What is preventative maintenance for concrete pavement and what is being prevented?
From: International Grooving & Grinding Association
Concrete is a durable, long-lived, sustainable pavement solution, but some conditions like temperature-change expansion and contraction, or deviations in mix ingredients, represent real-world challenges for any pavement, regardless of its material composition. Pavements are carefully engineered to accommodate challenging forces during their service life, but it is still important to regularly inspect roads, assess the extent of any pavement distress, and implement a fully adequate response.
Preventative maintenance is so named for a reason. Single problems can have a “domino effect”, and if left unaddressed, can eventually be responsible for multiple problems. Therefore, it is important to understand
FIRST) Goals and best practices for the initial design and construction of concrete pavement, and
SECOND) How maintenance schedules and activities should be conducted to maximize pavement life
Pavement Design & Construction Considerations
Concrete pavement distresses at times can manifest as cracking, broken slabs, buckling, or roughness, and these distress categories should be considered during a pavement’s design and construction phases.
CONTRACTION JOINTS are one critical consideration because reduced slab thickness along the line of a joint is intended to permit controlled cracking when the concrete shrinks—called a “control” joint. But joints can become filled with debris, or “incompressibles,” creating an overly rigid system that allows expansive stresses to build up. The compressive forces resulting from these stresses can cause cracking to occur in other areas of the pavement. Temperature ranges of more than 100º F during a given year can translate to expansion- and contraction-related changes of approximately 2/3-in. in a 100-ft .stretch of pavement.
—Modern transverse contraction joints are typically spaced a maximum of 15 feet apart, based on the thickness of the section
• If each joint successfully cracks throughout the depth of the slab below it, the pavement will function as designed, and can accommodate weather-related expansion
• However, if some of the joints fail to crack—for example, if the pavement cracks only at every second, third, or more joints—making the effective length of each panel much greater than 15 feet
• Consequently, when panels contract, they are opening the joint wider than was intended, allowing more incompressibles into the space
• When expansion next occurs, there is less volume for the concrete to expand into due to the imcompressibles filling the voids
• After several years of this cycle, as improper transmission of forces occurs, the pavement can buckle or break in its weakest points
• Minnesota:
– At the time of construction, to prevent future problems associated with joint function include driving heavy loads (such as full water trucks or dump trucks) along the pavement shortly after joints have been sawn
– Helps activate the joints
– Ensures that a majority of them successfully crack
– Keeps each crack tighter and more resistant to infill
• JOINT SEALANT can also help keep incompressible materials out
• LENGTHENING SPACING BETWEEN JOINTS at the time of construction—sometimes done as a cost-saving measure—is NOT RECOMMENDED
TIPS FOR LENGTHENING SERVICE LIFE OF CONCRETE PAVEMENT:
— EXAMINE PAVEMENT about every 10 years
— PERFORM SMALL REPAIRS at these intervals will save time and money over the life of a concrete pavement
— KNOW WHAT TYPE OF DISTRESS TO LOOK FOR
— A FEW KEY DETAILS ABOUT HOW DISTRESS IS PRESENTING will improve the efficiency and effectiveness of maintenance and repair procedures when there is concrete cracking:
• CROSS-STITCHING can be performed to arrest the movement if there is a concern that a longitudinal crack will widen and allow the pavement to separate
• Many longitudinal cracks do not require repair at all
• DOWEL BAR RETROFIT is often required with TRANSVERSE CRACKS to prevent faulting and the development of a rough ride
• JOINT SEALANT for both longitudinal and transverse cracks (even those not severe enough to require repair), is recommended to:
-minimize the intrusion of water
-protect against water-related spalling
-protect against base or subgrade softening
-protect against dowel bar corrosion
-protect against pavement joint blow-ups
-protect against materials-related distress
“BAND-AID REPAIRS”:
1—ASPHALT PATCH … REPAIR CONCRETE WITH CONCRETE!: One of the most important points when it comes to concrete pavement!! Where broken slabs or buckling require panel repairs, it has been too common for crews to saw cut and remove the damaged pavement and then replace it with an asphalt patch. The recommended procedure is to:
• Remove all deteriorated concrete and use full– or partial-depth repair (depending on the depth of deterioration)
• Often with dowels installed to achieve load transfer
—When concrete pavement is repaired using asphalt as anything more than a temporary solution…
• flexible bituminous material allows improper expansion
• causes significant pavement movement
• adds up to several inches over the course of a few years
• results in distressed areas across many square yards of the pavement surface with distresses only worsening over time
—Asphalt used to patch only the partial depth of a panel:
• Concrete remaining at the bottom is compromised
• Likely to buckle when under a heavy expansive load
“One of the most important points…
when it comes to concrete pavement,
is to repair concrete with concrete!”
