midterm 1 Flashcards
1
Q
caracteristics of sustainable material
A
durable
local or regional production
contain recycled materials
manufactured with minimal pollution
do not themselves pollute
min energy to produce
reusable
renewable rapidly
can be used in a way that lessen environmental, social and economic impact
2
Q
what is sustainable development
A
sustainable développement is a global concept that looks at every aspect of a cdertain industry over an infinite timeline, material are chosen on their total energy consumption from start to finish
3
Q
whats the life cycle of products and processes
A
material extraction-> material processing -> product manufacture -> construction process -> building -> demolition -> landfill
4
Q
wich are the two life cycle process that are the same step for concrete
A
product manufacture and construction process
5
Q
whats the embodied energy of steel(mini and conventional mill), concrete and wood?
A
mini mill steel 15Mj/kg
conventional mill 46Mj/kg
concrete 0.75Mj/kg
wood 5.8 Mj/kg
6
Q
whats the concrete usage vs population growth factor from 1970-2004
A
3.5x (cement) steel more than doubled
7
Q
what are the3 issues of concern for the concrete/cement industry and explain
A
-profitability: profit margin for cement small so can’t change things
-compliance to standards: verry regulated so not much innovation/trials
-sustainability: cant change concrete for greener alternative, can only make concrete greener
8
Q
how much concrete do we consume as humans?
A
concrete is the second most consumed thing behind water annually
9
Q
what are the negative impacts of concrte and steel production ?
A
enormity of ressources used
generation of large amount of CO2 (concrete single biggest polluting industry outside of power generation)
10
Q
how much CO2 is liberated per tonne of cement?
A
almost 1 tonne
11
Q
what are the CO2 emission sources in the concrete industry?
A
-material manufacturing
-concrete manufacturing
- construction
-repair and rehabilitation throughout service life
-demolition and recycling
-transportation at each stage
12
Q
what are the 3 key words for sustainability in order of importance and a quick def and how to effctively do it
A
Reduce: eliminate unecessary space in buildings, cconsume less mats when building and finally improve durability
reuse: renovate instead of rebuild, use mats in the construction phase that can be reused ex bolted connections instead of welds in steel, homogeneous mat instead of composite
recycle: less efficient than last two, but can be used for most mats concrete,wood,steel
13
Q
how can concrete become more sustainable?
A
-manufacture portland cement more efficiently
-using waste mats as fuel(burn rubber tires)
-replacing portland cement with SCM and or fillers
-make it more durable
-use recycled concrete as aggregates
-capture, store or utilize CO2 emission
-improve structural design and building code make them sustainable
-effective maintenance and repair Strats(not like Mtl)
14
Q
what are the four time scales over wich we need to examine industry environement interactions?
A
1)Past: remediate measure for dealing with innapropriaye waste disposal
2) present: prevent mistakes from the past by emphasizing waste minimazition, avoid toxic mats, control co2 emission
3)future: industry-environement interactions dictated by industrial products of today
4) far futur(50+years): industry environement interactions dictated by industrial process dev for futur use
15
Q
why is it more expensive to build a road of concrete instead of cement if asphalte is more expensive than conrecte
A
concrete doesnt flex like asphalte so need more concrete (thicker)
16
Q
what are engineering mats
A
defined as the inanimater matter that are useful to the engineering profession, consitute backbone of modern civilaztion
17
Q
what are mats science
A
refers to knowledge of physical science as general truth and Principe in particular physic and chem
18
Q
what are the four groups of eng mat
A
1: matal and alloys
2 ceramic and glass
3 organic polymers
4 composite
19
Q
descibe metal and alloys
A
metals: capable of changing shape permenantly, good thermal and electrical conductivity and reflective of light
alloys: combination of more than one metal (steel) all metals used in eng are alloyed with something(iron,steel,alluminum,copper)
20
Q
describe ceramic and glasses
A
-made from a combination of element from both the metaks and non metals of periodic table
-non metalic innorganic substances
-brittle
-good thermal and insulating prop
ex:bricks,tiles,silica
21
Q
describe organic polymers
A
-composed of large num of molecules joined like a chain
-majority of eng polys are hydrocarbons
-eng polymers are syntethic and natural(wood,rubber)
-relatively inert and light
-high plasticity
-good compatibility with human tissue
-resist atmospheric and other corrosion
-resiste elec current
ex PVC,PVA, epoxy,cotton
22
Q
descibe composites
A
- combination of other mats
ex concrete, fibre reinforced polymers
23
Q
three area of implementation of mats and what types do they all have in common
A
structural: objects without moving parts(bridge, dams)
machines: involves major parts(jet engines, elec motors)
devices:eng innovations (lasers, transistors)
metak and alloys, ceramic and glasses and polymers are all that can be in all 3
24
Q
mats caracteristics and properties wjat are they
A
-physicial (shape, size, finish, color, specific gravity, density, porosity, structure)
-Mechanical: strength, stiffness, elasticity, plasticity, ductility, creep, brittleness, hardness, toughness, resilience, impact resistance, fatigue behaviour)
-Thermal: specific heat, heat of transformation, thermal capacity, thermal expansion, heat transfer and thermal conductivity, thermal stresses, thermal fatigue, thermal shock capacity, latent heat of fusion)
-Electrical: resistivity, conductivity, relative capacity or dielectric constant, dielectric strength, semi-conductivity, superconductivity, corrosion resistance*
-Chemical: corrosion resistance*, atomic weight, valency, molecular weight, acidity, alkalinity, atomic number
-Magnetic: hysteresis, reductivity, retentivity, susceptibility, residual inductance, saturation value
-Optical: color, lustre, diffraction, fluorescence, reflectivity,
luminescence
-Technological: hardness, weldability, machinability, formability, castability
25
why is corrosion resistance in electrical and chemical properties?
because its an electrochemical reaction, electricity is created by movement
26
on what properties does bonding have a strong influence on?
strength and stiffeness
27
what are the five types of bonds atomic bonds? and an example for each
1)ionic(sodium chloride)
2)covalent(diamond)
3)metallic(sodium metal)
4)van der Waals(solid argon)
5) hydrogen
28
explain ionic bonds
forme when a cation(+) transfer an e- to an anion (-). generaly crystalline and higly soluble in water because of strong electrostatic binding force, rigid and high melting and boiling pts. generaly non conductors of heat and elec
29
explain covalent bonding
shares an e- between two atoms, formed by overlapping e- orbitals results in lower e- energy. localized and directional in nature so form definite angle between bonds. generaly soft, volatile, insolube, good insulators.
