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Structures

Proc

esse

s

Properties

Performance

MetalsCeramicsPolymers

Composites

Construction MaterialsAsphalt Cement

WoodsConcretes2nd semester 2006

Dept of Mat Eng 2

Materials use for construction of buildings, highways, bridges, mostly infrastructure.

Three most importance materials are Woods 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 cross

section, clearly reveals a nnual growth rings.

Radial Surface•cutting along a radius

of a round cross section

Tangential Surface•cutting at a tangent to the growth rings, 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

during growth periods that are interrupted by periods of 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 uncontrolled conditions 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.

Dept of Mat Eng 7

Wood shrinkage Wood is an anisotropic material (having

different properties in 3 dimensions) Three Dimensions in which Wood Shrinks

Longitudinal Shrinkage = 0.1% to 0.3%

Radial Shrinkage = 2.1% to 7.9%

Tangential Shrinkage = 4.7% to

12.7%

R RR

T

TT

L

Dept of Mat Eng 8

Mechanical Properties of woods Wood strength depends on density Given a high efficiency when subject to

tensile 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 10Oak 78 6 43 6Pine 73 2 33 3

Dept of Mat Eng 9

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 2.4E4Aluminum 127 2.7E41020 steel 50 2.7E4

Copper 38 1.4E4Concrete 15 0.9E4

Dept of Mat Eng 10

Types of wood construction 1) Beam element 2) Plate element

Structural plate Non-structural plate

3) Wood-plastic composite

Dept of Mat Eng 11

Wooden house

Dept of Mat Eng 12

Concretes Common construction material Strong hard but brittle Heavy and can not be recycle All ingredients compose of

diminishing raw material

Dept of Mat Eng 13

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

Dept of Mat Eng 14

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

Dept of Mat Eng 15

Cements The composition on the cement helps

determine the rate of curing and the final properties of the concrete

e.g. 3CaO . Al2O3 and 3CaO . SiO2 Rapid setting but low strengths

2CaO . Al2O3 Slowly during hydration but higher strengths

Stre

ngth

Time

•2CaO . Al2O3

•3CaO . Al2O3

•3CaO . SiO2

Dept of Mat Eng 16

Cements The concrete is expected 28 days for nearly

complete curing Some additional curing may continue 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 + =

Dept of Mat Eng 17

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 the holding defect

Dept of Mat Eng 19

Cements Reaction

Cement

Water

SandAggregate

•Hydration reaction occur

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 that

influence the properties of concrete The water cement ratio The amount of air entrainment The type of aggregate

Dept of Mat Eng 21

Properties of Concrete 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 test but - decreases the compressive strength of concrete- increases the shrinkage of concrete during curing & creating a danger of cracking

Dept of Mat Eng 22

Properties of Concrete 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 freeze thaw conditions, but – cause lower strength

Dept of Mat Eng 24

Properties of Concrete The amount of air entrainment

Dept of Mat Eng 25

Properties of Concrete The type and amount of aggregate The size of aggregate affects the

concrete 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

approximately 10% the strength of concrete in compression.

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 melting point thermoplastic polymers and oils.

Asphalt mix is composite of aggregate and bitumen.

Dept of Mat Eng 31

Asphalt Mix The aggregate use as in the

concrete that should be clean and angular.

Aggregate should have distribution of grain sizes to provide a high packing factor and good mechanical interlock between aggregate grains.

A B

Dept of Mat Eng 32

Composite and binder Binder is just enough for the aggregate

particle to 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 of asphalt 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 mix

soften at relative low temperature because it is a thermoplastic polymer.

Dept of Mat Eng 35

Asphalt construction