Concrete Manual Study Guide
What is the most frequently used fastener when constructing in formwork? (reference page: 208)
Double headed nails * The most common fastener is the nail in various sizes. Double headed nails are frequently used, as they can be withdrawn with minimum effort and damage to the structure
Which would be the proper method for installing dowels in a slab-on-grade? (reference page: 101)
Dowels must be carefully set parallel to the subgrade, secured to the centerline, and should not be coated with a lubricant
The ability of concrete to resist weathering action, chemical attack abrasion or other processes of deterioration is defined as: (reference page: 44)
Durability
What is the term for a condition where a soft surface and chalky condition occurs on formed concrete? (reference page: 106)
Dusting * Surface softness can occur on any kind of concrete surface. Dusting is evidence of a soft surface and is defined as a surface condition that can be a soil, chalky condition that occurs occasionally on formed concrete when the forms are removed
Calculate the modulus of elasticity for a beam with a load of 4000 psi that experienced a 1/2" deformation (reference page: 80-81)
E = loads in pounds / deformation at that load - 4000 psi / .5" = 8000 psi
A deposit of crystalline salts on vertical surfaces of hardened concrete or masonry, caused by evaporation is known as ________ (reference page: 113)
Efflorescence
Find the evaporation rate: Assume air temperature: 95 degrees; relative humidity: 60%, surface temperature of concrete: 90 degrees; wind velocity: 10 mph (reference page: 73 - Figure 5-4)
0.18 pounds per square foot per hour
A water cement ratio between _____ and _____ for normal structural concrete (reference page: 176)
0.40 and 0.60 * This requires a water cement ratio between 0.40 and 0.60 for normal structural concrete, giving us an amount of water in a cubic yard of concrete between 225 and 350 pounds, the exact amount depending on slump, materials, weather conditions & mix proportions
What is the maximum water cement ratio for concrete that is in contact with water and has a low permeability? (reference page: 218)
0.50 Find 'concrete that is in contact with water and has a low permeability' under 'exposure condition' column. Follow to 'maximum water cement ratio' column = 0.50
When pumping concrete, what is the MSA for a pipe that is 3 inches in diameter? (reference page: 311 - Table 15.1)
1 1/4 inch * Find '3' under 'Pipe or hose I.D., inches' column = 1 1/4" maximum size of aggregate
When concreting in hot weather, for each 10 degrees F in temperature the concrete needs how much more water for each cubic yard? (reference page: 409)
1 gallon
At 3 days, concrete containing calcium chloride can have a compressive strength as much as ______ psi stronger than plain concrete (reference page: 181)
1,000 * Concrete containing calcium chloride can have a compressive strength as much as 400 psi stronger at one day than plain concrete, 1000 psi stronger at three days and 900 psi stronger at seven days
When filling pits and voids in hardened concrete, which method of finishing leaves a thickness of mortar over the entire area? (referece page: 108)
A stoned finish * A stoned, or sand, finish is similar, except that the mortar is thick, creamy consistency. After the mortar has been spread, the surface is immediately rubbed with a carborundum stone, taking care to cover the entire area thoroughly. A thickness of mortar of about 1/32 inch should be left to provide a proper finish over the area as contrasted with sack rubbing, which fills the voids only, leaving the surface unchanged
When pumping concrete, what type of admixture significantly reduces line pressure and pumping resistance? (reference page: 312)
A super plasticizer
For concrete that is subject to freezing and thawing, what would be considered the most significant single factor contributing to durability of concrete? (reference page: 66)
Air entrainment
When testing for uniformity of concrete from a truck mixer, how many specimens should be made for a slump test? (reference page: 255)
3 * Each sample is then tested for slump, and (using the air meter) for unit weight and percent air. Following standard procedures, 6 by 12 inch cylinders for strength tests can be made at this time. Three specimens should be made for each test
What is the typical minimum thickness of a light duty residential slab-on-grade? (reference page: 338)
3 1/2 inch * Light duty floors are defined as those for residential and light commercial or similar occupancies where loads are not heavy and the concrete is not exposed to an aggressive environment. Local general building codes typically specify a minimum thickness of 3 1/2 inches for any slab supported directly on the ground
If the outside air temperature is 80 degrees, a 90 minute haul of 4 to 5" slump concrete in a mixer can result in a slump loss of ______ inches or more (reference page: 295)
3 inches * Long time mixing, either continuous or intermittent, without the addition of water to maintain the slump, results in a loss of slump or stiffening of the concrete. At an air temperature of 60 degrees F, concrete with a slump of 4 to 5 inches immediately after mixing will lose as much as 2 inches of slump after a 90 minute haul; 80 degrees F the slump loss will be 3 inches or more
In order to prevent rusting of steel in a concrete placement located near a seawater, how much concrete cover is required? (reference page: 98)
3 inches * Rusting of steel - Prevention is accomplished by proper design so that structural cracks will not form. Structures should be built of good dense concrete with at least 2 inches (3 inches in seawater) of cover over the reinforcing steel
A workable concrete mixture should have a slump within the range of _____ inches (reference page: 15)
3 to 6 inches * Workability is at a maximum in concrete of medium consistency, between 3 inch and 6 inch slump
Find the maximum percent of clay lumps that would be allowed in a fine aggregate (reference page: 154 - Table 8.3)
3%
