Shear Cracking Phenomena / Solutions John M. Becker, P.E. ACPA - - PowerPoint PPT Presentation

55th ANNUAL MEETING – Celebrating Concrete Victories! – NOV 27-29, 2018

Shear Cracking Phenomena / Solutions

John M. Becker, P.E. ACPA Pennsylvania Chapter

The Definition of a Good Presentation

A Go Good Beg Begin innin ing A Good

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1 – First Placement

In this example there are six 30-inch tie-bars per 15-foot long slab (tie-bars are equally spaced 30-inches apart)

15”

This was the tie-bar design standard in Pennsylvania (prior to circa 2008-10) #5 tie-bars, 30-inches long (either Grade 40 or Grade 60)

15”

Typically placed in warmer months

2 – Joints Don’t Open Uniformly

Note: Many causes, including high-friction, high-strength bases,

• r perhaps very low-friction bases, also thick pavements.

Mainline placed in warmer months

Dominant Joint (typically every third to fifth joint opens up first)

3 – Tied Shoulder Placement

Note: Ambient (seasonal) temperatures often different between mainline paving and shoulder paving.

Mainline placed in warmer months Typically placed in cooler months Dominant joints typically open up even wider with cooler temperatures First joint to open up in shoulder does not necessarily line up with mainline dominant joint

4 – The Following Summer Joints Try to Close Up

Note: Edge restrained from closing by tiebars, base friction, and/or mortar intrusion.

Shear Cracking –Driving Lane

Sinusoidal Shaped Shear Crack Cracks Initiate over Dowels

Shear Cracking –Passing Lane

Shear Cracking Across the U.S.

None (that C/S was aware of) One project (mortar intrusion sometimes cited as root cause) Occasionally

Source: Survey of ACPA Chapter/State Executives, October/November 2018

Alaska Hawaii

A Word About Corner Congestion

6-inches

Shear Cracking in Pennsylvania Five projects since 2004 150 slabs documented Only 1 project since 2010 (that project had a base design flaw) Topic discussed at Annual Tour/Meetings in 2004, 2008, 2016 With Spec Re-Write in 2018, Department wanted problem solved by October 31, 2018

PennDOT’s Proposed Solution for Preventing Shear Cracking

• Expansion Joints Every 180+/- feet
• 2. Outside Shoulder
• 1. Driving Lane
• 1. Passing Lane
• 3. Inside Shoulder
• 2. Outside Shoulder
• 2. Driving Lane
• 1. Passing Lane
• 1. Inside Shoulder

Concerns

Adjacent joints opening up resulting in loss of aggregate interlock Long-term performance of expansion joint material Constructability; how to slip form with DBI Has never been tried in the U.S. for preventing shear cracking

Preventing Shear Cracking

(2004 ACPA R&T Update)

Prevent Mortar Intrusion

Use tar or duct tape at transverse joints, both on the side and on the top When sawing joints for second placement, flush out saw slurry that gets into joints from first placement

Reduce friction of the slab/treated base interface with coat

• f curing compound or a thin layer of sand across the base

Sand bond-breaker (banned years ago by PennDOT) Curing compound (group questioned effectiveness)

Try to pave adjacent lanes in similar environmental conditions

Not always practical with project schedules and MPT schemes

Eliminate one or two tie-bars near the dominant joint

30” 30”

One Eliminated Per Standards in Circa 2008-2010 Have we adequately reduced the risk with this change?

Preventing Shear Cracking -Continued

(2004 ACPA R&T Update)

Eliminate one or two tie-bars near the dominant joint

Eliminate (by cutting off or not drilling into slab) one more on each side of a dominant joint if paving in the fall?

120” 60”

Preventing Shear Cracking -Continued

(2004 ACPA R&T Update)

30” 30”

Full-Depth Sawing of Shoulder allows Room for Mainline to Expand

Mainline dominant joint Sawcut Full-Depth the Shoulder to Match the Width of the Dominant Joint in the Travel Lane

This option works ONLY for Un-Dowelled Shoulders

Preventing Shear Cracking

Other Options (Done on One Project in 2004)

Encourage first joints to open up in the second placement to match Dominant Joint in First Placement By Creating a Weakened Plane

Absent intervention, these rarely line up When second placement is a shoulder, tooling shoulder (1” depth) in fall paving has been effective in preventing the development of shear cracks Tooling not suggested for travel lanes; use of an early entry saw could be considered for fall paving

Preventing Shear Cracking

(Other Options)

Where We Appear to Have Landed

Expansion joints will not be required  Re-emphasis on sealing/smearing of the sides of transverse joints to prevent mortar intrusion

Observations are that this is not consistently being done No more duct tape

Specifications already requires that first transverse joints to open up (i.e., the dominant joint) shall be marked

Observations are that this is rarely being done

Specification language already suggests that when doing multiple placements, the first joints cut in the second placement should be parallel to dominant joints in the first placement Consensus is that we may have already solved the problem by going from six tie-bars per 15-foot slab to five tie-bars per slab BUT…..

Where We Appear to Have Landed

• More

We will eliminate one additional tie bar at dominant joints when placing concrete pavement adjacent to slab previously placed or any slab placed Criteria still TBD

When temperature for second placement is below 50F OR when delta temperature for second placement is 35F below first placement OR simply between October 1 and March 1

Joints in second placement parallel to dominant joints may be saw-cut using an early entry saw or by other means to “encourage” the first cracks in the second placement to line-up with first placement dominant joints

Where We Are Heading

Pennsylvania

Tie-bar design will be re-evaluated as part of our Department /Industry Jointing Group for standard slabs /thicknesses

Seven #4 bars? Four #6 bars? Placement of tie-bar any closer than 30” from transverse joints off the table Other materials (e.g., FRP?)

Tie-bar spacings for non-standard slabs also to be evaluated

12x12 slabs 6x6x6 slabs

Keeping it simple is an objective!

ACPA R&T is valuable document but it merits updating

If Shear Cracks Develop

• My Recommendations

Drill 2-inch diameter stress relief hole and fill with flexible material Cross-stitch crack Cut tie-bars to eliminate stress

R&R

55th ANNUAL MEETING – Celebrating Concrete Victories! – NOV 27-29, 2018

Acknowledgements

• Geoff Clarke, Swank Construction
• Brian Eberhart, Callahan Paving
• Lowell Jensen, New Enterprise
• Rich Jucha, ACPA/PA
• Dennis Morian, QES
• Dave Scuillo, Golden Triangle
• Mark Snyder, PERC
• Clayton Stahl, Gulisek
• ACPA & Chapter/State folks
• Steve Waalkes (Author of ACPA R&T)
• Jenifer Albert, FHWA/Pennsylvania
• Terry Dreher, Turnpike
• George Dunheimer, PennDOT,

Philadelphia/King of Prussia

• Josh Freeman, PennDOT

Pavement Design

• Dave Jarvis, PennDOT/QA
• Bill Kovach, PennDOT, Uniontown
• Lydia Peddicord, PennDOT

Pavement Design

• Brent Trivelpiece, PennDOT/QA

55th ANNUAL MEETING – Celebrating Concrete Victories! – NOV 27-29, 2018

Thank You

John M. Becker, P.E., President ACPA Pennsylvania Chapter 800 N. 3rd Street, Suite 503 Harrisburg, PA 17102 Jbecker@pavement.com 717-215-0509 www.LongerLifePavement.com