concrete and masonry construction

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– Expensive– Low insulation volume

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.

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.

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

Portland cement manufacturing

Portland cement manufacturing

Portland cement manufacturing

Portland cement manufacturing

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

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.

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.

Water for making concrete should be clear, free of acids, alkalis, oils, and organic matter.

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.

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.

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.

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

Excessive amounts of silt or organic matter prevents a secure bond between the paste and aggregate.

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.

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

Slump is the measure of concrete consistency.

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.

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

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 = ?

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.

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

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.

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.

The actual yield of concrete is 60% of the volume of the total volume of materials.

Concrete Yield Example

Determine the yield of a 7 gal/sack concrete mixed using a

maximum aggregate size of 1½ inches.

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.

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.

Before pouring concrete, the job site must be properly prepared.

Remove the soft spots and fill them with soil, gravel, or crushed rock.

Grade area to approximate slope.

Excavate the site about three or more feet then backfill with compact material to prevent foundation sinking.

Construct forms for footing, foundation, and/or floor slab.

Wood forms should be oiled with form oil or used crankcase oil prior to concrete placement.

Immediately after the concrete is in place, it is struck off with a straight edge board, known as screeding.

Soon after screeding, the surface may be floated (smoothed) with a darby or bullfloat.

Forms may be removed from fittings or foundations in 24 hours; slabs and beams need in four to five days.

Curing is the time needed to complete the chemical reaction between portland cement and water.

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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.

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.

Stretchers are used for the bulk of the wall.

Corner blocks have one square end for wall corners.

Half blocks are used in alternate rows at openings.

Sash blocks have vertical grooves in one end for metal sashes.

Jamb blocks have 2 in by 4 in openings cut out at one end for a door jamb or wooden window sash.

Bull nose blocks have one rounded corner for smooth wall openings.

Partition blocks are for inside walls subject to small loads.

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.