1
APPENDIX I
Technical Memorandum
Updating Bituminous Stabilized Materials
Guidelines: Mix Design Report, Phase II
Task 9: Moisture Sensitivity: Part I (Improvement)
Final Report: Sept 2008
AUTHORS: KJ Jenkins
ME Twagira
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1. SUMMARY
1.1. Background
Several laboratory procedures have been developed for the identification of BSMs mixes with
unacceptable moisture sensitivity. Generally, the moisture conditioning for mix assessment
carried out using vacuum saturation of the compacted and cured specimen, in order to
accelerate any possible moisture damage. The conditioned and unconditioned specimens are
then compared in terms of retained strength e.g. Tensile Strength Retained (TSR) obtained after
ITS, or from UCS or ITT tests. Although this method provides an empirical measure of moisture
damage, it yields both variable and unreliable results. Task 9 presents the development of new
laboratory-based representative testing procedure and analysis protocol for the evaluation of
moisture damage, which distinguished from current over-simplified procedure.
1.2. Methodology
It is clear that simulations of moisture damage in a laboratory will always be an idealised
representation of reality; nevertheless, a reliable, cost effective procedure is required to
distinguish between research and classification (standard) testing for moisture susceptibility.
Although the laboratory simulation cannot be an exact replication of mechanisms that manifest
in service, it should represent the fundamental or key failure mechanism for the BSM mixes.
A testing and evaluation framework based on the MIST (Moisture Induction Sensitivity Test)
device for moisture conditioning and mechanical testing (short dynamic and static tests), is
proposed for determining the level of moisture damage in the mixture. Different saturation
levels investigated with experimental determination of stiffness ratio (Mr) and Shear Parameters
(C and ø) which are critical parameters for the performance of the BSMs. Different types of
aggregate blends, with and without RAP, with foamed bitumen or bitumen emulsion binders
were investigated. The rating of the severity of moisture related damage in these mixtures,
using the MIST test, discussed and the results validated with accelerated pavement testing using
a laboratory MMLS3 device. The influence and effect of the addition of active filler (cement or
lime) into these mixes also investigated.
1.3. Findings
From the study results, it found that the accelerated moisture induction process using MIST
device shows potential for use as a tool to condition specimens for tests that will determine the
relative moisture susceptibility of different BSM-Mixes. Mechanical testing to determine the
residual cohesion at maximum saturation levels shows better ranking of mixture in term of
moisture damage than for example a TSR test. MIST device test results show good validation
with the Accelerated Pavement Testing (MMLS3) device.
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2. BACKGROUND AND INTRODUCTION
2.1. What is Durability?
Durability in general terms is defined as enduringness, lastingness, persistence, changelessness, or everlasting. It is a measure of the useful life of physical phenomena. Conceptually, in engineering terms (for bituminous stabilize materials or BSM’s), durability is defined as lastingness of structures and materials i.e. the ability to maintain the initial performance properties with time above a certain threshold level, as shown in
Figure I.1. This achieved by resisting stress and strain or withstanding destructive agents within
which the materials comes in contact (i.e. air, water, light, temperature, chemicals and traffic
loading) over a long period. It is clear that durability has multidimensional parameters, and is
not only a measure of moisture resistance. In fact, moisture damage often manifests early in a
BSM’s life. For that reason, in this report moisture sensitivity considered as a major factor
influencing durability properties. Therefore, moisture damage treated as a separate distress
mechanism.
Figure I.1: Conceptual description of durability
2.2. The need of durability in the mix design
Most of the mix design models developed for the bituminous stabilized materials (BSM) focused
on long-term performance i.e. rutting as function of stress ratio and flexibility. Of all the aspects
of mix design, durability is one of the most difficult to address. This is due to a number of
factors, which are explained below:
- The diversity of ways in which the durability of materials measured, e.g. resistance of
binder to age hardening, resistance of mixture to moisture damage, resistance of wear
and tear of aggregates etc.
Time (years)
Minimum
Durability
Init
ial P
erfo
rman
ce P
rope
rtie
s
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- Difficulties in identifying the durability mode of failure of the bituminous stabilized
materials and mechanisms contributing to this failure.
- The variety of mix properties and intrinsic materials properties that can influence
durability e.g. gradation of mineral aggregate, hardness of aggregate, binder type and
content, use of active filler, etc.
- The variety of external factors that influences on durability e.g. climate, traffic load
speed, magnitude, configuration, etc and their variability.
- The difficulties in simulating durability effects in a manner that is not mutually exclusive
to different mix properties,
- Time and cost involved in modelling durability behaviour of materials simulating field
condition accurately through research.
Notwithstanding these difficulties, researchers, Jenkins, (2000), Collings, (2007), Long (2001),
Øverby, (2004), Paige-Green, (2004), have indicated that the fundamental durability of mixes
requires consideration in the mix design of bituminous stabilized materials. In particular, any
material needs characterization in terms of its basic component, critical parameters and
durability requirements. Although this section focuses on moisture susceptibility as the prime
factor in addressing durability requirements of bituminous stabilized mixes, the entire definition
outlined above is at the core of the issue.
Several laboratory procedures developed for the identification of BSMs mixes with undue
moisture sensitivity. Generally, these procedures stem from earlier findings of the Asphalt
Institute (1992) which entailed moisture conditioning of a compacted, cured specimen and
mechanical testing. The moisture conditioning carried out by vacuum saturation of the
specimen, in order to accelerate any possible moisture damage. Although this method provides
an empirical measure of moisture damage, it yields both variable and unreliable results.
Therefore, the need for improvement to this procedure is apparent.
2.3. Objectives
The objectives of Task 9 include;
- The development of upgraded or new laboratory-based representative testing
procedures, and analysis protocol for the evaluation of moisture related damage which
distinguish from current over-simplified procedure.
- Evaluation of MIST conditioning system by using BSM-foam and BSM-emulsion with
varying aggregates type.
- If warranted from findings, make appropriate recommendations regarding the use of the
new moisture conditioning and limits for screening BSM mixtures based on moisture
related damage for mix design.
It is clear that simulations of moisture damage are ideal, but a reliable, cost effective procedure
is required to distinguish between research and classification (standard) testing for moisture
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susceptibility. Although the laboratory simulation cannot be an exact replication of mechanism
that manifest in service, it should represent the fundamental or key failure mechanism for the
BSMs.
2.4. Scope of the work
Task 9 focuses primarily on the development and evaluation of a new conditioning system for
quantifying moisture damage in BSMs. The conditioning system uses cyclic water pressures to
accelerate moisture (pore pressure) induced damage in the mixtures.
A testing and evaluation framework based on MIST device and mechanical testing (short
dynamic and static tests) has been used to determine the level of moisture damage in the
mixture. Different saturation levels investigated with experimental determination of stiffness
ratio (Mr) and shear parameters (C and ø) which are critical parameters for the performance of
the BSMs. Different types of aggregate blends, with and without RAP, with foamed bitumen or
bitumen emulsion binders investigated. The rating of moisture related damage severity
predication on these mixtures by the MIST test is discussed and the results validated with
accelerated pavement testing using a laboratory MMLS3 device. The influence and effect of the
addition of active filler (cement or lime) into these mixes also investigated.
2.5. Report structure
- Section 3 of this report describes the durability requirements and the key areas to be
considered for the moisture damage potential for the bituminous stabilized materials.
- Section 4 provides description of the previous testing procedures developed for the
identification of bituminous stabilized maxes with undue moisture sensitivity. Key concepts
of MIST device introduced.
- Section 5 provides a detailed testing methodology for the MIST device conditioning and
mechanical testing (i.e. short dynamic and static tests). In essence it describes the
aggregates types and grading, binder type and content, moisture content, compaction,
curing, permeability, MIST conditioning variables, equipment and testing procedure and
mechanical testing variables.
- Section 6 provides detailed tests results database of BSM-foam and BSM-emulsion acquired
during testing program.
- Section 7 provides analysis and discussion of the testing results. Details of moisture
damage potential on either BSM-foam or BSM-emulsion and the influence of the additional
active filler in these mixes. Additional of advantage of using lime in the BSMs is discussed.
- Section 8 provides conclusions of the finding obtained from the studies.
- Section 9 provides the references used in the literature survey.
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3. DURABILITY REQUIREMENTS
The inclusion of bituminous binder in unbound aggregates reduces the moisture susceptibility of
the mix, However as the binder content reduces the mix permeability increases. BSMs do not
possess the same moisture resistance as HMA this is due to presence of moisture at the time of
mixing and the partial coating of the aggregate by the bitumen. Although this section addresses
moisture susceptibility of the bituminous stabilized mixtures (BSMs) the aggregates durability
also require consideration. Aggregate durability addressed by many researchers as contributing
factor to the durability of bituminous stabilized mixtures. Weinert, (1980) recommended that the
durability of aggregates should be the first properties to be determined when selecting a natural
aggregates for the road construction.
3.1. Aggregate durability
Granular material in bituminous stabilized materials makes up the largest part in both mass and
volume. Crushed stone, natural gravel, reclaimed asphalt pavement (RAP) and natural sand are
amongst the common granular materials used to produce BSMs. Weinert (1980) classified rock
forming minerals in South Africa as follows:
- Basic crystalline (i.e. dolerites and basalts),
- Acid crystalline (i.e. granites, felsites, rhyolites and gneiss),
- High silica (i.e. quartzite and hornfels),
- Arenaceous ((i.e. sedimentary conglomerates, gritstones and sandstones),
- Argillaceous (i.e. mudrocks),
- Carbonates (i.e. limestone and dolomites),
- Diamictites (i.e. tillites),
- Metalliferous (west product of iron and magnesium mines) and
- Pedogenic (i.e. calcrete, ferricretes and silcretes, which is in abundance in South
Africa).
Sampson, (1991) indicated that durability behaviour of these rocks (aggregates) in the un-
stabilised base layer varies considerably in terms of disintegration and decomposition. Sampson
further concluded that the process leading to the deterioration of the aggregates in the base
layer is the inter-particle abrasion and impact due to cyclical stress application and release in the
moist condition, normally in excess of the expected equilibrium moisture content. Paige-Green,
(1989a, 1989b) indicated that the materials properties suitable for the granular wearing course
are; Suitable particle size distribution, appropriate cohesion, adequate strength, and adequate
aggregates hardness.
Sampson, (1989) developed a test to identify potentials durability of aggregates in term of breakdown and generation of excessive plastic and non-plastic fines.
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Sampson pointed out that the available laboratory tests for measuring the durability of aggregates are 10% Fines Aggregates Crushing Test (10% FACT) and Aggregates Crushing Value (ACV). However looking at these tests, they all measure the strength and give indication of susceptibility of materials to absorb water and become weak. Sampson and Roux (1986) concluded that the test that show potential for simulating the likely breakdown of the materials in service and applicable for all material is the Durability Mill Index (DMI). The Acceptable DMI limits in
Table I.1 were established for the above-mentioned materials applicable for the mix design of
the un-stabilised basecourse under the thin surface seal.
