VAA Virginia Asphalt Fall/Winter 2020

20 FALL/WINTER 2020 New Carrots Popping Up In late 2011, then VDOT Chief Engineer Mal Kerley established the Asphalt Quality Task Force. This task force was charged with developing what the Chief Engineer described as “…A simple, workable contracting mechanism that would help encourage quality.” This simple charge by Kerley led to various ideas and approaches to encouraging quality. By 2015, VDOT Chief Engineer GarrettMoore laid out three measures to promote quality and work timeliness. The first was related to the installation of perma- nent pavement markings onmaintenance projects. While standard specifications would allow up to 30-days from completion of paving to install the permanent markings, Mr. Moore felt that having the markings applied sooner would substantially increase safety. To encourage this, Mr. Moore approved bonus language that would reward contractors who installed final markings within 14 or 21 days, depending on paving material (i.e. asphalt concrete or surface treatment). At the time, the pavement marking industry’s capacity was stretched thin, and the potential bonus was primarily designed to encourage new companies to enter the business or have existing companies expand. From the outset, this provision was given a 3-year active timeframe and then sunset. In the end, a few new companies started working in Virginia, and existing pavement marking contractors were able to increase staff and equipment. Overall, the carrot provided the desired result. Along with the pavement marking bonus, Chief Engineer Moore approved the inclusion of asphalt density bonuses and asphalt mix consistency bonuses on pilot projects for 2016. While VDOT, VTRC, and VAAworked together to improve the performance of asphalt mixes through changes in gradations, volumetrics, and laboratory design compac- tion, Moore understood the value of consis- tent mixes that were properly compacted in the field. For the first time, VDOT included a 5% bonus for proper mix compaction and consistency along with a 5% bonus for tight control of the liquid AC during production. For pilot projects with these specifications, contractors would receive a bonus when the average density as measured by cores exceeded the minimum requirements, and at least 80% of the sub lots in a lot had a density above the minimum requirement. The addition of density bonus payments changed howmany contractors approached a project. Contractors reported that they were more proactive in requesting patching before paving, pointing out concerns with scabbing after milling, using materials transfer vehicles, and being more attentive to weather forecasts and scheduling basic paving activities. While past approaches may have been good enough to achieve 100% payment, the “carrot” resulted in a paradigm shift. What would VDOT get from this shift? As many research reports have documented, lower in-place density can have a detrimental impact on performance. The hope was for longer-lasting, better performing pavements through increased andmore consistent compaction. After success with the 2016 pilot projects and widespread use in 2017–2018, VDOT and VAA agreed to adjust the disincentives and expand the situations where the bonus would be applicable. The percent- age of disincentives was increased for surface mixes (See Table 1), and the minimum traffic threshold for bonus routes was lowered from 5,000 vehicles per day to 2,000. Both parties felt the change in disincentives would emphasize quality, and the lower traffic level would increase the potential impacts to more of the network. Figure 2 shows the difference in average compaction since 2017. VDOT’s dense gradedmixes clearly show higher in-place values. At the same time density bonuses were implemented, so was specification language related to asphalt mix consistency. VDOT specifications utilize a statistical approach to evaluate andmonitor mixes during produc- tion. The average values for each lot of material (4,000 tons) are compared to acceptable limits through production tolerances on gradation sieves and AC content. If the lot’s average is within these limits for gradation and AC content, no production pay adjustment is assessed. Outside of these limits, payment adjustments are assessed on a project. Once more than one lot of material is produced, the material’s variability is calculated using standard deviation. Again, the standard deviation is applied to gradation and AC content results, and when the standard deviations are low, no pay adjust- ment is made. As the standard deviation exceeds thresholds, pay reductions are made. In extreme cases, the contractor can be required to remove out of spec, highly variable mixes. With Chief Engineer Moore’s desire for more consistent mixes, VAA proposed specification language related to the standard deviation for AC content and gradation. By reviewing the 2014 contractor production data on surface mixes, VAA proposed a maximum standard deviation of 0.15 for AC content andmaxi- mum standard deviation limits for specifica- tion sieves. Additionally, no lot of material could be outside of the production tolerances. If all criteria are met, then the contractor △ continued from page 19 Improvement (%) 2005 27 29 20 26 2006 2007 Statewide Average Percent Improvement in IRI After Paving 40 35 30 25 20 15 10 5 0 34 28 30 29 36 27 22 26 SR US IS Avg FIGURE 1: Improvement in Ride Quality