Foundry Byproducts as

Sustainable Geotechnical

Construction Materials

Craig H. Benson, PhD, PE, DGE

Wisconsin Distinguished Professor

Director, Recycled Materials Resource Center

University of Wisconsin-Madison chbenson@wisc.edu

www.recycledmaterials.org

© University of Wisconsin-Madison 2011

Participant Background

Which describes your training:

• Engineer

• Geologist

• Environmental scientist

• Other

Participant Background

Which describes your employment:

• Private sector

• Public sector

• Designer

• Regulator

• Construction

What is an iron foundry? • An iron foundry is a manufacturing

plant where molten iron is poured into molds to make iron products.

• Some common products include brake parts, gearboxes, propellers, and valves.

• Molds are formed with “green” sand, “no bake” sand, & “cores”

• Excess foundry sands used in construction usually are a mixture of green sand (predominant) and “core” or “no-bake” sand.

Foundry Byproducts

Two primary byproducts:

• Foundry sand – excess material generated at foundry as new ingredients are added to sand blend to ensure suitable properties (aka “excess sand” or “spent system sand”).

• Foundry slag – impurities that float to surface of molten iron (Ca, Mg, and other elements). Amorphous “obsidian-like” when slowly air cooled or porous “tuff-

like” when rapidly water cooled.

What is a core?

Black portion is “green”

sand mold.

Orange is core, which

is prepared with a

polymeric binder.

Cores form internal

cavities.

Green sand can be reconstituted into a new mold. Cores

generally are used one time.

Cores generally need to be crushed prior to use in

construction applications.

Foundry Sand Being Used as Fill

Spent

cores

Foundry sand

grades and

shapes easily.

Fines facilitate

compaction with

modest amount

of moisture.

Foundry sand being spread as highway sub-base.

Foundry sand sub-base being compacted.

Foundry Slag Used as Base Course

Recap Poll # 1 – True or False

• The basic types of iron foundry sands that might be encountered in a reuse application: green sand, core sand, no-bake sand. True or false?

• Foundry sand is discarded because the sand has the incorrect color. True or false?

• Foundry slag is synonymous with foundry sand. True or false?

Foundry Sand Composition

Foundry sands are sand-bentonite mixtures.

Base Sand

85%

Organic 3%

Water 5%Bentonite 7%

0

20

40

60

80

100

0.010.1110

Pe

rce

nt

Fin

er

(%)

Particle Diameter (mm)

14 Foundry Sands from

WI, IL, MI, & IN

Particle Size Distribution

Index Properties for Foundry Sands

• Fine Sand

• Fines: typically 10 to 12%

• 2 μm Clay: typically 3 to 10%

• Plasticity index (PI): typically NP to 5

• SC, SP, or SP-SM or A-2-4 or A-3

• Gs: 2.52 to 2.73 (Base Sand = 2.66)

• Subrounded to subangular (R = 0.5 to 0.7)

Index Properties for Foundry Slags

Material Gs

Bottom ash 2.67

Foundry slag 2.36

Glacial outwash sand 2.71

• Pea gravel to sand size (depends on crusher)

• Non-plastic

• SW, SP, GW,

• Gs = 2.2 to 2.4

Subbase Applications

• Compaction

• California bearing ratio (CBR)

• Resilient modulus

• Drainage

HMA or PCC

Base (slag)

Subbase (sand)

Subgrade

Compaction Curves

• Bentonite fraction imparts “bell” shape compaction curve, even with low bentonite content.

• Behaves like a finer textured soil.

With adequate moisture, readily compact to 95% of standard Proctor or 90% of modified Proctor. Relatively dry from foundry (3-5%) – water is needed.

ESS #Penetration

Curve TypeP200 PI Max CBR

1 Brittle 10.7 NP 40

2 Ductile 12.7 3 8.7

3 Brittle 4.3 NP 10

4 Brittle 1.1 NP 18

5 Ductile 14.3 1 19

6 Ductile 11.3 2 22

7 Brittle 2.7 NP 10

8 Ductile 12.1 8 27

9 Ductile 13.2 4 28

10 Ductile 12.4 5 4.3

11 Ductile 10.2 3 8.1

12 Ductile 16.4 6 16

13 Ductile 13.2 3 32

14 Brittle 10.0 NP 33

Reference Base 80

Reference Subbase 17

Typical CBRs

• Optimum

water content

and 95%

compaction.

