case study on performance of pavement constructed with

Case Study on Performance of Pavement Constructed with Modified Binder Meeting Extended BBR and DENT Specifications

Steven Manolis, P.Eng.

General Manager Coco Asphalt Engineering

Toronto, Ontario

Salman Bhutta, Ph.D., P.Eng. Principal

Engtec Consulting Inc. Vaughan, Ontario

Vince Aurilio, P.Eng. Executive Director

Ontario Hot Mix Producers Association Mississauga, Ontario

Selena Lavorato, B.Sc., C.E.T.

Quality Systems Manager Coco Asphalt Engineering

Toronto, Ontario

Garry Bates, C.E.T. Quality Manager Coco Paving Inc. Kingston, Ontario

Acknowledgements

The Authors would like to acknowledge the efforts of Gelu Vasiliu, Ryon Reid, and Taylor Lefebre from Coco Asphalt Engineering for their respective assistance with FTIR analysis, mix performance testing, and crack surveying. Hassan Salama and Salman Maih from Engtec Consulting Inc. are acknowledged for their work on permeability and FWD testing.

© Canadian Technical Asphalt Association 2016

238 PERFORMANCE OF PAVEMENT WITH EXTENDED BBR AND DENT BINDER

ABSTRACT

Understanding and preventing cracking in flexible asphalt pavements is challenging due the complexity of individual mechanisms and their interaction. Battersea Road in Kingston, Ontario was pulverized and resurfaced using a PG 58-28 binder meeting AASHTO M320, DENT, and Extended BBR specifications, however cracks formed within 5 years nonetheless. The focus of this study is to assess the performance of this road constructed using enhanced asphalt cement binder specifications and to investigate the causes of pavement cracks which have appeared.

Original binder and recovered binder properties from the HL3 surface course after six years of field aging satisfied project specifications. Asphalt cement contents were sufficient and compaction requirements were achieved. Performance testing (rutting, fatigue, low temperature cracking, and dynamic modulus) on plant-produced mix indicated acceptable properties. As such, it was determined that asphalt cement properties did not adversely affect cracking.

Upon further investigation, drainage issues arising from variable permeability within the granular and base materials appear to have contributed to the cracking on Battersea Road. Other factors included separation of the longitudinal centre line joint and differential settlement between widened bike lanes and the adjacent pavement. Good binder properties are essential but do not necessarily ensure cracking performance.

RÉSUMÉ

Comprendre et prévenir la fissuration des chaussées flexibles est difficile en raison de la complexité des mécanismes individuels et de leur interaction. Battersea Road à Kingston, Ontario a été pulvérisée et sa surface refaite à l'aide d'un bitume de classe PG 58-28 rencontrant la norme AASHTO M320 et les essais DENT et BBR Prolongé, mais des fissures se sont quand même formées en deçà de 5 ans. L'objectif de cette étude est d'évaluer la performance de cette route construite à l'aide de bitume conforme à des exigences accrues et d'enquêter sur les causes des fissures de la chaussée qui sont apparues.

Les propriétés du bitume d'origine et du bitume récupéré de la couche de surface HL3 après six ans d’utilisation rencontraient tous deux les exigences du projet. Les teneurs en bitume étaient suffisantes et les exigences de compactage ont été atteintes. Les tests de performance (orniérage, fatigue, fissuration thermique et module dynamique) sur l’enrobé fabriqué à l’usine d’enrobage, démontrait des propriétés acceptables. En tant que tel, il a été déterminé que les propriétés de l'enrobé n’ont pas contribué à la fissuration.

Après enquête, les problèmes de drainage découlant de la perméabilité variable dans les matériaux granulaires et la base semblent avoir contribué à la fissuration sur Battersea Road. D'autres facteurs comprenaient la séparation du joint longitudinal, la consolidation différentielle entre les pistes cyclables élargies et la chaussée adjacente. Des bitumes de bonne qualité sont essentiels, mais ne garantissent pas nécessairement une chaussée sans fissures.


MANOLIS, BHUTTA, AURILIO, LAVORATO & BATES 239

1.0 INTRODUCTION

Understanding and preventing cracking in flexible asphalt pavements is challenging due to a number of contributing factors, as well as the complexity of and the potential interaction between the individual mechanisms involved. Research in Ontario has focused on the influence of asphalt cement binder properties on pavement cracking performance [1-4]. This has led to the development of two specification tests intended to improve pavement cracking performance by enhancing asphalt cement binder quality.

The Ontario Ministry of Transportation (MTO) LS-299 Test Method [5] for determining the ductile failure properties of asphalt cement using the Double Edge Notched Tension (DENT) Test is intended to provide the basis of an improved asphalt cement fatigue property specification. This method uses a fracture mechanics based approach to quantify fatigue cracking parameters at intermediate temperatures.

The Extended Bending Beam Rheometer (Extended BBR) Test LS-308 [6] extends the low temperature conditioning time from 1 hr to 72 hr prior to testing the low temperature cracking properties of the binder using a Bending Beam Rheometer (BBR). The extended conditioning time allows the asphalt cement to isothermally harden to a greater extent than it would using the 1 hr conditioning time in the AASHTO M320 Standard Specification for Performance-Graded Asphalt Binder [7]. This test is intended to provide a more rigorous low temperature cracking evaluation based on the assumption that the isothermal physical hardening that the binder undergoes during the extended conditioning period affects mixture cracking performance.

Specifications for LS-299 and LS-308 were first used as acceptance criteria on a municipal contract completed in the City of Kingston, Ontario in 2009. Battersea Road was paved with two lifts of asphalt produced using asphalt cement meeting LS-308 Extended BBR and LS-299 DENT criteria. Full depth reclamation of the existing asphalt surface and underlying granular material was completed prior to resurfacing.

Preventive maintenance in the form of crack sealing was completed on Battersea Road in 2014 during its fifth year after construction. The focus of this study is to assess the performance of this road constructed using enhanced asphalt cement binder (LS-299 and LS-308) specifications and to investigate the causes of pavement cracks which have appeared.

2.0 SCOPE

Approximately 3.5 km of Battersea Road in Kingston, Ontario was resurfaced in 2009 using a polymer modified PG 58-28 binder meeting requirements for AASHTO M320 [7], DENT Test [8], and Extended BBR [9] specifications. This binder was used in both the base and surface course asphalt on this project.

Prior to paving, full depth reclamation of the existing asphalt surface and underlying granular materials was completed to a depth of 250 mm followed by grading. Approximately 25 mm of Granular A was placed and graded on top of the pulverized material. The base asphalt course consisted of 50 mm of Medium Duty Binder Course (MDBC) containing 15 percent Reclaimed Asphalt Pavement (RAP), followed by a 40 mm HL3 surface course with no RAP. Paving occurred in October 2009 and involved placement of 4,090 tonnes of HL3 surface and 5,000 tonnes of MDBC base mix.



Battersea Road consists of two lanes accommodating north and southbound traffic. As part of the resurfacing project, the road was widened to accommodate bike lanes on each side. The northbound lane of the south segment includes a separate right turn lane at the intersection of Battersea Road and Kingston Mills Road. The project was divided into a north and south segment separated by a middle segment believed to be a mill and pave overlay with extensive cracking, which was not part of this project.

Average Annual Daily Traffic (AADT) in 2005 was reported as 4,440 vehicles northbound and 4,757 vehicles southbound [10] for the north segment, and 6,767 vehicles northbound and 7,671 vehicles southbound for the south segment [11]. Forecast future traffic growth and the proportion of truck traffic as compared to passenger vehicles were not available. An investigation study was commenced in 2015 to study potential causes for the cracking experienced by this road.

