AASHTO re:source Q&A Podcast Transcript

Season 4, Episode 34: Common Findings in Aggregate Testing - Part 1

Recorded:  January 16, 2024

Released:  January 23, 2024

Hosts: Brian Johnson, AASHTO Accreditation Program Director; Kim Swanson, Communications Manager, AASHTO re:source 

Note: Please reference AASHTO re:source and AASHTO Accreditation Program policies and procedures online for official guidance on this, and other topics. 

Transcription is auto-generated. 

[Theme music fades in.] 

00:00:02 ANNOUNCER: Welcome to AASHTO resource Q & A. We're taking time to discuss construction materials testing and inspection with people in the know.  From exploring testing problems and solutions to laboratory best practices and quality management, we're covering topics important to you. Now here’s our host, Brian Johnson.

00:00:21 BRIAN: Welcome to AASHTO resource. Q&A I am Brian Johnson.

00:00:25 KIM: And I'm Kim Swanson. And we have another one of these fun episodes where I am going to get. Test the common nonconformity test method and I'll have no clue what I'm talking about. So the guests are going to be awesome and then Brian's going to actually tell you what the real common nonconformities are. So I'm excited about this. Are you excited, Brian?

00:00:45 BRIAN: I am it. It's always a wild ride for me going over these with you to see if you can guess any of them. Today we are going to cover aggregate tests and I I think your chances are pretty good for the first round here because we're going to talk about some common issues related to equipment that is used to. I will say prepare and test aggregate specimens. We are just going to cover the four most common aggregate tests that are also required in ASTM C1077. Those are the aggregate wash which is C 117, that's ASTM C117 and AASHTO T  11. The graduation. Which is ASTM C136 ash to T27 fine aggregate specific gravity which is ASTM C128 and AASHTOE T-84 and coarse aggregate specific gravity which is C127 and ASTM and T-85. In AASHTO.

00:01:47 BRIAN: So now that Kim is just dazzled by the listing of those specifications.

00:01:55 KIM: I know I have to kind of like prop my eyes open again. I was I may have glossed over while you were listing all those out, so I am really optimistic about the awesomeness.

00:01:55 BRIAN: And standards.

00:02:05 KIM: That my guess is going to be right now.

00:02:07 BRIAN: All right, we'll get into it, then we'll wake you up, back up. And it's time to talk about the equipment. There are two items that I'm going to cover that are the most common issues related to aggregate testing. And there is one for the bonus. Question that everyone thinks is a problem but is not.

00:02:28 KIM: OK. And you're talking about just the equipment for all the tests that you listed?

00:02:31 BRIAN: I'm talking about. Yeah, the equipment for aggregate tests.

00:02:33 KIM: That I didn't pay attention to.

00:02:35 BRIAN: Yeah. So just think of basic aggregate things that you would do with those.

00:02:37 KIM: I OK? Yes. Well, can I take an easy vague answer if something with calibration intervals? Are not met with this.

00:02:45 BRIAN: Ohh no no. I'm talking about specific items. You don't. You have to say what's wrong. Just name the equipment, type the the name of the.

00:02:47 KIM: Actual things are run. Oh. Something with the balance being wrong.

00:02:58 BRIAN: Yes, there are all sorts of issues with the balances which I didn't think was going to be very common, but it was more common than I expected. That is related to the capacity of the balance, the readability of the balance may not be what it should be for that particular test. The accuracy, so some. Someone checked the accuracy of the balance and found that it was not in line with the requirements of the standard and sensitivity. So sensitivity. The If you make a an incremental change in the the load on the balance will it register properly or will it register at all? Sometimes it won't because it's not sensitive enough, so those were some issues balances now those were not like super common findings, but they were. There was a notable. That I did not expect to see.

00:03:51 KIM: OK, if your laboratories experience an issue with balances during it, is it just like recalibration or get the right one or is it like an easy fix?

