civ204 materials of construction (2+2 ects...

CIV204

MATERIALS OF CONSTRUCTION

(2+2 ECTS 6)

Aims of the Course

To provide students comprehensive information on the basic

engineering properties of most common construction materials.

To introduce technologies of basic construction materials such as

concrete, steel, and composite materials.

To provide information about the structure of construction materials.

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No cell-phone during class.

Do not be late for the class!

Regular class and lab application attendance

is mandotory.

Materials for Civil and

Construction Engineers

CHAPTER 1

Materials Engineering Concepts

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.

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INTRODUCTION

Common civil

engineering materials:

steel

mineral aggregates

concrete

masonry

asphalt

wood

soil for geotechnical

engineers

Less common materials

aluminum

glass

plastic

Fiber-reinforced

composites


6

New Materials

Advances in

polymers

adhesives

composites

geotextiles

coatings

synthetics

High performance

materials

higher strength to

weight ratio

improved durability

lower costs


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Material Selection Considerations

Economic factors

Mechanical properties

Non-mechanical properties

Production/construction

considerations

Aesthetic properties

Sustainable considerations

Emphasis

client’s needs

facility’s function


1.1 Economic Factors

Factors to be considered

availability and cost of raw materials

manufacturing costs

transportation

placing

maintenance

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1.2 Mechanical Properties

Response of material to external loads

All materials deform under load depending on:

material properties

magnitude and type of load

geometry of the material element


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Loading Conditions

Static (Dead) Loads – long term

applied and removed slowly so no vibrations

usually due to gravity

Dynamic (Live) Loads – short term shock or vibration

periodic – repeating wave form (rotating

equipment)

transient – quick impulse that decays back to

resting (vehicles)

random – never repeats (earthquake)


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Static loading implies a sustained loading of the structure over a period

of time. Generally, static loads are slowly applied such that no shock or

vibration is generated in the structure. Loads that remain in place for an

extended period of time are called sustained (dead) loads. In civil

engineering, much of the load the materials must carry is due to the weight

of the structure and equipment in the structure.

Loads that generate a shock or vibration in the structure are

dynamic loads. Dynamic loads can be classified as periodic,

random, or transient

Periodic loading Random loading Transient loading


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Stress-Strain Relations

All solid materials deform under load

stress is like force (or load) with the size factored out

so that we can directly compare different sizes

stress = force / area

s = F / A (psi, ksi, kPa, MPa, GPa)

strain is like deformation with the size factored out

strain = deformation / original length

e = DL / L0 (%, in/in, mm/mm)


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Typical Stress-Strain Diagrams

s – e is usually linear in the low stress range but

transforms into non-linear

Glass and

chalk

Steel Aluminum

alloys

Concrete Soft

rubber


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Elastic Behavior

Instantaneous response to load

Returns to its original shape upon unloading stretches bonds between atoms without rearranging

them


Linear & Non-Linear Behavior

A linear material has a straight line stress-strain graph

An elastic material returns to its original shape

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Linear elastic

Non-linear elastic

Non-linear

inelastic


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Properties of an Elastic Material

Modulus of Elasticity or Young’s Modulus

E = Ds / De slope (rise over run) of the linear portion of stress-strain

curve

Poisson’s Ratio

n = -el / ea

relates lateral strain, el, to axial strain, ea

as material is stretched the cross section shrinks and vice

versa for compression

Range = 0 to 0.5 (practically 0.1 to 0.45)


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Generalized Hooke's Law

For three directions (3D = triaxial)

E

zyx

x

ssnse

E

xzy

y

ssnse

E

yxz

z

ssnse

y x

z

EE

E

AF

zzy

zz

yx

z

nssne

nse

ss

s

00

00

0

For axially loaded

members, no

stresses in the x

and y directions


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What if response is not linear?

How do we find the slope (Modulus of Elasticity)?

Strain

Str

ess

Initial

Tangent

Modulus

Secant

Modulus

Chord

Modulus

Tangent

Modulus


Typical E Moduli and Poisson’s Ratios

Material Modulus of

Elasticity

(GPa)

Poisson’s

Ratio

Aluminum 69 - 76 0.33

Brick 10 - 17 0.23-0.40

Concrete 15 - 40 0.11-0.21

Limestone ~58

Steel 200 0.27

Wood 6.2 - 15

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Elastoplastic Behavior Most materials are linear elastic in small stress range

and then plastic

the transition point is elastic limit

Elastic

stretches bonds between atoms without

rearranging them

recoverable deformations (springs back)

Plastic

atomic bonds slip past each other and rearrange

permanent deformations (doesn’t spring all the way

back)


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Str

ess

Total Strain

Elastic

Strain

Plastic

Strain

Force is applied resulting in

stress and strain

Strain

When force is removed,

stress returns to zero.

