Final Report (the a Team)

TERM PROJECT

The A team

Eduardo Schaefer Sombrio

João Victor Oliveira de Albuquerque Malta

Weverton Marques da Silva

Civil 5810 – Pavements Design

Submitted to

Dr. David Timm

December 5th, 2014

Table of contents

1. Introduction ..................................................................................................................... 1

2. Traffic characterization ................................................................................................... 1

2.1. Rigid Pavement ESAL Factor Calculation .................................................................. 2

2.2. Flexible Pavement ESAL Factor Calculation ............................................................. 3

3. Pavement design .............................................................................................................. 4

3.1. Flexible Pavement Design ........................................................................................... 4

3.1.1. AASHTO Flexible Pavement Design Method ............................................. 4

3.1.2. Comparison with the Asphalt Institute Method ........................................... 6

3.2. Rigid Pavement Design ............................................................................................... 6

3.2.1 AASHTO Rigid Pavement Design .............................................................. 6

3.2.2. PCA Method Comparison ............................................................................ 9

4. The A team recommendation .......................................................................................... 9

5. References ..................................................................................................................... 10

Appendix A: Traffic characterization ....................................................................................A-1

Appendix B: Flexible Pavement Design ................................................................................ B-1

Appendix C: Rigid Pavement Design .................................................................................... C-1

Appendix D: Drainage Calculation ........................................................................................D-1

CIVL 5810 Term Project

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1. INTRODUCTION

Our group was supposed to design a flexible and a rigid pavement for a two-lane

highway (State Highway 280) that goes from Opelika to Alexander City, on the state of

Alabama. The study that we provide is given between mileposts 90 and 96. On this report

you will be able to see different methods on how to design the flexible and the rigid

pavement, including our group recommendation as a final design. Each pavement was

designed for a 35-year period and a cost analysis was performed too.

The flexible pavement was designed according to the AASHTO flexible pavement

design method and then compared with the Asphalt Institute method. Furthermore, a jointed

plain concrete pavement and the final design was compared with the Portland Cement

Association (PCA) method.

Figure 1: Location along State Highway 280 (ALDOT, 2014)

2. TRAFFIC CHARACTERIZATION

To make the calculations of the design traffic for the AASHTO flexible and rigid

pavements we utilized the data about the weigh-in-motion (WIM) that was given to us from

Highway 280 for three months of 2008 (March, July, and October).


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The following equation gives the equivalent single axle load value (ESAL) for each

pavement:

ESALdesign = AADT ×%Trucks × Growth Factor × 365 × ESAL Factor × L.D.× D. D.

Where:

x AADT = average annual daily traffic (vehicle/day)

x % Trucks = % of AADT consisting of trucks

x Growth Factor = (1+𝑔)𝑛−1

𝑔

x Growth rate (𝑔) = rate of traffic growth for the pavement design life

x n = number of years for pavement design (35 in your case)

x ESAL Factor = average damage of a vehicle type relative to a single-axle 18-kip

load

x L.D. = lane distribution

x D. D. = directional distribution

During your calculations we faced four ALDOT stations on the assigned segment

(stations 806, 502, 501, and 803). We decided to choose the station that, in the end of

calculations, gives us the highest ESALdesign number.

We decided to use a lane distribution correction factor equal to 90% and 50% for

directional distribution (assuming that the traffic levels is equal in both directions).

As we needed to be the most conservative design as possible, the ESAL factor for the

scenarios was determined with calculations using a single ESAL factor for each of the three

months and selecting the highest value.