00:04:00 BRIAN: Yeah, all of that. I mean, if it's capacity you have to have the right balance, right? So I I think what what probably was going on in some of these cases is that either somebody moved the balance or a balance broke or they prepared a sample for demonstration purposes that was larger than what they normally do. And then it screwed. Them up so the the capacity one is kind of a little perplexing to me because I would think that you would know what you are testing beforehand and and make sure that it's large enough to accommodate the equipment. But it's possible that they just don't run that test normally. And and and these are these are. Two of them are very common. The washing graduation are extremely common, but I think sometimes people are not performing this. Specific gravity test. And maybe when they were asked to do it, they were kind of scrambling to figure out how they're going to do it with the equipment that they have. In their laboratory.

00:04:57 KIM: OK. So the net give you said there's two. More equipment ones.

00:05:01 BRIAN: There's another one I'd like you to guess. And then I and then and then I had the one where people often think that this is a problem, but looking at the data, I did not find this to be as.

00:05:03 KIM: OK. All right.

00:05:11 BRIAN: Big a problem as people thought.

00:05:13 KIM: OK, I'm going to say something with sitting, some sitting kind of thing.

00:05:17 BRIAN: You would be correct. Yeah, the sitting apparatus. So that. Yeah, that's that's great. So it's the.

00:05:21 KIM: I look at this. 2 for two on aggregate.

00:05:24 BRIAN: Baker so often there's a bad condition of the shaker. This could be, I think, the most common issue with the shaker was the timer. So they have these kind of dial timers that are not very precise. And the the big issue is either it's broken or it's like completely not working or. The laboratory may think that it's set for a certain time, but it might not actually be the time that they think so. One example would be. We always set our time our shaker for 10 minutes thinking it's going to be 10 minutes. But when the assessors there and they time the actual shaking, it was only 7 minutes. So there are all sorts of variation of that, so why? Why that matters is if they are trying to compare with another laboratory and they say, OK, you know, we get really consistent results at this time. And they say, OK, great. And then they do it for the same thing. They could be totally different. But for general use, as long as they're checking the sufficiency of the shaker at that time and they find it to be sufficient. Per the standard requirements then it, it probably doesn't matter that it wasn't the exact time that they thought.

00:06:37 KIM: Then they have to then document somewhere that we know that the 10 minute mark is not actually 10 minutes but 7 minutes. But it is sufficient because of XY and Z like they. Trail of that they know that's happening and that's OK.

00:06:54 BRIAN: And it it's it's funny that you should mention that because that is the that is the main issue is the lack of knowledge of that discrepancy. So it's fine if they know it and they say, hey, this is what it is, but you're going to see that it's off by this much. And as long as they know it and that everything else is right, that's OK. If they don't know. It it could become a problem.

00:07:18 KIM: That makes sense.

00:07:19 BRIAN: OK, so now the the third question about equipment is what is the most common? This is the most common piece of equipment that laboratories think they need to replace. When they get. A low proficiency sample result, but they don't typically need to replace it.

00:07:38 KIM: Something with the oven. Timers and element thermometer.

00:07:44 BRIAN: No, no, but the oven timer. What oven? Timer thermometer.

00:07:52 KIM: I don't know. Something, something in the thing, I don't know.

00:07:55 BRIAN: No, it was really. It is also related to sieving. It is the sieves themselves.

00:08:00 KIM: Alright, well I thought that was incorporated in it, so I'm going to. I mean, I didn't get it, but I'm still going to say.

00:08:01 BRIAN: Sorry, I no. I think he may that may be in unfair the way I asked that question and confusing. But the IT is said, So what? What happens most commonly when somebody gets a low rating on a graduation is the first thing the laboratory thinks that they need to do. The laboratory manager is replace the sieves. And that often does not solve the problem. And when I looked at the data for all the common findings related to ASTM C136 and AASHTO T 27. The condition of the sieves was not a very common issue. It's not to say that it doesn't happen, especially for the 200. But it is not that common to find sieves that are out of spec during an assessment. Now this was. Actually, we we did have a meeting not long ago with one of the DOT's where we were going over this very issue and there was there was an argument about the.

