concrete and masonry construction
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Concrete and Masonry Construction. BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay. Concrete has several properties that make it well suited for a wide variety of agricultural uses. Advantages: Plastic when first mixed Durable Sanitary Low maintenance Disadvantages: Heavy - PowerPoint PPT PresentationTRANSCRIPT
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Concrete and Masonry Construction
BSE 2294
Animal Structures and Environment
Dr. Susan Wood Gay
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Concrete has several properties that make it well suited for a wide variety of agricultural uses.
• Advantages:– Plastic when first mixed– Durable– Sanitary– Low maintenance
• Disadvantages:– Heavy– Expensive– Low insulation volume
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Concrete is composed of two components: paste and aggregate.
• Paste– Portland cement– Entrained air– Water
• Disadvantages– Heavy– Expensive– Low insulation value Cement plant in Iola, Kansas.
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Portland refers to the type of cement that is universally produced by all manufacturers.
• Carefully controlled mixture of:– Lime– Silica– Alumina– Iron oxide
• Burned and ground into fine powder
Stone quarries on the Island of Portland.
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Portland cement components
Portland Cement
Clinker
Clay
Gypsum
Shale
Limestone Cement Rock
Oyster Shells Coquina Shells
Silica Sand Iron Ore
Marl Shells Marl River Deposits
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Portland cement manufacturing
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Portland cement manufacturing
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Portland cement manufacturing
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Portland cement manufacturing
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Portland cement is available in five types as designated by ASTM.
Type Description
I Normal cement; suitable for general construction
II Modified cement; low heat-producing for very large concrete structures
III High-early-strength cement; hydrates rapidly for cold weather application
IV Low-heated cement; lower heat of hydration than Type II for large masses of concrete such as dams
V Sulfate-resistant cement; resists damage due to the high sulfate content of water
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Entrained air is important for good quality concrete.
• Uses less sand and water
• Reduces segregation
• Improves workability
• May be finished earlier
• Increases water tightness
• Resists freezing and thawing
• Resists surface scaling One cubic yard of concrete can contain 400 to 600 billion air bubbles.
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Normal portland cement is suitable for most farm and general construction work.
• 1 sack = 94 lbs or 1 ft3
• Dry storage is essential
• Do not use cement that contains lumps
Common products for home concrete use.
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Water for making concrete should be clear, free of acids, alkalis, oils, and organic matter.
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Both the cost and quality of the concrete are affected by the kind of aggregate selected.
• Aggregate should be:– Clean– Hard– Strong
• Sharp, rough, or flat aggregate requires more cement-water paste
• Fractured material severely reduces strength
Gravel Quarry in Southern Ontario.
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Aggregates size is determined by screening material through a Number 4 sieve.
• Number 4 sieve – ¼ inch openings – 16 openings/in2
• Fine aggregate – passes through a Number 4 sieve
• Coarse aggregate – does not pass through a Number 4 sieve Inclined aggregate screen.
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The use of well-graded aggregates will produce an economical mixture with the least amount of cement.
• “Well-graded” – a variety of materials ranging in sizes:– Fine sand– Coarse sand– Small stones
• Allows small particles to fill voids between large particles
• Use of aggregates from gravel banks not recommended
Well-graded aggregate fit together so perfectly that a minimum of paste is required.
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The maximum size of aggregate used depends on the size and shape of the structure and the distribution of rebar.
Structure Type Aggregate Size
Walls or columns ≤ 1/5 minimum dimension of the member
Slabs ≤ 1/3 slab thickness
Reinforced concrete ≤ 3/4 space between rebar
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Excessive amounts of silt or organic matter prevents a secure bond between the paste and aggregate.
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A silt test can determine whether aggregate should be washed.
• Glass jar– 2 inches of aggregate– 6 inches of water
• Shake vigorously and let stand for one hour
• If more than 1/8 inch of silt has settled at the top of aggregate – wash or abandon
2 in
1/8 in
Aggregate
Silt
The silt layer is only 1/8 in; therefore theaggregate is useable without washing.
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An organic matter test can determine whether aggregate should be washed.
• Glass jar– ½ pint of water– ½ pint of aggregate– 1 teaspoon lye
• Stir and let stand for 3 to 4 hours
• Observe color– Clear to light straw – use– Dark straw – do not use
The samples on the left and in the middle are useable; the sample on the right is not .
Free of OM
Some OM
Too much OM
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Slump is the measure of concrete consistency.
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Concrete strength is inversely proportional to the amount of water used.
1000
2000
3000
4000
5000
6000
7000
Com
pres
sive
Stre
ngth
(psi
)
07d 90d28d
5 gallons/sack
6 gallons/sack
7 gallons/sack
Moist-cure test at 70 degrees F.
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The concrete mix depends upon the desired application.
Kind of Work Water to Cement
Ratio
Maximum Size of
Aggregate
Mass Ratio (cement:
gravel:sand)
Concrete subjected to severe wear, weather, or weak acid and alkali solutions
5 gal/sack ¾ in
1½ in
1:1.9:2.3
1:1.7:3.1
Floors, driveways, walks, septic tanks, storage tanks, structural beams, columns, and slabs.
6 gal/sack ¾ in
1½ in
1:2.5:2.8
1:2.2:3.7
Foundation walls, footings, mass concrete, etc.
7 gal/sack ¾ in
1½ in
1:3.1:3.3
1:2.8:4.2
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Use the specific density of materials to determine the masses of materials needed for a specific concrete mix.
A 1:1.9:2.3 ratio mix = ?
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The specific gravity (γ) of a substance is a comparison of its density to that of water.
1 cup water 1 cup lead
Each glass contains equal volume of material; however, the glass with lead will weigh more than the glass with water.