Each A18 was calculated by multiplying the number of axles by an equivalent axle

load factor (EALF) and the EALF was calculated from the following equation:

EALF = Wt18/Wtx

x Wt18 = the number of standard (18-kips) axle load passes

x Wtx = the number of nonstandard axle load passes

2.1. Rigid Pavement ESAL Factor Calculation

To determine the EALF for each vehicle load we used the AASHTO equation for

rigid pavements:


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log (𝑊𝑡𝑥𝑊𝑡18

) = 5.908 − 4.62 log(𝐿𝑥 + 𝐿2) + 3.28𝑙𝑜𝑔𝐿2 +𝐺𝑡𝛽𝑥−𝐺𝑡𝛽18

𝐺𝑡 = log (4.5 − 𝑝𝑡4.5 − 1.5)

𝛽𝑥 = 1.0 +3.63 ∗ (𝐿𝑥 + 𝐿2)5.20

(𝐷 + 1)8.46 ∗ 𝐿23.52

x 𝐿𝑥 = axle group weight for a nonstandard axle (kips)

x 𝐿2 = axle type number: 1 for single, 2 for tandem, 3 for tridem

x 𝑝𝑡 = terminal serviceability value

x 𝐷 = thickness of the concrete slab

We assumed a slab thickness of 9 inches for EAFL calculations. For AADT > 10,000

vehicles/day the range of terminal serviceabilities (pt) is from 3.0 to 3.5 and we decided to

assumed pt as 3.0 for economic purposes. At the end, your ESALdesign for rigid pavement is:

𝐸𝑆𝐴𝐿𝑑𝑒𝑠𝑖𝑔𝑛 = 13,264 ∗ 0.11 ∗ 72.97 ∗ 365 ∗ 1.225 ∗ 0.90 ∗ 0.50 = 19,037,912.4 𝐸𝑆𝐴𝐿𝑆

For details see Table 5 in Appendix A: Traffic characterization.

2.2. Flexible Pavement ESAL Factor Calculation

To determine the EALF for each vehicle load we used the AASHTO equation for

flexible pavements:

log (𝑊𝑡𝑥𝑊𝑡18

) = 6.1252 − 4.79 log(𝐿𝑥 + 𝐿2) + 4.33𝑙𝑜𝑔𝐿2 +𝐺𝑡𝛽𝑥−𝐺𝑡𝛽18

− 𝐺𝑡 = log (4.2 − 𝑝𝑡4.2 − 1.5)

− 𝛽𝑥 = 0.40 +0.081 ∗ (𝐿𝑥 + 𝐿2)3.23

(𝑆𝑁 + 1)5.19 ∗ 𝐿23.23

x 𝐿𝑥 = axle group weight for a nonstandard axle (kips)

x 𝐿2 = axle type number (1: single, 2: tandem, 3 for tridem)

x 𝑝𝑡 = terminal serviceability value

x 𝑆𝑁 = structural number of the flexible pavement system.

The AADT > 10,000 vehicles/day, so, as we did for the rigid pavement design, a

terminal serviceability value equals to 3.0 is assumed for economic purposes. Another


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assumption that we made is 5.0 for structural number. At the end, your ESALdesign for flexible

pavement is:

𝐸𝑆𝐴𝐿𝑑𝑒𝑠𝑖𝑔𝑛 = 13,264 ∗ 0.11 ∗ 72.97 ∗ 365 ∗ 0.523 ∗ 0.90 ∗ 0.50 = 8,127,728 𝐸𝑆𝐴𝐿𝑆

For details see Table 6 in Appendix A: Traffic characterization.

3. PAVEMENT DESIGN

The table bellow shows the material proprieties considered in this report.

Table 1. Construction materials properties

Stockpile

A Stockpile

B Stockpile

C Soil HMAC PCC

Modulus (psi) 15,000 22,500 30,000 - 800,000 -

Structural Coefficient 0.068 0.11 0.141 - 0.54 -

Permeability (ft/day) 2 100 16,000 2.2×10-3 - -

Characterization Filter Filter Base Subgrade Surface Surface

Unit Cost ($/yd2/in) 0.3 0.33 0.36 - 3.65 4.3

D15 0.15 0.55 6.4 0.09 - -

D85 3.7 9.51 N/A 4 - -

3.1. Flexible Pavement Design

The flexible pavement design was based on the AASHTO flexible pavement design

method and compared with the Asphalt Institute method.

