The History of Cold Recycle Chuck Valentine Valentine Surfacing Co Highways & Engineering Conference

The Early Days – California and Arizona were the first states to utilize the “cold in-place” process. It was born out of the desire to create an “in-place” process and eliminate trucking. By the mid 80’s, other state DOT’s such as Oregon, New Mexico, and Montana were utilizing this new technology.

The Early Days California and Arizona were the first states to utilize the cold in-place recycling process. It was born out of the desire to create an “in-place” process and also to eliminate trucking issues. By the mid-80’s, other state DOT’s such as Oregon, New Mexico, and Montana were utilizing this new technology.

Cold Recycling Equipment The recycle “train” hasn’t changed much over time. The main components are the rotomill, a screening and crushing unit, and a mixing unit. The only real change is some contractors have consolidated the screening, crushing, and mixing unit on one trailer.

Rotomill Over the years, the major pulling unit, the rotomill, hasn’t really changed. Standard full lane width rotomills range in width from 12.5’ to 16.5’. Typically, on widths wider than 14’, a second rotomill is utilized to get the proper width.

Screening and Crushing Originally, a roll type crusher was used but was replaced by hammermill type crushers in order to boost production capacity.

Mixing Unit Generally speaking, the major components of the mixing unit are the twin shaft pugmill, weigh belt to weigh the RAP, and state of the art electronics to take the signal from the weigh belt and inject the proper amount of asphalt emulsion.

Emulsions Used In Early Days The type of emulsion used has always been somewhat of a “regional” preference. In the Northwest, primarily CMS-2S was used and still is. In the Southwest, “ERA” type products manufactured by Golden Bear were prevalent. In the Rocky Mountain region, High Floats were primarily used.

Knowledge Gained Originally, CIR was limited to low volume roadways and required hot mix overlays in all cases. The depth of recycle was experimented with – from 1” to 6” deep – it was found that 2”-4” was the optimal depth. Early on, the amount (and type) of recycling agent added to the RAP was a moving target. There were many attempts at adapting a mix design procedure to fit CIR – most if not all were unsuccessful.

Knowledge Gained - Continued Void Contents with CIR are higher than hot mix – 8-15% - if you get void content down to hot mix you will have stability issues. Project selection is crucial – there needs to be adequate mix depth and you can’t fix subgrade problems with CIR. Traffic control the first 24 hours is critical.

From the Mid 90’s to Present Day The quality of the CIR product is such that higher volume roads as well as Interstate highways are routinely cold recycled. With the addition of lime slurry, early strength characteristics and anti strip characteristics were enhanced. As a result of higher strengths and durability, thinner hot mix overlays and/or chip seals are now acceptable surface treatments resulting in substantial cost savings.

Successful Cold Recycle Programs Presently, every western state has done at least one CIR project. The WFLHD & the CFLHD also specify CIR. Numerous cities and counties in the West have utilized this process.

Nevada DOT’s Experience In 1997, NDOT began using a proactive Pavement Management System along with CIR to address their pavement rehabilitation. In the past 9 years, NDOT has successfully cold recycled over 770 centerline miles. By utilizing this approach, they have reduced their backlog of rehab projects by 60%.

NDOT Continued NDOT has assigned a structural coefficient to CIR of This is a conservative number – some states use as high as A year life expectancy is anticipated. The decision to place a structural overlay or chip seal is based on future ESALs.

NDOT Life Cycle Cost Analysis 20 year like cycle cost analysis on one centerline of road with projected 20 year ESALs of 2,000, inch CIR w/2.5” overlay and OGFC w/rehab in year 12 has a present worth cost of $306K 2 inch overlay and OGFC w/rehab in years 9 & 16 = $418K 3 inch mill, 3 inch overlay w/OGFC w/ rehab in year 12 = $415K

Washington DOT’s CIR Program WSDOT is producing a paper which summarizes their experience with CIR. WSDOT has been utilizing CIR since They have successfully performed 16 projects amounting to centerline miles of roadway.

Montana DOT’s Experience Montana DOT has done CIR since the mid-80’s. The last 4 projects have used Reflex emulsion – Red Lodge, Helena NW, Livingston South, and Bridger South.

Recent Innovations in CIR Advent of “solventless” emulsions. Environmental pressures to switch to a solventless product. - Difficulty in manufacturing traditional emulsions at the plant. Shorter cure times with solventless products. - Allows compaction to occur sooner. - Allows traffic on the recycled mat sooner. - Allows recycle in cooler temperatures.