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Concrete. Major Topics. History Uses Materials Used To Make Concrete Cement Aggregate Water Admixture. Major Topics con’t. Testing Slump Test Compressive Strength Test Air Content Test Strength Placing. Major Topics con’t. Transporting Curing Finishing Reinforced Concrete

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Major Topics

  • History

  • Uses

  • Materials Used To Make Concrete

    • Cement

    • Aggregate

    • Water

    • Admixture


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Major Topics con’t

  • Testing

    • Slump Test

    • Compressive Strength Test

    • Air Content Test

  • Strength

  • Placing


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Major Topics con’t

  • Transporting

  • Curing

  • Finishing

  • Reinforced Concrete

  • Pre-cast Concrete

  • Pre-Stressed Concrete

  • ICF (Insulated Concrete Form)


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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.


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Concrete Resources

Concrete Admixtures - The Concrete Network


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Uses

  • Foundations and Driveways

  • Architectural Details

  • CMU (Concrete Masonry Units)

  • Concrete Roofing (Arches & Domes)

  • Columns, Piers, Caissons

  • Walls and Beams

  • Bridges


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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


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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


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Aggregate

  • 2 classes

    • Fine – sand; < 1/4 “ 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


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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


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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


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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


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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


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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


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Admixtures con’t

  • 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


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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


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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


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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)


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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 – 19,000 psi used in columns for high- rise buildings


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Placing Concrete

  • Temperature

    • Optimum temperature for curing is 75 degrees F; may have problems curing if temperature below 50 degrees F. If temperature is lower or higher than normal curing ranges special provisions must be made.

  • Forms

    • Wood and metal commonly used (reused)

    • Clean and sufficiently braced to withstand the forces of the concrete being placed

    • Concrete weighs 135 – 160 pcf; if lightweight then 85 – 115 pcf; often in estimating the figure 150 pcf is used


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Placing Concrete con’t

  • Free falling distance should not exceed 4 feet due to the threat of “segregation” of aggregates occurring***

    ***This is according to the author (see page 103)

    In 2001 the ACI (American Concrete Institute) published research to indicate this is not the case


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Transporting Concrete

  • Method selected depends on quantity, job layout, and equipment available

    • Chutes

    • Wheelbarrows/Buggies

    • Buckets

    • Pneumatically forcing through a hose (shotcrete)

    • Pumps


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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


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Evaporation of Water Reduced by:

  • Cover with:

    • Wet burlap or mats

    • Waterproof paper

    • Plastic sheeting

  • Spray with curing compound

  • Leave concrete in forms longer


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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


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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


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Finishing con’t

  • 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


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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


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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)


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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)


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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


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Pre-Cast Concrete

  • Individual concrete members of various types cast in separate forms before placement (may be at job site or another location)

    • Tilt-up slabs are often pre-cast in the field

  • Walls and partitions are often made of pre-cast units


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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


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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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ICF’s

  • Insulated Concrete Forms

  • Combines the properties of concrete with the advantages of insulating material


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History: What is an ICF?

  • An ICF is basically a concrete wall that is constructed by using formed in place concrete forms.

  • A resistive foam insulation, such as polystyrene, is added to the product.

  • Since the pressure of wet concrete is high, specialized form ties are used. They also allow for the attachment of finishes later in the construction process.


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History cont.

  • The ICF technology was first established in the European marketplace in the late 60’s.

  • Mr. Werner Gregori patented a “Foam Form of Canada” in March of 1966.

  • The Europeans then took his idea to the scale that it is used today.

  • Canadian Energy Conservation policies helped build a strong market for ICF’s in Canada.


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History cont.

  • As problems such as high winds, high energy bills, fires, and other natural disasters in the United States, ICF became more popular.

  • ICF’s were sold as an alternate building material since the 1970’s.


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Characteristics of ICF

  • Polystyrene

  • Foam pieces contain: Plastic or steel components


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Uses of Material

  • Commercial

  • Residential


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Specific Uses

  • Commercial

    • Doctor’s Offices

    • Malls

    • Industrial Park Buildings

  • Residential

    • Homes

    • Basements


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Types of ICF’s

  • I-Form

  • E-Form

  • C-Deck


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Types: I-Form

  • Universal Design

  • 6” on Center Tie Placement

  • Loose Fir, Two Deep Snap-In Rebar

  • Multiple Rebar Positioning

  • Quick Concrete Flow

  • Superior Tie Fastening Device

  • Recessed, Full-Length Tie

  • Open 1” Tooth Design

  • Versatile Sizes

  • Universal 90 degrees and 45 degrees Corners

  • Corner Tie for Attaching Finishes


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Types: E-form

  • Perfect curing environment

  • Ship lap joints

  • Full-length tie

  • Efficient Installation

  • Quick Concrete Flow

  • Handy Rebar Chair

  • Trusted Design

  • Versatile Sizes

  • Molded 90 degrees and 45 degrees Corners


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Types: C-Deck

  • Customized System

  • Lightweight Materials

  • Self-Supporting Panels

  • Insulate Without Thermal Bridges

  • Built-in Ventilation Ducts & Utility Passages

  • Minimize Floor Thickness

  • Easy to Finish


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Sizes

  • Panels often come in sizes of:

    • 4’ x 8’

    • Planks—1’ x 8’

    • Block forms—16” x 4’

  • When delivered to the job site they are in separate 2” thick planks of form and then they are snapped into the wall with plastic crosspieces called ties.


