Further Development of Post- Tensioned Prestressed Concrete Pavement in Texas Short Course Material Stage I – Design of a PCP TxDOT Research Project 0-4035

Further Development of Post-Further Development of Post-Tensioned Prestressed Concrete Tensioned Prestressed Concrete

Pavement in TexasPavement in Texas

Short Course Material

Stage I – Design of a PCP

TxDOT Research Project 0-4035TxDOT Research Project 0-4035

Developed by Center for Transportation ResearchThe University of Texas at Austin

This CD was developed in compliance with TxDOT Research Project 0-4035 Task 10.5. The material contained here intends to serve as a guide for pavement engineers to learn about the procedure followed in this project to design a post-tensioned prestressed concrete pavement (PCP).

This material only presents the design procedure; however, complementary information about Project 0-4035 might be found in the technical reports prepared for the project. This reports can be accessed through the Internet at the Center for Transportation Research’s Library Website.

http://www.utexas.edu/research/ctr/

IntroductionIntroduction

For any questions or comments related to this material or project, please contact the research agency:

Center for Transportation ResearchCenter for Transportation Research

At’n. Dr. Cesar I Medina-ChavezAt’n. Dr. Cesar I Medina-Chavez

3208 Red River Suite 1043208 Red River Suite 104

Austin, TX 78712Austin, TX 78712

Phone (512) 232-3100Phone (512) 232-3100

E-mail address: [email protected] address: [email protected]

ContactContact

Acronyms found in the literature that refer to Prestressed Concrete Pavement are: PSCP, PTCP, PCP

BackgroundBackground

In prestressed pavement the concrete slab is preloaded (before traffic loads)

Post-tensioned: it means preload is applied after concrete has gained sufficient strength

Why use Prestressing Techniques?

Concrete is essentially a compression material

Its strength in tension is low

Prestressing naturally involves compressive loading prior to application of service loads

Tensile stresses are reduced or eliminated

BackgroundBackground

Improve the design and construction

techniques for a cost effective state-

of-the-art pavement structure and

apply them in a new design

Project ObjectiveProject Objective

Reference MaterialReference Material

Literature Review(Chapter 2)

PCP use in Texas

(Chapter 3)

Evaluation of PCP in Texas(Chapter 4)

Design of PCP(Chapter 5)

Materials and Construction

Specifications(Chapter 6)

Discussion of Developments

(Chapter 9)

Monitoring Plan for New PCP

(Chapter 7)

PCP and CRCP Comparison(Chapter 8)

Conclusions and Recommendations

(Chapter 10)

I. Evaluation of Previous WorkI. Evaluation of Previous Work

II. New DevelopmentsII. New Developments

Click here to open the report (5.5 Mb PDF file)

Report 0-4035-1Report 0-4035-1

Prestressing principles date from 1888

Eugene Freyssinet started applications in 1910

PCP application goes back to the 1940s in England and France

Brief Prestressing HistoryBrief Prestressing History

APPLICATION OVERSEAS

• First application in England in 1943

• Then in Paris, France at Orly Airport

• Other projects in Austria, Belgium, Germany, The Netherlands, Switzerland, etc.

• Japan

EARLY DOMESTIC EXPERIENCE

• In 1953 in Maryland (Airfield - 7 in. PCP Patuxent River Naval Air Station)

• In 1959 in San Antonio, TX (Taxiway at Biggs Air Force Base)

• Other experimental projects:Pittsburgh, PA (1971)

Dulles Intl. Airport, VA (1971)

EARLY DOMESTIC EXPERIENCE

• After a feasibility study the FHWA decided to develop PCP projects in 3 States

• Characteristics of PCPs in PA, MS, AZ– Only longitudinal post-tension was applied– Post-tensioning applied in gap slabs– 24 ft-wide placements– 6 in.-thick slabs

Gap Slab

Active JointActive Joint

24 ft

Gap SlabGap Slab

Used in projects in PA, MS, and AZ

Disadvantages of Gap Slabs:Require 2 joints per slab

Additional construction operation

Delayed opening to traffic

Greater chance of failure

Higher costs

PCPPCP SlabSlab

400-600’

GapGap SlabSlab GapGap SlabSlab

3-8’ 3-8’

Gap SlabGap Slab

IMPROVED DOMESTIC EXPERIENCES

• IL – O’Hare Intl. Airport (1980)• TX – Highway IH-35 (1985)• PA - Highway US220 (1988)• IL – Greater Rockford Airport (1993)

