土木工程材料 課件 Chapter 5 Portland Cement Concrete、Chapter 6 Masonry、Chapter 7 Asphalt and Asphalt Concrete

Materials in Civil

andConstructionEngineering土木工程材料Chapter

5PortlandCement ConcreteIntroductionComposition

of

Concrete5.3

TheMain

Technical

Propertiesof

ConcreteTheQuality

Control

of

ConcreteTheDesignofthe

MixProportionof

ConcreteContent5.1Introduction5.1 IntroductionConcrete

is

a

stone-like

material

obtained

by

permitting

a

carefully

proportioned

mixture

of

cement

sand

andgravel

or

other

aggregate

and

water

to

harden

in

formsof

theshape

and

dimensionsof

thedesired

structure.Concrete

is

widely

used

for

making

architectural

structures,

foundations,

brick/block

walls,

pavements,bridges/overpasses,

highways,runways,parking

structures,

dams,

pools/reservoirs,

pipes,

footings

for

gates,fences

and

poles,

and

even

boats.

Concrete

is

used

in

large

quantities

almost

everywhere

mankind

has

a

need

forinfrastructure.The

amount

of

concrete

used

worldwide,

ton

for

ton,

is

twice

that

of

steel,

wood,

plastics,

and

aluminumcombined.

Concrete's

use

in

the

modern

world

is

exceeded

only

by

that

of

naturally

occurring

water.

Given

thesize

of

the

concrete

industry,

and

the

fundamental

way

concrete

is

used

to

shape

the

infrastructure

of

the

modernworld,it

is

difficult

to

overstate

therole

thismaterial

plays

today.5.1 Introduction5.1.1 Characteristics

ofConcreteConvenientfor

use:thenewmixtureshavegoodplasticity

thatcan

becastintocomponentsandstructuresinvariousshapes

andsizes.Cheap:rawmaterials

areabundant

andavailable.More

than80%

of

themare

sand

andstone

whoseresources

arerich,

energyconsumption

islow,

accordingwith

theeconomicprinciple.High-strengthanddurable:thestrength

ofordinaryconcrete

is20-55

MPawith

gooddurability.Easy

tobeadjusted:

theconcrete

withdifferentfunctionscanbemadejustby

changingthevarietiesandquantitiesofcomposingmaterials

tomeetvariousdemandsofprojects.Environment-friendly:concrete

canmakefulluseofindustrialwastes,suchas

slag,

flyash

and

otherstoreduceenvironmentalpollution.(1)(2)(3)(4)(5)5.1 Introduction5.1.2 Classification

ofConcreteIn

Portland

Cement

ConcreteThe

binder

is

a

mixture

of

Portland

cement

and

water.

Asphalt

and

other

cements

are

used

to

make

varioustypes

of

concrete,

butcommonly

theterm

"concrete"

refers

to

Portland

cement

concrete.By

ApparentDensityConcrete

includes

three

types:Heavy

concrete:

0>2600

as

shielding

materials

of

atomicenergy

engineering.Normal

concrete:

0=2000-2500

in

several

bearingstructure.Lightweight

concrete:

0<1900

including

light

aggregate

concrete

and

porous

concrete.5.1 IntroductionBy

StrengthConcrete

includes

three

types:

ordinary

concrete,

high

strength

concrete,

super

strength

concrete.Ordinary

concrete:

compressivestrength

<60

MPa.High-strength

concrete:

compressive

strength>60

MPa.It

is

applied

largely

to

the

high-rise

building,

large

span

bridges

and

high-strength

prefabrication

componentsandso

on.Super-strength

concrete:

compressive

strength>80

MPa.By

Forming

or

Construction

TechnologyIt

includes

four

kinds

of

concretes:

deposit

concrete,

precast

concrete,

premixed

concrete

and

shotcreteconcrete.5.2CompositionofConcrete5.2 Composition

ofConcreteConcrete

is

made

up

of

paste

(cement

water),

aggregate

(sand,gravel)

and

admixture.

Generally,

the

amount

of

sand

and

stoneaccounts

for

above

80%

of

the

total

volume,

functioning

as

frame,so

they

are

respectively

called

as

fine

aggregate

and

coarseaggregate.

