Lesson 2: Prestressed Concrete Material Flashcards
when a material is subjected to repeated cycles of stress or strain and its structure breaks down and ultimately leads to fracture
fatigue
when a material is subjected to a load for a very long time it may continue to deform until a sudden fracture occurs
creep
it has an endurance limit of about 0.4 times its ultimate tensile strength (UTS)
low-carbon steel
it has a higher endurance limit than low-carbon steel
alloy steel
its endurance limit can vary depending on the alloying elements and the heat treatment
alloy steel
it has a lower endurance limit than steel
cast iron
its endurance limit can vary depending on its type and the casting process
cast iron
(*) 5 factors to consider regarding fatigue resistance
- type of steel reinforcement
- stress level
- number of load cycles
- presence of stress concentrations
- environment
(*) 4 design considerations to increase the fatigue resistance of steel
- use of high-quality materials
- design the member to minimize stress concentrations
- avoid overloading
- protect the member from corrosion
it is the time-dependent increase in strain under
constant stress
creep
is the time-dependent decrease in stress under constant strain
relaxation
4 design considerations to minimize creep and relaxation
- use high-strength steel
- design the member to minimize stress concentrations
- avoid overloading
- protect the member from moisture
3 factors to consider in creep and relaxation
- stress level
- temperature
- moisture content
2 effects of high temperature to steel
- loss of strength
- fire resistance
it is the effect of high temperature to steel wherein steel loses strength due to the reduction of its yield strength
loss of strength
2 effects of low temperature to steel
- increased steel stress relaxation
- increased risk delamination
what causes corrosion in prestressing steel?
- chloride ions
- carbonation
- hydrogen sulfide
- stress corrosion cracking
- hydrogen embrittlement
it is the cause of corrosion in prestressing steel, which can come from a variety of sources, including seawater and deicing salts
chloride ions
it is the cause of corrosion in prestressing steel, described as the reaction of carbon dioxide with the calcium hydroxide in concrete
carbonation
it is the cause of corrosion in prestressing steel, which can come from a variety of sources, including industrial emissions, sewage treatment plants, and decaying organic matter
hydrogen sulfide
it is the cause of corrosion in prestressing steel, as prestressed steel is subjected to high levels of stress and chloride ions
stress corrosion cracking
it is the cause of corrosion in prestressing steel, as prestressed steel is subjected to high levels of hydrogen
hydrogen embrittlement
3 effects of corrosion in prestressing steel
- loss of strength
- cracks in concrete
- fracture of the steel
the effect of corrosion in prestressing steel includes a reduction in the load-carrying capacity of the structure and an increased risk of failure
loss of strength
the effect of corrosion in prestressing steel in which cracks can allow water and other corrosive agents to penetrate the concrete and further accelerate the corrosion of the steel
cracks in the concrete
the effect of corrosion in prestressing steel which causes the structure to collapse
fracture of the steel
it is a failure in prestressed concrete structures
concrete cracking
it determines the maximum load that a structure can withstand
strength
determines how much the structure will deform under load
modulus of elasticity
it is the reduction in volume of concrete that occurs when it dries and hardens
shrinkage
it is the increase in strain in concrete that occurs under sustained loading
creep
5 factors to consider in order to reduce the amount of shrinkage and creep of the concrete
- type
- age
- moisture content
- temperature
- loading conditions
true or false:
shrinkage and creep decrease with the age of the concrete
false
shrinkage and creep decrease with the age of the concrete
true or false:
concrete with a low water-to-cement ratio will shrink and creep more than concrete with a high water-to cement ratio
false
concrete with a high water-to-cement ratio will shrink and creep more than concrete with a low water-to cement ratio
true or false:
concrete that is wet will shrink and creep more than concrete that is dry
false
concrete that is dry will shrink and creep more than concrete that is wet
true or false:
concrete that is exposed to low temperatures will shrink and creep more than concrete that is exposed to high temperatures
false
concrete that is exposed to high temperatures will shrink and creep more than concrete that is exposed to low temperatures
true or false:
concrete that is not subjected to sustained loading will shrink and creep more than concrete that is subjected to sustained loading
false
concrete that is subjected to sustained loading will shrink and creep more than concrete that is not subjected to sustained loading
4 ways to reduce the amount of shrinkage and creep
- using a low water-to-cement ratio
- using admixtures
- during the concrete properly
- designing the structure to minimize shrinkage and creep
3 methods used to predict shrinkage and creep
- theoretical models
- empirical models
- hybrid models
this method to predict shrinkage and creep are based on the understanding of the physical mechanisms of shrinkage and creep
theoretical models
this method to predict shrinkage and creep are based on empirical data
empirical models
this method to predict shrinkage and creep combines theoretical and empirical approaches
hybrid models
3 movements in concrete structures
- expansion
- shear
- bending
this movement in concrete structure occurs when concrete is heated; in contrast as concrete contracts when it is cooled
expansion
temperature changes can cause movements in concrete structures, potentially leading to shear stresses
shear
temperature changes can cause movements in concrete structures, potentially leading to bending moments
bending
4 ways to reduce the amount of movements in concrete structures
- using a concrete with a low coefficient of thermal expansion
- using a thermal break
- designing the structure to minimize thermal stresses
- using a control joint
it is the ability of a material to resist weathering or other destructive influences
durability
6 factors that can affect the durability of concrete
- water
- chlorides
- carbonation
- sulphates
- freeze-thaw cycles
- abrasion
4 things that can be done to improve the durability of concrete
- using a low water-to-cement ratio
- using admixtures
- curing the concrete properly
- protecting the concrete from the environment
these are materials that are added to concrete during mixing to improve its properties
admixtures
7 common types of admixtures
- water-reducing admixtures
- air-entraining admixtures
- cementitious admixtures
- retarding admixtures
- accelerating admixtures
- waterproofing admixtures
- corrosion inhibitors
these type of admixtures reduce the amount of water required to produce a workable concrete mix
water-reducing admixtures
these type of admixtures introduce tiny air bubbles into the concrete mix
air-entraining admixtures
these type of admixtures react with the cement in the concrete mix to improve its strength and durability
cementitious admixtures
these type of admixtures slow down the setting time of the concrete mix
retarding admixtures
these type of admixtures speed up the setting time of the concrete mix
accelerating admixtures
these type of admixtures reduce the permeability of the concrete mix
waterproofing admixtures
these type of admixtures protect the steel reinforcement in concrete from corrosion
corrosion inhibitors
it is a versatile material that can be used in a variety of applications
structural lightweight concrete
this material is a good choice for applications where weight, thermal insulation, or workability are important considerations
structural lightweight concrete
3 applications of structural lightweight concrete
- building structures
- industrial applications
- civil engineering applications
