CIV3703 Transport Engineering

Module 4 – Part 1Road Materials

Dr. Andreas Nataatmadja

4.1 Pavement

Natural soil usually not

strong enough to withstand

repeated application of

vehicle wheel loads.

Need to protect natural soil

from the wheel loading

effects by placing a structure

- pavement.

Example (Construction of Residential Road)

Materials Used in Pavements

Bituminous materials

Unbound granular materials

Cemented materials

Cement concrete

Pavement Layers

Subgrade may consists of several selected materials on top of natural subgrade

Pavement Types

� Flexible

• Asphalt/Seal on unbound granular

• Asphalt on stabilised subbase

• Full-depth asphalt

� Rigid

• Concrete base with joints and/or steel reinforcement

• Using Lean Mix Concrete (LMC) subbase

� Composite

• Flexible pavement with an LMC subbase

• Designed as a flexible pavement

4.2 Pavement Materials

Flexible Pavements:

• Granular materials: used in base, sub-base, selected material layers

e.g. crushed rock, soil-aggregate (unmodified/modified)

May be covered with sprayed seal or asphalt

• Stabilised/cemented aggregate: used as sub-base

e.g. cement treated crushed rock (CTCR) – subject to fatigue

Requires at least 175 mm asphalt base to stop reflective cracking

• Bituminous materials: used as surfacing or base

e.g. sprayed seal, asphalt (open graded, stone mastic, dense graded)

4.2 Pavement Materials

Rigid Pavements:

• Concrete: used as base in

• Plain Concrete Pavement (PCP)

• Jointed Reinforced Concrete Pavement (JRCP)

• Continuously Reinforced Concrete Pavement (CRCP): has no joint

• Fibre Reinforced Concrete Pavement (FRCP)

• Lean Mix Concrete (LMC): used as subbase

• Provides uniform support to the base

• Resists erosion and pumping

• Enhances load transfer across joints

• Granular materials: used in selected material layers

Rigid Pavement is outside the scope of CIV3703

4.3 Gravels

Crushed rock

Soil aggregate mixtures: In Queensland, observe the following terms

gravel: max size > 5mm

loam: max size < 5mm

Includes:

pit, ridge, creek or waterworn gravels

crusher products mixed with a soil binder

decomposed rock

sedimentary or metamorphic rocks

fine grained materials (loam, sand clay mixtures)

4.4 Factors Influencing Selection of Pav. Materials

Type of pavement (surfaced vs unsurfaced)

Position in the pavement ( base vs sub-base)

Climatic conditions (wet vs arid)

Traffic (low vs high volumes; light vs heavy)

Availability of materials (untreated vs stabilised)

Stress Distribution within a Flexible Pavement

Stronger materials are used to handle higher stresses (near the surface)

4.5 Location & Investigation of Natural Gravel Deposits

Search, based onavailable information, local knowledge

maps (soil, geological), aerial photos

similar locations to existing deposits

geology

Vegetation types

Preliminary examinationvisual, sampling, laboratory tests

Detailed investigationdetailed sampling, testing, determination of variation

4.6 Testing of Granular Materials

PROPERTIES OF IMPORTANCE:

1. Stability

ability to resist deformation and change

Strength (c, φ, UCS, CBR) an important component of

stability

strength depends on moisture, voids, conditions

under which stress is applied

strength tested e.g. California Bearing Ratio (CBR)

or inferred from classification tests

2. Resistance to Wear

not easily measured

inferred from classification and index tests

3. Permeability

inferred from classification and index tests

4. Workability: ease of spreading & compaction

inferred from classification tests

4.6.1 Particle Size Distribution

Determined by sieving and hydrometer analysis for finer fraction

4.6.2 Consistency Limits (Atterberg Limits)

Plastic limit (PL)

Liquid limit (LL)

Typical max 25% to 35%

Plasticity Index (PI) = Liquid limit - Plastic limit

Typical maximum for aggregates 6%

Weighted PI (WPI) = % passing sieve 0.425 mm x PI

Typical maximum = 200 - 400

4.6.3 Linear Shrinkage

• Gives indication of

volume change with

moisture variation.

• Maximum allowable 3%

to 6%, depending on

purpose of use and

climatic condition.

4.6.4 California Bearing Ratio (CBR)

Test originally developed by California Highways

Department to assess quality of fine crushed rock base

materials

Test compares strength of a material to a standard

crushed rock material.

Standard material has CBR of 100.

Good quality crushed rock has CBR ≥ 80.

Test Procedure

Material compacted into steel mould

sample 152 mm dia; 127 mm high

3 layers, 53 blows per layer for standard compaction

50mm steel plunger forced into material at

constant penetration rate

rate of penetration 1 mm/min

recording of load versus penetration

CBR value calculated

CBR Calculation

CBR at 2.5 mm penetration

Standard material requires load of 13 .3 kN for 2.5

mm penetration.