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Advantages for Builder

  • Stability

  • Versatility

  • Accuracy

  • No Moving Parts

  • Lighter weight

  • Design Simplicity/ Easy to use

  • Easily to form curves and ties

  • Cost Competitive

  • Internationally Proven & Code-Accepted


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Advantages for Homeowner

  • Greater comfort & lower energy bills

  • Reduces heating and cooling loads

  • Solid & lasting security

  • Peace & quiet

  • Less repair & maintenance

  • Healthier home and environment


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Disadvantage

  • As it existed 30 yrs ago the same types of challenges exist today.

  • The challenge is to convince an industry that does not readily accept change and to try something new by using ICF rather than the conventional construction.


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Why Consider ICFs?

  • ICF has become increasingly popular for several reasons:

  • Energy savings for ICF homes are in the neighborhood of 20% in comparison to wood frame homes which meet only minimum thermal insulation requirements.


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Why consider ICF’s (cont.)

  • Structural stability and soundness is also another major advantage of the ICF structure.

  • Studies have shown, noise levels from exterior sources tend to be lower in the interior of ICF homes. Design considerations such as “sound tightness” and number of windows and doors help the overall noise reduction.


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Application/Installation

  • Most important step is correctly installing footings.

  • They should be smooth, square, and level.

  • A line is chalked inside and outside the edges of a wall.

  • Vertically rebar reinforcements are critical to the strength of an ICF wall.

  • Light gauge metal guides are placed horizontally against the footings to hold the ICF form straight.


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Application cont.

  • Vertical rebar is tied to reinforcement dowels.

  • Minimum bracing is required every 10’ of wall space where there are no windows or doors to support the forms while the concrete is being poured and cured.

  • Place all door and window framing in place making sure they are securely braced, level, and plumb.


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Application cont.

  • Installation of a ledger board allows framers to correctly lay out floor joist as required (several method are required).

  • Concrete is then pumped in multiple lifts approximately 4’ high to insure proper consolidation of concrete.

  • After proper curing an approved basement exterior sealant that is compatible with expanded polystyrene is applied to the exterior walls.


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Application cont.

  • Stucco may be applied directly to the exterior walls or the recessed fastening strips are clearly marked by raised beads to attach wood, vinyl, or metal siding or any type masonry that is desired.

  • Any desired interior wall finish may be attached directly to furring strips with regular drywall screws.


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Related Technologies

  • ICF have been recognized by the American Lung Association for its participation for clean air environment.

  • ICF withstand measure wind speeds of more than 200 mph with virtually no wind damage.

  • In fire tests, ICF withstood intense flames and heat for as much as 4 hrs.


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Related Technologies (cont.)

  • ICF have been engineered to have excellent performance seismic zones.

  • ICF wall systems have been singled out by the American Architectural Review for promoting progress in the world of Architecture.


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New Developments

  • As technology advancements in technology, many companies are starting to manufacture ICF.

  • The number of ICF’s are increasing, it is estimated that between 23 and 40 manufacturers exist in North America.


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Additional Concrete Products

  • Stamped concrete

  • Flowable fill

  • Pervious concrete

  • Tilt-up

  • Translucent concrete—for information about this click on the link below

    http://www.litracon.hu/


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References

  • Construction Materials and Processes, 3rd Edition. Watson, Don A.. McGraw-Hill, 1986. Imprint 2000. ISBN: 0-07-068476-6

  • Construction Principles, Materials, and Methods, Seventh Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2001.

  • Architectural Materials for Construction, Rosen, Harold J. and Heineman, Tom. McGraw-Hill, 1996. ISBN: 0-07-053741-0

  • Basic Construction Materials, 6th Edition. Marotta, Theodore W. Prentice Hall, 2002. ISBN: 0-13-089625-X

  • Building Construction: Materials and Types of Construction, 6th Edition,Ellison, Donald C., Huntington, W.C., Mickadeit, Robert E.. John Wiley & Sons. ISBN: 0-13-090952-1.

  • Architectural Graphic Standards: Student Edition, Abridgment of 9th Edition. The American Institute of Architects. John Wiley & Sons. ISBN: 0-471-34817-1


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References

  • Concrete Homes and Buildings. (1998). Insulated Concrete Forms (ICF). Retrieved March 15, 2003 from www.crmca.org/ICF/default.htm.

  • Eco-Block Installation Manual

  • Reward Wall Systems. (2002). www.rewardwalls.com.

  • ICF Web. (2001). www.icfweb.com.

  • NAHB Research Center. (2001-2003). www.nahbrc.org.

  • Alby Material Incorporated. www.alby.com.

  • American Conform Industries. (2003). Smartblock. www.smartblock.com.

  • Insulating Concrete Form Association. www.forms.org.


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