Study of the Behaviour of Lateritic Materials in Road Pavements - C. Santos

CARLOS HENRIQUE ALVES DOS SANTOS
STUDY OF THE BEHAVIOUR OF LATERITIC
MATERIALS IN ROAD PAVEMENTS
Supervisor: Prof. Dr. Elói Figueiredo
Co-Supervisor: Prof. Luís Quaresma
Universidade Lusófona de Humanidades e Tecnologias
Faculty of Engineering
Lisbon
2017

CARLOS HENRIQUE ALVES DOS SANTOS
STUDY OF THE BEHAVIOUR OF LATERITIC
MATERIALS IN ROAD PAVEMENTS
Dissertation submitted as partial fulfilment of the degree of MSc (Specialization in
Structures and Constructions)
Dissertation defended in public examination at the
Universidade Lusófona de Humanidades e
Tecnologias on May 18, 2017, before the jury,
appointed by the order of nomination No.: 143/2017
of May 4, 2017, with the following composition:
President: Prof. Dr. António Manuel Gardete Mendes Cabaço
Examiner: Dr. Ana Cristina Freire (Main researcher of the LNEC Transport Department,
Laboratório Nacional de Engenharia Civil - LNEC)
Supervisor: Prof. Dr. Elói João Faria Figueiredo
Vowel: Prof. Dr. Sandra Cristina Gil Vieira Gomes
Co-Supervisor: Prof. Luís Quaresma
Universidade Lusófona de Humanidades e Tecnologias
Faculty of Engineering
Lisbon
2017

To my mother, who fought her whole life for my studies

Carlos Henrique Alves dos Santos
Study of the behaviour of lateritic materials in road pavements
Universidade Lusófona de Humanidades e Tecnologias Faculty of Engineering
i
Acknowledgements
I express here my gratitude to all those who, directly or indirectly, contributed to the
development, enrichment and conclusion of this work.
To the Roads Authority of Malawi, for granting me permission to use data and test results
collected during the M1 road rehabilitation project.
To Harold Bofinger, for sharing his vast and prestigious knowledge about road pavements
and for his friendship.
To Robert Geddes, for suggesting the research on this subject and for providing valuable
information, essential for the conclusion of this dissertation.
To Dr. Simon Gillett, Ramsey Neseyif and the organization Roughton International Ltd. for
enabling the conditions for the conclusion of this work.
To my supervisors Luís Quaresma and Dr. Elói Figueiredo for the guidance, clarifications,
suggestions and incentive during the completion of this work.
To my classmates for their support.
To my family for the support.

ii

iii
Summary
The subject of this dissertation arose from the observation, during a professional assignment
of the author in Malawi, of the impressive structural capacity of the lateritic materials found
on the M1 highway, which, although not meeting the minimum requirements of traditional
specifications, performed satisfactorily despite having surpassed the pavement design life.
Although there are several studies on the peculiarities of such lateritic materials, there is no
consensus on the reasons for their exceptional performance in road pavements. It was
attempted on this dissertation to establish several factors that justify the impressive and
eventual unsatisfactory behaviour of these materials, through the analysis of various
laboratory and in situ tests carried out on the M1 highway in Malawi.
It is important to note that the M1 highway, which is the subject of the case study of this
dissertation, can be divided in two main sections: in the first, the base and sub-base layers of
the pavement are composed of lateritic materials, which are low cost and of low
environmental impact; the second, is comprised of a high cost crushed stone aggregate base
layer. The first section, although not complying with traditional or regional specifications,
performed similarly to the second section, even when subjected to considerably higher
traffic volumes.
Several publications on this subject were analysed to provide the context of this dissertation,
in addition to the specifications developed exclusively for the lateritic materials, as the
traditional specifications neglect certain mechanical characteristics unique to lateritic
materials.
Through the numerous test results presented and analysed in the case study of this
dissertation, the extensive literature research on the characteristics of lateritic materials, and
the analysis of several specifications developed for these materials, this dissertation aims to
contribute scientifically to the development of the subject of this work.
Keywords: Lateritic soils, laterites, sustainable materials, pavement specifications, Malawi.

iv
Abstract
O tema desta dissertação surgiu da observação, durante atividade profissional do autor no
Malawi, da impressionante capacidade estrutural dos materiais lateríticos encontrados na
rodovia M1, que apesar de não cumprirem com os requisitos mínimos das especificações
tradicionais, desempenhavam satisfatoriamente sua função, mesmo tendo a vida útil do
pavimento há muito findado.
Embora existam diversos estudos sobre as peculiaridades dos materiais lateríticos, não há
um consenso quanto às razões do seu excepcional desempenho em pavimentos rodoviários.
Tentou-se nesta dissertação estabelecer alguns fatores que justifiquem o bom e insatisfatório
comportamento desses materiais, através da análise dos diversos resultados de ensaios
laboratoriais e in situ realizados na rodovia M1 no Malawi, o caso de estudo desta
dissertação.
Salienta-se que a rodovia do caso de estudo pode ser basicamente dividida em duas secções:
a primeira, com camadas de base e sub-base do pavimento compostas por materiais
lateríticos, de baixo custo e reduzido impacto ambiental; e a segunda, com camada de base
composta por agregado britado, de custo elevado. A primeira secção, apesar de não cumprir
com as especificações tradicionais ou regionais, demostrou um desempenho similar ao da
segunda secção, mesmo quando sujeita a volumes de tráfego consideravelmente superiores.
São ainda analisadas nesta dissertação diversas publicações sobre este tema bem como
algumas especificações desenvolvidas exclusivamente para os materiais lateríticos. Expõe-se
ainda o facto de as especificações tradicionais negligenciarem certas características
mecânicas peculiares aos materiais lateríticos.
Através da quantidade significativa de resultados de ensaios apresentados e analisados no
caso de estudo desta dissertação, da extensa pesquisa literária sobre as características dos
materiais lateríticos e da análise de diversas especificações desenvolvidas para estes
materiais, busca-se contribuir de forma cientifica para o desenvolvimento do tema deste
trabalho.
Palavras chave: Solos lateríticos, laterites, material sustentável, especificações para
pavimentos rodoviários, Malawi.

v
Abbreviation and symbols
AADT –Annual Average Daily Traffic
ACV –Aggregate Crushing Value
AASHTO – American Association of State Highway and Transportation Officials
BS – British Standards
CBR –California Bearing Ratio
COMESA – Common Market for East and Southern Africa
CS –Cumulative Sum
CSIR - Council for Scientific and Industrial Research, South Africa
DNIT – National Department of Transportation Infrastructure, Brazil (Departamento Nacional de
Infraestrutura de Transportes, in Portuguese)
DCP –Dynamic Cone Penetrometer
ESA –Equivalent Standard Axles of 80 kN
FWD –Falling Weight Deflectometer
IBGE – Brazilian Institute of Geography and Statistics (Instituto Brasileiro de Geografia e
Estatísticas, in Portugues)
IRI – International Roughness Index
KIA – Kamuzu International Airport, Malawi
LEA – Latoratory of Engineering of Angola (Laboratório de Engenharia de Angola, in Portuguese)
LHS – Left Hand Side
LL – Liquid Limit
LNEC – National Laboratory of Civil Engineering, Portugal (Laboratório Nacional de Engenharia
Civil, in Portuguese)
LS – Linear Shrinkage
MCT – Tropical mini compacted (Miniatura Compactado Tropical, in Portuguese)
MDD – Maximum Dry Density
MERLIN – Machine for Evaluating Roughness using Low-cost Instrumentation
MRWA – Main Roads Western Australia
OMC – Optimum Moisture Content
PI – Plasticity Index
RA – Roads Authority, Malawi
RHS – Right Hand Side
SATCC – Southern Africa Transport and Communication Commission

vi
SN – Structural Number
TRL – Transport Research Laboratory, UK
TP – Trial Pit
USCS – Unified Soil Classification System
WACCT – Western Australia Confined Compression Test

vii
Table of contents
Acknowledgements................................................................................................................................ i
Summary .............................................................................................................................................. iii
Abstract................................................................................................................................................ iv
Abreviation and simbols........................................................................................................................ v
1 Introduction .................................................................................................................................. 1
1.1 Scope.....................................................................................................................................1
1.2 Objectives..............................................................................................................................2
1.3 Structure of the dissertation.................................................................................................3
2 The lateritic soils and the laterites................................................................................................ 5
2.1 Definition...............................................................................................................................5
2.2 Geographical distribution......................................................................................................6
2.3 Formation..............................................................................................................................7
2.3.1 Introduction...................................................................................................................7
2.3.2 Weathering....................................................................................................................8
2.3.3 Natural cementation.....................................................................................................9
2.4 Chemical-mineralogical composition..................................................................................10
2.5 Classification........................................................................................................................12
2.5.1 Introduction.................................................................................................................12
2.5.2 MCT Classification .......................................................................................................13
2.5.3 Other classifications ....................................................................................................16
3 Requirements for the use of lateritic material in road pavements ............................................17
3.1 Introduction ........................................................................................................................17
3.2 Specifications for the use of lateritic materials in road pavements ...................................18
3.2.1 DNIT Specification, Brazil ............................................................................................18
3.2.2 Main Roads Western Australia....................................................................................20
3.2.3 Specification for the selection of fine sandy lateritic soils for base layers by Nogami e
Villibor 24
3.2.4 Recommendations for Southern Africa by Gourley & Greening.................................25
3.2.5 Laboratoire Central des Ponts et Chaussées, France..................................................27
3.2.6 Recommendations developed by Charman................................................................29
3.3 Construction recommendations for lateritic materials ......................................................30
3.3.1 Introduction.................................................................................................................30
3.3.2 Distribution and homogenization ...............................................................................30

