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Flowable Fill aka
Controlled Low-Strength Material
Charles Pierce
Civil & Environmental Engineering
University of South Carolina
4thAnnual South Carolina
Count on Concrete Conference
October 4, 2006
What isControlled Low-Strength Material?
Cement
+
Fly Ash
+
Fine Aggregate
+
Water+
[Admixtures]
=
CLSM
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ACI 229
Organized in 1984
Published 229R-94
Revised 229R-99
Reapproved in 2005
ACI Committee Reports
intended for guidance in
planning, designing, executing,
and inspecting construction.
ASTM
C09 Concrete and Concrete Aggregates
NOT THIS COMMITTEE
D18 Soil and Rock
D18.15 Stabilization with Admixtures
WHY?
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ASTM Standard Tests
Standard Practice for Sampling Freshly Mixed CLSM[D5971-01]
Unit Weight, Yield, Cement Content, and Air Content(Gravimetric) of CLSM [D6023-02]
Flow Consistency of CLSM [D6103-97]
Ball Drop on CLSM to Determine Suitability for LoadApplication [D6024-02]
Preparation and Testing of CLSM Test Cylinders[D4832-02]
Controlled Low-Strength Material
Is not concrete but is produced like concrete using the same materials.
Is not soil but, in many applications, has hardened properties
similar to compacted or stabilized earthen fill {hence
ASTM D18.15}.
Is somewhere in between CLSM is a self-compacted, cementitious material used
primarily as a [flowable] backfill as an alternative to
compacted fill [ACI 229R-99].
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Comparison
Mechanicalcompaction
Self-leveling, noequipment needed
Placement
1600-2000 kg/m3
[ 100-125 pcf ]
1840-2320 kg/m3
[ 115-145 pcf ]Density
< 0.3 MPa
[ < 50 psi ]
< 2.1 MPa
[ < 300 psi ] *
28-Day
Compressive
Strength
Compacted
Earth Fill
Typical
CLSMProperties
* By definition, must be less than 1,200 psi [ACI 229R-99].
CLSM has an Image Problem
Several terms are currently used to describe this
material, including flowable fill, unshrinkable fill,
controlled density fill, flowable mortar, plastic
soil-cement, soil-cement slurry, and other
various names [ACI 229R-99].
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State DOT Terms for CLSM
0 2 4 6 8 10 12 14 16 18
Flowable Fill
CLSM
Flowable Backfill
Controlled Density Fill
Flowable Mortar
Cement Mortar Flowable Backfill
Controlled Low Strength Backfill
Controlled Low Strength Flowable Fill
Flowable Concrete Fill
Flowable Select Material
Lean Mix Backfill
Low Strength Mortar Backfill
Slurry Cement Backfill
Structure Backfill (Flow-Fill)
Number of States
Advantages
Easy to place
Versatile
Fast return to
traffic
Will not settle
Can be excavated
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Applications
Backfills (e.g. pavement patches)
Structural fills
Pavement bases
Conduit bedding
Erosion control
Void filling
CLSM Placement
Bridge Approach
Orangeburg SC
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Cincinnati OHCourtesy of Rick Roth
Cincinnati OH
Courtesy of Rick Roth
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Cincinnati OHCourtesy of Rick Roth
Cincinnati OH
Courtesy of Rick Roth
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Cincinnati OHCourtesy of Rick Roth
Sumter SC
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Sumter SC
Sumter SC
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BackfillCourtesy of Tom Fox
Structural FillCourtesy of Tom Fox
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Void FillCourtesy of Tom Fox
Example Mixture Proportions (PCY)
41530008050-100WY
5002673None185AL
458 or 541250060050SC
200-5002800-300015-25020-50OK
WaterSSD FAFly AshCementState DOT
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Setting and Hardening
Setting time is the time when the CLSM
transitions from fluid-state to hardened-
state [< 24 hours]
Hardening time is when CLSM has sufficient
bearing capacity to support construction
loads [up to 2-3 weeks]
Hardening [ASTM D6024]
< 3 in. Diameter
Based on person
stomping on
surface [50 ft-lb]
Shortcomings Indentation diameter of 5.5 in.after 24 hrs.