Table I.1. Durability Mill Index, Limit for Rocks and Soils, Sampson (1991)
Aggregates type Rock and soil group DMI, Limit Granites, gneiss, granite Acid Crystalline
Hornfels, quartzite High silica
Dolomite, limestone, Carbonate
< 420
Calcrete, ferricrete, silcrete Pedogenic materials < 480
Sandstone, siltstone,
conglomerate Sandstone
Grey wacke, Tillite Diamictite
Mudrock, phillites, shale Mudrock
< 125
Basalt, Dolerite, Babbro Basic crystalline
ironstone, magnesite, magnetite Metalliferous
< 90
From the available test data, no indication of Durability Ball Mill test been
performed on the BSMs. It is therefore important that this test being evaluated on BSMs in order to establish the applicable limits for classification of BSMs in the mix design. The current DMI classification limits for un-stabilised materials might be too conservative for use in BSMs. The performance-related limits proposed for the un-stabilised basecourse materials under thin surface seal are indicated in Table I.2.
Table I.2. Durability Mill Index, Limit for un-stabilised base materials for mix design classification
Durability Mill Index limit Performance-related materials class
≤ 100 GOOD
≤ 125 FAIR
≤150 POOR
The previous and current research on performance of bituminous stabilised materials (BSMs) indicated that the rock type such as High silica, Carbonate and Pedogenic materials produce quality BSMs. That means , the proposed limits in Table I.2 seemed to be too conservative on these materials for use on BSMs, for which higher
value of DMI might prove to be suitable.
3.2. Durability of bitumen-aggregates interaction
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The strength and durability of bitumen-aggregates composite mix, and its performance under
varying load and environmental conditions are the key factors in determining pavement lifetime.
These factors strongly depend upon cohesive properties of the asphalt constituents and the
adhesive properties at the asphalt- aggregates interface (Labbi, 1992), Jenkins, (2000), and
Colas, (2002).
It is widely accepted that the mixture of filler and bitumen (mastic) in the BSMs is important
component that binds the large aggregates together. Jenkins (2000) investigated the mastic
stiffness of foamed bitumen mixes from different bitumen type (80/100 and 150/200) and filler
type (Hornfels and Granites) using Ring and Ball test method. The stiffness results indicated that
mastic at greater than 40% bulk volume produce brittle foam mixes. However, the influence of
bitumen ageing in the mastic was not investigated. It is therefore apparent that more
investigation is required to understanding of the ageing effect on mastic adhesion
characteristics.
The behavioural relationship of mastic cohesion and adhesion to large aggregates in-terms of
moisture susceptibility is unknown, therefore this aspect needs more investigation. In bitumen
emulsion mixes, cohesion and adhesion to large aggregates behave differently, Wirtgen (2004)
recommended that bitumen emulsion should not be used in combination with high fines content
due to high ability to retain water from emulsion, which resulting into slow curing process and
low gain in stiffness of the mix.
Shell Bitumen, (2003) and Serfass et al., (2008) indicated that during the breaking process and
water evaporation in bitumen emulsion, the bitumen droplets disperse in a thin film on both
coarse and fine aggregates, which provides adhesive properties in the mineral aggregates.
However, the influence of bitumen ageing and moisture susceptibility on cohesion and adhesion
behaviour of mastic to coarse aggregates is unknown; this aspect also needs further
investigation.
3.3. Moisture content applied to BSMs
The moisture in BSMs performs a multi-functional role in the behaviour and performance of
these mixtures. The water content of the mineral aggregates treated with foamed bitumen or
bitumen emulsion requires optimization at different stages of application (i.e. mixing,
workability, compaction, curing, and field performance). The role of water in the aggregates
before stabilization is that of a densification agent for the emulsion mixes and dispersion aid for
the foamed bitumen in the mixes. It also reduces the absorption of an emulsion’s water and
adsorption of bitumen constituents into the aggregate surfaces. Van der Walt et al., (1999)
indicated that binders adhere to the surface of aggregates during mixing whilst at an elevated
temperature. In addition, the binder sucked into the pores of aggregates during curing.
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Shell Bitumen, (2003) and Serfass et al., (2008) further commented that lower water content in
the mixture impedes dispersion of the foam, workability and compaction of the mix. Whilst
excess moisture increases the curing, time and reduces the density and strength of the
compacted mixture.
Although moisture in the BSMs assists in mixing, workability, and compaction, during curing and
moisture loss, the volume occupied by the moisture is replaced with air. Therefore, the fluid
component of the BSMs in the early stage of the mixtures’ life is dynamic and can vary
significantly. Jenkins (2000) in Figure I.2 illustrated the moisture regime in the BSMs, by
considering void in the mineral aggregates (VMA) with time following compaction of the foamed
bitumen layer and opening to traffic.
Figure I.2: Field variation in composition of the VMA of the BSM under traffic, (Jenkins 2000)
Where, VMA = voids in the mineral aggregate (%)
V air = volumetric composition of air in the mixture (%)
V water = volumetric composition of water in the mixture (%)
V binder= volumetric composition of binder in the mixture (%)
EMC = long term average equilibrium moisture content. (%)
The importance of optimum compaction and adequate curing graphically illustrated in Figure I.2.
The conditions where the gradient of the VMA line is shallower than the moisture loss line up to
EMC are preferred. Under these conditions, a suitable design life of a pavement layer realized,
with air voids remaining sufficiently high (above 2%). However, where compaction moisture
contents of the layer treated with foam or emulsion is high, and unfavourable conditions for
curing occurs, i.e. months where precipitation exceeds evaporation. In such a case, the slope of
the VMA line may exceed the slope of the moisture loss line; at this point, the BSM can
experience moisture damage through loss in bearing capacity by “zero air void “conditions.
VMA
Seasonal Variation
V EMC
Time
V binder
V air
VM
A (
%)
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Shackel et al. (1974) indicated that the lower the degree of saturation (Sr) of foamed mixes the
greater the resistance to permanent deformation.
The factors contributing to the increase in saturation of the BSMs base layer, which might occur
in conjunction with a high VMA, are; high voids content of the surfacing layer, cracks on the
surfacing layer, high water table of the subgrade layer, and infiltration of moisture from the
shoulder of the pavement structures etc. These factors need consideration during selection of
moisture resistant BSMs.
3.4. Factors influencing moisture susceptibility in BSMs
Some of the aspects of the mix design process, for example materials selection, are similar for
BSMs and HMA. However, some fundamental differences in the composition and preparation of
these mixes are applicable. Several surveys e.g. (Bowering, (1970), Semmelink, (1991), Acott,
(1989), Maccarrone, (1994), and Jenkins, (2000)) undertaken to understand which factors
should be considered in evaluating moisture damage in BSMs. Many variables that needs
identification includes, type of mix, binder characteristics, aggregates characteristics,
environmental effects, and the use of active filler. The reason why moisture susceptibility is
important in the mix design consideration listed below:
- The binder in the BSMs is thin film and does not completely cover the larger particles of
aggregate,
- Binder contents utilized in the mix are generally lower than equivalent HMA, which lives
more interconnect void in the mix.
- The mineral aggregate is moist at the time of mixing which reduces adhesion and,
- The air void content of the mix is usually relatively higher than HMA.
Various modes of failure considered important in the durability of the bituminous stabilized
materials, include loss of strength or stiffness in the presence of moisture under repeated
loading. This has led to the need for evaluation of the moisture durability properties of BSMs
during laboratory test designs. Variety of tests e.g. Indirect Tensile Strength (ITS) test, the
Unconfined Compressive Strength (UCS) test, Indirect Tensile (Resilient Modulus) Test, Marshall
Stability test, are used to determine moisture susceptibility after conditioning of sample with
moisture to simulate the in-service exposure. However, the relevance of these tests and their
failure mechanism require critical review in a rational approach to the design of BSMs.
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4. MOISTURE SENSITIVITY TEST METHODS
Several laboratory procedures in past applied for the identification of bituminous stabilized
maxes with excessive moisture sensitivity. Generally, these procedures stem from early findings
of the Asphalt Institute (1992) which entailed moisture conditioning of a compacted, cured BSMs
specimen and mechanical testing. The moisture conditioning at Asphalt Institute carried using
vacuum saturation of the specimen in order to accelerate any possible moisture damage.
Although this method provides an empirical measure of moisture damage, it yields both variable
and unreliable results.
Other numerous procedures investigated include, Ruckel et al. (1983) used similar vacuum
saturation technique at 23oC in water. In addition, stated that the technique simulate the effects
of prolonged exposure of subsurface to moisture during extended heavy rainfall in the road. Van
Wijlk and Wood, (1993) used also vacuum saturation to study the moisture-exposure effects of
foamed bitumen in terms of Marshall Stability tests. The test found to highlight the moisture
susceptibility of both RAP and virgin mixes. Hotte, (1995) compared the percentage of retained
Marshall Stability for 1 hour of vacuum soaking and 4 days of soaking at atmospheric conditions.
The results found that retained Marshall Stability is 6.4% higher on average for the six materials
tested. Robert et al. (1995) used a wet curing cycle of 3 days at 24oC and found that the
strength declined by 50% of that achieved by dry cured specimens. Higher binder contents were
found to ameliorate the effects of moisture on the tensile strength of BSMs. Humberto Castedo
Franco and Wood, (1982), and Lewis, (1998) recommended that the effective way of reducing
the moisture susceptibility of BSM-foam is through addition of active filler, such as lime or
cement.
Bowering (1970) and Bowering and Curie (1973) deigned bituminous stabilized mixtures
particularly foam, based on simple measurement of UCS, CBR, Resistance and Cohesion values
of cured specimens. Then decide on ranking material’s suitability for foam stabilization.
However, these static tests alone did not provide a means of consistently predicting how the
materials may behave in pavement subjected to traffic, without considering soaking or exposure
to moisture saturation.
Shackel et al. (1974), through triaxial testing of foamed treated breccia, found that Resilient
Modulus maximized at degree of saturation of approximately 60%, for the binder content of 4%.
In addition, the Resilient Modulus of foamed bitumen stabilised breccia increases under load
repetitions at binder content of 5% and 6%. Different bitumen type used 80/100 and 180/200
penetration. Shackel’s work showed that at 10000 load repetitions in the traxial test, the foamed
bitumen stabilised breccia’s optimum Resilient Modulus was not a function of not only degree of
saturation, but also binder content and penetration of the binder.
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The finding of Shackel et al. formed the basis of the Lancanster et al. (1994) approach to
foamed mix design, which includes the optimization of the binder content in terms of the peak
Resilient Modulus. Lancaster et al. proposed that this approach adopted for both dry and soaked
(24hr at 60oC) modulus tests on foamed specimens. Maccaronne et al. (1994) also proposed this
approach, although suggested the repeated load Indirect Tensile Test utilized for efficiency,
instead of triaxial testing. Serfass et al. (2004) prefer to use the compression mode of failure for
obtaining the ratio of strength between conditioned and unconditioned materials, as opposed to
the ITS mode first proposed. Serfass applied the Duriez test method with a lower load to test
the immersion compressive strength ratio for the fresh and cured specimen.
Walubita et al. (2002) showed that the dynamic tests on asphaltic materials subjected to traffic
and moisture damage, are more reliable than static tests. There is a strong correlation between
APT performance in the laboratory and the field, if dynamic test carried out on the materials
after conditioning. Cheng et al., (2002) focus their further research on the understanding of the
stripping and moisture damage using microchemistry of the three component materials i.e. the
surface free energy of the bitumen, aggregates, and water. Stripping analysis, using surface free
energy demonstrates that the adhesion of water to the aggregates is stronger than that of
aggregates with bitumen at normal temperatures. Nevertheless, pavements will not experience
stripping if little or no water can enter the aggregates-bitumen interface.