• During the early 1980s CTR introduced innovations based upon the successes and failures of projects in PA, MS, an AZ– Used Central Stressing Pockets instead of Gap

Slabs– Applied Longitudinal and Transverse Prestress

• A 6 in-thick PCP overlay was constructed in 1985 near West, Texas in McLennan County

• After almost 20 years of service the PCP is in excellent condition under heavy truck traffic

Texas CaseTexas Case

Concept Developed by CTR researchers

Requires 1 joint per slab

Advantages are:No delayed opening to traffic

Decreased construction time

Less chance of failure

Less maintenance

Central Stressing PocketCentral Stressing Pocket

Existing PCP in TexasExisting PCP in Texas


Total of 32 Prestressed Pavement SlabsTotal of 32 Prestressed Pavement Slabs

7 – 440 ft x [ 17 ft + 21 ft ]7 – 440 ft x [ 17 ft + 21 ft ] 9 – 240 ft x [ 17 ft + 21 ft ]9 – 240 ft x [ 17 ft + 21 ft ]

7 Slabs @ 440 ft = 3080 ft7 Slabs @ 440 ft = 3080 ft9 Slabs @ 240 ft = 2160 ft9 Slabs @ 240 ft = 2160 ft

Total = 5240 ftTotal = 5240 ft

IH - 35IH - 35 NN

Exit 351Exit 351Wiggins RoadWiggins Road

FM 1858FM 1858

FrontageFrontage

Waco 15 milesWaco 15 miles

Existing PCP in Texas on IH-35Existing PCP in Texas on IH-35

Cross section construction history, according to TxDOT’s files:

1952

JCP

Granular base

Natural soil

Lime stabilized sub-base

12"

5"

6"

1975

ACP4"

1985 and current

PCP6"


• Outline a procedure that can be used as a guide for designing any PCP

• Use past experiences and apply them in the new design• Foreign, PA, MS, AR, IL• TX – Old PCP and Precast Slab Concrete

Pavement in Georgetown, TX• Apply process to design a PCP on IH-35 near

Hillsboro, TX in Hill County

Design of New PCPDesign of New PCP

Methodology

• Literature review– Documentation of previous work (domestic and

abroad)

• Selection of construction site and evaluation of existing pavement conditions

• Site visits• Development of work plan


Approach

• Factors affecting design– Traffic Loads– Temperature effects– Moisture effects– Slab friction resistance– Prestress losses– Transverse prestress– Joint movement


Design Considerations

• Design variables– Foundation strength and embankment

properties– Pavement thickness– Magnitude of prestress– Slab length– Slab width


Design Considerations

• Design Steps for New PCP in Hillsboro, Texas– Embankment issues– Condition survey– Deflection measurement– Existing pavement back calculation– Traffic data analysis– Thickness design– Slab length


Implementation of Design Considerations

Location

Between Mileposts 365 and 368 both directions


Condition Survey- Evaluate existing pavement condition


Condition Survey- Evaluate existing pavement condition


– Pavement in Fair Condition

– Transverse Cracks

– Longitudinal Cracks

– Rutting

– Patches

– Alligator Cracking

Condition Survey Summary


Condition Survey Quantitative Analysis

•Use Pavement Distress Index (PDI)•Mathematical combination of distresses

•Assign weight factor (WF)•Assign severity factor (SF)

•14 different distresses•Severity: Low-Moderate-High•To calculate PDI, each distress is assigned WF and SF


Where:

Di = deducted points of the ith type distress,

Sij = weight of the jth severity class of the ith type of distress,

Eij = extent of the jth severity class of the ith type distress,

n = number of distress types,

m = number of severity classes

Pavement Distress Index (PDI)

n

i

m

jijij ESDiPDI

1 1

100PDI Chia-Pei-Chou

TRB Record 1592


n

i

m

jijij ESDiPDI

1 1

100PDI Chia-Pei-Chou

TRB Record 1592

Distress weight factor (49-100)

Severity factor (based on distress 0.24-1.00)

Extent (percent of area/occurrence frequency)Extent (percent of area/occurrence frequency)



Direction No. of subsections Group

Number

Scores*

NB 21 1,2 77 - 97

SB 22 1,2,33,4 91 - 86 - 6363 - 99

Maximum Score: 100.00

*PDI Chia-Pei-Chou TRB Record 1592/CTR Report

87.0

84.7

SummarySummary



Structural Evaluation of Existing Pavement


Deflection Data Collection Using RDD


Deflection Data Collection Using FWD


Back Calculation of Pavement Structure

1962 1977 1990 Current

Flexible base CRCP

Compacted foundation course

Natural soil

Lime stabilized subgrade

ACP

Flexible base

ACP

ACP

8"

4"

6"

6"

1"

3-5"


Back calculation of layer properties

1010

109134

194268

43513075

681760

Natural Soil

SG

SB

CRCP

ACP

Computed Modulus (ksi)

SB

Computed Modulus (ksi)

NBLayer No.