Mixed

with

water,

cement

becomes

cement

paste,

andcement

mortar

not

only

wraps

the

surface

of

particles

and

fillstheir

gaps,

but

also

wraps

stones

and

fills

their

gaps,

then

concretecoming

into

being

(Figure

5.1).

Cement

paste

can

function

asgreasing

before

hardening,

which

renders

concrete

mixture

withgood

mobility;

after

hardening,

aggregatesstick

together

and

forma

hard

entity,

knownasman-made

stone-concrete.1-coarse

aggregate;

2-fine

aggregate;

3-cement

paste.Figure

5.1

Thecement

structure5.2 Composition

ofConcrete5.2.1 CementCement

is

the

most

important

component

for

concrete

and

relatively

expensive.

There

are

many

types

of

concrete,

basedon

different

cements.

In

the

preparation

of

concrete,

the

choice

of

cement

varieties

and

strength

grades

are

directly

relatedwith

thedurability

and

economy

of

concrete.Selection

of

TypesSelect

according

to

the

different

environment.

The

six

general

cements

are

commonly

used

in

Portland

cement,ordinary

Portland

cement,

furnace-slag

cement,

Portland

pozzolan

cement,

Portland

fly-ash

cement

and

compositePortland

cement.

Theselection

principles

for

thesix

common

kinds

of

cement

can

be

referred

to

in

chapter

four.Selection

ofGradeThe

cementstrength

grades

are

corresponding

tothe

design

strength

grades

of

concrete.For

ordinary

concrete

the

cement

is

1.5-2

times

the

strength

of

the

concrete.

For

high

strength

concrete,

it

is

0.9-1.5

times

thestrength

of

theconcrete.Difference5.2 Composition

ofConcrete5.2.2

AggregateIn

cement

concrete,

60%-75%

of

the

volume

and

79%-85%

of

the

weight

are

made

up

of

aggregates.

The

aggregatesact

as

a

filler

to

reduce

the

amount

of

cement

paste

needed

in

the

mix.

In

addition,

aggregates

have

greater

volume

stabilitythan

the

cement

paste.

Therefore,

maximizing

the

amount

of

aggregate,

to

a

certain

extent,

improves

the

quality

andeconomy

of

the

mix.Generally,

the

aggregates

used

for

ordinary

concrete

can

be

divided

into

two

types

by

their

sizes.

The

one

whosediameter

is

more

than

5.00

mm

is

called

coarse

aggregate,

and

the

one

whose

diameter

is

less

than

5.00

mm

is

calledfineaggregate.1.Fine

AggregateThe

fine

aggregates

used

in

ordinary

concrete

generally

are

the

natural

sand

which

comes

into

being

when

thenatural

rock

(excluding

soft

rock

and

weathered

rock)

has

experienced

natural

weathering,

water

transportation,sorting,stacking,

and

other

kinds

of

natural

conditions;the

machine-made

sand

(is

made

by

grinding

and

sorting

by

machine,

and

the

diameter

of

the

rock

particles

is

lessthan

5.00

mm,

except

the

particles

of

soft

rock

and

weathered

rock.)

through

de-dust

treatment

and

the

mixed

sand(made

by

mixing

machine-made

sand

and

natural

sand)

arecollectively

callmanufacturedsand.5.2 Composition

ofConcreteAccording

to

different

sources,

natural

sand

can

be

divided

into

river

sand,

sea

sand,

mountain

sand

anddesalted

sea

sand.In

national

standards

Sand

for

Building

(GB/T

14684-2001)

and

Pebble

and

Crushed

Stone

for

Building(GB/T

14685-2001),

it

is

regulated

that

the

sand

for

building

can

be

classified

into

category

I,

category

II

,

andcategory

III

based

on

the

technical

quality

requirements.Category

I:

those

used

in

the

concrete

whose

strength

gradeis

more

thanC60;Category

II:

those

used

in

the

concrete

whose

strength

gradeis

betweenC30-C60;Category

III:

those

used

in

the

concrete

whose

strength

gradeis

less

thanC30.(1)

Grain

Gradation

and

CoarsenessofSandThegrain

gradation

andcoarseness

of

sandaredeterminedby

screenresidueanalysis.

