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CE 264 (Admixture) Exam Study Guide.
Admixtures - Answers✔ingredients other than portland cement, water, and aggregates that may
be added to concrete
Admixture - Answers✔to impart a specific quality to either the plastic (fresh) mix or the
hardened concrete (ASTM C494)
1. type, brand and amount of cement ;
2. water content
3. aggregate shape
4. gradation and proportions
5. mixing time
6. slump
7. temperatures of concrete and air - Answers✔The effectiveness of admixture depends upon
these factors:
1. air entrainers
2. water reducers
3. retarders
4. hydration controller admixtures
5. accelerators
6. specialty admixtures - Answers✔Admixtures are classified by the following chemical and
functional physical characteristics:
1. to reduce the cost of concrete construction
2. to achieve certain properties in concrete more effectively than by other means
3. to ensure quality of concrete during the stages of mixing, transporting, placing, and curing in
adverse weather conditions
4. to overcome certain emergencies during concrete operations - Answers✔The Portland Cement
Association (PCA) identifies four major reasons for using admixtures (Kosmatka et al., 2011):
1
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Air entrainers - Answers✔produce tiny air bubbles in the hardened concrete to provide space for
water to expand upon freezing
Critical saturation - Answers✔Upon freezing, water expands in volume by 9%. If the percent
saturation exceeds 91.7%, the volume increase generates stress in the concrete.
Hydraulic pressure - Answers✔Freezing water draws unfrozen water to it. The unfrozen water
moving throughout the concrete pores generates stress, depending on length of flow path, rate of
freezing, permeability, and concentration of salt in pores.
Osmotic pressure - Answers✔Water moves from the gel to capillaries to satisfy thermodynamic
equilibrium and equalize alkali concentrations. Voids permit water to flow from the interlayer
hydration space and capillaries into the air voids, where it has room to freeze without damaging
the parts.
Internal stresses - Answers✔reduce the durability of hardened concrete, especially when cycles
of freeze and thaw are repeated many times.
Critical saturation
Hydraulic pressure
Osmotic pressure - Answers✔three mechanisms contribute to the development of internal
stresses in the concrete
0.2% to 3% - Answers✔entrapped air voids represent approximately how much % of the
concrete volume
1mm - Answers✔All concrete contains entrapped air voids, which have diameters of
1% and 7.5% - Answers✔The entrained air voids are not connected and have a total volume
between
14 billion bubbles per cubic meter - Answers✔Concrete mixed for severe frost conditions should
contain approximately
Frost resistance - Answers✔improves with decreasing void size, and small voids reduce strength
less than large ones.
fineness of air voids - Answers✔is measured by the specific surface index, equal to the total
surface area of voids in a unit volume of paste.
23,600 m2 /m3 (600 in.2 /in.3 - Answers✔The specific surface index should exceed _______ for
frost resistance
air entrainment - Answers✔provides other important benefits to both freshly mixed and hardened
concrete.
2
CE 264 (Admixture) Exam Study Guide.
Admixtures - Answers✔ingredients other than portland cement, water, and aggregates that may
be added to concrete
Admixture - Answers✔to impart a specific quality to either the plastic (fresh) mix or the
hardened concrete (ASTM C494)
1. type, brand and amount of cement ;
2. water content
3. aggregate shape
4. gradation and proportions
5. mixing time
6. slump
7. temperatures of concrete and air - Answers✔The effectiveness of admixture depends upon
these factors:
1. air entrainers
2. water reducers
3. retarders
4. hydration controller admixtures
5. accelerators
6. specialty admixtures - Answers✔Admixtures are classified by the following chemical and
functional physical characteristics:
1. to reduce the cost of concrete construction
2. to achieve certain properties in concrete more effectively than by other means
3. to ensure quality of concrete during the stages of mixing, transporting, placing, and curing in
adverse weather conditions
4. to overcome certain emergencies during concrete operations - Answers✔The Portland Cement
Association (PCA) identifies four major reasons for using admixtures (Kosmatka et al., 2011):
1
, ©FYNDLAY
Air entrainers - Answers✔produce tiny air bubbles in the hardened concrete to provide space for
water to expand upon freezing
Critical saturation - Answers✔Upon freezing, water expands in volume by 9%. If the percent
saturation exceeds 91.7%, the volume increase generates stress in the concrete.
Hydraulic pressure - Answers✔Freezing water draws unfrozen water to it. The unfrozen water
moving throughout the concrete pores generates stress, depending on length of flow path, rate of
freezing, permeability, and concentration of salt in pores.
Osmotic pressure - Answers✔Water moves from the gel to capillaries to satisfy thermodynamic
equilibrium and equalize alkali concentrations. Voids permit water to flow from the interlayer
hydration space and capillaries into the air voids, where it has room to freeze without damaging
the parts.
Internal stresses - Answers✔reduce the durability of hardened concrete, especially when cycles
of freeze and thaw are repeated many times.
Critical saturation
Hydraulic pressure
Osmotic pressure - Answers✔three mechanisms contribute to the development of internal
stresses in the concrete
0.2% to 3% - Answers✔entrapped air voids represent approximately how much % of the
concrete volume
1mm - Answers✔All concrete contains entrapped air voids, which have diameters of
1% and 7.5% - Answers✔The entrained air voids are not connected and have a total volume
between
14 billion bubbles per cubic meter - Answers✔Concrete mixed for severe frost conditions should
contain approximately
Frost resistance - Answers✔improves with decreasing void size, and small voids reduce strength
less than large ones.
fineness of air voids - Answers✔is measured by the specific surface index, equal to the total
surface area of voids in a unit volume of paste.
23,600 m2 /m3 (600 in.2 /in.3 - Answers✔The specific surface index should exceed _______ for
frost resistance
air entrainment - Answers✔provides other important benefits to both freshly mixed and hardened
concrete.
2