What is the range of compressive strength specified for a reinforced concrete slab? (reference page: 25 - Table 3.1)
3,000 - 7,000 psi * Under column for 'Type or Location of Concrete Construction', Find 'Reinforced concrete beams, slabs, columns & walls' = 3000 - 7000 Specified Compressive Strength, psi
When shotcreting on vertical or overhanging surfaces, the mortar should be applied in layers not exceeding _____ inch thick (reference page: 478)
3/4 inch
A 40' girder with a shrinkage rate of 0.04 will shrink approximately how many inches? (reference page: 76 - Figure 5-6)
3/8 inches * Figure 5-6 - Find 'Length of element' - 40' follow up to 'rate of shrinkage' - 0.04 - follow to the left to find 'length of change' = 3/8"
What type of aggregate is desirable in high strength concrete with a high cement content? (reference page: 33)
3/8" to 3/4"
What is the minimum frequency for surface vibrators when consolidating a floor slab? (reference page: 317)
3000 vpm * The second group of external vibrators includes surface, pan or screed vibrators that operate on the surface of a floor, slab or pavement. Minimum frequency should be 3000 vpm
Calculate the compressive strength of a 6 inch concrete core 7 1/2 inches long broke at 4200 psi, using correction factors. (reference page: 26 - Table 3.2)
3900 psi * Length / Diameter - 7.5 / 6 = 1.25. Look up correction factor from table for 1.25 = 0.93. 4200 psi x 0.93 = 3906 psi
What slump is considered adequate for any slab placement? (reference page: 71)
4 inch slump * 4 inch slump is adequate for any slab placement, whether it's a driveway, floor or tilt up. Narrow walls, beams and similar structural elements will require somewhat more slump
What is the recommended maximum slump for concrete columns? (reference page: 223 - Table 12.5)
4 inches * 'Building columns' under 'concrete construction' - Follow to 'maximum slump, In.' column = 4"
What is the minimum number of strength tests per day when placing 600 cu yds of concrete per day? (reference page: 257)
4 test per day * Minimum number of strength tests per day - Once per day - Once for each 150 cu yds placed - Once for each 5000 sq ft of surface area placed
Transverse contraction joints in sidewalks should be located every _______, and ______ in driveways (reference page: 335)
4 to 5 feet; 10 to 12 feet
Specifications limit the amount of deleterious substances in the aggregate to a total of _____% by weight, with individual limits on certain substances (reference page: 153)
4 to 5%
When using a maximum size aggregate of 3/4", what is the range of total percent of air content for exposure class F2? (reference page: 187)
4.5 - 7.5% * Project specifications should allow the air content of the delivered concrete to be within (-1.5) and (+1.5) percentage points of the Table 9.2 target values. Table 9.2 - Find 3/4" under 'Maximum size aggregate' for 'Exposure class F2 and F3' = 6% - +/- 1.5%
Calculate the number of gallons of water needed for 8 bags of cement (reference page: 6)
40 gallons of water * 5 gal. water/bag cement - 8 bags of cement X 5 gallons per bag = 40 gallons of water
A Class 5 concrete floor will require a minimum compressive strength of _____ at 28 days (reference page: 328 - Table 15.1-D)
4000 psi * Find 'class 5' under 'floor class' column = 4000 psi @ 28 days
Calculate the compressive strength of a 6 inch concrete core 9 3/4 inches long broke at 4300 psi, using correction factors (reference page: 26 - Table 3.2)
4171 psi * Length / Diameter - 9.75 / 6 = 1.625. Look up correction factor from table. Must use interpolation - 1.625 is halfway between 1.5 and 1.75 in the table, therefore correction factor is halfway between the correction factors listed. 1.625 = 0.97 correction factor. 4300 psi x 0.97 = 4171 psi
Construction joints in slabs on grade should be located not less than ______ from any other joint to which they are parallel (reference page: 330)
5 feet
#5 bar has what nominal diameter in inches? (reference page: 369)
5/8 inch
What is considered the optimum temperature range for curing concrete to maximize strength development? (reference page: 36)
50 - 80 degrees * Concrete temperatures below 50 degrees F are unfavorable for the development of early strength. A concrete temperature of 80 degrees F or above during and immediately after placing will result in lower ultimate strength compared with concrete mixed and placed at 40 degrees F to 80 degrees F
Find the minimum design strength for concrete that is exposed to seawater? (reference page: 218 - Table 12.1)
5000 psi Find 'seawater' under 'exposure condition' column. Follow to 'minimum design strength' column = 5000 psi
Concrete for exterior walks and driveways should contain at least ______ pounds of cement per cubic yard and should have a slump between _______ inches (reference page: 325)
520 to 560 lbs; 2 and 4 inches
A subgrade for any type of slab, if it is water soaked much of the time, should be covered with a permeable layer of sand, or sand and gravel, to a depth of at least _______ inches (reference page: 323)
6 inches
When installing a vapor barrier in advance of a concrete slab placement on grade, the sheeting should be lapped ______ inches at joints (reference page 324)
6 inches * The barrier should be smooth and uniformly supported, lapped 6 inches at joints, and carefully fitted around pipes and other service openings, using tape or adhesive to hold it in place
When backfilling for a slab on grade, a base of granular soil compacted in layers should be about ____ inches thick (reference page: 322)
6 inches * This granular base should be permeable; hence, fine sands or silty soils should be avoided
At what point does concrete become classified a high strength concrete? (reference page: 39)
6000 psi compressive strength
What is the minimum time that normal concrete in structures should be cured? (reference page: 363)
7 days
According to ASTM C94 provisions, how many revolutions of the truck mixing drum need to be made to completely mix the concrete? (reference page: 292)
70 to 100 revolutions * Agitating speed should be just fast enough to prevent the concrete from settling and stratifying in the mixer drum. Manufactures recommend a speed between 2 and 6 rpm, the slower speed usually being adequate
