Synthesis of design and construction practices
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4. What is the form of the tools you use for design: a. Paper design guide / nomographs
b. Pavement catalogue
42 c. Pavement analysis software
d. Pavement design software
5. Specify the year in which the current design method was implemented within your
6. Give an estimated percentage of new roads constructed using: a. Flexible pavements ____%
b. Composite pavements* ____%
c. Rigid pavements ____%
* How much percentage are a result of HMA overlay over existing PCC** ____%
SECTION 3 : COMPOSITE PAVEMENT DESIGN INPUTS
7. Which environmental factors are taken into consideration in the design method used: a. Climatic zone(s)
b. Air temperatures
c. Pavement Temperatures
d. Detailed daily temperature data
e. Mean monthly/seasonal/annual temperatures
f. Maximum and minimum monthly/seasonal/annual temperatures g. Equivalent monthly/seasonal/annual temperatures
h. Precipitation
i. Frost index
j. Frost penetration depth
k. Other(s):_______________________________________________________ 8. What kind of traffic input do you use for the design of composite pavements? a. Equivalent Single Axle Load (ESAL)
b. Load spectra
c. Maximum axle or wheel load
9. What is the design life (in years) that composite pavements are typically designed for in your agency?
<20 20 25 30 40 50 >50 10. During the Pavement Type Selection (PTS) process for composite pavements, which of the following factors are considered?
a. Construction costs
b. Preventive maintenance costs
c. Rehabilitation costs
43 d. User-related costs (e.g., user delay)
e. Environmental impact
f. Other(s):_______________________________________________________ 11. Do you use Reliability as a part of the pavement design process? If so, what level of reliability do you normally consider for designing composite pavements?
a. No Reliability is used
b. 85%
c. 90%
d. 95%
e. 99%
f. Other: ________________________________________________________ 12. Do you use any other inputs for the design procedure (besides the material properties) not listed above? If so, please describe.
SECTION 4 : COMPOSITE PAVEMENT DESIGN CRITERIA
13. What method or design procedure do you use to design composite pavements? a. AASHTO modified method
b. US Navy and Military composite pavement design procedure c. NCHRP 1-37 – Mechanistic-Empirical Pavement Design Method d. Illinois Department of Transportation (IDOT) method
e. United Kingdom composite pavement procedure
f. Other: ________________________________________________________ 14. What types of layers comprise your typical composite pavement structure? a. Surface (flexible) layer i. Dense Graded / Hot-Mix Asphalt (HMA)
ii. Stone Matrix Asphalt (SMA)
iii. Open-Graded Friction Course (OGFC)
b. Base (rigid) layer i. Jointed Plain Concrete (JPC) pavement
ii. Continuously Reinforced Concrete (CRC) pavement iii. Roller-Compacted Concrete (RCC) 1 pavement
iv. Lean Mix Concrete 2
v. Cement-Treated Base (CTB) 3
vi. Soil Cement 4
vii. Other: _______________________________________________ 1 Dry concrete consistency; zero slump; vibratory compaction; compressive strength 4,000 to 10,000 psi; flexural strength 500 to 1,000 psi; modulus of elasticity 3,000,000 to 5,500,000 psi; cement content 9 to 18%. 2 Low strength concrete (low cement content); slump 1 to 3 in.; air content 4 to 8%; compressive strength at 7 days 500 psi (minimum), at 28 days 750 to 1,200 psi; cement-aggregate ratio 1:20 to 1:24 in volume. 3 Cement content 3 to 6% (weight); compressive strength at 7 days 650 psi, at 28 days 1,160 psi; modulus of elasticity 250,000 to 1,000,000 psi 4 Natural soil modified with 3 to 7% cement content; modulus of elasticity 50,000 to 100,000 psi.