viii
3.3.3 Compaction .................................................................................................................31
3.3.4 Drying or curing of the base layer...............................................................................32
3.4 Financial advantages of the use of lateritic materials in road pavements .........................32
3.5 Conclusion...........................................................................................................................33
4 Case study – M1 Highway in Malawi...........................................................................................35
4.1 Introduction ........................................................................................................................35
4.2 Existing Information on the construction of the section of study ......................................37
4.3 Traffic analysis.....................................................................................................................38
4.4 Analyses of materials and mechanic characteristics of the pavement...............................41
4.4.1 Introduction.................................................................................................................41
4.4.2 Laboratory tests ..........................................................................................................41
4.4.3 Dynamic Cone Penetrometer – DCP ...........................................................................49
4.4.4 Falling Weight Deflectometer – FWD..........................................................................60
4.5 Pavement performance ......................................................................................................68
4.5.1 Visual inspection .........................................................................................................68
4.5.2 Ruts..............................................................................................................................71
4.5.3 IRI.................................................................................................................................75
4.6 Subsections with unsatisfactory behaviour ........................................................................77
4.6.1 Introduction.................................................................................................................77
4.6.2 Subsection R1 – km 74 to km 77.................................................................................78
4.6.3 Subsection R2 – km 95 to km 97.................................................................................79
4.6.4 Subsection R3 - km 103 to km 105..............................................................................80
4.6.5 Conclusion...................................................................................................................81
4.7 Test results analysis.............................................................................................................82
4.7.1 Compilation of the results for the sections with base composed of crushed stone
aggregate and lateritic material..................................................................................................82
4.7.2 Correlation of results...................................................................................................85
4.8 Results analysis conclusions................................................................................................90
5 Final considerations ....................................................................................................................93
5.1 Conclusions .........................................................................................................................93
5.2 Future works .......................................................................................................................95
References...........................................................................................................................................96
Annexes.................................................................................................................................................. I
Annex 1 – DCP Results........................................................................................................................I

ix
Annex 2 – Laboratory tests results....................................................................................................II
Annex 3 – FWD Results ....................................................................................................................III
Annex 3a – FWD Results...............................................................................................................III
Annex 3b – Retro-analysis result for some sections using the ELSYM5 program........................III
Annex 4 – Visual Inspection .............................................................................................................IV
Annex 4.a – Visual Inspection - Photos ........................................................................................IV
Annex 4.b – Visual Inspection - Recordings .................................................................................IV
Annex 5 – Ruts...................................................................................................................................V
Annex 6 – IRI.....................................................................................................................................VI

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Table of Figures
Figure 1 - Geographic distribution of lateritic materials (Pinard et al, 2014)..........................7
Figure 2 – Schematic representation of tropical weathering profile (Charman, 1988) ............9
Figure 3 - Composition of lateritic materials (Pinard et al, 2014) .........................................11
Figure 4 – Tests methods for the MCT classification [Adapted from (Villibor et al, 2000)] 15
Figure 5– Defects related to excessive compaction of clayey lateritic materials (Nogami &
Villibor, 2009). .......................................................................................................................31
Figure 6 – Average annual rainfall in Malawi (DCCMS, 2006)............................................35
Figure 7 – Location of the highway case study on the map of Malawi (Nations Online
Project) ...................................................................................................................................36
Figure 8 – Schematic representation of sections of the road case study ................................40
Figure 9 – Excavation of trial pits and sampling [Photos: courtesy of Roughton International
Ltd.] ........................................................................................................................................42
Figure 10 – Dynamic Cone Penetrometer -DCP (TRL ORN 31. 1962/1993) .......................50
Figure 11 – DCP tests carried out on the M1 road, Malawi [Photos: courtesy of Roughton
International Ltd.]...................................................................................................................51
Figure 12 – Cementation state of lateritic material [Photos: Roughton International Ltd.]...51
Figure 13 – Deflection test - FWD Primax 1500 [Photos: Roughton International Ltd.] ......60
Figure 14 – Deflection Basin Parameters [Image: Roughton International Ltd.] ..................61
Figure 15 – Some common distresses found on the M1 road. [Photos: Roughton
Figure 16 – Areas of moisture variation (Ethiopian Roads Authority, 2011)........................71
Figure 17 – Method used for measuring ruts [Figure: courtesy of Roughton International
Ltd.] ........................................................................................................................................72
Figure 18 – Subsection in failure - R1 (74 + 000 to 77 + 000) [Photos: Roughton
Figure 19 – Subsection - R2 (95 + 000 to 97 + 000) [Photos: Roughton International Ltd.] 79
Figure 20 - Subsection in rupture - R3 (103 + 000 to 105 + 000) [Photos: Roughton

xi
Table of Charts
Chart 1 – Soil classification - MCT (Nogami & Villibor, 2009) ...........................................15
Chart 2 – Pavement layers profile. .........................................................................................42
Chart 3 – Particle size distribution of the lateritic material of the base layer.........................44
Chart 4 – Average particle size crushed stone aggregates - Base ..........................................45
Chart 5 – Average particle size curve of the lateritic material of the sub-layer.....................45
Chart 6 –Plasticity Index and liquid limit – Base...................................................................46
Chart 7 –Plasticity Index and liquid limit of the lateritic material - sub-layer.......................47
Chart 8 – Linear shrinkage of the lateritic material - base and sub-base................................47
Chart 9 –Lateritic material CBR - base ..................................................................................48
Chart 10 –Lateritic material CBR - sub-layer ........................................................................49
Chart 11 – Sample curve obtained with the results of the DCP test, km 4 + 200 ..................52
Chart 12 – CS of the base layer CBR obtained through the DCP tests ..................................54
Chart 13 – 10th Percentile CBR of the base layer..................................................................55
Chart 14 – CS of the sub-base layer CBR obtained through the DCP tests ...........................55
Chart 15 – 10th percentile CBR of the sub-base layer ...........................................................56
Chart 16 – CS of the subgrade layer CBR obtained through DCP tests.................................57
Chart 17 – 10th Percentile of the subgrade layer CBR...........................................................58
Chart 18 – CS of the DSN800 results.....................................................................................58
Chart 19 – DSN800 10th Percentile .......................................................................................59
Chart 20 –D0 CS for the left and right lanes...........................................................................63
Chart 21 –90th Percentile of the D0 - LHS.............................................................................64
Chart 22 –90th Percentile of the D0 - RHS.............................................................................64
Chart 23 – D0 CS for LHS & RHS combined ........................................................................65
Chart 24 –90th Percentile of D0 – LHS & RHS combined ....................................................66
Chart 25 – Percentage of the incidence of crocodile cracking according to degree of severity
................................................................................................................................................70
Chart 26 - Percentage of the incidence of longitudinal cracking according to degree of
severity ...................................................................................................................................70
Chart 27 – Ruts CS – LHS & RHS.........................................................................................73
Chart 28 – 90th percentile and average of ruts results - LHS ................................................74
Chart 29 – 90th percentile and average of ruts results - RHS ................................................74
Chart 30 – IRI CS – LHS &RHS............................................................................................75
Chart 31 – 90th percentile and average of IRI results - LHS .................................................76
Chart 32 – 90th percentile and average IRI result - RHS.......................................................77
Chart 33 – Comparison between CBR-Lab. and CBR-DCP of the base layer.......................85
Chart 34 – Correlation SN - Ruts ...........................................................................................86
Chart 35 – Correlation SN modified - Ruts............................................................................86
Chart 36 – Correlation SN – IRI.............................................................................................87
Chart 37 – Correlation SN modified – IRI .............................................................................87
Chart 38 – Correlation SN – Peak deflection .........................................................................88
Chart 39 – Correlation SN mod. – Peak deflection................................................................88
Chart 40 – Correlation Peak deflection - IRI..........................................................................89

