Influence of the Surface Roughness of Aggregates on the

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Influence of the Surface Roughness of Aggregates on the Adhesion

Quality of Asphalt-Aggregate Systems

By

María José Aroca Moscote

Presented to the Department of Civil and Environmental Engineering

Universidad de los Andes

For the Degree of Master of Science

Under Supervision of Professor Silvia Caro

Bogotá, Colombia

December 2019

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TABLE OF CONTENTS

LIST OF FIGURES ................................................................................................................................. 3

LIST OF TABLES ................................................................................................................................... 4

1 Introduction ..................................................................................................................................... 5

2 Research objectives .......................................................................................................................... 8

3 Materials .......................................................................................................................................... 9

3.1 Asphalt binder .......................................................................................................................... 9

3.2 Aggregates ............................................................................................................................... 9

3.2.1 Marble ............................................................................................................................ 10

3.2.2 Quartzite ......................................................................................................................... 10

3.2.3 Serpentinite..................................................................................................................... 10

4 Experimental methodology ............................................................................................................. 11

4.1 Experimental set-up ................................................................................................................ 11

4.1.1 Rock sample preparation ................................................................................................. 11

4.1.2 Determination of the roughness parameters of the rock samples ...................................... 13

4.1.3 Modified micrometer for the fabrication of the testing specimens .................................... 14

4.1.4 Aggregates-Asphalt-Stub (AAS) system preparation ....................................................... 15

4.2 Testing procedure ................................................................................................................... 15

5 Results and analysis ....................................................................................................................... 17

5.1 Roughness Profiles ................................................................................................................. 17

5.1.1 Sandblasting texturing method ........................................................................................ 17

5.1.2 Texture by means of the scalpel method .......................................................................... 19

5.2 Roughness parameters ............................................................................................................ 20



5.3 Mechanical performance of AAS systems ............................................................................... 25



5.3.3 Types of failure ............................................................................................................... 32

5.4 Comparison of results among rocks and texturing methods ..................................................... 33

6 Conclusions ................................................................................................................................... 35

7 References ..................................................................................................................................... 37

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LIST OF FIGURES

Figure 1. Serpentinite rocks and Marble rocks .......................................................................................... 9 Figure 2. Quartzite rock. .......................................................................................................................... 9 Figure 3. Experimental Set Up. .............................................................................................................. 11 Figure 4. Samples of quartzite textured through Sandblasting method. ................................................... 12 Figure 5. Samples of marble texturized through sandblasting method. .................................................... 12 Figure 6. Samples of serpentinite texturized by means of the scalpel method. ......................................... 13 Figure 7. Samples of marble texturized by means of the scalpel method. ................................................ 13 Figure 8. The roughness profile with its Mean Line, Arithmetical mean roughness Ra and Root mean-square

average Rq (Mahr Production Metrology, 2019). .................................................................................... 14 Figure 9. The roughness profile with its Maximum Roughness Depth Rmax (Mahr Production Metrology,

2019). .................................................................................................................................................... 14 Figure 10. Modified micrometer for AAS sample preparation Cala et al. (2019). ................................... 14 Figure 11. AAS system, all dimensions shown are in mm Cala et al. (2019). .......................................... 15 Figure 12. Experimental testing procedure setup Cala et al. (2019). ........................................................ 16 Figure 13. Low roughness profile from a sample texturized through the sandblasting method. ................ 18 Figure 14. Medium roughness profile from a sample texturized through the sandblasting method. .......... 18 Figure 15. High roughness profile from a sample texturized thorough the sandblasting method. ............. 18 Figure 16. Low roughness profile from a sample texturized by means of the scalpel method. ................. 19 Figure 17. Medium roughness profile from a sample texturized by means of the scalpel method. ........... 19 Figure 18. High roughness profile from a sample texturized by means of the scalpel method. ................. 20 Figure 19. Relationship between the Sandblasting pressure and the roughness parameter Ra. ................. 21 Figure 20. Relationship between the line angles and the roughness parameter Ra. .................................. 23 Figure 21. Load[N] vs. Displacement [mm] curves of quartzite samples textured through sandblasting

method. ................................................................................................................................................. 26 Figure 22. Load[N] vs. Displacement [mm] curves of marble samples textured through sandblasting method.

.............................................................................................................................................................. 27

Figure 23. Ra [μm] vs. 𝐹𝑚𝑎𝑥 [N] of quartzite and marble samples textured through sandblasting method.

.............................................................................................................................................................. 27

Figure 24. Area of contact [𝑚𝑚2] vs. 𝐹𝑚𝑎𝑥[𝑁] of the quartzite and marble samples texturized through

sandblasting method. ............................................................................................................................. 28 Figure 25. The Area of contact [𝑚𝑚2] vs. 𝑊𝑓[𝐽] of the quartzite and marble samples texturized through

sandblasting method. ............................................................................................................................. 28 Figure 26. Load[N] vs. Displacement [mm] curves of serpentinite samples textured by means of the scalpel

method. ................................................................................................................................................. 29 Figure 27. Load[N] vs. Displacement [mm] curves of marble samples textured by means of the scalpel

method. ................................................................................................................................................. 30 Figure 28. Ra [μm] vs. (𝐹𝑚𝑎𝑥)[N]] curves of serpentinite and marble samples textured by means of the

scalpel method. ...................................................................................................................................... 31 Figure 29. The Area of contact [𝑚𝑚2] vs. 𝐹𝑚𝑎𝑥[𝑁] graph of the serpentinite and marble samples

texturized by means of the scalpel method. ............................................................................................ 31 Figure 30. The Area of contact [𝑚𝑚2] vs. 𝑊𝑓[𝐽] graph of the serpentinite and marble samples texturized

by means of the scalpel method. ............................................................................................................. 32 Figure 31. Quartzite 80Qtz4 sample with a cohesive failure in the interface. ........................................... 32 Figure 32. Quartzite 60Mrb2 sample with a cohesive failure and substrate failure in the interface. .......... 33

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LIST OF TABLES

Table 1. Roughness parameters of the aggregates texturized through sandblasting (STD stands for standard

deviation) .............................................................................................................................................. 21 Table 2. Roughness parameters of the aggregates texturized by means of the scalpel method (STD. ....... 23 Table 3. The maximum load at failure and the work fracture results of samples of quartzite and marble

texturized through sandblasting. ............................................................................................................. 26 Table 4. The maximum load at failure and the work fracture results of samples of serpentinite and marble

texturized by means of the scalpel method. ............................................................................................ 29

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1 Introduction

Asphalt concrete has been widely used for roadway pavements due to its ability to provide structural

capacity and smooth surface. The rapid growth of traffic flow, the combined effect of environmental

conditions and the increase of the global temperature has led to premature damage of asphalt pavements

in their early life. Rutting, cracks, potholes and other road distresses seriously affect the pavement

performance conditions, and compromise driving safety (Cui, Xiao, Yan, Li, & Wu, 2018).

