Bahia HMA With FS

How to Use

Recycled Foundry Sand in Hot Mix Asphalt (HMA)

Hussain U. Bahia

University of Wisconsin-Madison

Foundry Sand Recycling Forum

“Foundry Sand in Infrastructure Applications”

October 31st, 2007

Chicago. IL

Overview of Talk

• Introduction: Why use these sands?

• What are the Important properties of Sands ? • Foundry sands can vary by metals and molding

binder systems

• Gradations, Angularity, Clay and Organic Contents

• Range in Properties measured

• Can sands result in acceptable Asphalt Mixtures? • Studies completed

• Effects on durability , constructibility, traffic resistance

• Moisture effects

• Guidelines for use

• Questions

Introduction

Why use these sands?

• For Asphalt contractors:

• Natural aggregates are becoming more

scarce.

• More energy/money needed to extract natural

aggregates.

• In some areas fine aggregates are not

available.

Sands can be Variable based on Source

(Metal + Binder)

• Properties of sands can vary by

• Metal type

• Binder system used

• DOE project- Most comprehensive study:

• Metal Poured (8 Metals)

• Binder System (10 Systems)

• Data base can be used as a guide

What are the Important Properties of Sands

for Hot Mix Asphalt Application

• Important properties are:

• Gradation

• Densities: Maximum, Effective and Bulk

• Angularity

• Organic Content

• Clay Content

Gradation- Size Distribution

Gradation of 17 Sands

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Sieve Size

Pe

rce

nt

Pa

ss

ing

#200 #100 #50 #30

It can be seen that the gradation varies widely,

so it can’t be assumed that foundry sands

have the same gradation.

Angularity

ASTM C1252 “Un-compacted Void Content of Fine Aggregates”

Used to determine the surface characteristics.

The more angular, the higher resistance to rutting.

Variation in Angularity of Sands

As measured by voids

38

39

40

41

42

43

44

45

46

Contro

l 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Source of Sand

An

gu

lari

ty, %

Vo

ids

Organic Content

Determined by AASHTO T267-86 “Determination

Of Organic Content (OC) in Soils by Loss on

Ignition” Expressed as percent loss.

Less OC is better.

Variation in Organic Content of Sands

0

1

2

3

4

5

6

Contro

l 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Source of Sand

Org

an

ic C

on

ten

t, %

mass

Clay Content

• Traditionally used Sand

Equivalent Test

• Due to carbon content,

this could not be used

• Modified AFS 2210-00-S

“Methylene Blue Clay

Test, Ultrasonic Method”

suspended clay

sedimented sand

clay reading

sand reading

graduated

cylinder

flocculating

solution

Sand Equivalent Test

Clay Content

Modified Method

• Used a

spectrophotometer

instead of filter paper to

determine “how blue is

blue”.

• Methylene blue index

(milligrams of methylene

per gram of sand- mg/g)

tested at a wavelength of

670 nm.

A typical bentonite has a MBV of about 387 mg/g,

so a foundry sand with a MBV of 20 contains

about 5% active clay.

Variation in Clay Content

As measured by Methylene Blue

0

5

10

15

20

25

30

35

40

Contro

l 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Source of Sand

Me

thy

len

e B

lue

Va

lue

mg

/g

High

Range

7 sands

Better than

control

Can Sands be used for production of

Acceptable Asphalt Mixtures ?

• Studies at UW-Madison

• First study (2000) by E. Miller

• Second Study (2001) by K. Delage

• Third Study (2002) by A. Braham

• Fourth study (2004) by T. Snyder

• With Penn State and First

• 17 sands from 11 different states.

• Developed Guidelines

Asphalt Mixture Performance Indicators

• Durability: • Asphalt Content

• Voids Filled with Asphalt (VFA)

• Mixture Stability / Volumterics: • % Maximum Density @ Nini, Ndes, Nmax

• Constructability • Paver Energy Index: PEI

• Rolling Energy Index: REI

• Resistance to traffic action • Traffic Densification Index: TDI

• Resistance to fatigue and moisture damage

• Indirect Tension Strength

Mix Designs – Superpave Technology

Loose mix is placed into compaction mold

Superpave Gyratory Compactor

compacts the sample

Ram used to compact sample.

Aluminum arm gyrates around sample

Optimum A.C.

3

3.5

4

4.5

5

5.5

6

6.5

9 1 11 7 8 10 15 17

Cont

rol

13 6 16 5 3 4 2 14 12

Op

t. A

.C.

(%)

Durability and Economics

Asphalt Content is not affected significantly

Constructability

Constructability is not affected significantly

Roller Energy Index

0

5

10

15

20

25

30

15 8 9 11 17 1 6 10

Cont

rol 5 13 14 2 4 12 3 7 16

RE

I

Resistance to Traffic Action

Traffic Resistance is not affected significantly

Traffic Densification Index

0

100

200

300

400

500

600

700

800

900

12 4 10 8 3 7

Cont

rol 5 2 17 15 6 13 14 11 9 16 1

TD

I

Resistance to Moisture Damage

For Some Sands, there is important Reduction

Tensile Strength Ratio

0

10

20

30

40

50

60

70

80

90

100

1 9 17 8

Con

trol

11 12 13 10 6 3 16 15 4 2 5 7

Sand

Ten

sile S

tren

gth

Rati

o (

%)

Current Knowledge

• Change in economics of HMA is minimal:

• Some sands showed an increase in asphalt content, while others did not.

• Asphalt contents ranged from 5.1 to 6.1% with the control at 5.5%

• Effect of sand on moisture sensitivity varies:

• 9 of the 17 foundry sands either caused an increase or no change in Tensile Strength Ratio values.

• Based on this, over half the sands can be used safely in HMA.

• Sodium Silicate binder system is detrimental to HMA.

Case Studies

• Departments of Transportation allows it:

• Pennsylvania: DOT allows 8-10% in all mixes

• Michigan: HMA producer use 10-20%

• Tennessee: HMA producer uses 10 %

• Ontario, Canada: HMA producer has used it for more than 10 years

• Concerns of UMA suppliers

• Consistency required

• Environmental classification

• Clay content

• Total amount

Where are Sands Used for HMA?

Sands are accepted by DOT

Sands used on experimental basis

Guidelines for Using Sands in

Asphalt Mixtures

• Foundry Quality Check

• Required: Report Binder system used

• Required: Report if sand contains any

Sodium Silicate

• Required: Measure Methylene Blue

value

• Optional: Size Distribution

• Optional: Anuglarity

Guidelines for Using Sands

in Asphalt Mixtures

• Asphalt Contractors: • Try first at a minimum of 10 %

• In general, do not cause an increase in asphalt content. Depends on specific foundry sand.

• Test for moisture damage is necessary. • If MB < 10, no additive is needed.

• If MB > 10, moisture damage needs treatment

• If moisture damage is evident: • Anti-stripping additives may not solve problem.

• Washing should be tried.

Step by Step Procedure

• Similar to other fine sands

• Measure gradation

• Measure angularity

• Measure clay content

• If passes all HMA limits by DOT, use as much as needed.

• If not ( too much fines, low angularity or high clay content)

• Add as much as possible to meet limits

• Always test moisture damage of HMA after compaction

Questions

Contact:

Hussain Bahia

Bahia@engr.wisc.edu