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cive 202 midterm > midterm 1 > Flashcards

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

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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

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3
Q

whats the life cycle of products and processes

A

material extraction-> material processing -> product manufacture -> construction process -> building -> demolition -> landfill

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4
Q

wich are the two life cycle process that are the same step for concrete

A

product manufacture and construction process

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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

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6
Q

whats the concrete usage vs population growth factor from 1970-2004

A

3.5x (cement) steel more than doubled

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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

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8
Q

how much concrete do we consume as humans?

A

concrete is the second most consumed thing behind water annually

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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)

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10
Q

how much CO2 is liberated per tonne of cement?

A

almost 1 tonne

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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

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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

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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)

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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

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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)

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16
Q

what are engineering mats

A

defined as the inanimater matter that are useful to the engineering profession, consitute backbone of modern civilaztion

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17
Q

what are mats science

A

refers to knowledge of physical science as general truth and Principe in particular physic and chem

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18
Q

what are the four groups of eng mat

A

1: matal and alloys
2 ceramic and glass
3 organic polymers
4 composite

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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)

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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

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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

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22
Q

descibe composites

A
  • combination of other mats
    ex concrete, fibre reinforced polymers
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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

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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

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25
Q

why is corrosion resistance in electrical and chemical properties?

A

because its an electrochemical reaction, electricity is created by movement

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26
Q

on what properties does bonding have a strong influence on?

A

strength and stiffeness

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27
Q

what are the five types of bonds atomic bonds? and an example for each

A

1)ionic(sodium chloride)
2)covalent(diamond)
3)metallic(sodium metal)
4)van der Waals(solid argon)
5) hydrogen

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28
Q

explain ionic bonds

A

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

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29
Q

explain covalent bonding

A

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.

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30
Q

explain metalic bonding

A

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

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31
Q

explain Van der Waals bonds

A

weak secondary bonds, can be found between covalent bonded chains of polys also formed when molecules undergo polarization

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32
Q

explain hydrogen bonds

A

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

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33
Q

what are the typical material for each bond types

A

ionic(ceramic, gypsum )
covalent(diamond glasses)
metalic metals
hydrogen water
van der waals thermoplastic polys

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34
Q

define a space lattice

A

infinite array of pts in 3D in wich every pts has the same surrounding identical to every other pts of the array

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35
Q

define a unit cell

A

smallest unit wich when replaced in space indefinetly will generate space lattice. so the smallest Volume that describe the structure of a mat

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36
Q

True of false metals are crystalline

A

true

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37
Q

true of fals glass is crystalline

A

False 0 crystal structure

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38
Q

why is glass not crystalline?

A

glass made of melted sand so crystal dissapear

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39
Q

unit cell diagram go see pp4

A

slide 2

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40
Q

how many space lattice are there

A

14

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41
Q

what are the thre basic configuration of space lattice?

A

simple cubic (SC) 1atom per unit cell
Body centered cubic (BCC) 2 a/uc
face centered cubic (FCC) 4 a/uc

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42
Q

go see crystal diagram pp4

A

yesssssssir

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43
Q

how can imperfectiton be classified on the basis of their geometry

A

point imperfection
line imperfection
surface imperfection
volume imperfection

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44
Q

describe point imperfection

A

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

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45
Q

descibre the 3 forms of point imperfections

A

vacancy: atoms missing, gonna fail where bonds are weaker aka hole
substitutional: a different atom (intruder)
interstitial: extra small atom

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46
Q

describe line imperfection or dislocations

A

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

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47
Q

describe edge dislocation

A

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

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48
Q

describe screw dislo

A

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

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49
Q

describe surface imperfection

A

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

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50
Q

descibre grain boundary

A

narrow region of atomic mismatch between two grains. shape determined by restriction imposed by neighbouring grain

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51
Q

define a phase

A

physically distinct chemically homogeneous and mechanically separable region of a system

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52
Q

define the components of a system

A

chemical species that comprise the system. can be elements, ion or compounds

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53
Q

what is the phase rule

A

aka gibbs eq F=C-P+2
degree of freedom in an eq

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54
Q

what are the two boundaries in a binary phase diagram

A

liquidus(between liquid and two phase region)
solidus (between solid and two phased region)

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55
Q

what is a eutetic phase diagram

A

when solid solubility is limited and melting pts of components are similar

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56
Q

how do you call the phase boundary where the solid solubility is limited?

