Polymers: Classification
• A) Thermoplastics such as polyethylene, which
soften on heating.
• B) Thermosets or resins such as epoxi which
harden when two components are heated
together.
• C) Elastomers or rubbers
• D) Natural polymers such as cellulose, lignin
and protein, which provide the mechanical basis
of most plant and animal life
From: Asby& Jones
CE 60
Instructor: Paulo Monteiro
Engineering Thermoplastics
• This term was first introduced by the General Electric
Co. in the 1960’s, & they defined it as a polymer alloy
which could replace metals in many applications.
• Polyethylene is the most common of them. It is a linear
polymer. That is why they soften when heated.
• Thermoplastics are made by adding together
(polymerizing) sub-units (“monomers”) to form long
chains.
H H
• Example:
-C - C
H R
R may be hydrogen (polyethylene), or
CH3 (polypropylene) or –Cl (polyvinylchloride)
CE 60
Instructor: Paulo Monteiro
A high-molecular-weight polyethylene has an average molecular weight
of 410,000 g/mol. What is its average degree of polymerization?
mass of the polyethylene mer :
(4 hydrogen atoms × 1 g/mol) + (2 carbon atoms × 12 g/mol) = 28
g/mol.
molecular weight of polymer (g / mol)
DP =
molecular weight of mer (g / mol / mer)
410, 000 g / mol
=
28 g / mol / mer
= 14, 643 mers
⎡H
⎢⏐
⎢C
⎢
⎢⏐
⎣Η
H⎤
⏐⎥
C⎥
⎥
⏐⎥
Η⎦
Thermoplastics
• Nylons are one example of an engineering
thermoplastic.
• Polycarbonates have a “ring” structure in
the chain which makes it very “stiff”
molecule which translates into a high
melting point.
CE 60
Instructor: Paulo Monteiro
What type of bonding exists within
the molecular chains of
thermoplastics?
• Within thermoplastic molecular chains,
covalent bonds exist.
Thermosetting Plastics
•
•
•
Thermoplastics are usually easier to mold into complex shapes. The
polymer is heavily cross-linked
but thermosetting polymers offer more of the following properties:
– High thermal stability
– High rigidity
– High dimensional stability
– Resistance to creep & deformation under load
– Light weight (as compared to metals)
– High electrical & thermal insulating properties
Today many thermosetting “resins” are available which have
superior properties. [See p. 330-340 in the Smith textbook].
CE 60
Instructor: Paulo Monteiro
Describe the atomic structural
arrangement of thermosetting
plastics.
• Most thermosetting plastics consist of
three-dimensional networks of covalently
bonded atoms, as compared to the long
chain-like molecules of thermoplastics.
Elastomeric Materials
• Elastomers are linear polymers with
occasional-cross links. These cross-links
provide a memory so it returns to its
original shape on unloading.
• Polymers which show “rubbery” behavior
at their operating temperature are called
“elastomeric” [See the Smith textbook].
• Some elastomeric polymers are
thermoplastics & others are thermosetting.
• The prototype is “natural rubber”.
CE 60
Instructor: Paulo Monteiro
Glassy plateau
E
Glass transition
Rubbery plateau
Viscous flow
Temperature
CE 60
Instructor: Paulo Monteiro
Portland Cement
A hydraulic cement capable of setting, hardening and
remaining stable under water. It consists essentially of
hydraulic calcium silicates, usually containing calcium
sulfate.
CE 60
Instructor: Paulo Monteiro
Manufacture
Raw Materials:
2/3 calcareous materials (lime bearing) - limestone
1/3 argillaceous materials (silica, alumina, iron)- clay
CE 60
Instructor: Paulo Monteiro
Based on the following notation:
C
CaO
S
SiO2
A
Al2O3
F
Fe2O3
H
H2O
CE 60
Instructor: Paulo Monteiro
Cement Minerals
C3S : 3CaOSiO2
C2S : 2CaOSiO2
C3A : 3CaOAl2O3
C4AF : 4CaOAl2O3Fe3O4
CE 60
Instructor: Paulo Monteiro
CHEMICAL REACTIONS
2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g
2C2S + 4H --> C3S2H3 + CH + 62 cal / g
C3A + CSH2 --> Ettringite + 300 cal / g
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Silicate Hydrate
Notation: C-S-H
C/S Ratio: 1.5 to 2.0
Main Characteristics: High Surface (100 to 700 m2/ g) ----> High Van
der Walls Force -----> Strength.
Volume % : 50 a 60
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Hydroxide ( portlandite)
Ca(OH)2
Volume % : 20 to 25
low Van der Walls force
problems with durability and strength
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Sulfoaluminate Hydrates
Volume % : 15 to 20
first : ettringite
after : monosulfate hydrated.
CE 60
Instructor: Paulo Monteiro
Hydration process – Initial Condition
Let’s study a cement paste with w/c= 0.63
Start with 100 cm3 of cement.