Asphalt concrete is composed mainly of two materials: aggregates, which form the skeleton of the

structure, and asphalt binder, which is the primary binding material. There are three main factors

affecting the durability of asphalt concrete related to the adhesion quality of the asphalt-aggregate

system, which include: 1) cohesion loss within asphalt, 2) strength reduction of aggregate particles, and

3) breakdown of adhesive bonding between aggregate and asphalt (Xu & Wang, 2016). Thus, to ensure

good durability of the asphalt concrete it is important to guarantee good adhesion quality between the

asphalt binder and the mineral aggregates. Hence, an understanding of the adhesion mechanisms

between the aggregate and bitumen is required to enhance the durability of road surfaces, and also the

optimum selection of the asphalt component materials to be used in a particular road infrastructure

project (Cui, Blackman, Kinloch, & Taylor, 2014) in order to have a better adhesion quality. In general,

the adhesion quality between the bitumen and the aggregates depends on several factors, including the

surface physical characteristics of the aggregates, their surface chemical constituents, and certain active

functional groups of asphalt constituents (Kuang, et al., 2019).

Aggregate particles are used in various layers of the pavement structure, either in granular conditions

for base and subbase layers (i.e., unbonded layers) or in a bonded condition as part of the asphalt mixture

for base and surface courses. Aggregates represent more than 90% of the pavement structure. Therefore,

the performance of the asphalt concrete is directly affected by aggregate characteristics, particularly

aggregate gradation, shape, angularity, and surface texture (Chen, Li, Wang, Wu, & Huang, 2015). It

has long been recognized that the surface texture of a particle of aggregate might be an important

property in determining the adhesion of binders to its surface. The degree of adhesion might, in turn, be

expected to influence the properties of the mix (Wright, 1995). In conclusion, the surface texture of the

aggregates has an important role in the adhesion quality between the mineral aggregates and the asphalt

binders, and therefore in the asphalt pavement performance and durability.

Previous works recognize the importance of the morphological characteristics of aggregates, including

their surface texture, in the adhesion quality between the binder and the aggregate and the relationship

between these characteristics and the performance of flexible pavements such as Cui et al. (2018), Hu

and Qian (2018), Kuang et al. (2017),and Singh et al. (2012) . In particular, these works have performed

methods to analyze the physical characteristics of the aggregates, such as geometry, porosity, shape

factors, angularity and surface texture, and the general mechanical performance of the asphalt mixture.

However, none of them has analyzed the roughness as the main physical parameter of the surface of the

aggregate and its relationship to the adhesion quality between the aggregate and the asphalt binder.

Cui et al. (2018) studied the effect of different morphological variables on the adhesion of aggregates

and the mechanical properties of asphalt mixtures, specifically they concluded that there are close linear

relationships between angularity or sphericity of aggregates and the asphalt-aggregate adhesive quality.

The higher the angularity, the rougher the texture, and the smaller the sphericity, the greater the asphalt

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coverage ratio is, which indicates better adhesion quality (Cui, Xiao, Yan, Li, & Wu, 2018).

Nevertheless, the study does not make a direct relationship between aggregates surface roughness and

the adhesion quality between the aggregate-asphalt binder system.

Similarly, Hu and Qian (2018) determined the influence of aggregates features on the adhesive failure

of the interface. Results from this study showed that the aggregate polarity, surface roughness and

texture of aggregates affect the interfacial transition zone between aggregates and asphalt mastic (Hu &

Qian, 2018).

The work conducted by Kuang et al. (2017) constitutes the closest approach for the evaluation of

aggregates surface roughness and its relationship with the adhesion quality between the aggregate and

the asphalt binder. This work evaluated the interfacial adhesion behavior between asphalt with

limestone and granite through surface microtopography comparison However, the study did not quantify

the roughness or the adhesion, and their conclusions were based on a visual comparison of the surface

through digital imaging technique and scanning electron microscope to characterize the interfacial

morphology of aggregates with asphalt binder.

Furthermore, Singh et al. (2012) developed a model that utilizes aggregate shape parameters as

angularity, texture, and form to estimate the dynamic modulus of asphalt mixes. The dynamic modulus

of asphalt mixes is considered an important parameter in the prediction of the performance of flexible

pavements (Ceylan, Gopalakrishnan, & Kim, 2009). Results from this study showed that the dynamic

modulus of the mix increases with an increase in the angularity and texture of aggregates, and that the

inclusion of shape parameters can enhance the prediction capability of the model developed that was

employed.

In addition, to obtain a measure of the adhesive bond strength in asphalt mixtures a couple of methods

have been used to compare the relationship between aggregate mineralogy and the adhesion quality with

the asphalt binder. In the first place, Canestrari et al. (2011) used the Pneumatic Adhesion Tensile

Testing Instrument (PATTI) to measure the adhesive and cohesive properties of asphalt-aggregate

combinations. In this test, a small asphalt layer is placed between a rock sample and a metallic pullout

stub. Subsequently, a pulling force is exerted using a pneumatic system until failure occurs when

adhesive failure is reached. Later, Moares et al. (2011) modified the PATTI test to the Bitumen Bond

Strength (BBS) test to quantitatively evaluate the adhesive bond between the asphalt and the aggregate

in a simple, quick and repeatable form for evaluating adhesion properties of asphalt-aggregate systems.

The BBS test places an 800 𝜇𝑚 asphalt layer between a rock sample and a metallic pullout stub and

tensile stress is applied until failure is reached. This test configuration, with minor modifications, has

been used in several studies (e.g. Yee et al. (2019), Mohammed et al. (2018), Zhang (2017)). More

recently, Cala et al. (2017) presented a new method for testing the adhesion strength based on the

mentioned test methods. The new method procedure allows a film thickness of 150 𝜇𝑚 and a test speed

of 10 mm/s.

Thus, as described previously, most of the approaches to characterize the relationship between

aggregates surface texture and the adhesion quality between the mineral aggregates and the asphalt

binder have been made adopting a group of physical characteristics of the aggregate surface such as

angularity, shape, form, texture, and evaluating adhesion or the asphalt mixture performance. On the

other hand, previous works that have quantified adhesion strength of asphalt-aggregate systems compare

the relationship between mineralogy of the rock and the adhesion quality, only taking into account the

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chemical characteristics. Therefore, more efforts are needed to evaluate the influence of aggregate

surface texture parameter, using roughness, as a unique physical parameter of the aggregate surface and

the adhesion quality between the aggregate and the asphalt binder.

Within this context, this work attempts to develop an experimental approach based on the Bitumen Bond

Strength Test (BBS) and the method proposed by Cala et al. (2019) to evaluate the adhesion strength of

asphalt-aggregate systems. The methodology consists in using a modified micrometer to prepare a thin

film of asphalt of 20 𝜇𝑚 between a metallic stub and a cylindrical rock core with controlled geometry.