3.1.1. AASHTO Flexible Pavement Design Method

The following equations were used on the calculations of the thicknesses of the

surface, base, and subbase layers:

D1 ≥SN1a1

D2 ≥SN2 − a1D1a2m2

D3 ≥SN3 − a1D1 − a2m2D2

a3m3

x 1: surface; 2: base; 3: subbase.

x SN1, SN2, SN3 = structural numbers

x a1, a2, a3 = structural coefficients


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x D1,D2,D3 = thicknesses

x m1,m2,m3 = drainage coefficients

We chose standard deviation (S0) of 0.35 according to AASHTO recommendations.

As we selected 3.0 for terminal serviceability (pt), our ΔPSI is 1.2. The AASHTO method

recommends reliabilities between 75% and 95%, so we decided to choose 90% to balance

other calculations on the traffic part, this number give us a Z-statistic (ZR) of -1.282.

The structural number (SN) affects the thickness of each layer. To calculate those

thicknesses we used the following equation:

log(W18) = ZRS0 + 9.36 log(SN + 1) − 0.20 +log ( ∆PSI

4.2 − 1.5)

0.4 + ( 1094(SN + 1)5.19

)+ 2.32 log(MR) − 8.07

x W18 = the number of ESALs for the flexible scenario

x ZR = Z-statistic at the design reliability

x S0 = standard deviation

x ∆PSI = (p0 − pt)

x p0 = initial serviceability

x pt = terminal serviceability

x MR = modulus of the underlying material (psi)

For the calculations of the effective subgrade modulus (𝐌𝐑,𝐄𝐅𝐅) (this number governs

the final SN) we considered a wet season that corresponds 30% of the year. An effective

subgrade modulus of 6,290 psi was calculated based on preexisting data and the above

assumptions. See Table 7 in Appendix B: Flexible Pavement Design.

We also assumed a drainage quality as ‘Excellent’ for each material, which means

that 95% of water is removed in 2 hours or less, and gives us a drainage coefficient 𝑚𝑖 = 1.2.

All combinations of stockpiles and asphalts were done (and the filter and clogging

criteria were checked), instead of using a single one and then they were subjected to the

AASHTO equations above. After the cost analysis we chose the cheapest combination.

Table 2. Cost analysis for flexible pavement

Layer 1 D1 (in) Layer 2 D2 (in) Layer 3 D3 (in) Total Cost ($/yd2) AC 10.5 Subgrade 0 - 0 38.33 AC 7.5 A 17 Subgrade 0 32.48 AC 6.5 B 15 Subgrade 0 28.68 AC 5.5 C 15 Subgrade 0 25.48 AC 6.5 B 3 A 19 30.42 AC 5.5 C 5.5 A 19 27.76 AC 5.5 C 2 B 16.5 26.24


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The highlighted combination was the one that we chose for our design.

Since there is no melt water condition, the water inflow was estimated as the surface

infiltration only. The discharge capacity of the drainage layer was calculated and was

acceptable. Our pipe size was estimated as 1.43 in. The minimum size available in the market

is 4 in, so that is the value that we adopted. See Appendix D: Drainage Calculation.

3.1.2. Comparison with the Asphalt Institute Method

WESLEA software was used to determine the maximum horizontal tensile strain at

the bottom of the asphalt layer and the maximum vertical compressive strain at the top of the

subgrade with the following equations.

𝑁𝑓 = 0.0796 (1𝜖𝑡)3.291

|𝐸∗|−0.854

𝑁𝑟 = 1.365 ∗ 10−9 (1𝜖𝑣)4.477

− 𝑁𝑓 = number of standard axle loads until fatigue failure

− 𝑁𝑟 = number of standard axle loads until rutting failure

Damage for both failure modes:

𝐷𝑓 =𝐸𝑆𝐴𝐿𝑁𝑓

𝐷𝑟 =𝐸𝑆𝐴𝐿𝑁𝑟

As the damage ratio for fatigue is higher than 1.0, we can conclude that according to

the Asphalt Institute Method the pavement is underestimated. See Table 8 in

3.2. Rigid Pavement Design

The rigid pavement design was based on the AASHTO rigid pavement design method

and compared with the Asphalt Institute method.