3.0 ASPHALT CEMENT PROPERTIES

A PG 58-28 binder meeting AASHTO M320 [7], in addition to LS-299 DENT [8] and LS-308 Extended BBR [9] criteria, along with restrictions on permissible asphalt cement modifiers, was supplied for this project. The actual true grade of the binder was PG 64.1-34.6. Certification data are presented in Table 1.

Table 1. Binder Data - Battersea Road PG 58-28 (AASHTO M320 + DENT + Extended BBR)

Sample

Tank Sample PG 58-28 (AASHTO M320 + DENT + Extended BBR)

Test Method QC Results CAE

QA Results City of Kingston

City of Kingston

Specification RTFO Residue AASHTO T240

MSCR, Jnr3.2 @58oC (kPa-1) AASHTO T350 0.42

MSCR, Average % Recovery @ 3.2 kPa and

58oC, (%) AASHTO T350 53.4

PAV Residue AASHTO R18

DENT CTOD (mm) LS-299 12.7 (CAE Lab) 13.4 (DBA Lab) 9.9 ≥ 10

1 hr BBR LS-308 -34.1 -33.2 LTLG

72 hr Extended BBR LS-308 -30.0 -29.2 ≤ - 28

Grade Loss (oC) 72 hr Extended BBR LS-308 4.1 4.0 ≤ 6

True Grade PG 64.1 – 34.6 Note: AASHTO is American Association of State Highway and Transportation Officials, BBR is Bending Beam

Rheometer, CAE is Coco Asphalt Engineering, CTOD is Crack Tip Opening Displacement, DENT is Double Edge Notched Tension, MSCR is Multiple Stress Creep Recovery, PAV is Pressure Aging Vessel, QA is Quality Assurance, QC is Quality Control, and RTFO is Rolling Thin Film Oven.



The LS-299 DENT test uses a fracture mechanics based approach to provide to characterize ductile failure in asphalt cement at 15oC. Crack Tip Opening Displacement (CTOD) is the output for the LS-299 DENT with higher CTOD values intended to indicate improved fatigue cracking resistance.

The LS-308 Extended BBR test allows asphalt cement to isothermally harden for 72 hours prior to testing for low temperature BBR properties based on the supposition that isothermal hardening of asphalt cement affects mix cracking performance. The warmest low temperature BBR grade measured after 1, 24, and 72 hours is selected at the Extended BBR Low Temperature Limiting Grade (LTLG). Grade Loss is calculated as the difference between the low temperature grade at 1 and the 72 hour LTLG.

The project involved a supplier prequalification process requiring submission of samples to be graded against AASHTO M320 PG 58-28 requirements, as well as additional DENT and Extended BBR criteria. The restrictions on modifiers for the supplier prequalification process were similar but not identical to those specified in the project tender documents. The difference was that for the supplier prequalification, up to 0.2 percent Polyphosphoric Acid (PPA) was permitted for use as a catalyst for epoxy functional polymers, whereas the type of polymer was not specified in the actual project tender specifications.

As this was the first project called with Extended BBR and DENT specification, criteria commercially produced material was not available for the supplier prequalification during the winter of 2009. A laboratory prepared sample meeting the prequalification criteria was submitted. The formulation was scaled up and adjusted as required based on process quality control testing in order to meet required specifications during full scale production.

A PG 58-28 binder meeting DENT CTOD value of 10 mm and a 72 hour Extended BBR LTLG of -28 or better along with a maximum permitted Grade Loss of 6oC was specified. Modification restrictions included a maximum limit of 0.2 percent PPA to be used only as a polymer catalyst, along with restrictions on air blown or catalytically oxidized asphalt cement and orthophosphoric acid [12]. Required specifications were met.

Replicate QC samples were tested for LS-299 DENT by two different laboratories. CTOD values of 12.7 and 13.4 mm were obtained by the laboratories, respectively. QA results provided by the City of Kingston indicated a CTOD of 9.9 mm which rounds to 10 mm. Required specifications were met. QA laboratories results were 2.8 to 3.5 mm lower than QC results. This variation is within the average 8.1 mm d2s for all laboratories and 7.1 mm d2s for QA and referee laboratories participating in MTO correlations between 2012 and 2015 [13]. The d2s variation for all laboratories excluding statistical outliers for the first 2016 MTO correlation was 7.4 mm with an average Coefficient Of Variation (COV) of 16.7 percent [14].

The product met Extended BBR specifications. Quality Control (QC) results measured the Extended BBR 72 hour LTLG as -30.0 with a Grade Loss of 4.1oC. Quality Assurance (QA) results provided by the City of Kingston were similar with a LTLG of -29.2 and a Grade Loss of 4.0oC. The d2s variation for all laboratories excluding statistical outliers for the first 2016 MTO correlation was 2.2oC for LTLG and 1.9oC for Grade Loss [14].

While not required by the specifications, Multiple Stress Creep Recovery (MSCR) testing was completed as per AASHTO T350 [15]. Average non-recoverable creep compliance at 3.2 kPa shear stress (Jnr3.2) was 0.42 kPa-1 was at the climatic high temperature for the region of 58oC. A corresponding MSCR Recovery of 53.4 percent was obtained which exceeded the minimum required MSCR Recovery of 36.9 percent for this Jnr3.2 value. The MSCR Recovery results were indicative of the elastomeric polymer used to modify the asphalt cement.



4.0 MIX DESIGN PROPERTIES

An HL3 virgin mix was utilized for the surface course. This mix was designed with the minimum 5.3 percent asphalt cement content required by the City of Kingston, no RAP, and a 3.6 percent air voids target. The design for MDBC base lift included the minimum 5.0 percent asphalt cement specified by the City of Kingston, 15 percent RAP, and 3.5 percent air voids. Both Marshall mixes were designed 75 blows per side (bps). The mix proportions and properties are presented in Tables 2 and 3.

The mixes included asphalt cement contents that were 0.3 percent higher than the minimum required by the OPSS 1150 [16] and thus low design asphalt cement content should not have been an issue contributing to mix cracking and durability issues.

5.0 PERFORMANCE TESTING ON PLANT PRODUCED MIX

Performance testing was completed on HL3 plant mix produced for Battersea Road using PG 58-28 meeting DENT and Extended BBR criteria. Comparative testing was completed on plant produced HL3 mixes produced using PG 64-28 and PG 58-34 binders. Favourable mix properties were obtained which trended with true PG binder grade (AASHTO M320). It is not anticipated that mix performance issues contributed to cracking on Battersea Road. The PG 58-28 HL3 mix used on Battersea Road had similar low temperature cracking and fatigue results to the mix produced with PG 58-34 and better fatigue and cracking properties than the 64-28 mix. While the PG 64-28 mix had the best rutting results, rutting was not observed on Battersea Road.

True binder grades were PG 64.1-34.6 (PG 58-28), PG 66.5-30.6 (PG 64-28), and PG 59.6-34.1 (PG 58-34) as shown in Table 4. Extended BBR specifications were met by the PG 58-28 and PG 58-34 binders but not by the PG 64-28. DENT specifications were only met by the PG 58-28 binder. MSCR testing was also completed on the binders. The PG 58-28 binder used on Battersea Road would have met MSCR recovery requirements had they been specified based on the Jnr3.2 value for this binder. The PG 64-28 and 58-34 binders would not have met the MSCR recovery requirements based on their measured Jnr3.2 results.

Mixes were tested at 7.0+/-5% air voids. Samples for the Thermal Stress Restrained Specimen Test (TSRST) and the Four Point Bending Beam Fatigue Test were conditioned in a forced air convection oven at 85oC for five days prior to testing in order to simulate long-term field aging [17].

Low temperature thermal cracking was evaluated using the Thermal Stress Restrained Specimen Test (TSRST) on beams measuring 50mm x 50mm x 250mm sample using a cooling rate of 10oC per hour [18]. Specimens produced with PG 58-28 and PG 58-34 cracked at very similar low temperatures of -33.4 and -33.2 oC respectively (Table 5). The PG 64-28 mix cracked at a mean low temperature of -31.2oC. Results trended with the AASHTO M320 true low temperature grade of the binders used to produce the mixes.