30
explain metalic bonding
e- are shared but not bound to individual or to pairs of atoms as covalent. instead free e- are free to move throughout metal, making good conductor. these bonds are delocalized ans non directional in nature
31
explain Van der Waals bonds
weak secondary bonds, can be found between covalent bonded chains of polys also formed when molecules undergo polarization
32
explain hydrogen bonds
special case of van der waals bonding from electrostatic interations between H atoms and O F or N atoms in molecules containing higly olar C-O, H-F or H-N bonds
33
what are the typical material for each bond types
ionic(ceramic, gypsum )
covalent(diamond glasses)
metalic metals
hydrogen water
van der waals thermoplastic polys
34
define a space lattice
infinite array of pts in 3D in wich every pts has the same surrounding identical to every other pts of the array
35
define a unit cell
smallest unit wich when replaced in space indefinetly will generate space lattice. so the smallest Volume that describe the structure of a mat
36
True of false metals are crystalline
true
37
true of fals glass is crystalline
False 0 crystal structure
38
why is glass not crystalline?
glass made of melted sand so crystal dissapear
39
unit cell diagram go see pp4
slide 2
40
how many space lattice are there
14
41
what are the thre basic configuration of space lattice?
simple cubic (SC) 1atom per unit cell
Body centered cubic (BCC) 2 a/uc
face centered cubic (FCC) 4 a/uc
42
go see crystal diagram pp4
yesssssssir
43
how can imperfectiton be classified on the basis of their geometry
point imperfection
line imperfection
surface imperfection
volume imperfection
44
describe point imperfection
imperfctions foudnin a point like region of the crystal. range from 1 to 2 atomic diameter in size and 3 forms:
1 vacancy
2 substitutional impurity
3 interstitial impurity
45
descibre the 3 forms of point imperfections
vacancy: atoms missing, gonna fail where bonds are weaker aka hole
substitutional: a different atom (intruder)
interstitial: extra small atom
46
describe line imperfection or dislocations
cause latice distortion around a line. created during solidification or during plastic defo of crystal structure. one dimensional and have 2 types
edge disloation
screw dislocation
47
describe edge dislocation
created when an extra half plane of atoms are inserted in crystal structure. represented by T up if incomplete start at top or T down if starts at bottom known as (+,-) edge dislo. store E in distorted region around the disco
48
describe screw dislo
formed when upward od downward shear stress is aplied to a crystal thats been separated by cutting plane. induces a spiral like distortion. here concentration of shear strain created and E is stored
49
describe surface imperfection
region of distortion that lie about the surface, thickness of a few atomic diameter. ex external surface of crystal itself and grain boundaries of crystal
50
descibre grain boundary
narrow region of atomic mismatch between two grains. shape determined by restriction imposed by neighbouring grain
51
define a phase
physically distinct chemically homogeneous and mechanically separable region of a system
52
define the components of a system
chemical species that comprise the system. can be elements, ion or compounds
53
what is the phase rule
aka gibbs eq F=C-P+2
degree of freedom in an eq
54
what are the two boundaries in a binary phase diagram
liquidus(between liquid and two phase region)
solidus (between solid and two phased region)
55
what is a eutetic phase diagram
when solid solubility is limited and melting pts of components are similar
56
how do you call the phase boundary where the solid solubility is limited?
solvus
57
what type of diagram is formed when the melting pts of the components are vastly different
peritetic phase diagram
58
definition of macrostructure
structure as examined by the naked eye or under low magnification
59
def of microstructure
structure as observed using optical microscopy
60
substructure definition
structure obtained by using a microscope with a much higher magnification and resolution than the optical microscope
61
what re the 4 level of structure
Crystal structure
electronic structure
nuclear structure
molecular structure
62
define crystal structure
atoms situated in an orderly repetitive arrangement wich occupies space. Provides the detail of atomic arraingement within a cell. suffiecent to describe arrangement of few atoms in the unit cell
metals are crystal and steel is made of microscopy crystal
63
define electronic structure
electrons in the outermost orbitals of individual atoms of the solid. spectroscopic tech are useful in determining elec structure
64
define nuclear structure
studied by nuclear spectroscopic tech such as nuclear magnetic resonnance
(can look inside concrete without damaging it)
65
define molecular structure
spatial arrangement of small groups of atoms wich are strongly joined togetehr within the group or molecule
66
what structure exerts a major influence on the mechanical and physical properties of the mat
electronic structure
67
what structure exerts a strong influence on mat behaviour
molecular and crystal
68
the deformation of a mat is strongly affected by what structure?
molecular and crystal
69
how can failure occure give ex
mat defect, variation in properties, inadequate design, inadequately controlled processing, poor workmanship, insufficient maintenance, abuse, negligence, etc...
70
failure analysis graph explain
(Econ,safety,function and appearance) -> design -> mats selection -> fabrication -> machining -> assembly -> service -> failure analysis -> back to design
71
the tests to determine the properties of different mats can be what ?
destructive or non destructive
72
define size effect
the larger the specimen, the more likely it is to have flaws of greater severity. so more likely to have a lower fracture strength
73
why do we take size effect into account
because when testing brittle mats like concrete and woods , the effect on strenght can be significant. a small wood specimen is stronger thsn a concrete specimen
74
define the tensile test
one of the most useful, a sample is elongated at cst rate and load necessary to produce a certain elongation is measured as dependant variable
75
True or false we test concrete in tension
false, since concrete as low tensile force
76
engineering stress formula
sigma = P/Ao
77
engineering strain formula
epsilon = (l-lo)/lo
78
Hookes law formula
sigma = E x epsilon
79
whats the young modulus?
elastic modulus (E)
80
with what does the young modulus help?
helps limit deflection
81
linear elastic stress strain curve go see
pp.7 s 5
82
why are brittle mats not stromg in tension?
