土木工程材料 课件 Chapter 1 Basic Properties of Civil Engineering Materials

Materials in Civil

andConstructionEngineering土木工程材料Chapter

1BasicProperties

ofCivilEngineering Materials1.1

BasicPhysical

Properties

of

Materials1.2

MechanicalProperties

of

Materials1.3

Durability

of

MaterialsContent1.1Basic

Properties

ofCivil Engineering

Materials1.1 Basic

Physical

Properties

of

Materials1.1.1

Density,

ApparentDensity

andBulkD1.DensityDensity

isthe

mass

per

unitvolumewhenthematerial

isin

the

absolute

densestate.Itcan

beshownthat:In

thisformula:

isthe

density

(g/cm3);misthemassunderdry

conditions

(g);V

is

thevolume

underabsolutely

compactconditions

(cm3).Volume

in

the

absolute

dense

refers

to

the

volume

of

the

individual

particles

only

(no

voids).

A

lot

of

civilengineering

materials

include

voids,

such

as

brick,

stone

and

concrete.

As

for

these

materials,

it

is

required

togrind

the

materials

into

powder,

then

dry

to

constant

weight

and

measure

its

volume

using

Li

Bottle,

which

is

alsocalled

density

bottle.mV

1.1 BasicPhysical

Properties

of

Materials2.

ApparentDensityApparent

density

is

the

massper

unit

volume

when

the

material

is

in

natural

state.In

this

formula:

ρ0

is

the

apparent

density

(kg/m3);m

isthemassunder

dry

conditions

(kg);V0

is

the

volume

under

natural

conditions

(m3).The

volume

in

natural

state

includes

the

volume

of

the

solid

and

internal

pores.

The

apparentdensity

varies

with

moisture

content.

Apparent

density

generally

refers

to

apparent

density

in

dry

state.0

mV0

1.1 BasicPhysical

Properties

of

Materials3.BulkDensityBulk

density

ismassper

unit

volume

when

powdery

or

particle

materials

arein

the

stacking

condition.In

this

formula:

0

is

the

bulk

density

(kg/m3);mis

the

massunder

dry

conditions

(kg);V0

is

the

volume

under

packing

conditions

(m3).Bulk

density

isnot

an

intrinsic

property

of

a

material;

it

varies

from

how

the

material

is

handled.0V0

mstacking

stateincludesparticle

volumeinter-particle

void

volumeinternal

pore

volume1.1 BasicPhysical

Properties

of

MaterialsTable

1.1

Density,

apparent

density

andbulkdensity

of

some

civil

engineering

materialsNameDensity/(g/cm3)Apparent

Density/(kg/m3)BulkDensity/(kg/m3)Steel7.857850-Granite2.6-2.92500-2850-Limestone2.6-2.82000-2600-Gravels

or

Pebbles2.6-2.9-1400-1700Ordinary

Sand2.6-2.8-1450-1700Sintered

Clay

Brick2.5-2.71500-1800-Cement3.0-3.2-1300-1700Wood1.55-1.60400-800-Asphalt

Concrete-2300-2400-Ordinary

Concrete-2100-2600-1.1 BasicPhysical

Properties

of

Materials1.1.2 Solidity

Porosity

and

VoidagePorosity

is

afraction

of

the

volume

of

voids

over

the

total

volume.Porosity

represents

the

densification

of

material.Porosity

includes

connected

pore

andclosed

poreaccording

to

its

structure,

andit

can

beclassified

into

coarse

pore,

fine

pore

and

micropore

accordingto

its

size.Voidage

is

the

proportion

ofspacing

volume

amongtheparticlestothe

bulk

volume

of

thenon-coherent

material

in

somecontainer.Figure1.1

Sketch

map

of

poresVoidage

is

animportant

parameter

when

controlling

thegradation

of

concrete

andcalculating

sand

content.0

V0

P

1

100%

1

100%V

0

V0

0

P

1

100%

1

100%V

Thehigherporositythe

lowerdensification1.1 BasicPhysical

Properties

of

Materials(a)hydrophilic

property

θ<90

(b)