xii
Chart 41 – Correlation Peak deflection - Rut .........................................................................90
Table of Tables
Table 1 – Conditions for the development of cementation in lateritic material (Huat et al,
2012).......................................................................................................................................10
Table 2 – Typical chemical composition of lateritic materials (Pinard et al, 2014)].............11
Table 3 – Mineral sesquioxides typically found in lateritic material (Pinard et al, 2014).....12
Table 4 – Lateritic classification systems (Charman, 1988) ..................................................16
Table 5 – Classification based on the molecular ratio SiO2/R2O3 [Adapted from (Autret,
1983)] .....................................................................................................................................16
Table 6 – Grading envelopes and maximum tolerances [Adapted from (DNIT, 2007)]........19
Table 7 – Criteria for selection of lateritic materials for base layer [Adapted from (DNIT,
2007)] .....................................................................................................................................19
Table 8 - Required classification numbers for lateritic gravel (Main Roads Western
Australia, 2003) ......................................................................................................................21
Table 9– Typical criteria for selection of lateritic gravel for base, based on granulometry and
classification tests (1)
(Main Roads Western Australia, 2003)................................................21
Table 10 – Typical criteria for selection of lateritic gravel on strength and classification tests
(Main Roads Western Australia, 2003)..................................................................................22
Table 11 –Selection criteria of lateritic gravel used in heavy duty pavements based on
granding and classification tests (Main Roads Western Australia, 2003)..............................23
Table 12 – Criteria for the selection of lateritic soil for the base layer [Adapted from
(Nogami & Villibor, 2009)] ...................................................................................................24
Table 13 – Proposed guidelines for the selection of lateritic material for base layer with
unsealed shoulders (Gourley & Greening, 1997) ...................................................................26
Table 14 – Recommended grading for bases in lateritic material (Gourley & Greening, 1997)
................................................................................................................................................26
Table 15 – Proposed guidelines for design of pavements with base layer composed of
lateritic material and unsealed shoulder (Gourley & Greening, 1997)...................................27
Table 16 – Recommended criteria for the use of lateritic material in road pavements
[Adapted from (Autret, 1983)] ...............................................................................................28
Table 17 – ESA for each traffic class [Adapted from (CEBTP, 1984)].................................28
Table 18 – Recommended selection criteria for lateritic gravel for base and sub-base of
surface-facing pavements in the tropics (Charman, 1988).....................................................29
Table 19 – Equivalent standard axles in one direction...........................................................39
Table 20 – Recommended spindles for base aggregates [Adapted from (SATCC, 1998 /
2001c)]....................................................................................................................................43
Table 21 – CBR results for base layer sections......................................................................54
Table 22 – CBR results for sub-base layer sections...............................................................56
Table 23 – CBR results for subgrade layer sections...............................................................57
Table 24 – DSN800 sections results.......................................................................................59

xiii
Table 25 – Deflection basin behaviour parameters [Adapted from (Horak, 1987)]...............61
Table 26 – D0 results sections – LHS & RHS........................................................................63
Table 27 – D0 results sections – LHS & RHS combined .......................................................65
Table 28 – Results of the parameters deflection basin and modulus of elasticity..................67
Table 29 - Modes, types and codes of degradations [Adapted from (SATCC 1998 / 2001b)]
................................................................................................................................................68
Table 30 - Classification of the severity of defects (SATCC 1998 / 2001b) .........................68
Table 31 – Ruts results sections – LHS & RHS.....................................................................73
Table 32 – IRI section results – LHS & RHS ........................................................................76
Table 33 –Subsection R1 general results................................................................................78
Table 34 – Subsection R2 general results...............................................................................79
Table 35 –Subsection R3 general results................................................................................80
Table 36 – Summary of test results obtained for different subsections of the highway.........83

Universidade Lusófona de Humanidades e Tecnologias Faculty of Engineering 1
1 Introduction
1.1 Scope
The theme of this dissertation arises from the need to demonstrate that lateritic materials,
usually excluded by traditional pavement specifications, demonstrate exceptional
mechanical behaviour when used in base and sub-base layers of road pavements.
Although this theme has been the subject of several past studies, it has been observed that
traditional specifications, with rare exceptions, continue to be adopted indiscriminately for
the use of lateritic materials in pavement. This is more evident in Africa, where such
materials are generally only used in unsealed pavements, low traffic volume roads, or in the
layers below the base layer of high traffic volume roads.
Despite the non-compliance with traditional specifications, there are numerous examples of
roads built with lateritic materials, most of which were designed for low traffic volumes, but
have unexpectedly remained in good condition, even when subjected to high traffic volumes
and years after the design life has ended, as is the case of the M1 highway in Malawi.
During the research presented in this dissertation, various sections of pavement on the M1
highway were analysed, including: sections of pavement composed of lateritic material that
exhibited satisfactory behaviour; sections of pavement composed of lateritic material that
presented unsatisfactory behaviour; and sections of the road of pavement with base
composed of crushed stone aggregate. The comparison of samples allowed establishing
correlations among the factors that may justify lateritic material performance.
The study of this theme is extremely important for the development of road networks in
developing countries where lateritic materials can be found abundantly, since most of these
countries lack sufficient physical and financial resources for the exploitation of other
materials that comply with the requirements of the traditional specifications.
Although several pertinent factors regarding the behaviour of lateritic materials exist, such
as their chemical and mineralogical composition, the focus of this dissertation is on the
mechanical characteristics and the performance of pavements constructed with such
materials.

1.2 Objectives
The primary objective of this dissertation is to provide evidence of the fact that certain
criteria of selection of pavement materials, imposed by specifications based on the
behaviour of materials from temperate climates, neglect certain peculiar characteristics of
some tropical climate materials, such as the laterites and the lateritic soils. Despite their non-
compliance with such specifications, these materials have generally demonstrated
satisfactory performance.
An extensive review of literature was carried out on the subject, aiming to explore several
studies and publications on the intrinsic characteristics of the lateritic materials, in order to
identify certain properties that may justify their remarkable behaviour. In addition, the
existing literature allowed an assessment of the feasibility of the use of lateritic materials in
base layers of sealed pavements subject to a significant volume of traffic.
In order to identify factors that justify the good behaviour of the lateritic materials in
pavements, an analysis of the mechanical characteristics of these materials was carried out
through a practical case, designated as the case study of this dissertation. The road that is the
subject of this the case study has a pavement composed of on lateritic soil base in the first
186 km, and crushed stone aggregate in the remaining extension An analysis of the data
obtained from sections composed of different materials allows a comparison of factors
pertinent to the performance of the pavement. In addition, some sections of the road that
presented unsatisfactory behaviour were analysed, in attempt to identify the factors that
contribute to the performance variation of the lateritic materials.
Additionally, evidence of the economic and environmental advantages of the use of lateritic
soils in the base layers of road pavements will be presented. The extra conservative and
constraining nature of current specifications instructs road authorities worldwide to explore
materials that meet the specifications by adopting costly alternatives, such as: the
exploitation of materials of better quality and / or transport of these from long distances; the
alteration of local materials through stabilization with lime, cement or bituminous binders;
or the attempt to improve the mechanical characteristics and grading deficiency of the
materials by mixing them with other materials of better quality.
Finally, the growing need to adopt sustainable constructive methods emphasizing the socio-
economic advantages derived from the construction of roads with low-cost and abundant
alternative materials, found in developing countries will be demonstrated.

1.3 Structure of the dissertation
This dissertation is divided in five chapters, each discussing a different topic pertinent to the
subject of this work.
The first chapter presents the scope and context of the topic of the dissertation, as well as its
importance for the interested parties, followed by the objectives and general structure of the
dissertation.
The second chapter aims to introduce the intrinsic characteristics of the lateritic materials.
Firstly, the definitions of different types of these materials, such as the laterite and lateritic
soil, are presented. Next, the geographic distribution and relevant aspects of the formation
process of these materials and their chemical-mineralogical composition are discussed, and
finally, some classification systems developed for this type of material are presented and
analysed.
The third chapter aims to introduce the main concepts of some specifications and studies
developed for the use of lateritic materials in road pavements. The specifications of the
National Department of Transportation Infrastructures of Brazil (DNIT), Main Roads
Western Australia (MRWA), Nogami and Villibor, and others are explored. Among the
specifications presented, the Brazilian specification (DNIT-098/2007-ES) stands out due to
its extensive use in thousands of kilometres of the road network of Brazil. The specification
developed by Nogami and Villibor, for economic pavements, is highlighted for its adoption
of unprecedented methods and criteria of selection of fine sandy lateritic soils for road
pavements. Finally, taking into account the particular properties of the lateritic materials,
some recommendations regarding best practice construction techniques for road pavements
with these materials are presented.
The fourth chapter refers to the case study of this dissertation, where the results of laboratory
and in situ tests carried out to evaluate the mechanical characteristics of the materials and
performance of the pavement on a 234 km section of the M1 highway in Malawi are
analysed. A discussion of the methodology used to perform each test as well as additional
components relevant to the behaviour of the pavement, such as; the number of standard
axles applied to the pavement; the climate of the region; information regarding the
construction of the road; and the geometric characteristics of the pavement layers, will
follow. In certain sections of the road the pavement has failed; an analysis of these portions
is presented to establish correlations among the factors that possibly contributed to the
satisfactory and unsatisfactory pavement behaviour. Furthermore, possible correlations
between different types of tests concerning the behaviour and mechanical characteristics of
the pavement are described. The chapter ends with an analysis of the results of the various in
situ and laboratory tests carried out, and a conclusion regarding the factors that justify the
good mechanical behaviour of the lateritic materials.
The fifth chapter is composed of a general conclusion that covers all the topics and aspects
discussed in the preceding chapters of this dissertation and some recommendations for future

works related to the design of economic road pavements constituted by lateritic materials
and innovative methods of selection of these materials.