44 c. Subbase i. Granular
ii. Cement Modified material/soil
iii. No subbase is used for the design
iv. Other: ________________________________________________ d. Subgrade i. Cement Modified material/soil
ii. Natural subgrade compacted
iii. Other: ________________________________________________ 15. Are there any minimum thickness requirements for some or all of the layers of the composite structure?
a. Surface course ______ in.
b. Base layer ______ in.
c. Subbase ______ in.
d. Subgrade ______ in.
e. No minimum thickness is required
16. For each of the layers described below, what characteristics are used in the design
a. Subgrade i. California Bearing Ratio (CBR)
ii. Resilient Modulus (elastic stiffness)
iii. Frost susceptibility
iv. Soil type/classification
v. Gradation
vi. Other(s): _______________________________________________ b. Subbase i. California Bearing Ratio (CBR)
ii. Resilient Modulus (elastic stiffness)
iii. Permeability
iv. Frost susceptibility
v. Soil type/classification
vi. Material strength (unconfined comp. strength) vii. Other(s): _______________________________________________ c. Base (rigid layer) i. Cement content
ii. Flexural strength @ 7
iii. Compressive strength @ 7
iv. Coefficient of thermal expansion
v. Other(s): _______________________________________________ d. Surface course (flexible layer) i. Elastic Modulus
ii. Dynamic Modulus
iii. Rheological properties
45 iv. Coefficient of thermal expansion
v. Fatigue resistance
vi. Rutting performance
vii. Other(s): _______________________________________________ 17. Please specify the typical properties of the following layers in your composite pavement system.
a. Surface course (flexible layer) i. Asphalt content ____%
ii. Air voids (target) ____%
iii. Other(s): _______________________________________________ b. Base (rigid layer) i. Typical cement content ____%
ii. Typical flexural strength @ 7 th day ____psi
iii. Typical compressive strength @ 7 th day ____psi
iv. Other(s): _______________________________________________ 18. Is there a design consideration/criteria regarding the mitigation or control of reflective cracking? If so, please describe.
a. Yes
__________________________________________________________________ b. No
SECTION 5 : CONSTRUCTABILITY
19. Have you used/placed any reflective cracking mitigation technique/method such as Stress Absorbing Membrane Interlayer (SAMI), Microcracking, Pre-Cracking, Geotextiles, etc.? If so, which ones and what has been your experience?
a. Yes
__________________________________________________________________ b. No
20. If you have used CTB or Soil Cement, where have you prepared this mix: a. In the field
b. In a plant
21. Please describe any issues or challenges that composite pavements brought in your
: COMMENTS 46 22. Please comment on any additional information that you believe could help to better the understanding, design, and construction of composite pavements. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ 47 APPENDIX B
The survey created during this study was sent to state DOT pavement design engineers. Responses were received from 34 state DOT’s. From these responses, 11 agencies responded as having experience designing composite pavements. Eight responses indicated the experience came from the rehabilitation of existing rigid pavements and 3 of the 11 indicated experience designing new composite pavements. The survey results presented in this appendix are based on the response of all 11 states that have the experience with composite pavement design.
48 Table B.1. Summarized Survey Results
SCDOT OhioDOT TxDOT MDOT MDSHA NJDOT Design method for composite pavements AASHTO 1993 AASHTO Modified FPS-19W
AASHTO 1993 AASHTO 1993 AASHTO 1993
in road network 2 0 4 0 0 0 Typical design life for composite pavements 20 20 20 20 20 20 Reliability used in the design process No Yes Yes Yes Yes Yes Flexible layer for CPS HMA HMA
HMA HMA
HMA, SMA HMA, SMA, OGFC Rigid layer for CPS CTB
JPCP CTB JRCP JPCP, CRCP
JPCP Subbase for CPS Cement modified material/soil, or no subbase Granular material No subbase is used Granular material No subbase is used Granular material Subgrade for CPS Natural subgrade compacted Cement modified material/soil, and/or natural subgrade compacted Lime modified material/soil Natural subgrade compacted Natural subgrade compacted Natural subgrade compacted Min. thickness for flexible layer (inches) 4 3 2 3.5
Min. thickness for rigid layer (inches) 6 8 8 Typical asphalt content 4 to 6%
7% 5%
5 to 6%
5% Typical air voids (target) 4 to 4.5% 3.5% 4%
4% 4%
4% Typical cement content 2 to 5% 600 lb
3 to 4%
Typical compressive strength 600 psi @ 14 days
350 psi @ 7 days
Design criteria or consideration for reflective cracking Yes Yes Yes Yes Yes Yes Comments Their philosophy is to use a low strength cement-treated base material to control shrinkage cracking and place that layer at a relatively high thickness to avoid fatigue cracking. Their design procedure for composite pavements consists of designing a rigid pavement and then reducing the thickness of the concrete by one inch and add a three inch asphalt surface. Microcracking of the CTB has been used reflective cracking on the surface course.
