with a vibratory roller weighing at least 10 ton. Vibrations per minute must
exceed 1000, and the roller shall not travel faster than 4 miles/h.
For the same purpose, a performance-based specification could be written as follows: compact
the HMA to at least 98% of laboratory density. Most specifications combine aspects of both methodand
performance-based specification.
Contracts for construction of asphalt pavements can be made through the low-bid system, bestbid
system, or negotiated contract. In the low-bid system, generally the lowest bidder is selected.
Although this system provides a fair and rational method of decision, it could lead to cutting
corners. In the best-bid system, more emphasis is placed on the performance and experience of the
contractor. In a negotiated contract, the owner negotiates the work with a specific contractor.
In the construction process, standards and specifications from ASTM and AASHTO are also
followed. Most agencies would prepare a project specification from a list of guideline specifications
from ASTM or AASHTO. Specifications and standards are particularly important with respect to
sampling and testing for quality control and quality assurance.
A good specification must include a description of the following