At 28 days, the relative compressive strength of Type IV cement will be approximately what percentage compared to regular cement? (reference page: 139 - Table 7.4)
75%
What is the hardness factor of a floor with a 3/4" aluminum oxide topping applied to the floor, prior to proper curing processes? (reference page: 348)
8
A carbon-steel #7 bar, grade 60 has a minimum tensile strength of _____________ (reference page: 370 - Table 18.1)
90,000 psi * Find 'carbon-steel' under 'type of steel' column - Follow to 'bar grade' column, find 'Grade 60' - follow to 'Minimum tensile strength' column = 90,000 psi
Which type of admixture improves the workability of fresh concrete and reduces bleeding and segregation tendencies? (reference page: 185)
Air-entraining agents * Admixtures of this type (commonly abbreviated AEA) are now accepted for use in nearly all concrete, especially in areas where the concrete is exposed to freezing and thawing. By improving workability of the fresh concrete, entrained air permits the use of harsh and poorly graded aggregate, reduces bleeding and reduces segregation tendencies
When a compound is completely devoid of water, it is referred to as ____________ (reference page: 4)
Anhydrous * All of the compounds in cement are anhydrous; that is, they are completely devoid of water. When combined with water, they actively react with the water, forming new hydrated compounds
What type of special concrete becomes the final finished surface that is permanently exposed to view? (reference page: 485)
Architectural concrete
Which class of wire bar supports are used when epoxy-coated bars are specified? (reference page: 395)
Class IA * Maximum protection - Epoxy-, vinyl - or plastic coated bright basic wire bar supports - intended for use in situations of moderate to maximum exposure where no grinding or sandblasting of the concrete surface is required. Class IA is generally used when epoxy coated bars are specified
Transporting & placing concrete for buildings has been revolutionized by the _______ (reference page: 3)
Concrete pump
Which type of concrete is not recommended to determine the flow of freshly mixed concrete using a flowmeter? (reference page: 248)
Concrete with a standard slump less than 2 inches * The manufacturer does not, however, recommend using it on concrete with a standard slump less than 2 inches. The flowmeter is a newly adopted ASTM standard test method (ASTM C1362) to determine the flow of freshly mixed concrete, either in the field or in the laboratory
Which term used to describe the workability of concrete is defined used to measure the wetness of concrete (reference page: 13)
Consistency
Chapter 6
Cracks and Blemishes (page 89)
A pattern of fine cracks consists of many small, shallow, random cracks in every direction usually following a roughly hexagonal or octagonal pattern is referred to as: (reference page: 100)
Crazing
The breaking away of a small fragment of concrete surface because of internal pressure that leaves a shallow conical depression is a ___________. (reference page: 47 - Figure 4-3)
A popout
A concrete with a specific gravity of 1.9 would indicate what quality of concrete? (reference page: 159)
A possibly porous, soft, or highly absorptive aggregate of potentially doubtful quality * The higher the specific gravity, the heavier the concrete. Low specific gravity (below 2.50) indicates a possibly porous, soft or highly absorptive aggregate of potentially doubtful quality, requiring additional tests to determine its suitability
What is a primary reason for using lightweight structural concrete? (reference page: 457)
A reduction in the weight of the structure, with resulting savings in cost by permitting smaller footings and a lighter supporting structure
What is the term for a movable form that advances as the concrete is placed? (reference page: 211)
A slipform * A slipform, or sliding form, is a movable form that is raised vertically as the concrete is placed. A form of this kind is called a vertical slipform and is used on building and silos. Horizontal slipforms are used for highway pavements, curb and gutter, and canal linings
What is the term for when reinforcing steel is joined to accomplish continuity in a steel placement? (reference page: 390)
A splice
At what point after placing concrete, can vertical forms on walls, beams and columns usually be removed? (reference page: 213)
The day following the placing of the concrete
What must be done to most forms to prevent adhesion of the form to the concrete? (reference page: 209)
The form must be treated with a form oil or parting compound * Exceptions are the overlaid plywoods and smooth fiberglass molds
What is the main problem in pumping lightweight concrete? (reference page: 314)
The loss of plasticity of the concrete resulting from absorption of water by porous aggregates during pumping
Where shall construction joints be located within slabs, beams and girders? (reference page: 300)
The middle third of spans
If the earth is over excavated for a foundation, what must be done to remedy the situation? (reference page: 300)
The over excavated portion must be back filled with select material and compacted to the specified density, or filled with low strength concrete * Excavation for foundations should extend into sound, undisturbed soil or rock. If earth is over excavated, the over excavated portion must be back filled with select material and compacted to the specified density, or filled with low strength concrete
What is considered the most common cause of abnormal shrinkage? (reference page: 70)
The use of high slump mixes * The most important requirement for minimizing shrinkage is that the total water per cubic yard should be kept low as possible. The use of high slump mixes, which is probably the most common cause of abnormal shrinkage, should be avoided
What type of special concreting technique uses the concrete floor of the building as a casting platform for wall panels? (reference page: 468)