Gradingregionandfinenessmoduluscan

beused

toexpress

the

gradationandthecoarseness

ofsand

particles

respectively.5.2 Composition

ofConcreteThe

relationship

between

the

cumulative

screen

residue

(which

refers

to

the

screen

residue

of

one

sieve

to

the

sumof

all

the

unit

screen

residue

percentages

whose

sieves

are

thicker

than

it)

and

the

unit

screen

residue

(which

means

themassof

screen

residue

to

the

massof

the

total

sample

sand)is

shown

in

Table

5.1.Table

5.1

The

relationship

between

cumulative

screen

residue

and

unit

screen

residueSievehole/mmUnit

screen

residue/%Cumulative

screenresidue/%4.75a1A1=a12.36a2A2=a1+a21.18a3A3=a1+a2+a30.60a4A4=a1+a2+a3+a40.30a5A5=a1+a2+a3+a4+a50.15a6A6=a1+a2+a3+a4+a5+a65.2 Composition

ofConcreteAccording

to

GB/T14684-2001,

there

are

three

grading

regions

of

sand

when

it

is

calculated

by

the

percentage

of

thecumulative

screen

residue

of

0.63

mmhole

sieve,shownin

Table

5.2.Table

5.2Grading

regions

of

sand

particles

(GB/T

14684-2001)Holy

size/mmTable

5.2

Grading

regions

of

sand

particles

(GB/T

14684-2001)Note:

①

Three

grading

regions

are

compartmentalized

by

accumulative

total

sieve

residue

percent

of

sieve

sizewith

0.63

mm.②

Comparedwith

the

numbers

listed

in

the

table,

the

accumulative

total

sieve

residue

percent

of

the

sand

can

go

beyond

5%

ofall

the

sand

except

5

mm

and

0.63

mm.Grading

regiongrading

curveof

sandisshowninFigure5.2.Hole

Size/mmGrading

RegionsⅠⅡⅢCumulative

ScreenResidue/%10000510-010-010-02.535-525-015-01.2565-3550-1025-00.6385-7170-4140-160.31595-8092-7085-550.16100-90100-90100-900.16100-90100-90100-905.2 Composition

ofConcreteThecoarseness

of

sand

isexpressed

by

finenessmodulus

(

f),

defined

as

follows:The

bigger

the

fineness

modulus

is,

the

coarser

the

sand

is.

According

to

fineness

modulus,

we

can

decide

thetypes

of

fineness

referring

to

Table

5.3.Table

5.3

Types

of

finenessItshould

beremindedthatthe

finenessmoduluscannot

reflect

thequality

of

their

gradingregions.Thesand

withthe

same

finenessmodulus

can

havevery

differentgrading

regions.

Therefore,

theparticlegradation

andthefinenessmodulus

should

beconsidered

in

thepreparation

of

concrete.

(

A2

A3

A4

A5

A6

)

5A1f100

A1

Types

offineness

fcoarse

sand3.1-3.7medium

sand2.3-3.0finesand1.6-2.2super

finesand0.7-1.55.2 Composition

ofConcrete(2)

Requirements

of

Aggregate①

ImpuritiesImpurities

hinder

the

hydration

or

causes

harden

cement

pastecorrosion,and

reduce

thebond

between

cement

paste

and

aggregate.Types:

mica,

clay,

siltand

organicsubstance.Damage:

hinder

the

bond

between

paste

and

aggregate,

weaken

thestrength

of

concrete,

increase

the

requirement

quantity

of

water,increase

the

shrinkage

of

concrete

and

bring

corrosion

to

hardencement

paste.Processing

methods:

wash

impurities

out

as

requested,

if

too

muchin

thesand.The

amount

of

impurities

must

be

in

agreement

with

GB/T

14684-2001(JGJ52-92)

(Table

5.4).Table

5.4

Amounts

of

impurities

(GB/T

14684-2001)TypeIndexⅠⅡⅢClay

content/%<1.0<2.0<5.0Clod

content/%0<1.0<2.0Mica/%<1.0<2.0<2.0Lightmatter/%<1.0<1.0<1.0Organicsubstance(colorimetry)EligibleEligibleEligibleSulfides

andsulfates/%<0.5<0.5<0.5Chloride/%<0.01<0.02<0.065.2 Composition

ofConcrete②

Particle

Shape

and

Surface

TextureParticle

shape,

surfacetextureand

their

influences

in

properties

arelisted

in

Table

5.5.Table

5.5

Particle

shape

and

surface

texture2.Coarse

AggregateAccording

to

shape

of

primary

coarse

aggregate,

it

can

be

divided

into

gravel

and

pebble.

