Monday, October 10, 2011

Cold In Place Recycling (CIR)

A few months back I received this email:


I came across this article tonight and I thought of you. I just wondered what you thought of it. The article says the technique California is starting to use to resurface their roads is way better than the old way. It is also greener. I was wondering if there were any drawbacks that you knew of. 

Keep in touch.


Recently I attended a meeting where we discussed this new process so I figured I'd discuss it here for you all.

I haven't actually seen this method in person but I've read a lot about it and saw a couple videos on it. The process is really cool to watch and there are a bunch of videos on youtube. Here is a video of one type of train in action:

The cold in place recycling process or "train" is a pretty simple process. A milling machine at the front of the train mills off the existing pavement down to base rock (typically 2"-4"). This material is then conveyed to a screening/crushing machine where the material is reduced to the size needed for the mix design. From here the material is mixed with a recycling emulsion and laid down on the roadway in windrows. The material is then picked up by a shuttle buggy and put in the hopper of a paving machine where it is laid down as a fresh mat. After that, traditional rollers are used to compact it. The material is a dull brown when it is laid down and as the moisture from the emulsion evaporates it turns to a nice black. Once it has changed to black, traffic can be put back on the road; this can be as soon as 90 minutes after paving.

There are some hesitations about this process here in California but overall it could be a much better method than traditional pavement as far as tax payers are concerned. Like the article Amanda mentioned says, most of the time it is much more monetarily beneficial because you don't have to pay to haul the old asphalt away and haul the new asphalt to the job. In California we're only allowed to put 15% recycled asphalt back into new asphalt mix for State jobs so we haul all of the asphalt back to the plant, crush it down, load some of it into the hot plant, send that mix to the job and lay it down again. With the "train" process it does it all in one place and uses 100% of the old asphalt. Also, this new method emits lower emissions and creates lower pollution. At a conventional hot plant you have to use fuel to dry out the aggregates and heat the asphalt binder. You then mix them together at a temperature of usually around 350 degrees so that the mix can make it to the job still hot. This creates a lot of fumes in the air. The train process doesn't heat up the material while mixing it with additives. This creates far less fumes than producing and transporting conventional mix would.

The biggest worry about the cold in-place method is whether you are getting as quality and consistent of a product. It is difficult to assure that you are not picking up base rock with the asphalt from the old road until it is too late. Many roads are laid in parts at different times as they need to be replaced so you could also be grinding a road that has different types of asphalt and knowing to adjust your equipment accordingly is extremely difficult and almost non-existent. In addition, the train may be milling a road that only has 2" of existing pavement but they are supposed to lay down 4" in its place. This may not be an issue if there have been an adequate number of cores taken. If the operator knows where the pavement is thinner than others he can make adjustments to how he is paving. In an instance where there is not enough pavement to recycle, windrows of RAP brought in from outside sources can be laid down and picked up by the machine to subsidize it. There has also been discussion that too much aggregate material is lost due to weathering over time and to make a similar product to that of the conventional mix you would have to add in the fine material that is lost over time due to water and traffic. Honestly though, I'm a strong believer that if it's been tested and proven in places all over the world then it's probably a good process.

It should also be noted that this process should only be used to recycled distressed PAVEMENT. It will not fix existing problems with the base or subbase and this process has a higher risk of failing if there is a soft subgrade.

I know they're using this method a lot in mountain areas and a lot of states up north because it is sometimes really hard to get material to and from a job site which could be hours from an asphalt plant. In addition, the process is completed so quickly that you only need to close down the lane for a few hours, so mountain roads with only two lanes don't have as much traffic build up. California has already seen a few big experimental jobs with this technology up and down the state and there are many people that say that this is the future of paving in our state so keep your eyes open!


  1. Good article Toni, very informative. All of the recent CIR projects in California require an "engineered approach". Every project has cores taken from project site of the existing asphalt, sent to a independent lab where a mix design is conducted. Because of this "engineered approach" along with the Just In Time Training (JITT) almost all of the projects have been a success. Many, many more agencies through out the State are getting on board. With cost savings 40% to 50% less than conventional and with a reduction in Green House Gases by up to 80%, it is a "Win-Win" for all. This is a very "Tax Payer Friendly" solution.

  2. Thanks for the insight James!