Topic 5 - Material Characterization
Transcript of Topic 5 - Material Characterization
Topic 5 – Material Characterization
Dr. Christos Drakos
University of Florida
Topic 5 – Material Characterization
1. Introduction
What material properties have we used up to now?
• Most paving materials are not elastic, but experience some permanent deformation after each load application
• If the load is small compared to the strength of the material and is repeated for a large number of times, the deformation is almost recoverable and can be considered elastic
Pavement design inputs covered in previous topics:• Predicted stresses and strains – load magnitude • Traffic – load cycles
Topic 5 – Material Characterization
Resilient Modulus (MR)
Time
Load
Time
Def
orm
atio
n
εr
εpr
dRM
εσ
=
Type and duration of loading is supposed to simulate that occurring in the field
Topic 5 – Material Characterization
1. Surface Course• Layer that comes to contact with traffic; normally contains the highest
quality material2. Base
• Provides additional load distribution and contributes to drainage and frost resistance
3. Subbase (optional)• Functions primarily as structural support but it can also help with
drainage and frost action4. Subgrade
• Native soil – the only non-engineered material in the pvt structure
Typical Flexible Pavement Structure
SUBBASE COURSE (Optional)
BASE COURSE
SUBGRADE (SOIL)
AC Decreasing Stiffness
Topic 5 – Material Characterization
Subgrade performance generally depends on:1. Load bearing capacity; subgrade must be able to support
loads passed on from the pavement structure2. Moisture content; it tends to affect a number of subgrade
properties including load bearing capacity3. Shrinkage and/or swelling; some soils shrink or swell
depending upon their moisture contentRemedies for poor subgrade conditions:1. Remove and replace; subgrade soil can be removed and
replaced with higher quality fill2. Stabilization; adding an appropriate binder – such as lime,
portland cement or emulsified asphalt – can increase subgrade stiffness and/or reduce swelling tendencies
3. Additional base layers; include a subbase, or increase thickness of base
Topic 5 – Material Characterization
Subgrade Seasonal Variations
Normal MR
50,000 psiFrozen MR
Thaw MR
FreezeTime
ThawTime
RecoveryTime
NormalTime
Total Time = 12 Months
MR
Time
Topic 5 – Material Characterization
2. Design Resilient Modulus (Base & Subgrade)
2.1 Correlations
Maybe there is information already available
Also:• MR=1500(CBR)• MR=1155+555(R)
Topic 5 – Material Characterization
• Basically a penetration test• Piston penetrates soil at constant rate – 0.05 in/min• Pressure is recorded• Take the ratio to the bearing capacity of a standard rock• Range: 0 (worst) – 100 (best)
2.1.1 California Bearing Ratio (CBR)
CBR =Pressure to cause 0.1” penetration to the sample
Pressure to cause 0.1” penetration for standard rock
Topic 5 – Material Characterization
2.1.1 California Bearing Ratio (CBR)
PistonDeflection dial (loading)
Deflection dial (swelling)
Proctor
6” Ø
Sample 4.5”
Surcharge (confinement)
Topic 5 – Material Characterization
5 or lessOH
15 or lessCH LL > 50%
10 or lessMH
5 or lessOL
15 or lessCL LL < 50%
15 or lessML
Fine-grained soils
5 - 20SC
10 - 40SM
10 - 40SP
20 - 40SW
20 - 40GC
20 - 60GM
30 - 60GP
40 - 80GW
Coarse-grained soils
CBR RangeUSC Soil TypeGeneral Soil Type
2.1.1 California Bearing Ratio (CBR)
Topic 5 – Material Characterization
• Resistance value of a soil determined by stabilometer• Closed-system Triaxial test• Apply vertical pressure• Measure horizontal pressure induced in the fluid
2.1.2 Stabilometer (R-value)
115.2100100
2
+⎟⎟⎠
⎞⎜⎜⎝
⎛−×⎟⎟
⎠
⎞⎜⎜⎝
⎛−=
h
v
pp
D
R
pv & ph = Vertical and horizontal pressure respectivelyD2 = displacement of stabilometer fluid to increase ph from 5 to
100 psi, measured in revolutions of a calibrated pump handle
Topic 5 – Material Characterization
2.1.2 Stabilometer (R-value)
Pressure Gauge TestingHead
BottomPlunger
SampleFluid under pressure
160 psi
160 psi
Apply the vertical pressure and then measure the resulting horizontal pressure
115.2100100
2
+⎟⎟⎠
⎞⎜⎜⎝
⎛−×⎟⎟
⎠
⎞⎜⎜⎝
⎛−=
h
v
pp
D
R
Topic 5 – Material Characterization
2.2 In-situ Testing (Plate Loading Test)
• Circular plate 30 in Ø; series of plates used to minimize bending
• Apply load at constant rate to reach 10 psi • Pressure held constant until the deflection increases no more
than 0.001 in/min for three consecutive minutes• Use average dial reading to determine the deflection
∆=
pk
k = Modulus of subgrade reactionp = pressure on the plate (10 psi)∆ = deflection of the plate
Topic 5 – Material Characterization
2.2 In-situ Testing (Plate Loading Test)
Reaction (Steel Beam)
∆
Pressure GaugeDeflection Dial @ 1/3 Points
Hydraulic Jack
∆=
pk
Figure 7.36 – Correlation of k with MR
Topic 5 – Material Characterization
2.3 Laboratory Testing (Triaxial Test)
Topic 5 – Material Characterization
2.3 Laboratory Testing (Triaxial Test)
Sample
= Confining Pressure (σ2,σ3)= Deviator Stress (σd)
σ1
σ2
σ3
In Triaxial cell (cylinder): σ2=σ3
Deviator Stress:Axial stress in excess of the confining pressure in Triaxial cell
31 σσσ −=d
What can affect the results?