00:09:05 BRIAN: Right. And this was not database. This was like based on recollection of of people in the room saying, well, my my recollection is that it's often this. Because and I'm saying, well, that may be recollection, but when I pulled the data, it didn't really support that. So I think they may be just because everybody jumps to that and thinks that that's what the issue is, is the bad sieve, but it's usually something they've done that wasn't correct. So it could and. It might not have. Anything to do with the test itself, it might be. Something weird they did with the sample before they tested it, or it might have something to do with the way they calculated the results, or it may have some. I mean, there's all sorts of things that can happen between when you get that box and when you enter the results. They could go wrong. So you really have to look at everything.

00:09:55 KIM: I can definitely see the desire to bloom it on the sieves. I can. Relate to that be like? Yeah, it's clearly the sieves and not the fact that I did something, or that my technician did something so I can I can relate to it. Not wanting to be human error, but also understand that it's likely. Human error.

00:10:15 BRIAN: Yeah, it's likely human error, and I find that that's that's generally the case most of the time in life. Right. It's like this thing isn't working and then you start looking into it. You're like, oh, that was that. That was my fault.

00:10:28 KIM: So many times, I'll e-mail our IT guy about something and then later be like operator error. My bad. Anyway that was equipment I did we cover on the.

00:10:38 BRIAN: That was just equipment. We didn't even get into the test, but I separated that out so we don't cover it on every single test.

00:10:43 KIM: Good. OK.

00:10:44 BRIAN: Ovens. I did not put on the list, but that did come up from time to time that ovens were set at the wrong temperature. But most of the time they were OK. The the the ovens in those tests are set at 2:30 Fahrenheit or 110 Celsius and those are really common temperatures and in oven for drying. So so usually the labs will have those dialed in pretty well. So let's get into the test. We'll we'll start with the wash. Is AASHTO T 11 and ASTM C117 so in this test method you're taking your. Aggregate put in a bowl. Wash it with water.  Usually a spoon and then you pour the wash water through a nested set of sieves and you collect whatever falls on the 200 sieve, which is the bottom sieve, and then you rinse it back into your sample. You dry it in the oven and then you use it for the graduation and you figure out how much wash is through that.

00:11:46 KIM: OK.

00:11:48 BRIAN: 200 screen.  All right, that's the test. So here's what goes wrong.

00:11:52 KIM: All right.  OK. No, I want to guess I.  Get a guess.

00:11:56 BRIAN: You you get, you get. OK. I'll let you have a guess.

00:11:57 KIM: I get one get I get one guess of the most common thing is that people wash for too long. They don't follow the standard timing of it too long or too short. I'll cover my bases.

00:12:00 BRIAN: All right.  OK.  I'm going to give you partial credit for that because there is there is a. A an element of that in here. So the this has to do with the automatic washing machine. So there are automatic washing machines that people will use and what you're supposed to do is you're if you're going to use that, you're supposed to compare the results.

00:12:20 KIM: OK, OK.

00:12:38 BRIAN: Of the automatic washing machine to manual to make sure that you don't overdo it or under do it. I think overdoing it is a bigger risk on the automatic washing machine because then you have.  Like a rock tumbler, basically, where you're changing the result of, you know, changing the result of the future graduation that you perform potentially. If you've got soft material, especially so you don't, you don't wash it too.  Much so yes. That is correct. That is one of the items that we were going to. So I'll give you more than partial credit, that's full credit for that because that is a finding. So you're on A roll. So I'm going to.

00:13:09 KIM: OK.  Right. OK.

00:13:13 BRIAN: Say go ahead and take another shot. Of this?.

00:13:15 KIM: Ohh OK, so another common one for that test would be something with collecting the. No, I don't know the collecting of like the material or. Like you don't get. It all or something like that.