Compute the mass of cement: Mc = 3.14* 100 = 314 g
Compute the mass of water: Mw = 0.63 * 314 = 200 g
Vw= 200 cm3
Vc= 100 cm3
CE 60
Instructor: Paulo Monteiro
ASTM Portland Cements
Type I-
General Purpose
Type II- moderate heat of hydration and sulfate resistance (C3A <
8%) : general construction, sea water, mass concrete
Type III- high early strength (C3A < 15%) : emergency repairs,
precast, winter construction.
Type IV- low heat ( C3S < 35%, C3A < 7%, C2S > 40%) : mass
concrete
Type V-
sulfate resistant ( C3A < 5%) : sulfate in soil, sewers.
CE 60
Instructor: Paulo Monteiro
Aggregates
• cost
• provide dimensional stability
• influence hardness, abrasion resistance,
elastic modulus
CE 60
Instructor: Paulo Monteiro
Aggregate Type
•Coarse aggregate ( > 3/16 in. - 4.75 mm of No. 4)
•Fine aggregate < 3/16 in. and > 150 (No. 200)
CE 60
Instructor: Paulo Monteiro
Aggregate Type -mineralogy
•Sedimentary Rocks (cost effective - near the surface),
•about 80% of aggregates
•Natural sand and gravel
•Sandstone, limestone (dolomite), chert, flint, graywacke
•Metamorphic Rocks: slate, gneiss : excellent
to poor
CE 60
Instructor: Paulo Monteiro
CE 60
Instructor: Paulo Monteiro
• Fineness modulus is the sum of the total
percentages retained on each of the
specified sieve divided by 100. The
specified sieves are 3, 1 1/2, 3/4 and 3/8
in and Nos. 4, 8, 16, 30, 50 and 100.
CE 60
Instructor: Paulo Monteiro
Characteristics of coarse aggregate
Characteristics of fine aggregate
Type Used:________________
Type Used: ______________
Max. Size:______1______ inch
F.M. _____2.93______________
B.S.G: 168 ______lb/ft3
B.S.G: 167 ______lb/ft3
Moisture deviation from S.S. D.=_-0.4%__ Moisture deviation from S.S. D.=0.7%__
Dry-rodded unit wt.__104_lb/ft3____
B.S.G of cement = 196 lb/ft3
CE 60
Instructor: Paulo Monteiro
Effect of moisture
CE 60
Instructor: Paulo Monteiro
Types of Elastic Modulus
Testing
ASTM Testing
CE 60
Instructor: Paulo Monteiro
Creep and Shrinkage
CE 60
Instructor: Paulo Monteiro
Importance
CE 60
Instructor: Paulo Monteiro
Compressive Strength
• Fundamental relationship
• S = So exp (-kp)
• Where So is the strength at zero
porosity, p is the porosity and k a
constant.
CE 60
Instructor: Paulo Monteiro
Interfacial Transition Zone
CE 60
Instructor: Paulo Monteiro
REASON
CE 60
Instructor: Paulo Monteiro
Microstructural improvement
• Use of silica fume
reduce the porosity of the ITZ
geometrical effect (no space)
reduces the amount of CH due to
pozzolanic reaction
CE 60
Instructor: Paulo Monteiro
Humidity
• Great importance of moist curing.
CE 60
Instructor: Paulo Monteiro
Temperature
• Cast and cured at the same temperature
• Cast at different temperature but cured at
the same temperature
• Cast at normal temperature but cured at
different temperatures.
CE 60
Instructor: Paulo Monteiro
Testing parameters
• Specimen Size: Fracture mechanics will
explain the importance of size effect.
• Loading Rate: Increasing rates lead to
increasing strength.
CE 60
Instructor: Paulo Monteiro
CE 60
Instructor: Paulo Monteiro
Thermal stresses
σt = K r
E
1+ϕ
α ΔT
where:
σt: tensile stress
Kr: degree of restraint
E: elastic modulus
α: coefficient of thermal expansion
ΔT: temperature change
ϕ: creep coefficient
CE 60
Instructor: Paulo Monteiro
Temperature Evolution
ΔT = placement temperature of fresh concrete + adiabatic temperature rise
- ambient or service temperature - heat losses.
CE 60
Instructor: Paulo Monteiro
Durability
•Durability of concrete: ability to resist
weathering action, chemical attack,
abrasion, or any process of
deterioration
CE 60
Instructor: Paulo Monteiro
Water Structure
CE 60
Instructor: Paulo Monteiro
Abrasion - Erosion
•Note: the deterioration starts at the surface,
therefore special attentions should be given
to quality of the concrete surface.
•Avoid laitance (layer of fines from cement and
aggregate).
CE 60
Instructor: Paulo Monteiro
The problem
The transformation of ice from liquid water generates a volumetric
dilation of 9%. If the transformation occurs in small capillary pores,
the ice crystals can damage the cement paste by pushing the capillary
walls and by generating hydraulicCEpressure.
60
Instructor: Paulo Monteiro
Deterioration by fire
•Concrete is able to retain sufficient strength
for a reasonably long time.