A

solvus

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57
Q

what type of diagram is formed when the melting pts of the components are vastly different

A

peritetic phase diagram

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58
Q

definition of macrostructure

A

structure as examined by the naked eye or under low magnification

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59
Q

def of microstructure

A

structure as observed using optical microscopy

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60
Q

substructure definition

A

structure obtained by using a microscope with a much higher magnification and resolution than the optical microscope

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61
Q

what re the 4 level of structure

A

Crystal structure
electronic structure
nuclear structure
molecular structure

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62
Q

define crystal structure

A

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

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63
Q

define electronic structure

A

electrons in the outermost orbitals of individual atoms of the solid. spectroscopic tech are useful in determining elec structure

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64
Q

define nuclear structure

A

studied by nuclear spectroscopic tech such as nuclear magnetic resonnance
(can look inside concrete without damaging it)

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65
Q

define molecular structure

A

spatial arrangement of small groups of atoms wich are strongly joined togetehr within the group or molecule

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66
Q

what structure exerts a major influence on the mechanical and physical properties of the mat

A

electronic structure

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67
Q

what structure exerts a strong influence on mat behaviour

A

molecular and crystal

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68
Q

the deformation of a mat is strongly affected by what structure?

A

molecular and crystal

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69
Q

how can failure occure give ex

A

mat defect, variation in properties, inadequate design, inadequately controlled processing, poor workmanship, insufficient maintenance, abuse, negligence, etc…

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70
Q

failure analysis graph explain

A

(Econ,safety,function and appearance) -> design -> mats selection -> fabrication -> machining -> assembly -> service -> failure analysis -> back to design

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71
Q

the tests to determine the properties of different mats can be what ?

A

destructive or non destructive

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72
Q

define size effect

A

the larger the specimen, the more likely it is to have flaws of greater severity. so more likely to have a lower fracture strength

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73
Q

why do we take size effect into account

A

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

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74
Q

define the tensile test

A

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

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75
Q

True or false we test concrete in tension

A

false, since concrete as low tensile force

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76
Q

engineering stress formula

A

sigma = P/Ao

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77
Q

engineering strain formula

A

epsilon = (l-lo)/lo

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78
Q

Hookes law formula

A

sigma = E x epsilon

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79
Q

whats the young modulus?

A

elastic modulus (E)

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80
Q

with what does the young modulus help?

A

helps limit deflection

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81
Q

linear elastic stress strain curve go see

A

pp.7 s 5

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82
Q

why are brittle mats not stromg in tension?

A

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)

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83
Q

wheter a mat is brittle or ductile depends on what?

A

atomic or molecular structure and service conduction

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84
Q

what are the 3 srvice condition affecting the behaviour of the mat

A

temperature
strain rate
degree of triaxility

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85
Q

see graphs on failure mode pp 07

A

s8-9-10

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86
Q

what is necking

A

during plastic deformation, volume doesnt change even though there is elongation, the cross sectional area diminishes so the V stays cst
Aolo = Aili = cst

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87
Q

where do ductile material tend to fail in tension?

A

in shearing at an angle of 45 deg

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88
Q

how do brittle mats fail under tension

A

fail due to crack propagation perpendicular to axis of loading, show little to no necking

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89
Q

see pp07 slide 13-14-15 mid term q

A

oh yeah

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90
Q

what is the flaw of the splitting tension test

A

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

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91
Q

whats th ration of tensil strength to compressive strenght for concrete

A

arond 10%

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92
Q

does necking arrise in the compression test?

A

no since the cross section of the specimen increases

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93
Q

how does concrete fail in the compression test

A

in tension/shear…

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94
Q

see pp 7 slide 21

A

yer

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95
Q

difference between three pts bending and 4 pts bending

A

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

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96
Q

what are the effects of shear stress

A

increased deflection

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97
Q

what are the shear formulas

A

go see pp 7 slide 25

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98
Q

what are the potential problems in bending test

A

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)

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99
Q

is hardeness a fundamental property of a mat

A

no purely empirical

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100
Q

how does the hardeness scale work?

A

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

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101
Q

whats the hardeness test

A

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 .

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102
Q

what is an impact test

A

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.

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103
Q

what is the charpy test

A

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.

