Properties of Materials

Properties of Materials

$Learning Objectives$

Distinguish physical, mechanical, thermal, chemical, durability, and functional properties of construction materials.
Calculate density, unit weight, specific gravity, porosity, moisture content, stress, strain, elastic modulus, and thermal movement.
Interpret stiffness, yield, ductility, resilience, toughness, hardness, creep, relaxation, and fatigue.
Relate measured properties to sampling, conditioning, test methods, specifications, and engineering decisions.
Select materials using performance, durability, constructability, compatibility, quality control, economy, and life-cycle criteria.

$Property, test result, and specification$

A material property is not separable from the way it is measured. Sampling, specimen geometry, conditioning, moisture state, temperature, loading rate, apparatus, and operator practice can affect the reported result. A defensible engineering comparison therefore identifies the property, the test method, the specimen condition, and the acceptance basis.

$\rho$

Mass per unit volume.

Density

Mass divided by measured specimen volume.

\rho=\frac{m}{V}

Variables

Symbol	Description	Unit
$\rho$	Density	kg/m³
$m$	Mass	kg
$V$	Volume	m³

$\gamma$

Weight per unit volume; unlike density, it is based on force.

Unit Weight

Relationship between weight, volume, density, and gravitational acceleration.

\gamma=\frac{W}{V}=\rho g

Variables

Symbol	Description	Unit
$\gamma$	Unit weight	N/m³ or kN/m³
$W$	Weight	N
$V$	Volume	m³
$g$	Gravitational acceleration	m/s²

$Specific Gravity$

Dimensionless ratio of a material density to the density of a specified reference substance, commonly water for construction-material tests.

Specific Gravity

General density-ratio form relative to water.

G_s=\frac{\rho_s}{\rho_w}

Variables

Symbol	Description	Unit
$G_s$	Specific gravity	-
$\rho_s$	Material density	kg/m³
$\rho_w$	Reference-water density	kg/m³

$Porous-material specific-gravity states$

Aggregates and other porous materials may use bulk dry, bulk SSD, and apparent specific gravity. These terms use different mass and volume conventions and must not be interchanged in mixture calculations.

$n$

Ratio of void volume to total bulk volume.

Porosity

Void volume divided by total bulk volume.

n=\frac{V_v}{V_t}

Variables

Symbol	Description	Unit
$n$	Porosity	decimal
$V_v$	Void volume	m³
$V_t$	Total volume	m³

$Gravimetric Moisture Content$

Water mass relative to a defined reference mass; the denominator is material- and method-specific and is commonly oven-dry mass for many porous materials.

Dry-Basis Moisture Content

Common gravimetric form using oven-dry mass as the reference.

w=\frac{m_{wet}-m_{dry}}{m_{dry}}\times100\%

Variables

Symbol	Description	Unit
$w$	Moisture content	%
$m_{wet}$	Wet mass	kg or g
$m_{dry}$	Dry reference mass	kg or g

$Soil phase relationships versus general materials$

Void ratio, degree of saturation, and $Se=wG_s$ are fundamental soil-mechanics relationships. Aggregates, timber, masonry, asphalt, and other materials use their own standardized moisture and volume definitions, so soil phase equations should not be applied automatically.

$Interactive physical-properties simulations$

Use the following simulations to explore density, porosity, moisture, specific gravity, and related porous-material relationships. Treat simulated values as conceptual demonstrations unless they explicitly reproduce a cited laboratory method.

Measured Material Properties

Change measured specimen quantities and observe exact property definitions. These calculations do not assign material grade or acceptance status.

Engineering calculatorUses entered measurements; measurement resolution and specimen/test conditions remain part of the reported evidence.

Relevant standards map

ASTM E8/E8M· MethodASTM E111· Method

Practice controls sampling/specimen preparation where applicable → test method defines measurement → specification/code defines required performance → project documents define the controlling acceptance basis. Do not infer acceptance from a standard designation alone.

Laboratory evidence chain

1. Sample / lot represented
2. Specimen identity and condition
3. Apparatus and verification status
4. Procedure and method-critical controls
5. Raw readings / observations
6. Checked calculation
7. Validity and deviation review
8. Engineering interpretation
9. Specification / code comparison
10. Traceable report and disposition

Mass12.6 kgBulk volume5.0 LAxial force60 kNLoaded area300 mm²Gauge length200 mmMeasured extension0.12 mm

Balance resolution0.010 kgLength resolution0.01 mm

Derived results

Density

2520 kg/m³

\rho=m/V

Unit weight

24.71 kN/m³

\gamma=\rho g

Engineering stress

200.0 MPa

\sigma=P/A

Engineering strain

0.000600

\varepsilon=\Delta L/L_0

Reporting gate: the displayed digits are instructional. Actual significant figures and uncertainty must reflect apparatus resolution, calibration/verification, specimen geometry, repeatability, and the governing method.