Then, the samples are left to dry for a duration of at least 24 hours and placed in a hydraulic press under

a displacement-controlled test velocity of 10mm/min until they fail. The procedure is conducted using

three different types of aggregates that were rigorously texturized, in order to represent a wide range of

surface roughness. The results of this study offer new and valuable information about the influence of

the aggregate surface roughness in the adhesive properties of asphalt-aggregate systems that can be used

to improve the selection of materials to produce asphalt mixes with better adhesion quality.

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2 Research objectives

The principal goal of this research is to determine the influence of the aggregate surface roughness of

aggregates with three different lithologies in the adhesive properties of asphalt-aggregate systems. The

specific objectives of this research are as follows:

1. Determine the relationship between the surface roughness of different types of aggregates and the

adhesion quality of the asphalt-aggregate system.

2. Determine the type of failure, adhesive or cohesive failure, between the asphalt-aggregate system.

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3 Materials

3.1 Asphalt binder

All the adhesion testing samples were prepared using an unmodified asphalt binder obtained from

the Barrancabermeja refinery, in Colombia with a penetration grade of 60/70 (1/10mm). This

asphalt is the most commonly used in road construction projects in Colombia.

3.2 Aggregates

The three types of aggregates: i) marble; ii) quartzite; and iii) serpentinite, used in this research were

selected based mainly on their homogeneous composition, their low porosity and on their hardness

property. The latter, because this property defines the possibility of modifying the roughness of the

rocks. They were collected for a previous work conducted at the Geomaterials and Infrastructure

Systems research group at Universidad de los Andes in 2016 in the department of Tolima,

Colombia. All the aggregates are metamorphic rocks. These types of rocks are the result of the

transformation or metamorphism or solid-state recrystallization of existing igneous and

sedimentary, and even metamorphic rocks. These changes occur in physical and chemical

conditions, principally heat, pressure, and the introduction of chemically active fluids and gases

(Haldar & Tisljar, 2014). The following sections present the three rocks used in the research and

their main properties and characteristics.

Figure 1. Serpentinite rocks and Marble rocks

Figure 2. Quartzite rock.

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3.2.1 Marble

Marble is a metamorphic rock formed by the contact metamorphism of the sedimentary rock

limestone (Pellant & Pellant, 2007). Marble is mostly made of the mineral calcite and/or dolomite.

It is also composed of minor minerals like forsterite tremolite, wollastonite, and diopside. It is often

white but can be yellowish brown, black, red or green. Different colors are the result of faults in the

limestone from which the marble is formed (Mattern, 2005).

3.2.2 Quartzite

Quartzite is a metamorphic rock derived from regional metamorphism of sandstones, siltstones and

silicic sediments, and it is composed almost entirely of quartz. It can also contain minerals such as

mica, sillimanite, garnet, feldspar, andalusite, and corundum. Quartz is a mineral consisting of one

part of silicon and two parts of oxygen 𝑆𝑖𝑂2. This type of mineral is exposed at the surface of the

earth (Best, 2003).

3.2.3 Serpentinite

This rock originates by the alteration of ultramafic igneous or metamorphic rock. The original

minerals were pyroxene and olivine. The secondary or derived minerals are those of the serpentinite

group, which are soft, flaky or fibrous, and usually too fine grained to be visible (Durrell, 1988)

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4 Experimental methodology

4.1 Experimental set-up

The experimental set up consisted of preparing cylindrical asphalt-aggregate-metallic stub (AAS)

testing samples, with asphalt films of 20 𝜇m thick, using a modified micrometer (Mitutoyo Ref: 293-

253-10) based on the experimental methodology developed by Cala et al. (2019). The AAS system was

kept at dry conditions and then the systems were failed under tensile stresses using a hydraulic press

(ELE Ref: Tritest 50kN) at a 10mm/min loading condition. The results of the test are the force

displacement curve, from where the maximum load at failure and the work of fracture (i.e., area under

the curve, Wf) can be obtained.

Figure 3. Experimental Set Up.

4.1.1 Rock sample preparation

Two different methods were used to generate different roughness levels in the aggregate samples.

The first methods consisted in using a sandblasting texturing technique, while the second consisted

in manually generating different textures using a scalpel. Both methods are explained next.

4.1.1.1 Sandblasting texturing method

This method consists on the following four main steps:

1. 25 mm (1 inch) rock slices are obtained in the laboratory from rocks collected from the field.

2. Both faces of the rock slices are texturized with a sandblasting machine using three different

pressures: 40 psi, 60 psi, and 80 psi.

3. The rock slices are cut to obtain cylindrical specimens with 25 mm of height.

4. The face of the cylindrical specimen that is not texturized is cut using a high precision cutting

and grinding machine (Struers Ref: Accutom-100). This ensures that the faces of the cores are

completely parallel (± 1 𝜇m tolerance).

The types of rocks texturized through this method were the Quartzite and the Marble rocks. The

result of the rock sample preparation through sandblasting for the quartzite lithology can be

observed in Figure 1, and the marble lithology can be observed in Figure 2. In the hardness scale

the Quartzite lithology is classified as one of the rocks with highest hardness, while the Marble

lithology is classified as one of the rocks with the lowest hardness. In order to obtain a wide range

of roughness, this process was applied to a hard rock, Quartzite, and a soft rock, Marble.

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Alternatively, the Serpentinite is a rock with a low hardness, this means that this rock can be easily

scratched such as the Marble. Therefore, the Serpentinite and the Marble lithology were texturized

through the second method which is explained below.

Figure 4. Samples of quartzite textured through Sandblasting method.

Figure 5. Samples of marble texturized through sandblasting method.

4.1.1.2 Texture by means of the scalpel method

This method consists on following four main steps:

1. 25 mm (1 inch) rock slices are obtained in the laboratory from rocks collected from the field.

2. The rock slices are cut to obtain cylindrical specimens with 25 mm of height.

3. The faces of the cylindrical specimens are cut in a high precision cutting and grinding machine

(Struers Ref: Accutom-100). This ensures that the faces of the cores are completely parallel (±

1 𝜇m tolerance).

4. One face of the cylindrical specimens is texturized with a scalpel making a line every 2

millimeters and in the following directions: at 30°, at 45°, and at 60°.

It is worth mentioning that a second texturizing method was selected besides the sandblasting

because the sandblasting method is a very abrasive method that has as result a very high roughness

in the face of the cylindrical specimens that had as consequence a loss of control over the thickness

of the asphalt layer applied to the sample surface. Therefore, a second texturizing method less

abrasive was applied in two types of rocks that can be easily scratched, Marble and Serpentinite.

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The result of the rock sample preparation by means of the scalpel method for the Serpentinite

lithology can be observed in Figure 3, and the Marble lithology can be observed in Figure 4.

