020301c Concret Mix Design Flashcards
(116 cards)
1
Q
The tensile strength of concrete is approximately 10% of the compressive strength. T or F
A
T
2
Q
The concrete used in most construction projects is between ___ and ____
A
14 mPa to 35 mPa
3
Q
A chemical reaction known as ____ occurs between the cement and water.
A
Hydration
4
Q
Hydration is what causes the solidification of the plastic concrete into a stone-like mass. T or F
A
T
5
Q
The cement paste, aggregate and reinforcing steel in reinforced concrete all have similar thermal expansion rates. T or F
A
T
6
Q
Why does rebar have lugs or deformations?
A
For the concrete to bond to the steel
7
Q
Why might cast in place concrete be more expensive than precast?
A
Because forms must be erected and stripped for each pour.
8
Q
Is case-in-place quality harder to maintain than precast concrete?
A
Yes. It is often cast in an uncontrolled environment.
9
Q
How is pre-stressed concrete achieved?
A
Post-tensioning or pre-tensioning.
10
Q
Pre-stressed concrete allows members to have long, clear spans with a smaller cross-sectional area than that of traditional reinforced concrete. T or F
A
T
11
Q
Does pre-stressed concrete reduce the weight of the building and the cost of construction. T or F
A
T
12
Q
____ is concrete that had the consistency of plaster.
A
Shotcrete
13
Q
Self-levelling gypsum concrete is used as a fire separation on floors of multi-storey wood frames residential structures and reduces the transition of sound between floors. T or F
A
T
14
Q
Portland cement accounts for 7% to 15% of the volume of concrete. T or F
A
T
15
Q
All Portland cements are _____ cements which set and harden through _______.
A
Hydraulic, hydration
16
Q
Portland cement is a finely ground powder manufactured from a variety of raw materials. These materials can be?
A
Limestone, iron, silica, alumina, gypsum
17
Q
Portland cement is a brand name. T or F
A
F
18
Q
Portland cement is a fine grey powder made with ____ _____ and limestone.
A
Calcium silicate
19
Q
______ _____ is a dry powder that, when mixed with water, forms the paste that binds aggregates together to form concrete.
A
Portland cement
20
Q
Property had high compressive strength, is durable, permeable or watertight. T or F
A
T
21
Q
Does Concrete has fire resistant and sound resistant qualities?
A
Yes
22
Q
Concrete can withstand harsh elements and resist corrosive chemicals, decay and abrasives. T or F
A
T
23
Q
A chemical reaction known as ______ occurs between the cement and water. This causes the solidification of the plastic concrete into s stone-like mass.
A
Hydration
24
Q
Aggregates are usually gravel and sand that are graduated so that the voids between the particles are filled with smaller particles. T or F
A
T
25
To be at the most sound, cement must entirely cover the surface of each aggregate particle and fill any voids between the aggregates. T or F
T
26
The strength of concrete depends on the ratio of water to Portland cement. T or F
T
27
What is the normal range for concrete used in most construction projects?
14 MPa to 35 MPa (2300 psi and 5000 psi)
28
Cement is strong in compression but weak in ______.
Tension
29
What helps concrete resist tensile forces?
Reinforced steel such as rebar.
30
Why does concrete have lugs or deformations?
Increases the bond between steel and concrete.
31
What allow cement paste, aggregate and reinforcing steel in reinforced concrete to work together?
They have similar thermal expansion rates.
32
A chemical action takes place during hydration that may clean small amounts of rust and corrosion from the surface of the steel. T or F
T
33
Cast-in-place concrete tends to be more expensive and quality control is harder to maintain. T or F
T
34
How are architectural concrete finishes created?
Different colours and surface textures, ranging from urged to a smooth, ceramic-like finish.
35
What is the benefits of Pre-Stressed concrete?
Allows members to have long, clear spans with a smaller cross-sectional area than that of traditional reinforced concrete. This reduces the weight of the building and the cost of construction.
36
What are 3 reasons concrete is a good paving material?
1. Can be used for architectural surfaces for sidewalks and patios and for non-slip surfaces.
2. Durable surfaces that resists the grinding action of traffic.
3. Withstand freeze-thaw cycles and de-icers.
37
For patterned concrete the face of the concrete form or casting bed is lined with plastic or rubber form liners. T or F
T
38
To achieve an exposed concrete surface the face form or surface of the concrete can be treated with a _____ that prevents the surface concrete from setting. After the base concrete sets, the surface is _____ washed leaving the aggregate exposed.
Retarder, pressure washed
39
What are some ways to achieve an exposed aggregate surface?
Sandblast, high pressure water jet to wash the mortar away from the aggregate before the concrete is completely set, grind the surface of the hardened concrete to expose the aggregates.
40
How does one attain a smooth terrazzo-like floor surface?