Path is parallel to the

initial slope of the curve.

Part of the strain is

“recovered,” this is

elastic behavior.

Part of the strain is

permanent, this is

plastic behavior.

Elastic Limit

New elastic limit

Reloading will resume to the highest

previous stress level.

Elastic limit is “reset to the previous

highest stress level.”

Response to further

loading follows

original stress-strain

behavior


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What if there’s no clear transition point?

Extension method Offset method


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Elements of Stress-Strain Diagram


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Definitions

Proportional Limit

transition between linear and non-linear behavior

Elastic Limit (Yield Point)

transition between elastic and plastic behavior – maximum stress with full recovery

Yielding

strain continues with little or no increase in stress (after elastic limit)

Ultimate Stress

maximum stress on the curve (tensile or compressive strength)


Definitions (Cont.)

Rupture Stress

point where specimen fractures or ruptures

Brittle Material

has little plastic deformation before failure (glass, concrete)

Ductile Material

has lots of plastic deformation before failure (structural steel, rubber)

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Viscoelastic Behavior

Strain is an instantaneous response to stress in elastic

and elasto-plastic materials.

In some cases, materials exhibit both viscous and elastic

responses, which are known as viscoelastic.

Viscosity: Resistance to flow (i.e., to shear force)

for linear materials:

= shear stress/rate of

shear strain, unit Pa.s or cP

Viscoelastic materials

have both elastic and viscous response

have delayed response to load application.

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Time dependent response of viscoelastic materials

(a good example is asphalt or some plastics)


Deformation in Viscoelastic materials depends on

oDuration of load

oRate of loading

A quick shock or pulse may cause little deformation, while a

sustained (or slowly increasing) load can cause much

deformation

o Temperature

Deformation increases with an increase in

temperature (i.e.viscosity decreases).

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Mechanisms associated with time-dependent deformation

Creep

Creep is the long-term deformation

of the materials under sustained

load. It can occur in metals, ionic

and covalent cystals and amorphous

materials.

In order to observe a creep

deformation on the materials, the

load needs to be applied for a long

time.

For example, concrete, can creep

over a period of decades.

Viscous flow

It is the other time-dependent

behavior of materials under

sustained loads. Viscous flow is

associated only with amorphous

materials and can occur under short

term load duration.

For example, asphalt pavements

can deform under traffic loads with

a load duration of only a fraction of

a second.


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Behavior of time-dependent materials

Creep Relaxation


Rheological models

used to model mechanically the time-dependent behavior of

materials

basic rheological elements

Rheological models are combinations of elements

Maxwell Kelvin

Prandtl

Burgers

Spring St. Venant Dashpot

33 Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.


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Rheological Models Rheological models are used to model mechanically the time-dependent

behavior of materials.

Rheology uses three basic elements, combined in either series or parallel

to form models that define complex material behaviors.

Linear spring

Linear elastic material

(Hook element)

Dashpot (absorber)

Perfectly viscous materials

(Newtonian element)

Sliding block

Shows the threshold

stress for movement


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Rheological Models

Kelvin Model Maxwell Model

Prandtl Model

Burgers Model (Standard solid body)


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Temperature & Time Effects

Temperature affects mechanical

behavior of all materials

high temp = ductile

low temp = brittle

Impact fracture test measures toughness at different

temperatures

Viscoelastic materials like asphalt and polymers are

greatly influenced by a change of only a few degrees

Metals require a much greater temperature change but

are similarly affected


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Work & Energy

Work (or Energy) = force x distance

Modulus of Resilience: energy required to reach yield

point

Toughness: energy required to fracture


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Failure and Safety

Several ways to fail –

fracture or breakage

fatigue (repeated stress)

general yielding

buckling

excessive deformation

For safety, structures are designed to carry loads

greater than anticipated


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Endurance Limit


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Factor of Safety

FS = (allowable stress / actual stress)

FS is proportional to cost and is chosen by:

cost

material variability

accuracy in considering all loads

possible misuse

accuracy in measuring material response

(good testing?)

FS = allowable

failure

s

s> 1

The factor of safety (FS) is defined as the

ratio of the stress at failure to the allowable

stress for design (maximum anticipated

stress):


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1.3 Non-Mechanical Properties

Other than load responses:

Density and Unit Weight

Thermal Expansion

Surface Properties

Abrasion & Wear Resistance

Surface Texture


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Density and Unit Weight

density = r = m / V

unit weight = g = W / V

specific gravity

w

Gr

r

Specific gravity is the ratio of the mass of a substance

relative to the mass of an equal volume of the water.