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The density of a material is calculated by multiplying its specific gravity by the density of water.
γsand/gravel = 2.65
ρH2O = 62.4 pcf
ρsand/gravel = (2.65)(62.4 pcf) = 165.4 pcf
γcement = 3.15
ρcement = (3.15)(62.4 pcf) = 196.6 pcf
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Concrete Volume Example #1
Determine the volume of a one-sack batch of concrete for a
storage tank. The maximum size of aggregate is ¾ inch.
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Concrete Volume Example #2
Determine the amount of concrete needed for a feeding floor 35
ft by 120 ft by 4 in thick. Include 5% for error.
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The actual yield of concrete is 60% of the volume of the total volume of materials.
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Concrete Yield Example
Determine the yield of a 7 gal/sack concrete mixed using a
maximum aggregate size of 1½ inches.
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The purpose of mixing is to achieve a uniform distribution of the ingredients and allow for air entrainment.
• Mixing times:– One minute for ≤ 1 yd3
– One minute plus 15 s/yd3 for large batches
• Mixing order (truck mixers):– Water– Little aggregate– Cement– Balance of aggregate Brand new cement mixing truck.
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Forms should be ready and in place before the concrete is mixed or before the ready-mix arrives.
• Form materials:– Plywood– Steel– Sheathing
• Forms should be:– Clean– Tight– Tied together to prevent bulging Form for concrete column consisting of
plywood and rebar.
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Before pouring concrete, the job site must be properly prepared.
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Remove the soft spots and fill them with soil, gravel, or crushed rock.
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Grade area to approximate slope.
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Excavate the site about three or more feet then backfill with compact material to prevent foundation sinking.
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Construct forms for footing, foundation, and/or floor slab.
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Wood forms should be oiled with form oil or used crankcase oil prior to concrete placement.
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Immediately after the concrete is in place, it is struck off with a straight edge board, known as screeding.
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Soon after screeding, the surface may be floated (smoothed) with a darby or bullfloat.
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Forms may be removed from fittings or foundations in 24 hours; slabs and beams need in four to five days.
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Curing is the time needed to complete the chemical reaction between portland cement and water.
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Fresh concrete develops 40% of its potential strength during the first 14 days of curing; 70% during the first 28.
1000
2000
3000
4000
5000
6000
7000
Com
pres
sive
Stre
ngth
(psi
)
07d 90d28d
5 gallons/sack
6 gallons/sack
7 gallons/sack
Moist-cure test at 70 degrees F.
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Curing is a hydration process; therefore, concrete must not be allowed to dry out during curing.
• Continuously sprinkle with water
• Cover with:– Damp sand– Damp straw– Plastic film
Plastic film over freshly poured slab.
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Concrete must be protected from freezing or excessive heat during the curing process.
• Optimum temperature ~ 75 °F
• Process slows down as temperature decreases
• Curing stops at 32 °F
• Permanent damage if freezing occurs with first 24 hours
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Reinforcing materials improve the strength of concrete structures by carrying tensile loads.
• Transfer of tensile forces
• Materials– Wire mesh– Reinforcing bars (rebar)– Synthetic fibers
Placing rebar and wire mesh prior to pouring.
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Wire mesh is a common reinforcing material for concrete.
• Advantages:– Can be formed into various
shapes– Tensile strength of 60,000 to
70,000 psi
• Disadvantages:– Difficult to install– Expensive– High labor
Wire mesh form.
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Rebar is ribbed steel bars installed in foundation concrete walls, footers, and other poured structures.
• Advantage:– Very high tensile strength
(70,000 to 90,000 psi)
• Disadvantages:– Difficult to install– Expensive– High labor– Cannot weld
Rebar in sealer.
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Synthetic fibers are replacing welded wire mesh, especially in residential slabs.
• Advantages:– Easy to install– Reduce plastic shrinkage cracks
• Disadvantages:– Very low tensile strength
Nylon fibers for concrete reinforcement.
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Walls constructed with concrete blocks bonded together with mortar are described as masonry construction.
• Advantages:– Durable– Fire resistant– Low maintenance– Relatively inexpensive
• Disadvantages:– More porous than concrete– More subject to cracking than
concreteConstruction of concrete block wall.
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The ASTM has developed a set of specifications for masonry blocks.
• Compressive strength:– Type A – 1000 psi (below grade)– Type B – 700 psi (above grade)
• Water absorption limited to 15 lb/ft3
• Moisture content ≤ 40%
• Free from defects
Concrete blocks must meet ASTM standards.
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Actual sizes of concrete blocks are 3/8 inch less than nominal size in each direction.
7 5/8 in
15 5/8 in7 5/8 in
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All dimensions should be planned to be in multiples of blocks or half-blocks.
• Minimize cutting and fitting
• Horizontal dimensions– Half blocks– Whole blocks
• Vertical dimensions– Whole blocks only
Setting concrete blocks.
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Block Dimensions
(in x in x in)Stretcher 8 x 8 x 16
Corner block 8 x 8 x 16
Half block 8 x 8 x 8
Sash block 8 x 8 x 16
Jamb block 8 x 8 x 16
Bull nose 8 x 8 x 16
Partition 4 x 8 x 16
Concrete blocks are available in several shapes.
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Stretchers are used for the bulk of the wall.
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Corner blocks have one square end for wall corners.
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Half blocks are used in alternate rows at openings.
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Sash blocks have vertical grooves in one end for metal sashes.
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Jamb blocks have 2 in by 4 in openings cut out at one end for a door jamb or wooden window sash.
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Bull nose blocks have one rounded corner for smooth wall openings.
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Partition blocks are for inside walls subject to small loads.
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Masonry Block Example
Determine the number of blocks required for the back wall of a
machinery shed. The wall is 40 ft long and 16 ft high.