The Four Point Bending Beam Test as per AASHTO T 321 [19] was used to evaluate flexural fatigue properties in constant strain mode at 20oC on 62.5mm by 50mm by 375mm beams. Fatigue life was determined by the number of cycles (Nf50) required to reach 50% of initial beam stiffness [17, 19].



Table 2. Battersea Road HL3 Surface and MDBC Base Course Mix Designs

Material Source HL3 Surface Course (%) MDBC Base Course with 15% RAP (%)

19 mm Stone Lafarge -- 16.8 HL3 Stone Lafarge 43.5 31.2 Asphalt Sand Fitzgerald 28.3 19.0 Screenings Lafarge 18.8 7.6 Manufactured Sand IKO 9.4 10.4 Reclaimed Asphalt Pavement Coco Paving -- 15.0 PG 58-28 AASHTO M320 + DENT + Extended BBR

Coco Asphalt Engineering 5.3 5.0

Note: AASHTO is American Association of State Highway and Transportation Officials, MDBC is Medium Duty Binder Course, and PG is Performance Grade.

Table 3. Battersea Road HL3 and MDBC Mix Design and Volumetric Properties

Property PG 58-28 AASHTO M320 + DENT & Extended BBR

HL3 Surface OPSS 1150 Specification

MDBC Base 15% RAP

OPSS 1150 Specification

Mixing Temperature (oC) 157 157 Compaction Temperature (oC) 147 147 Bulk Relative Density 2.404 2.433 Maximum Relative Density 2.904 2.520 Air Voids (%) 3.6 3.5 (COK) 3.5 3.5 (COK) Voids in Mineral Aggregate (%) 15.7 ≥ 15.0 14.1 ≥ 13.5 Asphalt Cement Content (%) 5.3 5.3 (COK) 5.0 5.0 (COK) Marshall Stability @ 60oC (N) 16,433 ≥ 8,900 19,100 ≥ 8,000 Marshall Flow @ 60oC 13.4 ≥ 8 13.9 ≥ 8

Sieve Size

26.5 mm 100 100 100 19.0 mm 100 96.8 94-100 16.0 mm 100 100 91.9 77-95 13.2 mm 99.1 98-100 86.5 65-90 9.5 mm 85.6 75-90 73.1 48-78 4.75 mm 58.3 50-60 49.5 30-50 2.36 mm 51.0 36-60 43.5 21-50 1.18 mm 45.0 25-58 39.0 12-49

0.600 mm 36.9 16-45 33.0 6-38 0.300 mm 18.0 7-26 16.2 3-22 0.150 mm 7.4 3-10 7.4 1-9 0.075 mm 4.9 0-5 5.1 0-6

Note: AASHTO is American Association of State Highway and Transportation Officials, BBR is Bending Beam Rheometer, COK is City of Kingston, DENT is Double Edge Notched Tension, MDBC is Medium Duty Binder Course, OPSS is Ontario Provincial Standard Specification, PG is Performance Grade, and RAP is Reclaimed Asphalt Pavement.



Table 4. Properties of Binders Used for Plant Produced Mix Performance Testing

Property Test Method PG 58-28

AASHTO M320 DENT + Extended BBR

PG 64-28 AASHTO

M320

PG 58-34 AASHTO

M320 RTFO Residue AASHTO T240

MSCR, Jnr 3.2 (kPa-1) @ 58oC AASHTO T350 0.42 0.65 2.8

MSCR, Average % Recovery @ 3.2

kPa and 58oC, (%) AASHTO T350 53.4 26.7 1.2

PAV Residue AASHTO R18

DENT CTOD (mm) LS-299 12.7 (CAE Lab) 13.4 (DBA Lab) 4.4 6.8

1 hr BBR Grade LS-308 -34.1 -31.4 -34.9 LTLG - 72 hr Extended BBR LS-308 -30.0 -26.5 -30.7

Grade Loss (oC) 72 hr Extended

BBR LS-308 4.1 4.9 4.2

True Grade AASHTO M320 PG 64.1 – 34.6 PG 66.5-30.6 PG 59.6 – 34.1 Note: PG is Performance Grade DENT is Double Edge Notched Tension BBR is Bending Beam Rheometer

AASHTO is American Association of State Highway and Transportation Officials RFTO is Rolling Thin Film Oven MSCR is Multiple Stress Creep Recovery CAE is Coco Asphalt Engineering LTLG is Low Temperature Limiting Grade

Table 5. Thermal Restrained Specimen Tensile Strength Test HL3 Mixture Results

Mix Type Asphalt Cement Type

Fracture Temperature (oC)

Fracture Strength (kPa) Number

of Samples Mean Standard

Deviation Mean Standard Deviation

HL3

PG 58-28 Extended BBR + DENT -33.4 0.8 579 37 4

HL3 PG 64-28 -31.2 2.6 483 34 5 HL3 PG 58-34 -33.2 1.3 495 68 5

Note: PG is Performance Grade AASHTO is American Association of State Highway and Transportation Officials DENT is Double Edge Notched Tension BBR is Bending Beam Rheometer

HL3 mixtures produced with PG 58-28 meeting DENT and Extended BBR specifications had the highest number of cycles to failure at 284,936 cycles, followed closely by the PG 58-34 HL3 mixture at 246,431 cycles (see Table 6). The mixture produced using PG 64-28 had the lowest mean number of cycles to failure at 160,824 cycles.



Table 6. Flexural Fatigue HL3 Mixture Test Results

Mix Asphalt Cement Cycles to Failure (Nf50) Initial Stiffness (MPa)

Mean Standard Deviation

No. of Samples Mean Standard

Deviation No. of

Samples

HL3 PG 58-28 Extended BBR + DENT 284,936 124,779 6 4,460 1,173 6

HL3 PG 64-28 160,824 129,369 6 3,775 785 6 HL3 PG 58-34 246,431 199,294 5 3,746 568 5

Note: AASHTO is American Association of State Highway and Transportation Officials BBR is Bending Beam Rheometer DENT is Double Edge Notched Tension PG is Performance Graded Rutting potential was evaluated on the plant produced HL3 mixes using the Asphalt Pavement Analyzer (APA) as per AASHTO T340 [20] in which a loaded wheel cycled back and forth over a pressurized rubber hose resting on the test specimen for 8,000 cycles. Rut depth was measured against the number of cycles [21]. Table 7 summarizes the results.

Table 7. Asphalt Pavement Analyzer Rut Depth for HL3 Mixes

Mix Asphalt Cement Mean Rut Depth After 8,000 Cycles at 58oC (mm)

Standard Deviation (mm)

No. of Samples

HL3 PG 58-28 Extended BBR + DENT 5.34 0.63 2 HL3 PG 64-28 3.45 0.75 3 HL3 PG 58-34 5.90 1.98 3

Note: AASHTO is American Association of State Highway and Transportation Officials BBR is Bending Beam Rheometer DENT is Double Edge Notched Tension

PG is Performance Graded Average rut depths after 8,000 cycles for the HL3 produced with PG 58-28 and PG 58-34 were similar at 5.34 and 5.90 mm, respectively. The HL3 produced with PG 64-28 had the lowest average rut depth at 3.45 mm. A study by the National Center for Asphalt Technology (NCAT) recommended a maximum 8 mm rut depth after 8,000 cycles [22]. All mixes satisfied this recommendation.

Dynamic modulus characterizes the viscoelastic response of a material under sinusoidal loading. The HL3 mixes in this study were tested for dynamic modulus using AASHTO TP 62 [23] as a guide at -10, 4, 21, and 37oC and over frequencies of 0.1, 1, 5, 10, and 25 Hz. Master curves for dynamic modulus versus frequency were using methodology described by Clyne et al. [24].

