Figure 24: Cleaned temperature profile [52

Figure 24: Cleaned temperature profile [52]

In 2016, the PMTPsystem was demonstrated for several DOTs including Alabama, Alaska, Illinois, Maine, Missouri, New Jersey, North Carolina, Virginia, and West Virginia. They asked personnel from the DOTs and corresponding contractors for their comments on the PMTP system with an overall positive response as can be seen in a few of the comments below [52]. • Improves communication between plant and paver personnel for material movement • Visual display allows operators to note which activities effect the temperature differentials • Good forensic tool to investigate nonuniform mat density • Allows contractors to immediately take action against a potentially underperforming pavement • Reduces the risk of contractors being penalized for undercompaction • Removes opinions from identifying mixture segregation • Provides full coverage inspection instead of random locations • Can be used to mediate disputes on uniformity • Reduces future maintenance costs by reducing premature cracking and raveling

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One disadvantage of this technology is that it has not been fully tested for warm mix asphalt (WMA) which is required by Publication 408 in Pennsylvania [54]. Extensive research has been performed on temperature segregation for HMA but there is limited testing on WMA despite having similar properties [55]. WMA is produced and mixed at temperatures about 212 –302°F (100 – 150°C) whereas HMA is around 250 – 375°F (120 – 190°C). WMA is typically compacted at least 68 – 86°F (20 – 30°C) lower than HMA. The PMTP system is advertised to work on HMA with little information on the ability to analyze WMA. However, a 2017 study used the infrared camera technology adopted by PMTP to identify temperature segregation in their study with success. Additionally, the same study determined different temperature segregation severity categories based on temperature differentials for WMA with a 4% air content [55]: • No segregation: <37.4°F (<3°C) • Low-level: 37.5 – 46.4°F (3 – 8°C) • Medium-level: 46.5 – 64.4°F (8 – 18°C) • High-level: >64.5°F (>18°C)

The differing temperature differentials to cause the same temperature segregation severity between WMA and HMA may need to be considered and farther researched to improve analysis of temperature profile data and to improve specifications.

3.1.1.2 Past and Present Experience

The increase in pavement performance has led to the adoption of this technology through regular use or having been researched by other DOTs and their respective research institutions. American Association of State Highway and Transportation Officials (AASHTO) has developed a standard for Continuous Thermal Profile of Asphalt Mixture Construction (AASHTO PP 80-20 2021 – [56]). This provides a template for standard thermal profiling using technology that is immediately behind the paver with the goal to improve quality control across asphalt paving. Categories were developed to establish the severity of temperature segregation in terms of

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temperature differentials [56]. These categories were adopted by many state departments into their own specifications. • None to Minor: 0°F – 25°F • Moderate: 25.1°F – 50°F • Severe: >50°F

Paver mounted thermal scanning has been incorporated into several state specifications. Texas Department of Transportation (TxDOT) began investigating temperature segregation and the possibility of including testing in their specifications in 2000 [57]. TxDOT began with thermal profiling requirements using thermal cameras or other imaging systems in 2012 which farther developed to include paver-mounted thermal imaging systems in 2015 [58]. TxDOT uses the PMTP system on their pavers and used webinars and construction demonstrations to introduce the new technology to contractors. This was met with wide success that was adopted quickly and enthusiastically by contractors, leading to an increase in higher quality asphalt pavements [57]. TxDOT adopted the AASHTO PP 80-20 severity categories and if the temperature differentials are significant and reoccurring, action must be taken to eliminate farther segregation or correct section of severe segregation. TxDOT also recommends marking areas of moderate and severe temperature segregation so that a density profile can be performed.

Following the implementation of automated thermal profiling by Texas, Louisiana Department of Transportation and Development (LaDOTD) also studied the effect of temperature segregation to create specification recommendations that suggest actions to be performed for a range of temperature differentials shown in Table 3 [48]. Louisiana also recommends a thermal profile system that constantly records the temperature across the full width of the pavement [59]. Minnesota Department of Transportation (MnDOT) has recently included the paver mounted thermal profile method in a special provision on asphalt specifications [60]. Ohio Department of Transportation has included the thermal and density profile measurements in their specifications to work towards pavement uniformity [61]. They found that while the use of PMTP was not a complete fix for temperature segregation, this device helped improve long term pavement performance [61]. As of 2014, several additional states are

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