because they have micro cracks that propagate under tension but they close in compression thus may have high compressive strength(gray cast iron and concrete)
83
wheter a mat is brittle or ductile depends on what?
atomic or molecular structure and service conduction
84
what are the 3 srvice condition affecting the behaviour of the mat
temperature
strain rate
degree of triaxility
85
see graphs on failure mode pp 07
s8-9-10
86
what is necking
during plastic deformation, volume doesnt change even though there is elongation, the cross sectional area diminishes so the V stays cst
Aolo = Aili = cst
87
where do ductile material tend to fail in tension?
in shearing at an angle of 45 deg
88
how do brittle mats fail under tension
fail due to crack propagation perpendicular to axis of loading, show little to no necking
89
see pp07 slide 13-14-15 mid term q
oh yeah
90
what is the flaw of the splitting tension test
since the load is applied in the middle if the major flaw isnt there then its not gonna fail at its weakest pts and calculate the minimizing stress
91
whats th ration of tensil strength to compressive strenght for concrete
arond 10%
92
does necking arrise in the compression test?
no since the cross section of the specimen increases
93
how does concrete fail in the compression test
in tension/shear...
94
see pp 7 slide 21
yer
95
difference between three pts bending and 4 pts bending
in three pts bending, we only test the center but in the four pts bending 1/3 of it is tested so its more accurate go check pp 7 slide 23
96
what are the effects of shear stress
increased deflection
97
what are the shear formulas
go see pp 7 slide 25
98
what are the potential problems in bending test
high localised stresses at loading pts(when building you want supports to be round not circular so stress less concentrated, corners induce cracking)
frictional force
torsional loading(make sure cross section is square)
99
is hardeness a fundamental property of a mat
no purely empirical
100
how does the hardeness scale work?
the higher number can scartch the lower number. and even if 2 mat have the ssame number doesnt mean they are alike they just performed the same for that test
101
whats the hardeness test
it measures the resisitance of a mat to an indenter or cutting tool. indenter usually hardened steel, sintered tungsten carbide or diamond and shape is ball pyramid or cone. a load is applied by pressing the indenter at a right angler for a given period of time on the surface of the sample .
102
what is an impact test
it measures a mat resistance of damage during an impact event. this is not a fundamental property since they are random in nature nd they are empirical in design. most of these test measre the energy required to fracture a standard specimen under specific conditions.
103
what is the charpy test
its an impact test that gives a relative indication on the notch toughness of a material under shock loading. it was specifically designed to evaluate the effects of temperature on steel behaviour.
104
true or false most metals are know to absorbe more energy when they fail in a ductile manner than in a brittle manner
true
105
what are th 4 loading conditions in construction mech
monotonically increasing (static)
high strain rate (impact)
repeated (fatigue)
sustained (creep)
106
define fatigue
happens under repeated stress, internal damage lead to a sudden fasilure with no significant prior deformation. it is more common in parts subjected to high cyclic loadig ( axles, drive shafts, propeller shafts/blade crank shaft) but can also occur in structural element (plane wings and fuselage, bridges, brains, etc)/
107
what are the two basic stages in fatigue failur
crack initiation
crack propagation
108
where do crack start?
they initiate at a free surface pts, a pts of high stress concentration ( preexisting flaw, discontinuity). they can start at any flaw or discontinuity (concrete, paste/aggregate interface)
109
what is a slip step
slippage between grain boundaries
110
what causes fatigue damage?
tensile and shear
111
see pp 8 slide 3 for crack propagation figure
yu
112
see slides 4-5 of pp8 fatigue curves
yeah
113
whats the goal of the fatigue test
it is to determine the number of cycles that a smaple material can safely endure for a given stress (S-N diagram)
114
what are the two basic types of machines for fatigue test
Constant load (load cycle remians constant, strain gradually increases as specimen sustains damage)
Constant displacement (displacement cycle remains cut , stress change as specimen sustains damage
115
at what speed are fatigue test usually run at
25-500 cycles per seconds
116
what is the triple point
point where there is 0 degress of freedom. all 3 states can be present at once at a specified pressure and temperature on a phase diagram
117
what are the drawbacks of a cst moment rotating bending machine
-not suitable for nonzero mean stress
-Specimen must be circular in cross section
118
how are specimen tested for fatigue testing
they are trsted to failure using different loads and num of cycles before failure is recorded for each load ans is then plotted on a S-N diagram .
119
true or false ferrous aloys ca be cycled for an indefinite num of times at stresses below fatugue lim or endurance lim
true
120
reciprocating bending machine caracteristics
flat specimen
zero or non zero mean stress
121
direct stress machine caracteristics
zero or non zero mean stress
direct tension or compression
122
what are the variability in fatigue results
- real mats have imperfections so no two samples are truly identical
- pretty much impossible to have the same test conditions over large num of tests
123
palmer miner hypothesis
used to calculate prelim estimates of fatigue life go see pp8 slide 13
124
what are the shortcoming of the palmgren miner hypothesis
assumes the damage accumulating in each cycle of loading is independant of stress history
assumes theres no effect due to the order in wich different stress levels are applied
125
what causes stress concetration to increase
increasing flaw size
decreasing radius of curvature of flaw tip
126
material properties effect on fatigue
grain size (finer grain improves fatigue res)
surface finish(smooth surface less susceptible to crack initiation),(grinding, eating, milling, etc all affect crack initiation potential)
residual stress in surface (tensil reduce fatigue life, compressive improves fatigue life)
127
environement effect on fatigue
increase in temp -> decreased fatigue life
fatigue lim may dissapear at high temp
thermal cycling can induce stress that lead to thermal fatigue failure if mat is restrained from expand or contracting (see formula pp8 slide 20)
128
what is the effect of corrosion on fatigue
surface pitting provides crack initiation pts, fatigue lim disappears in corrosive environement
129
define creep
known as the plastic deformation of a mat which occurs when it is subject to a cst stress or load
130
whats the creep test?
commonly thought of as the high temp test because at temps below 40% of absolute melting pts creep is negligibvle in most metals.
