Table 3: Specification recommendations for LaDOTD [48

working towards incorporating temperature segregation requirements into their specifications including Washington, Oklahoma, Tennessee, South Carolina, and Georgia [26].

Table 3: Specification recommendations for LaDOTD [48].

Temperature Differential (TD) from Target Laydown Temp (°F)

0 to 50

50 to 75

Above 75

Actions

• No action required • Require contractor to reduce TD to below 50°F • Require operation to stop if TD is not reduced • Measure field densities in affected area • Quality assurance cores may be taken from concerned area • Require contractor to reduce TD to below 50°F • Require operation to stop if TD is not reduced • Quality assurance cores may be taken from concerned area • Require contractors to remove affected area if density fails

3.1.1.3 What is needed for PA implementation?

In this report, the newest PMTP also known as Pave IR technology, Pave IR ScanTM, is considered for implementation in Pennsylvania. This set up is the least invasive, simplest, and most up to date technology.

When implementing this technology in a new state, DOTs often began with webinars and construction demonstration projects to teach about the new technology, how it can improve operations, and how to interpret the results [62]. This allows the DOTs and their respective contractors to see the technology in action and have a professional explain and answer any questions. At this point, the DOT can determine if they want to implement the technology in their state. The entire set up costs $30,000 - $35,000 with the bulk of the cost coming from the 36

infrared camera and on-board computer. Installation for this set up take less than 2 hours and initial training takes less than 4 hours [52]. No regular maintenance is necessary, and calibration is performed once a year in a lab with a blackbody source with accuracy of ±0.9°F ±0.25% and a stability of ±0.2°F [51,52].

Changing the specifications and the accompanying research is the most time-consuming aspect of adopting this technology, especially with the Pennsylvania’s use of WMA. DOTs often implement the AASHTO specification outlined above in AASHTO PP 80-20 [56]. However, since WMA is most often used in Pennsylvania, additional research will be needed to create a new specification to identify the severity of temperature segregation. Besides the severity categories, other aspects of the specifications are common amongst the current DOT using PMTP. There are allowable amounts of each severity in several specifications. Sebesta 2012 describes how TxDOT implemented PMTP [57]. This report recommends 50% allowable moderate severity because they found that many locations with moderate classification were barely over the threshold between minor and moderate. These areas may not be significant enough to warrant action but should be observed for potential premature distress. The report also allows 2% severe temperature segregation accepting that there will most likely be some significant temperature differentials when the paver begins and ends for the day. They also included a recommendation for night construction that the thermal profile should continue with the same specifications, but the ambient temperature should be noted.

3.2 Ground Penetrating Radar (GPR) for Asphalt Density

Research and industry best practices indicate that the long-term performance of hot mix asphalt (HMA) concrete is heavily reliant on the in-situ air void content/density of the compacted layer [63]. Key HMA characteristics, such as stiffness [64], strength [65], and dynamic modulus [66] have all been shown to correlate to air void percentage. Failure to meet compaction parameters can lead to premature pavement degradation including cracking, raveling, and/or oxidation [67]. This is especially prevalent in longitudinal joints which are regularly the weakest part of a HMA pavement. Most often separate lanes cannot be paved in tandem creating a cold joint. This creates an area of lower compaction at the joint when compared to the

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centerline of the lane inviting premature pavement deterioration and failure resulting in costly maintenance and reduced service life [60]. A nationwide study determined that each 1% increase in air voids over a 7% base led to approximately 10% reduction in pavement life [68]. To address the potential for underperforming longitudinal joints, PennDOT was one of the first states to include a minimum value of 91% for the theoretical maximum density (TMD) in their 2020 specifications [69].

Traditionally, HMA compaction testing is conducted through cores. This method is destructive, expensive, time consuming, and has limited in coverage, with typical random sampling measuring only 0.003% of pavement area [70]. Another significant shortcoming of coring is the while these measurements are useful for post-construction analysis, they cannot provide real-time feedback during the compaction operation [63]. An alternative approach is the nuclear density method. This method is non-destructive, has data collection on the same day as paving, and provides immediate results. However, the use of radioactive materials requires a special license, specialized equipment, and extensive training as incorrect operation of the device can result in great harm for inspectors and workers. Both these conventional methods put crew members in potentially dangerous situations where they are in close proximity to live traffic and heavy equipment [71].

To address the shortcomings of conventional methods, ground penetrating radar (GPR) is being used to quantify compaction through creating HMA density profiles [72]. This technology is a form of non-destructive testing that has been used for several decades. Originally this was a handheld device used to scan areas of concern or for quality assurance to analyze the subsurface features of a pavement, such as layer thickness or properties [71]. However, the effect of surface moisture on measurements made the previous use of this technology inadequate for real-time density measurements. Algorithm developments have since made accurate density profiles possible which will be farther discussed later in this section [71]. The American Association of State Highway and Transportation Officials (AASHTO) has since published preliminary standard practice for using GPR as a means to calculate HMA density profiles [72].

GPR systems work by sending electro-magnetic (EM) waves toward a target and receiving reflections from the varying of electrical properties between sub-surface materials. The

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