1. What’s New In Pavement Design
2018 KDOT/KAPA FALL FORUM
October 31, 2018

2. Outline & Learning Outcome Overview
December 2015 Life Cycle Actions & Structural Coefficient Changes
Pavement Design Software
AASHTOWare Pavement ME
PAVEXpress Investigation
Recent Pavement Investigations
Types of Surface Distress
Cores
Recommendation for solving pavement distresses
There are four items that I would like to discuss today. The first item includes discussing changes to life cycle actions used to calculate life cycle costs, changes to the composite HMA structural coefficient for asphalt pavement, and how KDOT selects pavement type. The second item is to briefly discuss where we are at with evaluation of AASHTOWare Pavement ME. The third item is to discuss a learning exercise we performed earlier in the year for KAPA. Lastly, I would like to share a recent pavement investigation we completed earlier this year.

3. Life Cycle Actions & Structural Coefficient Changes
New actions for calculating life cycle costs (see next slide)
Decreased credit from 12-years to 10-years based on historical pavement performance and overlay action timing
Composite structural coefficient changed from to 0.42 or 0.44 based on loading condition of 10-year flexible ESAL’s
Surfacing Selection Committee selects pavement type as of December 2015; No Alternate Bid
After a review of our life cycle actions and compared them to the actions that actually occurred over the life of our full depth HMA pavements that contained Superpave mixes that had been in service for years, it was decided to make changes highlighted above effective December You will see a comparison of actions used before and after December 2015 on the next slide. A review of overlay action history showed that KDOT was getting 7-9 years on average out of the full-depth HMA pavements with a maximum of 13 years before the next overlay action. When selecting the pavement type, there are many factors to consider including route continuity, future maintenance that can disrupt traffic, project phasing, initial and life cycle costs, and many other factors. As a result, we changed from bidding pavement alternates to having a surfacing selection committee made up of four executives and the District Engineer select pavement type based on many of the factors I just mentioned for new, full depth construction greater than 1-mile in length.
One thing to note about the structural coefficient is that a composite was very conservative. If the 10-year flexible ESAL’s are less than 3,000,000 then a composite 0.42 structural coefficient is used for HMA in the design. If the 10-year flexible ESAL’s are greater than 3,000,000 then a composite 0.44 structural coefficient is used for HMA in the design process. With Pavement ME, structural coefficients essentially go away and other volumetric parameters are used.

4. Updated Life Cycle Actions
Before December 2015
After December 2015
I realize this slide may be a little difficult to see, but on the left are life cycle actions used for cost calculation prior to December On the right, the actions were updated in December 2015 to better represent what could be selected as a rehabilitation action at each interval during the 40-year life cycle. It is important to note that the life cycle rehabilitation actions are used to calculate a future cost that gets brought back to a “present worth” for comparison of alternatives. It is also important to note that these costs are an estimate given a discount rate provided by the Feds each year.

