Embed Size (px)
DESCRIPTION
hi
Citation preview
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
