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European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 971

Effect of Thickness of a Sandwiched Layer of Bitumen

Between Two Aggregate on the Bond Strength

N. Ezhilarasi, PG Student

Dept. of Civil Engineering

PRIST University

Thanjavur, India

Abstract—The research was also to evaluate tack coat

materials and application rates for the Alabama Department of

Transportation (ALDOT). The project included a laboratory

phase and a field phase. For the laboratory work, the experiment

included two types of emulsion (CRS-2 and CSS-1) and a PG 64-

22 asphalt binder that are allowed by ALDOT’s specifications.

Bond strengths were measured with a shear type device at three

temperatures and three normal pressure levels. Three

application rates that encompassed the specification range were

investigated for each tack coat.

Laboratory prepared mixture samples included a coarse- graded blend and a fine-graded blend to represent two different

surface textures. The effects of tack coat type, application rate,

mixture type, testing temperature and normal pressure on the

bond strength were evaluated. In the laboratory phase, it was

found that all of the main factors used in the test plan affected

bond strength. Testing temperature had the most significant

impact on bond strength. As the temperature increases, bond

strength decreases significantly. Testing normal pressure affected

bond strength differently for high, intermediate, and low

temperatures.

Based on the laboratory work, a draft procedure was

developed for determining the bond strength between pavement

layers. An easy to use procedure was selected that was believed to

provide a good indication of the quality of the bond. The

procedure utilizes the simple shear device developed by NCAT

which is similar to bond strength devices used in several

European countries.

Index Terms — Asphalt binder; Polymer; Rheology;

Morphology; Nanomaterial; Bio-oil

I. INTRODUCTION (HEADING 1)

Bituminous mix is composed of aggregates, bitumen and

air-voids. A good bonding between the aggregates and bitumen

is important for satisfactory performance of the bituminous mix

in terms of proper load transfer and resistance to fatigue,

ravelling, moisture sensitivity etc. A large number of studies

have been conducted to understand the bond between

aggregate and bitumen. Contact angle measurement, inverse

gas chromatography, micro-calorimetry methods have been

used to estimate surface energy of aggregates-bitumen

bonding. Some research studies report tensile strength testing

between bitumen and aggregate or bitumen and other materials.

Marek and Herrin conducted tensile strength test on

bitumen film and found that with the increase in bitumen film

thickness, tensile strength first increases to a peak value and

then decreases and almost becomes constant. In their study, the

peak strength was observed at bitumen film thickness of about

20 μm. Frolov et al. found that for higher values of film

thickness, cohesive strength is independent of film thickness.

Canestrari et al. performed a number of tests with

Pneumatic Adhesion Tensile Testing Instrument (PATTI) test

set-up on different types of asphalt binders and aggregates.

They found that samples under dry condition primarily showed

cohesive failure and water conditioned samples showed

adhesive or cohesive failure depending on the affinity between

aggregate bitumen systems. Pouli kakos and Partl conducted

tensile strength testing on bituminous film placed between steel

or aggregates.

In their study, cohesive failure was observed at 23oC and

primarily adhesive-failure was observed at -10oC. As can be

seen from the above discussions that limited literature is

available on study of tensile strength between aggregate and

bitumen. This has motivated the present researchers to initiate a

further study in this direction.

II. LITERATURE STUDY

Scarpas et al., (1996) developed the CAPA (Computer

Aided Pavement Analysis) system using both 2-D and 3-D

finite element routines to study the contribution of

reinforcement layers to the overlay system, with the 2-D

program being capable of simulating crack propagation. This

program was eventually upgraded through the implementation

of a constitutive model for the material response of viscoplastic

Page 2 of 4

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 972

materials and elasto-viscoplastic-fracturing model. The new

system has since been used to evaluate different reinforcement

materials and the affect of bonding of the reinforcement

materials.

Owusu-Antwi et al., (1998) developed a mechanistic-based

reflective cracking model for HMA/PCC pavements, which

was developed to be used by practicing engineers.

The procedure used 2-D plain strain finite element

modeling for stress intensity computations and 3-D finite

element modeling for computing the required mathematical

expressions to determine the “J-integral” for temperature and

traffic loadings. The authors used 33 LTPP HMA overlaid

PCC pavement sections for their analysis and finally derived a

mechanistic-empirical model for predicting reflective cracks by

using optimization techniques.

Kohale and Lytton (2000) also developed a mechanistic- based reflective cracking model for evaluating different

reflective cracking mitigation techniques. The computer

program was used to develop design equations for flexible

overlays with Stress Absorbing Membrane Interlayers

(SAMI‟s) and Reinforcing Grids. The equations were then

calibrated using in-service data from the Florida Department of

Transportation. In 2000, identifying the lack of research

focused on the issue of reflective cracking in bituminous

overlays, the RILEM group of Europe sponsored the first

international conference solely dedicated to reflective cracking.

