Analyze Balanced Mix Design Trial Points Visually with LASTRADA's Performance Space Diagram


July 14th, 2022 05:03 AM / by Dan Ridolfi, PE

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Keeping track of all the variables that affect balanced mix design - aggregate products, aggregate gradation, virgin binder grade, RAP content, rejuvenators, rejuvenator dose rate, and many more - is a difficult task for many mix designers. LASTRADA's performance space diagram (PSD) guides mix designers through an organized process, with a visual tool that allows you to identify whether or not the many variables are balanced. 

In this Leveraging LASTRADA video, we show an example of how LASTRADA’s PSD was used to develop a balanced mix design. Our performance space diagram visually shows mix designers which trial points are balanced.

A demonstration is provided, and analysis can be duplicated using Microsoft Excel and LASTRADA™.

If you're currently having issues with Balanced Mix Design performance on a project and would like some additional assistance, you can request a consultation with one of our engineers.   


After this video, you’ll be able to:
  1. Visually identify which BMD trial points are balanced and which are not
  2. Analyze performance data along with traditional volumetric data
  3. Use LASTRADA's PSD tool to develop a balanced mix design


Developing a balanced mix design includes adjusting a lot of variables, like aggregate products, aggregate gradation, virgin binder content, virgin binder grade, RAP content rejuvenator, rejuvenator dose rate, and a long list of other potential variables. The performance space diagram is a tool to visually identify which trial points are balanced and which are not, guiding the designer to their optimized final result. In this Leveraging LASTRADA video, we will show you an example of how LASTRADA's performance space diagram was used to develop a balanced mix design.

LASTRADA users can visit our help desk to download the template used in this video. Non-LASTRADA users can download an excel version of the same report on our website.

Let's go ahead and open a mix design. I will use this Wisconsin 4LT mix design to demonstrate how a performance space diagram might be used in a mixed design process. Let's next go to the aggregate blend tab. This mix design contains two aggregate trial blends. The first aggregate trial blend is labeled base 0.2, it contains six aggregates, including a mineral filler, RAP and RAZ and an additive we've called RejuveX. The RejuveX is added as 0.2 percent, and if we hit this pencil here it's 0.2 percent as a percentage of the total binder content. Let's look at the second aggregate trial blend. The second aggregate trial blend is named reduce 0.05 percent. It contains the same six aggregate feeds as the first mixed design trial blend. It contains the same RAP and RAZ as the first trial as well, but it looks like the RejuveX has been reduced from 0.2 percent to 0.05 percent.

Let's move to the trial mix tab and look at volumetric data. The specification for this mixed design includes both traditional volumetric measurements, like air voids and VMA, as well as performance measurements. In this case Hamburg Wheel Tracking test, IDEAL CT, and IFIT fracture energy this mixed design is being developed as a balanced mix design. Both trial 2 and trial 1 have Hamburg IDEAL CT and IFIT data, so we need to determine which blends and trial points are in balance. To do that we're going to use a performance-based diagram.

Let's start by looking at the balance between Hamburg Wheel Tracking test results and IDEAL CT index. This test report contains tabular data for both trial blends with it's Hamburg and IDEAL CT data included when I scroll to the bottom of the page we find a performance space diagram and for a mix to be in balance in this diagram it would need to be in the lower right quadrant. That would indicate that the minimum IDEAL CT index is satisfied and that we're not violating the maximum rut depth with the Hamburg Rut tester.

I've zoomed in on this performance space diagram so we can take a closer look at which trial blends and trial mix points are within balance. If we start with trial blend 1, we can see that trial blend 1, trial mix 1 does not satisfy IDEAL CT trial blend 1, trial mix 2 appears to be on the border with IDEAL CT trial blend 1, mix number 3, appears to be on the border with Hamburg and trial blend 1, trial mix 4, appears to be out of specification for the Hamburg Wheel Tracking test. The square we call the design variant or optimum asphalt content for trial blend ,1 also appears to be within balance, if we follow the same data for trial blend 2, we find similar results. The first trial mix is out of specification for IDEAL CT not in balance, the second data point is in balance, the third data point is in this cluster here, that's in balance, the square or the optimal optimum asphalt content is in balance, it's under this cluster as well, and then we find that the fourth trial mix for blend 2, is out of balance, as it also fails the Hamburg Rut test. Trial blend 1, trial mix 3, is a really common occurrence with balanced mix designs. In this case, we see the IDEAL CT minimum has been satisfied but we're very close to the edge of the maximum Hamburg Rut test result and we need to ask ourselves can we maintain this balance, and it's a pretty easy question. We just look down a data point and up a data point to ask ourselves can we maintain the balance and if I look up and to the right to trial blend 1, trial mix 4 were significantly out of spec with the Hamburg rut tracking test. So, the answer is probably not, but let's look at the tabular data to confirm that.

So I'm going to go ahead and scroll up to the tabular results here's the data for trial blend number one. When we look at the Hamburg Wheel Tracking Rut depth for trial mix number three, we find that it's 12 millimeters and the maximum is 12.5 millimeters. When we look at trial mix number four, we see that the Hamburg Wheel Tracking Rut depth has increased all the way to 25 millimeters. Over double the spec and we've only increased a half a percent in binder content. So there's a big sensitivity between rut depth and binder content at this level. Our recommendation, to this customer, was that they start paying attention to their total binder volume in their mixes and that may give them some insight on what is the maximum binder volume that a mix can tolerate before the Hamburg Wheel Tracking tests begin to fail.

Ultimately trial blend 2, with an optimum binder content a 5.8 percent binder was chosen for this balance mix design, and that's in the center of this cluster down here. So the last step in determining whether we can make this mixed design is to go ahead and look at our performance for each of the individual properties that are in each specification and to do that you would use a report that looks something like this and this report is going to give us an idea of what our typical variation is for the properties that we have to maintain during production.

Thank you for watching, for more tips like this one check out our other Leveraging LASTRADA videos at LASTRADA Partners employs registered professional engineers and industry veterans that can help you solve problems such as this one. You can schedule a free consultation with one of our engineers by going to our contact page. Thank you.

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