問題一覧
1
The most used construction material by volume are
Concrete>timber>steel
2
The coefficients of thermal expansion of steel and concrete are
about the same
3
What is the annual emission of CO2 associated with concrete?
1-5 billion metric tons
4
What is the dominant mode of catastrophic failure associated with concrete structures?
Brittle fracture of concrete
5
Among all engineering materials, which is used the most by volume and weight?
Concrete
6
What is a dominant mode of catastrophic failure associated with polymer under load?
Creep of polymer
7
Grading of aggregates is quantified by
sieving of aggregates using sieves with a range of hole sizes, weighting the amount of aggregates left on each sieve
8
It is important to measure the moisture content in aggregates because
dry aggregates can absorb water in a concrete mix, the moisture content can influence the w/c ratio unless properly accounted for, wet aggregates brings additional water into the concrete mix
9
In a slump test, a workable concrete should
show several inches of slump with aggregate and paste in cohesive form
10
Angular and rough aggregates cans reduce workability of concrete, but can be compensated by use of water reducing admixture
True
11
The MAS appropriate for a job is determined by
the size of dorm work, the locally available aggregate size, the spacing between rebars
12
The role proper aggregate graduation plays in concrete workability is critical
True
13
It is important to measure the moisture content of aggregates because
it introduces additional amount of water brought into a concrete mix, if wet, it varies depending on weather exposure condition, it removes some amount of water which otherwise is meant for cement hydration, if partially dry, it is used to adjust the amount of mix water in order to keep the water to cement ratio at target value in the concrete mix design
14
The absorption capacity of aggregates can be obtained by using
the weight difference between the OD and the SSD weight
15
The numbering system on aggregate sieves indicate
the number of meshes per linear inch
16
The mositure content of aggregates can be obtained by
the weight difference between the stock pile weight and the SSD
17
Aggregates are size graded for the purpose of
reduce cement paste , enhance durability , economy, enhance workability
18
The dividing line between coarse and fine aggregate is
4.75 mm
19
The MAS suitable for a particular concrete job is determined by
the minimum clear spacing between reinforcing bars or between bars and framework, the concrete mixing and placing equipment , the thickness of concrete slab, the smallest dimension between sides of concrete formwork
20
The surface mositure of aggregates can be obtained by using
the weight difference between the stockpile weight and the SSD weight
21
Pervious concrete
is used to enhanced water drainage through concrete slabs and reduce runoff in cities , is obtained using a concrete with no fines
22
What is the particle size of Type I OPC cement grains?
15 micron on average and can be up to 50 micron
23
Type III Portland cement is
has lower long term strength than Type I OPC, a type that has high early strength , has finer particle size than Type I OPC
24
What are the essential compounds formed as a result of OPC hydration?
C3S2H8 and CH
25
The fineness of cement grain
governs the early age of compressive strength , governs the amount of heat of hydration , governs the long term compressive strength , governs the water demand for hydration
26
What are the most essential raw ingredients fed into a cement kiln to produce Portland Cement clinker?
limestone and clay
27
Cement gain strength over time due to
filling up the spaces with more solids , continued hydration
28
The main reason why aggregates are incorporated into concrete is
economical
29
Hydration of cement involves
the difusion of calcium ions into the mix water between cement grains, the filling up of space occupied by mix water , the formation of calcium-silicate-hydrate(CSH) and calcium hydroxide(CH)
30
Cement hydration involves the following ingredients reacting with water;
calcium silicate compounds
31
CaOH crystals looks like
platlets
32
Type C fly ash involves both pozollanic reaction and hydration reaction
True
33
Higher w/c ratio gives rise to smaller amount of capillary pores
False
34
The hydration of C3A is expansive and does not stop even when space is not available
True
35
Under microscope, CSH appears
gel like , crumbled paper
36
Under microscope, CH appears
platelets
37
The annual global production (tonnes/year) of the three materials, in order, is
concrete > wood > steel
38
The specific strength of parallel-to-grain wood is competitive to that of high strength steel
True
39
Clear wood refers to wood
with no defects , along grain
40
Wood properties are anisotropic inWood properties are anisotropic in
tensile strength, drying shrinkage, compressive strength
41
Hardwood is stronger than softwood
False
42
The compressive stress-strain curve perpendicular-to-grain wood shows a more-or-less plateau branch after the limit of proportionality because of
crushing of cell walls
43
The growth portion of a tree is
the cambium
44
Hardwood may or may not be stronger than softwood.
True
45
A well-designed concrete should have fresh properties that allows it to be
castable without segregation of ingredients , easy to finish , pumpable
46
The annual COz emission (tonnes/yr.), in order, is
steel > concrete > wood
47
Drying shrinkage is highest in the longitudinal direction of wood.
False
48
Optimal air content for durability should be in the range of
4-10%
49
The objective of concrete mix design is to proportion mix ingredients such that the resulting concrete
is economical , meets target durability , meets workability requirement
50
Under flexural load of clear wood, a crack from the tension side may bifurcate because
the microstructure of wood reduces the resistance to crack propagation in the along-grain direction.