5
2 The lateritic soils and the laterites
2.1 Definition
The definitions of the terms ‘lateritic soils’ or ‘laterites’, presented by several authors from
various fields of study, are quite variable and discrepant. These terms are sometimes used
loosely, lacking a detailed description of their formation and of the different definitions for
the same material, confusing the meaning of the term lateritic soil between practitioners of
different areas, such as engineers, geologists and agronomists, who sometimes refer to the
same material emphasizing different characteristics (Pinard & Netterberg & Paige-Green,
2014).
According to Maignien (1966), the term ‘laterite’ was first used more than 200 years ago in
India by Buchanan, who observed that such material could easily be cut into blocks while
fresh, but it hardened irreversibly on exposure to air. However, modern pedogenic
terminologies describe such material as plinthite (Pinard et al, 2014). Nevertheless,
Buchanan's definition does not apply to what is known as laterites these days, and most
African laterites do not harden irreversibly after being exposed to air (Gourley & Greening,
1997).
It should be noted that lateritic soil is not the same as laterite; the most evident differences
being its cementation state and the amount of iron and aluminium oxides in its composition
(Amu & Bamisaye & Komolafe, 2011).
There are several definitions for the term ‘laterite’; some emphasize the mineralogical
characteristics, and others the chemical characteristics of the material.
In 'As Laterites do Ultramar Português', the term ‘laterite’ is defined as a material of
vacuolar structure, often nuanced, with colours varying from yellow to red more or less
dark, consisting of a more or less continuous crust of thickness and hardness, often having
the appearance of a slag, or even containing isolated, oolitic and pisolithic concretions of
greater or lesser strength and mixed with a clayey part (LNEC& LEA & LEMMS, 1959).
The Brazilian Institute of Geography and Statistics (IBGE) defines laterite as:
"Rock formed or in formation phase through intense chemical weathering of pre-
existing rocks, including old laterites, under tropical or equivalent conditions. It is
characteristically rich in Fe and Al and poor in Si, K and Mg when compared to the
composition of the parent rock. It can be compact, solid, cohesive or non-cohesive,
earthy or clayey, with red, violet, yellow, brown to white coloration. Its mineralogical
composition generally involves iron, aluminium, titanium and manganese
oxyhydroxides, as well as clay minerals, phosphates and reinstates" (IBGE, 2004, p.
no pag.).

6
The term laterite in Malawi's Manual Design for Low Volume Sealed Roads is defined as
follows:
"A precipitate of aluminium and ferrous oxides whose behaviour is largely dependent
on the parent soil in which it is formed" (Ministry of Transport and Public Works -
Malawi, 2013, pp. 3-4)
Similarly, there are several definitions for the term 'lateritic soils'.
In ‘As Laterites do Ultramar Português’, the term lateritic soil is defined as a soil whose
clay fraction has a SiO2/R2O3 molecular ratio of less than 2.0 and presents low expansibility
(LNEC et al, 1959).
According to Gidigasu (1976), lateritic soils are all residual tropical or non-residual tropical
reddish-brown soil from the decomposition of rocks that form a chain of clay materials rich
in sesquioxides.
The definition of the term lateritic soil according to Morin and Todor is as follows:
"A soil that contains laterite; and any reddish-colored tropical soil derived from intense
weathering." (Morin & Todor, 1976, p. 6)
According to Lohnes & Handy (1968), lateritic soil is a tropical soil that has not leached or
cemented as severely as a laterite but still has a high content of sesquioxides and kaolinite as
well as primary silicates, however, they lack self-cementing properties.
Given the diversity of definitions, in the present dissertation the term 'laterite' refers to
lateritic material with a high degree of cementation and hardness. The term ‘lateritic soil’
refers to a lateritic material, which has not leached enough to form a laterite. The term
'lateritic material' will be used as a generic term referring to both laterite and lateritic soil.
2.2 Geographical distribution
Lateritic soils are typically found in regions of tropical and subtropical climates, namely
Africa, India, Southeast Asia, Australia, Central and South America (Gourley & Greening,
1997).
The distribution of lateritic soils in different regions of the globe is indicated in Figure 1.

7
Figure 1 - Geographic distribution of lateritic materials (Pinard et al, 2014)
It should be noted that due to changes of climatic zones in the geological era, lateritic soils
and laterites can occasionally be found in areas outside the tropics (Charman, 1988).
2.3 Formation
2.3.1 Introduction
The process of soil formation depends heavily on the environmental conditions where it
occurs. There are five main factors that influence the soil’s formation:
• Parent rock - Directly influences the properties of a soil;
• Climate - Mainly influences the volume of precipitation;
• Topography of the terrain - Affects the movement of water in a given terrain;
• Vegetation – Boosts the biological activity, determinant for the production of acids,
being one of the factors that determines the rate of dehydration of colloidal oxides
and also has protective effect that avoids erosions;
• Age - The geological age of the parent rock has great effect on the development of
soils.
Therefore, regions with a humid climate and high temperatures provide favourable
weathering conditions for the formation of lateritic materials (Tuncer, 1976).
According to Charman (1988), the average annual temperature required for the formation of
laterites is 25º C and the rainy season and high temperature season must coincide. The
average rainfall should be at least 750 mm. The higher the precipitation, the higher the
leaching effect will be.

8
It is difficult to identify which factor influences the formation process of lateritic soils most
significantly. However, one can intuitively speculate that the properties of a soil will be
directly dependent on the parent rock from which it has derived (Maignien, 1966).
2.3.2 Weathering
Weathering is one of the necessary components of the formation process of laterites, since it
favours the chemical and mechanical reactions necessary for its formation.
The weathering process involves the leaching of silica, the formation of sesquioxides and the
precipitation of oxides, increasing crystallization and dehydration as the rock becomes more
leached (Tuncer, 1976).
The lateritic soils or laterites are the product of a leaching process, past or current, which
produces the following effects:
• The parent rock is chemically enriched with iron and aluminium oxides and
hydroxides (sesquioxides).
• The clayey component is largely kaolinitic.
• The silica content is reduced.
This process generally produces more yellowish, brownish or reddish materials; being red
the predominating colour (Pinard et al, 2014).
The weathering can be developed through three processes: chemical weathering or chemical
alteration; mechanical weathering, or physical disintegration; and biological weathering,
which consists of physical or chemical alteration through the action of biological organisms
(Tuncer, 1976).
Chemical weathering includes the dissolution and alteration of rocks composed of minerals
into new constituents, since the minerals that form the rocks are vulnerable to the action of
water, oxygen and other chemical reagents such as the acidity of the air, rain and carbon
dioxide. Mechanical weathering consists of the disintegration of a rock into fragments,
usually caused by expansion and thermal retraction or abrasion. Biological weathering
causes rock fragmentation through the production of acids that react with minerals
increasing chemical activity (Huat et al, 2012).
The gradual alteration of the mineral elements from the rock to a residual soil completely
altered by weathering are shown in Figure 2.

9
Figure 2 – Schematic representation of tropical weathering profile (Charman, 1988)
2.3.3 Natural cementation
Natural cementation is one of the outstanding characteristics of the mechanical behaviour of
laterites and lateritic soils. Although some authors affirm that this does not always occur,
others attribute this to the good performance of these materials in road pavements.
The development of natural cementation in lateritic soils after enrichment with iron oxides
seems to be preceded by mechanisms such as chemical precipitation, crystallization and the
continuous development of cementation of the materials (Alexander & Cady, 1962).
The chemical composition alone or even the mineralogical and chemical composition
together, does not explain the cementation process of the laterites. According to Alexander
& Cady (1962), a completely cemented laterite crust, when compared to a lateritic material
found immediately below it, has practically the same chemical composition, differing only
in crystal size and water content.
Studies of lateritic materials found in Guinea showed that a material subjected to drying and
wetting cycles over a 15-year period cemented and formed a stiff crust while the same
material used on the walls of a house and kept continuously dry was still soft enough to be
scratched with a thumbnail (Alexander & Cady, 1962). Many other authors also suggest that
the main cause of cementation is the drying and wetting cycles that the material undergoes
over time.