III. EXPERIMENTAL STUDY

Locally available sand-stone aggregates and bitumen of

grade VG30 (penetration value obtained between 60 and 70)

are used in the present study. Irregular shaped aggregates are

cut into small cubes (approximately 25 mm each side) by using

a diamond cutter. The surface of the aggregate is polished

thoroughly by using a polishing equipment with abrasive

silicon carbide powder (of size 180 mesh) and water. Followed

by polishing, the samples are rinsed with water to remove any

abrasive powder stuck onto the polished surface. Roughness of

polished surface of five representative aggregate samples are

measured at the Manufacturing Sciences

Fig. 1. Sand-witched layer of bitumen between two polished aggregate

Laboratory, IIT K. The arithmetic mean parameter (Ra) is

obtained as 6.78 μm. In order to form a thin sandwiched layer

of bitumen, two aggregate samples are heated in an oven to

about 110oC and the polished surface of one of them is dipped

inside a pool of hot and molten bitumen maintained at a

temperature of about 150oC.

The aggregates are brought closer (with the bitumen dipped

surface facing the polished surface of the other aggregate) and

they are mildly pressed. Excess bitumen is removed using a

blade.

A. Failure Mechanism

The interaction between vehicle tyres and the pavement

surface is complex (Horak et al. 2009b). Despite significant

research efforts in this area, there remains no routine method to

account for tyre contact stress in pavement design (Al-Qadi &

Wang, 2011). The general forces and mechanisms acting on a

pavement from a passing tyre are, however, commonly

accepted as including normal and shear forces. Shear forces are

present under free-wheeling tyres but increase significantly

during braking and turning operations (Yoo et al. 2006). Raab

& Partl (2004) presented a simple diagrammatic description of

the stresses induced in a surface layer by a moving tyre and this

is reproduced

Page 3 of 4

European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 973

Fig. 2. Stress in a surface layer from a moving tyre

B. Achieved Bond Strength

A number of asphalt overlays were recently cored and the

interfaces with the underlying pavement tested in the

laboratory for direct shear strength. All overlays tested were

constructed following the standard practices outlined above

and all included asphalt designed to the typical airport

specification. Shear strength results and the calculated Mohr- Coulomb type envelopes are presented in Figure 6. At zero

normal stress the shear strength is provided solely by the

interface‟s cohesion, which is the tensile strength provided by

the tack coat. For the overlays tested, the cohesion values range

from 223-366 kPa with an average of 274 kPa. The slope of the

shear strength envelope represents the combined mechanical

interlock and friction contribution. This is characterised by the

friction angle. For the overlays tested, the friction angles

ranged from 33-55° with an average of 42°. For the nine cores

tested, the regression coefficients for the calculated shear

strength envelopes averaged 94% indicating a highly reliable

and linear relationship between normal stress and shear

strength.

C. Potential Improvements

Construction processes currently adopted for airport

overlays in Australia already take precautions to minimise the

risk of poor bond leading to delamination failures. Possible

additional improvements include the texturing of the surface in

a direction that is perpendicular to the direction of aircraft

movement as well as dry texturing of the existing surface. Both

of these initiatives are possible but impractical. Unless

texturing is allowed a few shifts in advance of the paving

operation, transverse texturing would have significant impact

on overlay productivity and therefore cost/duration of

resurfacing works. Dry texturing reduces the service life of

cold planing machine teeth and is resisted by contractors. It has

been performed on airports in the USA following bond-related

failures but is not widely adopted. Improved tack coat

performance is the primary improvement that could practically

be made.

Fig. 3. Jet Bond and CRS emulsion Interface Shear Strengths

IV. EFFECT OF BOND ON PAVEMENT PERFORMANCE

Several recent studies have evaluated the effect of the bond

on pavement performance using mechanistic pavement models.

In 2004, King and May presented an analysis of the effect of

bond between HMA layers using the program BISAR (11).

They analyzed a pavement structure with two 4-inch (100

mm) HMA layers over a 6- inch (150 mm) aggregate base and

two subgrade stiffnesses. Two load levels were used, 9 kip (40

kN) dual tire and 12 kip (53.4 kN) dual tire. The interface

between HMA layers was modeled in separate runs from a no

slip condition to full slip between (no bond) layers.

Program outputs analyzed included maximum stress and

strain at various locations and numbers of load repetitions to

failure. All of the outputs show a dramatic increase in stresses

and strains or decrease in pavement life when the interface

drops from full bond to about 90 percent bond. Figure 3 shows

fatigue life decreasing by about 50 percent for each

load/subgrade condition when the bond is reduced by 10

percent. Roffe and Chaignon (3) conducted a similar analysis

using the French pavement design program ALIZE. They

analyzed a pavement structure consisting of a 2.4 inch (60 mm)

surface layer, a 5.1 inch (130 mm) HMA intermediate layer

and 7.9 inch (200 mm) aggregate base. The program was run

with full bond and no bond between the HMA layers. Their

analysis showed that the service life of the pavement was

reduced from 20 years to between 7 and 8 years due to the lack

of bond between the HMA layers.

V. RESULTS AND DISCUSSIONS

T Failure of sample occurs due to development of crack at

the weakest point of the aggregate-bitumen-aggregate junction.

The crack may develop either at the aggregate bitumen

interface (i.e. adhesive failure) or within the bitumen (i.e.

cohesive failure) or combination of both. As the vertical

deformation increases the size of crack also increases. These

results in separation of two aggregates from each other and the

material fail to carry any further load.