hydrophobic

property

90

≤θ≤180

Figure

1.2

Sketch

map

of

wetting

angle

(θ)Asphalt,

paraffin

wax

and

some

plasticused

in

civilengineering

are

hydrophobic

materials.1.1.3 Hydrophilic

and

HydrophobicHydrophilic

property

refers

tothe

material

property

which

can

bewettedwhen

it

contacts

with

water

in

theair

(0

≤θ≤90

).Most

civilengineeringmaterials

belong

to

hydrophilicmaterials,

such

asstone,

brick,

block,

glass

andpottery.

Asforhydrophilicmaterial,

water-proof

processingmethodcanbeused

to

improveitswater

resistance.Hydrophobic

property

refers

tothematerialproperty

which

cannotbewettedwhen

it

contacts

with

water

in

theair

(90

≤θ≤180

).1.1 BasicPhysical

Properties

of

Materials1.1.4 Water

Absorption

and

Moisture

AbsorptionWater

absorption

refers

to

the

ratio

of

the

weight

of

water

absorbed

by

a

material,

to

the

weight

ofthe

drymaterials.Specific

absorption

ofquality:Specific

absorption

ofvolume:In

this

formula:

m1

is

the

mass

of

the

materialat

water-saturated

state(g);m2

is

the

massof

the

material

under

dry

condition(g);Vis

the

volume

of

material

under

natural

condition(cm3).

m1

m2m2

100%mWW

m1

m2

100%VV1.1 Basic

Physical

Properties

of

MaterialsThe

water

absorption

is

related

to

porosity.

Water

can't

enter

into

the

dead-end

pores.

As

for

smallinterconnected

pores,

the

more

the

pores

are,

the

higher

the

water

absorption

is.

Open

pores

are

big,but

it's

difficult

to

store

water,

so

its

water

absorption

is

less.

Different

material

has

diverse

waterabsorption

for

its

different

internal

structure.Moisture

absorption

refers

to

the

ratio

of

weight

of

materials

with

absorbed

water

in

the

moist

air

tothat

of

drymaterials.In

this

formula:

m1

is

the

quality

of

material

in

the

moisture

state(g);m2

is

the

quality

of

material

under

the

dry

condition(g).

m1

m2m2

100%mW1.1 Basic

Physical

Properties

of

MaterialsSuchitemsmay

beused

in

wetenvironments

or

underwaterto

specified

depths.Waterproofingdescribesmaking

anobjectwaterproof

or

water-resistant

(suchasacamera,

watch

or

mobilephone)."Waterresistant"and

"waterproof"often

refertopenetration

of

waterin

its

liquidstate

andpossibly

under

pressure

wheredampproofrefersto

theresistance

to

humidity

ordampness.

Inbuildingconstruction,waterproofing

isafundamentalaspect

of

creating

abuilding

envelope

which

is

acontrolled

environment.

Theroof

covering

materials,

siding,foundations,

andallofthe

various

penetrations

through

these

surfaces

need

tobewater-resistant

andsometimeswaterproof.WaterresistantObjects

relatively

unaffected

bywaterorresistingtheingress

ofwaterunderspecified

conditions.1.1.5 WaterResistant

and

Waterproofing1.1 BasicPhysical

Properties

of

Materials1.1.6 Anti-permeabilityAnti-permeability

refers

to

the

property

of

something

that

cannot

be

pervaded

by

a

liquid

underpressure.

Generally,

Permeability

coefficient

or

impermeability

grade

is

used

to

describe

the

property.Permeability

coefficient

derives

from

Darcy'slaw.Darcy's

law

at

constant

elevation

is

a

simple

proportional

relationship

between

the

instantaneousdischarge

rate

through

a

porous

medium,

the

viscosity

of

the

fluid

and

the

pressure

drop

over

a

givendistance.Figure1.3

Definitions

and

directions

forDarcy's

law1.1 Basic

Physical

Properties

of

MaterialsIn

this

formula:Q

isthe

total

discharge

(m3/s);k

is

theintrinstic

permeability

ofmedium;A

is

thecross-sectional

areaof

flow

(m2);(pb－pa)

isthe

totalpressure

drop(Pa);

is

theviscosity

(Pa·s);Lis

thelength

overwhich

thepressuredrop

is

taking

place

(m).Asforconcrete

or

mortar,

impermeability

gradeisrepresented

asthe

index

of

impermeability.

