Extending Pavement Life with Rapid-Set Polymer Based Technology

Background/History

Early 1980’s
The origins of this approach to concrete and asphalt repair began in the early 1980’s with a project to develop a method for quickly returning bomb damaged military runways to service at the 33 NATO bases in Europe. The Pavement Research Center at Tyndall Air Force Base in Florida initiated this program to evaluate suitable technologies.

The primary requirement for materials was to complete the repair in less than 30 minutes so that it would hold up for takeoff and landing of a fully loaded NATO bomber. The most effective material tested was a rapid curing polyurethane elastomer, which provided the necessary speed, bond strength, and load bearing properties.

Mid-1980’s
During this period Cal-Trans began investigating new and innovative ways to repair bridges and concrete roadways. They did extensive research and published much of the work in a report titled “New Materials and Techniques for the Rehabilitation of Portland Cement Concrete” (Krauss, 1985). Additional in-depth testing was also conducted by the Cal-Trans Translab (Ferroni, 1985).

There were a number of field trials done with quick-setting polyurethane systems in a variety of highway conditions around the state, both on asphalt and concrete surfaces. These trials went on until the end of the 80’s. The ultimate conclusion was that, after extensive, real world application, polyurethane based polymer concrete is well suited for use as a repair material for potholes, spalled concrete, alligatored asphalt, and other types of damage commonly found on roadway pavements.

1989 Loma Prieta Earthquake
One of the areas severely damaged in the San Francisco quake in 1989 was the Oakland Bay Bridge. At that time the bridge had an epoxy asphaltic overlay, which was badly spalled and cracked by the earthquake.  A rapid curing urethane was used to repair these defects and in less than 30 days the bridge was re-opened for traffic. The performance of urethane polymer concrete in this instance further demonstrated its advantages as a repair material for bridges and roadways.    

Early 1990’s to Present
In 1991 Cal-Trans announced that this technology was now beyond the experimental stage (Allison, 1991), and could be used where maintenance personnel felt it was appropriate. Since that time Cal-trans has officially approved Roklin’s FloMix and FlexSet, They have used several million pounds of polyurethane polymer concrete in thousands of installations in almost every part of California. Roklin systems are also used worldwide by other state DOT’s, cities and counties and in a wide range of private sector applications.

Methods/Concepts for Successful Concrete & Asphalt Repairs
Historically, Pavement repairs have been made using products similar to the materials being repaired. Portland cement based products are used to repair PCC, and asphaltic based materials are used to patch AC (asphalt-concrete) pavements. This approach would seem logical since the final properties of the patch should be similar to the pavement properties; however the problem with this idea is that the new patch material has widely different properties in the early stages than the existing aged pavement. The new portland cement based concrete must gain strength quickly and will shrink as it dries and cures. Since a bond line is present, stresses develop along the bond interface as the new patch material shrinks due to loss of hydration heat and loss of moisture over time.  Therefore it is not uncommon for PCC patching materials to crack and debond. Higher strength patch materials are even more prone to cracking and debonding than lower strength materials. This is usually due to the higher cement content or the use of fume silica that creates high strength, but a very rigid, brittle nature. The higher paste or use of fume silica also causes the patch to reach a higher heat of hydration, resulting in higher, earlier thermal cooling stresses, in addition to higher shrinkage due to drying. Structurally, high strength PCC materials are brittle, having a higher modulus of elasticity and lower creep. Consequently, when the new PCC materials shrink, stresses are higher, and remain in the bond line longer. The result is a high tendency for cracking and delamination in the patch.

These properties will minimize stress built within the patch material and at the bond interface while carrying traffic loads. It is essential, therefore to formulate products to exhibit the right balance of these properties to minimize bond, shrinkage and thermal stresses to enhance the performance and durability of the patch.

Products/Equipment
These quick setting repair systems, currently used by Cal-Trans and others, are manufactured by Roklin Systems of Lake Forest, CA. The products are two component polyurethane systems, which are specifically designed to support heavy traffic loads, but flexible enough to minimize bond stresses and thermal stresses, which cause failure in conventional materials.

Roklin now offers different types of formulations, aggregates, and equipment that can perform almost any type of asphalt or concrete repair.  

Flomix/FlexSet
The products currently approved by Cal-Trans are FloMix for asphalt and FlexSet for concrete. They are supplied in 3 & 5 gal. kits, which contain pre-measured amounts of chemical and polymer coated aggregate. Roklin uses rounded river sand coated with urethane to prevent moisture contamination, improve flowability, and promote adhesion of polymer to aggregate. These products are basically the same polymer except for pigmentation---Gray for FlexSet and Black for FloMix.  Each 5 gal. kit will cover an area of 50 sq. ft. at 1/8 inch thick, or approximately 0.4 cubic feet. For deep potholes and cracks, up to an additional 30-35% by weight of ¼” to ¾” aggregate can be used to further stabilize the repair and extend polymer coverage to 0.55 cubic feet. Roklin supplies a basaltic based 3/8” inch, polymer coated rock for this purpose.

Concrete Welder
This product was developed to be applied by a bulk dispenser for repair of third stage damage in pavement slabs. It is a low viscosity material that penetrates deeply into small cracks and crevices. The enhanced flow of Concrete Welder allows it to flow beneath the concrete slab, where it will fill any void, fill and bond cracks, and restore aggregate interlock. These actions will serve to stabilize the slab and prevent further deterioration caused by under-slab erosion. After applying Concrete Welder initially, either FloMix or FlexSet is used to complete the repair and restore grade.