10
Some authors suggest that the occurrence of petrification or cementation of lateritic
materials can be verified by subjecting them to drying and wetting cycles when carrying out
California Bearing Ratio (CBR) tests. The first indication of such cycles used to predict the
petrification of minerals was done by Da Silva et al (1967), where cycles of one day of
drying and four days of submersion were adopted (Pinard et al, 2014). Netterberg (1975)
concluded that the petrification effect is likely to occur in practice. However, that the mere
fact of wetting and drying any plastic material will make it denser, thus misleadingly
inducing petrification effects (Pinard et al, 2014).
Nascimento et al, (1966) analysed the degree of petrification of lateritic soils through the
ratio between the Retraction Limit (ws) and the Absorption Limit (AL), defined as the water
content of the specimen used to determine the retraction limit when placed to absorb water
in a porous plate. The inverse of the degree of petrification is designated as the degree of
absorption of the material.
Conditions for the development of self-cementation in lateritic materials, according to Huat
et al (2012), are presented in Table 1.
Table 1 – Conditions for the development of cementation in lateritic material (Huat et al, 2012)
Annual rainfall (mm) 750 - 1000 1000 - 1500 1500 - 2000
Humidity Index (1)
-40 a -20 -20 a 0 0 a +30
Dry season duration (months) 7 6 5
Material Type Rock or
Laterite hardpan
Hard
concretionary
gravels
Minimum
requirement to
concretions to
develop
Note:
(1) Humidity index according to Thornthwaite climate classification
Although there is evidence of self-cementation in pedogenic materials, it is difficult to use
such information in the selection and evaluation of such materials. Until mechanisms as self-
cementation and other factors influencing its development are better understood this can
only be considered on the basis of local experience and observation. Caution should be
exercised in approving the use of lateritic material merely on the basis of potential self-
cementation, since the base layer must still have adequate strength for opening to traffic
(Main Roads Western Australia, 2003).
2.4 Chemical-mineralogical composition
According to several researchers, the predominant minerals in lateritic soils composition are
kaolinite, gibsite and iron compounds (Tuncer, 1976).
The diagram shown in Figure 3 schematically presents the composition of lateritic soils and
laterites.

11
Figure 3 - Composition of lateritic materials (Pinard et al, 2014)1
The chemical components typically found in lateritic materials, according to Netterberg
(1985), are shown in Table 2.
Table 2 – Typical chemical composition of lateritic materials (Pinard et al, 2014)2
]
The main characteristics of the mineral sesquioxides generally found in lateritic materials
were synthesized by Netterberg, as shown in Table 3.
1
Madu, RM. (1980). The use of the chemical and physiochemical properties of laterites in their identification.
Proc. 7th
Reg. Conf. for Africa on Soil Mech. And Fndn. Eng, Accra, June 1980.
2
Netterberg (1985) Pedocretes. Chapter 10 in Brink, A.B.A. (Ed.), Engineering geology of
southern Africa, 4, 286‐307, Building Publications, Silverton. (CSIR Reprint RR 430).

12
Table 3 – Mineral sesquioxides typically found in lateritic material (Pinard et al, 2014)3
Notes:
(1) Compiled from several authors and Dixon & Weed (1989). Other non-sesquioxide minerals
include kaolinite, haloisite, metahaloisite, illite, smectite, chlorite and allophane; Organic matter may
also be present.
(2) Mostly from Klein & Hurlbut (1993) and Dixon & Weed (1989).
(3) A field term used to refer to natural hydrous iron oxides of uncertain identity (Klein & Hurlbut,
1993).
(4) Also given as Fe5O7 (OH) 4H2O, Fe2O3.2FeOOH 2.6H2O, Fe5HO8.4H2O, etc.
2.5 Classification
2.5.1 Introduction
The methodology of classification of traditional soils, when applied to lateritic soils,
presents a series of limitations and deficiencies that go from the aspects of geotechnical
classification of soils to the criteria of selection of materials for the use in road pavements.
Traditional classification systems such as HRB-AASHTO and USCS, widely adopted for
decades, considers fundamentally for its classification method the aggregates particle sizes,
the liquid limit and plasticity index of the materials. However, such indices are insufficient
and incapable of distinguishing the main types of tropical soils, such as lateritic and
saprolithic soils, inadequately designated as ‘residual’. The classification of soils HRB-
AASHTO is widely used for road pavements, but it classifies and hierarchizes the tropical
soils inappropriately. Therefore, certain soils that would be classified in a certain group
3
Netterber, F. (1988, partially updated to 2013). Laterites, Lateritic Soils and ferricretes in Road Construction.
A Review (Unpublished).

13
considered unsuitable for use in road pavements, can behave satisfactorily, if they are
lateritic soils (Portal da Tecnologia, 2010).
There have been several attempts to classify lateritic soils and laterites in the past, but none
of the proposed classification systems have been universally accepted (Tuncer, 1976).
Mohr & Van Baren (1954), point out that a classification system should have a
predetermined objective and most classification systems do not classify soils according to
their mechanical behaviour.
According to Maignien (1966), classification systems can be divided into (a) analytical
classification, based mainly on morphological characteristics inclined to genetic
considerations of the soil, and (b) synthetic classification based on genetic factors or
properties of pedogenetic factors or processes.
Traditional soil classification systems were used satisfactorily for the classification of soils
from temperate climate. However, it can be observed that such classification systems can not
accurately predict the mechanical behaviour of laterites and lateritic soils. The reason for
this failure may be the variation in plasticity and particle size characteristics of these soils,
resulting from the disruption the soils natural structure during sampling and excavation.
Therefore, the mechanical properties of laterites and lateritic soils are not reproducible. To
overcome these difficulties, some authors defend the classification of laterites and lateritic
soils for engineering purposes, based on the weathering degree of the material. Leaching
becomes an important factor in the case of tropical soils, simply because the environment in
the tropics leads to intense weathering (Tuncer, 1976).
2.5.2 MCT Classification
The MCT classification is probably the only system specifically developed to select tropical
soils for use in road pavements. It is a classification system extremely elaborated and widely
used in the state of São Paulo, in Brazil.
This classification system was developed by Nogami and Villior, in view of the difficulties
and deficiencies pointed out in the use of the traditional classifications developed for cold
and temperate climate soils when used tropical environments soils.
This classification system is based on a series of tests and procedures whose results
reproduce the actual conditions of compacted tropical soils layers, when used in pavements,
through the geotechnical properties that reflect the in situ behaviour of these layers (Portal
da Tecnologia, 2010).
The MCT classification divides the soils into two main groups: soils with lateritic behaviour;
and soils with non-lateritic behaviour (saprolithics), which are consequently divided into the
following subgroups:
Soils of lateritic behaviour, designated by the letter 'L':

14
• LA: Quartz lateritic sand;
• LA ': Sandy lateritic soil;
• LG ': Clayey lateritic soil.
Soils of non-lateritic behaviour (saprolithics), designated by the letter 'N', are subdivided
into four groups:
• NA: sands, silts and mixtures of sands and silts with predominance of quartz and / or
mica grains, non-lateritic;
• NA': mixtures of quartz sand with non-lateritic behaviour fines (sandy soils)
• NS': non-laterite silty soils
• NG': non-lateritic clayey soils
This methodology comprises two groups of tests: Mini-CBR and related and Mini-MCV and
related. The characteristics of soils suitable for pavement base layers can be obtained from
the Mini-CBR and related tests. Generally, after compaction, a series of properties, such as:
bearing capacity (Mini-CBR); expansion; contraction; infiltrability; permeability; etc., are
determined. The Mini-MCV and related tests provide parameters for the determination of
the coefficients c 'and e' which, in turn, allow the classification of soils according to the
MCT methodology (Nogami, & Villibor, 2009).
The coefficient c ', designated as the deformation coefficient, is obtained through the Mini-
MCV and related tests. This coefficient indicates the clayiness of the soil, a high coefficient
c’, above 1,5 characterizes the clays, whereas a coefficient of less than 1,0 characterizes the
non-plastic sands or silts. Other types of soils such as silty sands, clayey sands, sandy clays
and silty clays are usually found in the interval between 1,0 and 1,5.
The coefficient e', derives from the following equation:
where,
d’ – is the slope of the rectilinear part of the dry compaction curve of the mini-MCV test at
12 blows.
Pi – is the percentage of mass disaggregated in the loss of mass by immersion test (Nogami,
& Villibor 1995).
The tests that make up this classification system can be observed in Figure 4.