Higher

the

gradeis,

better

the

impermeability

is.Q

kA

(

pb

pa

)L

Higherthegradeisbetter

theimpermeability

isThenegative

signisneeded

because

fluid

flowsfrom

highpressuretolowpressure.1.1 Basic

Physical

Properties

of

MaterialsFreezing

ResistanceFreezing

resistance

refers

to

the

property

of

materials

that

can

endure

repeated

freezing

and

thawing

cyclewithout

damage

and

its

strength

can't

be

obviously

reduced.

Generally,

Dn

is

taken

as

frost

resistance

grade,

inwhich

n

is

themaximum

times

of

freezing

and

thawing

cycle

when

materials

reachtheregulated

damage

extent.Both

the

anti-permeability

and

the

freezing

resistance

are

related

to

voidage

of

materials.

Materials

with

lessvoidage

or

end

voidage

has

higher

anti-permeability

and

the

freezing

resistance.

The

small

and

connected

poresaredisadvantageous

to

these

properties.ThermalConduction

and

Specific

HeatThermalconduction

is

the

transferofheat

from

one

part

of

abodytoanother

or

from

onebodytoanotherthroughits

physical

contact.

Nonmetalshavealow

coefficient

ofthermalconductivity.

Metals

haveamuchhigherone

because

their

freeelectrons

transferthevibrations

much

more

rapidly.

Thus,

metalsare

goodconductors

ofheat.1.1 Basic

Physical

Properties

of

Materials1.1.8 Thermal

Conduction

and

Specific

HeatThe

rate

of

heat

transfer

by

conduction

is

dependent

on

the

temperature

difference,

the

size

of

the

area

incontact,

thethickness

of

thematerial,

and

thethermalproperties

of

thematerial(s)

in

contact.Thequantity

ofheattransferred

by

conduction

isdefined

as

follows:

Qd

At(T2

T1

)In

this

formula:λ

isthe

coefficient

of

thermalconductivity

of

thematerial[W/(m·K)];Qis

theconducted

heatquantity

(J);A

istheheat-transfer

area

(m2);t

isthe

time

for

theheattransfer

(s);T1

isthe

temperature

on

warmer

side

(K);T2

is

thetemperature

on

thecolderside

(K);d

is

thethickness

of

a

material

(m).1.1 Basic

Physical

Properties

of

MaterialsThe

specific

heat

is

the

amount

of

heat

per

unit

mass

required

to

raise

the

temperature

by

one

degree

Celsius.The

relationship

between

heat

and

temperature

change

is

usually

expressed

in

the

form

shown

below

where

c

isthe

specific

heat.

The

relationship

does

not

apply

if

a

phase

change

is

encountered,

because

the

heat

added

orremoved

during

a

phase

change

does

not

change

the

temperature.Table

1.2

lists

afew

construction

materials

andtheirthermalproperties

atnominalroom

temperature.Table

1.2Construction

material

thermal

properties

at

room

temperatureMaterialThermal

Conductivity

/[W/(m·K)]Specific

Heat/[J/(kg·

C)]Density/(kg/m3)Brick0.78401600Concrete–cast

Dense1.48402100Concrete–cast

Light0.410001200Granite1.7-3.982026001.1 Basic

Physical

Properties

of

MaterialsGlass

(window)0.88802700Hardwoods

(oak)0.161250720Softwoods

(pine)0.121350510Polyvinyl

Chloride0.12-0.2512501400Paper0.041300930Acoustic

Tile0.061340290Particle

Board

(low

density)0.081300590Particle

Board

(high

density)0.1713001000Fiberglass0.04700150Expanded

Polystyrene0.031200501.2Mechanical Properties

ofMaterials1.2 Mechanical

Properties

ofMaterialsThemechanical

properties

of

amaterial

describehow

itwillreact

toexternal

loads.Mechanical

propertiesoccuras

aresultof

thephysical

properties

inherent

toeachmaterial,

andaredeterminedthroughaseries

ofstandardized

mechanical

tests.1.2.1 StrengthStrength

is

the

material

capacity

of

resisting

breakage

by

the

external

force.