The existing asphalt pavement was visually inspected and a pavement distress index (PDI) was calculated for each highway direction.Next, pavement deflections were measured using the rolling dynamic deflectometer (RDD) and the falling weight deflectometer (FWD). Those deflections were used to estimate or backcalculate the elastic properties of the pavement.The next step involved the estimation of the projected traffic for the design lane. In this case, the calculation of the projected equivalent single axle loads (ESALs) was performed by TxDOT and the information was provided to the researchers to conduct a pavement fatigue analysis.

• Layer elastic properties were backcalculated using deflection information

• ESALs information was provided by TxDOT

• ESAL projections were done for 30 years


Design Process Recap

• Design of equivalent pavement30 year life

114 million ESAL applications

Concrete flexural strength: 700 psi

Concrete modulus of elasticity: 4,000 ksi

• Two different conditions were analyzedOverlay of existing pavement

Pavement on median

Design of New PCPDesign of New PCPElastic Design for Fatigue Loading


The design was performed for two different pavement cross sections, for an overlay of the existing asphalt pavement and a new pavement to be constructed on the existing median.In both cases, an equivalent continuously reinforced concrete pavement (CRCP) was designed using AASHTO’s design procedure.The thicknesses obtained were as follows:

Equivalent CRCP for overlay: 14 in.Equivalent CRCP for pavement on median: 15 in.

Equivalent CRCP for Overlay

15.0”

10”

8”

4”

6”

2

2

5,000 lb5,000 lb

12”

125 psi125 psi

CRCP: E = 4,000,000 psi = 0.15

AC: E = 760,000 psi = 0.35

CRCP: E = 3,075,000 psi = 0.15

Sub-base: E = 268,000 psi = 0.35

Subgrade: E = 134,000 psi = 0.35

Natural Soil: E = 10,000 psi = 0.40

TT

Equivalent CRCP for Pavement on Median

14”

7”

2

2

5,000 lb5,000 lb

12”

125 psi125 psi

CRCP: E = 4,000,000 psi = 0.15

AC: E = 700,000 psi = 0.35

Natural Soil: E = 10,000 psi = 0.40

TT


The next step was to calculate the minimum required prestress for various PCP thicknesses.The analysis included estimation of the prestress for various thicknesses from 6 in. to 15 in.The required prestress increased as the thickness decreased. This means they are inversely proportional. For instance, a 6 in.-thick PCP for the overlay design requires 49.1 psi of prestress to compensate for thickness. Likewise, a 14.0 in.-thick PCP will not require any additional prestress. That would be the equivalent CRCP entire thickness.

Thickness vs. Required Prestress

0

20

40

60

80

100

120

PCP Thickness (in)

Req

uir

ed

Pre

stre

ss (

psi

)

Existing Pavement Overlay 49.1 36.6 26.8 17.3 14.2 9.5 5.4 1.7 0

New Pavement on Median 107.6 82.6 62.6 46.8 34 23.2 14.1 6.5 0

6 7 8 9 10 11 12 13 1414 / 15

The next step in the design is to consider the effect of the combination of environmental stresses and wheel load stresses. The following conditions should be met:

• Critical stresses at PCP must not cause fatigue failure of the prestressed slab

• Combination of wheel loads, slab DT, and moisture stresses should not exceed flexural strength of concrete


Elastic Design for Environmental

Stresses and Wheel Loads

f = allowable flexural stress in the concrete

sp = effective prestress

st = stress caused by applied wheel load

sc = curling stress due to slab temperature differentials

sF = friction loss between slab and supporting layer


f + sp st + sc + sF

Elastic Design for Environmental

Stresses and Wheel Loads

The basic equation to be used is:


Using the basic equation previously shown, the PCP is designed as follows:

• Prestress at end of slab is computed• Prestress losses are estimated and discounted• Strand spacing is calculated

• Iterative process• Vary length and thickness

• Other properties considered are– Aggregate type, Poisson’s ratio, flexural strength,

modulus of elasticity– Climatic variables


It is recommended to design PCP using a spreadsheet and vary slab length and thickness. Final design characteristics are based on engineering judgment.

