Concrete: 4a Casting Concrete

Concrete: 4a Casting Concrete

Concrete: 4a Casting Concrete - Full TranscriptionSo we're going to look at two short videos. One, the first one is about the pouring or the placing of concrete. The second one is about finishing the concrete. So let's start here. Concrete is usually pumped into location unless it's a slab on grade and the ready mix truck can back up and with its chute deliver the concrete. In this image on the right we're looking at a metal deck with welded wire fabric which is basically temperature reinforcing. This stuff is not called rebar it's called welded wire fabric and it's basically tension sorry, it's basically temperature reinforcing because there is a beam here, there's another beam back there, and the metal deck is doing the span, so I don't need the rebar. The rebar is there just for temperature to prevent cracks from developing in the concrete. Very good. Let's look at the next one. So here the concrete is delivered, they're spreading it, it's depending on the proportion of the mix. It could be very runny or it could be very rigid, and then they'd have a hard time, the workers would have a hard time spreading the concrete. But in this case, it looks like it has a nice, reasonable slump. So it's going on top of the metal deck nicely. So they spread it, they level it, and there it's coming out very good. So they will trowel a little bit, but then mostly there is this power screed. Screed is to level the surface of the concrete, and this is a power one. A power screed, it vibrates as it smooths the concrete. Here's another picture of it. And then somebody will come back and really make it smooth after the power screed goes through. Most important is vibrating the concrete as it's placed because that prevents any honeycombing from happening. So here we can see this guy with the vibrator stuck in the wet concrete and it's vibrating it. Same with this guy. This pour here is for a tilt-up project. They pour it flat. They vibrate the concrete. They finish the concrete. there may be windows, there may not be windows, whatever it is, then a crane comes, picks up the panel, tilts it up. There is a video I prepared for tilt-up construction. You can see it there. Very good. So next thing that is important to do is the curing of the concrete. So here it's chemical curing. They're spraying a liquid here, a chemical rather, that will make the concrete cure faster versus a curing mat. They're going to cover, this is at a precast yard, they're going to cover the pore with this curing mat to keep the moisture in there for the concrete to continue hydrating. So we're going to look at some examples of the pouring of concrete. We're starting with the foundation, then we're going to go to a slab en grade, then a slab, etc. So looking at this image here, we have dowels that are in the concrete in the first pour of the foundation. They're in here and they're coming up and then a concrete column will be tied to these dowels. But we can see, where's the eraser? There's the eraser. We can see that the concrete footing is this square here. And it may be that deep. And it has these dowels sticking up that they're going to tie a rebar cage to once this concrete footing cures. So here is an overview. there's wall footings or spread footings. A wall, you can tell from the rebar, a wall is going to come in here and do something like that. And they'll tie to those dowels. So dowels are rebars that stick from one port into the next port to make the construction monolithic. A great beam over here is being poured. So this guy looks something like that. Oops. Something like that. And it's got some rebar in there. This slope here is because the dirt does not do that. That is sculpting it. So the dirt is going to fall in or it's going to be at its own angle of repose, and then they put some reinforcing in here, and then they pour. So we can see the concrete pump over here delivering the concrete. Here is a wall footing, and we can see the wall over here doing that. And it's just like the image I have over here that you've seen many times in drawings. it's basically a wall footing versus a column footing. A column footing is going to look more like that. So it's a square underneath the column. This image is going to shoot me in the foot, but typically this is X, X, X. That dimension is the same as the column footprint. So whatever this X dimension is, the footing will be 3X, and its depth is usually X. But I know this project, it's Houston, and the soil there is a clayey, clayey, clayey, clay. So they needed a larger footing. Here is more of a wall footing, and it looks like there's a column here. I can see the anchors. And then there's going to be a wall here. And on this wall, there's the footing for it. There will be a wall here doing that. Very good. They are laying block or there might be a concrete wall. I'm not sure. This one in this case, of course, is block. Here is the wall footing again. And we see the dowels sticking up from the pour. And what we're seeing here is something that looks like that. and they have the dowels in there. They're coming up and there's some kind of slab, sorry, footing reinforcing and the dowels are attached to that. They come up and they are poured to this level and then another column or wall cage will be built here which is what all of these dowels attach to. So this is