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Concrete

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The History of Concrete: Textual Concrete Admixtures - The Concrete Network *** Data from Architectural Graphics Standards, ... – PowerPoint PPT presentation

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Title: Concrete


1
Concrete
2
Major Topics
  • History
  • Uses
  • Materials Used To Make Concrete
  • Cement
  • Aggregate
  • Water
  • Admixture

3
Major Topics cont
  • Testing
  • Slump Test
  • Compressive Strength Test
  • Air Content Test
  • Strength
  • Placing

4
Major Topics cont
  • Transporting
  • Curing
  • Finishing
  • Reinforced Concrete
  • Pre-cast Concrete
  • Pre-Stressed Concrete

5
Concrete History Facts
The History of Concrete Textual
Noteworthy The Hoover Dam, outside Las Vegas,
Nevada, was built in 1936. 3 ¼ million cubic
yards of concrete were used to construct it.
6
Concrete Resources
Concrete Admixtures - The Concrete Network
7
Uses
  • Foundations and Driveways
  • Architectural Details
  • CMU (Concrete Masonry Units)
  • Concrete Roofing (Arches Domes)
  • Columns, Piers, Caissons
  • Walls and Beams
  • Bridges

8
Materials Used to Make Concrete
  • Portland Cement 5 types
  • Should conform to ASTM C150
  • Type 1 standard widely used columns, floor
    slabs, beams
  • Type 2 has a lower heat of hydration used in
    massive pours e.g. Dam construction
  • Type 3 high early strength suitable for cold
    weather
  • Type 4 termed low heat used in massive pours
    to diminish cracking
  • Type 5 sulfate resistant used in sewage
    treatment plants concrete drainage structures

9
Air-Entraining Portland Cement
  • Produces billions of tiny bubbles
  • Greatly reduce segregation of mix
  • Less water needed to produce a workable mix
  • Has a better resistance to freezing and thawing
  • Classified as Type 1A, 2A, 3A

10
Aggregate
  • 2 classes
  • Fine sand lt 3/8 large
  • Coarse gravel or crushed stone
  • Grading should conform to ASTM C33
  • Sieve analysis test (ASTM C136) and analyses for
    organic impurities (ASTM C40) often done
  • Represent 60-80 of the concrete volume

11
5 Aggregate Types
  • Natural sand and gravel
  • By-Product blast-furnace slag or cinders
  • Lightweight materials heated and forced to
    expand by the gas in them
  • Vermiculite a type of mica that will greatly
    expand
  • Perlite a type of volcanic rock which expands

12
The Critical Role of Water in Mix
  • Hydration chemical reaction caused by mixing
    the water with cement
  • Too much prevents proper setting
  • Laitance (bleeding) white scum or light streaks
    on the surface of concrete which are very
    susceptible to failure
  • Too little prevents complete chemical
    reaction from occurring

13
Proportioning of Mix
  • 1 2 4 concrete consisting of
  • 1 volume of cement
  • 2 volumes of fine aggregate
  • 4 volumes of coarse aggregate
  • Emphasis now on Water-Cement ratio methods of
    proportioning

14
Typical Design Mix (Yield 1 cu.yd. of 3,000 psi
of Concrete)
  • 517 lb. of cement (5 ½ sacks)
  • 1,300 lb. of sand
  • 1, 800 lb. of gravel
  • 34 gal. of water (6.2 gal. per sack)

Data from Architectural Graphics Standards,
2000
15
Admixtures
  • Materials added into the standard concrete
    mixture for the purpose of controlling,
    modifying, or impacting some particular property
    of the concrete mix.
  • Properties affected may include
  • Retarding or accelerating the time of set
  • Accelerating of early strength

16
Admixtures cont
  • Increase in durability to exposure to the
    elements
  • Reduction in permeability to liquids
  • Improvement of workability
  • Reduction of heat of hydration
  • Antibacterial properties of cement
  • Coloring of concrete
  • Modification in rate of bleeding

17
Testing of Concrete May Include
  • Slump Test ASTM C143
  • Determines the consistency and workability
  • Compressive (Cylinder) Strength ASTM C192
  • Determines the compressive unit strength of
    trial batches
  • Air Content