Figure 1 illustrates the master curves for the HL3 mixes produced with PG 58-28 meeting DENT and Extended BBR specifications, PG 58-34, and PG 64-28 binders. Higher frequencies correspond to lower temperatures lower frequencies equate to higher temperatures. Witczak et al. [25] report that dynamic modulus correlates to mix rutting and fatigue properties. High dynamic modulus at high temperatures (i.e., low frequencies) corresponds to better rutting properties, whereas as lower dynamic modulus values at intermediate temperature and frequency equate to improved fatigue characteristics.



Figure 1. Dynamic Modulus Master Curves for HL3 Plant Mixes Produced Using PG 58-28 Meeting Double Edge Notched Tension (DENT) and Extended Bending Beam Rheometer (Extended BBR)

Specifications, PG 58-34, and PG 64-28 Binders

The dynamic modulus trends agree with rutting and fatigue performance test results obtained for the HL3 mixes in this study. The HL3 mixes produced with PG 58-28 (meeting DENT and Extended BBR) and PG 58-34 had lower dynamic modulus values at low frequencies than the PG 64-28 mix, which agrees with the higher APA rutting results these mixes exhibited. At intermediate frequencies the PG 58-28 and PG 58-34 mixes had lower dynamic modulus values than the PG 64-28 mix. This agrees with the higher number of cycles to failure in the fatigue test obtained by the PG 58-28 and 58-34 mixes.

6.0 PAVEMENT EVALUATION

6.1 Recovered Binder

Core samples from Battersea Road taken six years after construction were extracted with n-propyl-bromide solvent [26] and the asphalt cement from the cores was recovered using the Rotavapor recovery process [27]. Given that the surface lift was a virgin mix while the base lift contained 15 percent RAP, the cores were cut and separated into base and surface course samples prior to extraction so that the recovered binder from each lift could be studied separately.

As shown in Table 8, the binder recovered from the HL3 surface course with no RAP had a 1 hour low temperature BBR grade of -32.5, a 72 hour Extended BBR grade of -28.9 and a corresponding grade loss of 3.6. While not part of the specifications, the recovered binder from the HL3 surface course met the required low temperature BBR requirements six years after construction. Recovered binder from the HL3 surface mix with no RAP had a 1h BBR grade that was 1.6oC warmer than the AASHTO M320 of the tank sample. The field aged Extended BBR grade was 1.1oC warmer than the tank sample Extended BBR grade. Recovered binder grade loss was 0.5oC better than the tank sample grade loss. The PAV aging procedure reasonably approximated AASHTO M320 and LS-308 properties after 6 years of field aging.

1

10

100

1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07

|E*|

, G

Pa

Frequency, Hz

58-28 DENT ExBBR 58-34 64-28



Table 8. BBR Properties of Recovered Binders from HL3 Surface and MDBC Base Mixes on Battersea Road

Sample

Recovered Binder PG 58-28 (AASHTO M320 + DENT + Extended BBR)

Test Method HL3 Surface Course (0% RAP)

MDBC Base Course (15% RAP)

1 hr BBR Low Temperature Grade LS-308 -32.5 -28.6 72 hr Extended BBR LTLG (oC) LS-308 -28.9 -21.3

Grade Loss (oC) LS-308 3.6 7.6 Note: AASHTO is American Association of State Highway and Transportation Officials BBR is Bending Beam Rheometer

DENT is Double Edge Notched Tension LTLG is Low Temperature Limiting Grade MDBC is Medium Duty Binder Course PG is Performance Graded

Recovered binder from the MDBC base course with 15 percent RAP had a 1 hour low temperature BBR grade of -28.6, a 72 hour Extended BBR grade of -21.3, and a grade loss of 7.6. It is hypothesized that the RAP likely influenced the extracted BBR properties of the binder from the MDBC mix. Researchers have found that 20 percent RAP may not detrimentally affect low temperature mix cracking performance [28]. Extracted binder properties from mixes containing RAP may not always reflect the cracking properties of the mix. Extraction and recovery ensures complete blending of the virgin and RAP binders, and this may in fact not occur between the virgin binder and RAP in the mix.

Freeston et al [29] presented findings at the 2015 CTAA Conference indicating recovered binder results from Battersea Road of -28oC for a 1 hour M320 grade, and a 72 hour Extended BBR LS-308 grade of -23oC. These results are in between the low temperature results for the surface and base mixes shown in Table 8. Neither the presentation slides nor the associated paper [30] indicated whether the results were from a combined base and surface mix sample, or from either the surface or the base mix. A weighted average calculation of the low temperature BBR data for the surface and base mixes in Table 8, assuming a 40 mm surface course with 5.3 percent AC and a 50 mm base course with 5.0 percent AC, returns a 1 hour weighted average BBR of -28oC and a 72 hour Extended BBR of -23oC. This weighted average result agrees with the data reported by Freeston et al [29] assuming that the surface (no RAP) and base (15 percent RAP) mixes were combined.

The closest weather station to the project is the Glenburnie weather station located north east of Battersea Road (see Figure 2). LTPPBIND v3.1 calculates a PG -34 design requirement at a 98 percent reliability and a PG -28 design requirement at a 91 percent reliability level for the Glenburnie station. The preconstruction geotechnical reports [10, 11] recommend a PG 58-34 binder for Battersea Road, which agrees with the 98 percent design reliability level from LTPPBIND v3.1. Located southeast of the project near Lake Ontario is the Kingston A weather station, which is identified as a PG -28 design location at a 98 percent reliability level. Environment Canada ceased recording data for the Glenburnie station in the 1990s. The Kingston A weather station was replaced the Kingston Daily Climate station, which is in very close proximity to the Kingston A station.

The coldest temperature in a given month for the months of November to March was compared between the Glenburnie Station and the Kingston A weather station between 1973 – 1996, which are the years in which data for both stations is available. It was found that the lowest recorded temperature in a given



month ranged between 2.2 to 6.6oC colder for the Glenburnie station than for the Kingston A station with an average of 4.8oC.

The lowest yearly pavement temperature range experienced by Battersea Road from 2010 to 2016 was estimated in Table 9 by assuming that the lowest air temperature at the Glenburnie weather station was 2.6 to 6.6oC colder than the lowest recorded temperature for the Kingston Climate weather station. An estimated pavement surface temperature range was calculated with the LTPP low pavement temperature model [31] using the estimated Glenburnie weather station data as inputs. The lowest estimated potential surface pavement temperature ranges were experienced in 2011 (-24 to -27oC), in 2014 (-24 to -27oC) and in 2016 (-25 to -28oC).

Figure 2. Kingston, Ontario Area Weather Station Locations

Table 9. Estimated Lowest Yearly Pavement Temperature for Battersea Road

Location 2010 2011 2012 2013 2014 2015 2016 Kingston Climate Station

Lowest Air Temperature (oC) -24 -30 -21 -24 -30 -28 -31

Glenburnie Station Estimated Lowest Air Temperature (oC)

-26 to -30

-33 to -37

-24 to -28

-27 to -31

-32 to -36

-31 to -35

-33 to -37

Battersea Rd Estimated Lowest Surface Pavement Temperature (oC)

-19 to -22

-24 to -27

-18 to -21

-20 to -23

-24 to -27

-23 to -26

-25 to -28

Battersea Rd Estimated Lowest Pavement Temperature at 40 mm

Depth (oC)

-17 to -20

-22 to -25

-15 to -18

-17 to -20

-21 to -24

-20 to -23

-22 to -25



The recovered binder from the HL3 surface course had a low temperature grade of -32.5 and an Extended BBR LTLG of -28.9, both of which exceeded the lowest estimated pavement surface temperature for Battersea Road. Assuming that estimates made in this analysis are valid, the recovered binder should have been able to withstand these temperatures and it does not appear that inferior low temperature binder properties contributed to the cracking experienced on Battersea Road.