Grind the surface of hardened concrete to expose the aggregates.
41
What are the most common methods to colour concrete?
Dry shake colour gardeners, colour admixtures, pigments, chemical stains, and white and coloured cements.
42
Dry shakes are designed for colouring and hardening the surface of new concrete. T or F
T
43
_____ _____ is a powder material that is spread on the surface of the concrete at a predetermined rate.
Dry shake.
44
Dry shake colour hardeners are mixed into the fresh concrete paste at the surface and a colour sealed is sprayed onto the surface after the concrete has been given its final troweling. T or F
T
45
Colouring agents (synthetic pigment admixture) increases the strength, improves workability and disperses the pigment uniformly throughout the concrete mix. T or F
T
46
What is a one benefit and one detractor for using colouring agents opposed to dry shake colouring?
Colouring agents cost increases proportionately to the desired concrete thickness but if the surface is damaged the colour is not lost. This is not the case when using a dry shake, since only a thin layer of the concrete surface is coloured.
47
Concrete can also be coloured by adding mineral oxide pigments directly to the concrete mix. T or F
T
48
Mineral oxide colour pigments DO alter the strength and workability of concrete. T or F
F. They do not
49
When should chemical stains be applied?
Properly cured. Atleast one month old and free of foreign matter that can prevent penetration and reaction of the stain with the concrete.
50
Chemical stain is not merely a surface coating; it penetrates the top layer of the concrete. T or F
T
51
To maintain the colour of concrete surfaces which were chemically stained, subjected to heavy traffic, a coloured wax or sealed must be applied and then reapplied as needed. T or F
T
52
Poor quality vertical architectural concrete surfaces are usually the result of loose joints in the formwork. T or F
T. This allows bleed water to escape, cause discolouration of the concrete.
53
Concrete masonry units are based on modules of ____.
100 mm (4")
54
What is shortcrete?
A concrete that has the consistency of plaster. It is placed with a pneumatic gun that shoots the concrete onto the form n
55
Self-levelling gypsum concrete is mixed with a high slump and its properties allow it to flow to a level surface and harden into a smooth surface without troweling. T or F
T
56
Finish flooring cannot be laid on self-levelling gypsum concrete. T or f
False
57
What is insulation concrete used for?
Used to protect structural steel components of s building from fire damage and to insulate underground heating ducts and pipes.
58
Where is heavyweight concrete used?
Used against x-rays, gamma rays and neutron radiation. Weighs up to 6.4 kg/m3
59
Where is soil cement used?
As a strong, durable base for asphalt pavements
60
Recycled concrete is often used as the aggregate for roller-impacted concrete. T or F
T
61
Ultra-High Performance Fibre Reinforced Concrete uses 2% fibre reinforcement. T or F
T. The fibre size is 0.2 mm diameter by 12 mm long.
62
What are some benefits of UHPC?
1. Thinner sections and longer spans 2. Reduction or elimination of reinforcing bars 3. Increased water tightness 4. Deform and support flex urial and tensile loads 5. Combined high compressive strengths with flexural strengths around 50 MPa
63
How does shrinkage compensating concrete work?
Offsets the natural contraction of concrete and the resulting cracking by using expansive cement or admixtures which causes the concrete to expand while hardening.
64
Where is self-consolidating concrete most ideally used?
Heavily reinforced or intricately detailed formwork.
65
How is self-consolidating concrete formed?
With aggregate size and super plasticizers that optimize its ability to flow and consolidate on its own while filling tight spaces without segregation or bleeding.
66
How does one measure the flow ability of SCC?
J-RingTest
67
Name three situations where Rapid Setting concrete is ideal?
1. Early strength is critical
2. Formwork has to be cycled quickly
3. Precast applications.
68
Rapid setting concrete is designed to maintain the required slump for placement for a 2 hour window then undergo a rapid strength gain allowing the removal of formwork approx. 4 hours from time of catching. T or F
T
69
Where is Controlled Density Fill commonly used?
CDF is a self-compacting cement based material that is commonly used for structural fill, pavement bases and conduit or pipe bleeding. Due to its flow able nature it is often used in area where placing and compacting of granular fills would be difficult.
70
Calcium chloride should not be used under what conditions?
With plain uncoated reinforcement steel is used (corrosion), when aluminum conduit is in the slab ( chemical reaction to create heat and gas bubbles), and with TYPE 5 concrete.
71
Which type of Portland cement is needed when meant to be put into service quickly?
Type 3 - High Early Strength
72
Which type of Portland cement type is used where there is a moderate danger of sulphate attack from ground water?