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104
Q

true or false most metals are know to absorbe more energy when they fail in a ductile manner than in a brittle manner

A

true

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105
Q

what are th 4 loading conditions in construction mech

A

monotonically increasing (static)
high strain rate (impact)
repeated (fatigue)
sustained (creep)

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106
Q

define fatigue

A

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)/

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107
Q

what are the two basic stages in fatigue failur

A

crack initiation
crack propagation

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108
Q

where do crack start?

A

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)

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109
Q

what is a slip step

A

slippage between grain boundaries

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110
Q

what causes fatigue damage?

A

tensile and shear

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111
Q

see pp 8 slide 3 for crack propagation figure

A

yu

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112
Q

see slides 4-5 of pp8 fatigue curves

A

yeah

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113
Q

whats the goal of the fatigue test

A

it is to determine the number of cycles that a smaple material can safely endure for a given stress (S-N diagram)

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114
Q

what are the two basic types of machines for fatigue test

A

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

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115
Q

at what speed are fatigue test usually run at

A

25-500 cycles per seconds

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116
Q

what is the triple point

A

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

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117
Q

what are the drawbacks of a cst moment rotating bending machine

A

-not suitable for nonzero mean stress
-Specimen must be circular in cross section

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118
Q

how are specimen tested for fatigue testing

A

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 .

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119
Q

true or false ferrous aloys ca be cycled for an indefinite num of times at stresses below fatugue lim or endurance lim

A

true

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120
Q

reciprocating bending machine caracteristics

A

flat specimen
zero or non zero mean stress

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121
Q

direct stress machine caracteristics

A

zero or non zero mean stress
direct tension or compression

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122
Q

what are the variability in fatigue results

A
  • 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
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123
Q

palmer miner hypothesis

A

used to calculate prelim estimates of fatigue life go see pp8 slide 13

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124
Q

what are the shortcoming of the palmgren miner hypothesis

A

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

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125
Q

what causes stress concetration to increase

A

increasing flaw size
decreasing radius of curvature of flaw tip

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126
Q

material properties effect on fatigue

A

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)

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127
Q

environement effect on fatigue

A

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)

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128
Q

what is the effect of corrosion on fatigue

A

surface pitting provides crack initiation pts, fatigue lim disappears in corrosive environement

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129
Q

define creep

A

known as the plastic deformation of a mat which occurs when it is subject to a cst stress or load

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130
Q

whats the creep test?

A

commonly thought of as the high temp test because at temps below 40% of absolute melting pts creep is negligibvle in most metals.

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131
Q

does temperature affect the creep in concrete?

A

no, concrete undergoes creep at virtually any temps unles fully frozen

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132
Q

whats a creep curve

A

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)

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133
Q

see pp 8 slide23 for creep curve

A

youpi

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134
Q

true or false increasing stress or temperature resutls in a decreased creep rate?

A

false, it is increased

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135
Q

True or false concrete hardens as it dries

A

false, once it dries it stops the reaction and doesnt get stronger

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136
Q

true or false concrete wont harden under water

A

false, it will!

137
Q

True or false concrete lasts forever

A

false, it will deteriorate

138
Q

True or false fc’ (compressive strength is a realistic number)

A

false, concrete cant fail in compression, number is a fallacy

139
Q

does structurral failure happen?

A

very very rare, failure are due usually as durability

140
Q

what are the 3 distinct phase of concrete

A

hydrated cement paste (hcp)
aggregates
interfacial transition zone (ITZ)

141
Q

what are the main ingredients in concreter

A

Portland cement
water
aggregates
also air(added to protect)
admixtures
Scms

142
Q

deinfe paste

A

cement + water

143
Q

define mortar

A

paste+fine aggregates

144
Q

what is added to mortar to make concrete

A

mortar+coarse aggregates

145
Q

who discovered Hydraulic cement

A

romans

146
Q

order of cement inventions

A

greeks
Egyptians
romans
then 1756 modern John Smeaton

147
Q

how do you manufacture portland cement

A

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
Q

what is clinker

A

cement, its what comes out of the kilne

149
Q

what are the raw mats used in portland cement manufacture

A

limestone, iron ore, clay, gypsum

150
Q

what are the oxydes used i cement

A

CaO = C
Al2O3 = A
SO3 = S(with bar on top)
Si)2 = S
Fe2O3 = F
H2O = H

151
Q

what are the compounds in portland cement

A

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
Q

what are the primary effects of the chemical compounds in concrete

A

C3S -> Early strength
C2S -> Ultimate strength
C3A -> Flux, Fast set, Sulfate reactive
C4AF -> Flux
CS_H2 -> prevents fast set

153
Q

is fast set good ?