3.2.1 AASHTO Rigid Pavement Design

The thickness of the concrete pavement slab (𝐷) was calculated from the AASHTO

rigid pavement design equation:

log(𝑊18 ) = 𝑍𝑅𝑆0 log

(

𝑆𝑐𝐶𝑑(𝐷0.75 − 1.132)

215.63𝐽 (𝐷0.75 − 18.42

(𝐸𝑐𝑘 )0.25)

)

+ 7.35 log(𝐷 + 1) − 0.06 + (log ( ∆𝑃𝑆𝐼

4.5 − 1.5)

1 + 1.624 ∗ 107(𝐷 + 1)8.46

) + (4.22 − 0.32𝑝𝑡 )


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x 𝑊18 = number of ESALs for the rigid scenario

x 𝑆0 = standard deviation

x 𝑍𝑅 = Z-statistic (at the design reliability)

x ∆PSI = (p0 − pt)

x p0 = initial serviceability

x pt = terminal serviceability

x 𝐸𝑐 = elastic modulus of concrete (psi)

x 𝑆𝑐 = modulus of rupture (psi)

x 𝐶𝑑 = drainage coefficient (base material)

x 𝑘,𝐸𝐹𝐹 = effective modulus of subgrade reaction (pci)

x 𝐽 = load transfer coefficient

We chose standard deviation (S0) of 0.35 according to AASHTO recommendations.

As we selected 3.0 for terminal serviceability (pt), our ΔPSI is 1.2. The AASHTO method

recommends reliabilities between 75% and 95%, so we decided to choose 90% to balance

other calculations on the traffic part, this number give us a Z-statistic (ZR) of -1.282.

For the calculations of the effective modulus of subgrade reaction ( 𝑘,𝐸𝐹𝐹 ), (this

number govern the slab thickness) we considered a wet season that corresponds 30% of the

year. Three effective modulus of subgrade reaction were calculated based on preexisting data

and the above assumptions and we decided to use the highest one (𝑘 = 55 psi), after the

correction for loss of support, which corresponds to the stockpile C. Also, a loss of support

correction factor of 2.0 was selected to account for uncertainty regarding the exact nature of

the material in stockpile C. See Table 9 in Appendix C: Rigid Pavement Design.

Using AASHTO design equations to calculate the elastic modulus (𝐸𝑐) and the

modulus of rupture (𝑆𝑐) of the concrete material we have:

𝐸𝑐 = 57,000√𝑓𝑐′ = 4,002,196 psi

𝑆𝑐 = 9√𝑓𝑐′ = 632 psi

A loss of support correction factor of 2.0 was selected to account for uncertainty

regarding the exact nature of the material in stockpile C. As the % Time Saturated > 25% and

our drainage quality is considered as ‘Excellent’, we decided to use the drainage coefficient

equals to 1.20.

% 𝑇𝑖𝑚𝑒 𝑆𝑎𝑡𝑢𝑟𝑎𝑡𝑒𝑑 =𝑆 + 𝑅365 ∗ 100%


8

x 𝑆 = days of spring thaw

x 𝑅 = remaining days with rain if pavement will drain to 85% in 24 hours

% 𝑇𝑖𝑚𝑒 𝑆𝑎𝑡𝑢𝑟𝑎𝑡𝑒𝑑 =0 + 108365 ∗ 100% = 29.6%

AASHTO recommends for tied configuration a load transfer ranging between 2.5 and

3.1 and for non-tied configuration it recommends 3.2. We decided to use 2.5 to be more

conservative on our assumption.

Table 3: Design Options and Cost Analysis

Load Transfer Coefficient Stockpile 3.2 2.5

A 11.5 10.2 B 11.5 10.2 C 11.5 10.1

A steel design was then performed for each configuration and a subsequent cost

analysis was performed to determine the cheapest option.

Table 4: Design Options and Cost Analysis

Design Option

PCC Thickness

(in)

Total PCC Cost ($/yd2)

Total Steel Cost ($/yd2)

Total Cost ($/yd2)

Non-tied 11.5 49.45 0.33 48.78

Tied 10.5 45.15 0.43 43.58

As the tied option is the cheapest one, we decided to choose it.