131
does temperature affect the creep in concrete?
no, concrete undergoes creep at virtually any temps unles fully frozen
132
whats a creep curve
plot elongation of tensile specimen vs time at a given temo under a cst load or true stress. 4 stage of elongation (instantaneous elongation then primary or transient creep then secondary or steady state creep finaly tertiary creep)
133
see pp 8 slide23 for creep curve
youpi
134
true or false increasing stress or temperature resutls in a decreased creep rate?
false, it is increased
135
True or false concrete hardens as it dries
false, once it dries it stops the reaction and doesnt get stronger
136
true or false concrete wont harden under water
false, it will!
137
True or false concrete lasts forever
false, it will deteriorate
138
True or false fc' (compressive strength is a realistic number)
false, concrete cant fail in compression, number is a fallacy
139
does structurral failure happen?
very very rare, failure are due usually as durability
140
what are the 3 distinct phase of concrete
hydrated cement paste (hcp)
aggregates
interfacial transition zone (ITZ)
141
what are the main ingredients in concreter
Portland cement
water
aggregates
also air(added to protect)
admixtures
Scms
142
deinfe paste
cement + water
143
define mortar
paste+fine aggregates
144
what is added to mortar to make concrete
mortar+coarse aggregates
145
who discovered Hydraulic cement
romans
146
order of cement inventions
greeks
Egyptians
romans
then 1756 modern John Smeaton
147
how do you manufacture portland cement
raw mats(limestone,sand,clay,iron ore)-> processing (quarrying,crushing mixing) -> firing (calcined and burned@1450 c produces clinker 10mm) -> gypsum -> grinding (size 1-100 nano m (avg 10) -> portland cement
148
what is clinker
cement, its what comes out of the kilne
149
what are the raw mats used in portland cement manufacture
limestone, iron ore, clay, gypsum
150
what are the oxydes used i cement
CaO = C
Al2O3 = A
SO3 = S(with bar on top)
Si)2 = S
Fe2O3 = F
H2O = H
151
what are the compounds in portland cement
Tricalcium Silicate (C3S)55%
Dicalcium Silicate (C2S)20%
Tricalcium aluminate(C3A)10%
Tetracalcium Aluminoferite (C4AF)8%
all 4 of these created during process then add gypsum(CSbarH2)5%
152
what are the primary effects of the chemical compounds in concrete
C3S -> Early strength
C2S -> Ultimate strength
C3A -> Flux, Fast set, Sulfate reactive
C4AF -> Flux
CS_H2 -> prevents fast set
153
is fast set good ?
no very bad
154
how do you make cement go from grey to white?
take out the iron ore
155
hydration of C3S and C2S what does it give
CSH + CH (mole gonna depend on whats associated before)
156
hydration of C3A what does it give
C3A + gypsum + H20= ettringite
ettringite + C3A + H20 = Monosulfoaluminate
157
what is the initial set?
point at wich the molecule come into contact. adding water from this point on is good as it helps the cure and wont affect the water cement ratio. before that point adding water is bad since it gets into the mix
158
whats the annual ressource consumption in concrete
16 billion tonne (aggregates 11 bil, limestone 3, clay 540 mill, water 1.5 bil)
159
define aggregate
inert, granular, inorganique material wich normally consist of stone or stone like solids
160
usage of aggregate
alone (road base, fill, drainaige layers)
particular composite (portland cement concrete, asphalte concrete)
161
aggregate proportion in volume in portland cement
65-80%
162
aggregates functions whjat are they
economy(inexpensive filler)
dimensional stability (shrinkage/expansion controle)
durability (wear resistance, chemical attack)
163
what are the three classification by specific gravity of aggregates
heavyweight (>3.5) (not used very much )
normal weight(1.5-3.0) (90% of N.A concrete)
lightweight (<1.0)
164
what are the two classification of aggregates and their types
natural : naturally occurring (sand, gravel), Modified (crushing, washing, sieving)
Artificial : industrial waste (blase furnace slag)
man made(lightweight)
reclaimed(recycled concrete)
use natural a lot more in concrete
165
what are the 3 ways aggregates are formed
Igneous (formed during cooling of molten rock ex granite)
Sedimentary (formed by deposition and consolidation of particles ex limestone, sandstone)
Metamorphic (formed from sedimentary rock by heat and pressure ex marble)
166
what are the desirable characteristic in aggregates
Hard, strong, durable
free of undesirable impurities
chemical stability (or beneficial reactivity)
167
what are the important properties in aggregates
shape and texture
size gradient
moisture content
specific gravity
bulk unit weight
168
why is shape and texture and important aggregate property
because it directly affects the workability of fresh concrete. sufficient paste is needed to coat aggregates to provide lubfrification and decrease interactions between aggregate particles in mixing.
the ideal particle workability are : spherical (no cornes, low surface to volume ratio ) and smooth(less friction between particles)
169
true of false, mechanical properties of concrete is affected by aggregate particle shape and texture
true, higher surface to volume ratio increases amount of surface are availabel for bonding, extreme change in shape can cause stress concentration
rough, texture surfaces improves mechanical bond
170
what aggregate property affects paste requirements
particle size and distribution (you want aggregates that fill the holes of the bigger ones),(making particles smaller doesnt make the packing smaller its actually the same)
171
hwo does sieve analysis work
agregate go through sieves and stop when they cant fit through a certain size. the particle size is di - di-1 size fraction
172
define Maxiumum Aggregate Size
smallest sieve opening through wich the entire aggregate sample will pass
173
define Nominal Maximum Aggregate Size
ASTM allows 5-10% retention on the largest sieve size
174
what determines the choice of max aggregate size
job condition:
1/5 narrowest dimension between forms
1/3 depth of slabs
3/4 clear spacing between reinforcinf and/or forms
most concretes limited to 1.5" or less
mass structure can go up to 6"
concrete testing can usually only handle 1.5"
175
see pp 12 slide 14 for aggregate grading examples
youpi
176
true or false a smaller maximum aggregate size reduce paste requirement
false, a bigger will reduce
177
see pp 12 slide 15 grading curves
oh yeah
178
what do we have to avoid when handling and storing aggregates
avoid segregation ( tall cone shaped piles, wind condition )
do not let aggregates run down a slope
179
define finenesse modulus
single parameter that describes the grading curve of a fine aggregate, used to check uniformity of grading between aggregate samples
FM = sum(cummulative % retained on standard sieves)/100
increasing FM = coarser aggregates
180
True or false two aggregate with the same FM are indentically graded
false, not necessarly
181
why is FM no normally used for coarse aggregate
less relevant
very high values
low sensitivty
182
where is FM required
mix proportioning since gradation has largest effect on workability
183
Define Oven Dry(OD)
all pores are empty of water. Heated in oven at 105°C to cst weightd
184
Define Air Dry(AD)
All moisture is removed from the surface but internal pores are partially full
185
define Saturated Surface Dry (SSD)
All pores are filled with water but there is no film of water on aggregate surface
186
define wet moisture content
all pores are filled with water and there is a film of water on aggregate surface
187
wich of the moisture content is used as reference state
SSD
since it is equilibrium moisture content
moisture content in the field are much closer to SSD
bulk specific gravity more accurate using SSD
moisture content can be calculated direclty from apparent specific gravity
188
what is absorption moisture content
the maximum amount of water that the aggregate can absorbe , the amount of water in the aggregate at SSD as a proportion of the dry aggregate weight
normal wight aggregat A = 1-2%
189
what is effective absoption (EA) moisture content
the amount of water needed to bring the aggregate from the AD state to SSD state.
