The Solution to Combating Composite Overlays

The Story of New York



The Solution to Combating Composite Overlays






The Story of New York

First, what is a composite overlay?

In most cases, it means that the original roadway was placed in the 1950’s – 1970’s. This roadway traditionally consisted of reinforced cement concrete pavement (RCCP). At some point this RCCP was overlaid with asphalt pavement creating a composite roadway. These composite pavements eventually fail due to base failure, cracking, and other environmental distresses.  Perhaps you remember the ba-bump,… ba-bump,.. ba-bump driving down the interstate?  This is a sure sign of deterioration in the roadway. This weakening can lead to a wide array of issues for the traveling public including damaged tires, potholes, and even accidents.

perpetual history of failure

There are several causes of failure, with the most common cause being reflective cracking.  This happens when joints in the old cement concrete are unstable due to loading from trucks and/or thermal contraction and expansion (growing and shrinking of the concrete due to temperature changes).  This instability happens most frequently when a series of joints get “locked up”, restricting movement.  The expansion/contraction doesn’t always happen at every joint like it is supposed to.  So instead of having an 1/8th” movement at every joint, there might be ½” movement at every 3rd joint.  This creates stress on the pavement that eventually leads to cracking.  That cracking then reflects up through the asphalt layer. This creates the ba-bump, ba-bump. 

Joint failure of the RCCP can also be caused by normal heavy-truck traffic.  The strain that the slab receives at the joint causes the base aggregate (stone) to crush and/or migrate. This leaves a small pocket under the slab at the joint and allows movement.  The movement at the joint causes the waterproofing joint sealant to fail. This water in combination with the rusting of the load transfer bars enhances the movement in slab.  The failure process is further accelerated when water occupies the space under the joint.  Water beneath the joint flows under the loading of traffic, this allows the flushing of fine aggregate out of the joint base course. Water then freezes and expands under the joint.  This freezing and subsequent flushing cause the space under the joint to get bigger.  What happens when nothing is holding up the pavement at the joints???  It bends and gets bumpy.  The RCCP will eventually crack when the bending becomes too much.  That’s why asphalt overlays are used to seal the roadway and bridge the loading space at the joint locations.

the roadway to a solution

The New York Department of Transportation (NYDOT) has tried many methods to prevent, retard, or control the development of reflective cracking in composite overlays throughout the years.  These solutions have been found to be costly as well as ineffective, with many exhibiting fair to poor reliability and results.  Additives used by the NYDOT in the past include road fabrics, stress-relieving interlayers, and increased overlay thickness. These methods were not delaying the onset of the reflective cracking or reducing the severity according to Jim Jordan, former NYDOT manager. He also noticed that secondary cracking would occur very quickly. Standard transverse joint repairs, commonly referred to as Deep Joint Pavement Repairs or Pre-Overlay Treatments proved to be the most effective remedy but still has significant ramifications.

So, what is Deep Joint Pavement Repair?

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Although it can vary from region to region in New York, the first step is identifying the reflective cracks on the composite pavement and determining the severity of the cracking. Medium to high level severity cracking typically requires more in-depth repairs. But the usual process involves milling a significant amount of the pavement down to the cement concrete.  The thickness of the overlays varies but a minimum 4 1/2 inches or more is common.

For instance, State Route 383 in New York’s Region 4 required 6” of asphalt to be milled 6’ wide and 3’ on each side of the crack.  The 6” of milled area of St Rt. 383 was then filled with a 19mm hot mix asphalt and compacted.  This process took 4 weeks of night work to complete. Crews then milled 2” and filled 2” with 12.5mm Superpave PG 64v-22, wearing course. 

For some regions, the option of reconstruction costs too much and repairs will consist of overlaying the RCCP with asphalt pavement. Adding strength to these more cost-effective options is paramount. NYDOT decided to use FORTA®’s synthetic asphalt fiber reinforcement, FORTA-FI® to add durability and reduce cracking. This engineered fiber is specially formulated to reinforce all working temperatures of asphalt mixes, creating longer lasting, more resilient pavement. On St Rt. 338, sections of the roadway were reinforced with FORTA-FI omitted the Deep Joint Repair. The NYDOT decided on a 2” mill and fill using a 2.5mm Superpave PG64s-22 with a fiber reinforced wearing course.

Benefits of skipping the costly repairs

There are many advantages to using fibers in lieu of standard joint repair. Starting with cost alone. Deep Joint Repair is a very expensive separate operation. Repairs can cost $50.00 to $100.00 per SY. Not to mention the elimination of WZTC (Work Zone Traffic Control). While there is a cost to add the fiber reinforcement, official can specify neat asphalt binder (64S-22) in the fiber sections in-lieu of polymer asphalt binder (64V-22) and ease the cost of the adding the fibers to the WMA (Warm Asphalt Mix).