Level of confinement
State of confinement defined by the first invariant
321 σσσθ ++=
σ3
σdσ1
Topic 5 – Material Characterization
• For Granular subgrade:– MR = function (confinement)– k1 & k2 experimentally determined values
2.3.1 Triaxial Test – Granular Material
Run Triaxial test at certain levels of confining pressure and vary the deviator stress. (Example 7.2 Huang)
log θ, psi
log
MR,
psi
k2
xk1
21
kR kM θ×=
Topic 5 – Material Characterization
2.3.1 Triaxial Test – Granular MaterialSample Conditioning1. Set the confining pressure to 5 psi, and apply a deviator
stress of 5 psi, and then 10 psi, each for 200 repetitions2. Set the confining pressure to 10 psi, and apply a deviator
stress of 10 psi, and then 15 psi, each for 200 repetitions3. Set the confining pressure to 15 psi, and apply a deviator
stress of 15 psi, and then 20 psi, each for 200 repetitions
Resilient Modulus TestAfter sample conditioning the resilient modulus test follows a constant confining pressure-increasing deviator sequence, and the results are recorded at the 200th repetition of each deviator stress
Topic 5 – Material Characterization
2.3.1 Triaxial Test – Granular MaterialTest Procedure1. Set the confining pressure to 20 psi, and apply a deviator
stress of 1, 2, 5, 10, 15 and 20 psi2. Reduce the confining pressure to 15 psi, and apply a
deviator stress of 1, 2, 5, 10, 15 and 20 psi3. Reduce the confining pressure to 10 psi, and apply a
deviator stress of 1, 2, 5, 10, and 15 psi4. Reduce the confining pressure to 5 psi, and apply a deviator
stress of 1, 2, 5, 10, and 15 psi5. Reduce the confining pressure to 1 psi, and apply a deviator
stress of 1, 2, 5, 7.5, and 10 psi; stop the test after 200 repetitions of the last deviator stress level or when the specimen fails
Topic 5 – Material Characterization
2.3.1 Triaxial Test – Granular Material
(psi) (psi) (mils) (µε) (psi) (psi)1 0.264 66 15151.5 612 0.496 124 16129.0 625 1.184 296 16891.9 65
10 2.284 571 17513.1 7015 3.428 857 17502.9 7520 4.420 1105 18099.5 801 0.260 65 15384.6 462 0.512 128 15625.0 475 1.300 325 15384.6 50
10 2.500 625 16000.0 5515 3.636 909 16501.7 6020 4.572 1143 17497.8 651 0.324 81 12345.7 312 0.672 168 11904.8 325 1.740 435 11494.3 35
10 3.636 909 11001.1 4015 3.872 968 15495.9 451 0.508 127 7874.0 162 0.988 247 8097.2 175 2.224 556 8992.8 20
10 3.884 971 10298.7 2515 5.768 1442 10402.2 301 0.636 159 6289.3 42 0.880 220 9090.9 55 2.704 676 7396.4 8
7.5 3.260 815 9202.5 10.510 4.440 1110 9009.0 13
1
20
15
10
5
Resilient Modulus, MR
Stress Invariant, θ
Confining Pressure, σ3
Deviator Stress, σd
Recoverable Deformation
Recoverable Strain, εr
(4) Distance GagenDeformatioeRecoverabl=εr
rd
εσ
=RM
3d 3σ+σ=ϑ
Topic 5 – Material Characterization
2.3.1 Triaxial Test – Granular Material
y = 3686x0.3511
1000
10000
100000
1 10 100
Stress Invariant, θ (psi)
Res
ilien
t Mod
ulus
, MR
(psi)
351.0R 3686M θ×=
Topic 5 – Material Characterization
2.3.2 Triaxial Test – Cohesive Material
Run Triaxial tests at certain values of deviator stress and varythe confining pressure. (Example 7.3 Huang)
σd, psi
MR,
psi
k2
k1
k3
k4
)( 231 dR kkkM σ−+=
)( 241 kkkM dR −+= σ2kd <∀σ
2kd >∀σ
• For Fine-grained (cohesive) subgrade:– MR = function (deviator stress, σd)– k1, k2, k3 & K4 experimentally determined values
Topic 5 – Material Characterization
