(6)construction materials

8/7/2019 (6)construction materials

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1

S t r u

c t u

r e s

P r o c e s s e s

P r o p e r

t i e s

Per formance

Metals

CeramicsPolymers

Composites

Construction Materials

AsphaltCement

WoodsConcrete2nd semester 2006



Composites

Dept of Mat Eng 2

Materials use for construction ofbuildings, highways, bridges, mostlyinfrastructure.

Three most importance materials areWoods Concrete

Asphalt

Construction materials



Dept of Mat Eng 3

Woods

Most familiar materials to mankind. Not a high-technology materials but fantastic. The only material that can be reproduced and

give oxygen to human. Woods is very strong but yet lightweight.



Dept of Mat Eng 4

Woods structure

Wood surface Cross sectional •portion of a round crosssection, clearly reveals an

nual growth rings.

Radial Surface•cutting along a radius

of a round cross section

Tangential Surface•cutting at a tangent to the growthrings, or the surface you would see if

you were to view the outside of a log



Dept of Mat Eng 5

Annual Ring trees grow in both diameter and height duringgrowth periods that are interrupted by periodsof rest.

Woods structure

Raining seasonHigh water time

Summer seasonLower water time



Dept of Mat Eng 6

Woods VS water

Water caused negative effect to wood Wood, if not predried, will dry while in use under uncontrolledconditions giving rise to warp, bow, twist, and similar defects.

Wet wood is susceptible to attack by decay and stain fungi. Water must be removed to provide

void space for preservatives if wood is

to be treated for prevention

against fungal

attack.


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Wood shrinkage

Wood is an anisotropic material (havingdifferent properties in 3 dimensions)

Three Dimensions in which Wood Shrinks

LongitudinalShrinkage

= 0.1% to 0.3%

Radial

Shrinkage

= 2.1% to 7.9%

Tangential

Shrinkage

= 4.7% to 12.7%R R

R

T

T

T

L



Mechanical Properties of woods

Wood strength depends on density Given a high efficiency when subject totensile strength parallel to the fiber direction

Wood species Tensile // fiber

(MN.m-2 )

Tensile radial

(MN.m-2)

Compress //

fiber (MN.m-2)

Compress radial

(MN.m-2)

Maple 108 8 54 10

Oak 78 6 43 6

Pine 73 2 33 3



Comparison of the specific strength

Specific strength (SF)= strength/density

Material SF strength

(kg.m2

.s-2

)

SF modulus

(kg.m2

.s-2

)Clear wood 178 2.4E4

Aluminum 127 2.7E4

1020 steel 50 2.7E4

Copper 38 1.4E4

Concrete 15 0.9E4



Types of wood construction

1) Beam element 2) Plate element

Structural plateNon-structural plate

3) Wood-plastic composite



Wooden house



Concretes

Common construction material Strong hard but brittle Heavy and can not be recycle

All ingredients compose ofdiminishing raw material



Concretes Concretes = a particular composite in which both

the particular and the matrix are ceramic material Concretes = Portland Cement + Sand +Aggregate (A cementation reaction between water and the mineral in cement provide a

strong matrix and good compressive strength)

CementsCementsSandSandAggregateAggregate



Cement binder a very fine in size

Compose of various ratio of chemical When water is added to the cement, a hydration reaction

occurs, producing a solid gel that bond the aggregate

particle

•3CaO+Al2O+SiO2+3CaO+SiO2+4CaO• +Al2O3+Fe2O3+other minerals

Cements



Cements

The composition on the cement helpsdetermine the rate of curing and thefinal properties of the concrete

e.g. 3CaO . Al2O

3and 3CaO . SiO

2 Rapid

setting but low strengths 2CaO . Al

2O

3 Slowly during hydration but

higher strengths

S t

r e n

g t h

Time

•2CaO . Al2O3

•3CaO . Al2O3

•3CaO . SiO2



Cements The concrete is expected 28 days for nearly

complete curing Some additional curing maycontinue for years

Types of cement Type 1: General purpose Type 2: Low rate of heat generation, moderate