15
Figure 4 – Tests methods for the MCT classification [Adapted from (Villibor et al, 2000)]
After the coefficients c' (abscissa axis) and e' (ordinates) are determined, the soil
classification is obtained using the chart presented in Chart 1.
Chart 1 – Soil classification - MCT (Nogami & Villibor, 2009)
The MCT classification can also be carried out using rapid test methods. Further information
on the MCT classification method can be obtained in the publication; 'Construção de
Pavimentos de Baixo Custo com Solos Lateríticos', by Nogami & Villibor (1995).
Mold
Hammer
(2270g)
(
Load
Soil
Soil Soil Soil
Soil Soil
Soil
Compaction Mini-CBR Expansion Permeability
Infiltrability Contraction Loss of mass
by immersion
Load
Porous
Plate

16
2.5.3 Other classifications
There are other classification systems for lateritic or tropical soils, but as mentioned, none
has been adopted on a global scale by roads authorities from countries of tropical climates.
A classification method for lateritic materials, proposed by Charman (1988), based on the
weathering and consequently the age of the material is indicated in Table 4.
Table 4 – Lateritic classification systems (Charman, 1988)
Little (1969) presented a classification system for residual soils based on the degree of
decomposition of the material. Ruddock (1969) suggested a classification system based on
the topographic position and depth of the sample as well as depth of the water table, which
are in fact factors that have a direct influence on the degree of weathering of the material.
Lohnes & Derimel (1973) suggested using specific weight, void index and degree of
weathering for the classification of tropical soils. However, none of these proposed
classification systems were widely adopted.
In the publication 'Latérites et Graveleux Latéritique' (Autret, 1983) a classification based
on the silica-sesquioxides molecular ratio (SiO2 / R2O3), which differentiates laterites from
lateritic soils and non-lateritic material, is presented in Table 5.
Table 5 – Classification based on the molecular ratio SiO2/R2O3 [Adapted from (Autret, 1983)]
Ratio S/R Material
< 1,33 Laterite
> 1,33 < 2,00 Lateritic Soil
> 2,00 Non Lateritic Materials
The silica-sesquioxides molecular ratio is also mentioned as a lateritic material classification
criterion by LNEC et al (1959) and is also adopted as a parameter for selection of lateritic
soils for base layers by the Brazilian specification DNIT-098/2007 ES.

17
3 Requirements for the use of lateritic material in road
pavements
3.1 Introduction
Conventional specifications have generally been developed based on the behaviour of
materials found in temperate and cold climates. However, it has been observed that these
specifications cannot accurately predict the mechanical performance of some materials
found in tropical climates, such as laterites and lateritic soils. Thus, such specifications are
considered too conservative to be adopted for pedogenic materials, since they are quite
restrictive regarding the particle size, bearing capacity and plasticity of materials. Moreover,
they do not take into account other unique aspects of the lateritic materials, such as low
swelling and permeability, as well as acceptable bearing capacity even in high water content
conditions (Nogami & Villibor, 1995).
Lateritic materials seldom meet the requirements of traditional specifications, mainly in
terms of grading and plasticity characteristics. However, there are numerous examples in the
literature of the satisfactory behaviour of these materials, despite non-compliance with
specified minimum criteria of these specifications (Pinard et al, 2014).
The use of traditional specifications to select materials from tropical climates results in the
rejection of local materials, which are generally found in abundance. Despite having
demonstrated good behaviour when used on road pavements, lateritic materials are generally
replaced or altered, thus making the construction of roads costly and consequently hindering
the development of the road network of countries with scarce financial resources.
There are several examples in the literature of the mismatch of traditional specifications
when used for tropical climate materials. For example, according to the recommendations of
the Portland Cement Association for cement stabilized materials, a structural equivalence
coefficient equal to 1.0, that is, negligible structural effect, should be adopted for cement
stabilised materials with a strength of less than 28 kg/cm2
. However, although the structural
capacity values of the more than five thousand kilometres of cement stabilised material
layers executed in Brazil rarely exceed this value, they nevertheless present satisfactory
behaviour (Jornadas Luso-Brasileiras de Engenharia Civil, 1967). This is just one example
among many that demonstrates that traditional specifications should sometimes be used with
some critical sense, especially when used in environments and climates completely different
from those in which they were initially developed.
Due to the need to adapt the selection criteria of traditional specifications to the reality of the
mechanical behaviour of tropical materials, some road authorities have developed their own
specifications for the use of lateritic materials in road pavements. There are also
specifications derived from studies or surveys of the behaviour of these materials in road
pavements, as well as from successful experience in their application.

18
The methodology adopted for the selection of lateritic material for roads pavements differs
considerably among the specifications presented in this chapter. The acceptance criteria for
materials adopted by different road authorities vary considerably according to local
experience in the use of this material. As a general rule, the plasticity index (PI) and the
liquid limit (LL) are the criteria that differ most from those established by the traditional
specifications. In some cases, these criteria are even considered obsolete for the selection of
lateritic materials and consequently unused.
The equivalent standard axle (ESA) is one of the factors that differs most among the
specifications developed for the use of lateritic material in road pavements. Some
authorities, mainly in Africa, restrict the use of these materials exclusively to low traffic
roads while others, such as the Brazilian National Department of Transport Infrastructure
(DNIT), foresee the use of lateritic materials for high traffic volume road pavements, usually
for ESA up to 5x106
or higher, provided certain requirements are met. There are also
specifications with more conservative requirements for the selection of lateritic materials,
according to the region's climate and estimated ESA for the highway.
In addition to the typical criteria of the traditional specifications, such as the bearing
capacity, grading, plasticity and particle hardness, some specifications for lateritic materials
introduce new criteria to identify and select these materials, such as the silica-sesquioxides
ratio adopted by the DNIT or the MCT methodology tests introduced by Nogami and
Villibor.
The successful use of lateritic materials in road pavements is not only conditioned to the use
of particular specifications, but also the constructive methods and techniques adopted during
construction, which must be adapted to the peculiarities of the lateritic materials in order to
enhance their mechanical performance and ensure the optimal behaviour of the pavement.
Thus, several recommendations for the construction lateritic material pavements are
presented in this chapter.
3.2 Specifications for the use of lateritic materials in road pavements
3.2.1 DNIT Specification, Brazil
The National Department of Transportation Infrastructure (DNIT) developed a specific
standard (DNIT 098/2007 ES) for the use of lateritic materials in base layers of road
pavements constructed in Brazil. This standard establishes the requirements regarding the
quality control of materials, equipment, execution, etc. (DNIT, 2007). However, only the
aspects regarding the selection criteria of lateritic material are highlighted in this chapter.
The DNIT specification, due to the satisfactory performance of the large highway network
of Brazil constructed with lateritic materials, is probably the most relevant specification for
the use these materials in road pavements.

19
The grading envelopes required for lateritic materials are shown in Table 6.
Table 6 – Grading envelopes and maximum tolerances [Adapted from (DNIT, 2007)]
The materials should also be analysed for their bearing capacity, plasticity, aggregate
hardness and swelling, according to the criteria presented in Table 7.
Table 7 – Criteria for selection of lateritic materials for base layer [Adapted from (DNIT, 2007)]
Properties Admissible values Specification
CBR (1)
% ≥ 60 DNER-ME 049/94
Swell % ≤ 0.5 DNER-ME 029
PI (2)
% ≤ 15 DNER-ME 122 e 082
LL % ≤ 40 DNER-ME 122
LA % ≤ 65 DNER-ME 035
Sand Equivalent % ≥ 30 DNER-ME 054
Notes:
(1) The CBR test shall be carried out in accordance with DNER-ME 49/74. Value indicated
for ESA ≤ 5x106
, for higher traffic volumes, the CBR should be ≥ 80%.
(2) Lateritic soils with PI> 15% may be used in mixtures with other materials PI ≤ 6%; the
resulting mixture must meet the following requirements:
• LL ≤ 40% and PI ≤ 15%
• The S/R ratio and the expansion or swelling defined in this specification.
• Absence of clays from the families of nontronites and / or montmorillonites.
In addition, this specification requires a silica-sesquioxide molecular ratio of less than two.
For the determination of the silica-sesquioxides the following formula should be used:
Sieve
e
Size
Envelopes
% by mass
A B
Sieve
e
% by mass

20
Where:
• S/R = Silica-sesquioxides molecular ratio
• SiO2 = Silica
• Al2O3 = Aluminum sesquioxide
• Fe2O3 = Iron Sesquioxide
The procedure to obtain the silica-sesquioxides ratio should follow the specification (DNER
ME 30/94).
3.2.2 Main Roads Western Australia
The specification, 'A Guide to the Selection and Use of Naturally Occurring Materials as
base and subbase in Roads in Western Australia', was developed by Main Roads Western
Australia (MRWA) for the use of lateritic material in base and sub-base layers in pavements
in the state of Western Australia, the region of the country where lateritic material can be
found.
This specification arose from the need to adapt the material selection criteria for base and
sub-base layers, in order to reduce construction costs. The Western Australia state has a vast
road network and a low population density. The successful use of low-cost materials
available, located close to the road alignment has driven the development of the region's
road network. The development of this specification is based on the following factors:
• Much of Western Australia has an arid or semi-arid climate
• Legal maximum axle loads in Western Australia are lower than those in Europe;
• Many roads located in remote areas of Western Australia are subject to low traffic
volumes;
• Improved techniques for the use of marginal materials and improved construction
methods for a high quality standard.
The selection criteria adopted by this specification are based mainly on local experience
(Main Roads Western Australia, 2003).
The type of material required for base layers of pavements in different climatic zones of the
state of Western Australia and different classes of ESA are shown in Table 8. For the use of
this table it is considered that the drainage characteristics of the pavement are appropriate.