Strength

includes

compressivestrength,

tensile

strength,shearingstrength

and

bending

strength

accordingto

thedifferent

formof

external

force.Thecompressivestrength

is

thecapacity

of

amaterial

orstructuretowithstandloads

tendingtoreduce

size.

Itcan

bemeasured

by

plotting

applied

forceagainstdeformationina

testing

machine.

Some

material

fracture

attheir

compressive

strength

limit;

othersdeform

irreversibly,

soagiven

amountofdeformationmay

beconsideredas

the

limit

forcompressive

load.Compressive

strength

isa

key

valuefor

design

ofstructures.1.2 Mechanical

Properties

ofMaterialsTensile

strength

is

not

the

same

as

compressive

strength

and

thevalues

can

be

quite

different.

Some

materials

will

break

sharply,without

plastic

deformation,

in

what

is

called

a

brittle

failure.

Others,whichare

more

ductile,

including

most

metals,will

experience

someplastic

deformation

and

possibly

necking

before

fracture.Shear

strength

is

the

maximum

shear

stress

which

a

material

canwithstand

without

rupture.

In

structural

and

mechanicalengineering

the

shear

strength

of

a

component

is

important

fordesigning

the

dimensions

and

materials

to

be

used

for

themanufacture/construction

of

the

component

(such

as

beams,

plates,or

bolts).The

flexural

strength

represents

the

highest

stress

experiencedwithin

the

material

at

its

moment

of

rupture.

It

is

measured

in

termsof

stress.

Three

and

four

points

bend

tests

are

commonly

used

todetermine

the

flexural

strength

of

a

specimen.the

maximum

stress

that

amaterialcan

withstand

while

beingstretched

orpulled

before

failingor

breakingTensilestrengtha

material's

ability

toresistforcesthat

can

causetheinternal

structure

of

thematerialtoslideagainst

itselfShearingstrengtha

material's

ability

to

resistdeformationunder

loadBendingstrengthorflexuralstrength1.2 Mechanical

Properties

ofMaterialsTable

1.3FormulaofstrengthClassificationSketchmapFormulaAnnotationsCompressive

strengthfcfc＝F/Af—Strength(MPa)F—Failure

load(N)A—Loaded

area(mm2)Tensilestrengthftft＝F/AShearing

strength

fvfv＝F/ABendingstrengthfmfm＝3FI/2bh2fm＝FI/bh21.2 Mechanical

Properties

ofMaterials1.2.2 Elastic

and

Plastic

DeformationIn

materials

science,

deformation

is

a

change

in

the

shape

or

size

of

anobject

due

to

an

applied

force

or

a

change

in

temperature.

A

temporary

shapechange

that

is

self-reversing

after

the

force

is

removed,so

thatthe

objectreturns

toits

original

shape,

is

called

elastic

deformation.

Elastomers

and

shapememory

metals

such

as

nitinol

exhibit

large

elastic

deformation

ranges,

as

doesrubber.

However,

elasticity

is

nonlinear

inthese

materials.Normal

metals,ceramicsand

most

crystalsshow

linear

elasticityand

a

smallerelasticrange.When

amaterial

distorts

under

pressure

butdoesnotreturnto

its

originalshape

afterthe

pressure

isreleased,

itiscalled

plasticdeformation.Figure1.4 Deformationcurve1.2 Mechanical

Properties

ofMaterialsThis

type

of

deformation

is

irreversible.

However,

an

object

inthe

plastic

deformation

range

will

first

have

undergone

elasticdeformation,

which

is

reversible,

so

the

object

will

return

part

wayto

its

original

shape.

