Jean-Pierre Jeunet - Faculty We Sites.ppt

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1、1,Concrete and MasonrySection 13Unit 39,2,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.,3,Concrete,4,Concrete,Concrete is“a mixture of stone aggrega

2、tes,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,5,Concrete-cont.,AdvantagesFireproofInsect&rodent proofDecay resistantStorm resistantWear resistantWaterproof(water resistant)Stron

3、g,AttractiveUV resistantDoesnt require expensive equipment.Available locallyLow original and maintenance costsSanitary and easy to keep cleanRecyclable,Concrete is truly a versatile building material.It can be formulated with very specific performance characteristics in mind and include lightweight,

4、heavyweight,porous,fiber-reinforced,mass,high-performance and cellular concretes.,6,Concrete-cont.,DisadvantagesLabor intensiveRequires moving a lot of weightRequires formsDense materialSpecial skills required to place and finish,7,Seven(7)Characteristics of Concrete,7.Resistant to freezing and thaw

5、ing,6.Weak in tension,5.Very strong in compression,4.Fire resistant,3.Resists manures and most chemicals.,2.Resists attack by water,1.Durable,8,Def:The ability of concrete to resist weathering action,chemical attack and abrasion while maintaining its desired engineering properties.,Characteristic 1D

6、urability,Concrete ingredients,their proportioning,interactions between them,placing and curing practices,and the service environment determine the ultimate durability and life of concrete.,9,Characteristic 2Resists Attack by Water,Watertightness:the ability of concrete to hold back or retain water

7、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.,10,Characteristic 2 Resists Attack by Water-cont.,

8、Permeability of the pastePermeability and gradation of the aggregateQuality of the pasteQuality of the paste-aggregate transition zoneRelative proportion of paste to aggregate,Factors that affect permeability and water tightness include:,Low permeability concrete requires a low water-cement ratio.Mo

9、ist curing also reduces permeability.,The same properties of concrete that make it less permeable also make it more watertight.,11,Characteristic 3Resists 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.R

10、esistance can be increased with surface treatments.Concrete is susceptible to deterioration by sulfates.,12,Characteristic 4Fire Resistant,The strength of concrete will deteriorate with high temperatures.,Concrete provides the best fire resistance of any building material.It does not burn,it cannot

11、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.,13,Characteristic 5Strong in Compression,The compressive strength depends

12、 on:The strength of the aggregateProportion of aggregate sizesType of Portland cementPurity of waterUniformity of mixtureProcedures used in placing,finishing and curing,14,Compressive Strength Influenced by Water/cement Ratio,15,Characteristic 6Concrete is weak in tension,Does this table and picture

13、 show why steel reinforcement is use in concrete?,16,Characteristic 7Concrete 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 v

14、olume than that of water.Air entrained concrete is less permeable.Example of freezing damage:,17,Concrete Constituents,18,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

15、 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:Air6%Portland cement11%Coarse aggregate41%Fine aggregate26%Water16%,19,20,Admixtures,“Admixtures are material

16、s 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.”,21,Admixt

17、ures-cont.,Addition of fiber to concrete makes it tough and fatigue resistant.Such type of admixtures are used extensively in important engineering projects.,Common admixturesRetarding admixturesAccelerating admixturesSuper plasticizersWater reducing admixturesAir-entraining admixtures,Additional ad

18、mixturesBonding,Shrinkage reduction,Damp proofing and Coloring.,22,Types of Cement,Different types of Portland cement are manufactured to meet many different applications of concrete.,Types I&IA are the most common.,23,Air Entrained,Developed during the 1930s,Recommended for nearly all concretes tha

19、t 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.,24,Increased freeze-thaw resistanceIncreased deicer-scaling resistanceImproved sulfate

20、 resistanceEquivalent StrengthImproved workability,Properties of Air Entrainment,25,Aggregate,26,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

21、 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),27,Aggregate-cont.,Aggregate dia

22、meter 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.,28,Purchasing Concrete,29,Purchasing Introduction,For large jobs in is common practice to ha

23、ve the concrete delivered to the site.The cost of having concrete delivered is determined by:QuantityMixMinimum chargeUnload feeMileage fee,30,Purchasing Concrete-Quantity Needed,Quantity neededConcrete is sold by the cubic yard(yd3).To determine the quantity need calculate the volume in cubic inche