18
Slump Test
Concrete sample is placed into a 12 sheet
metal cone using 3 equal volumes. Each layer is
tamped 25 times with a bullet-nosed 5/8 by 24
rod. Last layer is leveled off with the top of
the cone. Cone is removed The vertical
distance from the top of the metal cone to the
concrete is measured
19
Compressive Strength Test
  • Comply with ASTM C39
  • Basic steps
  • of samples taken vary (no less than 3)
  • 3 layers of concrete placed in a cardboard
    cylinder 6 in diameter and 12 high.
  • Each layer is rodded 25 times with a 5/8 steel
    rod
  • Samples are cured under controlled conditions
  • Test ages vary but usually done after 7, 14, and
    28 days
  • Sample removed from cardboard and placed in
    testing apparatus which exerts force by
    compressing the sample until it fails (breaks)

20
Strength of Concrete
  • Stated as the minimum compressive strength at 28
    days of age
  • Design strength
  • Typical residential 2,500 4,000 psi
  • Pre- or Post tensioned typically 5,000 7,000
    psi
  • 10,000 12,000 psi used in columns for high-
    rise buildings

21
Placing Concrete
  • Temperature
  • Optimum temperature for curing is 73 degrees F
    may have problems curing if temperature below 40
    degrees F
  • Forms
  • Wood and metal commonly used (reused)
  • Clean and sufficiently braced to withstand the
    forces of the concrete being placed
  • Concrete weighs 135 165 pcf if lightweight
    then 85 115 pcf often in estimating the figure
    150 pcf is used

22
Placing Concrete cont
  • Free falling distance should not exceed 4-5 feet
    due to the threat of segregation of aggregates
    occurring

23
Transporting Concrete
  • Method selected depends on quantity, job layout,
    and equipment available
  • Chutes
  • Wheelbarrows/Buggies
  • Buckets
  • Conveyors
  • Pumps

24
Curing
  • Proper curing is essential to obtain design
    strength
  • Key factor the longer the water is retained in
    the mix the longer the reaction occurs better
    strength

25
Evaporation of Water Reduced by
  • Cover with
  • Wet burlap or mats
  • Waterproof paper
  • Plastic sheeting
  • Spray with curing compound
  • Leave concrete in forms longer

26
Joints
  • 3 types
  • Isolation (expansion) allow movement between
    slab and fixed parts of building
  • Contraction (control) induce cracking at
    pre-selected locations
  • Construction provide stopping places between
    pours
  • Materials used
  • Rubber/plastic
  • Vinyl, neoprene, polyurethane foams
  • Metal/wood/cork strips

27
Finishing
  • Screeds used to level the concrete placed in
    the forms
  • Consolidation may be accomplished by hand
    tamping and rodding or using mechanical vibration
  • Floating done while mix still in plastic state
    provides a smooth surface

28
Finishing cont
  • Final stage may include
  • Incorporation of materials for toppings (adjust
    the look)
  • Non-slip finish use broom to rough-up the
    surface
  • Patterns accomplished by pressing form patterns
    into surface

29
Reinforced Concrete
  • Concrete has good compression strength but little
    tensile strength
  • Steel excels in tensile strength and also expands
    and contracts at rates similar to concrete
  • Steel and concrete compliment each other as a
    unit

30
Reinforcing Steel Rebar
  • Manufactured as round rods with raised
    deformations for adhesion and resistance to slip
    in the concrete
  • Sizes available from 3 to 18 the size is the
    diameter in eighths of an inch
  • Galvanized and epoxy coatings often used in
    corrosive environments (parking structures
    bridge decks where deicing agents used)

31
Reinforcing Bar
  • Placement, size, spacing, and number of bars used
    vary according to the specific project
  • Markings on bars include
  • Symbol of producing mill
  • Bar size
  • Type steel used
  • Grades (yield ultimate strength grades of 40,
    50, 60, 75 common)

32
Welded Wire Reinforcing
  • Also may be used as a reinforcement in concrete
  • 2 sets of wires are welded at intersections to
    forms squares/rectangles of a wire mesh

33
Pre-Cast Concrete
  • Individual concrete members of various types cast
    in separate forms before placement (may be at job
    site or another location)
  • Walls and partitions are often made of pre-cast
    units

34
Pre-Stressed Concrete
  • Concrete which is subjected to compressive
    stresses by inducing tensile stresses in the
    reinforcement
  • Attributes
  • Concrete strength is usually 5,000 psi at 28 days
    and at least 3,000 psi at the time of
    pre-stressing.
  • Use hardrock aggregate or light weight concrete
  • Low slump controlled mix is required to reduce
    shrinkage

35
Advantages of Pre-Stressed Concrete
  • Smaller dimensions of members for the same
    loading conditions, which may increase clearances
    (longer spans) or reduce story heights
  • Smaller deflections
  • Crack-free members
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