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Concrete and MasonrySection 13

Unit 39

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Introduction

• Most buildings have concrete and/or masonry

components.

• The ability to use concrete and masonry materials is an

essential skill for construction and, repair and

maintenance of buildings.

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Concrete

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Concrete

• Concrete is “a mixture of stone aggregates, sand, Portland

cement, and water that hardens as it dries.”* Concrete does not dry, it goes through a chemical reaction

called hydration.

*Agricultural Mechanics, Herren

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Concrete - cont.

Advantages

– Fireproof

– Insect & rodent proof

– Decay resistant

– Storm resistant

– Wear resistant

– Waterproof (water resistant)

– Strong

– Attractive

– UV resistant

– Doesn’t require expensive equipment.

– Available locally

– Low original and maintenance costs

– Sanitary and easy to keep clean

– Recyclable

Concrete is truly a versatile building material. It can be formulated with very specific performance characteristics in mind and include lightweight, heavyweight, porous, fiber-reinforced, mass, high-performance and cellular concretes.

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Concrete - cont.

Disadvantages

– Labor intensive

– Requires moving a lot of weight

– Requires forms

– Dense material

– Special skills required to place and finish

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Seven (7) Characteristics of Concrete

7. Resistant to freezing and thawing

6. Weak in tension

5. Very strong in compression4. Fire resistant

3. Resists manures and most chemicals.

2. Resists attack by water1. Durable

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Def: The ability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties.

Characteristic 1Durability

Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete.

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Characteristic 2

Resists Attack by Water

Watertightness: the ability of concrete to hold back or retain water without visible leakage.

Permeability: the amount of water migration through concrete when the water is under pressure or the ability of concrete to resist penetration by water or other substances.

Two characteristics; watertightness and permeability.

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Characteristic 2 Resists Attack by Water -cont.

1. Permeability of the paste

2. Permeability and gradation of the aggregate

3. Quality of the paste

4. Quality of the paste--aggregate transition zone

5. Relative proportion of paste to aggregate

Factors that affect permeability and water tightness include:

Low permeability concrete requires a low water-cement ratio.

Moist curing also reduces permeability.

The same properties of concrete that make it less permeable also make it more watertight.

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Characteristic 3

Resists manures and most chemicals.

1. Good quality concrete is resistant to the acids of manure.

2. Concrete is very alkaline, pH is usually greater than 12.5.

3. Resistance can be increased with surface treatments.

4. Concrete is susceptible to deterioration by sulfates.

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Characteristic 4

Fire Resistant

The strength of concrete will deteriorate with high temperatures.

1. Concrete provides the best fire resistance of any building material.

2. It does not burn, it cannot be 'set on fire' like other materials in a building and it does not emit any toxic fumes, smoke or drip molten particles when exposed to fire.

3. Concrete and its mineral constituents enjoy the highest fire resistance classification.

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Characteristic 5

Strong in Compression

The compressive strength depends on:1. The strength of the aggregate2. Proportion of aggregate sizes3. Type of Portland cement4. Purity of water5. Uniformity of mixture6. Procedures used in placing,

finishing and curing

Material Compressive

Strength (lb/in2)

Concrete 25,000 Wood* 2 – 4,000 Stone Granite 10,000 Limestone 10,000 Marble 10,000 Sandstone 5,000 *Parallel to the grain

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Compressive Strength Influenced by Water/cement Ratio

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Characteristic 6

Concrete is weak in tension

Does this table and picture show why steel reinforcement is use in concrete?

Material Tension Strength

(lb/in2) Concrete 2,500 Wood* 10 – 15,000 Steel 50 – 70,000 *Parallel to the grain

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Characteristic 7

Concrete is resistant to freezing and thawing

The resistance decreases as the permeability increases.

When concrete spaces are 91% or more full of water, freezing

will damage the concrete.

When water freezes to ice it occupies 9% more volume than

that of water.

Air entrained concrete is less permeable.

Example of freezing damage:

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Concrete Constituents

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Concrete Constituents

Concrete: a mixture of aggregate and Portland cement paste.

Aggregate: usually sand, gravel and/or crushed stone.