Also, we assumed a drainage quality of ‘Excellent’ for each material, which means

that 95% of water is removed in 2 hours or less, and gives us a drainage coefficient of 1.2. As

there is no melt water condition the water inflow was estimated as the surface infiltration

only. The discharge capacity of the drainage layer was calculated and was acceptable. Our

group opted to use a pavement with 12 ft lanes with 9 ft outer shoulders and 2 ft inner

shoulders. A 20 feet joint spacing was used, with 6 tie bars and 40 inches center-to-center

spacing.

With the objective of assist on the load transfers between the lanes, 24 18-inch long

dowels bars of 1. 25 inches diameter was used and 12-inch center-to-center spacing. The

dowel size was selected according to Friberg (1940) (See Huang, Y. H., page 194).


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3.2.2. PCA Method Comparison

We compared the final AASHTO design for the rigid pavement with the Portland

Cement Association (PCA) method. On this analysis we utilized the same traffic data from

March, 2008 used in the AASHTO procedure.

A load factor equals to 1.1, shoulders and dowels were used on the pavement concrete

design. Using the value of 10.5 for the slickness the total expected axle repetitions for each

axle load was calculated for your design period (35 year).

After all your calculations, we can conclude that PCA method showed that this

pavement configuration satisfies the fatigue and erosion requirements. See Appendix C:

Rigid Pavement Design.

4. THE A TEAM RECOMMENDATION

This report has the objective to show the best alternative when designed a pavement

for Highway 280 according to different methods, whether flexible or rigid. The next table

shows the most economical way to design it:

Design Option Total Cost ($/yd2)

Flexible 25.48

Rigid 43.58 As the flexible pavement is more economical than the rigid, we decided to choose it

for our design.


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5. REFERENCES

Timm, David (2014) “CIVL 5810: Notes.” Auburn University: Department of Civil

Engineering. Auburn, AL.

Huang, Y. H. (2004). Pavement Analysis and Design (2nd ed.).

Alabama Department of Transportation. (2014, November 28). Alabama Traffic Monitoring

Division. Retrieved December 1, 2014. http://algis.dot.state.al.us/atd/default.aspx

U.S. Climate Data. (2014). Retrieved December 2, 2014.

http://www.usclimatedata.com/climate/opelika/alabama/united-states/usal0413


A-1

APPENDIX A: TRAFFIC CHARACTERIZATION

Table 5. ESAL calculation for rigid pavement

Station Last Measured AADT (2013) TADT g Current Traffic

(2014) Growth factor ESALi

806 10790 12% 2.13% 11020 51.23 30,284,213.5

502 10790 11% 2.05% 11012 50.50 27,346,897.1

501 12760 11% 3.95% 13264 72.97 47,594,781.1

803 11630 12% 2.64% 11937 56.38 36,101,196.2

Maximum 47,594,781.1

ESALDESIGN = 19,037,912.4

Table 6. ESAL calculation for flexible pavement

Station Last Measured AADT (2013) TADT g Current Traffic

(2014) Growth factor ESALi

806 10790 12% 2.13% 11020 51.23 12,929,035.8

502 10790 11% 2.05% 11012 50.50 11,675,027.0

501 12760 11% 3.95% 13264 72.97 20,319,320.1

803 11630 12% 2.64% 11937 56.38 15,412,441.1

Maximum 20,319,320.1

ESALDESIGN = 8,127,728.0


B-1

APPENDIX B: FLEXIBLE PAVEMENT DESIGN

Table 7. Effective resilient modulus calculation

Season MR (psi) Duration (days) μf Weighted average MR,eff (psi)