Alternative methods of exposing mix to moisture and simulating the effects of moisture damage
have been reported by Van Wijk and Lovell (1986) by rotating a cylindrical specimen in water.
De Beer (1989) erosion test, Ventura, (2003) brushing test, their emphasis was on the loss of
fines from un-stabilised and cement materials to simulate pumping of fines though moisture
damage. However, these test methods might be unrealistically severe for the evaluation of the
bituminous stabilized mixtures and in a large extent, they are not simulating the in-service
pavement condition, i.e. they are highly empirical tests. Consequently, no single test has proved
to stand out as the most reliable moisture damage simulation: hence, the number and variety of
tests currently are used. It appears that a simulation technique and test combination has yet
established that is representative and simple in the simulation and evaluation of moisture
susceptibility of BSMs.
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5. EXPERIMENTAL PROGRAM
In this study, the key issues in moisture damage that have created significant discrepancies in
previous test results, such as the saturation method, degree of saturation and evaluation
parameters after conditioning (residual strength ratio versus retained stiffness) were observed.
Subsequently a simple device developed to assess moisture induced damage based upon pulsing
moisture into triaxial specimens. Different saturation levels investigated in a developed device
with experimental determination of stiffness ratio (Mr) and shear parameters (C and ø). These
parameters are known to be critical parameters for the performance of the BSMs. Several types
of aggregate blends, with and without RAP, with foamed bitumen or bitumen emulsion binders
investigated. The rating of moisture induced damage severity predication on these mixtures by
the MIST test discussed. The MIST test results validated with accelerated pavement testing
using a laboratory MMLS3 device. The influence and effect of the addition of active filler (cement
or lime) into these mixes also discussed.
5.1. Materials
5.1.1 Mineral aggregates
Two selected materials type used in this study i.e. reclaimed asphalt pavement, Hornfels-RAP,
and crushed virgin Quartzites (G4). The maximum aggregate size of the selected material is
19mm see the grading curves in Figure I.1 Figure I.3 and Figure I.4. Reclaimed Hornfels-RAP
collected from N7 rehabilitation project, and the crushed Quartzite collected from Prima Quarry
in Western Cape. Selected materials then stabilized in the laboratory with either foamed bitumen
or bitumen emulsion binder. Two percent (2%) residual binder content applied for both
Hornfels-RAP and Quartzite materials. The addition of 0% or 1% active filler (i.e. cement or
lime) also applied on the selected materials. The constitution of tested mixes led into 12 mixes.
Table I.3 show the matrix of the tested mixes.
Table I.3: Constituted mix type and testing matrix
Aggregates type Binder type Hornfels-RAP + 2% residual binder
Quartzite + 2% residual binder
Mix 1: 0% filler Mix 7: 0% filler Mix 2: 1% cement Mix 8: 1% cement
A - Emulsion
Mix 3: 1% lime Mix 9: 1% lime Mix 4: 0% filler Mix 10: 0% filler Mix 5: 1% cement Mix 11: 1% cement
B- Foamed bitumen
Mix 6: 1% lime Mix 12: 1% lime
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Table I.4: Aggregates type and grading for Hornfels-RAP and Quartzite
Aggregates type and grading
Hornfels -RAP Quartzite(virgin crushed aggregates)
MDD = 2177.3 (Kg/m3) MDD = 2240 (Kg/m3) OMC = 5.12 (%) OMC = 6.0 (%) Total Mass = 12 (Kg) Total Mass = 12 (Kg) Stockpile ratio in Mass in Stockpile Ratio in Mass in blend Blend (Kg) blend Blend (Kg) 19.0 -13.2 6.90% 0.828 19.0 -13.2 14.92% 1.790 4.75-13.2 40.60% 4.872 4.75-13.2 32.95% 3.954 2.36 16.00% 1.920 2.36 12.87% 1.544 <0.075 – 2.36 36.49% 4.379 <0.075 – 2.36 39.26% 4.711 Total 100.0% 12.00 Total 100.0% 12.00
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
19.0013.209.506.704.752.361.180.6000.4250.3000.1500.075
Upper Limit: TG2 Lower Limit:TG2 Ideal: TG2 Hornfel (RAP)
Upper Limit: Too Fine (Unsuitable)
Ideal: Suitable
Lower Limit: Too Coarse (Unsuitable)
Figure I.3: Grading curve of Hornfels-RAP aggregates in the envelop of BSMs limits
Per
cent
age
pass
ing
(%)
Sieve size (mm)
15
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
19.0013.209.506.704.752.361.180.6000.4250.3000.1500.075
Upper Limit: TG2 Lower Limit:TG2 Ideal: TG2 Quarzites
Upper Limit: Too Fine (Unsuitable)
Ideal: Suitable
Lower Limit: Too Coarse (Unsuitable)
Figure I.4: Grading curve of Quartzite crushed mineral aggregates in the envelop of
BSMs limits
5.2. Binder
5.2.1 Bitumen emulsion
The bitumen emulsion procured from COLAS used in this study. The emulsion type is AniB SS-60
stable grade anionic emulsion (60% residual binder and 40% emulsion water). The bitumen
emulsion content of 3.33% (i.e. 2% residual binder) used for stabilisation of the either Honfels-
RAP or Quartzite materials.
5.2.2 Foamed Bitumen
The bitumen from CALTEX, 80/100 pen grade used for foaming process. The 2% residual binder
content of foam bitumen used for treatment of virgin Quartzites crashed aggregates or Hornfels-
RAP materials. Before production of foam bitumen, the foaming properties of bitumen viscosity
(expansion ratio) and stability (half-life time) are determined at 3% foamant water as mass
percentage of the bitumen.
The expansion ratio and half-life time of the foamed bitumen found to provide a half-life of 18
seconds and an Expansion Ratio of 12 times. The bitumen procured from NATREF found to
produce relative inferior foam characteristics with a Half-life of 5 seconds and an Expansion
Ratio of 18 times. Similar behaviour occurred at different foamant water application rates.
Sieve size (mm)
Per
cent
age
pass
ing
(%)
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5.2.3 Moisture content and mixing process
The optimum moisture content (OMC) and maximum dry density (MDD) of the selected
materials determined by Modified AASHTO compaction. The summarised results are in Table I.5
for the two selected materials. The hygroscopic moisture in the mineral aggregates was 0.75%
for Quartzite and 0.5% for the Hornfels-RAP.
Table I.5: Summary of optimum moisture contents and maximum dry densities of blends
Blend Compaction OMC (%) MDD (Kg/m3)
Hornfels RAP Mod AASHTO 5.12 2177.3 (field comp)
Quartzite Mod AASHTO 6.0 2240
The mixing process for the bitumen emulsion and the foamed bitumen mixes differ. The BSM-
emulsion mixed in a standard laboratory vertical shaft mixer, and the BSM-foam mixed in the
twin-shaft pugmill placed in front of spaying nozzle of the WLB-10 foam plant.
The moisture content added during mixing with the bitumen emulsion is 65% of OMC and 80%
of OMC for the foamed bitumen. The initial mixing moisture added and mixed for one minute.
Then the aggregate sealed in a bag and left for three hours to allow absorption of the moisture.
Addition of cement or lime (active filler) took place before adding bitumen emulsion or foamed
bitumen and mixed for one minute, followed by addition of bitumen emulsion or foamed
bitumen. After stabilization, the mixture sealed in a bag to assist initial breaking of bitumen
emulsion before compaction.
5.2.4 Compaction
The compaction of BSM-foam and BSM-emulsion carried out using vibratory (BOSCH®)
compactor. Previous research on compaction methods of BSMs conducted by Weston et al.
(2002) uses Marshall, Hugo, Kango, Superpave Gyratory and pedestrian roller. The research
concluded that modified Kango Hammer® hammer could be a useful tool in the compaction of
BSMs. The advantages of Kango hammer® is that it requires low compaction energy to obtain
equivalent level of compaction compared to other method. Secondly it is relative cheap, easy to
use and simulate field compaction. In this study modified BOSCH® hammer used for
compaction see Figure I.5. For more details of its applicability and compaction procedure, refer
the report of Task1 12.
17
Figure I.5: Modified BOSCH® Hammer Figure I.6: Specimen in the mould
Currently, the modified vibratory BOSCH® Hammer compaction process is under investigation.
Therefore, compaction of triaxial specimens on this study carried-out using trial compaction
procedure. The trial procedure has shown quality variation on the compacted specimen. The
variations on the specimen mainly contributed by; change of grading during pouring of materials
in the mould (segregation), optimum moisture content, chiselling for bonding of subsequent
layer, and finishing of top layer. These variations need consideration during final preparation of
compaction procedures. The variations might influence significantly on mechanical tests of
prepared specimens.
5.2.5 Curing
The appropriate curing technique for BSMs has not yet developed and it is a topic in Task 7 and
Task 8, which is currently under analysis and approval. However, the curing technique used in
this study comprised the placement of compacted specimens in draft oven at 30ºC for 20hr
unsealed, followed by sealing and raising the temperature to 40oC for 48 hrs. The same curing
protocol followed for both bitumen emulsion and foamed bitumen mixes. After curing, the
specimen sealed in a different bag and left to cool at ambient temperature prior to the
conditioning and testing.
5.3. Testing variables
The main difficulty in developing a test procedure is the simulation the field conditions to which
bituminous stabilised materials are exposed. During the research, the water susceptible test will
have a conditioning and mechanical evaluation phase; all these are an attempt to simulate the
deterioration of bituminous treated materials in the field.
The testing control variables in this study include:
- Temperature level = ambient (25oC),
- Saturation level,
150 mm Dia X 250 mm Mould
BOSCH® Hammer
50mm layer
18
- Water pressure level,
- Pulsing cycles number,
Moisture Induction Simulation Test (MIST) device developed to evaluate the effect of moisture
damage in the BSMs, while simulating the field pulsing conditions due load repetitions. MIST
devices have several advantages over other conventional moisture susceptibility methods
mentioned in Section 5. These advantages include:
1) Ability to saturate compacted and cured BSMs by pulsing moisture into specimen in a
fashion similar to field condition.
2) Achieve conditioning and maximum saturation levels of BSMs in shortest possible time
3.2minutes or 100 pulsing cycles.
3) Ability to predict earlier the moisture susceptible BSMs suitable for mix design.
4) Require less skill to operate the device, once predetermined parameters are set.
5) It is cheap and easy to use on site for the quality control and quality assurance
6) The predetermined parameters for the MIST device i.e. pulsing pressure, and loading
time related to MMLS3 Model APT device. This is possible for the validation of moisture
susceptibility results determined by MIST device.
7) The applied test parameters on MIST device scaled to obtain the same pressure and
loading time on the MMLS3 device. The scaling process was done through trials.
8) Retained cohesion after MIST conditioning determined through static triaxial test set-up.
The specimen height : diameter ratio of 1:2 at maximum aggregates sizes of 19mm
provide reliable assessment of materials retained shear properties.
9) The damaging effect of cyclic pore water pressure applied to the material after pulsing is
determined using the Residual Modulus of materials. The adhesion and cohesion effect of
bitumen-aggregate interface needs to be determined through microscopic analysis.
