CIV3703 Transport Engineering

Module 5ADesign of Bituminous Surfacings – Part A

Dr. Andreas Nataatmadja

5.1 Types of Bituminous Surfacings

Purpose of bituminous surfacing:

shield pavement from traffic wear;

eliminate dust -> improve road user, comfort,

safety;

providing unchanging surface in all weather;

provide reasonable travel speed;

reduce maintenance requirements;

prevent moisture penetration into pavement.

5.1.1 Sprayed Treatments

Further subdivision:

1. Primes – preliminary, before more permanent

cover

2. Primerseals - temporary treatment with aggregate

3. Seals - permanent cover

4. Reseals - seal on an existing seal

5. Surface Enrichment - light binder applied to

existing seal.

Seals (Permanent Covers)

Three types commonly used

one application of binder and one layer of

aggregate (single/single)

one application of binder and two layers of

aggregate (single/double)

two applications of binder and two layers of

aggregate (double/double)(binder, 1st aggregate, binder, 2nd aggregate)

Single/Single Seal (S/S)

Single/single: Most common economical type of seal

new work and reseal treatments

Binder: C170, PMB

Aggregate: 7/10/14/16/20mm

Reference: This lecture is based on “Practitioner’s Guide to Design of

Sprayed Seals – Revision 2000 Method” – Austroads

(2002). Current guide: “Update of the Austroads Sprayed

Design Method” - Austroads (2006).

Single/Double Seal (S/D)

Single/Double: One application of binder and two layer of aggregate

Binder: C170, PMB

Aggregate: 1st layer is larger aggregate

2nd layer is ideally half size of 1st layer

Combinations: 20/10, 20/7, 14/7, 10/5 mm

Note: If not enough binder then more likely windscreen breakage

Double/Double Seal

Double/double: Better than a S/S for areas of high traffic loading &

shear stress (intersections, steep grades, tight curves)

Application: 2 layers of binder, and 2 layers of aggregate

Binder: C170, PMB

Aggregate: 1st layer is larger aggregate

2nd layer is ideally half size of 1st layer

e.g. 20/10, 20/7, 14/7, 10/5 mm

Reference: “Update of the Austroads Sprayed Seal Design Method” –

Austroads (2006). This has been superseded by “Update of

Double/Double Design for Austroads Sprayed Seal Design

Method” – Austroads (2013)

Resealing

Seal on an existing seal to maintain the assets.

Generally S/S is adequate.

Cutback bitumen or Bitumen Emulsion can be

used.

Surface Enrichment

spraying of a light grade of cutback bitumen or

emulsion with no aggregate

binder runs into the voids between the existing

seal stones

extends the life of surface

traffic has to be diverted for some time

Asphalt

A mixture of aggregate and bituminous binder, usually

produced in a mixing plant.

Asphalt (AUS) = asphalt(ic) concrete (USA), bituminous

concrete, hotmix

Bitumen (AUS) = asphalt cement (USA)

Uses of Asphalt

Construction of a new pavement;

Strengthening an existing pavement;

Correcting irregularities in an existing pavement;

Repairing an existing pavement;

Providing a new wearing surface.

Asphalt Types

Dense Graded Mix

usual type

grading of aggregate sizes from fine to coarse

stability depends on grading, binder content, air voids

and density

Open Graded Mix

high air voids, stability depends on interlock

Gap Graded Mix

stability depends on the stiffness of aggregate-binder

mix

5.2 Selection of Surfacing Type

Factors influencing selection:

the pavement structure

economic and financial considerations

riding quality, tolerable roughness

pedestrian use

safety

noise generation

plant, material availability

waterproofing requirements

5.3 Design of Sprayed Surfacings

5.3.1 Selection of Primer and Application Rate

Preliminary cover prior to applying more permanent cover.

