The usage of reclaimed asphalt pavement (RAP) is more important than ever for the roadbuilding industry. There are two main factors driving its increased importance. The first is the current direction of state and federal policy. The current congress in Washington worked hard to pass new pieces of legislation, the Infrastructure Investment and Jobs Act' (IIJA) which was passed into law in November of 2021, and the more recently passed Inflation Reduction Act (IRA).
These laws, working in tandem, allocate billions in new funds for infrastructure, but they incentivize projects and contractors who incorporate greener and more sustainable options. Bids that utilize, or companies that invest, in ecologically friendly technologies, practices and materials will see the greatest amount of return from these policies.
The other factor elevating RAP's importance is similar to what drove its initial growth in the 1970s era market. At that time it was a national oil crisis and imports embargo that suddenly highlighted how important RAP could be, and now, one could say that it’s a crisis of materials in general. All materials. The critical impacts on the supply chain are well documented and discussed at this point. At all levels of industry and construction, the costs and the availability of vital resources are influencing just about every corner of the post-pandemic market.
According to the Federal Highway Administration, an estimated 45 million tons of RAP are produced annually, though that number is based on incomplete data. From the FHWA website, "It has been estimated that as much as 36 million tons, or 80 to 85 percent of the excess asphalt concrete presently generated, is used either as a portion of recycled hot mix asphalt, in cold mixes, or as aggregate in granular or stabilized base materials. Some of the RAP that is not recycled or used during the same construction season that it is generated is stockpiled and is eventually reused."
Needless to say, the contractors who have the best handle on their RAP will have a high likelihood of seeing greater financial success in the coming years, because it is probable that these trends will continue on the current path, rather than moving in the opposite direction. While there are a number of possible manufacturers that offer RAP solutions for contractors at varying scales, Ammann and their engineers offer a lot to contractors looking to make the most of their operations with the implementation of their high recycling technology (HRT).
Their HRT is a combination of their RAP preparation methods combined with specific control systems, which can achieve extremely high percentages of RAP in an asphalt mix.
Let’s Talk About the Benefits
Maybe you're like me, I'm still fairly green in this industry, still learning a lot every day and with each new conversation I have with knowledgeable experts. Maybe you know a little bit about RAP, but it isn't a huge focal point for your business or your operation. Great! The next paragraphs are for you and me because I knew that RAP was beneficial, but I didn't have a clear understanding how it was directly affecting the bottom line.
If, however, you're not like me and you already know this stuff like the back of your hand, skip down to the next header, where we start digging into the ways to improve your RAP process to get the most out of it. That is going to be where you might find some new information to help you out. If you're still with me, let's take a look.
Reduced Resource Consumption
Easily the most obvious benefit to the contractor incorporating more RAP into their mix, is the reduced need for fresh or virgin liquid binder (bitumen) and new aggregates. Plain and simple, being able to reuse the removed pieces of road is going to reduce the costs on your bottom line.
Speaking with Carlos Machado, Business Development Manager for Ammann, he said, "It starts with a cost saving for the customer, to address material shortage or continue operating with some price peaks in the needed materials to produce asphalt. However, it is also becoming a point of how to handle environmental solutions in the asphalt industry."
Why does it become a matter of handling environmental solutions? The answer is in the outcomes. If you want to get out of your RAP, you have to put more careful and specific work into it. Proper mix gradation, avoiding the damage to bitumen in the recycling process, improving RAP quality screening, sorting and storage, these are all factors that play a part in maximizing the reintroduction of used materials into new mixes.
To get the highest cost savings, you are going to need to examine every part of your process:
- Removal from road
- Careful Sourcing
- Sorting / Screening
- Effective Receiving Inspection
- Initial Type Testing
- Mix Process
To skip over and neglect any one of these steps, will negatively affect the end result. Each one of them has an impact on the others, for instance: If you don't properly screen your RAP, the ability to incorporate and control your final mix effectively will be reduced. Likewise, if you analyze your aggregates properly, but your asphalt plant can't control the recycling process well enough, the mix quality will suffer.
Machado said, "The requirements for high rates of RAP are not only dependent on the asphalt plant itself. "It is all about a combination of state-of-the-art machinery, with handling correctly the preparation processes. Machado continued, "With higher use of RAP percentages, the Contractors must have a much higher control of the RAP they reclaim and process. " Let's look at what Ammann generally recommends when it comes to this higher level of control.
High Grade Aggregate
The very first step towards a better RAP percentage, and a higher rate of recycling is the removal process. Carlos Machado explained that an important of this step is, "Never mix the top layer with the bottom layers of your road, because in each layer, you have different types of aggregates." For many years RAP was handled in such a way, that would lead realistically only to a Down-Cycle, meaning re-use of a material for an inferior purpose (like stocked in piles with no direct use or used in landfills, for example).