Type 2 - Moderate
73
Fine aggregates consist of a range of particles not larger than ___ mm or smaller than ___ mm
5.0 mm, 0.33 mm
74
Coarse aggregates consist of a range of particles that are not larger than ___ mm or smaller than __ mm
40 mm, 5 mm
75
Patching mixes that have been modified with latex have a short pot life (working time) and must be placed within one hour of mixing. T or F
T
76
_______ improve the in permeability of hardened concrete and are useful for such items as tanks, pipes and swimming pools.
Waterproofed
77
What is the main difference between concrete and mortars/grouts?
Mortars and grouts contain no coarse aggregates. Mortars and grouts are specifically designed mixtures of cement paste and find aggregates.
78
What is the primary difference between mortars and grouts?
Mortars are bonding while grouts are filler.
79
What are the two most common types of mortars on the job site?
Masonry and tile mortars.
80
____ is added to mortar to increase its binding properties and to give it workability.
Lime
81
What are the two groups of grouts?
Structural and tile grouts
82
It is not important that the grout completely fills the void and does not shrink as it sets. T or F
F. It is important
83
What are the two groups of structural and repair grouts?
Cement and polymeric
84
Where should metallic grout not be used?
In damp areas or exposed to acid or alkali conditions.
85
Why are gassing agents sometimes added to concrete and grout?
To cause slight expansion prior to hardening.
86
What is a polymeric grout?
Resin-based and do not contain cement.
87
What three components is epoxy grout composed of?
Epoxy resin base, hardening agent and carefully graded aggregate.
88
Which polymeric grout would be better suited for grouting the bases of large equipment? Epoxy or urethane
Epoxy. Higher compressive strength.
89
What is the first step in creating an exposed aggregate surface?
Treating the form or surface of the concrete with a retarder agent that prevents the surface from setting.
90
Describe two methods of placing grout:
Stiff mix tamped with a rod.
Flowable.
91
List 5 basic characteristics of mortars:
1. Strong binding
2. Workability
3. Minimum shrinkage and settlement
4. Watertight joints
5. Range of compressive strengths
92
Which additive makes it easier to work hardeners into the surface when finishing concrete?
Air detainers. Decrease the air content and improve the surface quality and density.
93
To make the colour more vivid when using a colouring agent, what type of cement should be used?
White Portland cement
94
When bonding admixtures are used, the concrete and grouts should be used within what period of time?
One hour.
95
What additive can be used when the concrete is to be placed with a pump?
Pozzolan. Improves workability and easy to pump while reducing the heat generated by hydration. Replacement for extra water
96
Can accelerators be used as anti-freeze for cold weather concrete?
No.
97
Calcium chloride accelerators should not be used under what conditions?
Plain uncoated reinforcement is used, aluminum conduit is in the concrete, with Typr 5 (sulphate resistant)
98
When are super plasticizers added to the mix?
Just before it is discharged.
99
Concrete should contain ____ to ____ % of air-entrainment in order to be protected from damage by freezing.
5 to 8 %
100
What test is done to check for the presence of organic material in the aggregate?
Colorimetric
101
What tool is used for testing the strength of hardened concrete without having to damage the concrete?
Impact hammer
102
The compressive strength of concrete is measured by:...
Cylinder tests, 7,14,28 days
103
What does a slump test measure?
Workability and consistency of concrete.
104
In a traditional mix design of 1:2:3 what is the mix???
1 part cement 2 parts sand 3 parts gravel or crushed Rick
105
Which method is used to mix concrete at a ready-mix plant?
The absolute volume method. Mixing the 1:2:3. Weighing them out separately and adding just enough to water to make it workable.
106
What is the most likely result of adding water to ready-mix concrete on the job site?
Weaken the strength of the concrete
107
Why are different sizes of aggregate used?
To reduce the volume of the voids between the particles, which reduces cement paste.
108
Aggregates make up ____ to ____ of the total concrete volume and identify the 6 major qualities it must have.
60 to 80 %
109
What is the main difference between concrete and mortars/grouts?
Mortars and grouts do not use coarse aggregates and a rich mix
110
On slabs with a high requirement for flatness a ____ pass with the bullfloat may be required.
2nd
111
With concrete dividing patios and exterior slabs should be divided at intervals not greater than ____ m. While transverse are usually placed 1.5 to 2 m.
5-6 m
112
Using the colourimetric test, if the colour ranges from light to dark straw in colour, after 24 hours can it be used?
Yes it can. Don't use if dark chocolate brown.
113
Which type of Portland cement concrete is used it the tap water is very hard?
Type 5 sulphate resistant hard water usually indicates a high amount of sulphates in the ground water.
114
What is type 4 Portland cement?
Low heat of hydration. Generates head at a slower rate. Massive structures
115
It takes __ bags of premix to make one cubic foot and ___ bags to make one cubic metre.
3
| 36
116
It takes __ bags of premix to make one cubic foot and ___ bags to make one cubic metre.
3
| 36