190
what is surface moisture (SM)
the amount of water in excess of the SSD state)
191
why do we do moisture content adjustement
to adjust mix water so that absorbed by or shredded by the aggregates is accounted for and amount of water specified in conrete mix design is unaffected
with wet aggregate the excess water is immeadiately available (preferable condition)
with AD aggregates the amount of water absorbed is a fat of time (use 30 min absorption)
192
see pp 12 slide 27 bulking of sand
yeah
193
why are specific gravity of aggregates required in mix
because of proportiniong to establish weight volume relationship. (aggregates are not solid so they have pores eitheir permeable or impermeable) impermeable pores are considerd when determining specific gravity
194
difference between apparent specific gravity(ASG) and bulk specific gravity(BSG)
ASG refers only to solid mat excluding permeable pores but BSG take permeable pores into account
195
define unit weight
weight of a given volume of graded aggregate. sometimes cllaed Bulked density. V includes particles and space between them, affected by degree of compaction.
196
when does max unit weight usually occur
at a fine aggregate content of 35/40 % of total aggregate weight
197
whats the 3 tests for aggregates in order of importance
1: field perfomance concrete
2: Tests taht evaluate aggregate in concrete
3: tests on the aggregates themselves
198
How can aggregate be unsound
if the volume changes that accompany environemental changes lead to deterioration of the concrete. V change can be induced by freeze thaw or wet-dry
199
what are the 2 forms of freeze thaw due to unsoudness
pop-outs- D-Cracking
200
does aggregate play an important role in determining the resistance of concrete to surface abrasion and wear?
yes, particles must be hard,dense,strong and free of soft , porous or friable particles
201
where does most chemical durability come from
result from a reaction between reactive silica in aggregates and alkalis containe in cementif
202
if an aggregate doesnt meet ASTM standards what process may help?
see pp 12 slide 38
203
what four major factors must be considered with implementation of waste materials in concrete
economy
compatibility with other mats
concrete properties
consistency
204
see pp9 slide 32
yeu
205
is porosity good for concrete?
no, every 5% you lose 5% of strength
206
why is microstructure of hcp highly modified in the vicinity of inclusions(agg, fiber, steel)
increased porosity
less unreacted cement
207
the inability of cement particles to pack efficiently in close proximity of the embedment is due to what
to wall effect, raises local W/C ratio at interface. further rise in w/c due to localized bleeding
ITZ often dominant influence in concrete
208
true or false the slower the reaction of concrete, the more strength you eventually get
true
209
whare the 3 reason to add mineral admixture
replace cement
improve workability
enhance durability
210
what are the 3 mains categories of mineral admixture
pozzolanic
cementitious
non-reactive
211
what are the 2 types of SCM
cementitious and pozzolanic
212
define Blast furnace slag
SCM (cementitious), waste from steel blast furnace quenched in water to form glass, react chemicaly with water to produce aluminium substituted calcium hydrate (CSH)
cheaper than portland cement nd greener
213
what are the 3 most common pozzolanic mats and what they do
Fly ash - ash from burning coal
silica fumes- dust from the manufacture of silicon (durability and strength improvement due to small size)
calcinied clay - modified natural clay
they chemically react with CH and water to produce CSH
cant replace 100% of cement like slag
214
what are the general benefits of SCM
economics (excecpt silica fumes)
environemental friendly
lower heat hydration
improved durability
improved workability
increased strength
215
whats the replacement rate of scm
5% to 70%
216
why do we add chemical admixtures
brings out a desired effect on physical propertiesof the fresh and or hardened concrete
217
common types of chemical admixture
Water reducing (expanding)
air entrsining (gas forming)
set retarding (corrosion inhibiting)
set accelerating (permeability reducing)
218
define water reducing admixture
surfactants wich abstob at the solid water interface and prevemt cement grains from flocculatingin water
219
how can water reducing admixture be used
plasiticizer (increased workability at same W/C ration)
water reducer (decreased in W/C ratio at same workability
220
define air entraining admixture
surfactants wich act at the air water interface causing water to foam during mixing. bubbles remain stables and are locked into cement paste during hardening (its good )
221
advantageand disadvantage of air entraining admixtures
adavantage: improves freeeze thaw
improves sulfate résistance
improves workability
reduce segregation
disadvantage:
reduced strenght 10/20%
important characteristic :
amount 4-7%
must be dispersed but close
must be non interconnected
222
define set retarding admixture
delay the setting of concrete by slowing down early hydration reactions and thus rate of early strength development. doesnt affect ultimate strength, time to ultimate stress and doesnt affect slump loss
223
define set accelerating admixtures
accelerate setting of concrete by speeding up early hydration reaction and thus rate of early strength dev. do not affect ultimate strength, time to ultimate strenght but may affect slum loss
224
what are the primary step to concrete production
1.Batching - (weighing out ingredients)
2. mixing-(central mix, shrink mix, truck mix)
Transportating/placement (mixer truck, dump truc , bucket buggy conveyor chute premie)
finishing (compaction, strikeoff, floating, troweling, texturing)
curing (sprinkling, wet covering, ponding, waterproof membrane, steam)
225
define batching
batching of aggregates and cement is best done by weight. must follow strict guidelines for mat quantities so have to have high accuracy, only water and liquid admixtrue can be measure by volume
226
why is mixing essential
produces a homogeneous uniform concrete. inadequate mixing result in lower strength and greater variations within or between batches. overly long mixing time severly limit batching plant output, can cause aggregate breakdown and decreases air content
227
what are the factors to optimize mixing time
type of mixer
condition of mixer
speed of rotation
size of charge
nature of ingredients
mix design/proportioning
ambient temperature
228
what are the types of mixers
drum mixers (uses gravity to induce mixing, not very effective for low workability mixes)
pan mixers (good for low workability mixes and FRC)