21
Table 8 - Required classification numbers for lateritic gravel (Main Roads Western Australia,
2003)
Notes:
The designations Lt6, Lt10 and Lt16 refer to materials with a plasticity limit of 6, 10 and
16% respectively.
Table 9– Typical criteria for selection of lateritic gravel for base, based on granulometry and
classification tests (1)
(Main Roads Western Australia, 2003)

22
Notes:
(1) Selection criteria apply for basecourse roads with a thin bituminous surface, with a 20 year
design traffic loading up to 5x106
ESA. For higher traffic volumes, Table 11 is used.
(2) Non-laterite column (crushed aggregate) included for comparison purposes only.
(3) See Table 8 for climatic zones and applicable traffic
(4) Most lateritic gravel deposits contain unusual size materials that must be broken.
(5) Dry sieving and decanting according to (Test Method WA 115.1)
(6) Dust ration P0.075/0.425
(7) LL (using cone apparatus) PI and LS on samples air-dried at 50° C.
(8) For materials approaching the upper limit of PI or P0.425xLS, resistance suitability
confirmation is recommended.
(9) Maximum dry compressive strength by test method (Test Method WA 140.1)
(10) No specific test for particle hardness is specified up to this point. However, the lateritic
aggregates must be hard and durable.
(11) NS = Not Specified
(12) The base layer should be dried to a moisture content of less than 85% (about 60% for
Crushed Aggregate) of the OMC prior to application of bituminous surface.
Table 10 – Typical criteria for selection of lateritic gravel on strength and classification tests (Main
Roads Western Australia, 2003)
Notes:
(1) Selection criteria apply for basecourse roads with a thin bituminous surface, with a 20 year
ESA. For higher traffic volumes, Table 11 is used.
(2) See Table 8 for climatic zones and applicable traffic
(3) The West Australian Confined Compressive Test is a triaxial confined compression test
where cohesion and tensile strength are assessed at specified density for the project and the
design moisture content for the site. Performed according to (Test Method WA 142.1).
(4) Cohesion and tensile strength can be reduced to 45 kPa and 30 kPa respectively provided that
the friction angle is greater than 60 °. These parameters are not critical provided the shoulders
are sealed.

23
(5) The WACCT evaluation criterion may not be met when the testing specimens immediately
after compaction. In such cases the test specimens must be compacted at 100% of the optimum
moisture content, dried at design humidity and cured for 3 weeks without further loss of water
content prior to testing.
(6) CBR specimens compacted to OMC to the specified density for the project and tested at
design unsoaked moisture conditions: WA 141.1.
(7) Most deposits of lateritic material contain material of unusual size which must be broken
down.
(8) Grading Modulus = (300- (P2.36 + P0.425 + P0.075)) / 100
(9) Dust ratio P0.075/0.425
(10) No specific test for particle hardness is specified at this point. However, lateritic aggregates
must be hard and durable.
(11) The basecourse should be dried back to a moisture content of less than 85% of the OMC
prior to surfacing.
Table 11 –Selection criteria of lateritic gravel used in heavy duty pavements based on granding
and classification tests (Main Roads Western Australia, 2003)
Notes:
(1) Selection criteria apply to basecoure pavements with thin bituminous surface with a 20 year
.
(2) The particle size shall be as close as possible to the target particle size.
(3) Dry sieving and decantation. Test Method WA 115.1

24
(4) LL (using cone apparatus) PI and LS on samples air-dried at 50 ° C.
(5) Maximum dry compressive strength by test method: WA 140.1
(6) CBR according to the test method: WA 141.1. Specimen for soaking prepared at 96% of
MDD and 100% of OMC.
(7) Dust ration P0.075/0.425
(8) The basecourse should be dried back to a moisture content of less than 85% of the OMC
prior to surfacing.
The S/R ratio is not adopted as a selection criterion in this specification, according to Main
Roads Western Australia (2003), not all materials defined as lateritic found in Western
Australia satisfy the S/R< 2 relation as recommended by other publications.
3.2.3 Specification for the selection of fine sandy lateritic soils for base layers
by Nogami e Villibor
Nogami and Villibor developed a specification aimed at the use of fine sandy lateritic soil
(FSLS) in layers of road pavement bases.
According to the authors, the experience in the use of these materials has shown that the
typical selection criteria of traditional specifications, such as continuous grain size, liquid
limit and plasticity index, fail to represent the mechanical properties of lateritic materials.
Therefore, such criteria are abandoned and new test methods that better evaluate and
reproduce the unique characteristics of tropical soils used as basecourse in road pavements
are adopted (Nogami & Villibor, 2009).
The mechanical properties of the materials are evaluated using, among others, some tests of
the soil classification methodology MCT as presented in subchapter 2.5.2.
The properties and allowable values for the selection of fine sandy lateritic soils for road
pavements base layer are presented in Table 12.
Table 12 – Criteria for the selection of lateritic soil for the base layer [Adapted from (Nogami &
Villibor, 2009)]
Properties Admissible Values
MCT groups (1)
LA , LA' , LG'
MDD (g/cm3) > 2.0
Mini-CBR unsoaked (%) ≥ 40
Ratio RIS (%) (2)
≥ 50
Loss of bearing capacity by soaking (%) ≤ 50
Swell with standard load (%) ≤ 0.3
Axial contraction (%) 0.1 a 0.5
Absorption coefficient (cm/min1/2
) 10-2
a 10-4
Permeability coefficient (cm/s)(3)
10-6
a 108
Notes:

25
(1) MCT Groups as described in item 2.5.2
(2) The RIS Ratio consists of the relationship between soaked Mini-CBR without load and Mini-
CBR with the optimal moisture content of compaction.
(3) Optional test
The soils particle grading to be used in the base layers constituted of FSLS should be as such
that at least 90% of the fraction passes through the 2.0 mm sieve. It should be noted that the
coefficient c', as presented in subchapter 2.5.2, correlates roughly with the grading of the
material, which is designated as LA, LA' or LG' according to the value of this coefficient.
This specification is limited to 1500 AADT with 35% of commercial vehicles or up to 5x106
ESA (Nogami & Villibor, 1995).
By the end of the year 2003, the extension of road networks built according to this
methodology, in the state of Sao Paulo in Brazil, surpassed 7500 km (Nogami & Villibor,
2009).
3.2.4 Recommendations for Southern Africa by Gourley & Greening
Gourley and Greening (1997) presented in 'Use of' substandard lateritic gravels the roadbase
materials in Southern Africa', a specification for lateritic materials based on the study of
lateritic materials used in the southern region of the African continent aiming to propose
more permissive guidelines for the use of local materials in pavement layers.
The 129 km highway connecting Lilongwe to Mchinji, and an experimental stretch of 1 km,
located on the road linking Kasungu to Mzimba, both in Malawi, were presented as
examples of satisfactory behaviour of lateritic materials in base layers.
The mentioned experimental section is located in the road of the case study of this
dissertation, more precisely in the section 3 listed in Table 19. This stretch had already been
submitted to 0.5x106
ESA ten years after its construction, having the base layer in lateritic
soil CBR values ranging from 40 to 55% and PI between 18 and 20% (Gourley & Greening,
1997).
Through the analysis of the mechanic performance of lateritic material used in the southern
region of the African continent, Gourley and Greening proposed guidelines for the design
and selection of lateritic material for low traffic volume pavements.
The recommended selection criteria for lateritic materials that vary according to the traffic
and bearing capacity of the foundation of the pavement are presented in Table 13.

26
Table 13 – Proposed guidelines for the selection of lateritic material for base layer with unsealed
shoulders (Gourley & Greening, 1997)
Notes:
(1) Non-expansive subgrade.
(2) IP max = 8 x GM.
IP = Plasticity Index
PM = Plasticity Module
GE = Grading envelope
NS = Not Specified
The recommended envelopes for different aggregates with different maximum nominal sizes
are shown in Table 14.
Table 14 – Recommended grading for bases in lateritic material (Gourley & Greening, 1997)

27
Table 15 presentes the recommended thicknesses and CBR values for pavement layers,
varying according to the bearing capacity of the subgrade and traffic conditions.
Table 15 – Proposed guidelines for design of pavements with base layer composed of lateritic
material and unsealed shoulder (Gourley & Greening, 1997)
Notes:
(1) Non-expansive Subgrade;
(2) Gravel wearing course quality;
B = Base;
SB = Sub-base;
SF = Selected Fill
The CBR, in parentheses in Table 15, are obtained on test moulds with 100% compaction
degree relative to the modified Proctor test. The swell for CBR values of 45%, 55% and 60
to 80%, should be less than or equal to 0.5, 0.3 and 0.2, respectively. The CBRs for the
subgrade and sub-base layers are obtained on a compaction degree of 95% to the modified
Proctor test.
3.2.5 Laboratoire Central des Ponts et Chaussées, France
The study published by the Laboratoire Central des Ponts et Chaussées (LCPC) and Institut
des Sciences et des Techniques de L'Équipement et de L'Environnement pour le
Développement (ISTED) in 1983 entitled 'Latérites et Graveleux Latéritiques’ by Paul
Autret, presents a summary of the recommendations and guidelines for the use of lateritic
materials in basecourse layers, based on the analysis of the criteria adopted by several
African countries.
A summary of the recommendations for the base and sub-base layers that vary according to
the traffic class and base layer or sub-base is presented in Table 16.