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Penetration Resistance : Time
0
200
400
600
800
1000
1200
2 4 6 8 10 12 14
Elapsed Time (hrs. )
MortarPenetrationResistance(psi)
0
1000
2000
3000
4000
5000
6000
7000
8000
MortarPenetrationResistance(kPa)
Accelguard Standard (calcium c hloride)
Accelguard NCA (non-chloride)
Pocket
Penetrometer
(1.0 kg/cm2)
Pocket
Penetrometer
(> 4.5 kg/cm2)
Kelly Ball < 76 mm
Setting Time
Hardening Time
Effect of Accelerating Admixtures
50
60
70
80
90
100
110
0 10 20 30 40 50 60 70 80
Time (hrs.)
KellyBallI
ndentationDiameterAt5Dro
(mm)
Accelguard Standard (Calcium Chloride)
Accelguard NCA (Non-Chloride)
Control
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Strength : w/cm Ratio and Time
0
100
200
300
400
500
600
700
800
900
0 20 40 60 80 100
Time (days)
U
nconfinedCompressiveStrength(kPa)
w/b = 0.69
w/b = 0.82
w/b = 0.97
w/b = 1.00
w/b = 1.05
w/b = 1.14
Effect of Accelerating Admixtures
0
50
100
150
200
0 10 20 30 40 50 60
Time (days)
AverageUCS(psi)
0
200
400
600
800
1000
1200
1400
AverageUCS(kPa)
Accelguard Standard (calcium ch loride)
Accelguard NCA (non-chloride)
Control
Manual Excavation
Mechanical Excavation
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Questions?
For More Information
Conclusions (1)
State DOT Specifications Vary Widely
Prescriptive
Performance
Hybrid
Cement and Fly Ash Contents More Variable
than Fine Aggregate and Water Contents
Limited and Variable Field Testing of Flowability
and Setting and Hardening Time
ASTM Standard Test Methods for CLSM not often
s ecified
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Conclusions (2)
Wide Range of 28-Day Strengths
Some exceed CLSM limit
Minimum and maximum strength specifications needed
for excavatable and non-excavatable mixtures
Specifications Likely to Evolve as DOTs Gain
Experience
Slump Test
Slump
Requirements (in.)
0-5 or 6-8
3-10
7 min. 8 min.
9-11
10-12
Slump (in.)Flowability
> 8High
6-8Normal
< 6Low
ACI 229R-99
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Penetration Resistance Tests
(2) DCP
IL: 1.5 in. per blow at 3 days
Rebar Test
NM: 6 < blows < 25 to drive #6 rebar 12 in.
using 15 lb. fence driver at 24 hrs.
NV: #4 rebar does not penetrate surface
Pocket Penetrometer
MT: 2.5 tsf minimum at 24 hrs.
Setting and Hardening
Requirements
0
5
10
15
20
25
30
35
Not Specified Time Tested Engineer
Setting and Hardening Acceptance
N
umberofStates
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Strength Measurements
0
5
10
15
20
25
30
35
40
Not Specified 3 Day 7 Day 14 Day 28 Day 56 Day 90 Day 180 Day
Test Age
NumberofStates
20-1500 psi
Strength Measurements
ASTM D4832
6 states
ASTM C39 or AASHTO T23
7 states
Cylinder Size 4 x 8 in. (2)
3 x 6 in. (1)
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Temperature Restrictions
Ambient Temperature: 7 States
30-40F minimum
Mixture Temperature: 4 States
40F min. (3) or
50F min. (1)
Ground Temperature: 2 States Not on frozen ground
Freezing Protection
None, 9
24 Hours, 2
36 Hours, 10
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Flowability Requirements
Observed: Self-leveling / Self-compacting /
Not Specified, 15
Observed, 12
Measured, 20
How Flowability is Measured
0
2
4
6
8
10
12
14
Slump Spread Flow: CRD-C611-80
Test Method
NumberofStates
MA AllowsSlump or Spread
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