Concrete Pavement Research Highlights. Mike Bergin State Structural Materials Engineer FDOT Construction Conference February 20, 2013

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1 Concrete Pavement Research Highlights Mike Bergin State Structural Materials Engineer FDOT Construction Conference February 20, 2013

2 Highlights include; Update Recycled Asphalt Pavement (RAP) as aggregate in concrete pavement (completed) Maturity Meter (HES) concrete (on-going) New Work GTR New Idea RCC

3 RAP In Concrete Pavement The focus; Evaluate RAP for use in concrete pavement. Lots of RAP available Reduce modulus of elasticity (MOE) of concrete with the addition of RAP as a portion of the aggregate.

4 RAP Design a more flexible concrete pavement; may provide a longer service life is less brittle - able to move High MOE indicates a more brittle concrete which tends to restrict or limit slab movement Movement is needed to compensate for; thermal changes loading conditions

5 Mix Designs Modeled after a Class I Pavement. The components that varied; 4 different RAP sources Primarily limestone with polymer modified binder Virgin aggregate was replaced with 20%, 40%, 70% and 100% of RAP. Replacement of coarse and/or fine aggregate Some mixes included only coarse aggregate replacement Some had only fine aggregate replacement Some had both fine and coarse aggregate replacements w/c ratios were 0.45, 0.50 and 0.55 No SCM s used in these mixes

6 What we ve found As expected in both cases; As the RAP content increased, compressive strength was reduced As the w/c ratio went up the compressive strength was reduced The film of asphalt on the particle provides for a very slight movement of the aggregate particle when its loaded.

7 What we ve found The control mix (Class I Pav t) was compared to a RAP mix with a 20% replacement of coarse aggregate. The average compressive strength was reduced from 5376 to 4250 psi at 28 days. Less strength loss at early ages, Greater strength loss in long term ages. (ap. 18 to 24% reduction for all mixes with RAP at 56 and 91 days) ACI equations to relate compressive to flexural strength and MOE don t apply

8 RAP- What we ve found MOE reduced ap. 19% at 28 days. (from x 10^6 psi) ACI equation, over estimates MOE Flexural strength was reduced approx. 15% at 28 days ( psi) ACI equation under estimates flexural strength Splitting tensile strength was reduced approx. 17% at 28 days ( psi)

9 RAP- What we ve found CTE testing indicated a slight increase in thermal expansion from 4.40 to 4.60 (x10^-6/f) Several FEM programs along with the MEPDG were used to study; Critical loading conditions Stress strain conditions Failure loads

10 RAP- What we ve found Stress analysis indicates that Maximum stress in the pavement decreases as the RAP increases Flexural strength of concrete with RAP was lower than conventional concrete Computed stress to strength ratio for some mixtures (20-40 % RAP) was lower than conventional concrete When averaged, pavement with RAP had higher failure loads than the control concrete.

11 Conclusions Mixes with RAP Improves overall gradation Provides lower MOE Less cracking potential compared to conventional pavement concrete The research was completed in August of 2012 The final report provides guidance for pavement design using RAP. Available; FDOT Research Office website Full scale testing: US 301 test road.

12 Maturity Method for HES concrete ASTM C1074 identifies the Maturity Method Indicates maturity-strength relation for normal setting concrete It does not address concrete maturity with hydration periods in the 2 to 6 hour range. TWO for the project was initiated Dec This an short update

13 Research was Needed Determine the method best suited to predict maturity of high early strength concrete For slab replacement (early opening to traffic) Recommendations for construction practices Weather and temperature variations a concern How much temperature variation requires a new set of data?

14 Research Plan Batch concrete to simulate current construction practice; High cement contents Accelerating admixtures Implement current curing practice Vary ambient temperatures to simulate placements (40F, 73F and >110F )

15 Maturity Concept Two Maturity indexes (ASTM C1074) Temperature/time factor ( C) Nurse-Saul method Datum temp; to be determined (0 C good estimate) Equivalent age at some temperature ( K) Arrhenius method Example for temp/time factor Develop data from the laboratory The temperature at some time, indicates a maturity index of the concrete Break a cylinder to determine the strength- maturity relationship Verify in the field Thermo couples (temp) in the fresh concrete, then follow the same process to determine maturity.

16 Early in the Research Concrete batched at different ambient temperatures Evaluating the effects of the curing temperatures As expected temperature at curing has large effect on strength High temp higher initial strength Low temp lower initial strength

17 Early in the Research Part of the research includes; Visit an on-going job with Mix specific data verified in the lab Determine accuracy of lab data to field data for predicting compressive strength Research, should be competed by this time next year.

18 New Ideas in Concrete Paving Ground Tire Rubber as aggregate in concrete pavement Roller Compacted Concrete for pavement

19 Ground Tire Rubber Similar to the RAP usage; The TWO was initiated Aug Use of another waste material Can we reduce the MOE to provide a more flexible concrete pavement Use the GTR as a replacement to aggregate Fine replacement Coarse replacement- what size? Very early in the research, will update next year

20 RCC Access road to CSX terminal in Bartow area (non DOT) Construction technique is to : Basically prepare base Use pug mill to batch an econo-type concrete Very low slump Dumped onto base Smooth out to the approximate elevation with a motor grader Rolled, using a steel wheel roller.

21 RCC If base is prepared, the process is fast (possibly place one lane mile of pavement a day) Is not esthetically pleasing to look at. But is cheap to build Limits the speed of traffic (bumpier than other pavements) could it be ground? May have some potential uses where heavy trucks are traveling at slower speeds

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27 Thanks - any questions?