5.4. Equipment and test procedure
The Moisture Induction Simulation Test (MIST) device designed and fabricated to assist in
determining the failure mechanism of the BSMs in the presence of moisture. The goal is to
develop the test apparatus that would permit evaluation of mixture sensitivity in moisture
damage and rank them as Good, Medium and Poor, while simulating field conditions. Factors
contributing to the moisture sensitivity include:
- Degree of saturation
- Coefficient of Permeability (percentage of air void content)
- Volume change effect “zero air void” (oversaturation)
- Residual Modulus (short repeated loading)
- Retained cohesion (static loading)
- Adhesion (aggregate coating and stripping)
19
Using the MIST device, the above factors evaluated to determine the effectiveness of the device
relative to conventional testing procedures. The new testing procedure for the MIST device
validated using know APT laboratory MMLS3 testing device.
5.4.1 MIST testing system
The MIST testing procedure has the following major subsystems: 1) fluid saturation subsystem
by pulsing moisture into triaxial specimen. 2) loading subsystem using MTS Equipment.
5.4.1.1. Fluid condition subsystem This is the major system designed to simulate the field wet pulsing conditions due to repetitive
traffic loading. The MIST apparatus features consist of:
- A water tank with capacity of 20 litres of compressed water to a maximum of 600 kPa,
- A water pump, pressure control, and pressure gauge ranging from 0-400 kPa,
- A solenoid valves for water pulsing application (ON-OFF valve ranging from 0 seconds to
60 seconds),
- An inlet pipe to the tank from water supply,
- An inlet pressure pipe to the triaxial cell and outlet pressure pipe to the drain,
- A triaxial cell accommodating 300mm high and 150mm diameter specimen,
- An Oscilloscope displaying the pulsing wave (Maximum /Minimum pressures) applied to
the specimen, and
- Container, which retain overflowing water from triaxial cell.
This technique designed to accelerate the moisture saturation conditioning while simulating the
field conditions. Figure I.7 and Figure I.8 shows the MIST device feature for the fluid
conditioning.
Figure I.7: Oscilloscope
Impulse wave signal (kPa) and rest period (s)
20
Figure I.8: MIST device for the conditioning
5.4.1.2. Loading subsystem
The resilient modulus and shear parameters of the triaxial specimen tested using an MTS
Equipment. After curing the triaxial specimen conditioned using MIST device then short dynamic
(Mr) test performed at 2Hz, with confining pressure of 50kPa at ambient temperature (25oC).
The static (monotonic) loading test for the shear parameters (C & Φ) of the conditioned
specimen performed at a displacement rate of 2.1 mm/min with confining pressure of 50kPa,
100kPa, and 200Kpa at ambient temperature (25oC). The membrane used for triaxial test
manufactured in laboratory, the typical membrane and device are shown in Figure I.9
and Figure I.9. The conditioned specimen with the membrane placed in the triaxial cell
and loaded in the MTS loading frame as shown in Figure I.11 and I.12. The external LVDTs
positioned at the lower side of the triaxial cell wired to Spider 8 (signal condition unit) which in
turn wired to the computer for real time recording and data storage. The resilient Modulus and
shear parameters determined from the test presented in the Section 6.
Figure I.9: Rotary membrane device. Figure I.10: Produced membrane (150 x 550mm)
Water supply
Triaxial Cell
ON –OFF Solenoid valves
Pressure gaugePressure control
Water pump
ON -OFF Timer 0-60 sec
Pressurized Tank 20L
Conditioning of specimen
ON –OFF Solenoid valves
Pressure gaugePressure control
Water pump
ON -OFF Timer 0-60 sec
Pressurized Tank 20L
Conditioning of specimen
Triaxial Cell
Water supply
Water pressure gauge 600kPa
21
Figure I.11: Triaxial loading system (MTS) Figure I.12: Method of fitting
membrane to the wet specimen
5.4.2 MIST testing procedure
The testing procedure adopted in the MIST device testing system is summarised below. It
involves several steps, for proper ranking of the tested BSMs,
5.4.2.1 Evaluation and grouping of specimens
After curing, the wet bag removed and the specimens let to cool at ambient temperature (25oC)
for about one hour. Cover the specimens immediately if delay occurs for conditioning. After
cooling, the following physical tests and measurements of each specimen carried-out:
- The average height (t) and average Diameter (D)
- Rice’s density (Gmm) in accordance with THM1 Method C4
- Bulk relative density (Gmb) in accordance with THM1 Method C3
- The specimen volume (E) as a difference in specimen weighed in water and specimen
saturated surface-dry weight.
- Percentage air void (Pa) in accordance with THM1 Method C3.
Group the specimens into a set of two, with approximately equal void content (Pa). Separate
these sets with six (6) specimens for wet conditioning and static (monotonic) test, and other six
(6) for un-conditioning or dry static (monotonic) test.
Ext. LVDTs
22
5.4.2.2 Conditioning of specimens
- Set-up the test variables on MIST device i.e. ON-OFF timer at 0.54sec load time, and
1.40sec rest period, and regulate pressure gauge at 140kPa cyclic pulsing water
pressure. (Cyclic pressure might require adjustment to accommodate for the water
momentum).
- Place specimen in a triaxial cell base and assemble the cell firmly. Then connect the top
of the cell to the water pressure outlet, see Figure I.19.
- Start the MIST device and count 100 cycles, or time the haversine cyclic pulsing for 3.2
minutes then stop.
- De-assemble the triaxial cell, and remove the specimen carefully. Take weight of
saturated surface-dry specimen and transfer the specimen to the triaxial static
(monotonic) test set-up.
5.4.2.3 Calculation
Volume of air voids (Va) in specimen [cm3], 100
ΕΡ=
xV a
a Equation I.1
Volume of water absorbed (Vw) in specimen [cm3], ABVw −= Equation I.2
Degree of saturation (Sr) in specimen [%], 100xVV
a
wrs = Equation I.3
Where:
B = Weight of saturated-surface dry specimen [g]
A = weight of dry specimen in air [g]
Pa = air void content in specimen [%]
E = volume of specimen [cm3]
The degree of saturation should be at least 80% for accurate screening of the BSMs.
5.4.2.4Determination of Retained Cohesion ratio
- After conditioning, place the specimen into simple triaxial device set-up. Triaxial test is
performed in accordance with the procedure described in the Appendix to Simple triaxial
test protocol, Task 5.
- Two set of six (6) specimens with predetermined height and approximately equal void
content after conditioning are tested for static (monotonic) test at 50kPa, 100kPa, and
200kPa. Another two set of six (6) specimens tested unconditioned at 50kPa, 100kPa,
and 200kPa, with the applied rate of loading of 2.1mm/min.
- Shear properties (C and φ) of the conditioned and unconditioned sets of specimens are
determined in accordance with the procedure described in the Appendix to simple triaxial
test protocol, Task 5.
- Retained cohesion ratio calculated as follows:
23
100(CoD)mix,dry ofCohesion (CoW)mix, wet ofCohesion (RC)cohesion, Retained x= Equation I.4
Where, cohesion of wet and dry mix calculated from Mohr Coulomb cycle as per
Equation4.
Equation I.5
Where,
σ1f = Maximum principal stress at failure [kPa]
σ3 = confining pressure [kPa]
φ = internal angle of friction of the mix [deg]
C = cohesion of the mix [kPa]
5.4.2.4Determination of Residual Modulus ratio
- Two set of six (6) specimens grouped in section 5.4.2.3 above are tested for short
dynamic (resilient) test. Short dynamic test is non-destructive test; therefore, it
performed on specimen prior monotonic test.
- Short dynamic (resilient) test performed in accordance with the procedure developed in
Stellenbosch University (ITT, 2007). Conditioned and unconditioned sets of specimens
tested at Stress Ratio of 10% and confinement pressure of 50kPa at ambient
temperature (25oC). Three external LVDTs are mounted below triaxial cell to measure
materials recovery displacement.
- After application of 5000 load cycles, the specimen is conditioned in MIST device at
different saturation levels, i.e. 50%, 80% and 100% then Resilient Modulus determined.
For un-conditioned specimen, dry Resilient Modulus is determined after application of
5000 load cycles.
- After Resilient Modulus test, static (monotonic) test applied on the same specimen at
confining pressure of 100kPa to determine the shear properties (C and φ) of the
conditioned and unconditioned sets of specimens.
- Residual Modulus ratio calculated as follows:
100mix,dry of ModulusResilient
(100%) Sat ModulusResilient (RM)Modulus, Residual r x= Equation I.6
Where,
Sr = Degree of saturation [%]
Ranking of mixture in term of moisture damage severity is determined from the calculated
ratios. The BSMs with high ratio show good resistance to moisture damage and BSMs with lower
ratio shows poor resistance to moisture damage. A ratio in between can be ranked medium to
good or medium to poor.
The ranking of the BSMs validated by APT laboratory MMLS3 model device with related setting
applied on MIST device.
ϕϕσ
ϕϕσ
sin1cos..23
sin1sin1
,1 −+
−+
=C
f
24
6. TESTS RESULTS
6.1. Compaction density achieved by BOSCH® compactor
Table I.6: Compaction density achieved on BSMs using BOSCH® compactor
BSM-Mix
type
Compaction
moisture content
(5.12%OMC-H,
6%OMC-Q)
Weight after
compaction
[g]
Weight after
curing
[g]
Density
[Kg/m3]
after curing
Percentage MoD
AASHTO
(Target density
2177.3 Kg/m3-H,
2240Kg/m3-Q)
H+0C-F 4.5 (88%) 10 047.6 9 856.0 2 230.9 102
H+1C-F 4.7 (90%) 10 007.0 9 746.8 2 225.6 102
H+1L-F 4.9 (95%) 9 949.1 9 785.7 2 215.0 102
Q+0C-F 4.0 (70%) 10 250.7 9 959.1 2 254.0 101
Q+1C-F 4.3 (72%) 10 190.4 9 929.3 2 246.4 100
Q+1L-F 4.5 (75%) 10 224.0 9 955.7 2 253.4 101
H+0C-E 4.4 (85%) 10 130.2 9 899.0 2 240.4 103
H+1C-E 3.7 (72%) 10 014.8 9 864.0 2 232.7 103
H+1L-E 5.12 (100%) 10 151.3 9 921.7 2 245.9 103
Q+0C-E 3.6 (60%) 10 262.1 10 101.6 2 286.2 102
Q+1C-E 3.2 (53%) 10 328.6 10 156.3 2 300.1 103
Q+1L-E 4.3 (72%) 10 247.5 10 035.3 2 271.3 101
Note: Bracket values, is (% OMC) of moisture in the mixture during compaction.
6.2. Moisture content in specimens after curing
Table I.7: Percentage moisture in the specimen after standard curing
BSM-Mix
type
Compaction
moisture content
(5.12%OMC-H,
6%OMC-Q)
Weight after
compaction
(g)
Weight after
curing
(g)
Moisture
content after
curing
[%]
Percentage
moisture loss
[%]
H+0C-F 4.5 (88%) 10 047.6 9 856.0 2.6(51%) 1.9(37%)
H+1C-F 4.7 (92%) 10 007.0 9 746.8 2.0(39%) 2.7(53%)
H+1L-F 4.9 (96%) 9 949.1 9 785.7 3.2(63%) 1.7(33%)
Q+0C-F 4.0 (67%) 10 250.7 10 055.0 2.1(35%) 1.9(32%)
Q+1C-F 4.3 (72%) 10 190.4 9 998.7 2.4(40%) 1.9(32%)
Q+1L-F 4.5 (75%) 10 224.0 9 969.7 1.9(33%) 2.6(43%)
Note: Bracket values, is (% OMC) of moisture remained in the specimen after curing.
