In part 1 of this series, I underscored flaws in the way that our industry considers RAP. Flawed ideas have translated to decades of flawed specifications, flawed practices, and flawed roadways. Examples from the US to Taiwan were used to illustrate the path that we’ve been on and where it inevitably leads. So, maybe we’ve been doing it the wrong way. Okay. Then, what is the right way? Do we have any idea? Not only do we already understand how to improve RAP performance, we actually possess the blueprint for how to revolutionize RAP performance. You may have luck locating a copy of this blueprint under a pile of dust where it has apparently gone unnoticed for years. In the meantime, I’m happy to give my perspective on its contents.
The Proven RAP Blueprint: Japan’s Common-Sense Solution
Kanto Region, Japan, 2014 – A delegation of US asphalt industry leaders arrived in the Land of the Sun’s Origin with the goal of uncovering secrets of how the Japanese have become so successful at building very high-quality asphalt pavements while using lots of RAP.
Representatives included the Director of the National Center for Asphalt Technology (NCAT), Executive Management at the National Asphalt Pavement Association (NAPA), Chairman of the State Asphalt Pavement Associations (SAPA), State D.O.T. Officials and NAPA Associate Member Companies. The full NAPA report detailing this experience and key take-aways can be found here (minus the dust). Also, an overview of the report presented at the Southeastern Asphalt User-Producer Group (SEAUPG) annual meeting in November 2015 can be found here.
Image source: NAPA High RAP Asphalt Pavements report
Some very interesting points from the report include the fact that Japan averages 47% RAP consumption and as high as 73% in Kanagawa Prefecture compared to the US average of only 20%. Measured pavement performance data in Japan also indicates that 97.7 percent of RAP sections are meeting serviceability requirements (cracking ratios below 10%); whereas, only 30% of all US roadways are in good condition, according to the American Society of Civil Engineers (ASCE) report card, 2017. That’s not the extent of the ASCE report:
One out of every five miles of [US] highway pavement is in poor condition and our roads have a significant and increasing backlog of rehabilitation needs.
Not only is RAP usage relatively low in the US compared to Japan, but as highlighted in the first part of this series, numerous reports have been issued in the US indicating that premature pavement failures have been linked to prior attempted increases in the usage of reclaimed materials. So, we have previously tried to increase RAP % but have failed. In Japan, high RAP mixture performance is considered equivalent to virgin mixtures (Moden, 2014) and the data supports it. It is true that Japan has lower traffic loading compared to the US, but pavement engineers are fully capable of designing pavements to account for the higher axle loads.
Image source: NAPA High RAP Asphalt Pavements report
Europe Delivers Longevity under Extreme Traffic Conditions
European engineers have certainly had no problem handling the heavy traffic issue as pointed out in this 2016 article: Why are America’s Roads so much worse than Europe’s?
The article states that European autobahns carry “more traffic” and “considerably heavier truck weights” yet are “smoother” and “far sturdier” than American highways. European highways are designed and constructed to last 40 years. It isn’t an issue of traffic intensity but an issue of targeting longevity, including materials and specifications capable of delivering it.
All of this is achievable in the US, of course, even while using high percentages of RAP. It will not be accomplished, though, by using the same techniques that put us in this mess.
Now, back to Japan – let’s review…..
Four decades ago, RAP usage was becoming common practice in both the US and Japan. Over this period, what specifically led each country to such distinctly different outcomes relative to RAP usage and performance? Those who have demonstrated long-term success using high % RAP mixtures understand that solutions to three key problems must exist to optimize RAP usage. These fundamental keys are clearly present in Japan’s high-quality, high RAP mixtures. These keys, however, are either missing entirely from the US market or only apply in certain and even rare cases. The three problems follow:
1) The Low-Quality Binder Problem
This one is listed as #1 for a reason. Let’s not fool ourselves. The quality of RAP binder is awful according to paving-grade asphalt standards or any standard, really.
Japan treats RAP binder initially as a waste product, which it is. Japan requires that this low-quality waste binder be upgraded to a minimum asphalt binder quality standard using high-quality proprietary “rejuvenators” prior to introducing the waste binder into new paving mixtures. Makes perfect sense, right? The US does this also, right?
Well, unfortunately, in the US there is no such requirement to recover and test poor-quality RAP binder, much less upgrade it to a minimum standard. In fact, the variability in the quality of RAP binder from one stockpile to another (and possibly within the same stockpile) is considered an unknown variable in the US, yet it is still approved to replace an average of 20% higher-quality virgin paving grade binder in every mixture. Astounding!
Here is an example of a superior regenerative RAP binder additive commercially available in the US that can yield high percentage RAP mixtures containing binder that performs comparably to average PG-graded virgin binder. The best part is that by using regenerative (ReGen™) technology, the final high percentage RAP mixture is higher quality and lower cost than untreated 20% RAP mixtures, which is the baseline mixture in the US.
Remember, we are way behind. Japan is already utilizing lower cost, higher performing [high percentage RAP] mixtures because they recognized and solved the low-quality binder problem long ago!
2) The Energy (Heat) Problem
Japan is also diligent about stockpile moisture control and even pre-heating RAP to drive off excess moisture and condition the binder for “rejuvenation” (as highlighted in problem #1). Since high-RAP mixtures contain fewer pre-heated virgin aggregates, the heat energy necessary to activate RAP binder must come from elsewhere. Reducing moisture in the RAP stockpile, pre-heating RAP (more common in batch plants), super-heating virgin aggregates, and treating RAP binder with superior additives (as stated in problem #1), are all possible solutions or solution-combinations to this energy problem. The US has no requirements to reduce moisture in RAP stockpiles or to pre-heat the RAP. These variables, therefore, may lead to deficiencies in the energy needed to properly activate binder in high RAP mixtures. Although alternate solutions to the heat problem are possible, we should recognize that it is a problem with solutions available and should not be the governing factor limiting RAP percentage usage.
3) The Dust Problem
Japan also fractionates RAP and controls dust very well. Japan even limits dust (P200) in the RAP, which is known to have higher dust percentage. Although most US states require similar dust control in the final mixture, it is not uncommon for mix producers to cite excessive dust percentage as a limiting factor for using higher RAP content. Similar to problem #2 above, this variable should not play a restrictive role in how much RAP can be used. There are proven methods for overcoming dust contributed by RAP, including proper fractionation, mechanical equipment additions, and other processes that are known in the art to remove excess dust from RAP.
In the next installment of this blog series on RAP, we’ll dig deeper into the differences between the bid environment in Japan and the US and lay out specific tactics that will lead our industry in the right direction.