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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

Noteworthy:

The Hoover Dam, outside Las Vegas, Nevada, was built in 1936. 3 ¼ million cubic yardsof concrete were used to construct it.

The History of Concrete: Textual

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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 belowhttp://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.