In Situ Stabilization of Pavement Base Courses

Roads Pavement ForumThursday, May 17, 2001

Introduction

Clients– Gautrans– C&CI– SANRAL

Laboratory and Heavy Vehicle Simulator results from R243/1

One building block in a long-term process Focus on mechanical properties and

structural bearing capacity

Layout of presentation

Purpose of the study Materials Experimental plan Results for each laboratory test Conclusions

Purpose Assess the benefits of in situ stabilization in terms

of improvements in the mechanical properties and structural bearing capacity of the treated material

Mechanical properties– Resilient modulus– Compressive and tensile strength– Flexibility– Shear strength

Bearing capacity– Effective fatigue– Permanent deformation

Materials Basic material

– Ferricrete milled from HVS test site, including existing surfacing and upper portion of subbase

Treatment processes– Cement (Laboratory)

» 2 % cement

– Foam and cement (Laboratory and HVS)» 2 % cement, 1.8 % residual binder

– Emulsion and cement (Laboratory and HVS)» 2 % cement, 1.8 % residual binder

Materials: Untreated Nominal maximum aggregate size 37.5 mm

0.01 0.1 1 10 100

0

20

40

60

80

100

Sieve Size (mm)

Per

cent

age

pass

ing

by m

ass

Milled material Natural ferricrete

Grading envelope for G4 shown as a reference

Materials: Untreated Classification

– Grading G4– Atterberg limits G5– CBR G7

UCS, ITS, Flexural Beam Test

Treated materials only Foam and emulsion tested at 2 binder

contents– 1.8% residual binder content + 2% cement– 3.0% residual binder content + 2% cement

Flexural beam test Strain at crack initiation Indication of flexibility

LVDT#1 Model

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0 500 1000 1500 2000 2500 3000

Strain (Microstrain)

Str

ess

(MP

a)

Data Model

Strain at break: 335Stress at break (kPa): 383

Stiffness at break (MPa): 1143Initial stiffness (MPa): 3432

Beam Test No. ftb7Moisture Content 10.3%

Cement Content 2%% Binder 3

Dry Density 2030 kg/m³

Foamed Bitumen Beam

Triaxial Tests

Untreated and treated materials– 1.8% residual binder content, 2 % cement

Variables– Density– Saturation – Confining pressure– Stress ratio

Triaxial tests Static triaxial tests

– Shear strength parameters

Dynamic triaxial tests– Resilient modulus– Permanent

deformation response

Compressive strength:UCS Results

Cement-treated ferricrete has highest UCS Addition of binder reduces the UCS

0 1 2 3 4

0

1000

2000

3000

4000

Residual bituminous binder content (%)

UC

S (

kPa) Cement-treated

Emulsion-treated

Foam-treated

Tensile strength:ITS Results

Cement-treated ferricrete has highest ITS Addition of binder reduces the ITS

0 1 2 3 4

100

200

300

400

500

600

Residual bituminous binder content (%)

ITS

(kP

a)

Cement-treated

Emulsion-treated

Tensile strength:ITS Results

Samples dried to equilibrium MC at ambient temp 72 h in oven at 40º C

1 2 3 4 5

100

200

300

400

500

Residual bituminous binder content (%)

ITS

(kP

a)

Dry (mix design)

Flexibility:Flexural beam test

Flexibility only increases at higher binder content

0 1 2 3 40

200

400

600

Residual bituminous binder content (%)

Str

ain-

at-b

reak

(m

icro

stra

in)

Foam-treated Emulsion-treated Cement-treated

Elastic stiffness (Mr):Dynamic triaxial tests

0

1000

2000

3000

4000

Experimental section

Res

ilient

mod

ulus

(M

Pa)

Ferricrete Cement Emulsion Foam

Estimation of stiffness values

–Use regression model for untreated ferricrete

–Use ranges for treated materials

Comparative results:Average strain-at-break

0

100

200

300

400

500

174141

273

148

356

Bituminous binder content

Str

ain-

at-b

reak

(m

icro

stra

in)

0.0 1.8 3.0 1.8 3.0

Cement-treated

Emulsion-treated

Foam-treated

Comparative results: Effective fatigue life

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Mill

ion

Bituminous binder content

Str

ain-

at-b

reak

(m

icro

stra

in)

0.0 1.8 3.0 1.8 3.0

Cement-treated

Emulsion-treated

Foam-treated

SAMDM transfer functionsWorking strain of 125 b–values from flexural beam test

Comparative results:Cohesion

0

100

200

300

400

82

335 329303

Material

Coh

esio

n (k

Pa)

Ferricrete Cement Emulsion Foam

Comparative results:Friction angle

30

40

50

60

40

51

4749

Material

Fric

tion

angl

e (D

eg)

Ferricrete Cement Emulsion Foam

Comparative results:Shear strength at 3 = 50 kPa

0

500

1000

1500

2000

2500

529

2241

1943 1929

Material

She

ar s

tren

gth

(kP

a)

Ferricrete Cement Emulsion Foam

Comparative results:Bearing capacity (9 % PD)

1.0E+05

1.0E+06

1.0E+07

1.0E+08

Material

Bea

ring

capa

city

Ferricrete Cement Emulsion Foam

HVS tests:Pavement structure

30 mm Asphalt 250 mm FTG / ETG

- 1,8 % residual

bitumen

- 2 % cement In situ material In situ subgrade

HVS tests:Materials

Foam-treated

Emulsion-treated

HVS tests:Programme 2 x 100 m long experimental sections

– Foam-treated– Emulsion-treated

1st Phase of HVS testing– 80/100 kN tests (350 000/150 000 repetitions)– Completed

2nd Phase of HVS testing– 40 kN tests (750 00000 repetitions)– In process

HVS tests:Deflection result

-100

0

100

200

300

400

500

600

700

0 500 1000 1500 2000Distance (mm)

Def

lect

ion

(m

icro

ns)

10 1000 3000 105000 126500 229100

Conclusions:UCS, ITS and Flexibility

Complex relationship between UCS, ITS and– Percentage binder– Cementation – Curing procedure

Flexibility– No increase in flexibility at low binder content– Increase in flexibility and effective fatigue life at higher binder

content– Strain-at-break slightly higher for foam-treatment at higher binder

content Effective fatigue life models to be validated with HVS

results

Conclusions:Resilient modulus

Increase in resilient modulus with treatment Untreated ferricrete

– Resilient modulus influenced by» Relative density and saturation» Stress state

Treated ferricrete– Resilient modulus dictated by the stabilizing agent and

largely insensitive to the above parameters– No significant difference between stabilizing agents

Resilient modulus values to be validated by HVS back-calculation results

Conclusions:Shear strength and plastic strain

Shear strength increases with treatment Vastly improved bearing capacity in terms of

permanent deformation– Cement-treatment shows highest benefit– No significant difference between foam- and

emulsion-treatment Models need to be calibrated with HVS results

Conclusions:General

Only considered mechanical properties Other properties to investigate

– Permeability and erodibility– Workability– Shrinkage cracking– Time to opening the road – early strength

Improved understanding of mechanical properties and behaviour

Properties of stabilized material significantly different from untreated material even at low binder content

First structural design models for these types of materials