At Ammann we search ways of achieving a True Recycling use, which is when a reclaimed material is reused for the original purpose – use back into the new mix. That's part of what makes this different, because undefined RAP can have uses inside the production chain, but not at the higher level usage in the asphalt plants.
Once the road has been removed in layers, and is transported in trucks to the plant for processing, the next step in the process is to properly screen the RAP into a number of piles (ideally 2 to 3 sizes of RAP material), and, as Machado puts it, "the contractor must know as much as possible their RAP, including the gradation of the material, knowing the filler and bitumen content, and which type of bitumen is present in the RAP to select the right complementary additives. When you really know these aspects of the RAP, combined with the Ammann High Recycling Technology, then you are one step ahead to reach high levels of RAP usage and save asphalt production costs."
I'm sure everyone has seen vague piles of RAP sitting out, exposed to the environment elements, unprotected and for who knows how long. This can be one of the easiest places where contractor's experience a drop in aggregate quality. In addition to not allowing the materials to get mixed together, properly covering the RAP Stockpiles is an effective way to reduce moisture. Ammann supports the customers on finding better storage solutions with their on-site asphalt process engineers.
The Right Mix Method
Some like it hot...
One of the real challenges with RAP is the heating of the materials. In order for the RAP to be re-used, it has to be warmed up, but the speed at which that happens makes all the difference.
Adding recycling in a single drum, where the RAP is directly heated and mixed with virgin aggregates, can only reach limited levels of RAP percentage in the new mix. In this situation, it is common that the heating process is too quick and the quality of the bitumen together with its properties is permanently damaged through oxidation. Also, the bitumen becomes sticky and hard to handle inside a common dryer.
Warm recycling, in a dedicated RAP drum, can be a more effective way to get the RAP up to temperature gradually. But what about the higher levels and how does Ammann work with its customers to help them get there? According to Machado, "Ammann offers 4 ways to add RAP in the mix, which can be combined in different forms in both batch and continuous plants."
These are the following specs and methods they achieve with the HRT:
- Up to 30% RAP: Cold recycled material is added direct in the twin-shaft mixer. Each core component does its function with maximum efficiency. No RAP in dryer ensures less maintenance and prevents sticking, while the external mixer ensures the proper coating and dwell time.
- Up to 40% RAP: Cold recycled added in the middle collar up to 40% with possibility to further percentage added directly in the mixer. The special inner dryer parts ensure high temperature transfer to RAP and prevents sticking with correct flow of material. Fresh additional bitumen is added only in the twin-shaft mixer to ensure proper new HMA/WMA coating.
- Up to 60% RAP: RAP is warmed in a dedicated Dryer which ensure smooth transfer of temperature to RAP - target is to have a smooth increase of temperature to avoid bitumen properties losses.
- Up to 100% RAP: RAP is warmed in a dedicated Dryer which ensures the RAP reaches the final needed temperature for a Hot Mix Asphalt. In this solution, there is no need for secondary heat source, like overheating aggregates. The RAH100 eliminates that concern. It consists of two connected sections. One is a hot gas generator, and the other is a counterflow dryer. Clients can choose the RAP percentage they want to run their plant, either 70%, 80%, or 90%. It will depend on job needs and authorization from their customers – Authorities, DOTs, etc.
The Upper Limit
Another benefit to the Ammann technologies is that their engineers understand that not every contractor is looking for the same thing. You may not be interested or ready for a process that produces near 100% RAP mixtures, maybe you need variety and flexibility. Ammann's HRT systems can be retrofitted and adapted onto standard type plants. If and when that time comes, Ammann says that it is committed to customer support, and offers training and education for operators to get the most use out of their plants and their as1 Control Systems.
These systems include a dynamic RAP addition control where the operator can continuously change the RAP Ratio during the mix process with a slider, and the PIP system that allows operators and equipment managers to have plant information and performance topics directly sent to their smart mobile device with updated information on production, energy consumption, fuel consumption, RAP usage, and more.
However, what is the actual applicable reality of 100% or near to 100% RAP mixtures that uses very limited amounts of virgin aggregates, additives and fresh bitumen? Machado said, "This technology has been evolving, and it currently allows us to go up very close to the 100%. It all depends on the customer needs, the norms they must follow and their preparation with support of our equipment. We have several cases of High Recycling Technology applied in the field."
Not surprisingly, it has more to do with meeting the specific needs and tolerances of every job, treating them on a case-by-case basis. "The 100% RAP mix is theoretically possible. But the customer's mix will always have a certain tolerance and some proportion of fresh material will be required to adjust into the limits. The plant operators will likely need to add some fresh components to compensate and be within their tolerance, but the technology exists to produce at high RAP addition rates and if handled in the proper way, the contractors can get the most out of their recycled materials".