Widening the Scope of Pavement Materials for Use in the ...

Widening the Scope of Pavement Materials for Use in the Provision of Low Volume Sealed Roads

Andrew Otto, John Rolt, Kenneth Mukura, Leah Musenero

Presenters: Andrew Otto (TRL) and Kenneth Mukura (TRL)

Acknowledgements

• The UKAid for providing the funding through the ReCAP programme.

• The participating countries: Ghana, Mozambique, Uganda and Zambia for contributing to and participating in field and laboratory activities, and data analysis.

Presentation Topics

1. Background2. Study methodology3. Proposed revisions4. Selected case studies5. Conclusions and further research

recommendations

1. Background Challenges faced in provision of LVRs:• Large proportions of road network in Sub-

Saharan Africa are gravel and earth – passability, dust, accidents, etc

• Increasingly dwindling road material sources amid more restrictive land and environment laws

• Market forces – increasing construction costs• Maintenance backlogHence necessary to widen the range of materials using evidence-based approaches.

1. Background (continued ..1)

‘Development of Guidelines and Specifications for Low Volume Sealed Roads through Back Analysis’Objectives:• To review of performance of existing LVSRs• To improve guidelines and specifications for

pavement design and construction• To build capacity of counterparts • To disseminate the findings to enhance

uptake and embedment


Phase 1:Created the database (DB) and added initial data and information in DB (lvroadsdata.com).

Phase 2:Trained counterparts on the use of the DB, refined the DB and added more data. Also, identified gaps for further studies to refine specifications and design catalogues.

Identified gaps:o LVSRs with 10+ yrs in areas of high rainfallo Traffic loading in the range 0.5 MESA to 1MESA – very important

gap o LVSRs with weak subgrades for LVSRs.


Phase 3:• Carried out field

investigations to fill critical gaps identified in Phase 2,

• Analysed data and revised specifications, catalogues

• Disseminating findings.

2. Study methodology • Carried out Phase 3 with the

objective to fill gapso Selected new test sections – 24

test sections in 4 countries (Ghana, Uganda, Zambia and Mozambique)

o Carried out field and lab investigations and combined results with the rest of the data in the DB (Total = 110 sections

o Carried out performance analysis to fill data gaps

o Proposed revisions to catalogue and specifications.

2. Study methodology (continued ..3)

• Study population (110 Sections)

2. Study methodology

• Existing Design CatalogueSubgradeCBR

Traffic (MESA)

< 0.1 0.1 – 0.3 0.3 – 0.5 0.5 – 1.0 1.0 – 3.0

S2 (3-4%) 150 G65125 G30150 G15

150 G65150 G30175 G15

175 G80150 G30175 G15

200 G80175 G30175 G15

200 G80225 G30200 G15

S3 (5 – 7%) 150 G65100 G30100 G15

150 G65150 G30125 G15

175 G65150 G30125 G15

200 G80150 G30150 G15

200 G80275 G30

S4 (8-14%) 150 G65125 G30

150 G65200 G30

175 G65200 G30

200 G80150 G30

200 G80200 G30

S5 (15 – 29%) 125 G65100 G30

150 G65125 G30

150 G65150 G30

175 G80120 G30

200 G80120 G30

S6 (>30%) 150 G65 175 G65 200 G65 200 G80 200 G80

2. Study methodology (continued ..4)

• New structural numbers vs existing

SubgradeClass

Traffic (MESA)

< 0.1 0.1 – 0.3 0.3 – 0.5 0.5 – 1.0 1.0 -3.0

S1 (<3%) 1.65 1.65 1.65 2.00 2.50

S2 (3%- 4%) 1.65 (1.70) 1.65 (1.95) 1.65 (2.05) 1.65 (2.30) 2.00 (2.58)

S3 (5% - 7%) 1.45 (1.45) 1.45 (1.70) 1.45 (1.85) 1.45 (2.10) 1.60 (2.15)

S4 (8% - 14%) 1.25 (1.25) 1.45 (1.55) 1.45 (1.65) 1.45 (1.85) 1.50 (1.85)

S5 (15% -29%) 1.00 (1.00) 0.90 (1.25) 0.90 (1.35) 1.30 (1.50) 1.35 (1.54)

S6 (≥ 30%) 0.80 (0.7) 0.80 (0.85) 0.80 (0.95) 0.80 (1.0) 0.9 (1.06)

Note: values in brackets represent those in existing catalogue

3. Proposed revisions• Proposed New Design Catalogue

SubgradeClass (CBR)

Traffic (MESA)<0.1 0.1-0.3 0.3-0.5 0.5-1.0 1.0-3.0

S1 (<3%)Note 1

150 G45 150 G45 150 G60 175 G60 200 G60150 G25 175 G25 175 G25 175 G25 200 G25150 G15 150 G15 150 G15 150 G15 300 G15

S2 (3%- 4%)150 G45 150 G45 150 G60 150 G60 175 G60125 G25 150 G25 150 G25 150 G25 175 G25125 G15 150 G15 125 G15 150 G15 150 G15

S3 (5% - 7%)150 G45 150 G45 150 G60 150 G60 150 G60125 G25 150 G25 125 G25 150 G25 175 G25100 G15 100 G15 125 G15 150 G15 150 G15

S4 (8% - 14%)150 G45 175 G45 150 G60 150 G60 175 G60100 G15 150 G15 150 G15 175 G15 200 G15

S5 (15% -29%)175 G45 200 G45 150 G60 150 G60 150 G60

100 G25 100 G25 125 G25S6 (≥ 30%) 175 G45 200 G45 175 G60 200 G60 225 G60Note 1: If the subgrade is expansive, then a capping of at least 600 mm compacted in 3 equal layers isrequired. The capping should have a PI of between 10 and 20 but the material should not be expansive.The 150 G15 can form part of the capping. Other additional treatments for expansive clays should also beapplied.

