CONCRETE TECHNOLOGY EXAM COMPLETE
QUESTIONS AND ALL ANSWERS CORRECT
Silica fume and fly ash are described as secondary hydrators because: -
ANSWER They both requires Ca(OH)2 to hydrate
The different materials in cement C2S, C3S, C3A and C4AF all contribute to
strength, how ? - ANSWER C4AF makes little contribution
What is true for admixtures? - ANSWER Air entraining admixtures introduce
a system of air bubbles in the concrete to provide relief from pressure of
freezing water. Superplasticers significantly lower the water/cement ratio
required for a given workability and produces high strength concrete. Set
regarding admixtures can be beneficial in hot weather
The aggregate cement ratio depends on: - ANSWER The maximum aggregate
size, desired slump and aggregate grading
What does the alkalis refer to in cement ? - ANSWER The oxides of sodium
and potassium
Low heat of hydration cement is made by? - ANSWER Increasing C2S
The slump test is important because ? - ANSWER Tell us if it is suitably
workable or if something is wrong with it
What does the slump test not tell us - ANSWER If it has the correct amount of
cement/water or if the ingredients are correct proportion
Ironstone or some other source of iron is added to the kiln charge even though
C4AF has little effect strength. Why is this done ? - ANSWER Iron stone acts
are a fluxing agent or catalyst
Silica fume and fly ash are used in blended cements. Which property does this
material have ? - ANSWER Both are finer than cement with silica fume being
finer by a factor of 100 and fly ash being finer than cement. Both also mainly
contain silica with fly ash having 30% alumina
, During mix development, saturated surface dry coarse aggregate is used and the
moisture content of fine aggregate measured. In commercial production of
concrete the aggregates may be wet to varying degrees, depending on where
they have been stored. How is this problem overcome ? - ANSWER Using a
slump test ! By controlling the slump or the concrete
Water reducing agents act to increase fluidity of the concrete mix by ? -
ANSWER By reducing the tension and creating like charges on cement
particles to make them mutually repulsive
Sulphate resisting cement is made by? - ANSWER Reducing C3A
Why is the water cement ratio important in mix design - ANSWER The lower
the w/c rat the higher the concrete quality
What does the water cement ratio not determine - ANSWER How much paste
that is available and the workability
Aggregate grading is important as it determines - ANSWER The amount of
cement required in the mix for a given weight of aggregate
The aggregate grading does not determine: - ANSWER The suitability of the
aggregate, the amount of water required to produce workable concrete, the
strength of the concrete
What is true about superplasticers - ANSWER It is effective for a short period
of time, temperature effects it and it does not effect durability of concrete
What is gel ? - ANSWER The product of hydration
For high strength concrete what is untrue ? - ANSWER We do not need steam
curing !!
What do we need for high strength concrete ? - ANSWER We need:
superplasticer, well graded aggregates, blended cements, low water cement ratio
Gypsum is added to cement clinker before grinding because - ANSWER
Control the flash set of C3A
True or false: C2S and C3S contribute the same throughout hydration -
ANSWER False
QUESTIONS AND ALL ANSWERS CORRECT
Silica fume and fly ash are described as secondary hydrators because: -
ANSWER They both requires Ca(OH)2 to hydrate
The different materials in cement C2S, C3S, C3A and C4AF all contribute to
strength, how ? - ANSWER C4AF makes little contribution
What is true for admixtures? - ANSWER Air entraining admixtures introduce
a system of air bubbles in the concrete to provide relief from pressure of
freezing water. Superplasticers significantly lower the water/cement ratio
required for a given workability and produces high strength concrete. Set
regarding admixtures can be beneficial in hot weather
The aggregate cement ratio depends on: - ANSWER The maximum aggregate
size, desired slump and aggregate grading
What does the alkalis refer to in cement ? - ANSWER The oxides of sodium
and potassium
Low heat of hydration cement is made by? - ANSWER Increasing C2S
The slump test is important because ? - ANSWER Tell us if it is suitably
workable or if something is wrong with it
What does the slump test not tell us - ANSWER If it has the correct amount of
cement/water or if the ingredients are correct proportion
Ironstone or some other source of iron is added to the kiln charge even though
C4AF has little effect strength. Why is this done ? - ANSWER Iron stone acts
are a fluxing agent or catalyst
Silica fume and fly ash are used in blended cements. Which property does this
material have ? - ANSWER Both are finer than cement with silica fume being
finer by a factor of 100 and fly ash being finer than cement. Both also mainly
contain silica with fly ash having 30% alumina
, During mix development, saturated surface dry coarse aggregate is used and the
moisture content of fine aggregate measured. In commercial production of
concrete the aggregates may be wet to varying degrees, depending on where
they have been stored. How is this problem overcome ? - ANSWER Using a
slump test ! By controlling the slump or the concrete
Water reducing agents act to increase fluidity of the concrete mix by ? -
ANSWER By reducing the tension and creating like charges on cement
particles to make them mutually repulsive
Sulphate resisting cement is made by? - ANSWER Reducing C3A
Why is the water cement ratio important in mix design - ANSWER The lower
the w/c rat the higher the concrete quality
What does the water cement ratio not determine - ANSWER How much paste
that is available and the workability
Aggregate grading is important as it determines - ANSWER The amount of
cement required in the mix for a given weight of aggregate
The aggregate grading does not determine: - ANSWER The suitability of the
aggregate, the amount of water required to produce workable concrete, the
strength of the concrete
What is true about superplasticers - ANSWER It is effective for a short period
of time, temperature effects it and it does not effect durability of concrete
What is gel ? - ANSWER The product of hydration
For high strength concrete what is untrue ? - ANSWER We do not need steam
curing !!
What do we need for high strength concrete ? - ANSWER We need:
superplasticer, well graded aggregates, blended cements, low water cement ratio
Gypsum is added to cement clinker before grinding because - ANSWER
Control the flash set of C3A
True or false: C2S and C3S contribute the same throughout hydration -
ANSWER False