00:13:31 BRIAN: That's right. So one of the findings is after the material in the says was returned to the sample container, the excess water was not decanted through the number 200 sieve to avoid loss of material. So they go through all this effort and then they rinse the material back in front that was collected on the bottom sieve, they rinse it back into the bowl and then what you're supposed to do. That point just put it in the oven. Dry it out. So what? Sometimes people will do is they'll say I don't want to wait that long. I'm going to pour the excess water back out into the sink. It's like, well, you just did. You just saved it from to it from going down the drain. And so you don't want to put it back down the drain. So yeah, that's they try to carefully do that and like visually, make sure that no aggregates have have gone in there, which you know for a matter of practicality, they're probably could do that like fairly efficiently. But I I mean it's fast but. [KIM: OK] It's not necessarily. Accurate. So you don't you don't really want to do that.

00:14:33 BRIAN: OK. All right. So that's good. I'll go through the rest of them. So you know I think you I feel pretty confident that you could do.  Well, on this game though.

00:14:39 KIM: I I'm gonna say I've run out like those are my two ideas that I had for for T11 and C-17 or 1:17. So I have no other guesses, so I'm glad you're just going to say the answers.

00:14:53 BRIAN: Next one is about the protective sieve that was used. So you've got a 206 and then on top of it you're supposed to have a #16. And it can also be a #8 for ash though, but either people don't use one at all.

00:15:06 KIM: OK.

00:15:07 BRIAN: Or they use the wrong one, so they might not use any but, but that's not that. That's just for protecting the 200 so. So that's not a very critical issue. Yeah, you don't want like a piece of half inch aggregate falling on there and puncturing your two hundreds of because it's two hundreds, aren't that? Yeah.

00:15:13 KIM: Just so nothing like call. Then you would need to. Then replace the sieve. See.

00:15:25 BRIAN: That's right. And if you've got a 200 set with puncture holes in it because that mean it already has holes in it, right? Because it's a sieve. But if it's got the wrong size holes in it, which it would.  Have if you had puncture hole. Those then all of a sudden you've got the wrong test result because you've got larger aggregate passing through that number 200. So that's why that matters. Next, the Washington procedure was not performed by agitating the specimen in a container of water and decanting the wash water over the nest of sieves. They just took the aggregate and dumped it right on top and washed it. That is a very common finding.

00:15:59 KIM: So wait, I'm confused. What happens there? Can you explain that again?

00:16:02 BRIAN: So they've dumped instead of, so you you wash it in a bowl and you rinse the wash water. Maybe. I didn't explain this correctly. What? Rinse, rinse the wash water through the nested sieves.

00:16:12 KIM: OK.

00:16:13 BRIAN: Not dumping the aggregate on top. So yeah, I think I could have explained that better in.  The beginning so.

00:16:18 KIM: Oh, I would have totally gotten that if you explained it in the beginning, I would have definitely gotten it if I understood it fully for sure.

00:16:25 BRIAN: Right. So yeah, you're you're just, you're just putting the water through it. And and sure, some pieces are going to float into the screens, but you don't just dump the aggregate on top of.

00:16:36 KIM: OK.

00:16:37 BRIAN: That's a different test, but for for this one you just put the water through it.

00:16:41 KIM: OK. That is it for Astro T11 and ASTM C117, what is our next test or procedure?

00:16:53 BRIAN: Alright, next one. So we take it from the wash and we go to. The graduation so that that. We're gonna follow our specimen.  Out of the oven, so it went in the oven. It dried out and we take it out of the oven and we let it come to room temperature and then we put it in a nest of sieves and then into our sieve shaker, which we already talked about having potential issues once it comes out of there, you weigh each.

00:17:01 KIM: I like it.

00:17:21 BRIAN: Incremental amount of material and you write it down and you figure out what your percentage passing or retained is depending on what you're trying to do for each one. And you also check to see that you didn't lose material in the process so that that what went in should come out.

00:17:40 KIM: OK. Yeah.

