Evaluating the impacts of reducing the number of hot mix asphalt plant testing acceptance criteria on mix variability.
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2012-11-01
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Abstract:The acceptance testing of Hot Mix Asphalt (HMA) conducted at the HMA production facility is an
important portion of the overall acceptance process used by the Connecticut Department of
Transportation (ConnDOT) for paving projects. In 2004, ConnDOT made the decision to implement a
Quality Assurance (QA) approach to improve the quality of the construction of transportation
facilities in the state. Until the 2009 paving season, ConnDOT had over 26 different Quality
Assurance/Quality Control (QA/QC) criteria that HMA producers must meet (within limits) or face
penalties, rejection of material or plant shutdown. In 2009, ConnDOT reduced the number of quality
assurance metrics from 26 to 8 for the 2009 construction season. These eight metrics are: Va
(Voids); VMA (Voids Mineral Agg); Gmm (Max Theoretical Gravity); Pb (Binder); and, four gradation
control points (each mix has four control points that define the mix). The objective of this study was
to statistically analyze HMA quality assurance data collected by ConnDOT from the 2007, 2008, 2009
and 2010 construction seasons to determine what impact the change in specifications had on the
variability and overall quality of the mixes being produced. The results of this study indicate there
is no overall statistically significant decrease in variability due to the 2009 specification changes.
However, there is also no significant increase in variability due to the reduced testing. According to
ConnDOT, these changes in specifications have eliminated costly plant shutdowns, a monetary
savings to producers that will hopefully be passed down to ConnDOT in reduced pavement costs.
Furthermore, the elimination of plant shutdowns will save ConnDOT and the traveling public costly
project delays due to material not passing stringent quality assurance metrics, while not impacting
the quality of pavement being placed.
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