Concrete is an art; not a science.

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"The right to party is a battle we have fought, but we'll surrender and go Amish... NOT!" -Wayne Campbell

You don't need to be too precise for small non-structural applications. Usually it's a ratio like 4 shovels of sand, 4 shovels of gravel, one of Portland cement (I think... Been years since I had did it that way). You can use different aggregates, play with the ratios a bit, it's pretty forgiving depending on the application (I can guarantee you the concrete used in, say, pillars holding up bridges is mixed with a touch more accuracy!)

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Long Chile was a silly place.

It's possible they might have pre-weighed their materials. Otherwise, unless you really have no clue what you're doing its not too hard to hit a mixture with a useable compressive strength with modern materials.

First off thank your for calling it concrete and not cement.

Concrete is a science, not an art, if you are doing it at the structural level. These guys with the shovels may be doing some non-structural footing, curb, sidewalk, who know, but for minor stuff eyeballing the ratios is fine.

I like others on this forum deal in large commercial structures. Concrete starts out with an engineered mix specific for the application. They are looking to get a certain strength or properties out of the finished product, so the exact ratios of water, sand, aggregate and cement are all tested in a lab, with trials done to insure the strength and properties. Concrete coming out of batch plant, the redi mix trucks you se everywhere, are all computer batched. No guess work. We just finished a huge parking structure where a large portion of the slabs and beams did not pass the tests, which are done many days after the pour. Turns out the batch plant dude made a minor input error, and the entire days worth of pours (more than 50 truckloads) was bad concrete. Had to jackhammer out one whole floor. The redi mix plant paid dearly for that error.

Bakers just scoop cupfuls of sugar, flour, etc. into a bowl too.

For the type of concrete work they are most likely doing "shovelful" is almost certainly a precise enough measure. I'd be surprised if they aren't counting those.

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I'm beginning to think that we are much more fucked than I thought.

I'm always amazed, when I order concrete, the amount of detail the batch plant asks for. Air entrainment, aggregate, water temp, additives, etc. I've done some pretty cool stuff with concrete (on a smaller, residential scale, and usually decorative at that) but I'm always amazed at it's versatility.

Going to Italy and seeing buildings like the Pantheon blew my mind. Perfectly spherical dome (accurate within millimeters), continuously poured, walls tapering and using progressively lighter mixtures as the structure rose... All done by hand around 100 AD.

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Long Chile was a silly place.

I had a college prof go on a rant about cement vs. concrete and it has stuck with me ever since.

As well as masonary and columes.

But I digress.
I bet these guys were patching a sidewalk. No worries there.

>>the entire days worth of pours (more than 50 truckloads


That there is a metricshitton o' stuff

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RayGovett
Hughson CA
Be Prepared-- Strike Swiftly -- Who Dares Wins- Without warning-"it will be hard. I can do it"

Ugh, a bit more then that.

50 trucks is roughly 500 cubic metres. I believe a cubic metre weighs something like 2500 kg, so 1,250,000 kg or 2,750,000 lbs of concrete.

That's a lot of jackhammering. What was the cost of that delivery? Around $200-250k just for the concrete? (Not counting what I'm sure was significant labour cost to form, place, vibrate, finish, strip the work, people to block/direct traffic, crane time (assuming it was a crane job).

That's one hell of an oops!

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Long Chile was a silly place.

That's what I like about this place: somebody knows something about anything!

Pretty sure they were just doing a curb job, cool to learn that it's that precise in structural applications. The way things are built around here, I wouldn't be surprised if those 2 same guys were scooping the mix going into the new Champlain bridge pylons...

What did that structure cost per car? Not counting the screw up.

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Yes

Unit prices are generally not a good indicator. Too many factors. We are in California. Expensive. We are a union contractor. Expensive. The client wanted high end elevators and escalators. Expensive. High end light fixtures. Nice lobby. Slightly wider stalls, etc. The project in question was just under $20k per car (over 2000 cars). But we have done mixed projects (retail is office over parking) at 10k per car. Lots of things affect the bottom line unit cost. BTW, we didn't pay for the repair, they have insurance for a reaon.

It was probably closer to 500 cubic yards ;-)

I always find it funny how we measure up in cubic yards (as our forms are in imperial, it's always 16" x 6" footings for residential, walls x number of feet tall, etc), and order in cubic metres. Bugs the hell out of me. I love working in metric when I can get away with it.

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Long Chile was a silly place.

The material cost of the concrete was minimal compared to the demo cost plus the labor to re-form and replace all the beams and slabs. I realy don't want to divulge the extent of the cost, but it was a multi-week setback.

I can only imagine. I always find larger scale construction so fascinating. There's a lot of money going around per day, and considering how easily minor screw ups can cause massive problems it's a miracle jobs can run so smoothly.

A few years ago there was a large condo project going up. For whatever reason, reshoring on the slabs was removed way too early, and a whole floor collapsed. Thank God it happened on a Sunday when no one was working. Put the project behind by months. Recently on another large scale project a slab was poured before electrical conduit was run through. Oops.

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Long Chile was a silly place.

I build machines that put color into concrete and I just had to modify the program to use kg and meters for Canada. Around here basing mix designs on 94 pound sacks of cement has pretty much been replaced with cementitious content of a yard. But I don't see us moving to metric any time soon.

A little construction site humor for you

"If you can't finish high school, you can always finish concrete"

Pro tip: You can also replace "concrete" with "drywall" in the joke depending on how far along the job is

I just finished drywalling my bathroom. Now that is a skill, and a lucrative one to have. A good finisher, in my area, can easily make $100k a year. Boarders can do well too, but that job destroys your body.

I know a few concrete finishers who work for the city. With their flex days and long holiday breaks, they do side jobs like driveways and sidewalks for $60/hr.

Not bad for highschool drop outs!

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Long Chile was a silly place.

Yup, it was a toss up for the name of my sailboat . Side job or change order. Went with change order.

That's awesome!

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Long Chile was a silly place.

Smaller jobs are riskier because as a sum, margins are smaller.

In my experience, smaller general contractors tend to run smoother jobs.
I think it's because their staff of supers and PMs are more in touch with the value of money.
I always worked for large GCs until I started a subcontracting business.