Figure 6. Samples of serpentinite texturized by means of the scalpel method.

Figure 7. Samples of marble texturized by means of the scalpel method.

4.1.2 Determination of the roughness parameters of the rock samples

The roughness parameters of the texturized face of the rock samples were obtained using a portable

surface roughness tester (Mitutoyo Ref: Surftest SJ-210). A stylus detector goes over the rock

sample texturized face, and the results of the test are the surface roughness measurements through

surface profiles, filters, and roughness parameters. The roughness parameters were measured three

times per sample to obtain a representative roughness parameter of the surface.

1. 𝑹𝒑𝒓𝒐𝒇𝒊𝒍𝒆 – roughness profile: is the profile resulting from electronic high pass filtering of the

primary profile with a cut-off wavelength 𝜆𝑐 , as observed in Figure 5.

2. 𝑹𝒂- arithmetical mean roughness value: The arithmetical mean of the absolute values profile

deviations (𝒁𝒊) from the mean line of the roughness profile, as observed in Figure 6. Ra is used

to detect general variations in overall profile height.

3. 𝑹𝒒- also known as RMS, is the root mean-square average of the departures of the roughness

profile from the mean line. Rq has statistical significance because it represents the standard

deviation of the profile height.

4. 𝑹𝒎𝒂𝒙- maximum roughness depth: The vertical distance between the highest peak and the

lowest valley along the assessment length of the profile.

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Figure 8. The roughness profile with its Mean Line, Arithmetical mean roughness Ra and Root mean-square average Rq

(Mahr Production Metrology, 2019).

Figure 9. The roughness profile with its Maximum Roughness Depth Rmax (Mahr Production Metrology, 2019).

4.1.3 Modified micrometer for the fabrication of the testing specimens

The micrometer used in the experimental procedure to prepare the testing samples was a modified

micrometer previously used by Cala et al. (2017) to ensure a homogenous 20 𝜇m thick asphalt film

in the AAS systems. In this micrometer, a metallic stub with a diameter of 25 mm is placed at one

end, and a rock sample of the same diameter at the other end, as observed in Figure 8.

Figure 10. Modified micrometer for AAS sample preparation Cala et al. (2019).

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4.1.4 Aggregates-Asphalt-Stub (AAS) system preparation

The preparation of the AAS is made using the cylindrical rock specimens and the modified

micrometer following the same procedure presented by Cala et al. (2019):

1. “Metallic stubs are cleaned to remove possible residues or dust.

2. The rock sample and the metallic stub are introduced into an oven a 150°C for at least

30 minutes.

3. Simultaneously with step 2, 1.50 g of asphalt binder are introduced into the oven for 15

minutes (i.e. 15 minutes after the metallic stub is introduced in the oven in Step 2).

4. The metallic stub and rock sample are placed on the micrometer, as shown in figure 8.

5. The micrometer is zeroed at the point in which the metallic stub touches the rock

sample.

6. The asphalt binder is placed on top of the rock sample.

7. The metallic stub is lowered until the micrometer´s dial reaches 20 𝜇m.

8. The AAS system is left cooling down for at least 45 minutes. After this period, the AA

system can be dismounted from the micrometer. ”

The Aggregates-Asphalt-Stub (AAS) system can be observed in Figure 9.

Figure 11. AAS system, all dimensions shown are in mm Cala et al. (2019).

4.2 Testing procedure

The testing procedure was based on the method developed by Cala et al. (2018). It consists of

applying tensile forces on the AAS systems under a control displacement condition of 10 mm/min

until failure. According to Cala et al. (2019) this displacement condition was selected as it was the

fastest loading condition provided by the hydraulic equipment used for the experiment. Also, this

speed contributes to a minimal deformation of the asphalt binder which reduced the possibility of

only cohesive failures due to the viscoelastic properties of asphalt materials.

To perform the pull-off test on the AAS system, a couple of modifications were required on the

hydraulic press (Figure 10). During the test, loading data was captured using an Omega LC201-300

load cell. The initial results from the test are Force [N] vs. Time [s] data; these data are collected

every 0.1s. As explained previously, the results of the test are the maximum load at failure, 𝐹𝑚𝑎𝑥,

and the work of fracture, 𝑊𝑓.

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Figure 12. Experimental testing procedure setup Cala et al. (2019).

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5 Results and analysis

The samples that were texturized with the sandblasting method were labelled considering three

characteristics: i) Texture pressure (40 psi, 60 psi, 80 psi); ii) Rock lithology, Qtz (Quartzite), Mrb

(Marble) and iii) the replicate number. For instance, the sample 40Qtz1 corresponds to the first replicate

of a quartzite sample which texture was generated using a sandblasting pressure of 40 psi. If only one

number is shown, for instance 40Qtz, it refers to the average obtained for all replicates of that rock. The

samples that were texturized with the scalpel method were labelled considering three characteristics: i)

Angle between the lines (1 for 120°, 2 for 45°, 3 for 30°); ii) Rock lithology, STP (Serpentinite), Mrb

(Marble), Spt (Serpentinite); and iii) the replicate number. For instance, the sample 1Spt1 corresponds

to the first replicate of a serpentinite sample that has texture pressure made of lines every 120°. If only

one number is shown, for instance, 1Spt, it refers to the average obtained for all replicates of that rock.

The measurements were taken three times per sample in three different directions to have a

representative roughness of all the sample surface.

5.1 Roughness Profiles

For all the samples, three measurements of the roughness profile were obtained to calculate the

roughness parameters of the surface of the rock. The roughness profiles were classified in three

types according to the 𝑅𝑎 values obtained: Low roughness, that are the profiles with a 𝑅𝑎 value

between 0 𝜇𝑚 and 9 𝜇𝑚; Medium roughness, that are the profiles with a 𝑅𝑎 value between 9 𝜇𝑚

and 12 𝜇𝑚; and High roughness, that are the profiles with a 𝑅𝑎 value greater than 13 𝜇𝑚. As an

example, the profiles for three types of roughness: low, medium y high roughness are shown in

Figures 11-16 for the two types of texturization methods.

5.1.1 Sandblasting texturing method

The shape of the profiles obtained through this method were sharp, sudden and abrupt. They did not

present a homogeneous or harmonic shape. The profiles presented high peaks and deep troughs

combined with low peaks and troughs in a random form. The peaks of the profiles with low

roughness reached values of 20 𝜇𝑚 and the troughs of -40 𝜇𝑚. The value of the highest peak and

lowest trough of medium roughness profiles were 30 𝜇𝑚 and -50 𝜇𝑚 respectively. Finally, the peaks

for profiles with high roughness reached values of 45 𝜇𝑚 and the troughs reached values of -55 𝜇𝑚.