25
Table I.7: Percentage moisture in the specimen after standard curing
BSM-Mix
type
Compaction
moisture content
(5.12%OMC-H,
6%OMC-Q)
Weight after
compaction
(g)
Weight after
curing
(g)
Moisture
content after
curing
[%]
Percentage
moisture loss
[%]
H+0C-E 4.4 (85%) 10 130.2 9 899.0 2.1(40%) 2.3(45%)
H+1C-E 3.7 (72%) 10 014.8 9 864.0 2.2(42%) 1.5(30%)
H+1L-E 5.1(100%) 10 151.3 9 921.7 2.8(55%) 2.3(45%)
Q+0C-E 3.6 (60%) 10 262.1 10 101.6 2.0(33%) 1.6(27%)
Q+1C-E 3.2 (53%) 10 328.6 10 156.3 1.5(25%) 1.7(28%)
Q+1L-E 4.3 (72%) 10 247.5 10 035.3 2.2(36%) 2.1(36%)
Note: Bracket values, is (% OMC) of moisture remained in the specimen after curing.
6.3. Volumetric properties of BSMs prepared specimens
Table I.8: Bulk relative density, Rice density and voids content
BSM-Mix type Bulk Relative
density, BRD
[Kg/m3]
RICE density
[Kg/m3]
Voids content
[%]
H+0C-F 2 177 2590 16.0
H+1C-F 2 332 2593 13.5
H+1L-F 2 241 2592 14.0
Q+0C-F 2149 2572 16.5
Q+1C-F 2196 2573 14.6
Q+1L-F 2198 2561 14.5
H+0C-E
H+1C-E 2215 2577 14.0
H+1L-E 2237 2694 13.0
Q+0C-E 2139 2540 15.8
Q+1C-E 2201 2516 12.5
Q+1L-E 2273 2584 12.0
26
6.4. MIST saturation levels
Table I.9: Maximum saturation level of BSMs relative to %OMC
BSM-Mix
type
Pulsing time
{Fully
cycle=1.94sec}
[min]
Pulsing
cycle
[no.]
Moisture
content after
curing
(Dry cond.)
[%]
Moisture
content in the
spec after
MIST
[%]
Steady
saturation level
[%]
H+0C-F 1.1 35 2.6(51%) 4.7 73 (73)
H+1C-F 3.6 110 2.0(39%) 5.5 90 (102)
H+1L-F 3.2 100 3.2(63%) 6.1 99 (109)
Q+0C-F 1.3 40 2.1(35%) 3.6 48 (48)
Q+1C-F 1.6 50 2.4(40%) 4.1 62 (62)
Q+1L-F 1.6 50 1.9(33%) 4.0 61 (61)
H+0C-E 3.9 140 2.1(40%) 4.6 78 (78)
H+1C-E 9.7 260 2.2(42%) 5.3 100 (114)
H+1L-E 6.5 300 2.8(55%) 4.5 100 (112)
Q+0C-E 1.3 30 2.0(33%) 4.3 60 (60)
Q+1C-E 9.7 260 1.5(25%) 5.6 78(78)
Q+1L-E 5.5 170 2.2(36%) 5.7 87 (87)
Note: Bracket values, is (% OMC) of moisture in the specimen after curing are MIST cond.
6.5. Mechanical performance of BSMs before and after MIST test
Table I.10: Static (Monotonic) triaxial test at unconditioned and conditioned specimen
BSM-Mix type
specimen
Condition σ3 [kPa]
Fmax [kN]
Residual Deviator
Stress Ratio [50kPa]
Residual Deviator
Stress Ratio [100kPa]
C [kPa]
φ [deg]
Residual cohesion
ratio
H+0C-F
H+1C-F Incomplete tests due to in adequate no. of specimen made
H+1L-F
Q+0C-F02 Dry 50 27.34
Q+0C-F05 Dry-(Mr) 100 38.82
Q+0C-F08 Dry 200 43.97 269.0 48.02
Q+0C-F06 Wet 50 17.04 50
Q+0C-F01 Wet-(Mr) 100 17.19 60
Q+0C-F07 Wet 200 34.68 82.7 51.32 30.7
Note: DRY = specimen cured using standard procedure, WET= specimen conditioned in MIST apparatus
27
Table I.10: Static (Monotonic) triaxial test on unconditioned and conditioned specimen
BSM-Mix type
specimen
Condition σ3 [kPa]
Fmax [kN]
Residual Deviator
Stress Ratio [50kPa]
Residual Deviator
Stress Ratio [50kPa]
C [kPa]
φ [deg]
Residual cohesion
ratio
Q+1C-F07 Dry 50 36.04
Q+1C-F02 Dry-Mr 100 43.62
Q+1C-F04 Dry 200 55.50 297.0 51.61
Q+1C-F06 Wet 50 26.81 78
Q+1C-F05 Wet-Mr 100 37.24 83
Q+1C-F01 Wet 200 49.07 196.0 53.42 66.0
Q+1L-F03 Dry 50 23.60
Q+1L-F05 Dry-Mr 100 33.46
Q+1L-F02 Dry 200 43.09 187.0 51.24
Q+1L-F06 Wet 50 20.19 78
Q+1L-F01 Wet-Mr 100 25.22 84
Q+1L-F07 Wet 200 39.45 128.0 51.68 68.4
Table I.10: Static (Monotonic) triaxial test on unconditioned and conditioned specimen
BSM-Mix type
specimen
Condition σ3 [kPa]
Fmax [kN]
Residual Deviator
Stress Ratio [50kPa]
Residual Deviator
Stress Ratio [50kPa]
C [kPa]
φ
Residual cohesion
ratio
H+0C-E05 Dry 50 17.14
H+0C-E02 Dry-Mr 100 20.15
H+0C-E04 Dry 200 27.03 178.0 40.73
H+0C-E07 Wet 50 10.03 58
H+0C-E01 Wet-Mr 100 12.50 63
H+0C-E09 Wet 200 17.40 95.0 38.36 53.4
H+1C-E01 Dry 50 24.27
H+1C-E08 Dry-Mr 100 27.52
H+1C-E09 Dry 200 30.10 370.0 30.76
H+1C-E04 Wet 50 15.60 64
H+1C-E03 Wet-Mr 100 17.41 64
H+1C-E07 Wet 200 19.30 274.0 25.49 74.1
H+1L-E01 Dry 50 20.12
H+1L-E03 Dry-Mr 100 21.92
H+1L-E05 Dry 200 31.00 193.0 42.85
H+1L-E07 Wet 50 13.03 72
H+1L-E02 Wet-Mr 100 19.41 78
H+1L-E04 Wet 200 25.51 120.0 43.92 62.2
28
Table I.10: Static (Monotonic) triaxial test on unconditioned and conditioned specimen
BSM-Mix type
specimen
Condition σ3 [kPa]
Fmax [kN]
Residual Deviator
Stress Ratio [50kPa]
Residual Deviator
Stress Ratio [100kPa]
C [kPa]
φ [deg]
Residual cohesion
ratio
Q+0C-E Incomplete test
Q+1C-E05 Dry 50 18.61
Q+1C-E03 Dry-Mr 100 25.01
Q+1C-E06 Dry 200 32.30 173.0 45.64
Q+1C-E08 Wet 50 16.00 87
Q+1C-E01 Wet-Mr 100 23.57 93
Q+1C-E07 Wet 200 32.26 125.0 48.48 72.3
Q+1L-E01 Dry 50 12.86
Q+1L-E10 Dry-Mr 100 16.50
Q+1L-E02 Dry 200 26.66 88.0 46.50
Q+1L-E04 Wet 50 10.40 74
Q+1L-E05 Wet-Mr 100 10.93 75
Q+1L-E03 Wet 200 20.45 72.0 41.89 81.8
Note: DRY = specimen cured using standard procedure, WET= specimen conditioned in MIST apparatus
Table I.11: Dynamic (Resilient) triaxial test on unconditioned and conditioned specimen
Dry Mr-after 5000
rep at σ3=50kPa
[MPa]
Wet Mr-at σ3=50kPa different Saturation
level [MPa]
BSM-Mix type
specimen
Condition
Spec- MC Sr-50%
Sr-80% /90%
Sr-100%
Residual modulus
ratio
H+0C-F Incomplete
H+1C-F06 Dry 1165
H+1C-F03 Wet 1160 1001 728 0.62
H+1L-F06 Dry 682
H+1L-F05 Wet 751/1064 681 1.00
Q+0C-F05 Dry 680
Q+0C-F04 Wet 646 524 356 0.52
Q+1C-F06 Dry 926
Q+1C-F03 Wet 672 674 628 0.68
Q+1L-F05 Dry 833
Q+1L-F01 Wet 718 727 749 0.90
Note: DRY = specimen cured using standard procedure, WET= specimen conditioned in MIST apparatus
29
Table I.11: Dynamic (Resilient) triaxial test on conditioned and conditioned specimen
Dry Mr-after 5000 rep
at σ3=50kPa [MPa]
Wet Mr-at σ3=50kPa and different
Saturation level [MPa]
BSM-Mix type
specimen
Condition
Spec- MC Sr-50% Sr-80%
Sr-100%
Residual modulus
ratio
H+0C-E03 Dry 526
H+0C-E01 Wet 439 390 309 0.52
H+1C-E06 Dry 1451
H+1C-E03 Wet 1340 1218 1151 0.79
H+1L-E03 Dry 679
H+1L-E02 Wet 608 581 515 0.76
Q+0C-E07 Dry 436
Q+0C-E08 Wet 383 338 232 0.53
Q+1C-E03 Dry 1343
Q+1C-E01 Wet 1209 1097 1023 0.76
Q+1L-E10 Dry 743
Q+1L-E05 Wet 878 849 526 0.71
Note: DRY = specimen cured using standard procedure, WET= specimen conditioned in MIST apparatus
6.6. Correlation, MMLS3 trafficking on BSMs at dry and wet condition
Table I.12: Rut-depth after MMLS3 trafficking on wet BSMs specimens
No of load repetitions 500 1500 2500
BSM-Mix type specimen
Condition
Rut-depth [mm]
H+0C-E01 Wet 1.98 6.75 14.37
H+0C-E06 Wet 1.02 2.97 15.12
H+0C-E07 Wet 1.14 8.55 14.14
Average 1.38 6.09 14.54
Q+0C-E08 Wet 0.36 0.30 12.77
Q+0C-E06 Wet 0.78 0.57 12.16
Q+0C-E05 Wet 1.30 0.60 12.20
Q+0C-E04 Wet 0.64 1.18 12.39
Average 0.76 0.66 12.38
30
Table I.13: Rut-depth after MMLS3 trafficking on dry BSMs specimens
No of load repetitions 0 1500 2500
BSM-Mix type specimen
Condition
Rut-depth [mm]
H+0C-E02 Dry 1.20
H+0C-E03 Dry 0.99
H+0C-E04 Dry 0.81
H+0C-E08 Dry 0.85
Average 0.96
Q+0C-E07 Dry 0.78
Q+0C-E03 Dry 0.52
Q+0C-E01 Dry 0.76
Average 0.69
Table I.14: Rut depth after MMLS3 trafficking on wet BSMs specimens
No of load repetitions
200 3000 7000 15000 25000 40000 45000
BSM-Mix type
specimen
Condition
Rut-depth [mm]
H+1C-E02 Wet 0.53 0.69 0.19 -0.14 -0.23 0.12 0.1
H+1C-E03 Wet - - - - - - -
H+1C-E06 Wet 0.24 0.16 0.00 -0.28 -0.43 -0.24 -0.13
Average 0.39 0.42 0.10 -0.21 -0.33 -0.06 -0.01
H+1L-E08 Wet 0.25 0.05 0.07 -0.18 0.77 3.28 7.07
H+1L-E05 Wet 0.40 0.64 0.61 0.88 2.55 3.39 8.45
H+1L-E03 Wet 0.63 0.66 0.62 0.68 0.58 6.28 12.87
H+1L-E02 Wet 0.58 0.71 0.65 0.74 0.68 2.78 13.86
Average 0.47 0.51 0.49 0.53 1.14 3.98 10.56
1000 1700 4500
H+1C-E01 Dry 0.59 0.66 0.41
H+1C-E04 Dry 0.46 0.57 0.41
H+1C-E05 Dry 0.39 0.45 0.32
Average 0.48 0.54 0.4
H+IL-E09 Dry 0,59 0.76 0.91
H+1L-E07 Dry 0.43 0.53 0.33
H+1L-E06 Dry 0.56 0.43 0.47
H+IL-E01 Dry 0.56 0.71 0.72
Average 0.52 0.61 0.61
31
7. ANALYSIS AND DISCUSSION OF RESULTS
7.1. Compaction density; vibratory (BOSCH®) compactor versus MOD
AASHTO compactor
The MOD AASHTO compactor determined the maximum dry density and optimum moisture
content of the prepared specimen. The compaction level achieved on specimen by vibratory
(BOSCH®) compactor related to MOD AASHTO compaction level. In Table I.6, the compaction
result of BSMs shows that all specimens compacted more than 100% MOD AASHTO maximum
dry density.