A

no very bad

154
Q

how do you make cement go from grey to white?

A

take out the iron ore

155
Q

hydration of C3S and C2S what does it give

A

CSH + CH (mole gonna depend on whats associated before)

156
Q

hydration of C3A what does it give

A

C3A + gypsum + H20= ettringite
ettringite + C3A + H20 = Monosulfoaluminate

157
Q

what is the initial set?

A

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
Q

whats the annual ressource consumption in concrete

A

16 billion tonne (aggregates 11 bil, limestone 3, clay 540 mill, water 1.5 bil)

159
Q

define aggregate

A

inert, granular, inorganique material wich normally consist of stone or stone like solids

160
Q

usage of aggregate

A

alone (road base, fill, drainaige layers)
particular composite (portland cement concrete, asphalte concrete)

161
Q

aggregate proportion in volume in portland cement

A

65-80%

162
Q

aggregates functions whjat are they

A

economy(inexpensive filler)
dimensional stability (shrinkage/expansion controle)
durability (wear resistance, chemical attack)

163
Q

what are the three classification by specific gravity of aggregates

A

heavyweight (>3.5) (not used very much )
normal weight(1.5-3.0) (90% of N.A concrete)
lightweight (<1.0)

164
Q

what are the two classification of aggregates and their types

A

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
Q

what are the 3 ways aggregates are formed

A

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
Q

what are the desirable characteristic in aggregates

A

Hard, strong, durable
free of undesirable impurities
chemical stability (or beneficial reactivity)

167
Q

what are the important properties in aggregates

A

shape and texture
size gradient
moisture content
specific gravity
bulk unit weight

168
Q

why is shape and texture and important aggregate property

A

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
Q

true of false, mechanical properties of concrete is affected by aggregate particle shape and texture

A

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
Q

what aggregate property affects paste requirements

A

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
Q

hwo does sieve analysis work

A

agregate go through sieves and stop when they cant fit through a certain size. the particle size is di - di-1 size fraction

172
Q

define Maxiumum Aggregate Size

A

smallest sieve opening through wich the entire aggregate sample will pass

173
Q

define Nominal Maximum Aggregate Size

A

ASTM allows 5-10% retention on the largest sieve size

174
Q

what determines the choice of max aggregate size

A

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
Q

see pp 12 slide 14 for aggregate grading examples

A

youpi

176
Q

true or false a smaller maximum aggregate size reduce paste requirement

A

false, a bigger will reduce

177
Q

see pp 12 slide 15 grading curves

A

oh yeah

178
Q

what do we have to avoid when handling and storing aggregates

A

avoid segregation ( tall cone shaped piles, wind condition )
do not let aggregates run down a slope

179
Q

define finenesse modulus

A

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
Q

True or false two aggregate with the same FM are indentically graded

A

false, not necessarly

181
Q

why is FM no normally used for coarse aggregate

A

less relevant
very high values
low sensitivty

182
Q

where is FM required

A

mix proportioning since gradation has largest effect on workability

183
Q

Define Oven Dry(OD)

A

all pores are empty of water. Heated in oven at 105°C to cst weightd

184
Q

Define Air Dry(AD)

A

All moisture is removed from the surface but internal pores are partially full

185
Q

define Saturated Surface Dry (SSD)

A

All pores are filled with water but there is no film of water on aggregate surface

186
Q

define wet moisture content

A

all pores are filled with water and there is a film of water on aggregate surface

187
Q

wich of the moisture content is used as reference state

A

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
Q

what is absorption moisture content

A

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
Q

what is effective absoption (EA) moisture content

A

the amount of water needed to bring the aggregate from the AD state to SSD state.

