experience with superpave mixes in texas · to low volume roadways; from new construction to...

88th Annual Transportation Short Course Paul Hoelscher

EXPERIENCE WITH SUPERPAVE MIXES IN TEXAS

Table of Contents

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7-12

12-24

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26-28

3-6 Why Use Superpave Mixes

Initial Implementation and Results

Adjusted Implementation Plan and Results

Future Plan

Constructability Issues

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2

3

4

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ABILENE DISTRICT

Borden Scurry Fisher Jones

Kent Stonewall Haskell

Howard Mitchell Nolan Taylor Callahan

ABILENE

SuperPave Mixtures

Advantages – Can be used on medium to high volume roadways. – The binder content can be adjusted by adjusting the N-des level. – Stone on stone contact

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Typical Use – Versatile mix used for a variety of applications ranging from high volume

to low volume roadways; from new construction to overlays. – Used as base, intermediate and surface layers.

Why the Abilene District Transitioned from Conventional Mixes to Superpave Mixes??? – Desire to improve performance life – Higher Asphalt Content – Stone on Stone Contact

Binder Content - Statewide Averages

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Mix Type Dense-Graded SuperPave

Type A 4.2 4.7

Type B 4.5 4.8

Type C 4.7 5.5

Type D 5.0 6.1

Average Mix Cost

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$73.58

$86.40

65.00

70.00

75.00

80.00

85.00

90.00

Dense Graded SuperPave

$ / T

on

SuperPave Mixtures

Early Results – SP-A very course and appeared to be open to water intrusion. – Observed wet spots in SP-C surfaces the day after it rained. – Little or no improvement in asphalt contents (AC) – Compaction issues due to low AC – Observed premature cracking with 100-125 gyration mixes

and/or PG76-22

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History of Superpave Usage in the Abilene District – Began Transition in early 2000’s – Initially used SP-A base mix and SP-C surface mix – Initially used a N-des level of 100-125 gyrations – Utilized several grades of asphalt in the SP-C (PG70-22 & PG76-22) – Utilized PG64-22 in the base course

Built In 2003 US 84, Nolan Co. SP-C, PG76-22

Built In 2003 FM 89, Abilene TX SP-C, PG76-22

Built In 2003 SH 350, Snyder TX SP-C, PG70-22

Built In 2004 US 180, Roby TX SP-C, PG70-22

Built In 2004 FM 707, Taylor Co. SP-C, PG76-22

SuperPave Mixtures

Results – SP-B less course and appeared to be less susceptible to water

intrusion. – SP-C mixes had better compaction properties resulting in less water

intrusion. – SP-D mixes appeared to be tighter and less susceptible to water

intrusion. – Observed an increase asphalt content with 75 gyration mix designs.

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Implemented Changes to Achieve Desired Results – New specification with the 2004 Spec Book – Migrated from SP-A to SP-B base course – Started trying SP-D surface mixes – Reduced the N-des level to 75 gyrations – Only used PG70-22 in surface mixes – Continued to utilize PG64-22 in the base course

Binder Content - Statewide Averages

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Mix Type Dense-Graded SuperPave

Type A 4.2 4.7

Type B 4.5 4.8

Type C 4.7 5.5

Type D 5.0 6.1

Binder Content – Abilene District

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Mix Type SuperPave

Typical AC

SP-B 4.7

SP-C 5.2

SP-D 5.5

Built In 2005 SH 70, Nolan Co SP-C, PG70-22

Built In 2005 BI 20-M, Sweetwater TX SP-C, PG70-22

Built In 2005 US 83, Stonewall Co. SP-D, PG70-22

Built In 2006 BU 83-D, Abilene TX SP-C, PG70-22

Built In 2006 SH 36, Abilene TX SP-C, PG70-22

Built In 2006 US 83, Jones Co SP-D, PG70-22

Built In 2007 FM 617, Haskell Co. SP-D, PG70-22

Built In 2007 US 380, Haskell TX SP-D, PG70-22

Built In 2008 US 87, Big Spring TX SP-D, PG70-22

SuperPave Mixtures

10 Year Performance History – Performance overall is good. – Very little or no rutting observed. – Mix still appears to be too dry. – Minor cracking occurs too early in the pavement life.

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Implementing Additional Changes to Achieve Better Results – New specification with the 2014 Spec Book – Reducing the N-des level to 50 gyrations – Use more SP-C mixes

SuperPave Mixtures

Constructability Issues – More difficult to compact. – May have intermediate temperature tenderness (tender-zone).

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Issues Encountered

Tender Zone During Compaction A temperature range during the cooling process of the mat in

which the mix becomes tender. Excessive rolling in the “Tender Zone” can cause mat to shove

and crack

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SuperPave Mixtures

Possible Causes of Tender-Zone Issues – Placement on a smooth surface – Improper roller frequency and/or amplitude – Placement too thick for the mix type – Percent fines too high (especially field sand)

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Ways to Address Tender-Zone Issues – Design to avoid placement on smooth surfaces – Adjust roller frequency and amplitude – Avoid rolling the mix in the temperature range where the mix is

unstable during compaction – Ensure adequate tacking is achieved – Redesign

Primary Impact – Will affect ride quality if not controlled – Can leave rips and tears in the final mat

Questions?

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