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Questions and Answers
The ______ resistance of bare steel is poor.
The ______ resistance of bare steel is poor.
corrosion
The ______ that surrounds the steel provides excellent corrosion protection.
The ______ that surrounds the steel provides excellent corrosion protection.
concrete
The fire resistance of unprotected steel is impaired by its high ______ conductivity.
The fire resistance of unprotected steel is impaired by its high ______ conductivity.
thermal
Bars with a yield strength of 100 ksi are allowed to be used as ______ reinforcement.
Bars with a yield strength of 100 ksi are allowed to be used as ______ reinforcement.
Bars with a yield strength of 120 ksi are also available but not yet recognized by the ______ Code.
Bars with a yield strength of 120 ksi are also available but not yet recognized by the ______ Code.
The paste should be allowed to set for ______ to 4 hours after water has been added to the cement.
The paste should be allowed to set for ______ to 4 hours after water has been added to the cement.
For complete hydration, a water-cement ratio of ______ is needed chemically.
For complete hydration, a water-cement ratio of ______ is needed chemically.
For normal concretes, the water-cement ratio typically ranges from ______ to 0.60.
For normal concretes, the water-cement ratio typically ranges from ______ to 0.60.
Material coarser than a No. 4 sieve is classified as ______ aggregate.
Material coarser than a No. 4 sieve is classified as ______ aggregate.
ASTM C33 is a standard specification for ______ aggregates.
ASTM C33 is a standard specification for ______ aggregates.
The ______ of normal weight concrete with natural aggregates varies from 140 to 152 pounds per cubic foot.
The ______ of normal weight concrete with natural aggregates varies from 140 to 152 pounds per cubic foot.
Lightweight aggregates, such as pumice or cinders, are suitable for ______ concretes.
Lightweight aggregates, such as pumice or cinders, are suitable for ______ concretes.
An essential requirement for high-strength concrete is a low ______ ratio.
An essential requirement for high-strength concrete is a low ______ ratio.
Set-retarding ______ are used primarily to offset the accelerating effect of high ambient temperature.
Set-retarding ______ are used primarily to offset the accelerating effect of high ambient temperature.
Pozzolans qualify as ______ materials, also referred to as mineral admixtures.
Pozzolans qualify as ______ materials, also referred to as mineral admixtures.
For normal concretes, the water–cementitious ratio usually falls in the range from about 0.40 to 0.60 by ______, but for high-strength mixes it may be 0.25 or even lower.
For normal concretes, the water–cementitious ratio usually falls in the range from about 0.40 to 0.60 by ______, but for high-strength mixes it may be 0.25 or even lower.
The specified compressive strength fc is commonly in the range from 3000 to 6000 ______ for normalweight cast-in-place concrete.
The specified compressive strength fc is commonly in the range from 3000 to 6000 ______ for normalweight cast-in-place concrete.
To permit proper placement of what would otherwise be a zero slump mix, high-range water-reducing ______, or superplasticizers, are essential.
To permit proper placement of what would otherwise be a zero slump mix, high-range water-reducing ______, or superplasticizers, are essential.
The useful strength of ordinary reinforcing steels in tension as well as compression, that is, the ______ strength, is about 15 times the compressive strength of common structural concrete and well over 100 times its tensile strength.
The useful strength of ordinary reinforcing steels in tension as well as compression, that is, the ______ strength, is about 15 times the compressive strength of common structural concrete and well over 100 times its tensile strength.
High-strength concretes, with fc to 15,000 psi or more, are used with increasing frequency, particularly for heavily loaded ______ in high-rise concrete buildings.
High-strength concretes, with fc to 15,000 psi or more, are used with increasing frequency, particularly for heavily loaded ______ in high-rise concrete buildings.
In contrast to fly ash, silica fume contributes mainly to strength gain at early ages, from 3 to 28 ______.
In contrast to fly ash, silica fume contributes mainly to strength gain at early ages, from 3 to 28 ______.
On the other hand, steel is a high ______ material compared with concrete.
On the other hand, steel is a high ______ material compared with concrete.
For most effective reinforcing action, it is essential that steel and concrete deform together, that is, that there be a sufficiently strong ______ between the two materials.
For most effective reinforcing action, it is essential that steel and concrete deform together, that is, that there be a sufficiently strong ______ between the two materials.
______ is the slow deformation of a material over considerable lengths of time at constant stress or load.
______ is the slow deformation of a material over considerable lengths of time at constant stress or load.
Slag cement is another ______ cementitious material.
Slag cement is another ______ cementitious material.
This bond is provided primarily by the natural roughness of the mill scale on the surface of hot-rolled reinforcing bars and by the closely spaced rib-shaped surface ______ that provide a high degree of interlock between the bars and the surrounding concrete.
This bond is provided primarily by the natural roughness of the mill scale on the surface of hot-rolled reinforcing bars and by the closely spaced rib-shaped surface ______ that provide a high degree of interlock between the bars and the surrounding concrete.
The high-strength concretes are used with increasing frequency for long-span ______ (mostly prestressed) where a significant reduction in dead load may be realized.
