Bridge Materials. BRIDGE MATERIALS TECHNICAL STANDARDS BRANCH INTRODUCTION TO BRIDGES TRANSPORTATION Slide 2 A porous non-homogenous material that is.

Bridge Materials

BRIDGE MATERIALS

TECHNICAL STANDARDS BRANCHINTRODUCTION TO BRIDGES

TRANSPORTATION

Slide 2

• A porous non-homogenous material that is made of cement, water, fine aggregate (sand), coarse aggregate (gravel), and air.

• Ratios– Aggregate (75 to 80%)– Cement (10 to 15%)– Water and Air (remainder)

Concrete Material PropertiesWhat is Concrete?

BRIDGE MATERIALS


TRANSPORTATION

Slide 3

Admixtures

• Ingredients used to modify certain properties of concrete to have a desired function

• Air-entraining - improves air void structure

• Water reducers - reduces water in the mix

• Superplasticizers - increases slump

• Accelerators - increases set rate

• Retarders - decreases set rate

BRIDGE MATERIALS


TRANSPORTATION

Slide 4

Physical Properties• Compressive strength (28 day)

• Tensile strength (10% f’c)

• Permeability– Causes: - evaporation of bleed water

- excess water

- micro-cracking

- porous aggregates

- improper mixing, finishing

BRIDGE MATERIALS


TRANSPORTATION

Slide 5

stress

strain

Concrete Stress-Strain Diagram

BRIDGE MATERIALS


TRANSPORTATION

Slide 6

Concrete Damage & Deterioration

• Types of Cracks– Crazing - surface cracking, from surface drying– Shrinkage - tension caused by reduction in moisture– Temperature Cracking - restrained thermal changes– Flexural Cracking - tension from flexural bending– Shear Cracking - diagonal tension from loads

BRIDGE MATERIALS


TRANSPORTATION

Slide 7

Concrete Defects (cont’d)

• Scaling - freeze thaw, surface finishing• Pop-Outs - porous aggregate• Abrasion - wheel wear• Spalling - corrosion of steel• Delamination - debonding of substrate• Staining - rust• Alkali Aggregate Reaction• Carbonation

BRIDGE MATERIALS


TRANSPORTATION

Slide 8

Steel Material Properties• What is Steel?

– It is an alloy of iron, carbon and other trace elements.

• Ratios– Carbon 0.15 to 1.7%– Manganese 0.5 to 2%– Phosphorus 0.05 to 0.6%– Sulphur 0.02 to 0.06%– Silicone 0.80 to 1.5%

BRIDGE MATERIALS


TRANSPORTATION

Slide 9

Iron

• Iron in the pure form is a soft, shiny metal like aluminum.

• However, it is never found in this state.

• Iron oxidizes extremely easily.

• In nature it is always found as an oxide.

BRIDGE MATERIALS


TRANSPORTATION

Slide 10

Steel Making Process

• To convert iron ore to pig iron, ore is heated with coke.

• Pig iron has 2 to 5% carbon.

• Steel cannot have more than 1.7% carbon.

BRIDGE MATERIALS


TRANSPORTATION

Slide 11

Effects of Carbon• Increased carbon in steel:

– increases strength– increases hardness– increases hardenability (heating and quenching)– reduces ductility– reduces toughness– reduces impact properties– reduces machinability

BRIDGE MATERIALS


TRANSPORTATION

Slide 12

Physical Properties

• Compression

• Tension

• Fatigue

• Weldability

• Notch toughness

BRIDGE MATERIALS


TRANSPORTATION

Slide 13

Tension & Compression

Stress Strain Diagram

(-)

(-)

lengthen (+)

(+)stress tension

compression

shorten

BRIDGE MATERIALS


TRANSPORTATION

Slide 14

Concrete - Steel Combination

Reinforced Concrete• Mild steel for tension• Always cracks under load

Prestressed Concrete • High strength steel strands• Precompressed• Carry load without cracking

BRIDGE MATERIALS


TRANSPORTATION

Slide 15

Steel Damage and Deterioration

• Corrosion– moisture, oxygen, electrical potential

• Cracking– fatigue, impact, excessive loading

• Deformation– excessive loading, impact

BRIDGE MATERIALS


TRANSPORTATION

Slide 16

UNCONTROLLEDWELDING

IS NOT ALLOWEDON BRIDGE

STRUCTURES.

BRIDGE MATERIALS


TRANSPORTATION

Slide 17

Timber Material Properties

• What is wood?– A naturally occurring material containing

carbohydrate compound fibres and water.

(It grows on trees!)

BRIDGE MATERIALS


TRANSPORTATION

Slide 18

Cross Section of Tree

BRIDGE MATERIALS


TRANSPORTATION

Slide 19

Composition of Wood

• Carbohydrate fibres– oriented in longitudinal direction– not homogenous through cross-section

• Water– moisture can reach 200% of sap wood– 19% is considered seasoned

BRIDGE MATERIALS


TRANSPORTATION

Slide 20

Physical Properties

• Compression - perpendicular to grain

- parallel to grain

• Tension

• Bending

• Shear - horizontal shear

• Shrinkage - 60% radially

- 2% longitudinally

BRIDGE MATERIALS


TRANSPORTATION

Slide 21

Timber Damage & Deterioration

• Warping

• Checks & Splits

• Flexural Cracking

• Shear Cracking

• Fire Damage

• Decay

BRIDGE MATERIALS


TRANSPORTATION

Slide 22

Decay• Caused by fungi which feed on cellulose

• Growth of fungi depends on:– adequate moisture– supply of O2

– favorable temperature

• Moisture content below the fibre saturation point (30%) inhibits fungus growth.

BRIDGE MATERIALS


TRANSPORTATION

Slide 23

Decay (cont’d)

• Air is in wood cells, but constantly submerged piles will inhibit fungus by lack of oxygen.

• Fungus goes dormant over winter but will reactivate in the spring.

• High kiln drying temperatures will kill fungus, but the wood can be reinfected.

• Insects and borers are not a problem in Alberta.

BRIDGE MATERIALS


TRANSPORTATION

Slide 24

Treatment

• Treatment chemicals toxic to fungus, insects and man.

• Only exterior is protected

• Pressure treatment improves penetration

Bridge Materials. BRIDGE MATERIALS TECHNICAL STANDARDS BRANCH INTRODUCTION TO BRIDGES TRANSPORTATION Slide 2 A porous non-homogenous material that is.

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