00:17:41 BRIAN: Right. Theoretically yes. Now. Now what happens sometimes, and you no one's going to just know that this happens. But sometimes what happens is people will not realize that they didn't do a great job cleaning their sieves. Or you might have really angular material. They clogged some of the screens at the end, so you actually. It would come out with more than went in.  Even though you're not creating matter, you could have stuff that was left over that that then comes out because you did such a great job cleaning the screens this time. That you did not do the previous time or the other technician didn't do as well as you do when cleaning it out. So that's why when I said it should be the same going in and out. Sometimes it's more, sometimes it's less. It has to be within a certain amount though. Certain percentage of what went in to be a legitimate test result.

00:18:20 KIM: Yes, yes.  But so for that, if you get more.  Yeah, and it's just wrong automatically, but you get a little bit less. There's a wiggle room or is it the wiggle room plus or?  Minus or is. It the just minus.

00:18:47 BRIAN: There is wiggle room either way.

00:18:50 KIM: OK, I don't like that, but OK, I mean. I don't have no. I have no say of it. I don't love the idea of that, but OK, it does not.

00:18:54 BRIAN: It's not great. It doesn't give you confidence, does it?

00:18:58 KIM: I don't like the little room, but I mean.

00:18:59 BRIAN: No, it doesn't. It and it it. It gives you no confidence on the last result as well.

00:19:05 KIM: All right, well, good times there.

00:19:08 BRIAN: On that. OK, so I think I may have given out too many hints there of something that could go wrong, but I I wanted to make sure I explained why that it was possible to get more than went in.

00:19:12 KIM: You might have. Uh, huh.  So I'm going to say that's probably a common. It's a common finding is that the weight of the material is out of town. It's like.

00:19:27 BRIAN: It is, it is so it. It has to be within .3% of the original dry specimen. When you add everything up and if it's not, then it's not valid. So that happens quite a bit in these demonstrations. And I was, I I didn't look at the at every single result to see like what the worst was.

00:19:33 KIM: OK.

00:19:50 BRIAN: Because I figured there was.  Probably one that was just. Totally out of control and there probably was, but I didn't see anything too outlandish when I was scanning through there.

00:20:01 KIM: OK.

00:20:02 BRIAN: But that is certainly an issue. Anything else you think might have gone wrong.

00:20:06 KIM: I think. You kind of mentioned like a big. No, that's not it. I got nothing. I got nothing else.

00:20:16 BRIAN: I think the odds of you picking some of these without knowing the standards would be very difficult. So so I'll tell you one thing that. Goes wrong. Oh, go ahead.

00:20:23 KIM: No, I had an idea. Like I will say someone does something out of order. Like maybe is that a common finding that they missed steps?

00:20:29 BRIAN: That is not a a common finding for this.

00:20:32 KIM: That is not something that can happen.

00:20:33 BRIAN: I think that would.  Be physically difficult to do something out of order. On this OK again.

00:20:37 KIM: I've never seen this test run, so I'm just going off of your explanation in the.  Knowledge I had coming into this, which was very, very miniscule.

00:20:47 BRIAN: Yeah. OK. So I'm going to run through this really quickly. It's not there's this is not too complicated, but without knowing the tests, you wouldn't know. So #1 total passing 200 didn't include the amount washing that lost during wash. So like, if you looking at the the total mass starting at the original dry mass before washing, you'd want to factor in anything that was lost in the wall.

00:20:49 KIM: OK.

00:21:09 BRIAN: As passing the 200 screen so 200 screen is going to be the bottom of your set analysis in the in this example. So you'd want to take the what's in the pan at the end and add the amount lost in the wash to that to get your total -200 material next there. Are issues with setting sufficiency, so I talked about the Shakers, so one way to make sure that your shaker is working properly is you perform a one minute hand sieve. You don't have to do this during every test. This is something you do periodically, so you you you take that stack and you go through each one you take out, you put it, if it's not already an 8 inch diameter screen or so you.

