Concrete and Masonry Section 13 Unit 39

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.

Concrete

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

Concrete - cont. 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. 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 - cont. Disadvantages Labor intensive Requires moving a lot of weight Requires forms Dense material Special skills required to place and finish

Seven (7) Characteristics of Concrete 2. Resists attack by water 1. Durable 3. Resists manures and most chemicals. 4. Fire resistant 5. Very strong in compression 6. Weak in tension 7. Resistant to freezing and thawing

Characteristic 1 Durability Def: The ability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete.

Resists Attack by Water Characteristic 2 Resists Attack by Water Two characteristics; watertightness and permeability. 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.

Characteristic 2 Resists Attack by Water -cont. The same properties of concrete that make it less permeable also make it more watertight. Low permeability concrete requires a low water-cement ratio. Moist curing also reduces permeability. Factors that affect permeability and water tightness include: Permeability of the paste Permeability and gradation of the aggregate Quality of the paste Quality of the paste--aggregate transition zone Relative proportion of paste to aggregate

Resists manures and most chemicals. Characteristic 3 Resists manures and most chemicals. Good quality concrete is resistant to the acids of manure. Concrete is very alkaline, pH is usually greater than 12.5. Resistance can be increased with surface treatments. Concrete is susceptible to deterioration by sulfates.

Characteristic 4 Fire Resistant Concrete provides the best fire resistance of any building material. 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. Concrete and its mineral constituents enjoy the highest fire resistance classification. The strength of concrete will deteriorate with high temperatures.

Characteristic 5 Strong in Compression The compressive strength depends on: The strength of the aggregate Proportion of aggregate sizes Type of Portland cement Purity of water Uniformity of mixture Procedures used in placing, finishing and curing Characteristic 5 Strong in Compression

Compressive Strength Influenced by Water/cement Ratio

Concrete is weak in tension Characteristic 6 Concrete is weak in tension Does this table and picture show why steel reinforcement is use in concrete?

Concrete is resistant to freezing and thawing 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:

Concrete Constituents

Concrete Constituents Concrete: a mixture of aggregate and Portland cement paste. Aggregate: usually sand, gravel and/or crushed stone. Paste: Portland cement and water 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.

Proportion of Constituents Basic concrete mix: Air 6% Portland cement 11% Coarse aggregate 41% Fine aggregate 26% Water 16%

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.”

Admixtures - cont. Common admixtures Additional admixtures Retarding admixtures Accelerating admixtures Super plasticizers Water reducing admixtures Air-entraining admixtures Additional admixtures Bonding, Shrinkage reduction, Damp proofing and Coloring. Addition of fiber to concrete makes it tough and fatigue resistant. Such type of admixtures are used extensively in important engineering projects.

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.

Developed during the 1930’s Air Entrained Developed during the 1930’s Produced by using air-entraining cement or by using an air-entraining admixture. Recommended for nearly all concretes that are exposed to freezing and thawing, and deicing chemicals. Spalding is a characteristic of using concrete without air entrainment.

Properties of Air Entrainment Increased freeze-thaw resistance Increased deicer-scaling resistance Improved sulfate resistance Equivalent Strength Improved workability

Aggregate

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)

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

Purchasing Concrete

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

Purchasing Concrete - 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.

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: Adding 10%.

Purchasing - Mix Two factors which determine the ideal mix. Environment Intended use Environmental factors Soil phosphates Freeze – thaw De-icers Use factors Maximum Load Vibration

Purchasing – Basic Mix

Concrete Construction Purchasing – Slump The inches of slump indicates the water-cement ratio and the quality of the concrete. Concrete Construction Slump, in. Maximum Minimum Reinforced foundations walls and footings 3 1 Plain footings, caissons, substructure walls Beams and reinforced walls 4 Building columns Pavements and slabs Mass concrete 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.

Slump Test – cont. Steps: Moisten cone Place cone on moist, smooth non absorbent level surface that is larger the the lugs on the cone. While standing on the lugs, fill the cone 1/3 and uniformly rod 25 times. Fill the cone 2/3 full and rod the 25 times insuring the rod just penetrates the first layer. Over fill the cone and rod 25 times Strike off the excess with the rod. Slowly lift the cone vertically and place on surface beside concrete. 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. This distance is the inches of slump.

Mixing Concrete

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/

Quikrete http://www.quikrete.com/OnTheJob/ProductSelector.asp

Mixing Concrete Characteristics of good mix: Cement paste Each aggregate particle is covered with cement paste 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.

Concrete Mixes 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: 1 = 1 ft3 (sack) of Portland cement 2 = 2 ft3 of fine aggregate 2-1/4 = 2.25 ft3 of coarse aggregate The proportions can be used on a volume or weight basis

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 2-1/4 Severe Exposure 2

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 5 4-1/4 2-1/4 Severe 4-1/2 3-1/2 2

Water vs. strength

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%

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. Adding the 10% =

Estimating Materials - By Volume - cont. Step two: determine the yield of one batch of the receipt. Because the aggregate mixes together, the yield by volume will only be about 2/3’s of the total volume. 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 =

Estimating Materials - By Volume - cont. Step four: determine the Portland cement, fine aggregate and coarse aggregate.

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

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. Adding the 10% =

Estimating Materials - By Weight - cont. Step two: determine the yield of one batch. Step three: determine the number of batches.

Estimating Materials - By Weight - cont. Step four: determine the amount of cement, fine aggregate and coarse aggregate.

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: Portland cement thoroughly mixed Aggregate fully covered Aggregates evenly distributed Minimum amount of water Uniform color and consistency 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.

Preparing Concrete Forms

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.

Concrete Forms Information Use soft, clean straight lumber. Sharpen stakes evenly. Space stakes appropriately. Use a level to set the forms for the desired slope. Do not drive nails into concrete space. Insure stakes do not extend above the tops of the forms. Construct the inside surface of the forms to create the desired shape in the finished concrete. Coat all surfaces that will be in contact with the concrete.

Concrete Forms--Wall Example Board Tie 1” Boards or 3/4 Plywood Brace Stud Spreader Block Stake Wire Tie Wale Concrete Footing Agricultural Mechanics Fundamentals & Applications Herren--Fig 39-7

Concrete Forms--Slab Example Control Joint Concrete Straightedge Form Wall Stake Packed Damp Sand Agricultural Mechanics Fundamentals & Applications Herren--Fig 39-7

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

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

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.

Pouring, Finishing, and Curing Concrete

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.

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

(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.

(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

(4) Edging & Jointing Part of the finishing process may also be edging and jointing Edging Edging forces the large aggregate away from the corner and rounds the corner. Reduces breakage on the edge. Jointing The groove cut or formed or cut in the surface helps control the location of the cracks.

Curing Concrete

Curing Concrete Concrete hardens through a chemical process. Initial strength is reached in a week. Must be protected during this time Potential problems. Solutions 1a. Dampen base/forms before placing 1. Drying out 1b. Cover with plastic or canvas 2a. Insulate the surface 2. Excessive heat 2b. Dampen the surface 3a. Don’t place on frozen ground 3. Freezing temperature 3a. Don’t place when freezing temperature is expected

Curing Rate % 28 Days Days

Effect of Curing conditions % of 28 Days Days

Masonry

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.

Masonry Construction Disadvantages: Ancient method of construction. 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. 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

Masonry Units Building bricks Pavers Custom bricks Stone

Masonry Units-cont. Concrete blocks (Fig 39-15) Light weight blocks

Estimating number of block needed Additional Topics Estimating number of block needed Constructing footers Mixing mortar Laying block

Questions