The recovered binder from the MDBC base lift which begins at 40 mm below the pavement surface had a low temperature grade of -28.6, which was not exceeded by the estimated temperature estimated lowest temperature at the surface of the MDBC base lift. The estimated MDBC pavement temperature range did exceed and was colder than the recovered binder Extended BBR LTLG. It is however noted that recovered binder properties are not necessarily reflective of the cracking properties of mixes containing RAP as 100 percent blending of the RAP and virgin binder in the mix does not likely occur. While a very limited assessment was completed, cores taken through cracks showed cracking either partway through the top lift or all the way through both lifts. This suggests that the MDBC containing 15 percent RAP is not causing the cracking. As will be discussed in Section 6.4 of this paper, these observations do not preclude the possibility that shifts in materials underneath the pavement have contributed cracking distresses. It is not anticipated that the RAP in the MDBC contributed to the cracking experienced on Battersea Road.

6.2 FTIR Evaluation Properties

FTIR spectrometry has been used to qualitatively fingerprint asphalt cements and polymer modifiers, and with some limitations, to quantify the level of polymer in a modified binder [32]. An FTIR spectrum of Styrene-Butadiene-Styrene (SBS) modified asphalt cement is depicted in Figure 3. Identification of SBS in asphalt cement relies on absorptions at 699 and 966 cm-1, assigned to polystyrene and polybutadiene, respectively [33], as these generally appear as distinct absorption bands on FTIR spectra of SBS modified asphalt cement. The precise wave number attributed to polybutadiene and polystyrene in the literature varies slightly with some researchers assigning IR peaks at 700 cm-1 to polystyrene and 965 to 970 cm-1 to polybutadiene [32].

Various approaches to quantifying SBS content in asphalt cement are reported in the literature. Masson et al. [34] calculated SBS concentrations with a 10 percent error [35] by measuring absorbance values for polystyrene (699 cm-1) and polybutadiene (966 cm-1) and using the Beer-Lambert Law, which states polymer concentration (C) is directly proportional to absorbance (A) [32]. The peak-to-peak ratio involves normalizing the peak absorption intensity for polystyrene and polybutadiene to aliphatic C-H vibrations attributable to the asphalt cement that remain constant as SBS polymer concentration changes [32]. Polystyrene and polybutadiene peak heights are commonly divided by the peak height for the C-H rocking attributed to the methyl (CH3) group at 1,375cm-1 [35, 36], or sometimes reported as occurring at 1,377cm-1 [32]. Polymer peak absorbance heights have also been normalized to the peak absorbance height assigned to –C-H stretching for the CH2 alkane functional group located at 2,920cm-1[32].

The valley-to-valley integration approach involves integrating the area under the polystyrene and polybutadiene peaks and normalizing the results to the area under other bands on the FTIR spectrum. Examples of peaks that polybutadiene and polystyrene indices have been normalized to include the area under the methyl (CH3) peak [37, 38], the area under the CH2

peak [41], the sum of the areas under CH3 and CH2 peaks [39], and the sum of the areas of all the peaks in the FTIR scan [32].



Figure 3. Fourier Transform Infrared (FTIR) Spectrum of SBS Modified Asphalt Cement

Unless otherwise clarified, the FTIR indices presented in this study have been calculated by determining the area under the absorbance peak representing the compound that the index refers to, and normalizing this value to the area under the CH3 methyl group as shown in Equations 1 and 2 below.

𝐼𝑆 = 𝛴𝐴710/690

𝛴𝐴1400/1330 (1)

𝐼𝐵𝐷 =

𝛴𝐴983/955

𝛴𝐴1400/1330 (2)

Where: IS is the styrene index; ΣA710/690 is the area under the polystyrene absorbance peak (710 to 690 cm-1); A1400/1330 is the area under the methyl (CH3) absorbance peak (1400 to 1330 cm-1);

IBD is the butadiene index; and ΣA983/955 is the area under the butadiene absorbance peak (983 to 955 cm-1). FTIR Indices on recovered binders after six years of field aging as compared to the virgin tank sample binder are presented in Table 10. Testing was completed using a PerkinElmer Spectrum Two FTIR spectrometer operating in Attenuated Total Reflectance (ATR) mode. Styrene and butadiene indices relate to the SBS polymer modifier in the binder. A styrene index of 0.14 was obtained on the recovered binder from the HL3 mix (no RAP), which was higher than the 0.08 styrene index reported by the City of Kingston for the tank sample. The recovered binder butadiene index of 0.09 from the HL3 mix matches butadiene index reported by the City of Kingston on the tank sample binder. The styrene and butadiene indices on the binder recovered from the MDBC mix are 14 and 11 percent lower, respectively, than the indices on the recovered binder from the HL3 mix which may be due to the 15 percent RAP in the mix although the experimental variation associated with this type of analysis has not been studied sufficiently to conclude this definitively.

Styrene Peak (699 cm-1)

Butadiene Peak (966 cm-1)

Sulfoxide Peak (1030 cm-1)

Methyl (CH3) Peak (1375 cm-1)

Aromatic Peak (1600 cm-1)

Carbonyl Peak (1700 cm-1)

CH2 Peak (2920 cm-1)



Table 10. FTIR Indices for Battersea Road Asphalt Cement

Sample

PG 58-28 (AASHTO M320 + DENT + Extended BBR)

Tank Sample City of Kingston

QA Results

Recovered Binder HL3 Surface Course

(0% RAP)

Recovered Binder MDBC Base Course

(15% RAP)

Styrene Index (IS) 0.08 0.14 0.12

Butadiene Index (IBD) 0.09 0.09 0.08

Note: AASHTO is American Association of State Highway and Transportation Officials BBR is Bending Beam Rheometer DENT is Double Edge Notched Tension FTIR is Fourier Transform InfraRed MDBC is Medium Duty Binder Course PG is Performance Graded QA is Quality Assurance RAP is Reclaimed Asphalt Pavement

Results showing a styrene index of 0.11 on asphalt cement recovered from Battersea Road using a toluene, and a styrene index of 0.13 with dichloromethane solvent were presented by Freeston et al at the 2015 CTAA conference [29]. While neither the presentation slides nor the associated paper [30] indicated how the styrene index was calculated, it is noted that the recovered binder styrene index results presented reported by them agree with the findings in this paper. Freeston et al [29] also reported a styrene index of 0.34 on the tank binder sample which is 325 percent higher than the 0.08 styrene index reported by the City of Kingston. The results from the City of Kingston came with a note correctly estimating an SBS content of 2 to 3 percent at a corresponding styrene index of 0.08. A calibration curve was created by plotting styrene index against SBS content (see Figure 4). The curve correctly approximates the concentration of the SBS modifier added to the asphalt cement for Battersea Road. A range of between 2 to 3 percent SBS corresponds to a styrene index of between 0.08 and 0.16. The calibration curve results correspond to the recovered binder results reported in this paper and by Freeston et al [29]. The tank sample result for styrene index of 0.34 that was reported by them suggests a significantly higher SBS content than was actually used. The result does not agree with the styrene index of 0.08 for the tank sample reported by the City of Kingston, nor does it correspond to calibration curve data suggesting a 0.08 to 0.16 range for styrene index for SBS contents between 2 to 3 percent. Interpreting the differences in FTIR indices between tank samples and recovered asphalt cement binders must be undertaken with caution. The recovered binder styrene index for the HL3 mix in this study is 75 percent higher than the styrene index reported by the City of Kingston for the tank sample binder. Agbovi [39] tested binder properties on Highway 417 pavement trial near Ottawa, Ontario and normalized FTIR indices to the area under the CH2 peak. Styrene indices were 24 to 46 percent lower for field aged recovered binders containing SBS than the corresponding unaged binder index. Butadiene indices were 48 to 62 percent lower for the recovered field aged binders than they were for the unaged binders.



