Construction Materials Exam 1 Review
In theory, the minimum w/cm ratio for concrete is ______________, which is sufficient for the hydration process.
0.22
During pumping, the slump of concrete may decrease by about:
0.5~1 inch
To produce economical concrete that is easy to work with, you should select ______
1 1/2" gravel
For a small concrete job (10 ft^3), how many bags of cement is needed? 1 bag of cement=94 lb. Use nominal maximum coarse aggregate of 1 inch and air entrained concrete.
2.7
Portland cement was invented about __________ years ago
200
Unless otherwise specified, concrete strength fc' is tested using cylinder samples at the age of ______
28 days
Unless otherwise specified, concrete strength fc' refers to the average compressive strength of ______ tests.
3 tests
The specific gravity of cement is
3.15
Pizza is usually cooked at 400 degree F. To make cement, the kiln has to reach a temperature of
3000 degrees
Unless otherwise specified, concrete strength fc' is tested using cylinder samples with the size of ______
6"*12"
For a small concrete job (10 ft^3), how many ft^3 of wet coarse aggregate is needed? Use nominal maximum coarse aggregate of 1 inch and air entrained concrete.
6.35
The equation f'cr = f'c + 1.34s represents a reliability of ______
90%
In the United States, a standard sack of cement is
94 lb
A graph shows the stress-strain relationship of several concrete with different w/cm ratios. If the line in the middle of the graph is for normal concrete at w/cm=0.40, where would the line be for concrete with w/cm=0.30?
Above the 0.40 line because it is stronger and can handle more stress.
Which method would increase a concrete mix from 2" slump to 4" slump?
Add water reducer Use round aggregate rather than angular aggregate Add more water Add air entrainer
The primary product of cement hydration is
C-S-H
The purpose of adding gypsum is to react with _____________ to regulate the setting time of cement
C3A
A pozzolan is different from Portland cement because it does not react with water to form C-S-H, instead, it reacts with
Ca(OH)2
Which of the hydration product makes concrete susceptible to attack by sulfate and acidic waters?
Ca(OH)2
The arbitrary volume method states that "1:2:3" for
Cement : Sand : Coarse Aggregate
High-Performance Concrete can be engineered to meet special requirements such as
Durability in severe environment Ease of placement and compaction High early-age strength
Which of the following statement about extra high w/cm is NOT true?
Excess water DOES NOT increase the concrete's resistance to freezing and thawing. Excess water DOES increase the porosity and permeability of concrete. Excess water DOES increase the volume change of concrete which then leads to shrinkage cracking. Excess water DOES cause the development of capillary voids in the concrete.
Curing is only needed for concrete in the summer time. Since water won't evaporate in cold temperature, curing is not needed for concrete in cold temperature.
FALSE
For normal concrete such as those made in the lab of this class, the slump is usually 1~5 inches. However, SCC can have a slump much as 32 inches. The max slump is limited to the height of the slump cone, which is 12 in.
FALSE
If no air entrainer is used for a concrete mix, the air content test shall result with a value of 0%. If not, the air meter is wrong and should not be used for future testing.
FALSE
SCC is highly flowable because of the increased amount of water content (aka high w/c ratio)
FALSE
To help the compaction of concrete the vibration time should be as long as possible
FALSE
Water reducers reduce the need of water to complete hydration process, but they at the same time reduce slump, making the concrete hard to work with.
FALSE
Lightweight concrete used in applications such as ASCE concrete canoe which can float on water, is defined as concrete with a density smaller than water (62.4 pcf)
FALSE (has to be less than 115 pcf to be considered lightweight concrete)
By using high range water reducer, shrinkage-compensating concrete has very low c/c ration, hence eliminates the possibility of shrinkage
False
In addition to the interlayer space and capillary voids, air can be trapped in the cement paste during mixing. The trapped air can greatly increase the durability of the cement paste in resisting freeze and thaw. True or False?
False
Which supplementary cementitious material is sphere shape?
Fly ash
Which of the following statement is not correct regarding fly ash?
Fly ash DOES NOT accelerates the hydration process. FLY ASH DOES reduce the permeability of concrete, increase the ultimate strength of concrete, and increase the workability of the fresh concrete
Picture of someone rolling white paper sheets onto concrete shows which method of curing?
Impervious paper or plastic sheets
Portland cement was named after
Isle of Portland, UK
High permeability has many impacts to concrete. Which of the following is NOT a concern for the durability of concrete.
It allows CO2 to penetrate, which increases the pH level of concrete. NOW ALL OF THE FOLLOWING ARE CONCERNS FOR THE DURABILITY OF CONCRETE DUE TO HIGH PERMEABILITY: It allows water to penetrate, which causes corrosion of steel rebar. Also the water can freeze in the winter and break the concrete. It allows chemicals (ex. chloride ions from deicers) to penetrate, which can cause chemical attacks.
Which of the following property does NOT belong to high-strength concrete?
It can last for over 100 years THE FOLLOWING PROPERTIES DO APPLY: It has very low porosity It utilizes superplasticizers (high-range water reducer)
Which application does NOT utilize the benefit of accelerator admixture for concrete?
Placing concrete in hot temperature THE FOLLOWING DO UTILIZE THE BENEFIT OF ACCELERATOR ADMIXTURE FOR CONCRETE: Placing concrete in cold temperature Emergency repair of a concrete joint blow-up on I-90 Fast form release of a concrete building
Which curing method is NOT recommended for concrete in cold temperature?
