The next place we're going to go is concrete formwork. Concrete formwork is a temporary mold into which concrete is poured, cured and allowed to reach its desired strength. Formwork allows you to create a multitude of different applications for concrete. Including, but not limited to, foundation walls, beams, columns, domes, archways and interior partitions. On the screen is an example of poured in place concrete using formwork to design intricate structures, in this case, a causeway over New York City. Formwork is often made out of steel in modern construction, but can be also made of wood or aluminium. Formwork should not be removed until the concrete has developed sufficient strength to support all loads placed upon it. The time required before formwork removal depends on the structural function of the concrete, and the rate of strength gain of the concrete itself. As we reviewed earlier, the water to cement ratio and temperature during the curing process, influenced the rate of strength gain of concrete. Formwork removal should always be supervised by the structural engineer to ensure the quality of the hardened concrete in a structural member. These members should have minimum casting defects, such as honeycombing, size and shape defects. These defects in concrete greatly influence the strength and stability of the structure. Therefore, immediate repair work must be done or the concrete will be rejected. Formwork takeoff It is a simple procedure. The unit of measurement that you're going to use is square footage. That, of course, is calculated by measuring length times width. There are no conversions that need to be done when measuring formwork. And a good tip to remember is, that the surface area of the concrete will quantify the amount of formwork that is required for the project. That is, the face of the concrete that will be touching the actual formwork itself. So keep that in mind. Okay, on to some examples. Our first example, you are going to be playing the role of a client representative. You've been asked to quantify how much concrete would be required to place a slab on grade for a future parking lot. The slab on grade will need to be 50 feet wide by 75 feet long by 8 inches thick. The slab will be reinforced with number five rebar, and laid lengthwise 16 inches on center. The first operation that you want to perform is quantifying the area of the slab. So that calculation would simply be 75 feet multiplied by 50 feet for a grand total of 3,750 feet squared. You will then convert inches into feet. You'll take 8 inches divided by 12 and come up with a factor of 0.67. And then finally, you're going to solve for a cubic dimension 3,750 x 0.67 brings you to a total of 2,500 cubic feet. You must always remember to convert cubic feet into cubic yards. Therefore, the calculation would be 2,500 divided by 27, for a total of 92.59 cubic yards. The second action would be to quantify the length and quantities in the weights of the rebar. We know that we have a length of 75 linear feet, and that the rebar will be placed lengthwise. So we must convert, for the width of the slab into inches. That calculation is performed by multiplying 50 feet by 12 inches for a grand total of 600 inches. We also know that the rebar is going to be placed 16 inches on center apart from each other. So we can divide 600 inches into 16 for a total of 37 and a half total rebar for the entire project. You must then multiply the rebar by the total linear amount. So that calculation is performed by multiplying 37.5 times 75 linear feet for a total of 2,812.5 total linear feet of rebar. Finally, we need to understand what the anticipated weight of the rebar will be, as that's how it is priced, which you'll learn in a later module. So 2,812.5 total linear feet of rebar by the amount that we find on our ASTM table. We know that number five rebar weighs 1.0443 pound per linear foot. Therefore, the total weight will be 2,933.44 pounds of rebar. Finally, the last calculation that you're going to want to perform is, understanding the surface area of the concrete so you can determine the formwork quantity. So we take 0.67, which is the conversion from inches into feet, and multiply it by 50, because that is the width of the slab itself, and then you multiply that by 2, as there are two sides to it. And then similarly you will take the length, multiply it by the converted inches, and then multiply that by two. The total that you arrive at is 167.5 square feet of formwork.