00:21:54 BRIAN: Would put it. In an 8 inch diameter sieve and you would rotate it and tap it with your hand like rotate. They rotate, tap, tap, tap, tap and then you would weigh what came out and four AASHTO. It has to be no more than what 1/2 percent of the total mass.  And then it's OK. But for ASTM, it's no more than 1% of the mass retained on that sieve. During the one minute handshake. So it's slightly different requirements, which is not great. I wish it was the same but it gives you an indication of how well your your sub shaker is working at that time. That's how you set your time, by the way. So back to that timer issue. If my timer says 10 minutes. And I've determined that on all of my screens this past. And and I may be satisfied with that, right.

00:22:49 BRIAN: As long as it is, I know what that time is, so even if it's seven minutes, 8 minutes, 10 minutes, whatever it is, as long as I figure out what that time is and I know that it passes. But it what? What can happen on some of these mechanical shakers is you might find, and this people make this mistake sometimes where they. Say I don't really want to do that. I don't. I don't really want to take the time to to check specific sufficiency for the whole stack, so I'm just going to pick one screen in the middle.  Well, that's not great if it's doing a really bad job at the bottom and the top, which some shakers do and sometimes even the ones that perform pretty well, they have equipment malfunctions where they have the there's this one common one that has paddles in it and it kind of like wax it on the side. And if there's something that has gone wrong with the shaker, and that paddle is not functioning, it's not going to do as well on that screen. So that's a good way. You can't see inside the shaker. So if you check your setting sufficiency, that may give you an idea of whether it passed or not. So that the issue that that is caught during the assessments.

00:23:57 BRIAN: So our assessor will do this check and it will fail so that that tells them that it was not done properly, or maybe something has changed from when they did it to to that point in time. But anyway, it's a good I I think it's a helpful finding for people to say, OK, I need to redo this. Yes, but don't argue with the assessor that you only need to do one set, because that's not going to work for you. Oh, another thing is overloading the sieve, so sometimes, especially on the 8 inch sieves, that's not a lot of sitting area for a lot of material. So if you have more than I think it's like 194g. It's close to 200 grams retain on that screen. It's overloaded and what you would need to do is you need to split that out and run twice or however many times you need to to get the appropriate amount on that. So so that you get a good analysis. Last is reporting there's some reporting issues that. Come up. So one of them is that if the material has or if your specimen has less than 10% retain on the 200 screen, you have to report your passing 200 to the nearest .1%.

00:25:13 BRIAN: And sometimes people won't do that, so they'll report everything to 1%. But if it has a smaller than 10% amount, then they have to go to the nearest point. Percent and then some of them just didn't even report the passing 200 at all. And that's probably just whatever their spec.

00:25:28 KIM: What? What did you see? Is, yeah, or would it be just? They didn't, not nothing past. So it's zero, or is that known? For the case I.

00:25:36 BRIAN: Don't know if that's it. Seems like there's always something OK in there, so I'd be surprised if somebody. To find that nothing was unless it was like a known graduation, like if there was a stockpile of everything is the same. Size and the only thing that comes I guess even then you probably have some dust fall out like just from the abrasion. But yeah, I I don't know. I don't know. If that's possible or not, so I.  Well, I don't.

00:25:58 KIM: Mean that's it. Ohh, OK. Those are that was. The gradation test.

00:26:03 BRIAN: That was a g gradation.

00:26:04 KIM: OK, I think this is a good place to stop. I want to save our listeners from having to listen to an hour-long episode, so we're going to break up the common aggregate findings into two episodes. So next time we're going to talk about the remaining of. This, but for now the actual resource technical exchange it is coming up in March. It'll be in Boston, MA. So the 2024 AASHTO Resource Technical Exchange, March 18th through the 21st in Boston, MA, go over to asharesource.org/events For more information.

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00:26:42 ANNOUNCER: Thanks for listening to AASHTO re: source Q & A. If you'd like to be a guest or just submit a question, send us an email at podcast@aashtoresource.org or call Brian at 240-436-4820. For other news and related content, check out AASHTO re:source's social media accounts or go to aashtoresource.org.