The New Hot Mix Specification Item 3224

2011 Transportation

Conference

Dale A Rand, P.E. Flexible Pavements Branch

Construction Division

Why Do We Have to Keep Changing Our HMA Specifications?

Changes in the Past 10 Years

Rutting & Moisture Damage Then: Hveem Stability & Lottman testing Now: Hamburg Wheel test

Pavement design for Perpetual Pavements Then: Modulus of 500 ksi used or all HMA Now: Modulus of 650-800ksi …thinner pavement Then: AASHO Road Test – late 1950s – 6” HMA Now: NCAT test track, MEPDG (Mechanistic Empirical)

Asphalt Prices Then: PG 64-22 cost $163 per ton (CRCP?) Now: PG 64-22 cost $575 per ton (CRCP?)

Changes in the Past 10 Years

Use of Recycled Materials Then: Not worth the effort? Now: RAP and RAS are common and essential to

control cost increases, fractionation, process improvements

The Environment Then: Virgin mixes….the hotter the better Now: WMA, RAP, RAS, Tire Rubber, In-place recycling,

carbon foot print Ride Quality Measurement Then: Straight edge or profilograph (push behind) Now: high speed profilers

Changes in the Past 10 Years

Pavement Noise Measurements Then: Rarely done, way side measurement? Now: On board sound intensity (OBSI), easily

measured at highway speeds Asphalt Binder Grade Then: Grade bump to address rutting Now: Grade dump to address cracking

Thermal Segregation (best technology) Then: Infrared camera, measures <1% for >50K Now: Pave-IR measures 100% for <30K

Changes in the Past 10 Years New Kids on the Block Then: Superpave, CMHB, & Large Stone Mixes placed

in Thick Lifts Now: SMA, PFC, CAM, TOM, TBPFC, UTBHMWC, Thin

PFC……This is In! Asphalt Additives Then: Lime or liquid anti-strip Now: Lime, liquid anti-strip, fibers, fly ash, WMA

(foaming), WMA (chemical etc), shingles, RAP, crumb rubber etc

Other Issues Overlay Test, Micro Deval, Cantabro test, Sample

Custody, Trackless Tack, Toll Roads, CDA, Design Build

If You Use Yesterday’s Solutions to Solve Today’s Problems, You May Not Be in

Business Tomorrow

Standard Specification Rewrite

TxDOT has started the process to rewrite the 2004 Standard Specifications TxDOT will utilized a consultant contract to

“facilitate” the process In the past year +, the Flexible Pavements

Branch has been rewriting all the HMA specifications.

Current Status (Standard Spec Items) Item 340 (Dense Graded HMA – Method)

SP 340-003 Allows RAP & RAS - May 2009 – Required for Statewide Use

Item 341 (Dense Graded HMA – QCQA) Replaced by Special Specification 3224 in July, 2011 - Allows RAP,

RAS, Subst. Binder, WMA, SGC, Pave-IR , 96.5 target lab density, custody of cores, no waiving profiles – Required for Statewide Use

Item 342 (Permeable Friction Course - PFC) SP 342-002 – Requires 6.0% minimum AC, payment for AR based on

flow meters – Sept. 2006 – Required for Statewide Use Item 344 (Performance Design Mixtures)

SP 344-009 – Allows fractionated RAP – June 2008 – Optional for Statewide Use

Item 346 (Stone-Matrix Asphalt – SMA) SP 346-003 – Allows fractionated RAP – June 2008 – Optional for

Statewide Use

Overview of SS 3224 1. Allows “intermediate” aggregate as well as coarse & fine aggregate. 2. Adds wording that the engineer may test during production to insure 50%

of #4 aggregate comes from a Class A source. Applies only when contractor blends aggregates to meet Class A requirement.

3. Stipulates that engineer will perform Micro-Deval abrasion test during production. Test data is used to estimate the MgSO4 soundness loss.

4. Changed requirements on RAS gradation from a minimum of 90% passing the 3/8 sieve to minimum of 95% passing the 3/8 sieve.

5. Adds wording that addresses the possible consequences if a contractor fails to comply with a specification requirement to suspend production or placement. This is needed because there are at least 7 different circumstances when a contractor is supposed to “shut themselves down” (suspend operations).

6. Stipulates to use TxDOT provided software for reporting. 7. Addresses mixes that are too stiff. Essentially requires more asphalt. Also

allows the contractor some latitude.

8. Addresses concerns of paving at low (particularly day time) temperatures. 9. Stipulates when engineer will do Micro-Deval testing. 10. No longer allows waiving the thermal profile. It is required for every sublot

and documentation is required at the end of each lot. 11. Addresses the contractor using the PAVE-IR for specification compliance

and stipulates reporting requirements. 12. Under “material transfer devices” allows the PAVE-IR to be used in lieu of

a specified MTD. 13. Under “Hauling Equipment” adds additional requirements when dumps

are used. 14. Addresses potential damage caused by screed heaters being left on

during long paver stops. 15. Allows Lot 1 to be larger than 1,000 tons. 16. Allows small quantity clause to be used when mutually agreed even if

production does not meet default definition of small quantity production. 17. Requires engineer to obtain or witness all production sampling & retain

custody of samples.