Tilt up construction * This is a type of precast construction in which wall panels are cast in a horizontal position at the site, tilted to a vertical position, and moved into final location as part of the building. As a rule, the concrete floor of the building serves as the casting platform
Why are forms for suspended slabs and beams frequently cambered? (reference page: 204)
To allow for sagging or settlement * A common allowance is 1/4 inch per 16 feet of span
What is the objective of precast concrete shop drawings? (reference page: 427)
To clearly show all details and give complete information explaining how the components are made and how they are installed in the building
What is the most common method of sampling hardened concrete? (reference page: 267)
To extract cores from the structure using a diamond drill
What is the purpose of using pozzolans? (reference page: 145)
To keep the heat of hydration as low as possible in large massive structures and to reduce water permeability & improve resistance to aggressive solutions * Pozzolans are used in large massive structures, such as dams, where it is desirable to keep the heat of hydration as low as possible, in concrete exposed to seawater or sulfate attack, and as alkali-aggregate inhibitors
What is the main reason for using an admixture in a concrete batch? (reference page: 178)
To modify the properties of concrete so it will be more suitable for a certain usage
What is the basic requirement of any sampling procedure? (reference page: 241)
To obtain a sample that is truly representative of the material being sampled
What is the purpose of floating a concrete surface? (reference page: 344)
To smooth the surface by removing slight rough spots left by the previous operations, leaving the surface dense and smooth
What is one of the most common faults in workmanship that affect the durability of concrete? (reference page: 47)
Too much mixing water
Which type of loading force is characterized as a twisting force on a structural member? (reference page: 25 - Figure 3-1)
Torsion * Concrete structures are subject to many kinds of loadings besides compressive. (E) Torsion is a twisting
What three methods are used to place concrete underwater? (reference page: 474)
Tremies, bottom dump buckets and pumping
Which type of equipment used to haul ready mixed concrete to a jobsite would not allow the addition of water at the jobsite? (reference page: 287 - Figure 14-17)
Truck agitators * A word of caution: When central mixed concrete is transported to the jobsite in an agitator unit, no water can be added at the jobsite. The agitator is not designed to operate at mixing speed to remix the concrete after addition of water
Which type of air content test would be performed on lightweight concrete? (reference page: 250)
Volume air meter * Air content of lightweight concrete made with lightweight aggregate, slag or any aggregate of high porosity must be determined with the volumetric apparatus, which can also be used on normal weight concrete. For this reason, air content tests by the pressure method are not suitable for determining the air content of concretes made with lightweight aggregates
Chapter 9
Water and Admixtures (page 175)
What is possibly the best way to keep the entire surface of concrete continuously wet during curing? (reference page: 363)
Water saturated mats in close contact with the concrete
Chapter 23
Waterproofing and Damproofing (page 503)
What is the term for a premolded sealant that may be embedded in concrete? (reference page: 193)
Waterstop * Installed by compressing the sealant into a joint slot, called a compression gasket
Epoxy resins will not adhere to which type of surface? (reference page: 193)
Waxed or greased surfaces * Epoxy resins are designed for a wide range of temperature conditions, surfaces and applications. They will adhere to many materials, including concrete, plaster, wood, metals and most plastics. Some are formulated to stick to wet surfaces. They will not adhere to waxed or greased surfaces
What can cause bubbles and blisters in fresh concrete during troweling? (reference page: 347)
When the partially hardened slab is sprayed with water them dusted with cry dement
Which type of Portland cement contains no onion? (reference page: 137)
White Portland cement * White Portland cement, which contains no iron, meets all specification requirements for Type I Portland cement. It is pure white in color and range of tinted or colored concretes
What consideration must be made to prevent wood forms from swelling after concrete has been placed? (reference page: 301)
Wood forms should be moistened with water so that they will not absorb water from the concrete
The ease with which concrete can be handled and placed with a minimum loss of homogeneity is known as ________ (reference page: 5)
Workability
The characteristics of particle shape, when determining the type of aggregate, have what significance in the quality of concrete? (reference page: 152 - Table 8.1)
Workability, economy, shrinkage, and strength
What type of soil possess the property of high volume change upon wetting or drying? (reference page: 54)
Expansive soils
What surface treatment would be required for a class C concrete surface? (reference page: 486)
Filling of tie rod holes and repair of defective concrete * A class C surface is one in which roughness is not objectionable, such as surfaces to be backfilled, permanently submerged or otherwise concealed from view
The use of hot mixing water during cold weather can result in what condition? (reference page: 18)
Flash set
What type of admixtures are used to achieve strengths between 8000 and 20,000 psi? (reference page: 41)
Fly ash and silica fume
Chapter 11
Formwork (page 197)
Chapter 1
Fundamentals of Concrete (page 1)
A reinforcing bar with 3 grade lines would indicate what grade of bar? (reference page: 373)
Grade 80 * Grade 80 [550] bars can either have three grade lines or the grade mark 80 [6] or Figure 18-4
This method of finishing concrete includes removing stains of rust, form oil, curing compound or other materials and providing a uniform color on the surface (reference page: 491)
