Material Properties and Characteristics

• This chapter covers the properties of different types of materials and sources for data on material properties.
• The module aims to provide knowledge of general material properties (structural, physical, mechanical, electrical, thermal, chemical, and optical) and an understanding of physical and mechanical properties for construction.

Structural Properties

• Not directly properties, but definitions relating structure to properties
• The goal is to relate structure to properties

Composition

• Kinds and relative count of elements including chemical formula and alloy percentage
• A single composition can have different structures.
• Metals contain metallic elements.
• Ceramics contain metals and nonmetals.
• Polymers contain carbon and hydrogen.
• Metals have metallic bonding.
• Ceramics have ionic and covalent bonding.
• Polymers have covalent bonding.

Crystal Structure

• Atomic scale order where atoms or ions are arranged spatially
• Defined by unit cell geometry.
• Crystalline material has long-range order, contrasted with amorphous material.

Microstructure

• Structural features visible using a microscope
• Ranges from glassy to crystalline, including grain boundaries and phase structures.

Physical Properties

Bulk Density

• Ratio of mass to volume of material in its natural state, including voids and pores
• Expressed in kg/m³.
• Influences mechanical properties like strength, heat, and conductivity.
• Brick has a bulk density of 1600-1800 kg/m³.
• Sand has a bulk density of 1450-1650 kg/m³.
• Steel has a bulk density of 7850 kg/m³.
• Heavy concrete has a bulk density of 1800-2500 kg/m³.
• Light concrete has a bulk density of 500-1800 kg/m³.
• Granite has a bulk density of 2500-2700 kg/m³.

Porosity

• Volume of material occupied by pores
• The ratio of pore volume to material volume
• Influences thermal conductivity, strength, bulk density, and durability.

Durability

• A material's ability to withstand atmospheric and other factors
• More durable materials are useful for longer life.
• Maintenance cost depends on durability.

Density

• Ratio of mass to volume in a homogeneous state
• Influences most physical properties
• Steel has a density of 7800-7900 kg/m³.
• Brick has a density of 2500-2800 kg/m³.
• Granite has a density of 2600-2900 kg/m³.

Specific Gravity

• Ratio of the mass of a substance to the mass of water at 4°C for equal volumes
• Steel has a specific gravity of 7.82.
• Cast iron has a specific gravity of 7.20.
• Aluminum has a specific gravity of 2.72.

Fire Resistance

• Ability to withstand fire without changing shape or properties
• Tested by combined actions of water and fire
• Fireproof materials must provide more safety in case of fire.

Frost Resistance

• A material's ability to resist freezing or thawing
• Depends on density and bulk density
• Denser materials have more frost resistance.
• Moist materials have low frost resistance, lose strength, and become brittle in freezing conditions.

Weathering Resistance

• A material's ability to withstand atmospheric actions without losing strength and shape.
• Weathering affects material durability.
• Corrosion in iron is a weathering effect.

Water Absorption

• Capacity of a material to absorb and retain water
• Expressed as % of dry material weight.
• Depends on the size, shape, and number of pores.

Water Permeability

• Ability of a material to permit water to pass through it
• Dense materials (glass, metals) are called impervious and do not allow water through.

Refractoriness

• Property of a material that cannot melt or lose shape at high temperatures (1580°C or more)
• Fire clay is a high refractory material.

Mechanical Properties

• Materials in tension are subject to external forces that stretch it.
• Materials in compression are subject to forces that squeeze it.
• Stress is the force applied per unit area.
• Strain (e) is the change in length/original length when a material is subject to tensile or compressive forces.

Strength

• Ability to resist the application of forces without breaking.
• Tensile strength which is the maximum tensile stress a material can withstand without breaking
• Compressive strength which is the maximum compressive stress a material can withstand without being crushed.

Stiffness

• Ability of a material to resist bending
• Modulus of elasticity (Young's modulus) is a measure of stiffness.

Ductility

• Ability of a material to suffer significant deformation before breaking.

Malleability

• Describes the amount of plastic deformation under a compressive load.
• Malleable materials can be shaped by forging and rolling.

Toughness

• A tough material resists crack growth.
• Toughness can be defined as work required to propagate a crack through a material.
• Measured via impact tests like Charpy and Izod.

Hardness

• Measure of the resistance of a material to abrasion or indentation
• Measured using various scales.

Electrical Properties

Resistivity

• A materials resistance to the flow of electric current
• Important in semiconductors
• Depends on electronic structure, temperature, and microstructure

Conductivity

• Measure of how easily a material allows electrical current to flow
• Metals (copper, aluminum, iron) have higher conductivity than ceramics, plastics, glass, and rubber
• Reciprocal of electric resistivity

Thermal Properties

• Thermal properties include:

Linear Expansivity (a)

• Coefficient of linear expansion
• Measure of how much a material's length changes with temperature
• Defined as (change in length) / (original length x change in temperature)

Heat Capacity (c)

• Amount of heat needed to raise the temperature of an object by 1 K
• Specific heat capacity is the amount of heat per kilogram needed to raise temperature by 1 K

Thermal Conductivity (λ)

• Measures the thermal conductivity of a material
• Defined as the quantity of heat flow per second divided by the temperature gradient
• Measured in W m⁻¹ K⁻¹

Chemical Properties

Toxicity

• Ability of a material to damage or disrupt living tissue
• Can be acute or chronic
• Can be administered by contact, inhalation, ingestion, or injection

Chemical resistance

• Ability to that a material can withstand degradation from acids, solvents, water, or oxygen (corrosion)
• Marked by weight change, discoloration, cracking, or change in mechanical properties

Corrosion Resistance

• Electrochemical process related to the activity series
• Depends on environmental variables

Combustibility

• Ability of a material to catch fire and burn
• For organic materials and reactive metals (especially finely divided)

Passivity

• Loss of chemical reactivity by some active metals and alloys
• Frequently due to formation of a thin oxide surface coating.

Optical Properties

• Relate to a material's response to electromagnetic radiation (visible light)
• Light can be absorbed, transmitted, or reflected

Transmissivity

• Measure of a material's ability to allow light to pass
• The ratio of transmitted light to incident light

Absorptivity

• Measure of a material's ability to absorb light

Index of Refraction

• Ratio of the speed of light in a vacuum to the speed of light in a material
• Measures how much light bends when passing from one medium to another.

Photoconductivity

• Some materials become positively charged when exposed to radiation due to ejection of electrons
• Describes the increase in conductivity due to incident light

Polarization

• Orientation polarization results from the alignment of permanent electric dipole moments
• Used in sunglasses and LCDs

Explore material properties like density and porosity. Understand how these characteristics influence thermal conductivity, durability, and frost resistance. Learn to differentiate between crystalline and amorphous materials.