Recorded resolution context: balance ±0.01 kg; length reading increment 0.01 mm. A comparable material result still requires compatible specimen state, conditioning, geometry, loading rate, and method.

Soil Three-Phase Relationships

An ancillary soil-mechanics model showing internally consistent volume and mass relationships for a 1.00 m³ sample. Soil phase equations should not be transferred automatically to aggregates, timber or other construction materials.

Void volume Vv0.40 m³Water volume Vw0.20 m³Specific gravity of solids Gs2.65

AIR

WATER

SOLIDS

Void ratio e

0.667

Porosity n

40.0%

Saturation S

50.0%

Moisture w

12.6%

Bulk density

1790 kg/m³

Dry density

1590 kg/m³

Phase check:

Se=wG_s

→ 0.333 = 0.333.

$\sigma$

Applied force divided by the stated reference area, commonly the original cross-sectional area for engineering stress.

Normal Engineering Stress

Axial force divided by the reference cross-sectional area.

\sigma=\frac{P}{A}

Variables

Symbol	Description	Unit
$\sigma$	Normal stress	MPa
$P$	Axial force	N
$A$	Reference area	mm²

$\epsilon$

Change in gauge length divided by the original gauge length.

Normal Engineering Strain

Change in length divided by original gauge length.

\epsilon=\frac{\Delta L}{L_0}

Variables

Symbol	Description	Unit
$\epsilon$	Engineering strain	-
$\Delta L$	Change in length	mm
$L_0$	Original gauge length	mm

$E$

Measure of stiffness represented by the slope of the stress-strain response in the defined elastic range.

Linear Elastic Modulus

Stress-to-strain ratio for an idealized linear elastic response.

E=\frac{\sigma}{\epsilon}

Variables

Symbol	Description	Unit
$E$	Elastic modulus	MPa or GPa
$\sigma$	Elastic stress	MPa
$\epsilon$	Elastic strain	-

$Strength, stiffness, ductility, and energy absorption$

Yield strength: stress associated with the specified onset of permanent deformation; some products use a distinct yield point and others use an offset/proof-stress definition.
Ultimate strength: maximum engineering stress reached in a standardized test; it is not necessarily the fracture stress.
Ductility: deformation capacity before fracture, commonly quantified by elongation, reduction of area, curvature, or another method-defined measure.
Resilience: recoverable elastic strain energy per unit volume.
Toughness: energy absorbed per unit volume through fracture.
Hardness: localized resistance to indentation, scratching, or abrasion; hardness correlations with strength are material- and method-specific.

$Fatigue$

Progressive damage caused by repeated or fluctuating stresses, sometimes at stress levels below static strength; performance depends on stress range, cycles, details, defects, and environment.

$Creep$

Time-dependent strain under sustained stress.

$Stress Relaxation$

Time-dependent reduction in stress while total strain is held approximately constant.

$Interactive mechanical-properties simulations$

Use the simulations to compare stress-strain response and the effect of elastic modulus on deformation. Simulation curves should be interpreted as idealizations unless tied to a specified product and test method.

Illustrative Stress–Strain Shapes

Schematic curves show characteristic regions; they are not product test records or design curves.

Loading chart...

The dense low-strain points intentionally resolve the elastic/yield transition that the previous 0.01 strain sampling skipped. Actual yield plateau, hardening, elongation and fracture depend on grade, product and test method.

Elastic Modulus & Poisson Effect

Compare a deliberately small-strain, linearized response using illustrative modulus values. This is a constitutive teaching calculation—not an allowable-stress, strength, or acceptance check.

Illustrative materialAxial strain magnitude250 µε

Concrete modulus and Poisson values vary with mixture, aggregate, age, moisture, stress range and test method; timber is intentionally omitted because one isotropic E–ν pair does not represent its orthotropic response.

Axial strain magnitude

0.000250

Linearized stress response

50.00 MPa

Lateral strain magnitude

0.000075

|\sigma|=E|\varepsilon_{ax}|,\qquad |\varepsilon_{lat}|=\nu|\varepsilon_{ax}|

Even at small strain, use the actual measured/design modulus appropriate to the material, loading sense, direction, conditioning and governing method. The concrete preset is a simplified linearized secant illustration, not a complete nonlinear concrete model.

$k$

Property describing heat conduction through a material under a temperature gradient.

Free Linear Thermal Movement

Unrestrained length change caused by a temperature change.

\Delta L=\alpha L_0\Delta T

Variables

Symbol	Description	Unit
$\Delta L$	Free change in length	mm or m
$\alpha$	Coefficient of linear thermal expansion	1/°C
$L_0$	Original length	mm or m
$\Delta T$	Temperature change	°C

$Thermal movement is not automatically thermal stress$

The free-movement equation gives unconstrained dimensional change. Thermal stress additionally requires restraint, stiffness, geometry, connections, time-dependent behavior, and boundary conditions.