Therefore, the roughness obtained on the rock surface through this method is a complex shape made

of a series of variable peaks and troughs with varying heights, depths, and spacings, and it did not

provide a uniform texture on the rock surface. The principal reason of these results is that the

sandblasting is a method in which an abrasive material is propelled against the rock surface under

high pressure, this process breaks the rock giving the surface a high and variable roughness

depending on the type of rock texturized and its properties.

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5.1.1.1 Low roughness profile

In Figure 11 the roughness profile of the sample 60Qtz2 that has a Ra of 8.838 can be observed.

Figure 13. Low roughness profile from a sample texturized through the sandblasting method.

5.1.1.2 Medium roughness profile


Figure 14. Medium roughness profile from a sample texturized through the sandblasting method.

5.1.1.3 High roughness profile


Figure 15. High roughness profile from a sample texturized thorough the sandblasting method.

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3

3.8

4

4.0

6

4.2

7

4.4

84

.70

4.9

1

5.1

2

5.3

4

5.5

55

.76

5.9

8

6.1

9

Z [μ

m]

Distance [mm]

-50-40-30-20-10

01020304050

0.0

0

0.2

1

0.4

3

0.6

4

0.8

5

1.0

7

1.2

8

1.4

9

1.7

1

1.9

2

2.1

4

2.3

5

2.5

6

2.7

8

2.9

9

3.2

0

3.4

2

3.6

3

3.8

4

4.0

6

4.2

7

4.4

8

4.7

0

4.9

1

5.1

2

5.3

4

5.5

5

5.7

6

5.9

8

6.1

9

Z [μ

m]

Distance [mm]

19

5.1.2 Texture by means of the scalpel method

The shape of the profiles obtained through this method were soft and gradual. They present a

homogeneous shape. The profiles presented high peaks and deep troughs combined with low peaks

and troughs in a random form. The peaks of the profiles with low roughness reached values of 10

𝜇𝑚 and the troughs of -10 𝜇𝑚. The value of the highest peak and lowest trough of medium

roughness profiles were 30 𝜇𝑚 and -40 𝜇𝑚 respectively. Finally, the peaks for profiles with high

roughness reached values of 60 𝜇𝑚 and the troughs reached values of -80 𝜇𝑚. Therefore, the

roughness obtained on the rock surface through this method is a shape made of a series of variable

peaks and troughs with similar heights, depths, and spacings, and it provided a uniform texture on

the rock surface. The principal reason of these results is that this is a method in which the surface is

scratched with the same force and the scratches are made at a predetermined distance between them,

this process scratches the rock giving the surface a gradual roughness depending on the type of rock

texturized and its properties.

5.1.2.1 Low roughness profile

In figure 14 the roughness profile of the sample 0Spt1 that has a Ra of 1.35 can be observed.

Figure 16. Low roughness profile from a sample texturized by means of the scalpel method.

5.1.2.2 Medium roughness profile


Figure 17. Medium roughness profile from a sample texturized by means of the scalpel method.

-30

-20

-10

0

10

20

30

0.0

0

0.5

0

1.0

0

1.5

0

2.0

0

2.5

1

3.0

1

3.5

1

4.0

1

4.5

1

5.0

1

5.5

1

6.0

1

6.5

2

7.0

2

7.5

2

8.0

2

8.5

2

9.0

2

9.5

2

10

.02

10

.53

11

.03

11

.53

12

.03

12

.53

13

.03

13

.53

14

.03

14

.53

Z[ μ

m]

Distance [mm]

-80-60-40-20

020406080

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10

.0

10

.5

11

.0

11

.5

12

.0

12

.5

13

.0

13

.5

14

.0

14

.5

Z [μ

m]

Distance [mm]

20

5.1.2.3 High roughness profile


Figure 18. High roughness profile from a sample texturized by means of the scalpel method.

5.2 Roughness parameters

The only parameter that is universally standardized and is specified and measured far more

frequently than any other is the arithmetic average roughness height, or Roughness Average, Ra.

Therefore, this parameter was selected in this work for the analysis. However, other complementary

parameters (Rq, Rz and Rmax) were also computed as a reference. Additionally, the mean, the standard

deviation, and the Coefficient of Variation COV, were calculated to analyze the measurements

obtained. The COV is a measure of the dispersion of data points around the mean, the higher the

coefficient of variation, the greater the lever of dispersion around the mean. The results showed

high variability in all the surface roughness measurements.


With this method, it was expected that as the sandblasting pressure increased, the roughness

parameters (i.e., Rq, Rz and Rmax) of the rocks would also increase. Nevertheless, the sandblasting

pressure and the roughness parameter 𝑅𝑎 did not show any clear relationship; that is, the surface

roughness parameters of the aggregates obtained through the different applied pressures are random

(Figure 16). The highest value of 𝑅𝑎 obtained through this method was 13.27 𝜇𝑚, and the lowest

value of 𝑅𝑎 was 5.91 𝜇𝑚. The range of values of 𝑅𝑎 obtained through this method was 7.36 𝜇𝑚.

The most representative roughness parameters are presented in Table 1.

-80-60-40-20

020406080

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10

.0

10

.5

11

.0

11

.5

12

.0

12

.5

13

.0

13

.5

14

.0

14

.5

Z [μ

m]

Distance [mm]

21

Figure 19. Relationship between the Sandblasting pressure and the roughness parameter Ra.

Table 1. Roughness parameters of the aggregates texturized through sandblasting (STD stands for standard deviation)

Roughness Parameters for samples texturized with sandblasting method (μm)