Figure 4. Calibration Curve for Styrene Index Versus SBS Content in Asphalt Cement

A 2012 SHRP study on applications of field spectroscopy to construction materials indicated that sample heterogeneity was a major source of testing error due to the small sample size required for FTIR testing [32]. Differences between replicate batches of polymer modified asphalt due to factors such as time and temperature were hypothesized to contribute to error. Calibration curves plotting FTIR indices calculated using peak-to-peak ratios against polymer concentration exhibited decreasing repeatability with increasing SBS content – particularly when the polymer content jumped from 3 to 6 percent. Plotting the mean of several results at each SBS level produced reasonable coefficient of determination (R2) values, however the scatter between replicate results increased with increasing SBS concentrations. It was further noted regression constants changed slightly when the base asphalt cement was varied [32].

6.3 Extraction-Gradation and Compaction Results on Pavement Core Samples

Cores from Battersea Road were cut to separate the HL3 surface from the MDBC base mix prior to completing extraction-gradation and compaction testing. Asphalt cement content (minimum 5.3 percent in HL3 and 5.0 percent in MDBC) and aggregate gradation requirements were met. It does not appear that low binder content contributed to the cracking on Battersea Road.

The in-situ compaction (bulk specific gravity as a percent of maximum specific gravity) was determined for the MDBC and HL3 cores. Results ranged between 93.4 and 96.8 percent and exceeded the minimum 92 percent specified in OPSS 310 [40]. Thus it appears that high air voids leading to premature aging of the binder was a not a significant factor contributing to the cracking on Battersea Road.

6.4 Crack Survey

A visual survey was completed in 2016, seven winters after construction, in order to quantify cracking distresses. The pavement was generally in good condition in part due to the preventive crack sealing completed in 2014 considering the potential for drainage issues on this project. Distresses included mostly low severity, with some instances of localized medium severity, longitudinal, fatigue, and transverse cracking. The type and frequency of cracking is inconsistent and varied between different locations on the road. Other distresses include cracking along the longitudinal centreline joint and longitudinal cracking along the inside edge of the widened bike lane which is believed to be caused by differential settlement. Figure 5 shows some good performing sections of Battersea Road in 2016.

y = 0.0525x - 0.0009R² = 0.9966

0.00

0.04

0.08

0.12

0.16

0.20

0.00 1.00 2.00 3.00 4.00

Styr

ene

Inde

x (I

S)

SBS Concentration (%)



Figure 5. Batter Sea Road (2016)

Battersea Road was segmented into six sections (see Figure 6) with crack survey data normalized to a 500-m section length in order to facilitate comparison of distresses between sections. The survey was completed using guidance in the Distress Identification Manual for the Long-Term Pavement Performance (LTPP) Program [41], with results presented in Table 11.

Cracking along the centreline joint was observed along most of the job with multiple cracks having developed in some areas. Considering that paving was completed in October, using what was at the time a new modified binder (crews reported that the mix was stiffer and more difficult than normal to work with), it would not be unexpected that the centreline joint may have opened up after 5 to 7 years. As discussed later, poor permeability in the underlying granular and pulverized base materials may have also contributed to centreline joint cracking. Longitudinal cracking in the widened bike lanes was observed to varying degrees along the project and is attributed to differential settlement between the pre-existing road structure and the widened bike lanes. The southbound lane of section South C included an extra right turn lane, which had a longitudinal crack originating at the bike lane and extending through the right turn lane. It is hypothesized that the longitudinal cracking along the centreline, the bike path, and through the right turn lane is primarily attributable to longitudinal joint and differential settlement issues and for these reasons cracking distresses have been separated from the transverse, longitudinal, and fatigue cracking.



Figure 6. Battersea Road Sections Paved in 2009

Table 11. Battersea Road Crack Survey Summary (2016)

Section

Wheel Path Non-Wheel Path Transverse

(m/500m)

Longitudinal Joint and Differential

Settlement (m/500)

Fatigue (m2/500m)

Longitudinal (m/500)

Longitudinal (m/500m)

L M H L M H L M H L M H CL BL RTL North A – SB 1 4 0 35 0 0 66 0 0 64 4 0 418 324 n/a North A – NB 6 10 0 6 0 0 9 0 0 54 10 0 418 1 n/a North B – SB 2 12 0 79 0 0 127 0 0 38 4 0 521 78 n/a North B – NB 1 0 0 3 0 0 5 0 0 41 0 0 521 0 n/a North C – SB 1 0 0 34 0 0 19 0 0 35 9 0 506 86 n/a North C – NB 0 0 0 76 0 0 13 0 0 88 3 0 506 51 n/a South A – SB 0 0 0 0 0 0 21 0 0 90 4 0 713 196 n/a South A – NB 3 0 0 4 0 0 14 0 0 153 4 0 713 138 n/a South B – SB 0 0 0 44 0 0 8 0 0 151 0 0 789 283 n/a South B – NB 0 0 0 6 20 0 3 0 0 118 0 0 789 0 n/a South C - SB 3 0 0 7 0 0 17 0 0 68 5 0 484 80 n/a South C - NB 98 2 0 6 0 0 0 0 0 104 0 0 484 78 116

Note: NB is Northbound SB is Southbound L is Low severity M is Medium severity H is High severity CL is Centre Line BL is Bike Lane RTL is Right Turn Lane



Varying levels of mostly low severity with localized moderate longitudinal and fatigue cracking, as well as transverse cracking were observed. Figure 7 shows major differences in the in-lane longitudinal and fatigue cracking between sections. For example, the southbound lane of Section North B exhibits more than double the in-lane longitudinal and fatigue cracking than the southbound lane of the adjacent North A section. Figure 8 illustrates major differences in transverse cracking among sections. As an example, the southbound lane of Section South B has 136 percent more transverse cracking than the southbound lane of Section South A. The significant difference in the extent of cracking between sections suggests that factors other than binder properties are influencing cracking on Battersea Road. A more consistent pattern of cracking between sections would be anticipated if binder properties were controlling the cracking performance. Figure 9 visually illustrates variation in cracking with photos of relatively crack free segments contrasted with sections that show cracking distresses.

While thermal cracking on Battersea Road cannot be ruled out, it appears that not all of the transverse cracking on this road can be attributed to thermal cracking. The southbound lane of Section North B has the highest level of longitudinal and fatigue cracking along with low levels of transverse cracking.

Different traffic levels are not the cause. Traffic counts between the northbound and southbound lanes in the north section of Battersea Road were similar. Figure 10 shows an irregular transverse crack across this section of the road along with a corresponding crack in the concrete curb. A gap exists between the edge of the pavement and the concrete curb. It appears that this crack may not have been caused by thermal contraction of the pavement, but rather by other forces such as a shift in the sub pavement materials which cracked not only the pavement but the concrete curb as well.

Figure 7. Wheel Path and Non-Wheel Path Longitudinal (m/500m), and Fatigue Cracking (m/500m) on Battersea Road (2016). Excludes Centre Line, Bike Lane, and Right Turn Lane Cracking

attributed to longitudinal joint and differential settlement.

0.00

50.00

100.00

150.00

200.00

250.00

NorthA - SB

NorthA - NB

NorthB - SB

NorthB - NB

NorthC - SB

NorthC - NB

SouthA - SB

SouthA - NB

SouthB - SB

SouthB - NB

SouthC - SB

SouthC - NB

Fatigue(m^2/500m) Longitudinal (m/500m)



Figure 8. Transverse Cracking (m/500) Battersea Road (2016)

Figure 9. Varying amounts and types of cracking on Battersea Road. Relatively crack free portions of Section North A-NB and South C-SB. Longitudinal, transverse, longitudinal bike lane, and centre line cracking in Section South B. Longitudinal, transverse, and longitudinal bike lane

cracking in Section South C-NB.