conitnous mixers (allows continuous production of concrete)
229
what are the ready mixed concrete
Central mixed (mixed at plant, truck mixer only agitates 80% capacity)
Transit mixed(partially or completely mixed during transport)
shrink mixed (partially mixed at plant to reduce overall volume and mixing is completed in truck mixer)
truck mixed (completly mixed within truck mixer 63% capacity)
230
whats the importance of placement for concrete
proper handling is vital in prevention of segregation. seggregation could lead to formation of rock pockets and honeycombing. concrete should fall vertically though fall distance should bve limited. (3-5 feet)
231
what happens during vibration
entrained air goes up and some of it is lost so have to take that into account dring vibration
232
what are the fresh concrete properties
easily mixed and transported
uniform throughout a given batch and between batches
capable of flowing such that it completly fills the forms
compactable without the need for excessive energy
resistance to seggregation during placing and consolidation
capable of being finished properly
233
define workability
amount of mechanical work required to produce full compaction of the concrete without segregation
234
what are the factors affecting workability
seggregation and bleeding
235
define seggregation
seperation of components of fresh concrete resulting in nonuniform mix
236
what are the factore contributing to segregation
large max aggregate size and proportion of large particles
high specific gravity of coarse aggregate relative to fine
decreased amount of fines (sand or cement)
variations in particles shape away from smooth well rounded
mixes that are either too wet or too dry
237
define bleeding
upward movement of rhe water after concrete has been consolidated but before it has set.
238
why does water segregates from the mix
because its the lightest component of concrete
239
what causes bleeding
aggregates settling within the fresh concrete and being unable to hold all the mixing water. water on surface of concrete is the most common manifestation of bleeding
240
what leads to weakness porosity and rduced durability in concrete
bleeding may occur through distinct localized channels that later act to increase the permeability of the hardened concrete
upper layer of concrete may become rich in cement paste wich has very high W/C ratio,
water pockets may form beneath inclusion in the concrete leaving weak zones and reducing bonds
241
what happens if bleed water evaporates more quickly than bleeding rates
plastic shrinkage cracking can form. problematic in hot, dry and or windy weather.
242
define laitance
scum of fine particles or dissolved alts may be carried to the surface resulting in a weak and nondurable layer. laitance at top of a lift can prevent bonding and at the final surface can result in dusting
243
what does the slum test provide
a rough measure of consistency. but not an absolute measure of workability
244
what can the slump test not be used for
high slump concrete
low slum concrete
fiber reinforced concrete
certain admixtures
245
can air content test distinguish between entraspped and entrained air content
no
246
what are the 3 air content test
gravimetric
volumetric
pressure
247
define the gravimetric method
oldest and simplest. compares unit weight of concrete containing air with calculated unit weight of air free concrete. calculated is based on proportions and specific gravities of mix component. not suitable for field use due to accuracy required in SGs, batch proportions and moisture content
248
define the volumetric method
based on comparaison of volume of concrete containing air with volume of same concrete after air has been removed. air goes to the top so it gives air % of mixture. it requires a great physical effort to remove the air from concrete
249
descibre the pressure method air test
most common method for measure of c=fresh concrete air in field. based on measurmenet of the change in volume of the concrete when subjected to a given pressure. change in volume assumed to be entirely caused by compression of air. can then use boyle law to calculate air content
250
can unit weight be affected by presence of entrained air
yes
251
define setting
refers to the onset of rigidity in fresh concrete. must occur before hardening
252
define hardening
developpement of useful and measurable strength
253
what are the arbitrary values for initial set and final set
initial 500 psi
final 4000 psi
254
why is time of set important
help regulate mixing and transit times
gauge the effectivenensse of various set-controlling admixtures
help plan the scheduling of casting and finishing operations
qc test to monitor the accelerating/retarding effects of additive
255
how many test are recognized for time set
1: uses pseudo mortar specimen where the concrete is first passed through #4 sieve then diff size needles are used to determine penetration resitance over time. then inital and final set times are defined at 500 and 4000 psi
PR=F/A
256
why is curing important for concrete
affects btoh mechanical properties and durability characteristics and reduces volume changes due to shrinkage.
257
what are the 2 components required for curing
prevent loss of moisture through evaporation
supplies additional water for continued hydration
258
what would excessive evaporation from concrete cause
plastic shrinkage cracking
259
whats the W/C ration that provide complete hydration
theroetically 0.42 or hugher
260
when does the hydration reaction stop
when internal relative humidity drops below 80%
261
true or false Slags and pozzolans require shorter curing periode
false, they require longer to ensure the reaction takes place
262
what happens if you restart interrupted curing
increase in strength but ultimate strength wont be as high as continously cured concrete. fully resaturating concrete very hard in field, will usually only happen if concrete fully submerged. must maintain water in concrete as continuous liquid system. large capillaries begin to empty due to self desiccation causing menisci to form. preventing easy penetration of water
263
when should concrete be tested
in fully saturated region (conservative, strength cant go lower)
264
whats the temperature effect on cooling
affects rate of strength developpement and thus the length of curing necessary. at early age cement hydrate smore rapidly so increased strength. but high temp produce a nonuniform distribution of hydation products. leaves weak zones in hcp that govern strength
265
define water curing
continous supply of water to concrete surface. can be done by ponding, spraying, fogging, sprinkling ...must maintain water in concrete as a continous liquid system.