Quartize Marble

Sample Ra Rq Rz Rmax Sample Ra Rq Rz Rmax

40Qtz1

12.22 15.40 63.92 91.21

40Mrb1

7.09 21.64 37.06 74.64

10.11 12.86 53.77 77.46 6.98 18.12 34.98 44.01

11.12 13.90 56.96 73.18 8.04 25.85 38.84 68.68

Mean 11.15 14.05 58.21 80.62 Mean 7.37 21.87 36.96 62.44

STD 1.06 1.28 5.19 9.42 STD 0.58 3.87 1.93 16.24

COV 9.5% 9.1% 8.9% 11.7% COV 7.9% 17.7% 5.2% 26.0%

40Qtz2

12.95 16.35 65.70 93.50

40Mrb2

6.33 8.14 34.17 44.94

13.19 16.38 62.89 80.57 6.38 8.18 33.44 43.89

12.73 15.78 64.17 82.68 6.15 7.86 31.10 42.80

Mean 12.96 16.17 64.25 85.58 Mean 6.29 8.06 32.90 43.88

STD 0.23 0.34 1.41 6.93 STD 0.12 0.18 1.61 1.07

COV 1.8% 2.1% 2.2% 8.1% COV 1.9% 2.2% 4.9% 2.4%

40Qtz3

12.35 15.83 67.80 108.09

40Mrb3

6.34 8.00 32.55 49.06

10.93 14.44 60.37 107.03 5.11 7.12 29.81 49.35

10.99 14.76 58.49 106.53 6.28 7.75 33.33 41.16

Mean 11.42 15.30 62.22 107.22 Mean 5.91 7.62 31.90 46.52

STD 0.80 0.76 4.93 0.80 STD 0.69 0.46 1.85 4.65

COV 7.0% 4.9% 7.9% 0.7% COV 11.7% 6.0% 5.8% 10.0%

60Qtz1

11.71 14.14 52.40 62.68

40Mrb5

7.42 9.17 38.29 50.78

12.68 16.02 64.18 94.37 6.86 8.75 36.73 46.73

10.46 12.68 48.63 59.94 6.52 8.63 36.08 59.78

Mean 11.62 14.28 55.07 72.33 Mean 6.93 8.85 37.03 52.43

STD 1.12 1.67 8.11 19.14 STD 0.45 0.29 1.13 6.68

5

6

7

8

9

10

11

12

13

14

30 40 50 60 70 80 90

Ro

ugh

nes

s Ra

(μm

)

Pressure (psi)

Quartzite

Marble

22


Quartize Marble


COV 9.6% 11.7% 14.7% 26.5% COV 6.5% 3.2% 3.1% 12.7%

60Qtz2

10.18 15.16 52.03 116.60

60Mrb1

8.06 9.81 40.23 50.05

7.88 10.04 41.21 56.30 6.83 8.78 37.73 53.09

8.42 10.61 43.10 55.68 7.91 10.19 43.34 57.04

Mean 8.83 11.94 45.44 76.19 Mean 7.60 9.60 40.43 53.39

STD 1.20 2.81 5.78 35.00 STD 0.67 0.73 2.81 3.50

COV 13.6% 23.5% 12.7% 45.9% COV 8.8% 7.6% 7.0% 6.6%

60Qtz3

13.26 16.69 65.38 86.96

60Mrb2

8.97 11.49 47.75 69.96

14.31 18.01 70.79 91.46 10.32 12.94 53.33 62.96

12.23 15.86 61.55 83.50 8.88 1.26 43.97 60.84

Mean 13.27 16.85 65.91 87.31 Mean 9.39 8.56 48.35 64.59

STD 1.04 1.08 4.64 3.99 STD 0.80 6.36 4.71 4.77

COV 7.8% 6.4% 7.0% 4.6% COV 8.6% 74.3% 9.7% 7.45%

60Qtz4

11.44 14.03 54.61 64.90

60Mrb3

7.00 8.92 37.82 47.46

11.69 14.25 57.21 79.59 8.10 9.78 39.23 58.03

12.77 16.15 61.56 93.96 6.62 8.37 35.41 49.29

Mean 11.97 14.81 57.80 79.48 Mean 7.24 9.02 37.49 51.59

STD 0.70 1.17 3.51 14.53 STD 0.77 0.71 1.93 5.65

COV 5.9% 7.9% 6.1% 18.3% COV 10.6% 7.9% 5.1% 10.9%

80Qtz1

10.72 13.36 51.90 71.26

60Mrb4

7.98 10.48 44.46 70.02

11.68 15.97 54.45 80.92 7.38 9.37 39.19 49.70

9.06 11.61 43.95 65.63 7.38 9.55 41.56 60.72

Mean 10.49 13.65 50.10 72.60 Mean 7.58 9.80 41.74 60.14

STD 1.32 2.19 5.48 7.73 STD 0.34 0.60 2.64 10.17

COV 12.6% 16.1% 10.9% 10.6% COV 4.6% 6.1% 6.3% 16.9%

80Qtz3

8.76 10.70 44.75 63.63

60Mrb5

7.64 9.48 37.57 54.73

9.61 12.38 50.97 75.04 9.70 12.11 46.32 57.52

7.07 8.84 36.70 51.41 6.84 8.52 35.26 56.06

Mean 8.48 10.64 44.14 63.36 Mean 8.06 10.04 39.71 56.10

STD 1.29 1.77 7.15 11.82 STD 1.48 1.86 5.83 1.39

COV 15.2% 16.7% 16.2% 18.7% COV 18.3% 18.5% 14.7% 2.5

80Qtz4

8.25 10.52 44.38 57.94

80Mrb1

6.27 7.75 31.63 40.86

10.93 13.33 52.23 67.46 7.70 9.41 37.50 48.72

11.82 14.86 58.08 97.92 6.63 8.35 36.67 44.33

Mean 10.33 12.90 51.56 74.44 Mean 6.87 8.50 35.26 44.63

STD 1.86 2.20 6.87 20.89 STD 0.74 0.84 3.18 3.94

COV 18.0% 17.1% 13.3% 28.1% COV 10.8% 9.9% 9.0% 8.8%

80Qtz5

9.43 12.14 52.67 67.44

80Mrb2

9.14 11.20 43.84 57.15

8.26 10.70 46.83 58.91 8.38 10.34 41.23 50.29

8.06 10.04 43.56 54.38 6.33 8.40 33.31 59.83

23


Quartize Marble


Mean 8.59 10.96 47.68 60.24 Mean 7.95 9.98 39.46 55.76

STD 0.74 1.08 4.62 6.63 STD 1.45 1.44 5.48 4.92

COV 8.6% 9.8% 9.7% 11.0% COV 18.3% 14.4% 13.9% 8.8%


With this method, it was expected that as the angle between lines decreased, the roughness

parameters (i.e., Rq, Rz and Rmax) of the rocks would also increase. Nevertheless, the angles between

lines and the roughness parameter 𝑅𝑎 did not show any clear relationship; that is, the surface

roughness parameters of the aggregates obtained through the different applied angles are random

(Figure 17). The highest value of 𝑅𝑎 obtained through this method was 26.11 𝜇𝑚, and the lowest

value of 𝑅𝑎 was 6.85 𝜇𝑚. The range of values of 𝑅𝑎 obtained through this method was 19.26 𝜇𝑚.

The most representative roughness parameters are presented in Table 2.

Figure 20. Relationship between the line angles and the roughness parameter Ra.

Table 2. Roughness parameters of the aggregates texturized by means of the scalpel method (STD.