• To determine subgrade MR, Asphalt Institute suggests:– Confining stress σ3 = σ2 = 2 psi– Deviator stress σd = σ1 - σ3 = 6 psi
• For granular material:– For example use data from Fig 7.8
• For fine-grained material:– For example use data from Fig 7.9
2.3.3 Asphalt Institute Subgrade Characterization
Topic 5 – Material Characterization
5.9449123960 35.0
12
=⋅=
⋅= kR kM θ
2.3.4 Granular material example
k1 = 3960
k2 = 0.35
Topic 5 – Material Characterization
2.3.5 Fine-grained material example
2kd >σ
5910)2.56(3885600)( 241
=−+=−+= kkkM dR σ
Topic 5 – Material Characterization
3. Hot-Mix Asphalt3.1 Structural Layer Coefficient• Used in AASHTO design procedure• Describes the quality of the material• Function of MR & position in the pavement
3.2 Marshall Test• Used in the Marshall Mix Design procedure• Performed on cylindrical specimens• Measure Stability (fail load) and Flow (deformation)
3.3 Cohesiometer Test• Used to measure the cohesion of cemented materials • Apply load at controlled rate until failure
Why?
Topic 5 – Material Characterization
3. Hot-Mix Asphalt (cont.)
Topic 5 – Material Characterization
4. Bases4.1 Untreated Granular Base
Topic 5 – Material Characterization
4.2 Stabilized Granular Base
Bituminous Treated Cement Treated
Topic 5 – Material Characterization
5. Sub-Bases
Topic 5 – Material Characterization
6. DrainageImportant to keep water away from the pavement structure
6.1 Detrimental effects of water:• Reduces strength of unbound material & subgrade• Causes pumping, faulting, cracking & shoulder deterioration• Pore-pressure increase Pumping of fines Loss of
support– Load goes over saturated base & soil– Pore-pressure increases– Water is incompressible; moves up
• Causes heaving – swelling of soils• Pore-pressure within the AC layer causes stripping, durability
cracking• Frost action (in Northern climates)
Topic 5 – Material Characterization
6.2 Sources of water:i. Seepageii. Raise of water tableiii. Infiltrationiv. From proximity of water table
– Capillary moisture held in the pores from surface tensionv. Vapor movement
– Movement of water associated with fluctuating temperature and pressure
Topic 5 – Material Characterization
6.2 Sources of water:
Topic 5 – Material Characterization
6.3 Protecting the Pavement Structure:Need to minimize availability of water
• Impervious surface/shoulders. How? (sealants)• Drainage to remove water quickly (Ditch)• Drainage layer for subsurface water
Design phase / Construction
Three drainage installations for subsurface water:1. Drainage layer or blanket2. Longitudinal drain3. Transverse drain
Can be performed after construction
Topic 5 – Material Characterization
6.4 Drainage Deficiencies for Pavements with Ditch6.4.1 Typical Pavement with a Ditch
Topic 5 – Material Characterization
6.4.2 Water infiltrating from rutted shoulder
6.4.3 Water infiltrating due to debris caused ponding
Topic 5 – Material Characterization
6.4.4 Water infiltrating due to differential settlement
Topic 5 – Material Characterization
6.5 Subsurface Drainage
Base Course as drainage layer
6.5.1 Drainage layer / Blanket
Topic 5 – Material Characterization
6.5.2 Longitudinal drainage
Topic 5 – Material Characterization
6.5.3 Transverse drainageSame concept as longitudinal drainage, but in this case the drainage runs across the lanes
Where would we use the transverse drain?