Process: the paste binds the aggregates into a rocklike mass as the paste hardens because of the chemical reaction (hydration) of the Portland cement and water.

Paste: Portland cement and water

Proportion of Constituents

• Basic concrete mix:– Air 6%

– Portland cement 11%

– Coarse aggregate 41%

– Fine aggregate 26%

– Water 16%

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Admixtures

“Admixtures are materials other than cement,

aggregate and water that are added to concrete

either before or during its mixing to alter its

properties, such as workability, curing temperature

range, set time or color.” (http://www.toolbase.org/)

“Admixtures cannot compensate for bad practice and low quality materials.”

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Admixtures - cont.

• Addition of fiber to concrete makes it tough and fatigue resistant. Such type of admixtures are used extensively in important engineering projects.

Common admixtures Retarding admixtures

Accelerating admixtures

Super plasticizers

Water reducing admixtures

Air-entraining admixtures

Additional admixtures Bonding,

Shrinkage reduction,

Damp proofing and

Coloring.

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Types of Cement

Different types of Portland cement are manufactured to meet many different applications of concrete.

Type I Normal

Type IA Normal, air-entrained

Type II Moderate sulfate resistance (MSR)

Type IIA MSR, air-entrained

Type III High early strength (HES)

Type IIIA HES, air-entrained

Type IV Low heat of hydration

Type V High sulfate resistance

Types I & IA are the most common.

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Air Entrained

Developed during the 1930’s

Recommended for nearly all concretes that are exposed to freezing and thawing, and deicing

chemicals.

Produced by using air-entraining cement or by using an air-entraining admixture.

Spalding is a characteristic of using concrete without air entrainment.

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1. Increased freeze-thaw resistance

2. Increased deicer-scaling resistance

3. Improved sulfate resistance

4. Equivalent Strength

5. Improved workability

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Aggregate

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Aggregate

• Concrete should include at least two different sizes of aggregate--fine and coarse.– Fine = 1/4 inch or less (not to include fines)

– Coarse = 1/4 to 2 inch

• Standard practice is to crush stone and the use screens to separate the sizes.– The correct proportion of fine aggregate and coarse aggregate can

then be mixed together.

• Aggregate should be 60 to 80 % of the volume. (cheapest material).

• Stream bank aggregate must be tested for excessive silt and clay. (page 557, Fig 39-2)

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Aggregate-cont.

Aggregate diameter must not exceed 1/5 of void in forms were rebar is used.

The largest recommended aggregate size is 2 inches for most applications.

Aggregate diameter must not exceed 1/3 of slabs that do not use rebar.

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Purchasing Concrete

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Purchasing Introduction

• For large jobs in is common practice to have the concrete delivered to the site.

• The cost of having concrete delivered is determined by:• Quantity• Mix• Minimum charge• Unload fee• Mileage fee

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Purchasing Concrete - Quantity Needed

• Quantity needed Concrete is sold by the cubic yard (yd3). To determine the quantity need calculate the volume

in cubic inches (in3) or cubic feet (ft3) and convert to cubic yards (yd3 or just yd). 27 ft3 = 1 yd 46656 in3 = 1 yd

Common practice to add 5 to 10% for waste and volume errors.

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Purchasing Concrete – Quantity - Example

• Determine the yards of concrete that will be required to pour a driveway that is 26 feet wide, 120 feet long and 6 inches thick.

• Solution:

€

ft3 = 26 120 6 ft x ft x in x1 ft12 in

= 1, 560 ft3

€

yd3 = 1560 ft3 x1 yd3

27 ft3= 57.777... 58 or yd3

• Adding 10%.

€

58 yd3 1.1x = 63.8 64 or yd3

Purchasing - Mix

• Two factors which determine the ideal mix.– Environment

– Intended use

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• Environmental factors– Soil phosphates

– Freeze – thaw

– De-icers

• Use factors– Maximum Load

– Vibration

Purchasing – Basic Mix

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Purchasing – Slump

• The inches of slump indicates the water-cement ratio and the quality of the concrete.

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Concrete ConstructionSlump, in.