Roughness Parameters for samples texturized with scalpel method (μm)

Serpentinite Marble


0Spt1

1.32 2.09 14.11 29.23

0Mrb1

1.19 1.69 12.46 16.96

1.06 1.72 10.88 20.42 1.19 1.60 10.38 15.31

1.68 2.54 14.48 18.73 1.15 1.61 11.38 17.39

Mean 1.35 2.11 13.16 22.79 Mean 1.18 1.63 11.41 16.55

STD 0.31 0.41 1.98 5.64 STD 0.02 0.05 1.04 1.10

COV 23.1% 19.2% 15.0% 24.7% COV 1.8% 3.2% 9.1% 6.6%

1Spt1

9.37 12.59 56.80 76.54

1Mrb1

15.57 22.21 84.48 150.77

14.82 19.95 74.47 122.48 10.16 14.62 64.87 107.44

12.69 17.86 61.34 102.16 18.11 25.39 111.66 157.64

Mean 12.29 16.80 64.20 100.39 Mean 14.61 20.74 87.00 138.62

0

5

10

15

20

25

30

0 1 1 2 2 3 3 4

Ro

ugh

nes

s Ra

(μm

)

Angle between lines (1: 120°, 2:45°, 3:30°)

Serpentinite

Marble

24


Serpentinite Marble


STD 2.75 3.79 9.18 23.02 STD 4.06 5.54 23.50 27.22

COV 22.3% 22.6% 14.3% 22.9% COV 27.8% 26.7% 27.0% 19.6%

1Spt2

9.05 13.93 62.66 94.83

1Mrb2

7.56 11.99 54.85 97.07

10.05 14.07 58.67 70.15 5.52 8.56 44.44 71.93

12.54 16.77 77.23 100.09 7.48 10.94 49.91 72.94

Mean 10.55 14.92 66.19 88.36 Mean 6.85 10.50 49.73 80.64

STD 1.80 1.60 9.77 15.98 STD 1.16 1.76 5.21 14.23

COV 17.1% 10.7% 14.8% 18.1% COV 16.9% 16.7% 10.5% 17.6%

1Spt3

11.47 15.47 61.88 87.02

1Mrb3

13.68 18.55 84.65 124.54

10.65 14.25 55.33 77.63 9.14 12.85 51.01 84.73

11.05 14.92 63.24 80.88 13.01 17.03 70.49 93.02

Mean 11.06 14.88 60.15 81.84 Mean 11.94 16.14 68.72 100.76

STD 0.41 0.61 4.23 4.77 STD 2.45 2.95 16.89 21.00

COV 3.7% 4.1% 7.0% 5.8% COV 20.5% 18.3% 24.6% 20.8%

2Spt1

8.59 11.54 49.64 64.35

2Mrb1

20.97 27.04 114.25 148.73

10.11 13.27 53.19 67.80 20.82 26.66 100.86 171.45

8.39 11.49 50.10 77.35 18.29 23.30 89.45 135.88

Mean 9.03 12.10 50.97 69.83 Mean 20.03 25.67 101.52 152.02

STD 0.94 1.01 1.93 6.73 STD 1.50 2.06 12.41 18.01

COV 10.4% 8.4% 3.8% 9.6% COV 7.5% 8.0% 12.2% 11.8%

2Spt2

9.73 12.02 47.50 53.68

2Mrb2

13.36 19.95 83.19 126.24

8.93 11.88 49.05 61.17 11.98 18.39 73.35 125.51

8.45 11.22 47.70 63.10 8.65 12.43 53.32 72.97

Mean 9.04 11.70 48.08 59.32 Mean 11.33 16.92 69.95 108.24

STD 0.65 0.42 0.84 4.97 STD 2.42 3.97 15.22 30.55

COV 7.2% 3.6% 1.8% 8.4% COV 21.4% 23.5% 21.8% 28.2%

2Spt3

13.02 17.83 67.60 104.09

2Mrb3

13.40 19.32 74.62 117.19

9.37 12.38 51.86 70.80 14.91 21.10 81.76 131.61

14.31 17.89 71.72 82.76 11.27 17.22 69.76 111.51

Mean 12.23 16.03 63.73 85.88 Mean 13.19 19.21 75.38 120.10

STD 2.56 3.17 10.48 16.87 STD 1.83 1.94 6.04 10.36

COV 21.0% 19.7% 16.5% 19.6% COV 13.9% 10.1% 8.0% 8.6%

3Spt1

12.23 15.36 57.65 86.20

3Mrb1

19.06 24.91 87.64 142.85

13.77 16.81 60.69 77.85 16.26 19.72 87.04 128.18

12.21 15.05 56.93 64.91 11.96 17.35 74.27 117.87

Mean 12.74 15.74 58.42 76.32 Mean 15.76 20.66 82.99 129.63

STD 0.90 0.94 2.00 10.73 STD 3.58 3.87 7.55 12.55

COV 7.1% 6.0% 3.4% 14.1% COV 22.7% 18.7% 9.1% 9.7%

3Spt2 21.79 26.02 98.70 127.20

3Mrb2 23.11 28.71 103.59 147.97

15.86 20.59 78.43 121.58 19.29 24.12 96.83 123.54

25


Serpentinite Marble


20.32 24.00 88.12 115.23 15.89 21.20 80.61 140.96

Mean 19.32 23.54 88.42 121.34 Mean 19.43 24.68 93.68 137.49

STD 3.09 2.74 10.14 5.99 STD 3.61 3.79 11.81 12.58

COV 16.0% 11.7% 11.5% 4.9% COV 18.6% 15.3% 12.6% 9.1%

3Spt3

16.33 20.60 83.93 101.25

80Mrb1

27.68 34.68 124.40 181.89

14.76 18.22 73.71 102.99 28.26 34.17 129.94 160.46

12.64 16.73 75.61 100.47 22.39 30.41 112.21 163.71

Mean 14.57 18.52 77.75 101.57 Mean 26.11 33.09 122.18 168.69

STD 1.85 1.95 5.44 1.29 STD 3.24 2.33 9.07 11.55

COV 12.7% 10.5% 7.0% 1.3% COV 12.4% 7.0% 7.4% 6.8%

5.3 Mechanical performance of AAS systems

As explained before, the mechanical test results obtained from the mechanical pull-off test are the

Load [N] vs. Time [s] curve, and the maximum load at failure (𝐹𝑚𝑎𝑥)[𝑁]. These results can be

translated to Load [N] vs. Displacement [mm] curves, since the test velocity was set to be 10 mm/min

(0.166 mm/s). From the Load [N] vs Displacement [mm] curve of all the experiments the maximum

load at failure (𝐹𝑚𝑎𝑥[𝑁]) and the work of fracture (𝑊𝑓[𝐽]) were computed. In order to correlate the

mechanical results with the roughness properties of the rocks, the relationship between the aggregates

surface roughness and the maximum load at failure was explored, which can be plotted in Ra [𝜇𝑚]

vs. (𝐹𝑚𝑎𝑥)[𝑁] graphs. Besides, since the roughness profiles of the samples surface were measured,

the actual contact area of the surface 𝐴𝐶[𝑚𝑚2]) was calculated as 𝐴 = 𝜋𝑟2 in which the radius of

the sample surface was estimated as the total length of the roughness profile, and this allows to assess

the relationship between the aggregate surface that was in contact with the asphalt binder, and the

maximum load at failure, presented in a curve of the Area of contact 𝐴𝐶[𝑚𝑚2]) [𝑚𝑚2] vs. 𝐹𝑚𝑎𝑥[𝑁].