VariFlo Bulk Dispensers
Roklin manufactures two versions of low pressure dispensers for bulk application of product. This equipment utilizes Viking gear pumps and dispenses material at approximately 2 gal/minute through a 12” static mixer.

The smaller model can use 5 or 15 gallon drums of chemical. The larger model runs with 15 or 50 gallon drums, but has the same output.

The advantage of this equipment is to allow faster and more efficient application of product. The urethane does not have to be pre-mixed before applying. That is done in the static mixing tube. The flow of material can also be turned on and off at will. The VariFlo equipment is simple and easy to use, but like any mechanical device, requires some amount of maintenance.

VariFlo 30-50 Dispenser

Applications/Case Studies

FloMix-710 Freeway, City of Commerce

FloMix-City Street

FloMix-City Street

FlexSet- 101 San Luis Obispo

FlexSet-City Street

FlexSet-I-5, Las Pulgas Overpass, Camp Pendleton

Concrete Welder/FlexSet-I-10, San Bernadino

Advantages/Benefits of Urethane Polymer Based Repair Products

1. Minimal Preparation
   With most conventional repair materials there considerable time and labor involved with dig-out and haul-away prior to installation. Roklin products require only that you blow out, or vacuum the damaged area to remove loose rock, dust, and dirt. You don’t need saw cuts or primers, but it is important to remove any moisture from the application area. It is rare to spend more than 5-10 minutes for preparation
2. Simple Installation
   There is no need for heavy equipment or extensive worker training to apply Roklin materials. FlexSet and FloMix come in pre-measured, pre-weighed kits containing the exact amount to be mixed. They can be mixed with a bird cage mixer and a drill, or our Motor Mix Machine.
3. Lower Labor Costs
   Most applications can be done by a two man crew. In many instances two men can set up the road closure and do the installation. Most installations will be completed in less than an hour from start to finish, so that repair productivity is at a high level.
4. Quick Setting
   Roklin products usually set up within 12-15 minutes at 75°F. The repaired area can be put back into service, and will support high load traffic within 45 minutes to an hour. This allows for short closures and traffic delays, less exposure of workers to traffic, and contributes to lower cost overall.
5. Safe to Use
   As mentioned before, Roklin products have been used in thousands of installations over the last 20 years without incident. The materials contain no solvents or VOC’S, and have exhibited exposure levels substantially below OSHA limits in outdoor tests.
6. Seals and Waterproofs
   As opposed to many conventional repair materials, Roklin polyurethane repairs are completely impervious to water and effectively seal the pavement so the water cannot reach the sub-base to cause erosion, corrosion of rebar, or further deterioration.
7. Long Lasting/ Durable
   Due to the high strength properties and excellent adhesion of Roklin products to the substrate, our repairs last considerably longer than conventional materials. We have installations that have been in place for over 10 years in some very high traffic, heavy load bearing freeways in California. It is not possible to project the lifespan of a particular repair due to the many different types of damage, environments, substrates, base condition, traffic load, etc., however we can say with certainty that our repairs will outlast any conventional product by some multiple of time. For example, if a cold mix asphalt plug lasts for three months, a Flomix repair is going to last 3 to 10 times that long, or 9 months to 3 years.
8. Unaffected by Heat or Cold
   Not only can Roklin products be applied over a wide temperature range (-10°F to 140°F), they are not affected by extreme temperatures once they are in place. There is minimal expansion/contraction of the polymer/aggregate mix once the material is fully cured.
9. Good Chemical Resistance to Oils, Hydraulic Fluids and Diesel and Gasoline
   Our materials have been tested and show no deterioration or loss of physical properties when exposed to these chemicals that are commonly found on roadways and parking areas, etc.
10. Enhances Smooth Ride
    All Roklin products are self-leveling, and can be easily be feathered into the surrounding substrate to restore the original grade level to mismatched slabs or sunken areas.
11. Effective Load Transfer
    Because of the flexural properties, repairs done with Roklin products effectively transfer repeated impact loads between concrete freeway slabs. The rigidity of concrete under repeated impact load is one of the primary causes of corner spalling in roadway slabs.
12. Reduces Tort Liability
    We are all aware of how litigious our society has become. The capability of Roklin products to immediately repair hazardous conditions that may appear without warning can greatly reduce the possibility of lawsuits, justified or not, which could cost thousands of dollars.
13. Overall Cost Effectiveness
    Even though Roklin products are sometimes more expensive than conventional materials initially, the advantages listed above can actually save a significant amount of money in the long run. An example of cost savings is a recent job that was done by Cal-Trans in Valencia. As you may know, replacement cost for concrete freeway slabs is in excess of $5000 per slab, depending on the number of slabs replaced at one time. In Valencia, Roklin products were able to stabilize the base and repair 10 freeway slabs on I-5, in two hours of closure time, at a total cost of less than $4000.00. 

Conclusion
Roklin materials are specifically designed to fit the requirements of small to medium size repairs on any type of concrete or asphalt surface. They have proven performance and a successful track record in a wide range of applications over a number of years. At his point in time, with budget constraints and workforce reductions, they provide another option to road maintenance organizations that can extend pavement lifespan until funds become available for the major expenditures necessary for large remove and replace projects.