There is also a reduced risk of exposure to the travelling public and workers (both Contractor and Agency). By eliminating this labor-intensive operation there is reduced equipment on the ground and reduced “open holes” from the joint repairs that can create a hazard for the traveling public.

Adding reinforcement fibers are also shown to simplify the paving process. Typically, transverse joint repairs extend the project work by weeks, 4 weeks on St. Rt. 383 alone. By eliminating the joint repairs, the contractor can now drop the mill in and start production milling and production paving.

 

Adding fibers at the HMA/WMA Plant is also an easy process and it doesn’t impact the overall paving process- the contractor doesn’t need to change/alter their paving “plan”. There are no issues with hauling, spreading with the paver, and achieving the required compaction during the rolling operation. We have seen no issues with handwork.

what's the return on investment

The cost comparison between doing a Deep Joint Repair project and using FORTA-FI on the St. Rt. 383 project would have been an overall saving of 16% or $350,000, on this $2,180,000 project.  Construction time could have been reduced by 4 weeks had used fiber on all 5 lanes instead of the labor-intensive repairs.  That equates to a 30% to 50% reduction in construction time.  Just think if you could eliminate 4 weeks of night work.  That’s 4 weeks less exposure of workers to traffic at night. 

Typical maintenance procedures for composite overlays dictate crack sealing joint repairs (Reflective Cracking) after just 2 years. Experts have found that projects using FORTA-FI fibers are able to delay their maintenance programs and additional 2 years due to the reinforcement capabilities.

The expected life extension of the St. Rt. 383 pavement has also been increased by 2 to 3 years based on the delay of cracks and distress reduction as measured by Joe Kindler, Pavement Management Engineer/Consultant. Joe has calculated a savings of $364,000 for two extra years of pavement life on the 383 project or roughly 17% overall project savings based on just the extended pavement life. Total project savings on the St Rt 383 Project with the extended life is nearly 1/3 or 33%.  

"Overall, initial results of the high tensile strength engineered fibers look promising- it appears we are seeing a reduction in reflective cracking- hopefully, we’ll also see a reduction in fatigue and low thermal cracking and wheel path rutting with the use of fibers in HMA/WMA."
Jim Jordon
Former NYDOT Manager

Where's the proof?

The Army Corp of Engineers developed PAVER a Pavement Management System (PMS) to maintain their own properties in the late ‘70s.  This PMS has been improved yearly and is now used worldwide.  The inspection methodology they developed is the only one with an ASTM number – D 6433.  It is more involved than any other pavement inspection system, and consequently is more accurate and is repeatable when done by various knowledgeable inspectors. 

The process requires choosing sample areas (2,500 square feet each) amounting to approximately 10% of the pavement being inspected.  Each of these sample areas is located so it can be re-inspected at the next cycle.  In the sample every distress is listed, the severity is also recorded, and the quantity of each distress is determined, then this data is input into PAVER.  PAVER will then produce a Pavement Condition Index (PCI) for each sample which can be extrapolated across the section.

Inspecting NYDOT, District 4 - Rochester SR 383

This five-year-old pavement was inspected using the PAVER, ASTM D6433 inspection methodology, to determine the current condition of the FORTA-FI hot mix with the control section.  Six representative sample areas were chosen on each side.  The samples were 2,500 square feet in area and covered the right-hand lane in each direction only.  The main two distresses found were longitudinal and transverse cracking (“10”) and patching (“11”) with light (“L”) and medium (“M”) severities.  There was some minor rutting (“15”) in the outside lane North bound (control) in a couple of the samples with light (“L”) severity.

Sample FORTA-FI Side

10-L-340

10-L-290

11-M-110, 10-L-240

10-L-340

10-L-260

10-L-480

Average PCI

PCI

80

82

73

80

83

77

79

Sample Control Side

10-L-460

10-L-410, 11-L-320

10-L-370

10-L-520, 15-L-300

10-L-480, 15-L-300

10-L-340

Average PCI

PCI

77

70

79

60

61

80

71

“I have worked with PAVER for the past 25 years and understand the relationship of distresses and pavement life. It is my Professional opinion that delaying cracking by 2 or 3 years will increase the pavement life by a like amount.”
John Kindler
Pavement Management Engineer/Consultant

NOW WHAT?

Today, using time, money, and material resources is everyone’s goal. At FORTA, we have one goal: to create tougher, more durable pavements. Our products offer innovative solutions to protect and enhance the longevity of asphalt while expanding the life cycle of the pavement.  Over the years, our asphalt pavement projects have been put to the test in real-world, head-to-head trial projects around the country, and have withstood the test of time. NYDOT has found a way to create longer lasting pavement while cutting initial costs, increasing safety, and reducing future maintenance costs. Isn’t it time your state combats the issues associated with composite overlays?