Soft

thermoplastics

have

a

rather

large

plasticdeformation

range

as

do

ductile

metals

such

as

copper,

silver,

goldand

steel,

but

cast

iron

does

not.

Hard

thermosetting

plastics,rubber,

crystals,

and

ceramics

have

minimal

plastic

deformationranges.1.2 Mechanical

Properties

ofMaterials1.2.3 Ductility

andBrittlenessDuctility

and

brittleness

are

two

of

the

most

important

physicalproperties

of

materials

in

construction

engineering.

Brittleness

is

theproperty

of

a

material

that

will

fracture

without

appreciable

prior

plasticdeformation.

Brittleness

is

lack

of

ductility

and

for

a

brittle

material

thereis

no

plastic

deformation.

Theelastic

stage

is

followed

by

immediatefracture.

Typical

brittle

materials

include

glass,

concrete,

ceramics,

stone,and

cast

iron.

Ductility

is

the

property

of

a

material

that

can

be

plasticallydeformed

by

elongation

without

fracture.

Ductile

materials

can

typicallybe

plastically

elongated

with

more

than

15%

before

they

fracture.

Typicalductilematerials

includecopper,mild

steel,

and

thermoplastics.Figure1.5 Stress-straincurvesforbrittleandductilematerials1.2 Mechanical

Properties

ofMaterialsDuctility

of

a

material

is

its

ability

to

deform

when

a

tensile

force

is

applied

upon

it.

It

is

also

referred

toastheability

of

asubstance

to

withstand

plasticdeformation

without

undergoing

rupture.

Brittleness,

on

theother

hand

is

exactly

an

opposite

property

of

ductility

as

it

is

the

ability

of

a

material

to

break

without

firstundergoing

any

kind

of

deformation

upon

application

of

force.1.2.4 HardnessHardness

is

a

measure

of

how

resistant

solid

matter

is

to

various

kinds

of

permanent

shape

change

whenacompressive

force

is

applied.Hardness

isdependenton

ductility,

elastic

stiffness,

plasticity,

strain,

strength,

toughness,

viscoelasticity,and

viscosity.1.2 Mechanical

Properties

ofMaterialsCommon

examplesof

hard

matter

are

ceramics,

concrete,

certain

metals,

andsuper-hard

materials.

Thereare

three

main

types

of

hardness

measurements:

scratch,

indentation,

and

rebound.

Within

each

of

theseclasses

of

measurement

there

are

individual

measurement

scales.

Scratch

hardness

tests

are

often

used

todetermine

the

hardness

of

natural

mineral.

Steel,

wood

and

concrete

is

usually

determined

by

means

ofindentation

hardness

test.

Rebound

hammer

measures

the

surface

hardness

of

the

concrete.

The

surface

ofconcrete

gets

harder

as

concrete

gains

strength;

thus,

the

strength

of

concrete

can

be

estimated

using

thismethod.Figure

1.6

Concrete

test

hammer1.2 Mechanical

Properties

ofMaterialsStress

is

defined

as

force

per

unit

area.

It

has

the

same

units

as

pressure,

and

in

fact

pressure

is

one

special

variety

ofstress.

However,

stress

is

a

much

more

complex

quantity

than

pressure

because

it

varies

both

with

direction

and

with

thesurface

it

acts

on.

Strain

is

defined

as

the

amount

of

deformation

an

object

experiences

compared

to

its

original

size

andshape.It

is

unique

for

each

material

and

is

found

by

recording

the

amount

of

deformation

(strain)

at

distinct

intervals

oftensile

or

compressive

loading

(stress).

A

lot

of

useful

information

about

the

material

can

be

revealed

by

plotting

thestress-strain

diagram.

Figure

1.7

shows

the

typical

uniaxial

tensile

or

compressive

stress-strain

curves

for

severalengineeringmaterials.(a)

glass

and

chalk(b)

steel (a)

glass

and

chalk (d)

concreteFigure

1.7

Typical

uniaxial

stress-strain

diagrams

for

someengineering

ma