51
Cell walls of wood is made up of long molecular chains of (C6H1005)n.
True
52
The grading curves indicating grading limits in ASTM C33 varies with the maximum aggregate size
True
53
The three most common categories of chemical admixture used in concrete are
plasticizing admixture , air-entraining agent , set-controlling admixture
54
Water in wood dries out in the cell wall first, before water is evaporated from the lumin.
False
55
Prior to conducting concrete mix proportioning, it is necessary to collect job parameters, including
the dimensions of the structural element and reinforcement details , the climatic condition of where the construction/structural element is located , the type of element such as slab, beam, column to be constructed , the required 28-day compressive strength
56
Evaporable water can be found in the lumin and bounded water in the cell wall of wood.
True
57
Fresh concrete slump
should be chosen according to the type of construction
58
Evaporable water can be found in the lumin and bounded water in the cell wall of wood.
True
59
Air entrainment
should only be used if necessitated by freeze-throw durability consideration
60
The strength of wood is influenced by
the presence of seasoning defects., the slope of grain, the presence of bark pockets., the presence of tension and compression wood.
61
A concrete mix design represents
the weight of water, cement, coarse and fine aggregates, and admixtures for a given volume of concrete
62
The tensile strength of clear parallel-to-grain wood can reach
150 Mpa
63
Cell walls of wood is made up of 70% crystalline cellulose and about 30% amorphous lignin.
True
64
The specific gravity for most pozzolans
is lower than the SG of cement
65
The slump test is appropriate for fresh property testing of
most concrete mix except those design for self-consolidation
66
The embodied energy (MJ/m%) of the three materials, in order, is
steel > cement > wood
67
Wood properties are anisotropic in
drying shrinkage , compressive strength , tensile strength
68
Workability of fresh concrete is influenced by
water content , time and temperature , aggregate grading, shape and roughness, cement characteristics , admixtures
69
Segregation of aggregates in concrete may occur due to
insufficient fines, high SG of coarse aggregates , angular, rough coarse aggregates
70
Drying shrinkage of wood can lead to
splitting, checking, warping
71
For quality control of concrete, the following properties are measured for fresh concrete
air content , unit weight , slump
72
Compared to the compressive strength, the tensile strength of wood is
higher
73
Drying shrinkage increases rapidly below the fiber saturation point (FSP).Drying shrinkage increases rapidly below the fiber saturation point (FSP).
True
74
The workability of concrete is
fresh property of concrete relating the ease which it can be mixed, placed, consolidated and finished , good when the concrete can be compacted with minimum energy and without segregation
75
The specific stiffness of parallel-to-grain wood is better than that of high strength steel
True
76
Fresh concrete should
have no segregation of ingredients, including bleeding , be capable of being finished properly , uniform within a batch and between batches , be easily mixed and transported , completely filled the formwork , have the ability to be fully compacted
77
Caution should be used in applying chemical admixture in concrete because excessive amount can lead to
undesirable amount of chloride , undesirable strength loss, undesirable slump
78
The specific strength of parallel-to-grain wood is competitive to that of high strength steel
True
79
The workability of fresh concrete is measured using
ASTM C231, the slump test
80
Under oven-dry condition, wood can shrink in volume by as much asUnder oven-dry condition, wood can shrink in volume by as much as
20%
81
Chemical admixtures in concrete are used to
adjust slump and to enhanced ease of placement of the fresh concrete , control the amount of air in the concrete , reduce the amount of water while maintaining workability , control the set time of the fresh concrete after casting
82
During spring growth period, cells that are formed
have relatively thin walls, have open texture
83
Wood characteristics of interest for construction includes the broad classes of
visual characteristics , durability characteristics, fire characteristics , environmental characteristics , basic physical characteristics , mechanical characteristics
84
Test standards used by the concrete industry include standards published by
CSA in Canada , RILEM in Europe , ASTM in the US, CNS in Taiwan
85
Compare to that in the perpendicular direction, the compressive strength of wood in the parallel direction
can be several times
86
Sample of concrete for quality control at the construction site should
be tested within 5 minutes after collection , be taken from a full stream of concrete coming off the chute from a ready-mix truck
87
For control quality control, concrete samples are typically made
by collecting representative concrete material at the job site
88
Wood characteristics
vary across tree species, vary across each cut board
89
Some disadvantages of wood as a construction material include its being
susceptible to fire damage, susceptible to insect damage, susceptible to dimensional change under varying humidity, susceptible to fungi attack
90
The wall panels for the building shown in the video are
16 inch thick solid wood
91
ASTM standards are used for concrete testing for the purpose of
standardizing test method , standardizing specimens preparation procedure , standardizing specimen size and shape , standardizing to allow comparison of test data conducted by different laboratories
92
Seasoning of wood is needed for the purpose of
stabilizing its moisture content, reducing dimensional changes when in use
93
If the slump test is too small, water can be added at tbe construction site to enhance workability
False
94
The material property which governs brittle fracture is
facture toughness
95
The unit of fracture toughness is
MPa (m)^1/2