Maximum Minimum

Reinforced foundations walls and footings 3 1

Plain footings, caissons, substructure walls 3 1

Beams and reinforced walls 4 1

Building columns 4 1

Pavements and slabs 3 1

Mass concrete 3 1

Slump is determine through a slump test.

Slump - Test

• A slump test is conducted using an Abram’s cone, slump cone.

• A slump cone is 8 inches in diameter at the bottom, 4 inches in diameter at the top and 12 inches tall.

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Slump Test – cont.

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• Steps:

1 Moisten cone

2 Place cone on moist, smooth non absorbent level surface that is larger the the lugs on the cone.

3 While standing on the lugs, fill the cone 1/3 and uniformly rod 25 times.

4 Fill the cone 2/3 full and rod the 25 times insuring the rod just penetrates the first layer.

5 Over fill the cone and rod 25 times

6 Strike off the excess with the rod.

7 Slowly lift the cone vertically and place on surface beside concrete.

8 Place rod across the top of the cone and the concrete and measure the distance from the bottom of the rod to the surface of the concrete.

9 This distance is the inches of slump.

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Mixing Concrete

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Introduction

• Small jobs can be mixed at the site.

• Concrete weights over 4,000 pounds per cubic yard.

• Therefore, it is important to determine amount of

concrete first, because even a small volume of concrete

can require moving a lot of material.

• Using Quikcrete is a popular option to reduce the work.

For more information go to:http://www.nrmca.org/aboutconcrete/

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Mixing Concrete

• Characteristics of good mix:1. Each aggregate particle is covered with cement paste

2. Each aggregate particle is bound to others

• Cement paste– Water--cement ratio must be exact proportions.

– Water in aggregate must be accounted for and deducted from water added to mix.

• Water--cement ratio must be adjusted for different service conditions.

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Concrete Mixes

€

1 ⋅2 ⋅2 - 1/4 1 = 1 ft3 (sack) of Portland cement 2 = 2 ft3 of fine aggregate2-1/4 = 2.25 ft3 of coarse aggregate

• The proportions of water, Portland cement, fine aggregate and

course aggregates are not the same for all concrete jobs.

• When mixing concrete it is common to express the mix (receipt)

as a proportion. For example:

• The proportions can be used on a volume or weight basis

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Proportions

• The proportions must be changed to meet the service conditions.

Intended use Cement

Fine Aggregate

Coarse Aggregate

Mild Exposure 1 3 4

Normal Exposure 1 2-1/4 3

Severe Exposure 1 2 2-1/4

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Mixing--cont.

• The amount of water in the aggregate must be included in the calculations.

• Effect of water in aggregate. (Fig 39-3)

Intended Use

Maximum Aggregate Size (in)

Water (gal) added to 1 ft3 of cement if sand is:

Suggested Mixture for 1 ft3 Trial Batch

Cement (ft3)

Aggregates

Damp Wet Very Wet

Fine (ft3)

Coarse (ft3)

Mild 1-1/2 6-1/4 5-1/2 4-3/4 1 3 4

Normal 1 5-1/2 5 4-1/4 1 2-1/4 3

Severe 1 4-1/2 4 3-1/2 1 2 2-1/4

Water vs. strength

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Effect of Adding Water

• Adding 1 gal of water to 1 yd3 of concrete:– Increases slump 1 inch

– Decrease compressive strength by 200 psi

– Increases shrinkage by 10%

– Increases permeability by up to 50%

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Estimating Materials - By Volume

• Determine the amount of materials that will be required to pour a concrete slab that measures 12 ft x 10 ft x 3 in. A 1-2.1/2-3.1/2 mix will be used. Step one: determine the volume required.

€

ft3 = 12 10 ft x ft x3 in x1 ft12 in

⎛ ⎝ ⎜

⎞ ⎠ ⎟

= 30 ft3

• Adding the 10% =

€

30 ft3 1.1x = 33 ft3

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Estimating Materials - By Volume - cont.

Because the aggregate mixes together, the yield by volume will only be about 2/3’s of the total volume.

€

1 + 2.5 + 3.5( ) = 7.0 ft3

Step two: determine the yield of one batch of the receipt.

€

7.0 ft3 0.66x = 4.62 ft3 Step three: determine the number of batches required.

