Essay 1-2 pages Cost & estimating

3/19/2021

1

Concrete

Lecture 8

Estimating Concrete

 Separate concrete by:

 Type

 Strength

 Color

 Special testing

 Special curing

3/19/2021

2

Concrete Footings

 Found on:

 Wall sections

 Foundation plan

 Look for different sizes under different walls

Concrete Footings

Volume = Length x Width x Depth

 Measured in cubic yards

 Waste: 8% for slabs, 5% for other

elements

3/19/2021

3

Placing Concrete

Typical Productive Rates

Type of Placement LHR/c.y.

Continuous Footing - Direct Chute 0.4

Spread Footings – Direct Chute 0.873

Drilled Piers 0.320

Formed Piers 0.873

Foundation Walls – Direct Chute 0.5

Grade Beams 0.4

Slab – Direct Chute 0.32

6

Reinforcing Steel

 Type of steel: grade, smooth/deformed, type

of coating

 Size: #3 to #14

 Unit: ton (2000 lbs)

 Lap Splicing

 Waste: 10% when the bars are cut and bent

on the job

 Keeps type of placement (i.e., beams, columns, etc.) separate

 Supports: chairs, spacers, bolsters, wires,...

3/19/2021

4

Rebar Properties Bar

Designation Nominal Diameter

Cross-sectional Area

Weight (pound per ft)

2 1/4” 0.05 0.167

3 3/8” 0.11 0.376

4 1/2” 0.20 0.668

5 5/8” 0.31 1.043

6 3/4” 0.44 1.502

7 7/8” 0.60 2.044

8 1” 0.79 2.670

9 1-1/8” 1.00 3.400

10 1-1/4” 1.27 4.303

11 1-3/8” 1.56 5.313

8

3/19/2021

5

9

Welded Wire Mesh

 Designation: 6x6 10/10 long. spcg x

trans. spcg. gage long. x gage trans.

 Available in 5' x 150' rolls

 Unit: 100 sf (CSF)

 Can be estimated by roll or sheet

 Lap: one transverse spacing, i.e., 10%

for 6x6 10/10

 Waste: 5%

BCN 5618 10

3/19/2021

6

Reinforcing Productivity

Type of Placement Productivity Rate (Labor Hrs/Ton)

Beams #3 to #7 22

Columns #3 to #7 24

Footings #4 to #7 15

Walls #3 to #7 11

Slab on Grade #3 to #7 13

Wire Mesh 1 per roll

Vapor Retarder

 Estimated by the roll

 Best to sketch a layout

Sq. Ft of Vapor Barrier Labor Hour per 1,000 Sq. Ft.

Up to 1,000 1.5

1,000 to 5,000 1.25

Over 5,000 1

3/19/2021

7

Accessories

 Expansion joint covers

 Expansion joint fillers

 Waterstop

 Manhole frames and covers

 Trench frames and covers

14

Curing

 Cement hydration requires time (3 to 14 days), favorable temperatures, and moisture. Curing options are:

 leaving forms in place

 sprinkling

 spray mists

 moisture retention covers

 seal coats (curing compound)

 Hot and cold concreting

3/19/2021

8

Concrete Transportation

 Truck chutes

 Buggies

 Crane and bucket

 Crane and hopper

 Tower and buggies

 Forklifts

 Conveyors

 Pumps

Forms

 Often bid by the square foot contact area

 Be sure include:

 Both sides

 Ends

 Bottom (if required)

 Cost is affected by number of uses

3/19/2021

9

17

Forms

 Selection and design of forms are the responsibility of the general contractor.

 Unit: square feet of contact area (SFCA)

 Number of times the form may be reused

 Length of time the form must stay in place

 To rent or purchase

 Types of forms: wood, metal, fiberglass

 No deductions in the area for opening less than 30 sf

18

Forms  Forms estimate includes: materials; labor to

assemble, erect, strip, clean, and repair; and equipment.

 Factors affecting the cost of concrete wall forms:  height of the wall

 shape of the building

 Factors affecting the cost of concrete floor  floor-to-floor height

 reusability of the forms

 length of the time forms must be in place

 type of shoring and support used

3/19/2021

10

Form Productivity

Application Productivity Rate (Labor Hours per SFCA)

1 use 2 use 3 use 4 use

Foundation Wall (Plywood) 0.44 0.28 0.25 0.22

Footings 0.14 0.09 0.08 0.07

Slab on Grade 1.2 1.1 1.0 0.8

Columns 0.180 0.146 0.143 0.140

Beams 0.2 0.18 0.15 0.14

Precast Concrete

 Double tee

 Single tee

 I girder

 Inverted T beam

 Box girder

 Hollow core slab

 Columns

 Channel slab

 Wall panel

3/19/2021

11

BCN 5618 21

22

Precast Concrete

 Concrete members that are cast in separate forms and then placed in the structure.

 Advantages over cast-in-place concrete:  faster erection during all weather conditions

consistent finishes because of controlled environment at the plant

 sophisticated finishes and shapes may be produced in a plant

 for longer spans prestressed concrete is used, either pretensioned or posttensioned.

3/19/2021

12

23

Precast Concrete (Unit)

 floor, wall, and ceiling: SF with the thickness noted

 beams and columns: LF with each different size kept separately

 Anchorage devices, inserts, and any other special requirements must be noted

 Responsibility of the supplier regarding installation including welding, finishing of concrete, and caulking must be determined.

Estimating Precast

 Simply reinforce or prestressed?

 Coordination with:

 Mechanical

 Electrical

 Concrete fill (topping)

 Fire rating

 Welding