Functions of a prime:

provide bond between pavement and seal coat;

minimise effect of dust after sweeping;

strengthen pavement surface by increased cohesion;

provide short term running surface prior to sealing;

allow proof testing of pavement;

act as waterproof membrane which assist in stabilisingthe pavement moisture condition

PrimerPrimer: Typically cutback bitumen, (AMC00 – AMC1) or

Specially formulated emulsion primer

Selection: Based on knowledge and experience

Rates: Application rates vary from 0.6 L/m2 (damp pavement) to 1.3

L/m2 (dry pavement)

PRIME is preferred treatment for new roads before more

permanent cover (only for limited trafficking).

5.3.2 Selection of Primerseals

Aim: 1. Temporary treatment to carry traffic several months.2. Allows the normal seal coat to be applied in more

favourable weather.

Primerbinders: Typically cutback bitumen (AMC 4 or 5)Winter use: 15% cutter: Summer use: 10% cutterCRS emulsion (60 & 70% bitumen) can be an alternativeBase rates plus allowances. Typically 1.2 – 1.4 L/m²

Aggregate: 5, 7 & 10 mm (usually less than 7 mm)

Typical life: Up to 12 monthsApply final permanent cover to complete the treatment.

5.3.3 Design of Seals and Reseals

1. Select type of seal.

single/single; single/double; double/double

2. Select aggregate size.

� Depends on the type of treatment; traffic; noise;

pavement condition; alignments.

� For two aggregate coasts: 2nd half size of the first.

3. Select aggregate type.

4. Select aggregate application rate.

Larger aggregate (≥ 10 mm):

• Conventional bitumen: 900 / ALD (m2/m3)

• Polymer modified binder: 750 / ALD (m2/m3)

For 7 mm aggregate: 200 to 250 (m2/m3)

Allow allowances for loss: spreading, whip-off; stockpile.

Typical: 5% for 20mm; 10% for 7mm

Multiple application work:

1st - as for single/single

2nd - past experience/trials (70% single/single ?)

5. Select binder type.

Bitumen; cutback bitumen; multigrade bitumen; fluxed

bitumen; bitumen emulsion; polymer modified binders.

Most common in Australia: C170, some C320 in hotter

areas

Flux - usually maximum of 5% by volume.

Cutter - mainly depends on road/air temperatures and

traffic volume. Use Fig. 5.3 to determine quantity.

6. Select binder application rate.

Basic application rate (litres per square metre)

= ALD x Void Factor (VF)

Void Factor (VF) = Vf + Va + Vt

Vf – Basic Voids Factor (based on traffic volume)

Va – Aggregate adjustment

Vt – Adjustment for traffic effects

Basic Void factor

Upper limit: BleedingLower limit: Stripping

Table 5.6 Aggregate Adjustment (Va)

Table 5.7 Traffic Effects Adjustment (Vt)

Example

Design the surfacing for

New England Highway, 8 km north Warwick

Reconstruction: 2 km length, 2 lane road

Traffic: 3800 vehicles per day

Pavement condition: “Hungry”

Basalt aggregate available:

Nominal size ALD (mm)

20 mm 12 mm

15 mm 10 mm

10 mm 7 mm

7 mm

1. Select Surface Treatment

Prime and seal

2 coat seal (D/D) – why?

Traffic: 3800 veh/day (includes 22%

commercial)

2. Design of Prime

Porous surface: use heavy primer, AMC1 cutback bitumen

Application rate 1.0 l/m2

Any aggregate?

AMC00

AMC0AMC1, AMC2

3. Design of Seal - Aggregate

Aggregate?

(a) 20 mm + 10 mm

Application?

(b) 83 m2/m3 + 150 m2/m3 (including reductions)

3. Design of Seal - Binder

Type?

(c) Bitumen + Cutter

How much cutter?

Assume road temperature: 35°C

Cutter: 2%

3. Design of Seal - Binder

Application rate?

Design void factor (VF)

Application: 1.5 l/m2 + 1.0 l/m2

Summary

Prime: AMC1

Seal – Class 170 bitumen + 2% cutter

1st coat: 20 mm aggregate @ 83 m2/m3

Binder 1.5 l/m2

2nd coat: 10 mm aggregate @ 150 m2/m3

Binder 1.0 l/m2

End of Module 5 – Part 1