The high-strength concretes are used with increasing frequency for long-span ______ (mostly prestressed) where a significant reduction in dead load may be realized.
The thermal expansion coefficients of the two materials, about 6.5 × 10 - 6 per ˚ F for steel vs. an average of 5.5 × 10 - 6 per ˚ F for ______.
The thermal expansion coefficients of the two materials, about 6.5 × 10 - 6 per ˚ F for steel vs. an average of 5.5 × 10 - 6 per ˚ F for ______.
Lightweight aggregates for structural concrete can weigh as high as ______ pcf if ores are used for the fines only and steel for the coarse aggregate.
Lightweight aggregates for structural concrete can weigh as high as ______ pcf if ores are used for the fines only and steel for the coarse aggregate.
Structural lightweight concretes typically have unit weights between 70 and ______ pcf.
Structural lightweight concretes typically have unit weights between 70 and ______ pcf.
ASTM C618, “Standard Specification for Coal Fly Ash and Raw or Calcified Natural Pozzolan for Use in ______,”
ASTM C618, “Standard Specification for Coal Fly Ash and Raw or Calcified Natural Pozzolan for Use in ______,”
For many years, bar sizes have been designated by ______, Nos. 3 to 11 being commonly used and Nos. 14 and 18 representing the two special large-sized bars previously mentioned.
For many years, bar sizes have been designated by ______, Nos. 3 to 11 being commonly used and Nos. 14 and 18 representing the two special large-sized bars previously mentioned.
Other additives include fly ash and, most notably, ______ fume.
Other additives include fly ash and, most notably, ______ fume.
______ strains are also proportional to stress in the range, this permits definition of the creep coefficient.
______ strains are also proportional to stress in the range, this permits definition of the creep coefficient.
Lower density lightweight concretes typically have compressive strengths of 1000 to ______ psi and are chiefly used as fill.
Lower density lightweight concretes typically have compressive strengths of 1000 to ______ psi and are chiefly used as fill.
The ______ of the fine and coarse aggregates are based on material in the saturated surface dry condition.
The ______ of the fine and coarse aggregates are based on material in the saturated surface dry condition.
The trial-batch method involves selecting a water-cement ratio from information like that in Fig. 2.1, and then producing several small ______ with varying amounts of aggregate.
The trial-batch method involves selecting a water-cement ratio from information like that in Fig. 2.1, and then producing several small ______ with varying amounts of aggregate.
Concrete consistency is most frequently measured by the ______ test.
Concrete consistency is most frequently measured by the ______ test.
Slumps for concretes in building construction generally range from 2 to ______ in.
Slumps for concretes in building construction generally range from 2 to ______ in.
Conveying of most building concrete from the mixer or truck to the form is done in bottom-dump buckets or by ______ through steel pipelines.
Conveying of most building concrete from the mixer or truck to the form is done in bottom-dump buckets or by ______ through steel pipelines.
The chief danger during conveying is that of segregation, the separation of the individual components of concrete because of their ______.
The chief danger during conveying is that of segregation, the separation of the individual components of concrete because of their ______.
Flashcards
Water-Cement Ratio
Water-Cement Ratio
The ratio of water to cement by weight required for hydration.
Fine Aggregate
Fine Aggregate
Aggregates that pass a No. 4 sieve, typically natural sand.
Coarse Aggregate
Coarse Aggregate
Material that does not pass a No. 4 sieve; larger than fine aggregates.
Unit Weight of Concrete
Unit Weight of Concrete
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Lightweight Concrete
Lightweight Concrete
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Heavyweight Concrete
Heavyweight Concrete
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Admixtures
Admixtures
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Corrosion Resistance
Corrosion Resistance
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Yield Strength
Yield Strength
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Rebar
Rebar
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ASTM A615
ASTM A615
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Ductility
Ductility
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Water-Cementitious Ratio
Water-Cementitious Ratio
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High-Strength Concrete
High-Strength Concrete
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Superplasticizers
Superplasticizers
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Bond between Steel and Concrete
Bond between Steel and Concrete
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Interlock
Interlock
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Thermal Expansion Coefficient
Thermal Expansion Coefficient
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Zero Slump Mix
Zero Slump Mix
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Silica Fume
Silica Fume
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Reinforcing Bars (Rebar) Sizes
Reinforcing Bars (Rebar) Sizes
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Calcium Hydroxide
Calcium Hydroxide
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Set-retarding Admixtures
Set-retarding Admixtures
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Pozzolans
Pozzolans
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Compressive Strength (fc)
Compressive Strength (fc)
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Creep
Creep
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Slag Cement
Slag Cement
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Fly Ash
Fly Ash
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ASTM Standards
ASTM Standards
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Unit Weight
Unit Weight
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Compressive Strength
Compressive Strength
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Saturated Surface Dry Condition
Saturated Surface Dry Condition
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Trial-Batch Method
Trial-Batch Method
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Slump Test
Slump Test
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Segregation
Segregation
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Study Notes
Concrete, Reinforced and Prestressed Concrete
- Concrete is a stonelike material made from a mixture of cement, sand, gravel (or other coarse aggregate), and water.