266
define sealed curing
sealing of the concrete surface to prevent evaporation. can be done using waterproof paper, plastic sheeting or membrane forming curing compound. convenient and lower labor reqs have made them popular. sprayed curing compund consist of solid mats dissolved in a solvent that form a membrane as the solvent evaporates. colored pigment are added to see where it has been applied
267
when should sealed curing never be used
between lifts or bonded overlas or when surface is painted
during the fall on pavement to be exposed to deicing salts.
268
what is a common problem of sealed curing
self desiccation
269
does sealed curing provide aditional hydration
no
270
what is plastic shrinkage cracking
phenomenon when rate of evaporation of free water from the concrete surface becomes excessive. as concrete begin to stiffen and set, shrinkage is restrained and tensile stresses develop. under extreme condition, can lead to severe cracking of the concrete surface if left unprotected.
271
272
what are the 3 factors influencing plastic shrinkage
concrete air temp
relative humidity
wind velocity
273
what is the desirable concrete temps
50-60 f
above 75 must take precaution
274
what are the effects of hot temps on concrete
accelerated slump loss
inceased rate of setting
difficulty in controlling air content
increased loss of moisture during curing
increased risk of plastic shrinkage cracking
higher concrete temp
greater thermal variation within concrete
275
what are the precaution to take for hot weather concrete
cool concrete mat
coool/protect handling equip
cool/moisten forms
increases relative humidity of air
avoid hottest periods of the day
reduce time between mixing and curing
protect from the wind
implement proper curing methods
use set retarding admixture
use low heat of hydration cement
276
define cold weather in concrete world
more than 3 succesive days the mean daily temp is 40 f
277
effect on fresh concrete of cold wather
accelerated slump loss
decreased rate of setting
increased risk of plastic shrinkage cracking
extreme damage if concrete allowed to freeze
278
what are the precautions to take for cold weatehr concreting
heat concrete mat
insulate forms
avoid coldest periods of the day
reduce time between mixing and curing
protect from the wind
use shelters/heaters to keep concrete warm
use air entraining admixtures
use high early strength cement
279
whats the portland cement concrete mean compressive strength
35-50 Mpa
280
go see lasts couple slide graphs pp 10
pop
281
what are the 5 categories of durabiliy
temporary (up to 10 yrs)
short life (10-24 yrs)
medium life (25-49 yrs)
long life (50-99 yrs)
permanent (100 yrs min)
282
what are the 2 categories of deterioration mechanism
chemical attack
physical attack
283
what are the 3 primary transport mechanism that allow aggressive agents penetration
absorption
permeation
diffusion
284
what is absorption
transport of liquids into unsaturated porous solids due to surface tension acting in capilaries
285
what is permeation
movement of gases or liquids through a saturated porous medium due to a pressure gradient
286
what is diffusion
transfer of mass by random motion of free molecles or irons in the pore solution due to a concentration gradient
287
what is the number one factor that affects durability
W/C ratio
288
what is the hardest challenge with concrete durability
predicting the concrete behaviour decades in the futur based on short term lab tests
289
define leaching
the hydrolysis of cement paste components (CH) by water flowing through the concrete
290
what is the difference between hard water and soft water
hard water comes from lakes, river and contains chlorides sulfates bicarbonates of calcium and magnesium and is not detrimental to concret while soft water comes from rain, melting snow and it contains no calcium ions or minerals so it dissolves the calcium containing products like concrete
291
what is leaching rate dependant on and what can we do to prevent it
dependant on the amount of dissolved salts in water and the temperature of the water. we can prevent it by minimizing transport properties (low W/C, SCM) and by minimizing calcium hydroxyde content of hcp (SCMs)
292
when is efflorescence a problem?
when it actually comes from the concrete
293
what is the alkali silica reaction
a chemical reaction between the soluble alkalis contained in the hcp and certain reactive forms of silica found in the aggregates
294
can you explain the ASR reactions step by step
1: pore water becomes alkaline due to hydration
2: active aggregates react with alkaline pore water solution to produce amorphous sicilate gel
3: amorphous silicate gel imbibes pore water and greatly expands
4: gel expands into surrounding hydrated cement paste
295
what factors affect the ASR reaction?
nature of reactive silica
amount of reactive silica
particle size of reactive material
amount of alkalis available
amount of moisture available
296
what factor influence the time elapsed between concrete casting and appearance of damage due to ASR
the nature of the silica involvedh
297
how can we prevent ASR
indentify and avoid reactive aggregates
limit the amount of alkalis available in the hcp
Na2) + 0.65K20 < 0.60
add an SCM to the concrete mix
298
how do we detect ASR
UV fluroescence technique
299
what is alkali carbonate reaction (ACR)
expansive reactions involving carbonate rocks
300
what feature does carbonate rock succeptible to expansive reaction possess
very fine grained dolomite
considerable amount of fine grained calcite
abundant interstial clay
dolomite and calcite crystals evenly dispersed in clay matrix
301
what is a sulfate attack
a chemical reaction between sulphate ions and certain components of hcp. damage may include expansion and cracking of the concrete as well as softening and disintegration of the paste
302
what are the primary forms of sulfate attack
external sulphate attack
physical sulphate attack
thaumasite
internal sulphate attack (DEF)
waste/sewage
303
explain the steps of the sulfate attack
1: sulphates must first enter the concrete usualy from an outside source
2: sulphates react with CH to produce gypsum ( CH + SO4(2-) -> Cs-H2 + 2OH-)
3: the gypsum reacts tih the monosuploaluminate in the hcp (C4ASH12 + 2CSH2 + 16H -> C6AS3H32)
steps 2 and 3 are both expansive
304
whats the effect of seawater on a sulfate attack
though high levels of sulphates are present, an attack is mitigated to some extent. because magnesium hydroxide chemically protect against them and gypsum ans etringite are more soluble in solutions containing chloride ions
305
what is a internal sulphate attack
Delayed ettringite formation (DEF), curing at high temps destroys ettringite and sulphate is absorbed by CSH but after cooling the sulphate becomes available again to form ettrigite results in expansion and cracking
306
what is an acid attack?