28
Table 16 – Recommended criteria for the use of lateritic material in road pavements [Adapted
from (Autret, 1983)]
Criteria
importance
Characteristic layer
Traffic Class
T1 T2 T3 T4 T5
Acceptability
Criteria
CBR %
SB ≥ 25 ≥ 30 ≥ 30 ≥30-35 ≥30-35
B ≥ 60 ≥ 80 ≥ 80 - -
Selection
Criteria or
Quality Index
Los Angeles %
SB ≤ 60 ≤ 60 ≤ 50 ≤ 50 ≤ 50
B ≤ 45 ≤ 45 ≤ 40
Fines
(< 0,08 mm) %
SB ≤ 25 ≤ 25 ≤ 20 ≤ 20 ≤ 20
B ≤ 15 ≤ 15 ≤ 15
PI %
SB ≤ 25 ≤ 25 ≤ 20 ≤ 20 ≤ 20
B ≤ 20 ≤ 15
Swell %
SB 1 a 2
B 0.5 a 1
MDD. Proctor
(ton/m3
)
SB > 1.90
OMC B > 2.00
In addition to these criteria, this paper presents grading envelopes for lateritic materials
found in savannah and in forest areas.
The number of standard axes for each traffic class listed in Table 16 are presented in Table
17.
Table 17 – ESA for each traffic class [Adapted from (CEBTP, 1984)]
Class T1 T2 T3 T4 T5
ESA < 5 x 105
5 x 105
– 1,5 x 106
1,5 x 105
– 4 x 106
4 x 106
– 107
107
– 2 x 107

29
3.2.6 Recommendations developed by Charman
Charman (1988), in the publication 'Laterite in road pavement', suggested the criteria listed
in Table 18 for the selection of lateritic materials for three types of roads.
Table 18 – Recommended selection criteria for lateritic gravel for base and sub-base of surface-
facing pavements in the tropics (Charman, 1988)4
Notes:
(1) Granulometric Modulus = (300- (P2.0 + P0.45 + P0.075)) / 100, where P2.0, P0.45 and P0.075 is
the percentage passed on the sieves 2.0, 0, 45 and 0.075 mm, respectively.
(2) Plasticity modulus = Plasticity index multiplied by the percentage passed in the sieve 0.425mm.
(3) CBR in samples with 95% compaction degree (Proctor modified) submerged 4 days in water.
(4) CBR in samples with 100% compaction degree (Proctor modified) soaked for 4 day.
(5) Los Angeles abrasion value on fraction retained on sieves of 2.0 or 2.36 mm.
N.S = Not specified
The criteria recommended by Charman, varies both according to the type of road and the
climate of the region, similarly to the specification of MRWA presented in 3.2.2. This
specification is limited to pavements with a maximum ESA of 3x106
.
The selection criteria recommended in this publication, for certain cases, do not differ much
from those of the traditional specifications, for example, for a pavement located in a moist
wet tropical region with an ESA up to 3x106
. This demonstrates that these recommendations
4
Table from Pinard et al, (2014)

30
are quite conservative, especially when compared to the DNIT standards, which allows a
base layer with CBR ≥ 60% and PI ≤ 15%, for ESA up to 5x106
.
3.3 Construction recommendations for lateritic materials
3.3.1 Introduction
Generally, layers consisting of lateritic material are constructed using conventional methods
and equipment (Pinard et al, 2014). However, due to the peculiar characteristics of the
lateritic materials, such construction methods are not sufficient to prevent certain defects
related to constructive techniques from occurring. Thus, certain aspects of construction
techniques require special attention (Nogami & Villibor, 2009).
The thickness of layers composed of lateritic material must obey the design method adopted.
However, layers consisting of these materials must have a thickness of more than 10 cm; for
layers with a thickness of more than 20 cm, the compaction should be subdivided into partial
layers (DNIT, 2007).
This subchapter portrays some of the peculiar constructive aspects to be considered for the
use of lateritic materials in road pavements.
3.3.2 Distribution and homogenization
The variability of lateritic materials is evidenced by several authors as one of the
disadvantages of their use in pavements as the material can vary considerably, even when
extracted from the same deposit. In order to minimize the effects of material variability,
additional care should be taken during the construction phase.
Some properties of the material can also be altered during the process of exploration of the
borrow area. It is recommended that the excavated material be stored and additional tests
performed on representative samples of the stored material. The storage of the material
before it is used in the pavement helps to minimize its variability (Pinard et al, 2014).
The variation of the moisture content of the material prior to compaction should also be
controlled, avoiding uneven distribution of water in both transverse and longitudinal
directions. Measures should also be taken to reduce the effect of insolation and winds, which
make the top of the layer less moist, consequently causing variations in the apparent specific
mass of the material during compaction. In order to decrease the variation of the layer
humidity, it is recommended that the wetting is carried out in the late afternoon and that the
layer is sprayed in the morning the following day. The layer must be compacted
immediately and the moisture content must be controlled (Nogami & Villibor, 2009).

31
3.3.3 Compaction
The compaction of the lateritic materials should be initiated with a long sheepfoot vibratory
roller and continued until there is no more penetration of the roller in the compacted layer.
The use of short sheepfoot vibratory roller leads to a low maximum dry density in the
bottom of the layer. Pneumatic rollers or heavy sheepfoot rollers must then be used and the
finish must be made with variable pressure pneumatic rollers or, where these are not
available, a vibrating roller should be used. The latter is not recommended for more than two
passages, since the drum can cause corrugations and unbound sub-layers, especially in more
clayey materials (Nogami & Villibor, 2009).
Particular attention should be paid to the compaction of the edges of the pavement, as
inadequate compaction can lead to future edge breaking. The compaction should always be
started from the edges and continued to the centre of the pavement, and from the lower to
the higher edge in the curves (Nogami & Villibor, 2009).
A high degree of compaction is required for the material to retain adequate bearing capacity
even when saturated (Gracie & Toll, 1987). However, Nogami and Villibor (2009) suggest
that, for clayey lateritic materials, the side effects related to excessive compaction are more
burdensome to the pavement life than a compaction below the specified, since the excessive
compaction of this type of materials may cause the formation of mini-layers that weaken the
layer structure and potentiate defects in the pavement surface, as shown in Figure 5.
Figure 5– Defects related to excessive compaction of clayey lateritic materials (Nogami & Villibor,
2009).
It can be seen in Figure 5, on the left, the cracking of the surface of the layer, and on the
right, the disintegration of material by the formation of unbound mini-layers due to
excessive compaction.

32
3.3.4 Drying or curing of the base layer
The drying or curing process is of extreme importance to take advantage of the structural
abilities of lateritic materials, providing more uniform moisture contents in the finer
fractions of the material that consequently results in a greater density uniformity of the
compacted layer. The compacted base layers should be allowed to dry to a moisture content
of at least 80% of the OMC (Main Roads Western Australia, 2003).
The compacted base layer should be allowed to dry for a period of 48 to 60 hours depending
on local conditions. This provides a considerable increase in the layer bearing capacity and
improves the conditions for the execution of the surface layer. Moreover, it allows the
expected cracking to occur prior to surfacing (Nogami & Villibor, 2009).
After the drying curing period, if necessary, the base should be swept to remove any loose
material, and then lightly irrigated to facilitate the penetration of the bituminous material
(Nogami & Villibor, 2009).
3.4 Financial advantages of the use of lateritic materials in road
pavements
The financial advantages related to the use of lateritic materials in road pavements are
evident, since these materials generally do not require any expensive mechanical treatment
to be used on pavements.
The financial benefits of using lateritic materials in base and sub-base layers of pavements
are even greater for cases where better quality materials are inaccessible, insufficient or non-
existent.
In substitution of the lateritic materials, usually excluded because they do not meet the
requirements of the traditional specifications, other expensive options such as: transport
from long distances of natural material that comply with the specifications; stabilization of
marginal material with lime or cement; or the use of crushed stone aggregates for the base
layers (commonly adopted in Malawi), are generally adopted. All of these options can be
prohibitively expensive and suppress the development of a country's road network (Gourley
& Greening, 1997).
The paving with low-cost materials makes it possible to construct more kilometres of roads
with fewer resources, and consequently has a considerable economic and social impact in
the region, since: the industrial sector benefits from better transport conditions to export its
products; farmers can sell their products at more competitive prices; residents of rural areas
may have access to education and medical care in large cities; among others (Nogami &
Villibor, 2009).

Study of the Behaviour of Lateritic Materials in Road Pavements - C. Santos

Study of the Behaviour of Lateritic Materials in Road Pavements - C. Santos

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