How Much Concrete Pavement Should You Remove?
To ensure the success of full-depth repair, it is critical to determine the size of the section to be removed and replaced. Repair boundaries should extend beyond any affected areas. The most commonly used design methodologies recommend full-lane-width replacement for structural stability purposes, and typical minimum lengths vary from 3-6 ft. If patches are too small, they can rock under heavy traffic and punch into the road’s subbase. Depending upon the boundary conditions and location of the repair area, combining two small patches into one large patch area may reduce costs; however, the longest patch length should not exceed the pavement’s longest slab without reestablishing the transverse contraction joint when repairing jointed plain concrete pavements and jointed reinforced concrete pavements.
—International Grooving & Grinding Association’s Full-Depth Repair fact sheet, June 2020
2—IMPROPER ALIGNMENT OF A DOWEL BAR OR BASKET DURING CONSTRUCTION: (“band-aid” solution to concrete maintenance results in more extensive and costlier repairs later can be seen when dealing with concrete damage)
• Improper transfer of loads across the doweled joint
– causes pieces of concrete to break out
– if patched with asphalt instead of using a technique that restores load transfer, stresses will continue to build, having an effect across many square yards of pavement
3—ROUGHNESS vs. SMOOTHNESS: A final consideration when it comes to pavement maintenance. During construction, concrete pavements can achieve the International Roughness Index (IRI) measurements of 30 in./mile or less, creating a very pleasant driving surface. After 8-10 years, however, the variance in moisture content and/or temperature between the top and bottom of a pavement slab can possibly cause some degree of:
• CURLING: given the right conditions
• Can create ROUGHNESS
• ADDS as much as 20-40 in./mile to the IRI
• DIAMOND GRINDING is the concrete pavement preservation (commonly known as CPP) technique that will restore smoothness to concrete pavement
– can lower the IRI of a pavement by 50 in/mi.
– can result in IRI values as low as those achieved during original construction
– cost-effective
– requires minimal traffic disruption
– provides better ride quality
– improves motorist safety
– keeps a pavement smooth
– extends its life by minimizing impact loads
– improve vehicle fuel efficiency
– make smooth pavements more sustainable
– reduce fuel (pass savings along to the public)
– reduce vehicle repair costs (pass savings along to the public)
Q: “To maintain or not to maintain?”
A: “YES!”
Well-designed and -constructed concrete pavement can last many decades.
But, to ensure that it reaches its full-service life
—and has optimal rideability during each year of its life—
agencies should develop a preventative maintenance plan.
Small, regular interventions save time, money, and effort in the long run.
Matthew J. Zeller, P.E., Executive Director-Concrete Paving Association of Minnesota (CPAM)
RESOURCES:
Cross- and Slot Stitching, IGGA, https://www.igga.net/wp-content/uploads/2020/08/Aug2020_Cross_and_Slot_Stitching_1_pager.pdf
Dowel Bar Retrofit, IGGA, https://www.igga.net/wp-content/uploads/2020/06/FSJUNE2020_Dowel_Bar_Retrofit_Rebuilt_to_Last.pdf
Full-Depth Repair, IGGA, https://www.igga.net/wp-content/uploads/2020/06/FSJune2020_Full_depth_repair_FDR.pdf
Partial Depth Repair, IGGA, https://www.igga.net/wp-content/uploads/2020/07/FSJuly2020_Partial_Depth_Repair_PDR.pdf
For the “For ConsructionPros (FCP)” online magazine article titled “Preventative Maintenance for Concrete Pavement: What Is It & What Does it Prevent?”, please go to: www.forconstructionpros.com/concrete/article/22080835/igga-international-grooving-grinding-association-preventative-maintenance-for-concrete-pavement
For the VIDEO titled “A Progressive Concrete Pavement Preservation Strategy Improves City Streets in Minneapolis” that coincides with this article, please click below, or go to the ISCP home page and click on the video post/article: www.concretepavements.org/2022/03/23/video-45-yr-o-concrete-pavement-progressive-concrete-pavement-preservation-techniques-improves-city-streets/