Grout cleaning
Chapter 15
Handling and Placing the Concrete (page 299)
Chapter 19
Hot and Cold Weather Concreting (page 407)
_______ is the name of the reaction that takes place when Portland cement comes in contact with water and forms a new compound (reference page: 4)
Hydration * To lead to a better understanding the reaction that takes place when Portland cement comes in contact with water. The reaction is called hydration, which is defined as the process of reacting with water to form new compounds
When should sealing compounds be placed on formed surfaces? (reference page: 364)
Immediately after removal of the forms
What benefits are provided by using entrained air in fresh concrete? (reference page: 22)
Improved workability, lowered unit weight and reduced rate of bleeding
What is one of the most prevalent causes of dusting? (reference page: 107)
Incorrect finishing, such as premature floating and troweling
What mix adjustment would be made for a 2 percent increase in sand? (reference page: 240)
Increase water 2 percent content * Other suggestions include: 0.10 increase in sand FM = Increase sand percent by 1/2 percentage point; 1-inch increase in slump = Increase water 3 percent; 1 percent increase in sand = Increase water 1 percent content; 1 percent increase in air content = Decrease water 3 percent, Decrease sand 0.5 to 1 percent
_________ is the term for the period of time measured from the time water and cement are combined until concrete will just support a certain type of steel needle (reference page: 4)
Initial setting time * The initial setting time is an arbitrary period of time measured from the time water and cement are combined until a small pat of cement paste will just support a certain size and weight of steel needle. Final set is determined with a heavier and larger needle
Chapter 25
Inspection of Concrete Construction (page 525)
All of the following are causes of harshness in a concrete mixture except for: 1. Too much mix water 2. Coarse sand 3. Low cement content 4. Introduction of entrained air (reference page: 16)
Introduction of entrained air * Causes of harshness, other than high slump resulting from too much mix water, are low-cement content, lean mixes, coarse sand, a mix deficient in fines, rough and angular aggregates, or aggregate containing an excess of elongated or flat particles. The harshness of a mix can be reduced by the introduction of entrained air
Chapter 24
Introduction to Inspection (page 511)
Which type of joint should be provided whenever fresh concrete is placed adjacent to previously placed concrete? (reference page: 104)
Isolation (or expansion) joints * Isolation joints should be provided whenever concrete abuts previously placed concrete, such as a previously placed slab, wall or footing
Tight joints in formwork results in what benefit during concrete placement? (reference page: 200)
It restricts the leakage of mortar * Proper spacing of studs and walers prevents bulging; adequate fastening, bracing and wedging restrain movement of the form under pressure of the concrete while it is being vibrated; and tight joints restrict leakage of mortar from the concrete
For lightweight concrete, a magnesium float should be performed at what point in the finishing process? (reference page: 462)
It should begin as soon as the free moisture disappears from the surface, followed immediately by the first flat troweling
A light grey or white substance consisting of cement particles, water and fine particles of silt and clay, appearing on concrete surfaces during consolidation is known as: (reference page: 114)
Laitance
What is caused by performing concrete finishing while bleed water is still on the surface? (reference page: 21)
Laitance * Floating and troweling too early and too much, or performing the finishing while bleed water is on the surface, will cause laitance
What are the 3 types of splices in rebar? (reference page: 391)
Lap splice, Mechanical splice, and welded splice * Lap splices are the most common and easiest to make
Chapter 21
Lightweight and Heavyweight Concrete (page 455)
What are the two types of lightweight concrete? (reference page: 456)
Lightweight structural concrete and lightweight insulating concrete
Which type of concrete, used to control shrinkage, expands slightly and develops as much as 5000 psi compressive strength in 24 hours? (reference page: 77)
Magnesium phosphate concrete * Chemical control of shrinkage - Also available is a magnesium phosphate concrete that is said to harden at low temperatures, expand slightly and develop as much as 5000 psi compressive strength in 24 hours
The opening and closing of gates by hand operated levers and controls is known as ___________ (reference page: 283)
Manual batching * Manual batching, that is, opening and closing of gates by hand operated levers and controls, with cutoff controlled by the operator's observation of a scale dial or indicator, is somewhat slower than automatic or semiautomatic batching
The optimum condition for good workable concrete in normal structural use is: (reference page: 13)
Medium slump and good compaction by means of vibrators * Good, workable concrete does require some effort or work in placing. The optimum condition for normal structural use is a medium slump and good compaction by means of vibrators
What type of cement should be used for mass concrete projects? (reference page: 102)
Modified or low-heat cement
________ is a concrete mixture that uses only sand-size material? (reference page: 5)
Mortar * When the aggregate consists of sand-size material only, all less than about 1/4 inch in diameter, the mixture is called mortar
A concrete floor with foot and light vehicular traffic anticipated in a commercial building, would require which type of final finish? (reference page: 327 - Table 16.1-A)
Normal steel trowel finish * Find Class 4 concrete = Normal steel trowel finish
Contraction joints, whether sawed, grooved or formed, should extend into the slab to a depth of ______ the slab thickness (reference page: 334)
One fourth
