SIP

Ultra Thin Concrete Pavements:Addressing the design issues

• Louw du Plessis

•

HVSIA 11 – 13 August 2014

HVS Program update:GPGRT and CSIR

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Linking APT to reality: Retrospective analysis of HVS predictions vs true real life performance

• History of UTRCP testing• Mechanistic analysis of as-built information of

test pavements• Comparing HVS testing results with true

performance• Mechanistic analysis on results• Latest testing results (2013 – 2014)

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UTRCP History: The Roodekrans Experiment

© CSIR 2011

© CSIR 2011 www.csir.co.za

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Experimental section layoutSections 1 to 7

Section 1 2 3 4 5 6 7

Surfacing

75 mm SFRC

75 mm SFRC

75 mm SFRC

50 mm CRCP

75 mm CRCP

100 mm CRCP

100 mm butt

jointed concreteLeveling

layer25 mm ETB

50 mm ETB

25 mm ETB

Support

140 mm foam

concrete125 mm stabilized subbase

In situ compacted gravel

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Traffic

Design traffic 40 000 to 60 000 E80sActual traffic by June 2005

39 months 500 000 E80s 35% overloaded (10% : 400% overloaded)4 E80s per vehicle1.4 E80s per axle4 wet seasons

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Mechanistic evaluation

Pavement structure3 layers - concrete surfacing, stabilized base, subgrade

Stiffness concrete28 GPa

Stiffness of base1000 MPa

Stiffness of subgrade support Between 140 MPa and 70 MPa

Focus on tensile stress of the concrete Indicate potential for cracking

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Mechanistic evaluation (4)

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200Slab Thickness (mm)

Max

. Ten

sile

Stre

ss (M

Pa) 300 unbonded

300 bonded

1500 unb.

1500 bonded

12000 unb.

12000 bonded

Base stiffnesses

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Mechanistic evaluation

98.00%

100.00%

102.00%

104.00%

106.00%

108.00%

110.00%

112.00%

40 50 60 70 80 90 100 110

Percentage of subgrade stiffness

Perc

enta

ge o

f ten

sile

str

ain

50 mm 75 mm 100 mm 140 mm

SG Reference stiffness = 140 MPa

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Significance

Incorrect to conclude - thin concrete sections can be used for any application

Understanding of reasons for performancePostulated - reason good performance

Relatively strong support and high bond provided by the substructure

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Mamelodi Investigation

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GAUTENG DPTRW – 20T PROJECTS MAMELODI STREETS

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-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 50 100 150 200 250 300 350 400 450 500

Def

lect

ion

(mm

)

CBR(

%)

Chainage (m)

CBR and Deflection results: Road 3

CBR: Base layer CBR: Subbase CBR: Subgrade Max Deflection (mm) Unmarked areas

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Road #(mm) std Base std Subbase std Subgrade std

1 1.01 0.21 18.7 8.9 15.5 9.6 12.9 7.702 1.00 0.30 46.0 41.0 16.0 11.6 14.9 20.553 1.15 0.59 13.2 6.1 8.4 2.6 12.1 9.594 0.95 0.18 12.8 3.7 12.0 2.4 11.0 2.005 0.84 0.47 9.8 2.6 6.5 2.5 10.3 0.506 1.35 0.47 13.8 4.3 7.8 1.9 6.0 2.45

Ave 1.05 0.37 19.02 11.08 11.0 5.11 11.2 7.13

DCP CBR derived resultsRSD Deflections

Summary of Ave deflections and CBR data

Compare to Roodekrans: CBR = 75

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HVS Evaluation : R80

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SOSHANGUVE BUS ROUTE

Earthworks and shapingof in-situ layer

Competed UTRCP roadwith side drain

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Ave deflection (excl ash section) = 0.59mm

Comparison: Soshanguve & R80 HVS UTRCP sites

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Analysis performed using EverFE 2.24 and cncPave 404,

Assumed material properties 30-40 MPaconcrete:

MOR = 4.0 MPa, ft = 2.0 MPa

E = 30 GPa, Poisson’s ratio 0.2

Coef. of thermal expansion: 12 10-6 /ºC

Pavement surface temperature : 40 ºC

Temperature differential: 4 ºC

Analysis

© CSIR 2011

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MOR = Flexural strength of concrete

Because it’s a specialised test the compressive strength are used (fc)

MOR = k√fc K = spring stiffness (MPa/mm):

stress on SG/deflection ≈ 0.74

Thus for a 30MPa concrete MOR = 4 MPa

SG is modelled as a dense liquid (winkler spring)

- Westergaard 1926 -

Modulus of Rupture (MOR)

© CSIR 2011

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Deflection survey: Average Deflections 0.