resistance to sulphate Type 3: Rapid setting Type 4: Very low rate

of heat generation Type 5: Good sulphate

resistance

+ =



Sand

Chemically sand = silica (SiO2) Fine minerals The order of 0.1 to 1.0 mm diameter Contain at least some absorbed water *** Fill voids between the coarser aggregate Giving high packing factor Reducing amount of open (or interconnected) porosity in the

finished concrete Reducing disintegration of the concrete due to repeated

freezing and thawing during service



Dept of Mat Eng 18

Aggregate

Gravel & Rock Aggregate must be clean, strong, and durable Angular aggregate particles provide strength due to

mechanical interlocking between particles More surface on angular particles may form voids or

cracks The large size of aggregate is preferred

Aggregate particles should not be larger than about 20%of the thickness of the structure or it will cause theholding defect



Dept of Mat Eng 19

Cements Reaction

Cement

Water

SandAggregate

•Hydration reactionoccur

3CaO . Al2O3+6H2O ->Ca3Al2(OH)12 + heat

2CaO . SiO2+xH2O ->Ca2SiO4 . xH2O + heat

3CaO . SiO2+ (x+1)H2O

-> Ca2SiO4 . xH2O+Ca(OH)12 + heat



Dept of Mat Eng 20

Properties of Concrete

The most importance factors thatinfluence the properties of concreteThe water cement ratioThe amount of air entrainmentThe type of aggregate



Dept of Mat Eng 21


The water cement ratio Too little water causes low strength A high water cement ratio

- improve the workability of concrete

** Workability can be measured by slump testbut

- decreases the compressive strength of

concrete- increases the shrinkage of concrete duringcuring & creating a danger of cracking



Dept of Mat Eng 22


The water cement ratio



Dept of Mat Eng 23

Properties of Concrete The amount of air entrainment A small amount of air is entrained into concrete

during pouring 1-2.5% (sometimes up to 8%) by volume of the

concrete may be trapped by air

The entrained air- improves workability of concrete- minimise problems with shrinkage and freezethaw conditions, but

– cause lower strength



Dept of Mat Eng 24


The amount of air entrainment



Dept of Mat Eng 25


The type and amount of aggregate The size of aggregate affects theconcrete mix

- More water is required for smaller

aggregate The volume ratio of aggregate in the

concrete is based on the bulk density of

the aggregate-about 60% of the true density



Dept of Mat Eng 26

Cements Curing and Properties



Dept of Mat Eng 27

Compression vs Tension

Concrete in tension is approximately10% the strength of concrete incompression.



Dept of Mat Eng 28

Reinforced and Pre-post-stressed Concrete

Concrete for construction material Reinforced Concrete Pre-stressed Concrete Post-stressed Concrete



Dept of Mat Eng 29

Concrete Construction



Dept of Mat Eng 30

Asphalt Asphalt is bitumen. Bitumen is the organic binder,

composed of HC with low meltingpoint thermoplastic polymers and oils.

Asphalt mix is composite ofaggregate and bitumen.



Dept of Mat Eng 31

Asphalt Mix

The aggregate use as in the concretethat should be clean and angular. Aggregate should have distribution

of grain sizes to provide a highpacking factor and good mechanicalinterlock between aggregate grains.

A B



Dept of Mat Eng 32

Composite and binder

Binder is just enough for the aggregate particleto touch, but voids are minimized. Excess binder is weakening asphalt under load

due to viscous deformation. When asphalt mix is compress, the binder can

squeeze into voids. Too much void space permit water to enter the

structure; increase the rate of deterioration ofasphalt and may also embrittle the binder



Dept of Mat Eng 33

Operation of Asphalt Mix



Dept of Mat Eng 34

Asphalt Mix Problem

Asphalt (bitumen) in asphalt mixsoften at relative low temperaturebecause it is a thermoplastic polymer.



Asphalt construction

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