CE 60
Instructor: Paulo Monteiro
Effect of High Temperature on
Cement Paste
•(a) degree of hydration
•(b) moisture state
•de-hydration:
•ettringite > 1000C
•Ca(OH)2 500-6000C
•CSH ~ 9000C
CE 60
Instructor: Paulo Monteiro
Electrochemical process of steel corrosion in concrete
CE 60
Instructor: Paulo Monteiro
Volumetric change
CE 60
Instructor: Paulo Monteiro
The chemistry is simple
1) The high pH in the cement paste promotes the hydrolysis of silica
Si-O-Si + H OH ÆSi-OH+ Si-OH
aggregate paste
2) Si-OH react with the paste to form Si-O3) Si-O-, adsorbs Na, K, and Ca to form a gel.
CE 60
Instructor: Paulo Monteiro
Expansive Reaction
In the presence of sulfates
• C3A + gypsum Æ C3A.3C$.H32 (ettringite)
C3A.C$.H18 (monosulfate)
CE 60
Instructor: Paulo Monteiro
Sodium sulfate attack:
• Na2SO4 +Ca(OH) 2 +2H2O Æ
CaSO4.2H2O + 2NaOH
the formation of sodium hydroxide as a by-product
of the reaction ensures the continuation of high
alkalinity in the system, which is essential for the
stability of the cementitious material C-S-H.
CE 60
Instructor: Paulo Monteiro
Magnesium sulfate attack
• MgSO4 +Ca(OH) 2 +2H2O Æ
CaSO4.2H2O + Mg(OH) 2
• 3 MgSO4 + 3CaO .2SiO2 .3H2O + 8 H2OÆ 3 CaSO4.2H2O + 3
Mg(OH) 2 + 2SiO2.H2O
•
•
•
the conversion of calcium hydroxide to gypsum is accompanied
by the simultaneous formation of relatively insoluble magnesium
hydroxide.
In the absence of hydroxyl ions in the solution C-S-H is no
longer stable and is also attacked by the sulfate solution.
The magnesium sulfate attack is, therefore, more severe on
concrete.
CE 60
Instructor: Paulo Monteiro
Factors influencing sulfate attack
• amount and nature of the sulfate present,
• level of the water table and its seasonal
variation,
• flow of groundwater and soil porosity,
• form of construction,
• quality of concrete.
CE 60
Instructor: Paulo Monteiro
Determine the lattice points per cell
in the cubic system
Simple cubic:
Lattice points are located only at the corners of the cube
8 corners (1/8) = 1
In BCC unit cells, lattice points are located at the corners and the center of the cube:
8 corner (1/8) + 1 center (1) = 2
In FCC unit cells, lattice points are located at the corners and faces of the cube:
8 corners (1/8) + 6 faces (1/2) = 4
CE 60
Instructor: Paulo Monteiro
Calculate the radius of an atom that
will just fit into a cubic site
2R + 2r= 2R sqrt(3)
r/R = 0.732
R
2R + 2r= 2R sqrt(3)
r
2R
CE 60
Instructor: Paulo Monteiro
Problem
• Calculate the change in volume that
occurs when BCC iron is heated and
changes to FCC iron. The lattice
parameter of BCC iron is 2.863 A and of
FCC iron is 3.591 A
Volume of BCC cell = a3 = 2.863 = 23.467
Volume of FCC cell = a3 = 3.591 = 46.307
But the FCC unit cell contains four atoms and the BCC unit cell contains only two
atoms. Two BCC unit cells with a total volume of 46.934 will contain 4 atoms.
Volume change/atom = (46.307 -46.934)/46.934 = -1.34%
Steel contracts on heating!!
CE 60
Instructor: Paulo Monteiro
Hypoeutectoid Phase Diagram
• If a steel with a composition x% carbon is cooled from the Austenite
region at about 770 °C ferrite begins to form. This is called
proeutectoid
(or pre-eutectoid) ferrite since it forms before the
pro
eutectoid temperature.
CE 60
Instructor: Paulo Monteiro
Problem
CE 60
Instructor: Paulo Monteiro
An Example
(Assume a Eutectoid Low Carbon Steel)
(a) Water-quench to room Temperature.
(b) Hot-quench at 690°C & hold 2 hr; water-quench
(c) Hot-quench at 610°C
& hold 3 min; water-quench
Pearlite
Pearlite
(d) Hot-quench at 580°C
& hold 2 sec; water-quench
Bainite
(e) Hot-quench at 450°C &
hold 1 hr; water-quench
50% pearlite + 50 martensite
CE 60
All martensite
Instructor: Paulo Monteiro
Types of Atomic & Molecular Bonds
• Primary Atomic Bonds
Ionic Bonds
Covalent Bonds
Metallic Bonds
• Secondary Atomic & Molecular Bonds
Permanent Dipole Bonds
Fluctuating Dipole Bonds
CE 60
Instructor: Paulo Monteiro