Concrete and Pavement Properties:

28-day Flexural Strength f = 700 f = 700 f = 700Safety Factor (ACI=2) SF = 2 SF = 2 SF = 2

Allowable Flexural Stress f design = 350 f design = 350 f design = 350

Concrete Modulus of Elasticity (psi) E = 4500000 E = 4500000 E = 4500000Concrete Poisson's Ration 0.15 0.15 0.15Coefficient of Thermal Expansion (/°F) = 6.00E-06 = 6.00E-06 = 6.00E-06

Concrete Unit Weight (pcf) 144 144 144Slab Length (ft) L = 250 L = 300 L = 350Temperature Differential (°F/in) T = 3 T = 3 T = 3Coefficient of Friction (slab-support)

max= 0.92 max= 0.92

max= 0.92

Thickness (in) D1 D2 D3 D1 D2 D3 D1 D2 D3

D = 8 9 10 D = 8 9 10 D = 8 9 10Tensile Stress at Bottom of Slab (psi)

t = 63.9 54.4 51.3 t = 63.9 54.4 51.3

t = 63.9 54.4 51.3Critical Stress Factors (edge condition) CSF = 1.3Required Fatigue Prestress (psi)

PR = 27 17 14 PR = 27 17 14

PR = 27 17 14

Wheel Load Stress (corrected, psi) t design = 83.1 70.7 66.7

t design = 83.1 70.7 66.7 t design = 83.1 70.7 66.7

Curling Stress at Slab Center (psi) c = 381 429 476

c = 381 429 476 c = 381 429 476

Friction Stress (psi) F = 115 115 115

F = 138 138 138 F = 161 161 161

Concrete and Pavement Properties

Prestressing Tendon Properties:

Tendon Ultimate Strength (psi) Ss = 270000 Tendon Yield Strength (psi) Sy = 229500Tendon Elastic Modulus (psi) Es = 28000000 Tendon Yield Force (lbs) Fy = 49572

Tendon Area, 0.6 in. Diameter (in2) a= 0.216 Tendon Prestressing Force (lbs) F = 34700Tendon Wooble Coefficient K= 0.001 Time After Stressing (design hr) t hr = 262800

Design Tendon Strenght (decimals) DSs= 0.8 Fjack= 46656

Concrete Shrinkage Strain (in/in) s = 0.00015

Concrete Creep Strain (in/in) k = 0.000075

Concrete Strain (Shrinkage and Creep) cu = 2.25E-04Time After Stressing (design yrs) t = 30

Design of PCP Using Spreadsheets

Prestressing Tendon Properties

Climatic Factors: Max - MinSeasonal Temperature Change from Summer to Winter (T Season) = 86 45 41Temperature Change During Summer Day (T Summer) = 110 86 24Temperature Change During Winter Day (T Winter) = 48 10 38

Climatic Factors



Summary of PCP Characteristics

Design Feature Recommendation

Design life 30 years

Projected traffic for design life 114 million ESALs

Concrete design flexural strength 700 psi

Concrete modulus of elasticity 4,000 ksi

Thickness of PCP slab 9 in.

Length of PCP slab 300 ft

– A similar expansion joint as in previous PCP in McLennan County will be used

– Joint has proven to be durable and adequate– A better neoprene seal will be used

Asphalt Concrete Layer

Existing JCP Pavement

Weld

Neoprene Seal

½” ØNelsonDeformed Bars

1 ¼” ØStainlessSteel Dowel

DowelExpansionSleeve

*L4 x 3 x ¼

*

Transverse Expansion Joint

Design Practical ConsiderationsDesign Practical Considerations

Transverse

Expansion

Joint

• The new design is based on improvements of previous experiences (PCP near West, TX)

• New PCP is an interesting project that will promote research and innovative construction practices

• Two designs have been conducted– PCP overlay on existing asphalt pavement– PCP on median

• Joint spacing will be limited to 300 ft• Thickness will be 9 in.

Discussion of DevelopmentsDiscussion of Developments

• Construction of PCP allows a more efficient use of construction materials• Less concrete

• Application of prestressing forces makes use of the compressive strength of concrete and reduces tensile stresses

• A well constructed PCP highly reduces maintenance tasks costs

Concluding RemarksConcluding Remarks

Dr. B. Frank McCulloughProject Supervisor, CTR

Dr. Moon C. WonProject Director, TxDOT

AcknowledgementsAcknowledgements

Documents

Further Development of Post- Tensioned Prestressed Concrete Pavement in Texas Short Course Material Stage I – Design of a PCP TxDOT Research Project 0-4035