0.00

50.00

100.00

150.00

200.00

250.00

NorthA - SB

NorthA - NB

NorthB - SB

NorthB - NB

NorthC - SB

NorthC - NB

SouthA - SB

SouthA - NB

SouthB - SB

SouthB - NB

SouthC - SB

SouthC - NB

North A-NB

South B (NB and SB)

South C-NB South C-SB



Figure 10. Irregular transverse crack running across Section North B. Cracked concrete curb, apparent drainage issues in this part of Section North B, along with irregular direction of transverse crack suggest that sub base conditions may have cracked the pavement and the concrete curb (does

not appear to be thermal cracking)

As shown in Figure 11, the land adjacent to the southbound lane in this area of the road is elevated and slopes down towards the pavement. Water travels towards the road during rain events. A limited investigation, to be discussed in further detail, into the granular materials under the pavement on Battersea road showed variable permeability results. One area showed a permeable base while another had poor permeability. The poor drainage caused by land sloping down towards the southbound lane, combined with the possibility of poor permeability in the underlying pulverized base, provides a plausible explanation for the high levels of cracking observed in the southbound lane of Section North B. The northbound lane of Section North B has the lowest in-lane fatigue and longitudinal cracking of all the sections. The northbound lane is on the opposite side of the elevated land that slopes towards the pavement and also has storm drains installed for water drainage. The improved drainage features in the northbound lane versus the southbound lane provide a plausible explanation for the significantly higher levels of cracking in the southbound lane than in the northbound lane. It is anticipated that similar circumstances of poor drainage and/or possibly poor permeability of the pulverized base under the pavement may have contributed to other instances of longitudinal and transverse cracking in this road.

Figure 12 show examples of the transverse cracks that extend partway across the pavement and/or travel in irregular directions. These may not all be thermal cracks. Thermal cracks would be expected to extend across the width of the pavement structure, somewhat equally spaced, and somewhat perpendicular to the direction of the road. Cracks from built up thermal stresses in the pavement typically seek relief by extending to the edge of the pavement. In cases where the centreline is cracked, the thermal crack may be offset slightly between lanes at the centreline as the open or cracked joint provides an edge. Instances of cracks extending across the pavement perpendicular to the direction of travel do exist on Battersea Road. While thermal cracking cannot be ruled out, factors such as poor drainage and inconsistent permeability of the pulverized base beneath the pavement are likely contributing the cracking.



Figure 11. Section North B – Significant cracking in northbound lane compared to southbound lane.

Elevated land slopes down towards northbound lane (potential sub pavement drainage issue for northbound lane), while storm sewers drain water from southbound lane.

Figure 12. Examples of varying types and degrees of transverse cracking. Factors other than thermal cracking may be contributing to these cracks given their irregular direction and the lack of

extension across the pavement to a pavement edge.

The level of drainage along Battersea Road appears to vary. Some areas have deep ditches that allow water to drain away from the road. Other areas have shallower ditches that may not provide good drainage. There are also sections which have bulrushes growing on one or both sides of the road. These plants grow in standing water and it is anticipated that this water could seep into and affect the performance of the roadway. The storm pipe in a storm sewer installed adjacent to the road was observed to be above the level of standing water below the pipe which results in water not being drained away from

Southbound Lane

Southbound Lane

Northbound Lane



the road. Pre-construction geotechnical reports also note poor drainage on Battersea Road, and indicate that improvements to drainage would improve the performance of the road. The pre-construction geotechnical reports describe the ditching in the north section as marginally adequate to inadequate, while the ditching in the south section is deemed inadequate [10, 11].

Permeability testing was completed by Engtec Consulting Inc. on the materials underlying the asphalt pavement on Battersea Road. Slabs of pavement were saw cut from the road to expose the underlying material in order to exclude the possibility of creating excess fines, which could influence permeability results if borehole samples were taken. Table 12 shows the permeability results. It was found that the material sampled from the north section of Battersea Road was permeable while the sample from the south section had poor permeability [42]. While the section from which the sample was taken is noted, it may not be assumed that the results are representative of the entire roadway section given the limited nature of the sampling. The results show inconsistent permeability results which supports the possibility that inconsistent drainage and/or permeability of the granular and pulverized material under the pavement may be influencing the inconsistent levels of cracking between sections observed on Battersea Road.

Table 12. Compaction and Constant Head Permeability Results for Granular/Pulverized Base on Battersea Road

Section

Maximum Dry

Density (kg/m3)

Optimum Moisture Content

(%)

Constant Head Permeability

Result (cm/sec)

Permeability Criteria (cm/sec) Comment

Permeable Poor Impermeable

North C SB 2,040 8.7 1.53 x

10-3

> 10-4 10-4 to

106 < 10-6

Permeable

South B SB 2,020 8.5 5.47 x

10-5 Poor

Permeability

The centreline and bike lane cracking likely provided entry points for water to infiltrate the roadway, which may have accelerated cracking in sections with poor underlying material permeability as the water may not have been able to readily drain out of the pavement structure. Some instances of minor mix segregation were observed, which may have contributed to some of the shorter in-lane longitudinal cracks in the road.

The HL3 surface and MDBC mixes appeared to be well-bonded to each other based on cores and slabs cut from Battersea Road. While tack coat was not used on this project and it has been shown that the lack of a good bond between pavement layers can result in premature cracking [42], it does not appear that the lack of tack coat significantly contributed to cracking on this road.

6.5 Falling Weight Deflectometer (FWD) Testing

FWD testing was completed on Battersea Road in November 2015 by Engtec Consulting Inc. using a Dynatest 8082 Heavy Weight Deflectometer normalized to 40 kN at 21oC to assess the structural condition of this pavement. Table 13 shows the normalized deflection and deflection basin area data for the north and south sections of Battersea Road [43].



Table 13. Normalized Deflection and Deflection Basin Area for Battersea Road

Section

Normalized Deflection Bowl Parameters

do (mm)

do/d200 (mm) Area

Base Layer Index

(µm)

Middle Layer Index

(µm)

Lower Level Index

(µm) North - NB 0.221 1.266 495 59 48 23 North - SB 0.242 1.270 497 64 53 26 South - NB 0.211 1.278 486 58 47 24 South - SB 0.217 1.277 482 59 49 24 Criteria for Collector / Minor Arterial Road [43] ≤ 0.5 ≤ 1.4 ≥ 600

Criteria for Pavements with ESALS < 3 x 106 - Sound <200 <100 <55 Criteria for Pavements with ESALS < 3 x 106 -Warning 200-500 100-200 55-100 Criteria for Pavements with ESALS < 3 x 106 - Severe >500 >200 >100

The centre plate deflection (do) indicates pavement stiffness and subgrade strength. The ratio of centre plate deflection to sensor deflection at 200 mm (do/d200) represents the strength of the subgrade relative to the pavement structure. Increasing do/d200 values indicate increasing horizontal tensile forces, which translate to a measure of asphalt strain and the potential for cracking to occur. Recommended criteria for these parameters where met indicating acceptable structural strength. Results for the normalized area for the deflection basin, which indicates the ability to effectively distribute vehicle loading, were lower than the acceptance criteria. It is possible that the underlying bedrock may be influencing the deflection basin area results. Pre-construction boreholes indicated varying bedrock depths with auger refusal at between 0.7 to 1.3 m for some boreholes, while in other cases refusal was not encountered at depths of approximately 2 m [10, 11].

