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 • Pre-cast Concrete • Pre-Stressed Concrete • ICF (Insulated Concrete Form)
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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Uses • Foundations and Driveways • Architectural Details • CMU (Concrete Masonry Units) • Concrete Roofing (Arches & Domes) • Columns, Piers, Caissons • Walls and Beams • Bridges
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
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
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
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
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
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
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
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
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
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
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
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)
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
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
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
Transporting Concrete • Method selected depends on quantity, job layout, and equipment available • Chutes • Wheelbarrows/Buggies • Buckets • Pneumatically forcing through a hose (shotcrete) • Pumps
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
Evaporation of Water Reduced by: • Cover with: • Wet burlap or mats • Waterproof paper • Plastic sheeting • Spray with curing compound • Leave concrete in forms longer
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
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
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
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
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)
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)
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
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
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
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
ICF’s • Insulated Concrete Forms • Combines the properties of concrete with the advantages of insulating material
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.
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.
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.
Characteristics of ICF • Polystyrene • Foam pieces contain: Plastic or steel components
Uses of Material • Commercial • Residential
Specific Uses • Commercial • Doctor’s Offices • Malls • Industrial Park Buildings • Residential • Homes • Basements
Types of ICF’s • I-Form • E-Form • C-Deck
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
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
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
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.
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
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
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.