• Higher CBR

obtained with a

more non-

plastic fines.

• Plastic fines

reduce CBR

Non-Plastic Sands:

gd in kN/m3, P200 in %, R is Krumbein

roundness (use 0.6), BC = bentonite

content (%)

CBR = -361 + 32.4gd - 1.93P200 -

264R

Plastic Sands:

CBR = -7.6gd + 4.25 BC +

178R

0

100

200

300

400

500

600

700

800

0 200 400 600 800 1000 1200

Resili

ent M

odulu

s (

MP

a)

Bulk Stress (kPa)

Resilient Modulus

θ = bulk stress

k1 and k2 = fitting parameters

Measured externally (traditional) and internally (modern)

M

r=k

1qk2

Summary resilient modulus (SRM) at bulk stress = 208 kPa.

0 100

100 103

200 103

300 103

400 103

0 200 400 600 800

ESS 1

ESS 4

ESS 5

ESS 7

ESS 14

Base

Reference

Subbase

Reference

Mr (k

Pa)

sb (kPa)

Resilient Modulus: BC < 6%

Many foundry sands have modulus falling between conventional subbase & base.

Tested at optimum water content & 95% compaction. Bulk Stress (kPa)

Re

silie

nt

Mo

du

lus

(kP

a)

SRM ≈ 140 MPa

0 100

100 103

200 103

300 103

400 103

0 200 400 600 800

ESS 2

ESS 6

ESS 8

ESS 9

ESS 10

ESS 11

ESS 12

ESS 13

Base

ReferenceSubbase

Reference

Mr (k

Pa

)

sb (kPa)

Resilient

Modulus:

BC > 6%

More plastic

foundry sands

(higher

bentonite

content) have

lower modulus

Bulk Stress (kPa)

Re

silie

nt

Mo

du

lus

(kP

a)

SRM ≈ 110 MPa

Resilient Modulus of Foundry Slag

• Recommend

SRM = 100-120

MPa. Similar to

foundry sand,

but drains

readily.

• Use as base or

subbase.

SRM ≈ 100 MPa

0.14 m Salvaged Asphalt Base Layer

Subbase

0.115 m Grade 2 Gravel Base Course

0.125 m Asphalt Layer

0.84 m Breaker run

0.84 m Breaker Run

0.60 m

B. Ash

0.84 m

F. Sand

0.84 m

F. Slag

Soft Subgrade (ML or CL)

1 < CBR < 4

100 kPa < qu < 150 kPa

Full-Scale Field Test: Wisconsin

State Highway 60

Pavement

Structure

0

500

1000

1500

2000

2500

3000

3500

4000

Ela

stic M

od

ulu

s (

MP

a)

Working Platform (Subbase)Season May, 2005

Control

(W)

F/Slag F/Sand B/Ash Control

(M)

F/Ash Geocell GC GG Control

(E)NonW

GT

GT

0

500

1000

1500

2000

2500

3000

3500

4000

Ela

stic M

od

ulu

s (

MP

a)

Working Platform (Subbase)All Seasons

Control

(W)

F/Slag F/Sand B/Ash Control

(M)

F/Ash Geocell GC GG Control

(E)NonW

GT

GT

(There are 5 outlier points from 4000 to 10000 MPa in F/Ash Section) (a)

(b)

Field Performance:

Five Years After Construction

• Foundry sands compact like fine textured soils with a bell-shape compaction curve. True or False?

• Foundry sands have comparable CBR and modulus as conventional base course materials. True or False?

• Field data have shown that foundry sands and slags can perform comparable to conventional construction materials in the field. True or False?

• Foundry sands with higher bentonite content have higher CBR and modulus. True or False?

Recap Poll # 2 – True or False

Retaining Structure Backfill/Structural Fill

• Shear strength of foundry sands.

• Interface shear strengths with woven geotextile and geogrid.

• Pullout with geotextile and geogrid.