0-0

.5-1

.0-1

.5-2

.0-2

.5

Mamelodi

Defle

ctio

n [m

m]

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

R80

Def

lect

ion

[mm

]

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

Shoshanguve

Def

lect

ion

[mm

]

Mamelodi: 1.0 mm HVS R80: 0.7 mm Shoshanguve 0.6 mm

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Matching measured deflections Mamelodi

Layer Thickness Modulus [MPa] Poisson’s ratio Concrete slab 50 30 000 0.2 Granular 150 70 0.35 Granular 150 60 0.35 Granular 150 50 0.35 Subgrade ∞ varied N/A

Subgrade modulus [MPa]

Spring stiffness (k) [MPa/mm]

Deflection [mm]

Maximum tensile stress [MPa]

50 0.258 0.659 7.62 40 0.206 0.696 7.68 20 0.103 0.859 7.90 10 0.052 1.13 8.17 5 0.026 1.58 8.46

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Comparing stresses at different sections

© CSIR 2011

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cncPave Analysis of the Mamelodi structure

Pavement Model as above with a SG moduli of 15 Mpa (to get to the ave surface deflection of 1mm with a 80kN load)

Loading according to cncPave Urban load Spectra

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cncPave Analysis of the Mamelodi structure

The results from the analysis indicate:• There is a 50% probability that the surface area with shattered concrete will

be excessive after 7 years, and• a 80% probability that shattering will be excessive after 10 years.

• Analysis in agreement with what was observed: an unacceptably short life for a concrete pavement, which are typically designed to last past 20 years.

cncPave decision criteria UTRCP

Decision variable Good Acceptable Excessive

% shattered concrete below 0.2 % 0.2 % to 0.5 % over 0.5 %

% pumping below 2 % 2 % to 5 % over 5 %

Crack spacing 0.3 m - 0.5 m 0.2 m to 0.7 m below 0.2 m or over 0.7 m

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Design approach: Transfer function of the new American Mechanistic Empirical Pavement Design Guide (MEPG 2004)

© CSIR 2011

0.00.10.20.30.40.50.60.70.80.91.0

1.E+00 1.E+05 1.E+10 1.E+15 1.E+20 1.E+25 1.E+30

stre

ss/s

tren

gth

ratio

Load repititions to failure (N)

NCHRP 1-37A

1

1

bd

MORaN

=σ

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Latest HVS testing

• Original UTRCP design of 50mm is for Residential and low vol road applications. CSIR & GDRP is looking at a 75mm version (with more steel) and better support to be used in higher order roads such as provincial roads (typically up to 10 million E80s during lifespan)

• Preliminary results look very promising, indicating that this technology can be used with success on higher order roads.

• Parallel to this CSIR & GDRT are continuing its research on the performance of RCC using a high percentage of hand labour

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Design Traffic ES 10: 3 - 10 million ES 1: 0.3 - 1million E80s

Ref 193 mesh (200x200 Ref 193 mesh (200x200x 5.6mm dia) x 5.6mm dia)

75mm UTRCP (30MPa)150mm C3 (parent G4) (1.5 - 3 Mpa, 97% MOD AASHTO) G4 (min CBR 80, 98% MOD AASHTO)150mm C4 (Parent G6) (UCS 0.75 - 1.5MPa, 95% MOD AASHTO) G6 (min CBR 25, 95% MOD AASHTO)150mm

Ref 289 mesh (100x200 x 5.6mm dia)

G6 (min CBR 25, 95% MOD AASHTO)G9 Roadbed prep 93% MOD AASHTO

3.5m

100m

Test sections

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75mm UTRCP Construction

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RCCUTRCP

Slide Number 1Linking APT to reality: Retrospective analysis of HVS predictions vs true real life performanceSlide Number 3Slide Number 4Experimental section layout�Sections 1 to 7Slide Number 6Slide Number 7Traffic Mechanistic evaluationMechanistic evaluation (4)Mechanistic evaluationSignificance Mamelodi InvestigationGAUTENG DPTRW – 20T PROJECTS MAMELODI STREETSSlide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23SOSHANGUVE BUS ROUTESlide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 3675mm UTRCP ConstructionSlide Number 38Slide Number 39