5. AASHTOWare Pavement ME
Pooled Fund Research with New York State Department of Transportation (NYSDOT)
Composite Pavements: Asphalt over existing Concrete
Asphalt Overlay of Full-Depth Asphalt Pavements
K-TRAN Project KSU 18-2
New Full-Depth Asphalt Pavement
As most in this room may be aware, Pavement ME is a paradigm shift from AASHTO ’93 in terms of design methodology. AASHTO ‘93 is the current design methodology for many states including Kansas. The difference between Pavement ME and AASHTO ‘93 is that AASHTO ‘93 is an empirical design method based on one road test near Ottawa, IL while Pavement ME includes both mechanistic and empirical design methodology. Think of Pavement ME more as modeling your pavement structure over time by predicting distresses that hopefully coincide with what is actually occurring on your in-service pavements over time. The struggle is that KDOT has had difficulty to date matching the distresses that are actually occurring on our in-service pavements in the field with the Pavement ME distress predictions over time. This is giving us mixed results (in some cases thicker pavement than AASHTO ’93 and in some cases much thinner pavement than what we have placed in the past). This is why we have proceeded with caution and are continuing to evaluate.
For the Pooled Fund project, the team went through a process identifying highway section candidates in each of the 6 districts for both the asphalt over concrete and the asphalt over asphalt projects. For the asphalt over asphalt projects, we were looking for full-depth new construction or reconstruction that had been built in the mid-1990’s or later to focus on Superpave mixes and overlays, which is standard KDOT practice. We came up with 24 candidate highway segments split equivalently across the 6 Districts. This past year, the Pavement Design team went through a data mining effort to provide materials data to the K-State researchers including existing layer thickness, air void percentages, effective binder content, unit weight, mixture aggregate gradations, FWD data if available, transverse cracking, rutting/permanent deformation data, and fatigue cracking data. Currently, we are wrapping up the data collection for the AC over AC projects and will be getting into validation once the local coefficients are determined.
We plan to compare the thickness results against what AASHTO ‘93 would have given us. We also plan to look at distresses that have actually occurred over time on these segments of pavement and compare to what the software is predicting for distresses over the same time period. If not comparable, we’ll need to make some adjustments during this process.
For full-depth HMA, we went through a quick, yet robust effort back in late 2015 that wrapped up in Spring During that process we determined further evaluation was needed including the following:
Better characterize typical HMA mixtures (virgin and with RAP/RAS) used in new flexible pavement for Kansas by performing the dynamic modulus test and fracture critical testing.
Investigate low-temperature cracking behavior of HMA mixes using the creep compliance and indirect tensile strength tests.
Obtain soil samples to perform more resilient modulus testing of the soil both in treated and non-treated states.
Derive coefficients K1-K3 from repeated loading permanent deformation tests.

6. KDOT Design vs. PAVEXpress Background
In March 2018, KAPA asked KDOT if already completed flexible designs could be run with PAVExpress as a learning exercise and to verify the PAVExpress program for AASHTO ‘93 design compliance for flexible pavements. It is important to mention that the purpose of this exercise is not meant to be a proprietary product endorsement. KDOT agreed to do this and spent a few hours in a conference room using the same inputs from already completed designs to compare results.
To provide some background, we chose two highway segments in different regions of the state with different traffic, soil, and climate conditions. The first route we chose was K-27 in Wallace County from 7.7 miles north of the Wallace/Greeley County line north to approximately 2-miles south of the west K-27/US-40 intersection. The second highway segment we chose was US-169 in Allen County from the Allen/Neosho County line north to 0.4 miles south of the US-169/US-54 intersection. On this slide, you can see the differences in flexible design ESAL’s on the left.
The K-27 highway segment had a 2015 AADT volume of 1,300 vehicles and a 2015 AADTT volume of 501 vehicles. and in soil resilient modulus on the right. The US-169 highway segment had a 2018 AADT (annual average daily traffic) volume of 6,150 vehicles and a 2018 AADTT (average annual daily truck traffic) volume of 1,476 vehicles.
Both K-27 and US-169 are considered Class C routes based on the KDOT Route Classification system. US-169 is a secondary freight route in SE Kansas. The loading on US-169 was more than 3 times that on K-27.
On the right, you can see the difference in the design resilient modulus of soil, which is an important parameter that describes the ability of compacted subgrade soil to provide sufficient stiffness for the loading condition and pavement structure. The design resilient modulus of the K-27 soils was almost double the US-169 soils.
I don’t want to get into all the specific inputs for both designs, but the most important for full-depth flexible pavement is the traffic loading, resilient modulus of the soil, and reliability.