3. Proposed revisions (continued …2)

• Particle size distribution (fine grained)- Ghana


• Particle size distribution (cobbles and boulders)


• Particle size distribution (bases and sub-bases)

0102030405060708090

100

0.01 0.1 1 10 100

Perc

enta

ge Pa

ssin

g (%

)

Particle Size Distribution (mm)

Recommended Grading Envelope for Bases and Subbases

Grading of GoodPerforming Bases

Grading of GoodPerforming Bases

GradingSpecifications forBasesGradingSpecifications forBasesRecommendedGrading Spec

RecommendaedGrading Spec


• Plasticity characteristicsBases (> 0.5MESA) Sub-bases (> 0.5MESA)

PI PM LL PI PM LL

Max 23 1206 44 27 1755 50

Min 0 0 0 2 182 19

Mean 11 335 30 13 564 30

50th Percentile 13 275 31 11 416 30

90th Percentile 18 708 37 18 918 36

80th Percentile 16 545 35 16 784 35

10th Percentile 6 0 24 7 191 24

20th Percentile 6 0 27 9 273 25


• Plasticity characteristicsSubgrade Property Upper limit of design traffic classclass 0.1M 0.3M 0.5M 1M 3MS2 PI <16 <16 < 16 < 13 < 13

PM < 540 < 540 < 540 < 270 < 270PI <12 <12 <9 <9 <6PM <300 <240 180 180 90

S3 PI <16 <16 < 16 < 13 < 13PM < 540 < 540 < 540 < 270 < 270PI <15 <15 <12 <9 <6PM 320 320 240 180 90

S4 PI < 16 < 16 < 16 < 13 < 13PM < 540 < 540 < 540 < 270 < 270PI <15 <15 <12 <9 <6PM 320 320 240 180 90

S5 PI < 16 < 16 < 16 < 13 < 13PM < 700 < 540 < 540 < 270 < 270PI <15 <15 <12 <9 <6PM 400 320 240 180 90

S6 PI < 16 < 16 < 16 < 13 < 13PM < 700 < 700 < 540 < 270 < 270PI <15 <15 <12 <12 <6PM 550 500 240 240 90

Notes: Recommended Specifications are in italics

4. Selected case studies• Some examples to inspire confidence

4. Selected case studies (continued ..1)

• Thin amalgamated Seals• 20+ years old• Heavy traffic


• Surfacing induced failure


• Surfacing induced failureSection Crack

Index (0-25)

Surface Thickn

ess (mm)

Rut Depth (mm)

Flakiness Index (%)

Bitumen Content

Extraction (%)

Mean 90% ile

Samfya – Musaila. Section 1 (Cracked) 20 10 5 9 - 5.8

Samfya – Musaila. Section 2 (Good) 0 10 7 13 19 4.3

Section Layer Mean FMC/OMC

Mean In-situ DCP-CBR (%)

Samfya - Musaila 1 (Cracked)Base 1.0 114Sub-base 1.1 137Subgrade 1.1 30

Samfya - Musaila 2 (Good)Base 0.8 212Sub-base 1.0 141Subgrade - 28


• Drainage (defying the norm)


• Crown height anomaliesSection Layer Crown

Height (m)

FMC/OMC

DCP-CBR

Rut Depth (mm)

Section Condition

90th

%ile

Macia – Chokwe 1 (Coarse Macadam base)

Sub-base0.2

0.9 4011 Good

Subgrade 1.6 50

Macia – Chokwe 2 (Cement treated sand base)

Sub-base1.5

0.7 968

Poor (Potholes, patching

and cracks)

Subgrade 2.9 10


• Crown height anomaliesSection Layer Crown

Height (m)

FMC/OMC

DCP-CBR

Rut Depth (mm)

Section Condition

90th

%ile

Boane – Namaacha 1Sub-base

0.21.0 45

16

Poor (Potholes, patching

and cracks)

Subgrade 1.8 13

Boane – Namaacha 3Sub-base

0.70.8 91

8 GoodSubgrade 1.2 49


• Comparison of pavement balance curvesBalance Curve of the poor section Balance Curve of the good section

5. Conclusions• Failures mostly induced by surfacing defects or poor drainage;

not structurally induced (low rutting). Also no subgrade failure • Most of the pavements studied carried much more traffic(up

to 5MESA) than what the existing LVSRs specifications suggested they would carry.

• LVSR definition: ≤ 3 MESA, traffic volume defined by LoS (D or E), use locally available material.

• It is recommended to design long-life LVR pavements where possible; this involves the use of Macadam and Telford bases where materials are locally available (at low cost). These can then be sealed with thin, amalgamated surfacings.

• It is recommended that partner countries adopt the revised catalogues and specifications.

5. Further research recommendations

• A detailed study involving some advanced investigations into the performance of surfacings and specialised tests on materials (bituminous and non-bituminous) is required.

• Need standard way of testing or specifying very coarse bases and sub-bases.

• Need to develop appropriate construction techniques (both labour-based and mechanized) to encourage the wider use of very coarse bases and sub-bases.

Thank You

Contacts:

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