for Hot Bituminous Mix By Priyansh Singh

Indian Institute of Technology Guwahati

Mix Design

Introduction

• Asphalt Mix design is first traced in 1860s, using Tar as binder in Washington, D.C.

• Richardson used ‘Pat Test’ for optimum test to determine optimum mix design.

• Hubbard-Field Method.

• Mix design is the method to determine that whether a suitable mixture can be prepared with the available materials and to determine the best combination of these materials for optimum performance.

Requirements

• Sufficient asphalt to ensure a durable pavement

• Sufficient stability under traffic loads

• Sufficient air voids – Upper limit to prevent excessive environmental

damage

– Lower limit to allow room for initial densification due to traffic

• Sufficient workability

Elements of Mix Design

Items must be evaluated during the mix design to ensure that optimum performance is obtained.

• Resistance to Permanent Deformation

• Fatigue Resistance.

• Resistance to Low Temperature Cracking

• Durability.

• Resistance to Moisture Induced Damage

Elements of Mix Design

• Skid Resistance.

• Workability.

• Gradation and Maximum Density Curves.

Methods of Mix Design

• Haveems Method of mix design.

• Marshall Method of mix design.

• Superpave Method of mix design.

Marshall Method

• The method is developed by Bruce Marshall around 1939 for design of Air Field Pavements.

Steps for Marshall Method

1. Aggregate Evaluation.

2. Asphalt Cement Evaluation

3. Preparation Of Marshall Specimens

4. Density And Voids Analysis

5. Marshall Stability And Flow Test

6. Tabulating And Plotting Test Results

7. Optimum Asphalt Content Determination

Preparation of Marshall Specimens ASTM D6926–10 Standard Practice for Preparation of Bituminous Specimens

Using Marshall Apparatus

• Equipment required

– Specimen Mold

Assembly

Equipment required

– Specimen Extractor

– Compaction Hammers

Equipment required

– Specimen Mold-Holder

– Ovens, Heating Pots or Hot Plates

– Mixing Apparatus, etc.

Preparation of test Specimens

• Preparation of Aggregates: Dry aggregates to constant weight. Oven drying should be done at 105 to 110°C (221 to 230°F). After cooling, separate the aggregates by dry-sieving into the desired size fractions.

• Determination of Mixing and Compacting Temperatures

Determination of Mixing and Compacting Temperatures

• The asphalt cement used in preparing the samples must be heated to produce viscosities of 170 ± 20 cP (0.17 ± 0.02 Pa·s) and 0.28 ± 0.03 Pa·s (280 ± 30 cP) for mixing and compacting, respectively. An example of a viscosity temperature chart is given in Fig. 2 of D2493

Determination of Mixing and Compacting Temperatures

Determination of mixing and compaction by use of equation.

• the chart coordinates are logarithm of the logarithm of the viscosity in centipoise as the ordinate, and logarithm of the absolute temperature in degrees Rankine (degrees F + 459.7) as the abscissa. However, viscosity in poise, and the temperature in degrees Fahrenheit is shown in the chart for convenience.

Determination of Mixing and Compacting Temperatures

.1

.2

.3

.5

1

10

5

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Vis

cosi

ty, P

a s

Compaction Range

Mixing Range

Determination of Mixing and Compacting Temperatures

• If we have two point data

• 𝑦 − 𝑦1 =𝑦

1−𝑦

2

𝑥1−𝑥

2

(𝑥 − 𝑥1)

• 𝑦 = −2.318𝑥 + 7.0849

• For this equation for Viscosity 150 cp the temperature is 373 °F (189 °C).

Viscosity Temperature

367 cP 302 °F

2245 cP 221 °F

Preparation of test Specimens

– Preparation of mold and hammer.

– Preparation of mixture.

– Placing in mold and compaction.

Density and Void Analysis

Density and Void Analysis

• Bulk specific gravity of compacted sample.

• Maximum specific gravity of loose mix.

Stability and flow

• 60oC water bath (30 to 40 minutes)

• 50 mm/min loading rate.

• Max. load = uncorrected stability

• Corresponding vertical deformation = flow

Stability and flow

Stability and flow

Stability and flow ASTM D6927 – 06 Standard Test Method For Standard Test Method for Marshall Stability

and Flow of Bituminous Mixtures

Use of Data

Asphalt Institute Procedure

Air Voids, %

Asphalt Content, %

Stability

Asphalt Content, %

Unit Wt.

Asphalt Content, %

Target optimum asphalt content = average

4%

Use of Data

Asphalt Institute Procedure

Flow

Asphalt Content, %

VMA, %

Asphalt Content, %

Use target optimum asphalt content to check if these criteria are met

Lower Limit

Upper limit

Minimum

OK

OK

Use of Data NAPA Procedure

Air Voids, %

Asphalt Content, %

Target optimum asphalt content =

the asphalt content at 4% air voids

4%

Use of Data NAPA Procedure

Stability

Asphalt Content, %

The target stability is checked

OK

Use of Data NAPA Procedure

Flow

Asphalt Content, %

VMA, %

Asphalt Content, %

Use target optimum asphalt content to check if these criteria are met

Lower Limit

Upper limit

Minimum

OK

OK

Marshall Design Criteria

Light Traffic Medium Traffic Heavy Traffic ESAL < 104 10 4 < ESAL< 10 ESAL > 106

Compaction 35 50 75 Stability N (lb.) 3336 (750) 5338 (1200) 8006 (1800) Flow, 0.25 mm (0.1 in) 8 to 18 8 to 16 8 to 14 Air Voids, % 3 to 5 3 to 5 3 to 5 Voids in Mineral Agg. (VMA) Varies with aggregate size

Marshall Design Criteria

Table 500-19 Requirements for Bituminous Pavement Layers (MoRTH Section 500)

Minimum Stability 9.0

Minimum Flow 2

Maximum Flow 4

Compaction Level 75 blows each face

Per cent air voids 3-6

VMA Table 500-12

VFB 65-75

Loss of Stability on immersion in water Min. 75% retained strength

32

Marshall Design Method

• Advantages – Attention on voids, strength, durability.

– Inexpensive equipment.

– Easy to use in process control/acceptance .

• Disadvantages

– Impact method of compaction.

– Does not consider shear strength.

– Load perpendicular to compaction axis.

Thanks Prentation By Priyansh Singh