Class Update

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Class Update

• Exam 2 Schedule Need evening hours (6-8PM).
• April 13, 14, or 15.
• Extra Credit Field Trip Bluegrass Army Depot
  April 2nd Afternoon

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CE 403 Extra Credit Opportunity

• Groups who volunteer to present on April 22nd
  will receive 4 points added to Exam 1.

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CE403 Construction Methodology

• Concrete Construction

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Concretes Origins

• 690 B.C. The Assyrians used a mixture of one
  part lime, two parts sand, and four parts
  limestone aggregate to create a crude concrete
  for the Bavian Canal
• 1824 Joseph Aspdin files a patent in England on
  Portland Cement
• 1825 Erie Canal, used the first modern concrete
  to be manufactured in the USA

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Concrete Materials Properties

• Components
• Water
• Cement
• Aggregate
• Additives

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Water

• Primary reason is to provide the moisture for
  hydration of the portland cement.
• Hydration is the chemical reaction between the
  cement and the water that produces hardened
  concrete.
• The heat produced is called the heat of hydration
  exothermic.
• The desired characteristics are related to the
  water-to-cement ratio
• (ranges from 0.30 to 0.70 by weight).

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Portland Cement
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Aggregates

• 60 to 80 of the mixture.
• Free of Fines
• Angularity increases strength

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Additives

• Air-Entraining agents increase resistance to
  freezing and thawing and scaling.
• Good for pavements.
• Plasticizers - increase the slump and workability
  of a concrete mix
• Retarder slow the rate of hardening of concrete.
  Used sometimes to offset high temperatures.
• Accelerators decrease the setting time and
  increase the high early strength of concrete.
• Calcium Chloride is most common, and corrosive to
  steel.
• Pozzolans, i.e. fly ash,
• Replace some cement in mix
• increases the workability

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Distribution of Concrete Construction Costs

• Formwork
• Labor Equipment 39
• Material 10
• Concrete
• Labor Equipment 24
• Material 8
• Reinforcing Steel
• Labor Equipment 7
• Material 12

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Cast-In-Place Concrete

• Walls Wall Footings

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One-way Slabs

• Advantages
• Low cost formwork
• Fast
• Disadvantages
• Low shear capacity
• Low Stiffness (notable deflection)

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Two-way Slab

• Advantages
• Carries heavy loads
• Attractive exposed ceilings
• Fast
• Disadvantages
• Formwork with panels is expensive

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Pre-Cast Concrete

• Subsets pre-stressed, tilt-up, lift slab
• Applications lots!!
• Advantages quality control, all-weather
  construction, fast-track concurrency (no
  form-work reqd concrete already cured)
• Disadvantages fab plant overhead (more cost),
  transport cost, lifting equipment (larger
  cranes), and require economic quantities (need to
  exploit repetition)

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Precast Beam Shapes
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Pre-Cast Concrete

• 3 types of joints (concrete to concrete)
• Exposed, lapped rebar
• Dowels, sleeves, grout
• Topping Slab

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Prestressed Concrete

• Concrete in compression state before load is
  applied
• 2 types
• Pretensioned
• Tension cables tensioned in the concrete form
  before concrete is placed
• After concrete hardens, tensioning devices are
  removed
• Done in fab shop can be difficult to transport
• Post tensioned
• Tension cables tensioned after the concrete
  member has been erected
• Done in field QC can be challenging

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Prestressed Concrete Beam
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Prestressed Concrete

• Concrete in compression state before load is
  applied
• 2 types
• Pretensioned
• Tension cables tensioned in the concrete form
  before concrete is placed
• After concrete hardens, tensioning devices are
  removed
• Done in fab shop can be difficult to transport
• Post tensioned
• Tension cables tensioned after the concrete
  member has been erected
• Done in field QC can be challenging

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Tilt-Up Construction

• Vertical wall elements are cast horizontally and
  then tilted into place
• Advantage save formwork expense
• Lifting stresses may control geometry of design.

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Tilt Wall Construction

• Ideal for projects where time and budget are
  critical
• Appropriate for large, horizontal projects with
  three stories or less

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Tilt Wall Construction

• Engineering Intensive
• Tilt-up structures require less maintenance
  (mason blocks are likely to crack and leak water)
• Safer to build more work at grade

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Lift Slab Construction

• Floor slabs cast one on atop another
• Slabs raised with column-mounted jacks.

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Lift Slab Construction

• Advantages minimize form costs speed up
  construction
• 1987 failure LAmbiance Plaza (Connecticut)
• 28 fatalities
• Cause column to slab connection

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Lift Slab Construction
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Steel Fiber Reinforced Concrete

• Fiber Content 0.5 to 0.2 by weight
• Added paste (needs more cement and sand) needed
  to coat fibers
• Advantages resistance to impact, cracking,
  thermal shock, and fatigue
• Applications cavitations exposures (foot of dam,
  tunnel lining)
• Problems loose fibers

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Roller-Compacted Concrete

• Zero slump concrete mix placed with earthmoving
  and compaction concrete (pretty crude no great
  tolerances)
• Applications dams and pavement
• Advantages no forming/finishing, fast
  construction, economical

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Transporting Handling

• Equipment commonly used
• Wheelbarrows,
• small amounts max distance 200
• Buckets
• good for low slump
• Buggies,
• Manual or powered
• Powered can carry up to 14 cf traverse up to
  1000
• Chutes, Swivel over large area
• Conveyors,
• Horz. or Vert. optimum slump 2.5 to 3
• Pumps,
• can move material up to 5000 horizontally and
  1000 vertically

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Placing Consolidating

• The movement of plastic concrete into its final
  position is called PLACING. NOT POURING
• Avoid Segregation when handling.
• Height of free fall should be limited to 5ft.
• Forms should be clean tight, and the interior
  of forms should be oiled or coated with a parting
  agent for later form stripping.
• When placed directly on the subgrade, the
  subgrade should be moistened, or provided with a
  moisture barrier.

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Finishing Curing

• Finishing - bringing the surface to its final
  position and imparting the desired surface
  texture.
• Screeding - striking off the concrete to get the
  right grade, or elevation.
• Floating - smoothing the concrete and compacting
  the surface.
• Troweling - to create a smooth dense surface.
• Brooming - to create a skid-resistant surface.
• Curing - adequate moisture favorable
  temperature.

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Concrete Formwork

• General Requirements for Formwork
• safe
• produce the desired shape surface texture
• economical
• Formwork Design will be covered later.

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Slab-On-Grade Bulkhead
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Typical Wall Form
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Gang Forms

• AKA prefabricated forms

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TypicalForm Ties
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Maturity Method
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Maturity Method
Calibrate Mixture
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Maturity Method
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Reinforcing Steel, ReBar
Also welded wire fabric and spirals
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