190
Q

what is surface moisture (SM)

A

the amount of water in excess of the SSD state)

191
Q

why do we do moisture content adjustement

A

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
Q

see pp 12 slide 27 bulking of sand

A

yeah

193
Q

why are specific gravity of aggregates required in mix

A

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
Q

difference between apparent specific gravity(ASG) and bulk specific gravity(BSG)

A

ASG refers only to solid mat excluding permeable pores but BSG take permeable pores into account

195
Q

define unit weight

A

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
Q

when does max unit weight usually occur

A

at a fine aggregate content of 35/40 % of total aggregate weight

197
Q

whats the 3 tests for aggregates in order of importance

A

1: field perfomance concrete
2: Tests taht evaluate aggregate in concrete
3: tests on the aggregates themselves

198
Q

How can aggregate be unsound

A

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
Q

what are the 2 forms of freeze thaw due to unsoudness

A

pop-outs- D-Cracking

200
Q

does aggregate play an important role in determining the resistance of concrete to surface abrasion and wear?

A

yes, particles must be hard,dense,strong and free of soft , porous or friable particles

201
Q

where does most chemical durability come from

A

result from a reaction between reactive silica in aggregates and alkalis containe in cementif

202
Q

if an aggregate doesnt meet ASTM standards what process may help?

A

see pp 12 slide 38

203
Q

what four major factors must be considered with implementation of waste materials in concrete

A

economy
compatibility with other mats
concrete properties
consistency

204
Q

see pp9 slide 32

A

yeu

205
Q

is porosity good for concrete?

A

no, every 5% you lose 5% of strength

206
Q

why is microstructure of hcp highly modified in the vicinity of inclusions(agg, fiber, steel)

A

increased porosity
less unreacted cement

207
Q

the inability of cement particles to pack efficiently in close proximity of the embedment is due to what

A

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
Q

true or false the slower the reaction of concrete, the more strength you eventually get

A

true

209
Q

whare the 3 reason to add mineral admixture

A

replace cement
improve workability
enhance durability

210
Q

what are the 3 mains categories of mineral admixture

A

pozzolanic
cementitious
non-reactive

211
Q

what are the 2 types of SCM

A

cementitious and pozzolanic

212
Q

define Blast furnace slag

A

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
Q

what are the 3 most common pozzolanic mats and what they do

A

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
Q

what are the general benefits of SCM

A

economics (excecpt silica fumes)
environemental friendly
lower heat hydration
improved durability
improved workability
increased strength

215
Q

whats the replacement rate of scm

A

5% to 70%

216
Q

why do we add chemical admixtures

A

brings out a desired effect on physical propertiesof the fresh and or hardened concrete

217
Q

common types of chemical admixture

A

Water reducing (expanding)
air entrsining (gas forming)
set retarding (corrosion inhibiting)
set accelerating (permeability reducing)

218
Q

define water reducing admixture

A

surfactants wich abstob at the solid water interface and prevemt cement grains from flocculatingin water

219
Q

how can water reducing admixture be used

A

plasiticizer (increased workability at same W/C ration)
water reducer (decreased in W/C ratio at same workability

220
Q

define air entraining admixture

A

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
Q

advantageand disadvantage of air entraining admixtures

A

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
Q

define set retarding admixture

A

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
Q

define set accelerating admixtures

A

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
Q

what are the primary step to concrete production

A

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
Q

define batching

A

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
Q

why is mixing essential

A

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
Q

what are the factors to optimize mixing time

A

type of mixer
condition of mixer
speed of rotation
size of charge
nature of ingredients
mix design/proportioning
ambient temperature

228
Q

what are the types of mixers

A

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
Q

what are the ready mixed concrete

A

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
Q

whats the importance of placement for concrete

A

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
Q

what happens during vibration

A

entrained air goes up and some of it is lost so have to take that into account dring vibration

232
Q

what are the fresh concrete properties

A

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
Q

define workability

A

amount of mechanical work required to produce full compaction of the concrete without segregation

234
Q

what are the factors affecting workability

A

seggregation and bleeding

235
Q

define seggregation

A

seperation of components of fresh concrete resulting in nonuniform mix

236
Q

what are the factore contributing to segregation

A

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
Q

define bleeding

A

upward movement of rhe water after concrete has been consolidated but before it has set.

238
Q

why does water segregates from the mix

A

because its the lightest component of concrete

239
Q

what causes bleeding

A

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
Q

what leads to weakness porosity and rduced durability in concrete

A

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
Q

what happens if bleed water evaporates more quickly than bleeding rates

A

plastic shrinkage cracking can form. problematic in hot, dry and or windy weather.

