MnDOT Investigation of Full Depth Repairs

2013 Fall National Concrete Consortium – Asheville, NCSeptember 25, 2013

Maria Masten, MnDOT Concrete Engineer

Acknowledgements• Gordy Bruhn, Concrete Rehab Specialist, MnDOT

Concrete Unit• Matt Zeller, Concrete Paving Association of Minnesota

• Construction Materials• CPR, Inc.• Diamond Surfaces, Inc.• Interstate Improvement• PCI Roads• Simplex Construction Supplies

• Steve Olson, MnDOT Concrete Research Unit• Kyle Hoegh, University of Minnesota

I-90 – Full Depth Repairs

SP 2280-126 - I-90

I-90 EB FWD Data

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

138.5 139 139.5 140 140.5 141 141.5 142 142.5 143 143.5 144 144.5 145

Average LTE 27%st dev 11%

minimum 5%maximum 83%

SP 2280-126 I-94 Alden6 dowel bars25.4% Trucks7,668 AADT

I-90 Investigation• Full Scale Investigation of other CPR projects

constructed between 2007 and 2012• Was the switch from 11 dowels to 6 (3 per WP)

or 8 (4 per WP) depending on traffic going too far? But it works for retrofit dowel projects…

• Where did the material go? We used more than we needed? Did it break down, was it durable?

• Is Spec constructible?• Place the bonding agent into the drilled holes

to completely fill the void.

Multiple Projects TestedRoad MP 2010

ADT2010

%TrucksDowels per lane

FWD LTE Range

CPRYear

I-90 138-145 7,668 25.4 6 5-83% 2009I-90 185-193 11,416 11 11 86-95% 2010I-94 157-194 43,500 10.3 6 25.7-46.4% 2009I-94 209-217 100,725 9.5 8 19-80% 2010

MN23 112-124 3,290 12.9 8 97-97.5% 2011MN77 1-5 65,000 2.2 11 31-95% 2007

• Visual examination of the cores• FWD Testing

• We have never done FWD testing on FDR until now…• What is a good LTE?• Does LTE tell us what we need to know?• Michigan DOT suggested looking at deflection….

I-94 (2 projects)

SP 2780-64 I-94 Maple Grove

8 dowel bars9.5% Trucks

100,725 AADT

SP 8680-155 I-94 Dist36 dowel bars9.5% Trucks

42,978 AADT

I-90 (Top) & TH 23 (Bottom)

SP 5080-155 I-90 Dist611 dowel bars

11% Trucks11,416 AADT

SP 1204-19 Hwy 23 Dist 86 dowel bars

424 Trucks/Day Prior to Repairs

Results of Investigation During investigations we found a lack of bonding

agent around the dowels from all of the Contractors

“I watched them install dowels on many projects and thought they were filled.”

Change standard back from 8 dowel bars to 11 dowel bars due to problems we have encountered with workmanship

Time to discuss with Concrete Industry and educate Inspection Personnel

Agency-Industry Meeting• December of 2012• Focused on premature failure of full depth repair

project• Investigation of other projects and information

sharing with Industry• “It has been working for 30 years – what’s

changed?”• Workmanship and Best Practices were the end

result• How good can we really do? Let’s go to MnROAD

and find out….

MnROAD – checking workmanship

MnROAD Results – Phase I• What did we try?

• Epoxy dip and stick, Epoxy double dip, Epoxy – fill and twist, grout box, 1 hour old grout, grout capsules, polygripepoxy

• Tested with MIRA to see if provide information non-destructively

• Best performers• Grout Anchoring Capsules• Polygrip epoxy

2013 Construction Season

Current Construction Practices• How much anchoring material do

we actually need?• What is good enough?

• Contractors concerned with subjectivity.

• Best coverage was determined by what application method / materials had the least amount of holidays in the annular space between the dowel bar and the drill hole.

2013 Construction Season• I-694 North of Minneapolis• Noticed existing Full Depth Repairs faulted (9 years old)• Original pavement placed – 1964 & 1985

2013 Construction Season• MnDOT randomly cored every

CPR project in 2013 • One Contractor took initiative

to core and check their own workmanship

• Most effective cause for Contractor to change was when MnDOT cored each project – even when Contractors were working on multiple projects

2013 – Acceptable Anchoring Methods Ambex Grout Anchoring Capsules Modified Grout Bag Method

Faster than the hole drilling crew now!!!

MnROAD Field Installation –Phase 2• No grout, grout bag, grout capsule, epoxy (2 types)• Controlled location• FWD testing seasonally• Coring• Monitoring over time• Laboratory Testing - Phase 3???

• Using what was learned in NCHRP 10-69• Considering using a Shear Test to determine how strong

the anchoring material is and how it will perform over time

Prescriptive or performance with anchoring procedures?

• Dowel Bar Anchoring Test Section• Complete FDR at least one (1) day prior to startup • Install 11 dowels in accordance with appropriate FDR• Cure the dowel bar anchoring adhesive at least 4 hours before coring. • DO NOT PLACE CONCRETE IN THE DOWEL BAR TEST SECTION.• Take (3) – 6” full depth cores centered on the dowel and 1 1/2" from the

sawed vertical face.

• Dowel Bar Anchoring Assurance Coring• At the Engineer’s discretion, the Contractor will take additional cores to

confirm consistent dowel bar anchoring. • For each 1500 Lineal Feet of FDR,the Engineer will randomly choose 2

separate repairs and mark 2 dowel bars for assurance coring.

Additional Data Analysis• Look at deflection data from FWD testing• Look at Pavement Management Data

• Break down performance of projects utilizing full depth repair techniques

• Consider base support and type

• In my opinion …• “Full Depth Repairs are an excellent technique for

concrete pavement preservation – just remember it is sometimes the simple things that can cause the biggest problems.”

Thank you!