18. Stipulates when the contractor will obtain samples for informational Cantabro & Overlay testing. We are trying to establish a database for future specification consideration.

19. Addresses VMA calculations. 20. Table 14 shows contractor responsible for obtaining Cantabro & Overlay

samples. 21. Addresses the consequences of VMA being out of specification. This is

important to prevent dry mixes because we do not have minimum asphalt binder requirements.

22. Specifically defines what is and is not considered “miscellaneous” and what is subject to air void testing.

23. Requires engineer to witness coring operations. Requires onsite trimming of cores. Allows for trimming at an alternate location. Stipulates engineer will maintain custody of core or use CST protocol to provide a secure means and process that protects the integrity of the cores during transport.

24. Segregation (density profiles) are required every sublot. Waiving the density profile is no longer an option. They are required for every sublot and documentation is required at the end of each lot similar to the segregation profile. Note: FHWA stewardship assessment showed that density & thermal profiles were not being performed as required.

25. Similar to thermal profiles and density profiles, joint density evaluations are required on every sublot and documentation is required at the end of each lot.

26. Recovered asphalt dynamic shear Rheometer (DSR) is not required when the Pave-IR system is used for specification compliance since the PAVE-IR provides a continuous profile of the mix temperature.

27. To receive bonus contractor is required to comply with specification requirements to report results for required tests.

28. Table 16 – when target density is 96.5 or 97.0, pay adjustments are the same but we does not allow continued production if the lab density exceeds target by ±1.0%. Flushing & rutting are concerns when the lab density gets too high.

29. The engineer may allow failing placement sublots to be left in place without payment in lieu of removal and replacement. This makes placement similar to production.

Coming Changes to Item 3224 1. Under the Additives Section, it is required to provide

documentation such as the bill of lading to prove the quantity of additives used in the project.

2. For any stockpile that contains RAS, the entire stockpile will be considered to be a RAS stockpile and limited to no more than 5.0% of the HMA mixture in accordance with Table 5.

3. When RAS or RAP is used, calculate and ensure that the ratio of the recycled asphalt binder to total binder does not exceed the percentages shown in Table 5 during mixture design and HMA production.

4. During HMA production, use a separate cold feed bin for each stockpile for RAP and RAS.

5. The recycled binder ratios in Table 5 were reduced 5% for the surface and non-surface mixes.

Coming Changes to Item 3224 6. Unfractionated RAP allowable amounts for non-surface mixes were

reduced to 10%. 7. Note added for the ride quality measurement to require the profiler and

operator to be certified at the Texas Transportation Institute facility. Level IB no longer required for operator.

8. In QCP, add procedures for adding and verifying rates of RAP & RAS. 9. During trial batch production, development and approval of JMF2, JMF

adjustments, and JMF3 approval, the mixture has to meet the requirements listed in Table 5, Maximum Allowable Amounts of Recycled Binder, RAP & RAS.

10. During conditional approval of JMF1 and authorizing trial batch, the Engineer will verify conformance with recycled materials too.

11. Under the Total Adjustment Pay Calculation Section, production and placement lot quantity definitions were added.

Overall Goals Be Proactive

Improve HMA Quality Reduce HMA Cost

Compliance with FHWA Regulations

Take Advantage of Technology Improvements

Be Better Stewards of Our Environment

Improve HMA Quality Increasing target lab density – increases asphalt

content - improves durability Pave-IR system implementation – reduce thermal &

physical segregation & improve quality of paving Encourage use of WMA – better in-place density &

less aggregate absorption – improve durability. Improve ride quality when paving over rubberized crack seal.

Substitute binder – blends softer binder with more oxidized binder from RAP & RAS – prevents over-stiffening the HMA

Reduce HMA Cost

RAP, RAS & Substitute Binders – can reduce HMA material cost significantly (approx.10% - 30%)

Pave-IR system – eliminates the need to manually perform thermal & density profiles. Allows opportunity to pave at lower temperatures.

Contractor provided “ticket taker” – eliminates TxDOT need to have contract employees or DOT inspector providing service

WMA systems – some systems result in an overall savings (fuel cost, density bonuses, extension of paving “season”)

Compliance with FHWA Regulations

2008 Stewardship Assessment & Recent

Stimulus Oversight by Office of Inspector General (OIG) Identified Concerns

Department representative must witness or take samples – TxDOT often not in compliance

Core samples were in contractor custody prior to TxDOT getting the samples

Many other more minor issues were identified

Take Advantage of Technology Improvements (since 2004)

Fractionated RAP Recycled Shingle Grinding WMA Systems Pave-IR System

Be Better Stewards of Our Environment (Reduce Carbon Foot Print)

RAP & RAS – reduces need for virgin asphalt

& aggregate & cost to transport such materials

WMA Systems – reduces emissions & fuel consumption

Improving HMA Quality (durability) – extends the life of HMA

Summary & Conclusions TxDOT is revising all HMA specifications in a

proactive effort to: Improve HMA Quality Reduce HMA Cost Be in Compliance with FHWA Regulations Take Advantage of Technology Improvements Be Better Stewards of Our Environment

Efforts should be completed with the next 3 months and will include review by TxDOT, Industry & FHWA