Dowel Bars: How Epoxy Coating Extends Concrete Pavement Life
KEY TAKEAWAYS
- Dowel bars transfer load between adjacent concrete slabs at pavement joints
- Epoxy-coated dowel bars remained in excellent condition after 20+ years of service in a New York DOT case
- Approximately 18 million dowel bars are used in the US every year
- 26 of 36 surveyed DOT agencies currently use epoxy-coated dowel bars
- Dowel bars must pass seven rigorous AASHTO T253 tests, including corrosion-abrasion and cathodic disbondment testing
- Epoxy-coated dowel bars are manufactured to meet AASHTO M 254 standards and are produced in CRSI-certified plants
Want to see epoxy-coated dowel bars in action? Browse Project Examples from real infrastructure projects across the country.
Dowel Bars: How Epoxy Coating Extends Concrete Pavement Life
A vast majority of the nation’s highways and roads are made of jointed concrete pavement, and dowel bars play a critical role in keeping those joints functional for decades. The Epoxy Interest Group has researched this extensively when it comes to dowel bars and reinforcing steel. These joints allow for deformation and movement due to thermal and environmental conditions. These joints are assumed to be approximately 1/8″ gaps between two adjacent slabs. Dowel bars are located at these joints and used to transfer load from one slab to an adjacent slab. The 1993 AASHTO pavement design guide indicates that dowel bars “should be resistant to corrosion when used in those geographic locations where corrosive elements are a problem and epoxy-coated bars have been used to provide this corrosion resistance. In a survey conducted by the Kentucky Department of Highways in 2005, the following comment was received from New York DOT: “I was involved in two CPR projects where transverse joints were removed and replaced. In both cases the epoxy coated dowels were in excellent condition. Both repair projects were on PCC pavements that had been in service in excess of 20 years.”
Dowel bars are typically 32 to 38 mm (1.25 to 1.5 inches) in diameter, 460 mm (18 inches) long and spaced 305 mm (12 inches) apart. They are generally inserted into the middle of the slab and coated with a bond-breaker, which reduces bond of the bars to the concrete slab. Dowels prevent the slabs from moving in a vertical direction relative to each other, but allow them to move with changes in temperature and concrete shrinkage. Dowels may be used in both new and repaired concrete slabs.
A recent survey of 36 DOT agencies found that 26 of them were currently using epoxy-coated dowels and a study by Iowa State University found that there were approximately 18 million dowel bars used in the US per year. Almost all epoxy-coated dowels are manufactured to meet AASHTO M 254 Standard Specification for Corrosion-Resistant Coated Dowel Bars.
In order to be accepted, coatings for dowel bars undergo stringent tests according to AASHTO T253 Standard Method of Test for Coated Dowel Bars. This test standard requires coated bars to pass load-deflection, pull-out, corrosion-abrasion, chemical resistance, cathodic disbonding, coating hardness, and coating impact tests. These tests are briefly described below.
The load-deflection test evaluates dowels in concrete and places limits on the concrete deflection under load, while the pull-out procedure evaluates the ability of the dowels to move within the concrete. Failure of the dowels to move would result in pavement cracking or buckling.
The corrosion abrasion test first subjects the dowel to 10,000 cycles of concrete abrasion followed by freezing and thawing exposure in a salt solution. After this test the bars are examined for corrosion.
The chemical resistance tests evaluate the performance of the coated dowels in four different solutions including distilled water, calcium chloride, sodium and calcium hydroxide. Cathodic disbondment tests are conducted using a salt solution and a potential of 2V over a period of 30 days.
Coating hardness is evaluated using a dropped tup, with an impact force of 80 in-lb and hardness is determined using the Knoop hardness test.
Most dowels are manufactured in plants that conform to the Concrete Reinforcing Steel Institute Fusion-Bonded Epoxy Coating Applicator Plant Certification, initiated in 1991.
Learn More about how epoxy-coated dowel bars and rebar can extend the service life of your pavement and infrastructure projects. Learn More
FAQ
What are dowel bars used for in concrete pavement?
Dowel bars are placed at the joints between concrete slabs to transfer load from one slab to the next. They allow slabs to move horizontally with temperature changes while preventing vertical movement, which helps prevent cracking and faulting at joints.
Why are dowel bars epoxy-coated?
Epoxy coating protects dowel bars from corrosion, which is especially important in regions exposed to deicing salts and other corrosive elements. The 1993 AASHTO pavement design guide recommends corrosion-resistant dowel bars in these conditions.
What testing do dowel bars have to pass?
Epoxy-coated dowel bars must pass seven tests under AASHTO T253, including load-deflection, pull-out, corrosion-abrasion, chemical resistance, cathodic disbondment, coating hardness, and coating impact tests.
How many dowel bars are used in the US each year?
According to Iowa State University research, approximately 18 million dowel bars are installed in concrete pavement across the US annually.
Are epoxy-coated dowel bars widely used by state DOTs?
Yes. A survey of 36 state DOT agencies found that 26 currently use epoxy-coated dowel bars in their pavement projects.
How long do epoxy-coated dowel bars last?
Field data from New York DOT found epoxy-coated dowel bars in excellent condition after more than 20 years of service in pavement that had been repaired and reopened to traffic.
FOOTNOTE
i. “Epoxy Coated Dowel Bars Used in Portland Cement Concrete Pavements,” Results of Survey by Kentucky Department Of Highways, Division of Materials, December 27, 2005