In order to further assess the structural properties the Base Layer Index (indicates base layer structural condition), Middle Layer Index (indicates subbase structural condition), and Lower Level Index (indicates subgrade and/or bedrock structural condition) were calculated as shown in Table 13. This analysis indicates a sound pavement structure with acceptable structural support. It is acknowledged that the FWD testing did not indicate a weakened pavement structure as might have been associated with drainage issues. However the FWD testing was completed in November when the pavement was drier than it would be in the spring when thawing conditions would be expected to contribute to loss of structural support.

7.0 FINDINGS

Battersea Road is in generally good condition after seven years of service. Preventive crack sealing after five years was instrumental in maintaining the condition of the road and the pavement would be in worse condition had this not been undertaken considering the drainage problems noted on this section of roadway. Distresses include cracking along the centreline longitudinal joint, wheel path and non-wheel path longitudinal cracking, transverse cracking, and longitudinal cracking along the inside edge of the widened bike lanes. The majority of the cracking is low severity with localized instances of medium severity cracking.



The following findings were drawn from a comprehensive laboratory and field evaluation of the performance of Battersea Road:

Asphalt cement binder properties met AASHTO M320, DENT, and Extended BBR specifications as well as required restrictions on modifiers. The AASHTO M320 true performance grade of the supplied binder met the 98 percent low temperature design reliability (LTPP Bind v3.1) for the geographic location of the pavement. The asphalt cement did not adversely affect cracking performance.

Recovered binder from the HL3 surface mix (0 percent RAP) after six years of field aging had low temperature BBR and Extended BBR properties that were similar to the properties of binder supplied to for the project. In this specific case study, the PAV laboratory aging procedure on tank sampled binder approximated low temperature binder properties after six years of field aging.

Recovered binder properties from the MDBC base mix were influenced by the 15 percent RAP in the mix. RAP must be accounted for when interpreting low temperature AASHTO M320 BBR, and LS-308 Extended BBR and Grade Loss properties as recovering the binder assumes full mixing of the virgin binder with the RAP binder. Complete mixing of the virgin binder with the RAP binder may not occur in real pavement systems and as such recovered binder properties may from mixes containing RAP may not be completely indicative of mix properties.

FTIR testing indicated equal or higher SBS polymer content in the asphalt cement recovered from the road after six years of field aging as compared to the tank sampled binder supplied to the project. The styrene index was higher in the recovered binder from the HL3 (0 percent RAP) surface mix than the tank sampled binder. The butadiene index for the binder recovered from the HL3 mix was equal to the butadiene index measured on the tank sample. The recovered binder styrene index from the HL3 (0 percent RAP) mix agreed with a correlation curve plotting the styrene index versus SBS content. Styrene and butadiene indices in binders recovered from the MDBC base mix containing 15 percent RAP were 11 to 14 percent lower than the binder recovered from the HL3 virgin mix. It is cautioned that while FTIR styrene and butadiene indices on recovered field aged asphalt binder agree with corresponding properties from a tank sample of binder supplied to the project in this specific case study, that other research has shown significant discrepancies in styrene and butadiene FITR indices between tank sampled binders and recovered field aged binders. Interpretation of such comparisons should be undertaken with caution.

Mix performance testing (APA rutting, four point bending beam fatigue, TSRST low temperature cracking, and dynamic modulus) on the HL3 plant produced surface mix yielded results that trended with the AASHTO M320 true grade of the binder and did not indicate any mix performance issues when compared to mix produced with two different binders for comparison purposes. It is not anticipated that mix properties adversely influenced cracking performance.

Specified minimum asphalt cement contents, which appear to be sufficient, were met. Low asphalt cement content did not contribute to cracking.

Adequate compaction was achieved on the project and poor compaction did not appear to contribute to cracking. This is further corroborated by recovered binder from the HL3 surface mix (0 percent RAP) which has low temperature BBR properties after six year of field aging that correlated to the



low temperature of the binder supplied to the project. The field aged binder does not appear to be excessively aged from high voids (poor compaction) in the mix.

The types and amount of cracking after seven years vary significantly between different sections of the project. This further suggests binder properties are not negatively impacting cracking as a more consistent pattern of cracking would be expected if binder properties were the controlling factor.

Inconsistent permeability properties (limited testing indicated one area with poor permeability and another with good permeability) of granular and pulverized materials beneath the pavement combined with observed drainage problems in some areas appear to be contributing to the inconsistent cracking on Battersea Road.

While thermal cracking cannot be ruled out and might be expected to some degree after seven years, not all transverse cracks appear to be thermal. An instance of a transverse crack extending across the pavement and through a concrete curb indicates a possible shift in materials beneath the pavement. Examples of transverse cracks which travel in irregular directions and do not extend to the edge of the pavement may also be caused by other factors.

Longitudinal cracking along the inner edge of the widened bike lanes appears to be due to differential settlement between these widened sections and the adjacent roadway. Cracking along the longitudinal centre line joint probably began when the joint opened and was furthered by water infiltration and possibly poor drainage or inconsistent drainage in the underlying granular and pulverized base materials.

This case study demonstrates that good binder properties are necessary but do not solely ensure good cracking performance.

REFERENCES

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[2] Huber G, Marks P, Brown A, Raymond C. “Relationship of Asphalt Binder Properties to Cracking in Five Year Old Test Sections”, Proceedings, Canadian Technical Asphalt Association, 57, 322-348 (2012).

[3] Hesp SAM, Soleimani A, Subramani S, Phillips T, Smith D, et al. “Asphalt Pavement Cracking: Analysis of Extraordinary Life Cycle Variability in Eastern and Northeastern Ontario”, International Journal of Pavement Engineering, 10 (3), 209-227 (2009).

[4] Oluranti PG, Hesp SAM. “Physical Hardening in Asphalt Mixtures”, Int. J. Pavement Res. Technol., 5 (1), 46-53 (2012).

[5] “Method of Test for the Determination of Asphalt Cement’s Resistance to Ductile Failure Using Double Edge Notched Tension Test (DENT)”, Test Method LS-299, Rev. No. 27, Laboratory Testing Manual, Ministry of Transportation, Ontario (2012).



[6] “Method of Test for Determination of Performance Grade of Physically Aged Asphalt Cement Using Extended Beam Bending Rheometer (BBR) Method”, Test Method LS-308, Rev. No. 26, Laboratory Testing Manual, Ministry of Transportation, Ontario (2011).

[7] American Association of State Highway and Transportation Officials (AASHTO) M320-10, “Standard Method of Test for Performance-Graded Asphalt Binder”, Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part 1B, 30th Edition, Washington, DC (2010).

[8] “Method of Test for the Determination of Asphalt Cement’s Resistance to Ductile Failure Using Double Edge Notched Tension Test (DENT)”, Test Method LS-299, Rev. No. 24, Laboratory Testing Manual, Ministry of Transportation, Ontario (2007).

[9] “Method of Test for Determination of Performance Grade of Physically Aged Asphalt Cement Using Extended Beam Bending Rheometer (BBR) Method”, Test Method LS-308, Rev. No. 24, Laboratory Testing Manual, Ministry of Transportation, Ontario (2007).

[10] Houle AC. “Geotechnical Investigation and Pavement Evaluation – Rehabilitation of Battersea Road Between Unity Road and Aragon Road, City of Kingston, Ontario”, Houle Chevrier Engineering Ltd., July (2009).

[11] Houle AC. “Geotechnical Investigation and Pavement Evaluation – Rehabilitation of Battersea Road Between River Ridge Drive and Thompson Crescent, City of Kingston, Ontario”, Houle Chevrier Engineering Ltd., June (2009).

[12] Engineering Department. “City of Kingston Contract ENG-2009-15, Road Resurfacing on Battersea Road Contract and Specifications”, The Corporation of the City of Kingston, Ontario (2009).

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