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Measuring Concrete Work in Construction
Preparing a quantity takeoff of concrete work requires the estimator to measure a combination of items—some of which are shown on the drawings, while others are to be inferred from the drawings. When drawings are well prepared, items of concrete such as footings, walls, and columns are clearly shown, but nowhere on the drawings will the estimator find details of the formwork required for this work. The assessment of formwork requirements will be based on the estimator’s knowledge of what is required for each of the different concrete components.

Because the concrete is detailed on the drawings, it makes sense to begin the takeoff by measuring the volume of concrete in an item. Then, after the concrete dimensions are defined, consider the formwork requirements, followed by the finishes that are needed and so on. Also, in accordance with the basic principles previously discussed regarding taking off by assembly, a good practice is to measure all work associated with one concrete assembly before passing on to consider the next assembly.

For example, if there are concrete footings, walls, and columns to consider on a project, we would begin with the footings. First we would ascertain the dimensions of footing concrete from the drawings, then reuse these dimensions to calculate the area of formwork and the length of keyway required and conclude this assembly by measuring anything else associated with the footings. After the work on the footings is measured, we would turn our attention to the walls and measure all the items associated with them. Finally, we would deal with the columns in the same way.
 
This approach allows the estimator to focus on one piece of work at a time and fully understand all of its requirements before moving on to the next item. Alternative approaches such as measuring all the concrete volumes and then all the formwork areas require the estimator to be constantly jumping about from one type of item to another. He or she may have to come back to footings three or four times with this method, which is not an efficient way to proceed.

Concrete Measuring Notes

In general:
1. Concrete shall be measured in cubic yards net in place. Calculate the volume of concrete from the dimensions given on the drawings with no adjustment for “add-on” factors. Additional material required because of spillage, expanding forms, and wastage will be accounted for later in the pricing process by means of a waste factor added to concrete items.

One exception to this general rule applies to the situation where concrete is placed on rock or shale. In this case, the “overbreak” in the excavation is generally required to be filled with concrete and, as this volume will not be indicated, the estimator will have to add an assessed amount to the quantity of concrete to allow for this “overbreak.”

2. Do not adjust the quantity of concrete for reinforcing steel and insets which displace concrete. Also, do not deduct for openings in the concrete that are less than one cubic foot (0.05 cubic meters) of volume.
 
3. Classify concrete and measure separately in the following categories:
a. Underpinning
b. Pile caps
c. Isolated footings
d. Continuous footing
e. Retaining walls
f. Grade beams
g. Columns and pedestals
h. Beams
i. Slabs on grade
j. Suspended slabs
k. Floor toppings
l. Stairs and landings
m. Curbs
n. Manholes
o. Equipment bases
p. Roads
q. Sidewalks
r. Other structures not listed

4. If different mixes of concrete are used in any of the categories listed in item 3, measure each mix separately. For instance, where different strengths of concrete are specified for columns on a project, separately calculate the quantity of concrete for each type of concrete in columns (Figure 1). Often on a project all the concrete for a certain use, for example footings, is specified as the same mix, in which case there is no need to note the mix on the takeoff as it will not have to be considered until the recap and
pricing stage is reached.
 
Mixes are further complicated by the different types of cement that could be specified. For instance, concrete in contact with soil may have to be made with type V, sulfate- resisting cement. Furthermore, air entrainment may or may not be required, to say nothing of super- plasticizers. The many combinations of variables result in a multitude of possible concrete mixes. To simplify the pricing of concrete, the items listed on the recap are priced  for the cost of placing (labor and equipment) only. A separate list of the amounts of the various mixes is prepared, and against each item on this list the price of the particular mix of concrete is entered.

5. Where columns and walls extend between the floors of a building, measure these components from the top of the slab below up to the under surface of the slab or beam above.

6. Beams may be measured separately from slabs, but if they are to be poured monolithically with the slabs, the quantity of concrete in the beams should be added to the slab concrete for pricing.

 








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