poured up to here first. The footing first is poured. Then the dowels stick up. Then they do the formwork for the wall. Then they pour the wall. So deep foundations versus shallow foundations. These foundations were shallow. So deep foundations are basically either caissons. Caisson, where am I going to write so you can see it? Caisson. Let's change colors or maybe increase the pen weight. Let's just increase the pen weight. So it's already huge. Okay, so a caisson. It's basically they put a sleeve, maybe they pour concrete in it. Then the sleeve is taken out and you're left with that concrete pour with rebar sticking out. another column is going to come on top of. These are dowels for the column, the next column to attach to. That's too fat. Okay, so here again is another example. So here they're putting reinforcing and they're going to do a pile cap. So they're going to put a cap on top of the caisson and then maybe there's multiple caissons and they're joined by this cap and then a column will go on top of those. So here it is, and getting ready to be poured. Versus these piers. Piers are the same as caissons, but this one is drilled, a drilled pier. Again, this is Houston, and it was excavated, so they became exposed. But there's a pile cap here, joining whatever load you have on this pile cap is going down. to two piers. And these guys in Houston, specifically on the Gulf Coast, it's all clay clay, and therefore you don't get much end bearing. So you're counting on the friction with the soil on the perimeter of the pier. So, okay, there is another video on foundations. We'll talk more in depth about that. Here's an example of a mat or a raft foundation that is huge. It's underneath the entire high-rise building. It's thickness. Can we see the thickness? First of all, here are those piles supporting the roadway and whatnot. And it's a huge pore underneath a high-rise. and you can tell by the number of ready-mix trucks that are delivering the concrete, it's a huge pour, and they're probably trying to make it in one go. The reinforcing, oh, we were talking about the height of this thing. The pile foundation, or sorry, the mat foundation or raft foundation is usually one floor tall, so it may be 8 feet, 10 feet, 12 feet thick. and then the whole building sits on it. We can see the dowels for the columns coming up here. Then they'll start working. Once this mat is poured, they'll come in and they'll start working on it and shuttering the columns and going up and doing slabs and whatnot. So I just wanted to show you the scale of this thing and the complexity of the rebar. And whenever it's inclined like this, It's a staircase being attached, anchored in the concrete. Looks like there's several staircases here. This is from another project in California. Again, the scale of a matte foundation is just huge. So placing the concrete slab on grade, we talked about it in many videos. Underneath this plastic sheet or polyethylene, 6 mil polyethylene sheet, typically, There is a bed of gravel to prevent any moisture and other chemicals from coming up from the ground and hitting the bottom of the slab. Then there is this welded wire fabric, again, not reinforcing, just temperature reinforcing. Then they're placing the concrete. Excellent. Versus the elevated slabs, again, it's going to be pumped. We have open web joists on the roof because it's not occupied. There is no big live load, so they can use open web joists. Versus if it's a floor such as this one, they have to have beams. And let me zoom in a little bit. Undo. Zoom in. There's these shear studs here. These shear studs are telling me that there is a beam under here. And there is another beam here. And so the deck is spanning this much. And usually the metal deck can go 4 foot, 6 foot, 8 foot, 10 foot, 12 foot. That's a reasonable span for the metal deck. I see more shear studs here. There's a beam under there. I can't really tell the scale. But usually 8 foot to 12 foot is very reasonable. So the concrete is pumped. It comes in. They smooth it. They screed it, they vibrated, they do all that good stuff. Now that I have this picture here, you can see the texture on the metal deck. This texture is so that the concrete bonds with the deck. And the profile of the deck is it's trapezoidal. Because a roof deck is more straight, it doesn't have this trapezoidal profile. And it doesn't have the texture because it's not going to get any concrete. A roof deck will get insulation, typically will not get concrete. Very good. So columns, everything is delivered by pump. And it has to be supported in two directions. Otherwise, it'll tip over while it's cast. and the concrete formwork might explode if the concrete is dropped from a high distance or if the column is very tall. And again, we see the rebar extending beyond the formwork for the next pour. Here's the pouring of walls. Again, the concrete is pumped and dumped in there and they're vibrating. This is a pretty tall wall versus this one is less tall. So they're doing it with a hopper and a chute, and they move it along as they go. And somebody is going around with a vibrator, making sure that the concrete is smooth. Very good. So this is the end of the first video. I'm going to stop the recording and then start it again, and there will be two separate videos. The second one is about finishing the concrete. So now let's talk about finishing.