I’ve often wondered what happened to the concrete that is washed out of the mixing trucks and other equipment used in laying concrete. Some questions include:
What uses are there for the washout material?
What are the properties of the washout material?
What are the disposal requirements for washout material (are there limitations on where it can be dumped)?
What are the effects of washout material being deposited around the foundation of a building (both structural and effect on water systems)?
Even though it’s a zombie, I’ll answer. I work for one of the largest producers of concrete and RMX in the world.
There are no uses, but they can and do recycle the solids and water. Washout is somewhat corrosive and is considered a deleterious substance to water (in Canada, anyhow).
Leftover RMX and water.
It varies in each jurisdiction, and I only know the requirements for WCAN, but it is a hazardous substance. You can’t just dump it at the site (or aren’t supposed to, anyhow). Our guys drive back to the RMX facility where we have a specific area for washout water.
It’s mostly an issue of potential environmental effects. It could move in to an aquifer and contaminate water, or in to surface water and kill aquatic life. Depending on how much actual concrete was left in the washout and where it was dumped, I suppose it could affect the structure, but I doubt it.
btw, cement is the stuff that holds it all together (the glue) and it is mixed with aggregate (rocks) to create ready mix or concrete. Those trucks are called ready mix trucks.
[moderator note]
Just so everyone can figure out what’s going on, the OP was added to a thread from 2004, and I split it (and the responses to it) out into a new thread, since it really didn’t contribute to the original.
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From the previous portion of the thread, it sounded like the water was added at the plant when the truck is filled. Why don’t the trucks get filled with dry ingredients and have the water added and mixed when the truck arrives at the destination? Or is that what is done?
Edit: The topic of this thread has changed, but it seems like you would know the answer.
I’m not 100% sure, but I would guess that it’s so the ready mix has time to…mix. No use bringing all the dry ingredients to the site, adding water, then sitting there while it all mixes together - may as well do it on the drive there.
Also, if they added water at the sites, that means we’d also have to have water trucks driving around adding water to mix. I’m looking out my window right now at the RMX plant, and there are about a dozen trucks lined up. Truck after truck goes through during busy season - how many water trucks would we need to add to our fleet if we added water at the site? That would mean more drivers, which means less profit, which means higher prices.
On top of that, you may need industrial water permits for the water, which are location specific.
Interesting, it would seem beneficial for cases where delivery time was questionable. I just recalled seeing a truck stuck in traffic once with the (what is the rotating thing on the back called?) turning, and wondering what would happen if the traffic didn’t get moving. But maybe they were on the way back and spinning as part of the cleaning process. Thanks for the info.
It’s called the drum here, but may have a different name elsewhere.
The turning motion is what keeps it from hardening, so being stuck in traffic isn’t a big deal (it keeps turning, just not quite as fast). They have additives they can add prior to and at delivery to make it more viscous if needed.
The RMX or concrete isn’t going to harden within hours in the drum. As an example, we were able to get tailings from deliveries to fix the posts for our fence. The driver would come by our house at the end of the job if he had a few yards of extra (rather then dumping it in the lock blocks) and we used it. This product was at least 4 hours old.
I think I was thrown off by a 1.5 hour time in one these threads, or just my misreading.
This is off topic now, but do you have some idea of the largest sized aggregate that could be used in a mix delivered by truck, and I guess also what pumps would be able to handle (aggregate size wise)?
Actually, there used to be cement trucks that worked using that principle, I do not know if they are still in use, haven’t seen one in quite a while.
The cement, aggregate and water would be contained separately and the appropriate ratios would be mixed at the job site depending and quantity required and the concrete strength needed. I know this is frown on by some construction people but do not know what the issues are.
Do drivers still carry sacks of sugar to toss into the drum to prevent horrible disasters like a full drum hardening while stuck in a traffic jam? IIRC, the sugar slowed the cure, but also resulted in poor concrete - fine for fence posts, but no good for roads, bridges, etc.
Speaking of hot loads, some friends of mine built a large outdoor kitchen and barbecue with free concrete. Think all they did was let the local concrete plant know they could take a few yards this way, and soon they had drivers all too happy to have a good place to get rid of those pesky leftovers. The downside was that they had to be ready with wheelbarrows on about 15 minutes’ notice.
I’ve not heard of the sugar thing, but like I mentioned, they have additives they can toss in now in those situations.
We had the same situation with our fence posts and getting the tailings as your friend. We had about 15 minutes notice and had to be ready with wheelbarrows when they arrived. Some times when they called, we just couldn’t do it, and when it did work out, we were able to fill about five or six post holes. It took us about 10 days to get everything done, but it saved us a couple of grand in the end. Totally worth it.
There was an episode of Dirty Jobs where Mike got to use a jackhammer to remove the accumulated concrete from the inside of a drum. Not the result of a whole-load-hardening disaster, but just the accumulation of a lot of loads which got 98% cleaned out rather than 100%. The plant worker indicated that each drum in their fleet got the jackhammer treatment every few months.
It looked & sounded like one of the more awful jobs he ever did. The only thing it had going for it was nothing smelled like festering feces.
In my area they often dump the tail ends of loads at the side of the rural road or let it dribble onto the roadway at a traffic signal. I’ve driven past one pile about 2 inches high and 4 feet long and 6 inches wide that is on a lane line at a signal for about 7 years now. It slowly gets smaller and rounded off at the top.
It’s the price you pay for getting free concrete. My BBQ-building friends did wind up with about three wheelbarrows’ worth of extra. They poured it out in blobs on their hard-packed ground, and once it set up, it was easy to take the lumps to the local dump.
Cleaning out the mixers is one of the grunt jobs you’d give to the new kid.
One summer a friend of mine a year older than I was (20 at the time) got a “cushy” job with the state highway crew, was inside the drum cleaning it out, when someone turned it on (no lock-out/tag-out obviously). I can’t imagine a more horrific way to die.