$Chemical, corrosion, and fire performance$

Chemical resistance is exposure-specific and depends on agent, concentration, temperature, duration, permeability, cracking, and material composition.
Corrosion resistance of metals depends on electrochemistry, moisture, oxygen, chlorides, pH, coatings, geometry, and galvanic contact.
Fire performance includes combustibility, heat release, flame spread, smoke, temperature-dependent property loss, charring or spalling, and assembly-level load-bearing/separation performance.

$Property-to-test-to-decision framework$

Engineering question	Evidence family	Decision supported
Is aggregate properly graded?	Representative sample + sieve analysis	Blend, accept, reprocess, or reject per specification
Is fresh concrete consistent with the approved mixture?	Sampling + slump/flow, air, temperature, density	Place, adjust through approved procedure, or investigate
Does steel have required properties?	Product traceability + tensile/bend/toughness tests as applicable	Accept heat/lot or investigate
Is timber suitable for the service condition?	Grade + moisture/product data	Condition, protect, accept, or reject
Is asphalt adequately compacted?	Density/air-void evidence	Continue compaction or apply contract disposition

$Material selection criteria$

Required structural strength, stiffness, ductility, fatigue, creep, impact, and fracture performance.
Exposure to moisture, chemicals, corrosion, ultraviolet radiation, biological attack, temperature cycles, abrasion, and fire.
Constructability: placing, curing, welding, machining, joining, pumping, compaction, finishing, and repairability.
Compatibility at interfaces: differential movement, galvanic effects, bond, chemical interaction, and moisture transport.
Variability, representative sampling, inspection, test availability, and quality-control sensitivity.
Initial cost, local supply, transport, labor, maintenance, replacement, service life, and end-of-life options.
Verified environmental data and equivalent functional performance when sustainability is compared.

$Common materials-testing errors$

Nonrepresentative sampling or selective sampling of visually good material.
Using the wrong moisture, temperature, or conditioning state.
Comparing different specimen shapes or methods without an accepted basis.
Mixing SI and inch-pound quantities without controlled conversion.
Reporting more digits than the measurement system supports.
Treating a correlation-based estimate as equivalent to a direct standard test.
Ignoring equipment verification, alignment, loading rate, timing, or operator effects.
Calling a precise result accurate without evaluating bias against a valid reference.

Key Takeaways

Material properties are meaningful only with defined sampling, specimen, conditioning, and test conditions.
Strength, stiffness, ductility, toughness, fatigue, creep, thermal response, and durability are distinct performance dimensions.
Porous materials require the correct moisture and specific-gravity reference states.
Material selection is a system decision based on performance, exposure, construction, compatibility, QC, economy, and service life.
The core workflow is representative sample → standardized measurement → checked calculation → interpretation → specification comparison → documented decision.

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Learning Objectives

Property, test result, and specification

Density (ρ\rhoρ)

Density

Unit Weight (γ\gammaγ)

Unit Weight

Specific Gravity

Specific Gravity

Porous-material specific-gravity states

Porosity (nnn)

Porosity

Gravimetric Moisture Content

Dry-Basis Moisture Content

Soil phase relationships versus general materials

Interactive physical-properties simulations

Measured Material Properties

Derived results

Soil Three-Phase Relationships

Engineering Stress (σ\sigmaσ)

Normal Engineering Stress

Engineering Strain (ϵ\epsilonϵ)

Normal Engineering Strain

Elastic Modulus (EEE)

Linear Elastic Modulus

Strength, stiffness, ductility, and energy absorption

Fatigue

Creep

Stress Relaxation

Interactive mechanical-properties simulations

Illustrative Stress–Strain Shapes

Elastic Modulus & Poisson Effect

Thermal Conductivity (kkk)

Free Linear Thermal Movement

Thermal movement is not automatically thermal stress

Chemical, corrosion, and fire performance

Property-to-test-to-decision framework

Material selection criteria

Common materials-testing errors

$Learning Objectives$

$Property, test result, and specification$

$\rho$

$\gamma$

$Specific Gravity$

$Porous-material specific-gravity states$

$n$

$Gravimetric Moisture Content$

$Soil phase relationships versus general materials$

$Interactive physical-properties simulations$

$\sigma$

$\epsilon$

$E$

$Strength, stiffness, ductility, and energy absorption$

$Fatigue$

$Creep$

$Stress Relaxation$

$Interactive mechanical-properties simulations$

$k$

$Thermal movement is not automatically thermal stress$

$Chemical, corrosion, and fire performance$

$Property-to-test-to-decision framework$

$Material selection criteria$

$Common materials-testing errors$