7. KDOT Design vs. PAVEXpress – K-27 Wallace
KDOT Design – K-27 Wallace
PAVEXpress Design – K-27 Wallace
On this slide, you can see a comparison of the pavement design results for K-27 in Wallace County. This was a 30-foot roadway segment consisting of 2-lane pavement plus 3-foot paved shoulder construction on new alignment. You can see that the PAVEXpress design yielded a total HMA thickness of 0.5” greater than KDOT’s AASHTO ‘93 design. It is important to mention that there could be discrepancies between background equations, rounding, factor of safety, and a few other factors between the design methods compared above. In general, the KDOT calculated designs versus PAVEXpress designs yielded comparable results, which tells us that PAVEXpress is running AASHTO ‘93.

8. KDOT Design vs. PAVEXpress – US-169 Allen
KDOT Design – US-169 Allen
PAVEXpress Design – US-169 Allen
On this slide, you can see a comparison of the results for one project on US-169 in Allen County. This was a 44-foot roadway segment consisting of 2-lane pavement and 10-foot shoulder reconstruction on existing alignment. You can see that the design thickness turned out the same for this project. In general, the KDOT calculated designs versus PAVEXpress designs yielded comparable results, which tells us that PAVEXpress is running AASHTO ‘93.

9. RS-359 Cunningham, Kingman County
In early October 2017, we were contacted by one of our design consultants to investigate the cause of significant surface distress in a new pavement widening on RS-359 in Kingman County in the town of Cunningham, Kansas that had only been in service since roughly February As you can see, the primary surface distress was rutting and slippage cracks, which are crescent-shaped cracks that form in the surface.

10. RS-359 Cunningham, Kingman County
You can see the deterioration in the roadway consisted of rutting and shoving outward of material in the outside wheel path of the new, widened, full-depth construction.

11. RS-359 Cunningham, Kingman County
The HMA material in the five control cores was intact and mainly in good condition. The HMA material in cores retrieved from deteriorated sections was in good to fair condition. The tack layers between the top and bottom HMA layers were de-bonded in three (3) of the five (5) deteriorated cores ranging from 1.25” to 1.625” in depth. Four (4) of the five (5) cores in the deteriorated areas were shorter in length than the corresponding control core. The thickness variation ranged from 0.25” to 1.38”.
Pavement modulus values ranged from 126,000 to 276,000 PSI. The average back-calculated pavement modulus in the deteriorated areas was 162,000 PSI. Pavement modulus values for HMA in good condition range from 200,000 to 500,000 PSI.
The average back-calculated resilient modulus was 4,450 PSI in the outside wheel path in non-deteriorated areas. The average back-calculated resilient modulus was 4,270 PSI in the outside wheel path of the deteriorated areas.
Dynamic Cone Penetrometer (DCP) testing was done at each core hole. California Bearing Ratio (CBR) values were determined from the DCP data collected. The overall CBR values averaged 13 and ranged from averages of 8 to 17. In one deteriorated location, the subgrade had a CBR of 4 ranging from 4.8” to 11.4” in depth. In another location the subgrade had a CBR value of 3 ranging from 4.3” to 10.3” in depth. Overall, the CBR values show that the subgrade appeared to have sufficient stiffness to provide support for the pavement structure, but was inconsistent throughout the limits of the pavement investigation.
This analysis confirms the distresses that occurred.

12. RS-359 Cunningham, Kingman County
To address the pavement deterioration, we recommended a 2.0” Cold Mill + 2.0” Overlay to mill out the rutted material, establish a better bond, and replace with new material. In the severely rutted areas where rutting extends beyond the base material, we recommended a full-depth HMA patch. The total estimated cost of the fix was approximately $30,000.

13. When you discover broken concrete pavement where you thought there was smooth asphalt pavement!!

14. Acknowledgments Nat Velasquez, Jr. Ben Hagan Emilie Metheny
Thomas Nordling, Jr.
Douglas Hilmes
All District & Area folks that assist our Pavement Design Team as we perform investigations around the State of Kansas

15. QUESTIONS?
Ryan Barrett, P.E. Kansas Department of Transportation Pavement Design Leader