242
Q

define laitance

A

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
Q

what does the slum test provide

A

a rough measure of consistency. but not an absolute measure of workability

244
Q

what can the slump test not be used for

A

high slump concrete
low slum concrete
fiber reinforced concrete
certain admixtures

245
Q

can air content test distinguish between entraspped and entrained air content

A

no

246
Q

what are the 3 air content test

A

gravimetric
volumetric
pressure

247
Q

define the gravimetric method

A

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
Q

define the volumetric method

A

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
Q

descibre the pressure method air test

A

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
Q

can unit weight be affected by presence of entrained air

A

yes

251
Q

define setting

A

refers to the onset of rigidity in fresh concrete. must occur before hardening

252
Q

define hardening

A

developpement of useful and measurable strength

253
Q

what are the arbitrary values for initial set and final set

A

initial 500 psi
final 4000 psi

254
Q

why is time of set important

A

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
Q

how many test are recognized for time set

A

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
Q

why is curing important for concrete

A

affects btoh mechanical properties and durability characteristics and reduces volume changes due to shrinkage.

257
Q

what are the 2 components required for curing

A

prevent loss of moisture through evaporation
supplies additional water for continued hydration

258
Q

what would excessive evaporation from concrete cause

A

plastic shrinkage cracking

259
Q

whats the W/C ration that provide complete hydration

A

theroetically 0.42 or hugher

260
Q

when does the hydration reaction stop

A

when internal relative humidity drops below 80%

261
Q

true or false Slags and pozzolans require shorter curing periode

A

false, they require longer to ensure the reaction takes place

262
Q

what happens if you restart interrupted curing

A

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
Q

when should concrete be tested

A

in fully saturated region (conservative, strength cant go lower)

264
Q

whats the temperature effect on cooling

A

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
Q

define water curing

A

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
Q

define sealed curing

A

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
Q

when should sealed curing never be used

A

between lifts or bonded overlas or when surface is painted
during the fall on pavement to be exposed to deicing salts.

268
Q

what is a common problem of sealed curing

A

self desiccation

269
Q

does sealed curing provide aditional hydration

A

no

270
Q

what is plastic shrinkage cracking

A

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
Q
A
272
Q

what are the 3 factors influencing plastic shrinkage

A

concrete air temp
relative humidity
wind velocity

273
Q

what is the desirable concrete temps

A

50-60 f
above 75 must take precaution

274
Q

what are the effects of hot temps on concrete

A

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
Q

what are the precaution to take for hot weather concrete

A

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
Q

define cold weather in concrete world

A

more than 3 succesive days the mean daily temp is 40 f

277
Q

effect on fresh concrete of cold wather

A

accelerated slump loss
decreased rate of setting
increased risk of plastic shrinkage cracking
extreme damage if concrete allowed to freeze

278
Q

what are the precautions to take for cold weatehr concreting

A

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
Q

whats the portland cement concrete mean compressive strength

A

35-50 Mpa

280
Q

go see lasts couple slide graphs pp 10

A

pop

281
Q

what are the 5 categories of durabiliy

A

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
Q

what are the 2 categories of deterioration mechanism

A

chemical attack
physical attack

283
Q

what are the 3 primary transport mechanism that allow aggressive agents penetration

A

absorption
permeation
diffusion

284
Q

what is absorption

A

transport of liquids into unsaturated porous solids due to surface tension acting in capilaries

285
Q

what is permeation

A

movement of gases or liquids through a saturated porous medium due to a pressure gradient

286
Q

what is diffusion

A

transfer of mass by random motion of free molecles or irons in the pore solution due to a concentration gradient

287
Q

what is the number one factor that affects durability

A

W/C ratio

288
Q

what is the hardest challenge with concrete durability

A

predicting the concrete behaviour decades in the futur based on short term lab tests

289
Q

define leaching

A

the hydrolysis of cement paste components (CH) by water flowing through the concrete

290
Q

what is the difference between hard water and soft water

A

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
Q

what is leaching rate dependant on and what can we do to prevent it

A

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
Q

when is efflorescence a problem?

A

when it actually comes from the concrete

293
Q

what is the alkali silica reaction

A

a chemical reaction between the soluble alkalis contained in the hcp and certain reactive forms of silica found in the aggregates

294
Q

can you explain the ASR reactions step by step

A

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
Q

what factors affect the ASR reaction?