33 cubic feet of concrete is required, each one sack batch will yield 4.62 cubic feet.

The number of batches =

€

Batches= 33 ft3 x1 batch

4.62 ft3= 7.14 batches

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Estimating Materials - By Volume - cont.

• Step four: determine the Portland cement, fine aggregate and coarse aggregate.

€

Portland Cement: 1 7.14x = 7.14 sacks

Fine aggregate: 2.5 7.14x = 17.8 ft3

Coarse aggregate: 3.5 7.14x = 25 ft3

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Concrete Mixes--cont.

• When concrete ingredients are measured using weight, density

conversions must be used.

– Portland cement = 94 lb/ft3 (100 lb/ft3 often used)

– Fine aggregate = 100 lb/ft3

– Coarse aggregate = 110 lb/ft3

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Estimating Materials - By Weight

• Determine the amount of materials that will be required to pour a concrete slab that measures 18 ft x 12 ft x 4 in. A 1-2.-3.1/2 mix will be used. Step one: determine the volume required.

€

ft3 = 18 12 ft x ft x4 in x1 ft12 in

⎛ ⎝ ⎜

⎞ ⎠ ⎟

= 74 ft3

• Adding the 10% =

€

74 ft3 1.1x = 81.4 ft3

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Estimating Materials - By Weight - cont.

Step two: determine the yield of one batch.

€

1 + 2 + 3.5 = 6.5 ft3

6.5 ft3 0.66x = 4.29 ft3

Step three: determine the number of batches.

€

Batches= 81.4 ft3 x1 batch

4.29 ft3= 23.26 batches

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Estimating Materials - By Weight - cont.

• Step four: determine the amount of cement, fine aggregate and coarse aggregate.

€

Portland Cement: 1 23.6x = 23.6 94sacks xlb

sack= 2, 218. 4 lb

Fine aggregate : 2.0 x 23.6 = 47.2 ft 3 x 100lb

ft3= 4, 720 lb

Coarse aggregate : 3.5 x 23.6 = 82.6 ft 3 x 110lb

ft3= 9, 086 lb

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Workable Mix

• Workability of concrete refers to the consistency of the wet concrete.– Wetter concrete is more workable, but the higher the water

content--the poorer the quality of the concrete.

• Characteristics of a workable mix:1. Portland cement thoroughly mixed

2. Aggregate fully covered

3. Aggregates evenly distributed

4. Minimum amount of water

5. Uniform color and consistency

6. Can be mixed, moved and placed with a shovel or spade

Curing rate

Concrete gains strength rapidly at first but continues to cure for years.

Industry standard is to compare strength at 28 days.

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Preparing Concrete Forms

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Concrete Forms

• Form: a metal or wooden structure that confines the concrete to the desired shape or form until it hardens.

• The more complex the shape of the concrete--the more complex the forms.

• Normal concrete weights between 100 & 150 lb/ft3, therefore any forms supporting the weight of concrete must be well engineered.

• Forms can be constructed from dimensioned lumber and plywood, or in some cases, metal forms can be purchased or rented.

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Concrete Forms Information

1. Use soft, clean straight lumber.

2. Sharpen stakes evenly.

3. Space stakes appropriately.

4. Use a level to set the forms for

the desired slope.

5. Do not drive nails into concrete

space.

6. Insure stakes do not extend

above the tops of the forms.

7. Construct the inside surface of

the forms to create the desired

shape in the finished concrete.

8. Coat all surfaces that will be in

contact with the concrete.

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Concrete Forms--Wall Example

Board Tie

1” Boards or 3/4 Plywood

Brace

Spreader Block

Wire Tie

Stud

Concrete Footing

Stake

Wale

Agricultural Mechanics Fundamentals & Applications Herren--Fig 39-7

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Concrete Forms--Slab Example

Form

Wall Stake

Control JointConcrete

Straightedge

Packed Damp Sand

Agricultural Mechanics Fundamentals & Applications Herren--Fig 39-7

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Concrete Joints

• Three (3) types of joints are used for concrete.