During vibratory compaction however, the OMC determined by MOD AASHTO compactor found
to be on the wet side of optimum. This is due to nature of compaction method, i.e. vibration
versus impact. The higher moisture content during vibration compaction resulted into loss of
slurry (moisture and binder) through bleeding, see photo Figure I.13. It is recommended that
the proper correlation of OMC and maximum dry density of these compaction methods need to
be critically determined.
Figure I.13: Loss of slurry during vibratory compaction due to higher MC
7.2. Moisture content after curing
The curing procedure followed in this study show that BSM-foam mixes and BSM-emulsion mixes
do not lose moisture equally. It is clear from the results Table I.7 that moisture loss on different
BSMs during curing procedure is not uniform. The relative higher moisture loss in average
occurred on BSM-foam than BSM-emulsion. The attributes of the different moisture losses
described as followed:
32
- the mixing moisture varies from different mixes.
- some moisture loss occurred during vibratory compaction.
- the size of the oven and oven set-up
- number of specimens in the oven (big number less moisture loss due to high humidity)
- nature of binder on the BSM-foam and BSM-emulsion
The results presented in Figure I.14 shows that aggregates type either hornfels or quartzites
have no particular trend on different loss of moisture after curing. The percentage moisture is
calculated relative to %OMC. Similarly, there is no clear trend of losing moisture contributed by
the use of active filler or not.
Figure I.14: Variation of moisture loss during curing of BSMs
7.3. Volumetric properties
The vibratory (BOSCH®) compaction packs the aggregate particles in specimen closely, similar to
field condition. However, the inter-particle voids in the BSMs are usually higher than in HMA. The
attribute of higher voids content in BSMs relates to lower binder content, higher viscosity (cold to
warm) binder, and presence of moisture during mixing, which later evaporates. The determined
inter-particle voids in the BSM-foam and BSM-emulsion, see Table I.8, fall in a range of 12% to
17%. Whereby, BSM-foam shows relatively higher inter-particle voids than BSM-emulsion.
The Bulk Relative Density (BRD) and Rice density were determined as per THM1, Method C4 and
Method C3. However, weak specimen broke during BRD test, then alternative of sealing specimen
with plastic before BRD test opted. The results on Table I.8 show that some BRD values are
lower than the maximum dry density. This irregularity of BRD values might have occurred due to
penetration of water through sealed plastic during soaking. For statistical reliability, three
specimens are required for BRD tests.
0
10
20
30
40
50
60
H+0C
-F
H+1C-F
H+1L-F
Q+0C
-F
Q+1C
-F
Q+1L-F
H+0C
-E
H+1C
-E
H+1L-E
Q+0C
-E
Q+1C-E
Q+1L-E
Per
cent
age
moi
stur
e lo
ss [
%]
H = Hornfels -RAP Q = Quartzites
BSM-Mixes
33
The results presented in Figure I.15 and Figure I.16 show that aggregates type i.e. either
Hornfels or Quartzites, has no particular influence on different voids content on BSM mixes.
However, there is clear trend of increase in voids content on BSM without filler compared with
the one with addition of active filler (i.e. lime or cement).
Figure I.15: Percentage void content on tested BSM-mixes
Figure I.16: Influence of active filler on void contents on BSM-Mixes
7.4. MIST saturation level
The particle inter-lock, particle type, and binder content determine the steady saturation level of
the BSMs. The mixes with high void content shows higher erosion due to high void pore pressure
developed during pulsing time. Table I.9 shows the pulsing time or pulsing cycle to achieve
steady saturation level. The saturation level related to OMC of the mixes. From the results, see
Table I.9 and Figure I.17, it is clear that moisture susceptible mixes shows severe erosion
0
4
8
12
16
20
24
H+0C
-F
H+1C
-F
H+1C
-E
H+1L
-F
H+1L
-E
Q+0C
-F
Q+0C
-E
Q+1C
-F
Q+1C
-E
Q+1L-F
Q+1L-E
0
4
8
12
16
20
24
H+0C
-F
H+1C
-F
H+1L
-F
Q+0C-
F
Q+1C-
F
Q+1L-F
H+1C
-E
H+1L
-E
Q+0C-
E
Q+1C-
E
Q+1L-E
BSM-Mixes
Per
cent
age
void
con
tent
[%
]
H = Hornfels -RAP Q = Quartzites
BSM-Mixes
Per
cent
age
void
con
tent
[%
] H = Hornfels -RAP Q = Quartzites
34
(damage) at wet saturation. BSMs with Quartzites had lower wet saturation before damage
occurred. The causes of severe damage are; firstly higher void content. Secondly, low cohesion
and adhesion of binder to mix. These factors contributed significantly to the serious erosion
during pulsing of water pressure into specimen. Figure I.17 show stripping and erosion condition
of BSMs with Quartzite after 1minute of MIST saturation.
Figure I.17: Stripping and erosion on specimen after 1min of MIST saturation
The degree of saturation (steady saturation level) calculated as a ratio of the volume of water to
the volume of total void space in the specimen, Equation I.7.
Equation I.7
Where,
Sr = Degree of saturation [%]
Vw = Volume of water in the specimen [m3]
Vv = Volume of void in the specimen [m3]
The calculation of the degree of saturation takes into account that the OMC of the compacted
BSM-mixes occurs when the degree of saturation is 80%. Savege, (2006) did mathematical
formulation indicating different legs of degree of saturation see Figure I.18. Savege further
concluded that after 80% of saturation level any addition of water push the particle apart or
destroying interlock and density fall occurs.
vvwv
rs =
35
Figure I.18: Mathematical model of the 80% saturation level at OMC of the mixes
The steady level of saturation in this study determined by checking that there is no change in wet
mass on specimen on consecutive numbers of pulsing cycles (i.e. prohibiting more moisture
ingress in a specimen). Moisture content of specimen at steady level of saturation determined as
per THM1 Method A11T. The results in Table I.9 show that less moisture susceptible BSMs have
tendency of prohibiting moisture ingress then resulting into steady saturation level around %OMC
of the mixes. While the high moisture susceptible BSMs have a tendency of stripping binder and
erosion at steady saturation level less than %OMC of the mixes.
Aggregates particle type also contributes to saturation level. Quartzites aggregate particles show
less ability to retain moisture. Although some of the Quartzites mixes are less moisture
susceptible, but their steady saturation level are less than the OMC, see Table I.9 and Figure
I.19. This is attributing to the glassy type of particles, which is resistance to moisture absorption.
For the Hornfels-RAP aggregates type, the retention of moisture was around OMC for both
moisture susceptible mixes and less moisture susceptible mixes.
Figure I.19: Saturation level of different BSM-mixes
0
20
40
60
80
100
120
0 2 4 6 8 10 12
H+0C-F H+1C-F H+IL-F Q+OC-F Q+1C-F Q+IL-F
H+OC-E H+1C-E H+IL-E Q+0C-E Q+1C-E Q+1L-E
MIST pulsing time [min] Max
imum
sat
urat
ion
leve
l as
%O
MC
36
The results in Figure I.19 can be summarised as follows:
- After curing, one specimen selected and conditioned to determine how long can
withstand the cyclic water pressure. After conditioning, moisture ingress in the mix is
determined to calculate the degree of saturation. The number of pulsing cycles or time
determined to obtain steady saturation level then used on the remained specimens for
determination of retained cohesion of the BSMs.
- The steady saturation level before damage on specimen found to be different on
different BSMs. The BSMs that are susceptible to moisture (weak in cohesion) withstand
low MIST pulsing cycles or pulsing time at least 2minutes (62 cycles). While the BSMs
resistant to moisture damage (high cohesion), withstand high number of MIST pulsing
cycle above 3.2minutes (100 cycles) with no damage.
- The difference in MIST pulsing cycles (time) on BSMs, relates well with the residual
cohesion determined by static dynamic triaxial test. The BSMs that withstand higher
number of pulsing cycles shows high residual cohesion. While the BSMs that withstand
lower pulsing cycles show less cohesion strength.
- From Figure I.19, it can be seen that most BSMs attain steady saturation level after 3.2
minutes pulsing time (100 pulsing cycles). Therefore, conclusion can drawn that
3.2minutes pulsing time or 100 pulsing cycles is threshold to screening of the BSMs.
BSMs which cant withstand the threshold is regarded highly susceptible to moisture
damage. Therefore, its selection in the mix design needs proper consideration. While
BSMs, which can withstand the threshold value, justify it’s selected in the mix design.
- By using the MIST threshold values, the following ranking criteria Table I.15 can be
proposed for the BSMs mix design in relation to moisture damage.
Table I.15: Recommended Retain Cohesion after MIST conditioning MIST
Pulsing cycle
[no.]
MIST
pulsing time
[min]
Equivalent residual
cohesion percentage
[%]
Possible equivalent
design material
≥ 75 BSM 1
≥ 60 BSM 2
100
3.2
≥ 50 BSM 3
The general characteristics found on MIST device after testing different BSMs are:
- Saturate compacted and cured BSMs by pulsing moisture into specimen in a fashion
similar to field condition.
- Achieve conditioning and steady state saturation levels of BSMs in shortest possible time
3.2minutes or 100 pulsing cycles.