Value for CBR at 5 mm penetration calculated using

a value of 20 kN for standard material.

4.6.5 Ten Percent Fines & Wet/Dry Strength Variation

Ten percent fines value

test measures resistance of rock to crushing.

a variation of the Aggregate Crushing Value test.

load to produce 10% fines measured.

Wet/Dry strength variation

looks at 10% fines value difference for the material in

wet and dry conditions.

4.6.6 Washington Degradation Test

Used to assess the extent of alteration or weathering of

igneous or metamorphic source rocks.

Sample crushed to pass 19 mm sieve

Shaken in water for 20 minutes

Sample washed with flocculating agent

Amount of sediment measured

Test value calculated (using a complex scale)

Values < 60 a concern. Values of 30 to 40 may be okay for sub-

bases.

4.7 Bituminous Surfacing Materials

All bituminous road surfacings consist of 2 essential components:

• mineral aggregate - resists the wearing effect of tyres

• bituminous binder - acts as adhesive or glue, to hold aggregate particles in place, and to bond surfacing to underlying base.

http://www.highway1.co.nz/sma-fibres.html

Commonly Used Bituminous Surfacings in Australia

Bituminous seal or sprayed seal

Thin layer of bitumen sprayed on the road surface to hold

a layer of relatively large aggregate particles.

Asphalt, plant mix, or bituminous concrete Intimate mixture of aggregate particles and bitumen

binder, produced in a mixing plant.

Sprayed (Chip) Seal Surface

4.8 Road Surfacing Aggregates

Functions are to resist abrasion by traffic, and to transmit

wheel loads to base.

Aggregate needs to be durable, to possess hardness,

toughness, wearing resistance, crushing strength and

polishing resistance (to withstand traffic).

In addition, aggregates should have good microstructure

that provides skid resistance.

Source of Aggregates

Naturally occurring unconsolidated

sediments

gravels & sands

Crushed quarried rock

typically igneous rocks - basalt, gabbro or granite

metamorphic rocks - quartzite, schist

Crushed artificial rocks

blast furnace slag

steel slag

Size/Grading of Aggregate for Surfacing

Narrow particle size distribution (PSD) used for sprayed seal

applications (i.e. one sized aggregate)

In plant mix (asphalt) a wide partial distributions is used to

form interlocking (except Open Graded Asphalt or OGA)

Aggregate greater than 37.5 mm is not normally used for

surfacing

Coarse aggregate > 4.75 mm; fine aggregate is between 4.75

and 75 µm; passing 75 µm is known as fillers.

4.9 Desirable Properties of an Aggregate

Mechanically strong

Resistant to wear

Resistant to degradation by

weather

Good shape (angular, near

cubical shape)

Provides surface texture

(microtexture) for skid

friction

Clean, ready to be mixed

with binder

4.10 Testing of Aggregates

4.10.1 Strength & Resistance to Wear

Los Angeles Abrasion Test; Agg. Crushing Value

4.10.2 Resistance to Decomposition

Soundness; Wet/Dry strength variation

4.10.3 Particle Shape and Surface Texture

Flakiness, Angularity, ALD

4.10.4 Resistance to Polishing by Traffic

Polished Aggregate Friction Value

Los Angeles Abrasion Test

5,000 g of coarse aggregate is rotated for 500 revolutions with either 10 or 11 steel balls.

Amount of generated fines is determined (passing 1.7mm sieve) i.e. percent loss

Typical maximum loss:

25% for seal coat

Aggregate Crushing Value

Sample: aggregate passing 13.2 mm and retained

on 9.5 mm

Constant loading for 10 minutes up to 400kN

Passing 2.36 mm sieve is determined

Flakiness Index (FI)

Percent by mass of aggregate particles having a least

dimension < 60% of the mean aggregate size. Determined as

the ratio of the mass passing a specific slot to the total mass of

the aggregate fraction.

Low FI (e.g. 15%) → cubical shaped stone (desirable)

High FI (e.g. 30%) → flaky shaped stone (undesirable)

QDTMR Spec MRTS22 → FI ≤ 35%

Angularity Number

Highly angular fine aggregates are used to

produce high stability asphalt concrete mixes.

Crushed fine aggregates (manufactured) tend to

be more angular than natural ones.

Angularity number is the amount of voids exceeding 33%

Average Least Dimension (ALD)

must be representative

poor practice to use “assumed ALD”

check prior to sealing

Used to calculate:

Binder spray rate

Aggregate spread rate

Design assumes sealthickness equal to ALD after

some trafficking

What happens with non-single sized aggregate ?

Source: Austroads

Skid Resitance Test

Pendulum skid resistance tester: measures the

polished aggregate friction values (PAFV).

End Module 4, Part 1