Dry 7850 (Average) 257 0.1086 0.1816 6290

Wet 4710 (Average - 40%) 108 0.3552

Table 8. Asphalt Institute comparison

εt (10-6in/in) = 183.28

εv (10-6in/in) = 388.29

E* (psi) = 800000

Nf (ESALs) = 1.44×106

Df = 5.65

Nr (ESALs) = 2.54×107

Dr = 3.20


C-1

APPENDIX C: RIGID PAVEMENT DESIGN

Table 9. Effective modulus of subgrade reaction calculation

Material A B C

Season Dry Wet Dry Wet Dry Wet

Roadbed Soil Modulus, psi 7850 4710 7850 4710 7850 4710

Subbase Modulus, psi 15000 15000 22500 22500 30000 30000

composite k-value (pci) figure 3.3 410 260 445 275 480 290

k-value on rigid foundation Fig. 3.4 680 460 770 490 840 515

Relative Damage, ur Fig. 3.5 82.35 97.63 77.57 95.14 74.27 93.18

Weighted Average Relative Damage, ur 86.87 82.77 79.86

Composite k-value (pci) 605 673 725

keff 50 52 55

Table 10. Input information for performance evaluation according to PCA method

Thickness of slab (in) = 10.5

k-value (pci) = 55

LSF = 1.1

Concrete Shoulders? no

Dowels? yes

Sc (psi) = 632

Table 11. Performance evaluation according to PCA method for single axles.

Single Axles Fatigue Erosion Axle Load (kips)

Axle Load*LSF Expected Reps

Allowable Reps

% Consumed

Allowable Reps

% Consumed

34 37.4 95 6,048 1.6% 2,261,131 0.0% 30 33 95 46,197 0.2% 5,014,808 0.0% 28 30.8 855 128,648 0.7% 8,032,822 0.0% 26 28.6 2660 448,197 0.6% 13,852,433 0.0% 24 26.4 10641 3,509,364 0.3% 26,709,862 0.0% 22 24.2 29642 Unlimited 0.0% 62,440,563 0.0% 20 22 112202 Unlimited 0.0% 224,335,664 0.1% 18 19.8 365201 Unlimited 0.0% 11,657,544,852 0.0% 16 17.6 795862 Unlimited 0.0% Unlimited 0.0%

Subtotal - Singles 3.3% 0.2%


C-2

Table 12. Performance evaluation according to PCA method for tandem axles.

Fatigue Erosion Axle Load (kips)

Axle Load*LSF Expected Reps

Allowable Reps

% Consumed

Allowable Reps

% Consumed

52 57.2 0 232,981 0.00% 1,446,669 0.00% 50 55 1443 478,340 0.30% 1,830,709 0.10% 48 52.8 2309 1,207,912 0.20% 2,348,677 0.10% 46 50.6 4619 4,439,238 0.10% 3,061,614 0.20% 44 48.4 9239 40,223,929 0.00% 4,066,777 0.20% 42 46.2 37822 Unlimited 0.00% 5,525,570 0.70% 40 44 71313 Unlimited 0.00% 7,719,510 0.90% 38 41.8 148401 Unlimited 0.00% 11,171,136 1.30% 36 39.6 0 Unlimited 0.00% 16,931,499 0.00% 34 37.4 0 Unlimited 0.00% 27,355,848 0.00% 32 35.2 0 Unlimited 0.00% 48,600,586 0.00% 30 33 0 Unlimited 0.00% 101,134,818 0.00% 28 30.8 0 Unlimited 0.00% 291,231,200 0.00% 26 28.6 0 Unlimited 0.00% 2,796,149,258 0.00% 24 2.2 0 Unlimited 0.00% Unlimited 0.00%

Subtotal-Tandem 0.60% 3.50%

Total Life Consumed 4.00% 3.70%


D-1

APPENDIX D: DRAINAGE CALCULATION

Table 13. Drainage parameters

Surface Infiltration Steady-State Inflow

Ic (ft3/day.ft2) = 2.4

Kd (ft/day) = 16000

Nc = 3

S = 0.02

Wp (ft) = 24

Hd (ft) = 0.5

Wc (ft) = 24

L (ft) = 22

Cs (ft) = 40

q = 250.9

qi (ft3/day.ft2) = 0.36

Criteria (q > qdL) -> OK In this case qd = qi

𝐷 = [𝑛𝑞𝑝𝐿053𝑆0.5]

0.375

= [0.01 × (0.36 × 12) × 500

53 × 0.250.5 ]0.375

⇒ 𝐷 = 1.43 in

Documents

Final Report (the a Team)