37
- Ability to predict earlier the moisture susceptible BSMs suitable.
- Easily to operate, once predetermined parameters are set.
- Potential for the quality control and assurance on the field
7.5. Mechanical performance of BSMs before and after MIST test
The mechanism of failure of BSMs through moisture damage is uncertain. For this reason, it is
necessary to carry out mechanical tests before and after MIST saturation in order to determine
the effect of the moisture exposure on shear properties and stiffness of mixes.
Static (monotonic) triaxial test procedures have been performed on BSMs under two conditions
i.e. maximum saturation and dry state. The ratio of wet to dry states give an indication on how
the ingress of moisture in mixes destroys the aggregate-binder cohesion and aggregates
interlocking strength. In addition to mechanical tests, further analysis on micro-structural level
of moisture effect on the interaction between foamed bitumen mastic filler-aggregates is
required.
The results in Table I.11 indicate the BSMs shear properties before and after MIST saturation.
The residual cohesion ratio calculated as a ratio of cohesion of wet mix to cohesion of dry mix as
in Equation I.4 above.
(CoD)mix,dry ofCohesion (CoW)mix, wet ofCohesion (RC)cohesion, Retained = Equation I.4
Where, cohesion of wet and dry mix calculated from Mohr Coulomb cycle as per Equation I.5.
Equation I.5
Where,
σ1f = Maximum principal stress at failure [kPa]
σ3 = confining pressure [kPa]
φ = internal angle of friction of the mix [deg]
C = cohesion of the mix [kPa]
The results in Table I.11 indicate that in average BSM-foam have lower residual cohesion ratio
compared to BSM-emulsion. The characteristics of binder-aggregates types and their interaction,
has influence on the residual cohesion ratio. Quartzites aggregate stabilised with either foamed
bitumen or bitumen emulsion without active filler has shown lower residual cohesion ratio
compared to Hornfels-RAP aggregates.
The influence of active filler cement, or lime on the resistance to moisture damage on BSMs is
clear. The Quartzites aggregates treated with 1% cement or lime and stabilised with either
foamed bitumen or bitumen emulsion, has 56% more water resistant than without active filler.
ϕϕσ
ϕϕσ
sin1cos..23
sin1sin1
,1 −+
−+
=C
f
38
While Hornfels-RAP aggregates treated with 1% cement or lime and stabilised with bitumen
emulsion is 22% more water resistance than without active filler.
From the results of residual cohesion ratio, ranking of BSMs can be classified as GOOD, MEDIUM,
and POOR using the following designed limit, Figure I.1.
Figure I.20: Proposed limits for the Retained cohesion of BSMs after MIST saturation.
The comparisons of residual deviator stress ratio at 50 kPa and 100kPa see Figure I.21, show
that these ratios are less sensitive to moisture damage in the BSMs. Whilst, better moisture
sensitivity is indicated in the Retained cohesion ratio. It is there recommended that moisture
susceptible on BSMs determined using Residual Cohesion ratio.
Figure I.21: comparison on sensitivity of Retained cohesion and Retained Deviator Stress of BSMs
The short dynamic (resilient) triaxial test performed to determine the Residual Modulus (Mr)
ratio. The Residual Modulus ratio calculated as a ratio of Resilient Modulus of wet mixes to
Resilient Modulus of similar dry mixes. The short dynamic test performed at confining pressure of
0
10
2030
40
50
60
7080
90
100
Q+ 0C -F Q+ 1C -F Q+ 1L -F Q+ 1C-E Q+ 1L -E H+ 0C -E H+ 1C -E H+ 1L -E
Retained Cohesion Deviator Stress Ratio at 50kPa Daviator Stress Ratio at 100kPa
Tested BSMs
Ret
aine
d D
evia
tor
Stre
ss [
%]
0102030405060708090
Q+ 0C
-F
Q+ 1C
-F
Q+ 1L
-F
Q+ 1C
-E
Q+ 1L
-E
H+ 0C
-E
H+ 1C
-E
H+ 1L
-E
BSM 1BSM 2
BSM 3
Res
idua
l coh
esio
n [%
]
Tested BSMs
39
50 kPa to reduce the effect of pore water pressure in the specimen. However, 50kPa confining
pressure seemed to be uncontrollable during the test. Un-steady confinement provides variable
results. Therefore, 50kPa confinement not recommended for determining residual modulus ratio.
However, the higher confining pressure say 100kPa might yield better results.
Table I.11 shows the results of Resilient Modulus at different saturation levels and Residual
Modulus ratio at 50kPa confining pressure. From the results, it is clear that the resilient modulus
decreases as the saturation level increases. This behaviour indicates that ingress of moisture in
the BSMs destroys stiffness behaviour of the mixes. The BSM-emulsion experiences a consistent
drop of resilient modulus as saturation level increases see Figure I.22. On the other hand, BSM-
foam has an inconsistent in resilient modulus as saturation level increases.
On average, the BSMs both Quartzites and Hornfels without addition of active filler in a state of
dry or wet condition ,have lower resilient modulus compared to the mixes with additional active
filler. The influence of active filler (cement or lime) on the increase of resilient modulus is
evident for both BSM-foam and BSM-emulsion in all aggregates.
Figure I.22: Resilient Modulus of BSMs at different saturation level
Figure I.23, shows the comparison of BSM-foam and BSM-emulsion stiffness reduction due to
ingress of moisture in the mix. The ingress of moisture in BSM-foam has more effect on stiffness
reduction compared to BSM-emulsion. However, the addition of active filler in the BSM-emulsion
has significant contribution to its stiffness retention even after the ingress of water. Some
interesting behaviour noted on the BSM-foam and BSM-emulsion with addition of lime. The anti-
striping behaviour of lime causes an increase in resilient modulus as saturation of the mixes
increase. However, the effect on stiffness reduction occurs at high saturation levels above the
OMC of the mixes. Although this is not a general behaviour of all of the lime mixes. it a
phenomenon that needs to be recognised, when either cement or lime selected for the BSM mix
design.
0
200
400
600
800
1000
1200
1400
1600
Q+0C-
F
Q+1C-
F
Q+1L-F
H+1C
-F
H+1L
-F
Q+0C-
E
Q+1C-
E
Q+1L-E
H+0C
-E
H+1C
-E
H+1L
-E
Sr-0% Sr-50% Sr-80% Sr-100%
Tested BSMs
Res
ilien
t Mod
ulus
[MPa
]
40
The use of MIST devices has provided some insight on the failure behaviour of BSM with the
ingress of water. The residual cohesion and retained modulus determined after MIST saturation
yield results that are consistent with mechanical performance of BSM mixes under different
moisture conditions.
Figure I.23: Resilient Modulus versus Saturation levels of BSM-foam and BSM-emulsion
Figure I.24, show the relationship between the Residual Cohesion (RC) and Retained Modulus
(RM) of the BSMs. These two parameters seem to have good correlation, though with some
variability.
Figure I.24: The relationship between Retained Cohesion and Residual Modulus of
BSMs
During short dynamic test three external Linear Variable Displacement Transducers (LVDTs) were
used to improve statistics of the captured results. However, the results on these LVDTs provided
significant variability. However, due to computer set-up it was possible to analyse the captured
0
10
20
30
40
50
60
70
80
90
100
Q+1C-F Q+1L-F H+0C-E H+1C-E Q+1C-E Q+IL-E
Residual Cohesion (RC) Reatained Moudulus (RM)
0
200
400
600
800
1000
1200
1400
1600
Sr-0% Sr 50% Sr 80% Sr 100%
Q+0C-E Q+1C-E Q+1L-EH+OC-E H+1C-E H+1L-E
0
200
400
600
800
1000
1200
1400
1600
Sr-0% Sr 50% Sr 80% Sr 100%
Q+OC-f Q+IC-F Q+1L-F H+1C-F H+IL-F
Lime behaviour
Saturation Level [%]
Res
ilien
t Mod
ulus
[MPa
]
Saturation Level [%]
BSM-Foam BSM-Emulsion
Tested BSMs
Ret
aine
d C
ohes
ion/
Mod
ulus
[%]
41
results promptly and do a repeat test where results were not logical. This was possible due to
experience with stiffness behaviour of BSMs and the past results of similar mixes. The
inconsistencies of external LVDTs on a repeat test show that this method is not reliable as
ranking criteria for the moisture susceptibility. Some inconsistency on the capture resilient
modulus is shown in Figure I.25.
.
Figure I.25: Example of inconsistence results captured by LVDT’s during short dynamic test.
It is obvious that resilient modulus of BSMs, tested at a confinement pressure of 50kPa and
stress ratio of 10%, will not be 3882 MPa, also its average. Therefore, repeat tests were
inevitable, to provide a logical value. For this reason, a short dynamic (triaxial) test with
external measuring LVDT’s is not recommended for screening BSMs. Ranking of BSMs with
respect to moisture susceptibility should be carried out with MIST and static (monotonic) triaxial
test.
7.6. Correlation, MMLS3 trafficking on BSMs at dry and wet condition
The representativeness of the performance of BSMs conditioned in the MIST device could not be
verified without a correlation test. The selection of MMSL3 for correlation test takes into account
its known performance and ability to simulate field condition. Similar testing matrix of BSMs
Table I.3 prepared for the MMLS3 testing. Wet and dry trafficking carried-out to determine the
residual tensile strength. The residual tensile strength was determined by carrying out ITS tests.
However, ITS test provides inconsistence results, therefore ravelling depth (RvD) determined
during MMLS3 wet trafficking was correlated to MIST Residual Cohesion (RC) ratio.
Figure I.26 presents the cumulative rut-depth of the BSM-emulsion (Quartzites and Hornfels)
without addition of active filler. The mixes trafficked under wet condition at 25oC with MMLS3
axle load of 1.8kN, tyre pressure of 420kPa and trafficking speed of 7200 wheel per hour. The
average cumulative rut-depth/ ravelling-depth was 14 mm after 2500 load applications. These
results show that BSM-emulsion without active filler is highly susceptible to moisture damage.
Similar conclusions can be drawn from the residual cohesion ratio determined on MIST
saturation and static dynamic test.
DRY-REPEAT
DRY
Recorded
1194 LVDT1
739 LVDT2
3882 LVDT3
1223 LVDT1
827 LVDT2
1446 LVDT3
1938
1165
1165
42
The effect of moisture damage during MMLS3 wet trafficking resulted in the loss of aggregates.
No side heaving occurs in the wheel path, instead, moisture ingress into the mixes destroys the
cohesion properties of the mixes, and hence aggregate particles become loose. The spalling of
coarse and fine aggregates occurs due to traffic loading coupled with moisture ingress.
Figure I.26: Cumulative ravelling-depth of BSM-emulsion (Quartzite & Hornfels) with NO active filler, tested at 25oC, 1.8kN, 420kPa and 7200 w/hr
The highly moisture susceptible BSMs were trafficked first, followed by less moisture susceptible
BSMs. Figure I.27 presents the cumulative rut-depth/ravelling-depth of the BSM-emulsion
(Hornfels) with addition of 1% cement or lime.
The MMLS3 wet trafficking on BSM-emulsion (Hornfels) with active filler, used similar test
conditions applied on BSM-emulsion without active filler stated above. The average cumulative
rut-depth/ravelling-depth of 0.6 mm after 45000 load application occurred on cement mix.