– Isolation joints: allow expansion and contraction of a concrete slab without generating potentially damaging forces within the slab itself or the surrounding structures

– Control (Contraction) joints: this type of joint allows only for contraction or shrinkage of the slab, as can be anticipated during the curing process

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Concrete Joints-cont.

• Construction joints: Construction joints can be horizontal or vertical and are formed when placement of the concrete is interrupted for some reason. It may be the end of a day's

work or May be that some other work

needs to be completed before resuming the placement.

New concrete is placed against concrete that has solidified or skimmed over.

Butt

Dowel

Key

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Reinforcing Concrete

• Concrete is strong in compression, but weak in tension.• Reinforcement is used to increase the tension strength.

• The type, size and spacing of the reinforcement is determined by the thickness of the slab and the designed load.

• Fibers are also being used to reinforce concrete.

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Pouring, Finishing, and Curing Concrete

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Pouring (Placing)

• Concrete should be placed--not poured.• Concrete must be placed as closes to the final location as

possible.– Heavy--labor intensive to move.– Moving causes the aggregate to segregate.

• Inspect forms and bracing before starting the placing.• Insure all of the tools and help are available and ready before

starting.– Starts to harden in 15 minutes– Once in place and hardening process has started--its there.

• Ensure concrete does not dry out.– Dampen the soil/sand base before placing.– Protect top surface after placing.

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Finishing Concrete

• The number of processes and type of process used is determine by the desired finished surface. Trowel Broom Exposed aggregate Grooved Stamped Burlap Etc.

• The finishing process has at least Four (4) steps.• Screeding• Floating• Final surface• Edging & jointing

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(1) Screeding & (2) Floating Concrete

The process used is determined by the use of the concrete and the desired finished surface.

1. Screeding– Screeding is striking off the concrete

surface to insure it is level with the forms

– Pushes large aggregate below the surface

– Starts the smoothing process

– Can be accomplished with a straight board

2. Floating– Brings fine aggregate and cement paste

to the surface

– Produces smoother surface

– Uses a wooden or magnesium float– Floating should not be attempted until the concrete has hardened to

the point that stepping on it makes a very faint imprint.

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(3) Finishing Concrete

• Many options are available for the finished surface of concrete.– Molded

• Individual• In forms

– Stamped

– Exposed aggregate

– Colored

– Smooth surface

– Rough surface

– Other

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(4) Edging & Jointing

Part of the finishing process may also be edging and jointing

Edging forces the large aggregate away from the corner and rounds the corner.

Reduces breakage on the edge.

Jointing

Edging

The groove cut or formed or cut in the surface helps control the location of the cracks.

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Curing Concrete

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Curing Concrete

• Concrete hardens through a chemical process.– Initial strength is reached in a week.

– Must be protected during this time

• Potential problems.

1. Drying out

2. Excessive heat

3. Freezing temperature

• Solutions

1a. Dampen base/forms before placing

1b. Cover with plastic or canvas

2a. Insulate the surface

2b. Dampen the surface

3a. Don’t place on frozen ground

3a. Don’t place when freezing temperature is expected

Curing Rate

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Days

%28Days

Effect of Curing conditions

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Days

%of28Days

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Masonry

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Introduction

• Masonry is “Any type of construction using brick, stone, tile or

concrete units held in place with Portland cement.”• Masonry units are held in place with mortar

– Mortar = Portland cement, sand and water

– Other materials may be added.

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Masonry Construction

• Ancient method of construction.

• Advantages:– Fireproof

– Insect and rodent proof

– Decay resistant

– Storm resistant

– Wear resistant

– Water (proof) resistant

– Strong

– Attractive

– Can be installed without expensive equipment

– Available locally

– Low original and maintenance costs

– Recyclable

• Disadvantages:– Strength, durability and

water resistance of finished product dependent on strength, durability and water resistance of masonry units.

– Labor intensive

– Different skills required than for wood frame or concrete.

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Masonry Units

• Building bricks

• Pavers

• Custom bricks

• Stone

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Masonry Units-cont.

• Concrete blocks (Fig 39-15)

• Light weight blocks

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Additional Topics

• Estimating number of block needed

• Constructing footers

• Mixing mortar

• Laying block

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Questions