Cold in-place recycling is rapidly becoming more important throughout the world. This worldwide trend is being driven by three common objectives:

Quality, Speed, and Economics.

Over the past five years, owner agencies, contractors and suppliers have learned that when a 100 percent cold in-place recycle job is properly designed and tested, it can be akin to making a "silk purse out of a sow's ear"!

New methods and machines have made this possible. Cold in-place processes have been developed around the world using asphalt emulsions, asphalt foam mix, cement, lime, coal combustion fly ash and other chemical additives or modifiers. These process developments are capable of providing a new, high strength, flexible base.

The newest and most advanced processes incorporate a "train" of equipment designed and integrated to incorporate several of the above-mentioned materials and additives into one comprehensive, predictable operation.

The addition of cement in slurry form has proven to be a dust-free, environmentally friendly method of incorporating this binder/strength-enhancing material into the cold in-place process. Uniform distribution throughout the in-place material results from introducing the additive in liquid form.

Emulsions of cement or lime or fly ash, or foam-mix cement, are now commonly used in many areas around the world.

The cement-emulsion enhances the binding characteristics of emulsified asphalt and the strength and binding characteristics of cement through the water/cement chemical reaction. This allows the highway agency owner/designer to:

Evaluate the future strength requirements of an existing highway cross section
Re-use 100 percent of all existing materials and their related investment cost, and
Add binders and strength-enhancement additives that achieve a new, predictable structural value prior to a surface course.

And all this with a minimum amount of truck traffic and highway user disruption.

In summary, today's more advanced cold in-place recycle processes incorporate many of the social, economic and environmental themes important to all of us. Consider these obvious major advantages:

• 100 percent re-use of all in-place materials, asphalt and base

• 100 percent of previous investment(s)

• Cold in-place recycle means very low energy requirements (and cost), and limited truck movement (and cost)

• Today's machines and processes allow deeper recycling, up to 8 to 10 inches

• New materials, technology, additives and processes allow greater structural values in the end product
  

• Jobs progress quickly, minimizing user delay and inconvenience

• As a general rule, cold in-place jobs cost 15 to 30 percent less than other methods

• Cold in-place recycle processes are environmentally compatible and acceptable, with no smell, no visible emissions, no exposure to fumes. Permits and EPA compliance procedures are greatly simplified

• Cold in-place jobs use common, every day construction equipment, most is already owned by contractor and government agencies. Water trucks, compactors, graders, pulverizers, milling machines, pavers, brooms and loaders comprise the mix of equipment required for the job

• Design and testing requirements have been proven and are readily available. No special high-cost laboratory equipment or technicians are required, which also eliminates delays in obtaining results.

Today's cold in-place recycle process is a true "win-win" scenario. The world's highway industry now is incorporating cold in-place recycling to solve the majority of reconstruction challenges.

Adapted from a presentation by Stu Murray, president, WirtgenAmerica Inc., to the 1st Asphalt Conference and Exposition (ACE) of Asphalt Contractor Magazine, Atlanta, March 22, 1999.

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