a chemical reaction between an external source of acidic liquid and hcp and in some cases aggregates
307
what is the acid attack sequence
attack usually limited to surface of concrete only but progresses inward.
dissolution of compounds soluble in the given acid takes place virtually instantly
in most cases this reactions forms insoluble calcium salts wich build up and protects the concrete from further attack
308
where on the ph table do you find sulfate attacks
acid attack on hcp begins around 7 and severe attack around 4
309
what is freezing & thawing
damage induced by internal tensile stresses wich are a direct result of repetitive cycles of freezing and thawing. this damade is through attrition. one cycle does very little damage but after many cycles, damage adds up to significant levels
310
what are the factor affecting freeze thaw
expansion of water
hydraulic pressure
solar heating
litvans model
311
whats the effect of water expansion on freeze thaw
just before freezing, volume increases by 9%
312
what is the effect of hydraulic pressure on freeze thaw
all the water in concrete doesnt freeze at the same time but freezing begins in larger cavities and progress to smaller ones due to pore pressure. this produces hydraulic pressure as the expansion forces unfrozen water ahead of the freezing front. this is a function of concrete resistance to flow, distance to void boundary and rate of freezing. the smaller the pore the lower the freezing temp and the higher pressure wich leads to more damage
313
wich type of air is freeze thaw resistant
entrained air
314
what is solar heating effect of freeze thaw
two directional freezing at surface due to daily thawing from incident solar radiation
315
what is litvans model effect on freeze thaw
vaport pressure gradient is created between surface ice and super cooled pore water. induces movement of water toward surface. dense impermeable surface layer will restrict this movement and potentially cause mechanical failure
316
why does concrete withstand fire
because of low rate of heat penetration
317
what factors contribute to low heat penetration in concrete
low thermal conductivity
heat is consumed by evaporation of water
heat is consumed in decomposition of hydration products
some aggregates also decompose and consume heat
decomposed material has even lower thermal conductivity
318
what are the effects of water loss and shrinkage in concrete
strength reduction and tensile stresses. results in cracking and spalling
319
why is concrete less susceptible than steel to heat?
steel conducts heat rapidly causing severe loss of structural integrity in beams and columns
320
what is the number 1 worldwide durability issue with concrete
corrosion of reinfrocement
321
what is corrosion effect on concrete
electrochemical attack mechanism affecting the reinforcing steel wich results in a volume increase, thus inducing tensile stresses in the concrete.
322
true or false concrete protects the steel from corrosion?
true, it provides excelleent protection
323
how does concrete protect steel from corrosion
physically , the concrete restricts ingress of the basic components requires to initiate corrosion(water, oxygen and chlorisdes)
chemcally, the pore solutuon in concrete typically has a very high ph wich leads to formation of protective iron oxide film around the steel bar (passivation film)
324
what are the primary reason for loss of protection of the steel by the concrete
physical :
insufficient cover over reinforcement
concrete with poor transport properties
failure to protect concrete from chrloride sources
damage to concrete (cracking, spalling, scalling)
chemically:
penetration of chlorides in the concrete. passivation layer is destroyed when chloride ions reaches 0.2-0.4% in region adjacent to steel
carbonation due to CO2 exposure of concrete leads to a reduction of ph. depassivation occyrs as ph approaches 11
325
what type of process is corrosion
electrochemical, requires formation of a cathode and an anode with an electrical current flowing between them
326
define anode
iron mettalice atoms are oxidized to Fe2+ ions wich dissolve into the surrounding solution also producing electrons (where you get most damage)
327
define cathode
electrons are consumed and OH- ions are formed. water and oxygen are required for this to occur
328
what are the two deleterious effect of corrosion of steel in concrete
reduction of the cross sectional are of the steel and the anode
spalling or cracking of the concrete due to the expansion stresses created by rust formation
329
what can you do in design to prevent corrosion
sufficient cover
improved transposrt properties
corrosion inhibitors
corrosion resistant reinforcement (galvanized steel, stainless steel, epoxy coated steel, fibre reinforced plastics)
330
how can you protect/repair existing strucutre with corrosion
remove, clean , replace
corrosion resistant reinforcement
corrosion inhibitors
cathodic protection (sacfrificial anode, cancellation current)
protective overlay (waterproof membrane, watertight concrete overlay)
331
what is surface wear
progressive mass loss from a concrete surface due to repetitive attrition cycles
332
what are the 3 mechanisms of surface wear
abrasion
erosion
cavitation
333
define abbrasion
refers to dry attrition as another solid object moves along or rubs against the concrete surface. primarly relates to vehicular traffic or mechanical device but can also occur in walls or silos or bins
334
define erosion
wear caused by the abrasive action of solid particles suspended in fluids. caused by the physical action of debris impacting rubbing rolling and grinding agaisnt the concrete surface. common on canal lining, spillways and pipes for water or sewage transport
335
what is cavitation
loss of mass caused by the formation of vapour bubbles and their subsequent collapse due to sudden changes of direction in rapidly flowing water. requires water flow(more than 12m/s) and surface irregularities
336
what happens at irregularities during cavitation
water flow separates from concrete surface creating zone of lowered vapour pressure causeing bubbles to form. as bubbles move downstream to regions of normla presure, they collapse violently wich creates a shock wave. this induce high tensil stress in concrete if it occurs near the surface
337
what are the negative impacts of seawater on concrete
leaching (constant exposure to seawater and or flow)
AAR if reactive aggregate is present
sulphate attack (chemical reaction + crystalization)
acid attack high co2 content possible
freeze/thaw accentuated in tidal zone
corrosion high Cl-
surface wear flow,waves,sediment,floating objects
338
what are the types of cement and a quick descriptions
GU : general purpose
MH : Moderate heat hydration (moderatly low on C3S)
MS : Moderate sulfate resistant (moderatly low on C3A)
HE: high early strength (high C3S or finer grind)
LH: Low heat hydration (low in C3S and C3A)
HS: Sulafate resistant (Low in C3A)