Ponding THE FOLLOWING ARE MORE RECOMMENDED: Insulating blankets forms left in place steam curing
Which statement is NOT true about RCC
Requires slump as low as 1" THE FOLLOWING ARE TRUE: mainly used for construction of dams costs about 1/3 of conventional concrete because of its low cement content can be constructed fast because no framework
During the pour of a concrete bridge deck in this summer, a thunderstorm was approaching in 10 minutes and was expected to last for 30 minutes. What admixture could be used to save the truck of concrete that just arrived on site?
Retarder
The picture of a truck pouring concrete into a rectangular area and it flows to cover the whole area illustrates which unique feature?
Self-consolidating concrete
Silica fume has unique properties. Which statement is not correct?
Silica fume DOES NOT slow down the hydration process. Silica fume DOES/CAN greatly increase the strength of concrete. The particle size of silica fume IS extremely small (1/100th of cement). Silica fume CONTAINS primarily amorphous SiO2
Which statement is NOT correct about fiber-reinforced concrete?
Similar to steel reinforcement, fiber-reinforced concrete greatly increases the strength of concrete, hence reduces the size of structural beams and columns THE FOLLOWING ARE CORRECT: Fiber-reinforced concrete can use fibers made from steel, plastic, glass, and natural materials The addition of fibers to concrete reduces the workability Fiber-reinforced concrete can have up to 30% higher flexural strength than normal concrete
Which of the following is NOT an admixture to concrete?
Slag Cement ALL OF THE FOLLOWING ARE ADMIXTURES TO CONCRETE: Air Entrainer Water Reducer Corrosion inhibitor
Which supplementary cementitious material is a byproduct of steel manufacture?
Slag cement
Concrete should be deposited continuously as close as possible to its final position in order to:
Speed up the construction process Avoid Segregation Improve the appearance (uniform and consistent)
Shortcrete is also known as
Sprayed concrete
Air entrainer also increases the slump of fresh concrete, making the concrete easier to work with.
TRUE
The two key parameters to control during concrete curing are moisture and temperature.
TRUE
A residential driveway project was constructed this August. One week after the pouring, the customer complained about the appearance of "tiny cracks" on the brand new concrete request a redo of the whole project. What might be the cause of this problem?
The aggregates were too dry in August but no adjustment of water was made to compensate for it The w/cm was too high The fresh concrete was not cured well cause the loss of surface water
Heavyweight concrete has special applications such as the following, EXCEPT:
The construction of 24 concrete ships in WWI due to lack of steel CERTAIN APPLICATIONS FOR HEAVY CONCRETE ARE: Nuclear power plant The cancer center in Dubuque Concrete liner for the "Runit Dome" Anywhere with radiation or nuclear activity
During the process of designing a concrete mix, engineers should consider:
The fresh concrete should be easy to work with The concrete should be economical The hardened concrete should have sufficient strength
In concrete industry, "Abrams' Law" states that
The strength of a concrete mix is inversely related to the mass ratio of water to cement.
During the concrete mix design process, the strength fc' called for by the structural engineer is factored to a greater value f'cr to account for ______
The variation of batching and mixing the concrete The variation of materials (especially aggregates) The variation of placing the concrete
By weight, the primary compound of Portland cement is
Tricalcium Silicate C3S
The Rountree Trail in Platteville, WI was delayed so the concrete had to be poured in December. One way to assure a good quality concrete is by using ________________ cement
Type III
Despite the benefit of short construction time, Type III high early strength cement is not used in all project due to
Type III cement is more expensive due to the stricter grinding requirement. Only 4% of cement produced in U.S. are Type III cement. High early strength can also be achieved by increasing the cement content.
The most important difference between ACI Weight-based method and ACI Volume-based method is that ______
Volume-based method considers the volume of air.
Ingredients of concrete (coarse and fine agg) in most concrete plants are measured by
Weight
Both aggregate and cement paste, when tested individually, exhibit linear stress-strain behavior. However, the stress-strain relation of concrete is nonlinear. This is because _____________
When concrete is under loading, microcracking forms at the interface between aggregate and cement paste.
Bowling ball competition BBmass is 5.5 +/- 0.5 kg BBdiameter is 200 +/- 15 mm BB was measured as 6.0 kg and 200 mm diameter, was this made of lightweight concrete? (has to be less than 115 pcf which is equal to 1842.12 kg/m^3)
Yes, it was made of lightweight concrete
Comparing to Type I Normal cement, Type III High early strength cement
has similar composition but much finer
One way to make economical concrete is to select aggregates as ______ as possible
large (the larger the aggregates, the less you use making it more economical)
Generally, more severe exposure conditions require ______ w/cm ratio
lower
In practice, concrete has a w/cm higher than the theoretical minimum. This is in aim to
make the fresh concrete "soupy" enough for placement
Curing not only increases strength, but also ______
reduces permeability, hence increases resistance to chemical attack increases the resistance to freeze and thaw reduces the chance of drying shrinkage
The purpose of adding gypsum into clinker is
slow down the setting time of cement
Cement are very fine powders. 1 pound of cement has a total surface area of 1500 to 2000 ft^2, which can cover the area of a
volleyball court
Among all factors that engineers can control, the most significant factor that controls the strength of concrete is __________
w/cm ratio
In concrete industry, w/cm stands for
water-cementitious materials ratio