Conventional

Retaining Wall

Mechanically

Stabilized Wall

0

20

40

60

80

100

0 10 20 30 40 50 60

Sh

ear

Str

ess (

kP

a)

Normal Stress (kPa)

ca (kPa)f

aSoil

28.050oFoundry Sand A

16.739oFoundry Sand B

19.243oFoundry Sand C

28.042oFoundry Sand D

5.542oPortage Sand

8.342oBase Sand

A

DC

B

BaseSand

PortageSand

Soaked

f ~ 40o

c’ ~ 0

Unsoaked:

f ~ 40o

c’ varies

Direct Shear Strength of Foundry Sands

Compacted at optimum water content and maximum dry unit weight

LVDT

Load Cells

Porous Stone Substrate

Soil

Pressurized

Air Bladder

LVDT

Geosynthetic

Direction of

Displacement

Track

Lower

Shear Box

Clamp Geosynthetic

Clamp

Large-Scale (D 5321) Direct Shear Machine

Geogrid

Woven

Geotextile

Frictional Efficiencies

E(%) = tand’/tanf’ x 100

Geotextile:

Base Sand - 83%

Foundry Sands - 61 to 74%

Geogrid:

Base Sand - 96%

Foundry Sands - 51 to 71%

d’ = interface friction angle

f’ =internal friction angle

Retaining Wall and Structural

Fill Design Recommendations

for Foundry Sands

• f’ = 40o, c’ = 0

• E = 55% for geogrids

• E = 65% for geotextiles

• Compact dry of optimum water content

Material Friction Angle

Outwash sand 37o

Bottom ash 44o

Foundry slag 38o

Recommendations for Foundry Slags

Slag

Sand

Ash

• f’ = 38o, c’ = 0

• E = 90% (geogrid)

• E = 80% (geotextile)

Particle crushing

Particle crushing can occur at higher

stresses (> 400 kPa, ~ 30 m deep)

Using Foundry Slag in Deep Fills

Slag

Sand

Particle Size Curves Showing Crushing of Slag Under High Stress

Slight reduction in particle size due to compaction.

Substantial reduction in particle size due to crushing at high stress.

For deep fills, measure shear strength and compressibility for site-specific conditions.

Drainage & Foundry Sands

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

0 5 10 15 20

Laboratory Data

Mean of Field Ks

SDRI

Hyd

raulic

Co

nductivity (

cm

/sec)

Bentonite Content - By Weight (%)

13

2

Foundry

sands are

poorly

draining

unless

bentonite

content is low.

4

6

8

10

12

14

16

18

4 5 6 7 8 9 10 11 12

P200

= 6.8% + 0.73BC(%)Fin

es C

on

tent,

P2

00 (

% <

0.0

75 m

m)

Bentonite Content, BC (%)

Fines Content & Bentonite Content

• Foundry sands have much higher friction angle than their base sand. True or False?

• Geogrids have higher efficiency than geotextiles when used as reinforcement with foundry sand or slags. True or False?

• Foundry slags are more compressible under high stress than natural quartz sands. True or False?

• Except for the highest bentonite contents, foundry sands drain well. True or False?

Recap Poll # 3 – True or False

Sand 68%

Fly Ash 18%

Water 12%

Cement 2%

Foundry Sands in Flowable Fill

• Flowable slurry mixed & delivered like concrete.

• Modest strength, but excavatable

• Trench backfill, underground void backfill, pipeline grouting.

Strength and Mix Design

Use water-cement ratio of

9 to 12 to ensure

strength in correct range

(0.3 – 1.0 MPa).

Flow just right

Too low!

Good Flow Too Low

Flow Test

Ensuring Adequate Flow

Water-Solids Ratio to Achieve Target Flow

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20

Foundry SandFoundry Sand and Fly Ash

Wa

ter-

So

lids R

atio

Bentonite Content of Sand (%)

Mass of Sand = 2000 gMass of Cement = 80 gMass of Fly Ash (if present) = 500 g

Sands with more bentonite require more water to achieve target flow of 200 mm. Bentonite binds with water, increasing viscosity of mix.

• Flowable fill is designed to be adequately strong, but not so strong that it cannot be excavated. True or False?

• The water required in a flowable fill increases with bentonite content. True or False?

• A water-cement ratio within 9 – 12 will achieve appropriate strength. True or False?

Recap Poll # 4 – True or False