Ongoing research has shown Strata and other interlayer mixtures to be effective, binder rich surfaces such as SMA and OGFC perform better that SUPERPAVE, geo- textiles have not been very effective.
49 Transportation Agency GaDOT CODOT TnDOT ConnDOT IowaDOT Design method for composite pavements AASHTO 1972 AASHTO 1993 AASHTO 1993 AASHTO Modified AASHTO 1993 Composite pavements in road network 0 0 2 0 0 Typical design life for composite pavements 20 20 20 20 20 Reliability used in the design process No Yes Yes Yes Yes Flexible layer for CPS HMA, SMA, OGFC HMA, SMA HMA HMA
HMA Rigid layer for CPS JPCP, CRCP JPCP, CTB, Soil Cement CTB, Lime Fly-ash JPCP, JRCP JPCP, CRCP Subbase for CPS Granular material Granular material, Cement modified material/soil, or no subbase is used. No subbase design unless soil conditions (CBR less than 3) warrant cement modified soil. Granular material Granular material Subgrade for CPS Cement modified material/soil, natural subgrade compacted Cement modified material/soil, natural subgrade compacted Natural subgrade compacted Natural subgrade compacted Natural subgrade compacted Min. thickness for flexible layer (inches) 5.5 9.25 3 3 Min. thickness for rigid layer (inches)
Typical asphalt content 5% 5.5%
3 to 8% 5%
6% Typical
air voids
(target) 7% 4% 4% 4% Typical cement content
4%
Typical compressive strength
Design criteria or consideration for reflective cracking Yes No No Yes No Comments
A drainage layer is used on top of the rigid base layer.
Requirement: PCC Modulus of Rupture (700 psi), also PCC Elastic modulus (typically 3,500,000 psi) Modulus of Rupture (MOR) of 650 psi @ 28 days
50 Detailed Survey Results
The following are plots and pie charts that represent the 11 responses from the DOTs that had some degree of experience with composite pavements.
Figure B.1. Survey participants (in red [dark]).
51
Figure B.2. Survey participants indicating experience with composite pavement design (in green [dark]). 52
agency/company for flexible pavement design?
agency/company for rigid pavement design?
53
agency/company for composite pavement design?
pavements, which of the following factors are considered?
Figure B.7. Response to Question 14, What types of layers comprise your typical composite pavement structure?
54
Figure B.8. Response to Question 15, Are there any minimum thickness requirements for some or all of the layers of the composite structure? 55 Survey Comments
The following lists the comments from the survey responses from the 11 states that have some degree of experience with composite pavements:
• All DOTs use ESALs as the preferred traffic input parameters for designing composite pavements.
• TxDOT, SCDOT, and TnDOT construct new composite pavements (i.e., composite pavements that are not the result of a HMA overlay of an already in-service rigid pavement).
• MDSHA is the only transportation agency that recommends the use of a permeable drainage layer on top of the rigid base layer. They state that this permeable drainage layer works well enough, especially when compared to some cases where no drainage layer exists.
• Most DOTs—with the exception of CODOT, TnDOT, and IowaDOT—have a design consideration or criteria regarding the mitigation or control of reflective cracking.
• SCDOT: Uses a low-strength CTB to control shrinkage cracking and places that layer at a relatively high thickness to avoid fatigue cracking. This results in pavements with very low surface deflections (2-5 mils at 9-kips).
• Ohio DOT: Design procedure for composite pavements consists of designing a rigid pavement and then reducing the concrete thickness by one inch and add a three inch asphalt surface course.
• ConnDOT: — Sawing and sealing performance has been observed to depend on very accurate placement of saw cut (within 2 in. in many cases), and its beneficial effects are higher the thinner the AC layer over PCC. — Milling to expose the PCC slab and full-depth repair of PCC joints that are deteriorated in the existing PCC slab is essential to achieving performance in their experience. — Have not considered building brand-new composite pavements as the benefits are unclear (beyond perhaps noise reduction). tải về 1.81 Mb. Chia sẻ với bạn bè của bạn:
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