24、s(in3)or cubic feet(ft3)and convert to cubic yards(yd3 or just yd).27 ft3=1 yd46656 in3=1 ydCommon practice to add 5 to 10%for waste and volume errors.,31,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

25、and 6 inches thick.Solution:,Adding 10%.,Purchasing-Mix,Two factors which determine the ideal mix.EnvironmentIntended use,32,Environmental factorsSoil phosphatesFreeze thawDe-icers,Use factorsMaximum LoadVibration,Purchasing Basic Mix,33,Purchasing Slump,The inches of slump indicates the water-cemen

26、t ratio and the quality of the concrete.,34,Slump is determine through a slump test.,Slump-Test,A slump test is conducted using an Abrams 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.,35,Slump Test cont.,36,Steps:Moisten conePl

27、ace 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 timesStrike

28、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.,37,Mixing Concrete,38,Introd

29、uction,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 i

30、nformation go to:http:/www.nrmca.org/aboutconcrete/,39,http:/,Quikrete,40,Mixing Concrete,Characteristics of good mix:Each aggregate particle is covered with cement pasteEach aggregate particle is bound to othersCement pasteWater-cement ratio must be exact proportions.Water in aggregate must be acco

31、unted for and deducted from water added to mix.Water-cement ratio must be adjusted for different service conditions.,41,Concrete Mixes,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 aggreg

32、ates 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,42,Proportions,The proportions must be changed to meet the service conditions.,43,Mixing-cont.,The amount of w

33、ater in the aggregate must be included in the calculations.Effect of water in aggregate.(Fig 39-3),Water vs.strength,44,Effect of Adding Water,Adding 1 gal of water to 1 yd3 of concrete:Increases slump 1 inchDecrease compressive strength by 200 psiIncreases shrinkage by 10%Increases permeability by

34、up to 50%,45,46,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%=,47,Estimating Materials-By Volume-cont.,Because t

35、he aggregate mixes together,the yield by volume will only be about 2/3s of the total volume.,Step two:determine the yield of one batch of the receipt.,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 o

36、f batches=,48,Estimating Materials-By Volume-cont.,Step four:determine the Portland cement,fine aggregate and coarse aggregate.,49,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=

37、100 lb/ft3Coarse aggregate=110 lb/ft3,50,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%=,51,Estimating Materials-By

38、Weight-cont.,Step two:determine the yield of one batch.,Step three:determine the number of batches.,52,Estimating Materials-By Weight-cont.,Step four:determine the amount of cement,fine aggregate and coarse aggregate.,53,Workable Mix,Workability of concrete refers to the consistency of the wet concr

39、ete.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 mixedAggregate fully coveredAggregates evenly distributedMinimum amount of waterUniform color and consistencyCan be mixed,moved an

40、d 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.,54,55,Preparing Concrete Forms,56,Concrete Forms,Form:a metal or wooden structure that confines the concrete to the desired shape

41、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,me

42、tal forms can be purchased or rented.,57,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.Const

43、ruct 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.,58,Concrete Forms-Wall Example,Board Tie,1”Boards or 3/4 Plywood,Brace,Spreader Block,Wire Tie,Stud,Concrete Footing,Stake,Wale,Agricultural Mechanic

44、s Fundamentals&Applications Herren-Fig 39-7,59,Concrete Forms-Slab Example,Form,Wall Stake,Control Joint,Concrete,Straightedge,Packed Damp Sand,Agricultural Mechanics Fundamentals&Applications Herren-Fig 39-7,60,Concrete Joints,Three(3)types of joints are used for concrete.Isolation joints:allow exp

45、ansion 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,61,Concrete

46、 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 days work or May be that some other work needs to be completed before resuming the placement.New concrete is placed

47、against concrete that has solidified or skimmed over.,Butt,Dowel,Key,62,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

48、 designed load.Fibers are also being used to reinforce concrete.,63,Pouring,Finishing,and Curing Concrete,64,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 segregat

49、e.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 minutesOnce in place and hardening process has started-its there.Ensure concrete does not dry out.Dampen the soil/sand base before placing.Protect t

50、op surface after placing.,65,Finishing Concrete,The number of processes and type of process used is determine by the desired finished surface.TrowelBroomExposed aggregateGroovedStampedBurlapEtc.The finishing process has at least Four(4)steps.ScreedingFloatingFinal surfaceEdging&jointing,66,(1)Screed