CIVIL AND STRUCTURAL ENGINEERING DESIGN & CONSTRUCTION TUTORIAL RESOURCES SITE

ESTIMATING CONCRETE WORKS FOR CIVIL ENGINEERING PROJECTS

Concrete is estimated by the cubic yard (cy) or by the cubic foot (cf) and then converted into cubic yards. Concrete quantities are measured in cubic yards as it is the pricing unit of the ready-mix companies, and most tables and charts available relate to the cubic yard.

Roof and floor slabs, slabs on grade, pavements, and sidewalks are most commonly measured and taken off in length, width, and thickness and converted to cubic feet and cubic yards (27 cf # 1 cy). Often, irregularly shaped projects are broken down into smaller areas for more accurate and convenient manipulation.

When estimating footings, columns, beams, and girders, their volume is determined by taking the linear footage of each item times its cross-sectional area. The cubic footage of the various items may then be tabulated and converted to cubic yards.

When estimating footings for buildings with irregular shapes and jogs, the estimator must be careful to include the corners only once. It is a good practice for the estimator to highlight on the plans which portions of the footings have been figured.

When taking measurements, keep in mind that the footings extend out from the foundation wall; therefore, the footing length is greater than the wall length.

In estimating quantities, the estimator makes no deductions for holes smaller than 2 sf or for the space that reinforcing bars or other miscellaneous accessories take up. Waste ranges from 5 percent for footings, columns, and beams to 8 percent for slabs.

The procedure that should be used to estimate the concrete on a project is as follows:

1. Review the specifications to determine the requirements for each area in which concrete is used separately (such as footings, floor slabs, and walkways) and list the following:

(a) Type of concrete

(b) Strength of concrete

(d) Any special curing or testing

2. Review the drawings to be certain that all concrete items shown on the drawings are covered in the specifications. If not, a call will have to be made to the architect-engineer so that an addendum can be issued.

3. List each of the concrete items required on the project.

4. Determine the quantities required from the working drawings. Footing sizes are checked on the wall sections and foundation plans. Watch for different size footings under different walls.

Concrete slab information will most commonly be found on wall sections, floor plans, and structural details. Exterior walks and driveways will most likely be identified on the plot (site) plan and in sections and details.

ASPHALT PAVING BASIC INFORMATION AND TUTORIALS

The asphalt paving required on the project is generally subcontracted to someone specializing in paving. The general contractor’s estimator will make an estimate to check the subcontractor’s price.

Asphalt paving will most commonly be hot-mix and is generally classified by traffic (heavy, medium, or light) and use (walks, courts, streets, driveways, etc.).

The estimator will be concerned with subgrade preparation, subdrains, soil sterilization, insulation course, subbase course, base courses, prime and tack coats, and the asphalt paving required.Not all items are required on any given project, so the estimator should determine which items will be required, the material and equipment necessary for each portion of the work, and the requisite thickness and amount of compaction.

Specifications.

Check the requirements for compaction, thickness of layers, total thicknesses, and materials required for each portion of the work. The drawings will also have to be checked for some of these items.

The drawings will show the location of most of the work to be completed, but the specifications should also be checked. The specifications and drawings will list different requirements for the various uses. (These are called traffic requirements.)

Estimate.

The number of square feet (or square yards) of surface area to be covered is determined, and the thickness (compacted) of each course and the type of materials required are noted. Base courses and the asphalt paving are often taken off by the ton, as this is the unit in which these materials must be bought.

The type of asphalt and aggregate size required must also be noted. Two layers of asphalt paving are required on some projects: A coarse base mix may be used with a fine topping mix. Equipment required may include a steel-wheel roller, trailers to transport equipment, dump trucks, paving machines, and various small tools.

To estimate the tons of material required per 1,000 sf of surface area, refer to Figure 9.44. Different requirements will be listed for the various uses (walk, driveway, etc.), and the different spaces must be kept separately.

In many climates, the asphalt paving has a cutoff date in cold weather, and the paving that is not placed when the mixing plants shut down will not be laid until the start-up time in the spring. The plants may be shut down for as long as four months or more, depending on the locale.