Exterior plywood with resin-impregnated fiber facing material fused on to the surface is called: (reference page: 205)
Overlaid or plastic coated plywood * Called overlaid or plastic coated, it is ordinary exterior plywood with resin-impregnated fiber facing material fused on one or both sides. The overlay hides the grain of the wood, resulting in a very smooth surface
Vertical shoring under a beam or slab form would include: (reference page: 210)
Permanent Shores & Reshores
What can be done to relieve the stress induced in the concrete by shrinkage? (reference page: 331)
Placing contraction joints in the concrete at regular intervals * The drying shrinkage of the concrete in a large slab will cause random cracks in the slab unless means are provided to relieve the stress induced in the concrete by shrinkage. This relief is furnished by contraction joints (sometimes called control joints) made in the concrete at regular intervals
Chapter 7
Portland Cement (page 125)
What two components when mixed act as a patching compound, setting in a few minutes and developing strength rapidly? (reference page: 195)
Portland cement and aluminous cement
The period of time during which a material can be used after it has been mixed is referred to as its _______ (reference page: 193)
Pot life * Pot life is the period of time during which the material can be used after it has been mixed. It is different formulations and decreases with rising temperature. Epoxies have a relatively short pot life
Chapter 20
Precast and Prestressed Concrete (page 423)
Which type of form is pre manufactured and becomes a permanent part of the building? (referemce page: 211)
Precast concrete forms
Chapter 12
Proportioning the Concrete Mixture (page 215)
Chapter 26
Quality Control (page 539)
What is the most important factors in plastic cracking? (reference page: 92)
Rapid evaporation * When cracks develop during finishing, the finisher sometimes close and seal the surface by going over the cracked area with a float. Rapid evaporation is one of the most important factors in plastic cracking
If concrete dries due to moisture content loss during curing stages, what effect does it have on the compressive strength of concrete? (reference page: 32 - Table 3.3)
Results in a 40 percent decrease in compressive strength * Summary of compressive strength test variables - Under 'Testing' Section, in the Cause' column, Finding 'Curing' (item 54) - 'Moisture content' which the 'probable occurrence' is 'when specimens dry' has a '40 percent decrease' in strength of concrete
Which type of admixture slows the chemical process of hydration so that the concrete remains plastic and workable for a longer time (reference page: 183)
Retarders
Regarding the texture of an aggregate, which would be the most desirable? (reference page: 159)
Roughness * Roughness is desirable, as it provides better bond with the cement paste, thereby making concrete of better strength compared with smooth surfaced aggregate particles
What is the first consideration when designing formwork? (reference page: 200)
Safety
What is the term for the sloughing away or peeling of the surface in thin flakes? (reference page: 115)
Scaling * It is one of the worst blemishes that can befall a horizontal concrete surface, yet control measures are available and are relatively easy to apply
Intermediate guides placed on the forms for slabs or floors to assure the correct grade or elevation of the slab are known as: (reference page: 323)
Screeds * Forms for slabs or floors of large area can be set in the same way but, because of the large are, it is necessary to provide intermediate guides to assure the correct grade or elevation of the slab
Separation of coarse aggregate from the mortar in a concrete mixture is termed ________ (reference page: 19)
Segregation * Because of these dissimilar properties of the several materials, forces are attempting to cause them to separate from each other. This separation is called segregation, usually manifested by the separation of the coarse aggregate from the mortar
What problems have been associated with belt conveyors when placing concrete? (reference page: 306)
Segregation of concrete and loss of concrete that adheres to the belt
An assembly comprised of 2 nut washers, 2 waler rods and a central tie rod is referred to as a __________ (reference page: 209)
She-bolt
Pneumatically placed concrete is another term for _________ (reference page: 476)
Shotcrete * Shotcrete is the term used to designate a mortar or small MSA concrete that is conveyed through a hose in a stream of air and shot (pneumatically projected) onto the surface at high velocity. It is also commonly known as pneumatically placed concrete
Which type of admixture is a key ingredient in the production of very high strength concrete? (reference page: 146)
Silica fume * Silica fume is an admixture is used to provide a more impermeable concrete for applications such as parking deck slabs exposed to chlorides from de-icing salts. Silica fume is also a key ingredient in the production of very high strength concrete (15,000 psi or greater)
Chapter 16
Slabs on Ground (page 321)
A sheet metal cone, open at both ends, 12" high with the base 8" in diameter and the top 4" in diameter, provided with foot pieces and handles is commonly referred to as the _________ (reference page: 245)
Slump cone
What test can be performed to determine the placability of fresh concrete? (reference page: 5)
Slump test
What term is used for a simple diagonal wrap tied around the two intersecting bars with the wire ends twisted together on top? (reference page: 396)
Snap tie
Chapter 22
Special Concreting Techniques (page 467)
Which type of nondestructive test can be performed to determine the approximate compressive strength of hardened concrete? (reference page: 30)
Swiss Hammer * There are two simple instruments available for determining the strength of concrete in place. One of these, called a Swiss hammer, is a quick, nondestructive test that can be used for the determination of the approximate compressive strength of concrete in place
