Concrete Measurement and Estimation Notes

Converting Measurements for Concrete

  • Concrete companies sell concrete by cubic yard.
  • Common measurements:
    • Roof and floor slabs, slabs on grade, pavement, sidewalks: volume calculated using length, width, and thickness in feet.
    • Conversion: 1 cubic yard = 27 cubic feet.

Handling Irregular Shapes

  • Irregularly shaped items can be broken down into smaller, regular areas to facilitate easier calculations.
  • Calculate volumes of smaller areas and combine for the total volume.

Measurement Techniques

  • Volume of footings, columns, beams, and girders:
    • Determined by multiplying linear footage by cross-sectional area.
    • Items' volumes are calculated in cubic feet and then converted to cubic yards.
  • When estimating footings for irregular shapes, only include corners once.

Estimation Best Practices

  • Highlight portions of the footing taken off on architectural plans.
  • Footings generally extend behind foundation walls, thus the length is greater than the wall length.
  • Do not deduct holes smaller than 2 square feet.

Waste Allowance

  • Waste percentages:
    • 5% for footings, columns, beams.
    • 10% for slabs.
  • Best practice: account for waste when estimating quantities.

Procedure for Estimating Concrete Requirements

  1. Review specifications for concrete needs (footings, slabs, walkways).
    • Specifications impact price (e.g., stronger concrete requires more cement).
  2. Identify concrete types based on:
    • PSI (strength), color, admixtures, curing methods.
  3. Review drawings to ensure all items are covered in specifications. Contact the architectural engineer if specifications are missing.
  4. Calculate concrete quantities based on drawings, checking for different footing sizes under different walls.

Example Footing Calculation

  • For continuous footings:
    • Dimensions: 3 ft 2 in width, 1 ft thickness.
    • Total linear feet of different widths calculated and totaled:
    • A: 39 ft 10 in
    • B: 34 ft 4 in
    • C: 14 ft 10 in
    • Example calculations lead to 10,68 cubic feet total volume.
    • Convert cubic feet to cubic yards: 10.68 / 27 = 39.6 cubic yards.
    • Adding waste for total order: 39.6 + 5% = 41.6 cubic yards.

Drilled Piers

  • Drilled piers may require casing for stability, especially in loose soil or high water tables.
  • Types of casing include heavy-duty cardboard tubes or steel casings.
  • The depth of drilling determines the foundation stability.

Calculating Foundation Walls

  • Similar process as footings, but specific dimensions vary and respect the foundation wall shape.
  • Do not double-count corners when measuring perimeter.

Rebar Estimation

  • Calculate using lengths for vertical and horizontal bars around footings and walls, ensuring coverage per engineering specs:
    • Lapping adds approximately 5%-18% to the estimate depending on the size of the bar.

Summary of Concrete Estimations

  • Estimation summary should cover total quantities for:
    • Footings
    • Foundation walls
    • Spread footings
    • Concrete beams
    • Slabs on grade
    • All labor and material costs included.

Waste Factors for Rebar

  • Waste for precut bars can be less than 1%, while cut and bent bars may be as high as 10% based on field conditions.
  • Rebar is often estimated based on concrete calculations.

Importance of Accurate Measurement and Calculation

  • Always rely on precise measurements from plans.
  • Highlight areas properly to avoid missed estimations or waste. Display calculations transparently to ensure justification for quantities ordered.

Final Notes

  • Remember to communicate with engineers for clarifications.
  • Understand the type of reinforcement necessary based on structural demand.