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Specific Gravity


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Thermal Expansion

All materials expand and contract with temperature

Linear Coeff. of Thermal Expansion

aL = (DL / DT) / L0

Volumetric Coeff. of Thermal Expansion

aV = (DV / DT) / V0

for isotropic materials aV = 3aL

Stresses develop because of different rates of

thermal expansion and contraction for different

materials that are connected together

use expansion joints


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Expansion joint


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Surface Characteristics

Corrosion and Degradation

Abrasion and Wear Resistance

Surface Texture


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1.4 Production and Construction

Production

availability and ability to fabricate material into

desired shapes

Construction

ability to build the structure on site (trained work

force)

o High early strength concrete used for early traffic

opening in pavement


1.5 Aesthetic Characteristics

The civil engineer is responsible for working with the

architect

The mix of artistic and technical design skills makes

the project acceptable to the community

Engineers should understand that there are many

factors beyond the technical needs that must be

considered

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1.6 Sustainable Design

Sustainable design in the philosophy of designing

physical objects, the built environment and services

to comply with the principles of economic, social, and

ecological sustainability.

The materials used for CE projects are important to

the sustainability of the project.

The Green Building Council developed the

Leadership in Environment and Energy Design,

LEED, building rating system to evaluate the

sustainability of the project.

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Sustainable Design (Cont.)

For new construction and major renovations the rating

areas include:

Sustainable sites

Water efficiency

Energy and atmosphere

Materials and resources

Indoor environmental quality

Innovation in design

Regional priority

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1.7 Material Variability

All materials have variability

Some materials are more uniform than others

oSteel vs. concrete vs. wood

Three sources of variance:

Material

Sampling

Testing

Use good sampling and testing techniques to

minimize those variabilities


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Precision: measure many times and get same result

Bias: tendency to deviate in one direction from true

value

Accuracy: close to true value; absence of bias

Exactness of measurements

Precise but not accurate Accurate but not precise Accurate and precise


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Sampling

Proper sampling must ensure that a random and

representative sample is taken from the population (e.g.,

stockpile, lot, etc.)

Random: have an equal chance of being selected

Representative: perfect average of the entire stockpile

Sample size:

depends on materials variability & tolerance level of

results

more variability dictates a larger sample

Rigorous statistical evaluations required for special

applications:

high quality asphalt and Portland cement concrete


Describes many populations that occur in nature,

including material properties

Area under the curve between any two values

represents the probability of occurrence

Normal

Distribution

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Decrease inspection frequency

Early detection of troubles

Provide a record of quality

Basis of acceptance

Control

Charts


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Experimental Error

Caused by 3 factors:

Procedural errors

Are often undiscovered

Machine errors (bias)

If known and constant can be easily corrected

Human errors

Minimize by repetition, double-checking, etc.

o Always do more than one test


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1.8 Laboratory Measuring Devices Direct

Ruler, dial gauge, calipers

Physical & material properties are usually measured (time, deformation, force, etc.)

Indirect

LVDT, strain gauge, load cell

measuring changes in electric voltage and relating to deformation, stress, or strain

must be calibrated

Electronic sensors can be easily connected to digital devices or computers:

CDAS (computerized data acquisition system)


Dial Gauge

LVDT

Strain

Gauge

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Proving

Ring

Load

Cell

Extensometer

Non-Contact

Extensometer

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Important considerations:

Sensitivity

Accuracy

Calibration

Sensitivity of measuring devices:

the smallest value that can be read on the device’s

scale

sensitivity is not accuracy or precision

accuracy cannot be better than the sensitivity

When choosing a device, sensitivity depends on the

required accuracy, which depends on the type of

test.


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Laboratory Experiment List

Experiment 1: Tension Test of Steel

Experiment 2: Sieve Analysis of Aggregates

Experiment 3: Specific Gravity and Absorption of Coarse Aggregate

Experiment 4: Specific Gravity and Absorption of Fine Aggregate

Experiment 5: Bulk Unit Weight and Voids in Aggregate

Experiment 6: Slump of Freshly Mixed Portland Cement Concrete

Experiment 7: Unit Weight And Air Content of Fresh Concrete

Experiment 8: Making and Curing Concrete Cylinders and Beams

Experiment 9: Compressive Strength of Cylindrical and Cubic

Concrete Specimens

Experiment 10: Flexural Strength of Concrete

Experiment 11: Rebound Number of Hardened Concrete (Non-

destructive test on concrete.

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