A

nature of reactive silica
amount of reactive silica
particle size of reactive material
amount of alkalis available
amount of moisture available

296
Q

what factor influence the time elapsed between concrete casting and appearance of damage due to ASR

A

the nature of the silica involvedh

297
Q

how can we prevent ASR

A

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
Q

how do we detect ASR

A

UV fluroescence technique

299
Q

what is alkali carbonate reaction (ACR)

A

expansive reactions involving carbonate rocks

300
Q

what feature does carbonate rock succeptible to expansive reaction possess

A

very fine grained dolomite
considerable amount of fine grained calcite
abundant interstial clay
dolomite and calcite crystals evenly dispersed in clay matrix

301
Q

what is a sulfate attack

A

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
Q

what are the primary forms of sulfate attack

A

external sulphate attack
physical sulphate attack
thaumasite
internal sulphate attack (DEF)
waste/sewage

303
Q

explain the steps of the sulfate attack

A

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
Q

whats the effect of seawater on a sulfate attack

A

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
Q

what is a internal sulphate attack

A

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
Q

what is an acid attack?

A

a chemical reaction between an external source of acidic liquid and hcp and in some cases aggregates

307
Q

what is the acid attack sequence

A

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
Q

where on the ph table do you find sulfate attacks

A

acid attack on hcp begins around 7 and severe attack around 4

309
Q

what is freezing & thawing

A

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
Q

what are the factor affecting freeze thaw

A

expansion of water
hydraulic pressure
solar heating
litvans model

311
Q

whats the effect of water expansion on freeze thaw

A

just before freezing, volume increases by 9%

312
Q

what is the effect of hydraulic pressure on freeze thaw

A

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
Q

wich type of air is freeze thaw resistant

A

entrained air

314
Q

what is solar heating effect of freeze thaw

A

two directional freezing at surface due to daily thawing from incident solar radiation

315
Q

what is litvans model effect on freeze thaw

A

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
Q

why does concrete withstand fire

A

because of low rate of heat penetration

317
Q

what factors contribute to low heat penetration in concrete

A

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
Q

what are the effects of water loss and shrinkage in concrete

A

strength reduction and tensile stresses. results in cracking and spalling

319
Q

why is concrete less susceptible than steel to heat?

A

steel conducts heat rapidly causing severe loss of structural integrity in beams and columns

320
Q

what is the number 1 worldwide durability issue with concrete

A

corrosion of reinfrocement

321
Q

what is corrosion effect on concrete

A

electrochemical attack mechanism affecting the reinforcing steel wich results in a volume increase, thus inducing tensile stresses in the concrete.

322
Q

true or false concrete protects the steel from corrosion?

A

true, it provides excelleent protection

323
Q

how does concrete protect steel from corrosion

A

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
Q

what are the primary reason for loss of protection of the steel by the concrete

A

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
Q

what type of process is corrosion

A

electrochemical, requires formation of a cathode and an anode with an electrical current flowing between them

326
Q

define anode

A

iron mettalice atoms are oxidized to Fe2+ ions wich dissolve into the surrounding solution also producing electrons (where you get most damage)

327
Q

define cathode

A

electrons are consumed and OH- ions are formed. water and oxygen are required for this to occur

328
Q

what are the two deleterious effect of corrosion of steel in concrete

A

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
Q

what can you do in design to prevent corrosion

A

sufficient cover
improved transposrt properties
corrosion inhibitors
corrosion resistant reinforcement (galvanized steel, stainless steel, epoxy coated steel, fibre reinforced plastics)

330
Q

how can you protect/repair existing strucutre with corrosion

A

remove, clean , replace
corrosion resistant reinforcement
corrosion inhibitors
cathodic protection (sacfrificial anode, cancellation current)
protective overlay (waterproof membrane, watertight concrete overlay)

331
Q

what is surface wear

A

progressive mass loss from a concrete surface due to repetitive attrition cycles

332
Q

what are the 3 mechanisms of surface wear

A

abrasion
erosion
cavitation

333
Q

define abbrasion

A

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
Q

define erosion

A

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
Q

what is cavitation

A

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
Q

what happens at irregularities during cavitation

A

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
Q

what are the negative impacts of seawater on concrete

A

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
Q

what are the types of cement and a quick descriptions

A

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)

cive 202 midterm (3 decks)

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