What is the least destructive method of obtaining an approximation of the strength of hardened concrete? (reference page: 270)
Swiss hammer * The windsor probe is a hardness tester similar to the swiss hammer and gives similar results. It measures hardness to a greater depth than the swiss hammer, but making the test is a little more complicated, and small holes or indentations are left in the surface of the concrete
Chapter 13
Testing and Controlling the Concrete (page 239)
Chapter 4
The Durability of Concrete (page 43)
Chapter 2
The Fresh Concrete (page 11)
Chapter 18
The Reinforcement (page 367)
Chapter 3
The Strength of Concrete (page 23)
What is the typical tolerance for the outside length of a side of square stirrup? (reference page: 384 thru 385)
+/-1/2 inch * Construction tolerance table
Chapter 10
Accessory Materials (page 191)
Chapter 8
Aggregates (page 147)
Chapter 17
Finishing and Curing the Concrete (page 341)
For maximum flexural strength in formwork, the outer gain of plywood should be _________ to the studs (reference page: 111 Figure 6-21)
Perpendicular
U-shaped configurations of small bars placed around the main steel of a beam in order to resist diagonal tension is known as: (reference page: 368)
Stirrups
What might be considered the most important property of fresh concrete? (reference page: 12)
Workability
When using strength to determine water cement ratio, the selected strength should exceed the specified strength by at least ______ (reference page: 223)
1200 psi
The weight of fresh concrete is approximately _____ pounds per cubic foot (reference page: 110)
150 pounds * A form is a temporary structure that must be accurately built to carry heavy loads, not only the weight of the fresh concrete at 150 pounds per cubic foot, but also the weight of the workers and equipment necessary to construct the form and place the concrete
When mixing concrete for cold weather applications, the temperature of the water should not exceed ______ degrees at the time of mixing with aggregates (reference page: 418)
175 degrees
Concrete in walls, footing, beams or any other structural components of appreciable height should be placed in horizontal layers not exceeding about ______ inches in depth (reference page: 315)
18 inches
Find the specific concrete cover for a #7 rebar in a slab on ground that is cast against forms? (reference page: 401 - Table 18.9)
2 * Exposed to weather or ground but cast against forms - Greater than #5 bar = 2
Which of the following would not affect the rate of hydration? 1. Fineness of the cement 2. UV exposure 3. Temperature 4.Presence of admixtures (reference page: 4)
2 - UV exposure * The rate of hydration is affected by the composition of the cement, fineness of the cement, temperature, the amount of water present and the presence of admixtures
What is the suggested mixing time for a 4 cubic yard mixer? (reference page: 286 - Table 14.1)
2 1/2 minutes * Find '4 cu yd' under 'Capacity of mixer' column = 2 1/2 minutes
Because of its lower density, lightweight concrete can be handled with _____ inches less slump than normal weight concrete? (reference page: 461)
2 inches
Plastic shrinkage cracks are typically less than _______ inches in depth (reference page: 92)
2 inches * The cracks vary in width from fine hairlines to an eighth of an inch, and in length to several feet. Depth seldom more than 2 inches, although the cracks may extend through a thin slab
If a horizontal construction joint is necessary in a concrete application subject to frost action, how far above the high water line should it be placed? (reference page: 58)
2 to 3 feet above * Horizontal construction joints should be avoided if possible. However, if a joint is necessary, it should not be located near the water or ground line, but should be 2 or 3 feet above the ground line or high water line or the same distance below the ground or low water line
What is the minimum specified compressive strength for structural concrete? (reference page: 24 - Table 3.1)
2,500 psi * ACI 318 Standard (section 19.2.1.1) indicates a minimum specified compressive strength of 2500 psi for structural concrete. Simply stated, strength less than 2500 psi
Find the minimum spacing of supports for D6 wire mesh where the wire is spaced 6" (reference page: 402 - Table for wire support spacing)
2-3 feet * Under 'wire size column find 'W or D4 to W or D8' for 'less than 12' = 2-3 ft support spacing
Contraction joints in walls should be spaced not more than about _____ feet apart and within ______ to ______ feet of corners (reference page: 104)
20; 10-15 * Contraction joints in walls should be spaced not more than about 20 feet apart and within 10 to 15 feet of corners
A 20' long sonotube fiber form with an inside diameter of 30" would weigh approximately how many pounds? (reference page: 207 - Table 11.1)
236 lbs * Under 'Inside Diameter in inches' find '30' - follow to 'Weight per ft in pounds' = 11.8 - 11.8 x 20 feet long = 236 lbs
Thermal shock can cause cracking when the temperature difference between the concrete and curing water is greater than _________ degrees (reference page: 98)
25 degrees * Temperature effects. Sudden changes in temperature can stress the concrete and cause cracks. This is called thermal shock. For best results, the temperature difference between the concrete and curing water should not exceed 25 degrees F
Fly ash is limited to _____ percent of the total weight of required cementitious materials (reference page: 218)
25%
What standard has become the measurement for early strength of concrete? (reference page: 41)
28 day compressive strength test
Reinforcements in concrete that is exposed to seawater, must have at least _____ inches of coverages (reference page: 52)
3
A temperature rise of 10 degrees in fresh concrete will decrease slump by _______ inch (reference page: 16)
1/2 to 3/4 inch
The maximum size of aggregate should not exceed ______ the depth of a slab (reference page: 222)
1/3 * The MSA should not exceed one third the depth of a slab, three fourths of the minimum clear spacing between reinforcing bars or between reinforcing bars and forms, or one fifth of the narrowest dimension between sides of forms, whichever applies to the structure under consideration