Gravel

is

thewidely

used

primary

coarse

aggregate.By

quality,

there

are

three

types:

Ⅰ,

Ⅱ

and

Ⅲ.

Ⅰ:

those

used

in

the

concrete

whose

strength

grade

is

more

thanC60;

Ⅱ:

those

used

in

the

concrete

whose

strength

grade

is

between

C30-C60;

Ⅲ:

those

used

in

the

concretewhose

strength

gradeis

less

than

C30.TypeParticle

ShapeSurface

TextureWorkabilityStrengthRiver

sandRound

or

ellipticalLubricityWellLowSeasandMountain

sandPointedRoughBadHigh5.2 Composition

ofConcrete(1)

The

Grain

Composition

of

Stone

andthe

Maximum

Particle

DiameterThe

grain

composition

of

stone

includes

continuous

size

fraction

and

single

size

fraction

which

are

alsodetermined

by

sieveanalysis.

Thedeterminationmethod

is

thesame

withthat

of

fineaggregate.Continuous

size

fraction

has

priority

in

the

design

of

concrete

mixture

ratio.

Single

size

fraction

can

be

used

inthe

composition

of

required

continuous

size

fraction

and

also

used

with

continuous

size

fraction

to

improve

thegrading

or

to

prepare

the

continuous

size

fraction

of

larger-sized

particles.

The

single

size

fraction

should

not

beused

"singly"

in

the

preparation

of

concrete.

If

it

must

be

used

lonely,

the

technical

and

economic

analysis

shouldbe

made

and

the

experiment

should

be

conducted

to

prove

that

there

will

be

no

segregation

or

any

impact

on

thequality

of

concrete.The

maximum

nominal

size

of

stone

particle

is

the

maximum

particle

diameter

of

this

size

fraction.

If

themaximum

diameter

increases,

its

total

area

decreases

when

quality

remains

the

same.

Thus,

from

the

economicperspective,

cement

can

be

saved

by

increasing

the

maximum

diameter.

Therefore,

the

bigger

maximum

sizeshould

be

chosen

if

thecircumstance

allows.5.2 Composition

ofConcrete(2)

Requirements

of

Aggregate①

ImpuritiesClay

content,

clodcontentandthe

content

of

needle

shape

particles

and

slice

shapeparticles

(Figure5.3)

must

be

inagreement

with

GB/T

14685-2001

(JGJ52-92).Details

of

alkali-aggregate

reaction

will

be

introduced

later

in

durability

ofconcrete.

If

there

is

potential

danger,

the

alkali

content

should

be

less

than

0.6%.A

special

test

is

neededwhen

we

use

the

admixturewith

potassium

and

sodium.②

Particle

Shape

andSurface

TextureTheparticle

shape

and

surfacetexture

is

thesame

with

that

of

thesand.③

AggregateStrengthFigure

5.3

Needle

and

slice

shape

particlThere

are

two

methods

to

measure

the

strength

of

the

aggregate

strength:cubic

strength

of

rock

and

crushing

index

of

gravel.5.2 Composition

ofConcreteThe

compressive

strength

of

the

cube

is

measured

in

saturated

water.

For

ordinary

concrete:

Aggregate

strength≮1.5

fcu

forHSC:

Aggregatestrength

≮2.0

fcu.Alsoselect

thestrength

of

rock

accordingto

the

rocks

types

(Table

5.6).Table

5.6

Aggregate

strength

of

different

types(3)

Crushing

Index

of

GravelMethod:

put

the

gravel

with

the

diameter

of

10-20

mm

into

the

standardcylinder

threetimes,press

them

to

200

kNand

shiftthem

in

2.5mm

sieve.In

thisformula:

m0

is

themass

of

dry

gravel

beforecrushing;m1

is

themass

of

dry

gravel

aftercrushing

and

sifting.Crushing

index

m0

m1m0RocksStrengthIgneousrock≮80

MPaMetamorphic

rock≮60

MPaAqueous

rock≮30

MPa5.2 Composition

ofConcreteCrushing

index

of

gravelor

scree

is

listed

in

Table

5.7

and

Table

5.8.Table

5.7

Crushing

index

of

gravel

of

different

typesTable

5.8

Crushing

index

of

scree

(GB/T

14685-2001)Types

of

rockConcrete

strength

gradeGravel

crushingindex/%Aqueous

rockC60-C40≤C35≤10≤16Metamorphic

rockor

plutonic

igneous

rockC60-C40≤C35≤12≤20IgneousrockC60-C40≤C35≤13≤30ConcretestrengthgradeC60-C40≤C35Crushingindex/%≤12≤165.2 Composition

ofConcrete5.2.3 WaterforConcreteCombining

water

with

a

cementitious

material

forms

a

cement

paste

by

the

process

of

hydration.

The

cementpaste

glues

the

aggregate

together,

fills

voids

within

it,

and

makes

it

flow

more

freely.

However,

impure

waterused

to

makeconcrete

can

cause

problemswhen

settingor

in

causing

premature

failure

of

the

structure.We

should

use

drinking

water

and

clean

natural

water

for

mixing

and

conserving

concrete.Thesubstance

content

in

water

for

concrete

should

accord

with

thelimits

of

JGJ

63-89

in

Table

5.9.Table

5.9

Limits

of

the

substance

content

in

water

for

concreteTypesPrestressed

concreteReinforced

concretePlain

concretepH>4>4>4Insoluble

matter/(mg/L)<2000<2000<5000Solublematter/(mg/L)<2000<5000<10000Cl-/(mg/L)<500<1200<3500SO

2-/(mg/L)4<600<2700<2700S2-/(mg/L)<100--5.2 Composition

ofConcrete5.2.4 Concrete

AdmixtureChemical

admixtures

are

materials

in

the

form

of

powder

or

fluids

that

are

added

to

the

concrete

to

give

itcertain

characteristics

not

obtainable

with

plain

concrete

mixes.

In

normal

use,

admixture

dosages

are

less

than

5%by

mass

of

cement

and

are

added

to

the

concrete

at

the

time

of

batching/mixing.

The

common

types

of

admixturesareas

follows.1.

Water-reducing

AgentWater-reducing

agent

refers

to

the

admixture

used

for

reducing

water

consumption

and

strengtheningfunctions

when

the

slump

degrees

of

mixtures

are

basically

the

same.

By

raw

materials

and

chemicalcomponents,

water-reducing

admixtures

can

be

divided

into:

lignin

sulfonate,

alkylaryl

sulfonates

(commonlyknown

as

coal

tar

water-reducing

admixture),

sulfonated

melamine-formaldehyde

resin

sulfonate

(commonlyknown

as

melamine

water-reducer),

molasses

and

humic

aid

water-reducer,

and

others.

Based

onperformances

and

functions,

water-reducing

admixtures

can

be

divided

into:

ordinary

water-reducer,

effectivewater-reducer,

hardening

water-reducer,

retarder

water-reducer,and

airentraining

water-reducer.5.2 Composition

ofConcrete2.

AirEntraining

AdmixtureAir

entraining

admixture

refers

to

the

admixture

that

entrains

a

large

number

of

uniform,

stable

and

closed

tinybubbles

in

the

process

of

mixing

concrete

to

reduce

the

segregation

of

concrete

mixture,

improve

the

workability,

andalso

enhance

anti-freeze

ability

and

durability

of

concrete.

It

is

a

kind

of

surfactant,

too.

It

has

influences

on

concreteas

follows:It

can

improve

theworkability

of

concrete

mixtures.It

can

enhance

impermeability

and

frost

resistance.It

can

reduce

strength.

If

the

air

content

in

concrete

increases

by

1%,

its

compressive

strength

will

decrease

by4%-6%.

Thus,theadding

amount

of

air

entraining

admixture

should

be

appropriate.3.Hardening

AcceleratorHardening

accelerator

refers

to

the

admixture

that

can

accelerate

the

development

of

early

strength

of

concrete.

Itapplies

to

the

construction

that

is

constructed

in

winter,

emergency

engineering

and

time-limited

ones.

The

use

ofhardening

accelerator

can

make

C20

reach

demoulding

strength

within

16

hours

and

the

strength

allowing

floor

slabinstallment

on

it

within

36

hoursso

as

to

speed

up

theconstruction.5.2 Composition

ofConcreteSetRetarderAnt