- The mixture hardens into the desired shape.
- Curing is the process of controlling conditions after placement.
- Concrete is a universal building material dating back to lime mortars (12,000-6000 BCE) in Crete, Cyprus, Greece, and the Middle East.
- Reinforced concrete combines the benefits of both concrete and steel: low cost, good weather/fire resistance, good compressive strength, and excellent formability (of concrete) with the high tensile strength and greater ductility/toughness (of steel).
- 60 ksi is the common steel strength used.
- Prestressed concrete uses steel and concrete of very high strength.
- Prestressing reduces deflection and cracking.
- Reinforced concrete is used in cylindrical shell or folded plate structural forms.
Structural Forms
- Doubly curved shell surfaces can be generated mathematically (e.g. through circular arcs, parabolas, hyperbolas).
- Hyperbolic paraboloids, created by a concave downward parabola moving along a concave upward parabolic path, are commonly used.
- Bridges, such as the award-winning Napoleon Bonaparte Broward Bridge, use complex/creative design.
- The Bennett Bay Centennial bridge is a continuous, segmentally cast-in-place box girder structure.
Loads
- Loads on structures are broadly categorized as: dead loads, live loads, and environmental loads.
- Dead loads are consistent and fixed throughout the structure’s life (mainly its own weight).
- Live loads include occupancy loads (buildings) and traffic loads (bridges), which can vary and change location.
- Tabulated live loads used for design are not always accurate and building occupancy is crucial for calculating appropriate loads.
- Highway bridge live loads are specified by AASHTO in LRFD Bridge Design Specifications.
- Environmental loads include snow loads, wind pressure, earthquake loads, soil pressures, and potential ponding.
Safety Provisions of the ACI Code
- A maximum load factor of 1.0 is used for wind load (W) and earthquake load (E) because these loads are expressed at the strength level.
- ASCE/SEI 7, Minimum Design Loads for Buildings and Other Structures is used for load calculation.
- Dead load (D), earthquake load (E), live load (L), rain load (R), snow load (S), and fluid load (F), are among the loads considered.
- Cumulative effects, including creep and shrinkage, are also considered.
Materials - Cement
- A cementitious material bonds aggregates into a solid mass.
- Hydraulic cements are used in structural concrete.
- Hydration is the chemical process where cement hardens into a solid mass.
- Water is needed in the cement hydration process
- Portland cement is the most common hydraulic cement, first patented in England in 1824.
- Five standard types of portland cement have been developed.
- Type I (normal portland cement) is the most common (over 90% of construction in the US); takes 1-2 weeks to reach sufficient strength, fully hardened in 28 days.
- Type III is a high early strength cement, reaching Type I strength in 7-14 days.
Materials - Aggregates
- Aggregates (fine and coarse) make up 65-75% of concrete volume.
- Natural aggregates, including fine aggregate (passes a No. 4 sieve - 4 openings per linear inch) and coarse aggregate (larger than a No. 4 sieve).
- ASTM C33 details standards for concrete aggregates.
- Normal weight concrete with natural aggregates has a unit weight of about 140-152 pounds per cubic foot.
- Lightweight and heavyweight concretes are sometimes used.
Materials - Admixtures
- Admixtures alter concrete performance.
- Accelerators reduce setting time and increase early strength.
- Retarders increase setting time, allowing better placement.
- Water reducers lower water requirements for a given slump.
- Air-entraining agents create air bubbles to prevent freezing and improve workability/durability.
- High range water reducers or superplasticizers are used to make high strength concrete with very low water-cement ratio.
Concrete Properties
- Concrete's performance under load is heavily affected by its stress-strain relationship.
- Plain concrete's fatigue limit is 50-60% of its static compressive strength.
- The modulus of rupture and splitting tensile strength measurement are used to understand concrete's tensile strength.
Reinforcing Steel
- Reinforcing steel is 15 times stronger in tension/compression than concrete.
- Steel is a high-cost material compared with concrete.
- Bond between steel and concrete is crucial for effective reinforcing action.
- Thermal expansion coefficients of steel and concrete are about 6.5x10-6 °F for steel versus 5.5x10-6 °F for concrete.
- Fire resistance of steel is impaired by its thermal conductivity and strength decrease at high temperatures.
- Common rebar grades include 40 ksi, 60 ksi, 75 ksi, 80 ksi, and 100 ksi.
- Larger bars (1 3/4-2 1/4 in) also exist.
Prestressed Steel
- Prestressing steel enhances strength & durability.
- It comes in three forms: wires, strands, and alloy steel bars.
- Wires have diameters from 0.192 to 0.276 inch.
- Strands and alloy steel bars exhibit higher tensile strengths (2.5-6 times the yield strength of commonly used reinforcing bars).
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Description
This quiz explores the characteristics, uses, and history of concrete, reinforced, and prestressed concrete. It covers the benefits of using reinforced concrete and the mathematical aspects of structural forms. Test your knowledge on this essential building material and its applications.