The usual amount of slope for an exterior slab is ______ inch per foot (reference page: 324)
1/4 inch * Exterior slabs should always be sloped for drainage; the usual amount is 1/4 inch per foot. Anything less is apt to result in ponding or "bird baths" on the surface
Estimate the length change for 60' girder changing in temperature from 50 degrees to 70 degrees (reference page: 79 - Figure 5-9)
1/4 inch * Figure 5-9 - Find 'length of element' for 60' girder. Follow up to 20 (70 degrees - 50 degrees = 20 degrees temperature difference) - follow to left = 1/4"
If the maximum size of coarse aggregate is 3/4", how many pounds of water would be needed for 10 cubic feet of concrete? (reference page: 236 - Table 12.12)
100 lbs * Find '3/4" under column for 'maximum size of coarse aggregate' - both air entrained and non air entrained concrete require the same quantity of water per cubic foot of concrete in lbs. - 10 pounds per cubic foot = 10 lbs per cu. Ft. x 10 cubic feet of concrete = 100 pounds of water
After placement, how long should normal concrete be maintained at a minimum temperature between 45 and 55 degrees? (reference page: 420)
At least 3 days
Chapter 14
Batching and Mixing the Concrete (page 273)
How long after concrete has been placed should control joints be sawed into a slab on grade using wet cutting techniques? (reference page: 333)
Between 4 and 12 hours
Surplus water in the concrete that rises to the top surface of the concrete is called: (reference page: 20)
Bleeding * During the period after concrete has been leveled off, surplus water in the concrete rises to the top surface of the concrete. Especially noticeable in flat slabs, this movement of water to the surface is called bleeding, or water gain
How is a non-slip finish applied after troweling? (reference page: 347)
By brooming or brushing the surface * The surface resulting from troweling is hard, dense and very smooth. The smoothness may be desirable in some situations, but it will be slippery, especially when the concrete becomes wet. For this reason, a nonslip finish is usually applied
When placing concrete near a window opening, what can be done to decrease cracking? (reference page: 97 - Figure 6-8)
By delaying concrete placement on top of opening by 2 hours, adding a construction joint at the top of the window opening & placing diagonal rebar in corners
Which admixture should not be used in hot weather? (reference page: 412)
Calcium chloride * A retarder can be used to slow or extend the setting time of the cement
Which component of concrete would be added into the mixer last? (reference page: 291 - Figure 14-21)
Cement * The best charging sequence is one in which the water leads and follows all solid materials, with the coarse aggregate leading and following the cement. Admixtures should always enter the mixer at the same point in the sequence
What is the main cause of volumetric changes in concrete resulting in cracking? (reference page: 91)
Changes in moisture content, temperature variations or internal reaction between components of concrete
Which ACI 318 exposure class of concrete is exposed to freezing and thawing conditions but will not be continually wet or in contact with de-icers? (reference page: 186)
Class F1 * The ACI 318 required air contents for concrete exposed to freezing and thawing conditions are shown in Table 9.2. Exposure Class F1 (moderate exposure) is an environment in which the concrete is exposed to freeze-thaw conditions but will not be continually wet nor exposed to water for long periods before freezing, and will not be in contact with de-icers
Which type of Portland cement would be used in high early strength concrete? (reference page: 135)
Type III * High early strength cement is used where high strengths are desired at early periods, usually a week or less
What type of cement produces concrete with normal 7 day strength at 3 days, & normal 28 day strength 7 days? (reference page: 37)
Type III Cement * High early strength cement - Known as Type III, this cement produces concrete with normal seven day strength in approximately three days, and normal 28 day strength in seven days
What type of cement is frequently used to accelerate setting of concrete in cold weather conditions? (reference page: 419)
Type III Cement * Set acceleration is desirable to reduce the length of time the concrete requires protection. Protection of the seeks to prevent freezing damage until the concrete has gained sufficient strength to resist. Type III cement is frequently used for this purpose and can be used in any structural application
Which type of Portland cement would be specified according to ASTM C1157 for moderate sulfate resistance? (reference page: 136)
Type MS * ASTM C1157 provides for six base types of cement that correlate to the performance aspect of the six types of Portland cement in ASTM C150: Type GU - General use; Type MS - Moderate sulfate resistance; Type MH - Moderate heat hydration; Type HE - High early strength; Type LH - Low heat of hydration; Type HS - High sulfate resistance
When concrete is exposed to seawater, what treatment can be made for protection? (reference page: 49 - Table 4.1)
Using Type II or V cement
Which would not be used when trying to achieve impermeable concrete? 1. Concrete with a water-cement ratio of less than 0.50 by weight 2. 3-7% entrained air 3. Well-graded sound aggregates containing at least 560 lbs of cement per cu. yd. 4. Using a slump mixture not over 6 inches (reference page: 86)
Using a slump mixture not over 6 inches * Keep the slump as low as possible for placing. the concrete vibration, not over 4 inches for slabs and 5 inches for structures
Which is not a cause of rock pockets? 1. Loss of cement grout or mortar by leakage through the forms 2. Failure to consolidate the concrete thoroughly 3. Segregation of the concrete 4. Using entrained air in the concrete mixture (reference page: 109-110)
Using entrained air in the concrete mixture
Chapter 5
Volume Changes and Other Properties (page 69)