FDR/CTB

Washington County’s Experience and

Recommendations

FDR = Full Depth Recycling

CTB = Cement Treated Base

Full Depth Recycling – Existing road section is reverted with a milling machine to a specified maximum aggregate size and depth.

Cement Treated Base – Cement is added to the mix based on a “mix design” prepared by a certified testing lab.

Mix Design – The compressive strength of the mix is the main design parameter that is met through successive test runs with varying portlandcement amounts.

Design Parameter – For a base component, a typical design strength is 400 pounds per square inch (PSI). Normal concrete is 3,000 to 5,000 PSI. For 2012 projects this was met by adding 7% cement.

Reason for FDR-CTB

1. Gravel Road Upgrades were beginning to show greater than expected failures.

2. County hired Duval Engineering through a Consultant Services contract to investigate possible causes during the fall of 2011.

3. While many other possible reasons were investigated, a primary cause for the failures as identified through this study was the result of insufficient base rock thickness (pavement structure).

4. Duval recommended a minimum of 10 inches of base rock. Current practice is for a minimum of 6 inches.

Problems with 10” of base rock:

1. 10” rock would be about $1.80 per s.y. more expensive.

2. R/W not available (more dollars and time)

3. Ditches would be set back (more dollars and time).

4. This would still be an inadequate structural section, according to AASHTO pavement design process.

Problems with FDR / CTB

1. Cost

2. Environmental concerns (water quality, air pollution, crop damage)

Advantages of FDR / CTB

1. Much stronger structural section, meeting AASHTO pavement designprocess.

2. Consistent base preparation throughout the entire project.

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Jackson School 5600 22 13689 97,328$ 95,649$ 192,977$ (FDR - CTB) 7.11$ 6.99$ 14.10$ per syThornburg 5164 22 12623 60,113$ 86,410$ 146,523$

4.76$ 6.85$ 11.61$ per syGroveland 5475 22 13383 16,275$ 69,385$ 85,660$

1.22$ 5.18$ 6.40$ per syHahn 5274 22 12892 19,630$ 101,799$ 121,429$

1.52$ 7.90$ 9.42$ per syDavidson 7102 22 17360 74,942$ 119,944$ 194,886$

4.32$ 6.91$ 11.23$ per sy69948 6.76$

Average without Jackson School Road 9.75$ per syFDR is more expensive than standard by: 45%

2011 Gravel Road Upgrades - Surface Costs

Legal LoadStandard 80,000 lb. Log Truck

17k 17k 17k 17k 12k

ESALS = (0.8) (0.8) (0.8) (0.8) (0.19)

1 Log Truck = 3.39 ESALSESAL: Equivalent Single Axle Load (relative to 18,000 lb Axle)

FDR - Cement Treatment Cost --- 12" ThickBased on 2011 Contract for Jackson School Road and Brookman Road

Cement Cost 100.00$ per tonCement rate 7% application rate

Subgrade 115 pcf densityThickness 12 inches deep

72.45 lb/sy cement

Rock Cost 16.50$ per ton for 3/4"-0 level rockRock Depth 2 inches of 3/4-0 level rock

120 pcf Level rock density3.62$ per sy for cement treatment2.00$ per sy for full depth reclamation1.49$ per sy for level rock7.11$ per sy FDR Total6.99$ per sy BST Total

14.09$ per sy TotalSN = 3.28 ESALS = 220000

Log Trucks = 64897 Option 1

Cement Information

Level Rock Information

Standard 3x BST with 6" base rock9.75$ per sy (includes base rock and surf. Prep.)

Log Trucks < 500 Option 2

Standard 3x BST with 10" base rock6.76$ per sy 3x BST Cost4.46$ 6" additional 3/4"-0 cost3.00$ additional widening cost (unknown)

14.22$ Log Trucks < 500 Option 3

Modified FDR and CTB Treatment

Cement Cost 100.00$ per tonCement rate 5% application rate

Subgrade 115 pcf densityThickness 8 inches deep

34.5 lb/sy cement

Rock Cost 16.50$ per ton for 3/4"-0 level rockRock Depth 2 inches of 3/4-0 level rock

120 pcf Level rock density1.73$ per sy for cement treatment2.00$ per sy for full depth reclamation1.49$ per sy for level rock5.21$ per sy FDR Total6.99$ per sy BST Total

12.20$ per sy TotalSN = 2.28 ESALS = 25000

Log Trucks = 7375 Option 4

Cement Information

Level Rock Information

Regular Base Prep and 3" ACBase Prep 3.18$ (to provide 6" of base rock)3" of AC 9.72$ (@ $60/ton)

12.90$ SN = 1.92 ESALS = 8500

Log Trucks = 2507 Option 5

Option 1 (FDR / CTB)

Option 2 (current)

Option 3 (10" base

rock)

Option 4 (mod.

FDR/CTB)

Option 5 (3" AC)

Cost per s.y. 14.09$ 9.94$ 14.22$ 12.20$ 12.90$

Cost per mile (22' wide) 181,855$ 128,292$ 183,533$ 157,461$ 166,496$

R/W Needed? N N Y N N

Ditching Needed? N N Y N N

No. of 80,000 Trucks 64897 < 500 < 500 7375 2507

Option Summary

Option Descriptions1. Option 1 – Full Depth Reclamation to 12” deep and adding 7% cement

capped with 2” of base rock and a 3 shot chip seal.

2. Option 2 – Current standard practice. Add enough rock to ensure 6 inches of base rock then cap with a 3 shot chip seal.

3. Option 3 - Current standard practice but add enough rock to ensure 10 inches of base rock then cap with a 3 shot chip seal. May require additional ditching and right of way.

4. Option 4 – Modified FDR/CTB. Full depth reclamation to 8” deep and adding 5% cement then cap with a 3 shot chip seal.

5. Option 5 – Similar to Option 2, but cap with 3” of hot mix asphalt.

Case Study 1

Moreland Road – Upgraded in 2008 with a 3-shot chip seal. Experienced significant damage and patched, mostly in 2011. Subject to intermittent heavy loads and logging traffic.

Length = 9,274 feet (1.76 miles)

Surface Maintenance Cost since 2008 = $51,467 ($29,300 per mile)

Case Study 2

Solberger Road – Upgraded in 2005 with a 3-shot chip seal. Has required frequent surface maintenance since construction. Subject to intermittent heavy loads and logging traffic.

Length = 4,500 feet (0.85 miles)

Surface Maintenance Cost since 2005 = $54,990 ($64,522 per mile)

Case Study 3

Sewell Road – Upgraded in 2004 with a 3-shot chip seal. Acceptable performance. Is subject only to commuter traffic and light farm use.

Length = 5,536 feet (1.05 miles)

Surface Maintenance Cost since 2004 = $5,292 ($5,047 per mile)

Recommendations

1. Very limited budget for summer 2012 (FY 12/13 budget year) so continue with Jacktown and Evers with past practice, but make a concerted effort in design to identify and address soft spots.

2. Future years continue current practice but do a more intense design effort by proof rolling in spring and subgradetesting with DCP).

Recommendations

3. On more heavily used roads (e.g. Moreland, Solberger), use a modified FDR/CTB process.