Whilst an average of 10mm rut-depth/ ravelling-depth after 45000 load application occurred on
lime mixes. These results show that BSM-emulsion with the addition of cement is less
susceptible to moisture damage relative to similar mix with addition of lime. Similar conclusions
can be drawn for the residual cohesion determined on MIST saturation and static dynamic test.
-2
0
2
4
6
8
10
12
14
16
0 500 1000 1500 2000 2500 3000
H+0C-E01 H+0C-E06 H+0C-E07 Q+0C-E08
Q+0C-E06 Q+0C-E05 Q+0C-E04 AVERAGE
Cumulative number of load application
Rav
ellin
g-de
pth
[mm
]
43
Figure I.27: Cumulative ravelling-depth of BSM-emulsion (Hornfels) with 1% cement or lime, tested at 25oC, 1.8kN, 420kPa and 7200 w/hr
In conclusion, the MMLS3 rut/ravelling-depth on wet trafficking of the BSM-emulsion shows good
correlation with MIST and short dynamic tests. More testing is underway to be able to correlate
ravelling versus retained cohesion on each mix on the test matrix. Future research should also
look at the micro-level of the effect of moisture damage on BSMs after the MIST and MMLS3 for
accurate modelling the mechanism of BSMs failure under known moisture conditions.
The phenomenon of increasing stiffness at partial saturation levels (below OMC), was identified
for BSMs with addition of lime. This phenomenon needs further investigation at micro- structural
level and carrying-out proper triaxial test i.e. LVDT’s mounted on specimen. Better understating
of the lime performance in the BSMs might justify the advantages of applying moderate amounts
of lime instead of applying cement, to achieve the same mechanical performance. Further
identification of failure mechanisms of foam mastic- aggregates system in presence of water
requires attention.
Research done by Yong et al., (2006) investigates the potential contribution of lime as anti-
stripping agent of the HMA. The investigation looked deeper into the micro-structural level
Figure I.28 and concludes that lime provide mastic stiffing. The lime mastic stiffening induces
better resistance of moisture diffusion, and enhancement of aggregates-binder interfacial
bonding. This bonding produces better resistance to stripping. Similar investigation need to
looked for the BSM-foam and BSM-emulsion.
Figure I.28: The analysis of the effect of lime as un-stripping argent in HMA
-2
0
2
4
6
8
10
12
14
16
0 10000 20000 30000 40000 50000
H+1C-E02 H+1C-E06 AVERAGE H+1L-E08
H+1L-E05 H+1L-E03 H+1L-E02 AVERAGE
Cumulative number of load application
Rav
ellin
g-de
pth
[mm
]
44
8. CONCLUSIONS AND RECOMMENDATIONS
The performance and fundamental characteristics of BSMs associated with moisture damage has
been studied through MIST device conditioning method. Based on the data of the study, the
following conclusions and recommendations are drawn:
Research approach employed in this study successful accomplished study objectives:
- Development of new laboratory-based representative testing procedure, and
analysis protocol for the evaluation of moisture related damage which
distinguish from current over-simplified procedure.
- Evaluation of MIST conditioning system by using BSM-foam and BSM-emulsion
mixes of varying aggregates type.
- Make appropriate recommendations regarding the use of the new moisture
conditioning and limits for screening BSMs based on moisture related damage for
mix design.
8.1. Compaction of BSMs using vibratory (BOSCH®) compactor
- Vibratory (BOSCH®) compactor has shown potential to be a tool for compacting BSMs.
- All BSMs specimens compacted by vibratory (BOSCH®) compactor achieved
more than 100% MOD AASHTO compaction.
- The compaction procedure however, shows that OMC determined by MOD AASHTO is on
the wet side of the vibratory (BOSCH®) compaction.
- Wet side compaction using vibratory (BOSCH) compactor results in loss of slurry, (i.e.
moisture and binder), which might influence the mechanical performance of the mix.
8.2. Moisture content after curing
- The current curing procedure show that BSM-foam and BSM-emulsion do not achieve
equivalent equilibrium moisture contents (EMC).
- The effect on unequal EMC might result in an inconsistent mechanical performance.
- The moisture loss on BSM-foam is relatively higher than BSM-emulsion.
- The factors influencing the difference in moisture loss are nature of binder, specimen’s
preparation (i.e. mixing MC, compaction method etc) and curing.
- The aggregates type either Hornfels or Quartzites have no particular impact on
differences in loss of moisture in BSMs. Similarly, no clear trend of moisture loss
contributed on use of active filler or not. Although some BSMs with addition of active
filler seem to retain more moisture compared to BSM without active filler.
45
8.3. Volumetric properties
- The determined inter-particle voids in the BSM-foam and BSM-emulsion show a range of
12% to 17%. Whereby, BSM-foam shows relatively higher inter-particle voids than BSM-
emulsion.
- BRD values are variable for weak mixes due to penetration of water into sealed
specimens. For statistical reliability, three specimens should be analysed.
- The aggregates type, in this case either Hornfels or Quartzites, has no particular affect
on differences in voids content of BSMs. However, there is clear increase in the voids
content of BSMs without active filler compared to BSMs with the addition of active filler
(i.e. lime or cement).
8.4. MIST saturation level
- The MIST saturation level related to OMC of the mixes. It is clear from the results that
moisture susceptible mixes shows severe erosion (damage) at wet saturation. BSMs with
Quartzites had lower wet saturation before damage occurred. The causes of severe
damage are; firstly higher void content. Secondly, low cohesion and adhesion of binder
to mix. These factors contributed significantly to the serious erosion during pulsing of
water pressure into specimen.
- The steady saturation level before damage on specimen found to be different on
different BSMs. The BSMs that are susceptible to moisture (weak in cohesion) withstand
low MIST pulsing cycles or pulsing time at least 2minutes (62 cycles). Whilst BSMs
resistant to moisture damage (high cohesion), withstand high number of MIST pulsing
cycle above 3.2minutes (100 cycles) with no damage.
- The difference in MIST pulsing cycles (time) on BSM mixes, relates well with the residual
cohesion determined by static dynamic triaxial test. The BSMs that withstand higher
number of pulsing cycles shows high residual cohesion. While the BSM-mixes that
withstand lower pulsing cycles show less cohesion strength.
- From results, it can be seen that most BSMs attain steady state saturation after 3.2
minutes pulsing time (100 pulsing cycles). Therefore, 3.2minutes pulsing time or 100
pulsing cycles is threshold to screening of the BSMs. BSMs which cant withstand the
threshold is regarded highly susceptible to moisture damage. Therefore, its selection in
the mix design needs proper consideration. While BSMs, which can withstand the
threshold value, justify it’s selected in the mix design.
46
8.5. Mechanical performance of BSMs before and after MIST test
- The mechanisms of failure of BSM-Mixes under moisture exposure achieved through
static and short dynamic triaxial tests on wet and dry prepared specimen.
- Binder-Aggregates type has influence on the residual cohesion ratio. Quartzites
aggregate treated with either foamed bitumen or bitumen emulsion without active filler
has shown lower residual cohesion ratio compared to Hornfels-RAP aggregates.
- The influence of active filler, cement or lime on the resistance of moisture damage on
BSMs is clear. The Quartzites aggregated treated with 1% cement or lime and stabilised
with either foamed bitumen or bitumen emulsion is 56% more water resistance than
without active filler. Hornfels-RAP aggregates treaded with 1% cement or lime and
stabilised with bitumen emulsion is 22% more water resistance than without active filler.
- The ingress of moisture in BSM-foam has more effect on stiffness reduction compared to
BSM-emulsion. However, the addition of active filler in the BSM-emulsion has significant
contribution to its stiffness retention even after the ingress of water. Interesting
behaviour noted on the BSM-foam and BSM-emulsion with addition of lime. The anti-
striping behaviour of lime causes an increase in resilient modulus as saturation of the
mixes increase. Although this is not a general behaviour of all of the lime mixes. it is a
phenomenon that needs to be recognised, when either cement or lime selected for the
BSM mix design.
- The use of external LVDTs on short dynamic triaxial test shows inconsistence result.
Therefore, this measuring system is not appropriate method for ranking BSM-Mixes in
terms of moisture related damage.
8.6. Correlation, MMLS trafficking on BSMs at dry and wet condition
- The MMLS3 wet trafficking on BSM-emulsion (Hornfels) with active filler, used similar test
conditions applied on BSM-emulsion without active filler stated above. The average
cumulative rut-depth/ravelling-depth of 0.6 mm after 45000 load application occurred on
cement mix. Whilst an average of 10mm rut-depth/ ravelling-depth after 45000 load
application occurred on lime mixes. These results show that BSM-emulsion with the
addition of cement is less susceptible to moisture damage relative to similar mix with
addition of lime. Similar conclusions can be drawn for the residual cohesion determined
on MIST saturation and static dynamic test
- The MMLS3 wet trafficking on BSM-emulsion (Quartzites or Hornfels) without addition of
active filler resulting into cumulative ravelling-depth of 14mm after 2500 load application.
Whilst cumulative rut-depth/ ravelling-depth on the BSM-emulsion (Hornfels) with addition
of active filler (1% cement) was 0.6mm and 10mm for the addition of 1% lime after 45000
load application.
47
- The installation of Vinite or rubber mate layer on top of the specimen had effect at early
stage of deformation. However, as load application increase further reduction on
cohesion of the material occurs exponentially, which results into ravelling. Therefore
moisture related damage on BSMs coupled with traffic resulting to progress ravelling
(loss of aggregates)
- The MMLS3 ravelling-depth on wet condition of the BSM-Emulsion shows good
correlation with MIST and short dynamic test. However, more testing is required to
validate the complete testing matrix of retained cohesion versus wet trafficking on BSMs.
8.7. Recommendations
- The compaction procedures using vibratory (BOSCH®) compaction, shows that OMC
determined by MOD AASHTO is on wet side of the vibratory (BOSCH®) compaction. It is
recommended that this parameter given proper consideration.
- The phenomenon of increasing stiffness at saturation level on BSM-mixes with addition of
lime needs further investigation at micro- structural level.
- The comparisons of residual deviator stress ratio at 50 kPa and 100kPa show that these
ratios are less sensitive to moisture damage in the BSMs. Whilst, better moisture
sensitivity is indicated in the Retained cohesion ratio. It is there recommended that
moisture susceptible on BSMs determined using Residual Cohesion ratio.
- By using the MIST threshold values, the following ranking criteria Table I.15 can be
proposed for the BSMs mix design in relation to moisture damage
Table I.15: Recommended Retain Cohesion after MIST conditioning
MIST
Pulsing cycle
[no.]
MIST
pulsing time
[min]
Equivalent residual
cohesion percentage
[%]
Possible equivalent
design material
≥ 70 BSM 1
≥ 60 BSM 2
100
3.2
≥ 50 BSM 3
- The use of external LVDTs on short dynamic triaxial test shows inconsistence result.
Therefore, this measuring system not recommended for ranking BSM-Mixes in terms of
moisture related damage.
- The use of Vinite or reinforced rubber mate layer reduces wheel abrasion at early stage
of deformation. However, become ineffective after high reduction on cohesion of
materials. Nevertheless, for the correlation purposed shown good correlation with MIST
device, hence recommended for further BSM moisture evaluation.
48
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