Additionally, the information from the mechanical test can be translated to Area of contact [𝑚𝑚2]

vs. 𝑊𝑓[𝐽], so a relationship between the aggregate surface contact of the specimen with the asphalt

binder and the work of fracture can be obtained. Finally, the mean, the standard deviation, and the

Coefficient of Variation COV, were calculated to analyze the results obtained


The results of 𝐹𝑚𝑎𝑥, 𝑊𝑓 and 𝐴𝐶 of the aggregate surface with the asphalt binder for the samples of

quartzite and marble texturized through sandblasting are presented in Table 3. In addition, the

mechanical performance of a quartzite and a marble sample without any texture in the surface was

presented in order to have control samples. The mechanical results of these samples were obtained

by a previous work presented by Cala et a (2019). The Load vs. Displacement curves for all the

samples of Quartize can be seen in Figure 17, while the test results for all the samples of Marble

can be seen in Figure 18. The Ra vs. 𝐹𝑚𝑎𝑥 of the quartzite and marble can be observed in Figure 19.

Additionally, the 𝐴𝐶 vs. 𝐹𝑚𝑎𝑥 of the quartzite and marble can be seen in Figure 20. Finally, 𝐴𝐶, c,

vs. 𝑊𝑓 of the quartzite and marble samples can be seen in Figure 21.

26

Table 3. The maximum load at failure and the work fracture results of samples of quartzite and marble texturized

through sandblasting.

Quartzite Marble

Sample Ra

[𝝁𝒎]

𝑭𝒎𝒂𝒙

[𝑵]

𝑾𝒇

[𝑱]

Area

[𝒎𝒎𝟐] Sample

Ra

[𝝁𝒎]

𝑭𝒎𝒂𝒙

[𝑵]

𝑾𝒇

[𝑱]

Area

[𝒎𝒎𝟐]

40Qtz1 11.15 271.39 0.08 602.82 40Mrb1 7.37 413.61 0.03 560.79

40Qtz2 12.96 559.01 0.17 603.56 40Mrb2 6.29 397.38 0.23 549.90

40Qtz3 11.42 643.71 0.21 604.23 40Mrb3 5.91 573.13 0.46 546.59

60Qtz1 11.62 1136.37 0.38 581.97 40Mrb5 6.94 752.40 0.30 561.66

60Qtz2 8.84 155.99 0.07 576.60 60Mrb1 7.60 583.01 0.21 555.75

60Qtz3 13.27 1087.69 0.44 601.60 60Mrb2 9.39 507.48 0.18 569.85

60Qtz4 11.97 789.81 0.28 597.95 60Mrb3 7.24 707.94 0.27 556.18

80Qtz1 10.49 30.35 0.01 583.34 60Mrb4 7.58 162.34 0.08 571.52

80Qtz3 8.48 337.46 0.29 574.41 60Mrb5 8.06 479.25 0.25 558.57

80Qtz4 10.33 41.64 0.02 583.17 80Mrb1 6.87 577.36 0.52 557.64

80Qtz5 8.59 85.40 0.07 579.00 80Mrb2 7.95 618.30 0.37 557.00

Mean 10.83 467.17 0.18 589.88 Mean 7.38 524.75 0.26 558.68

STD 1.66 405.73 0.15 12.03 STD 0.94 162.76 0.15 7.38

COV 15.4% 86.9% 80.7% 2.0% COV 12.7% 31.0% 55.7% 1.3%

Figure 21. Load[N] vs. Displacement [mm] curves of quartzite samples textured through sandblasting method.

0

200

400

600

800

1000

1200

1400

1600

0.0

0

0.0

8

0.1

7

0.2

5

0.3

3

0.4

2

0.5

0

0.5

8

0.6

7

0.7

5

0.8

3

0.9

2

1.0

0

1.0

8

1.1

7

1.2

5

1.3

3

1.4

2

LOA

D [

N]

DISPLACEMENT [mm]

Qtz Control Sample

40Qtz1

40Qtz2

40Qtz3

60Qtz1

60Qtz2

60Qtz3

60Qtz4

80Qtz1

80Qtz3

27

Figure 22. Load[N] vs. Displacement [mm] curves of marble samples textured through sandblasting method.

From Figure 17 and Figure 18, it can be seen that there are three types of Load vs. Displacement

curves. The first type of curve has an increment of load with a constant slope and when it reaches

the maximum load at failure the slope and load falls immediately (e.g., 60 Qtz1 curve). The second

type of curve has an increment of load with a constant slope and when the maximum load at failure

is reached, the load maintains constant for a certain period after the slope and load falls immediately

(e.g., 80Mrb1 curve). Finally, the third type of curve exhibits an increment of load with a constant

slope, and when it reaches the maximum load at failure it presents a decrease of load with a constant

slope, until it reaches a load of 0 N (e.g., 40Mrb2 curve). The average maximum load at failure for

the quartzite samples is 467 N, while the average maximum load at failure for the marble samples

524 N, this value is very similar for both types of rocks with a difference of 12.32% between them.

It is difficult to know at this time what is the cause in the differences in this mechanical behavior

among samples. It is speculated that the lack of control over the thickness of the asphalt film

between samples and the different values of Ra among them could partially explain this behavior

since a higher thickness of the asphalt film tend to promote cohesive failure, lower values of the

maximum load at failure (𝐹𝑚𝑎𝑥) and different mechanical performance in the test.

Figure 23. Ra [μm] vs. 𝐹𝑚𝑎𝑥 [N] of quartzite and marble samples textured through sandblasting method.

0

200

400

600

800

1000

1200

0.0

0

0.0

8

0.1

7

0.2

5

0.3

3

0.4

2

0.5

0

0.5

8

0.6

7

0.7

5

0.8

3

0.9

2

1.0

0

1.0

8

1.1

7

1.2

5

1.3

3

1.4

2

1.5

0

1.5

8

LOA

D [

N]

DISPLACEMENT [mm]

Mrb Control Sample

40Mrb1

40Mrb2

40Mrb3

40Mrb5

60Mrb1

60Mrb2

60Mrb3

60Mrb4

60Mrb5

R² = 0.5427

R² = 0.0013

0

200

400

600

800

1000

1200

7 8 9 10 11 12 13 14

F ma

x[N]

Ra [μm]

Quartzite

Marble

Poly. (Quartzite)

Poly. (Marble)

28

From Figure 19, it can be observed that in the group of samples that were texturized by means of

the sandblasting method there is no clear relationship between Ra and 𝐹𝑚𝑎𝑥 . Nevertheless, if the

quartzite samples are analyzed individually, a positive relationship between these two variables can

be observed. As Ra increases, 𝐹𝑚𝑎𝑥 increases. If the marble samples are analyzed separately, there

is not a clear relationship between both parameters.

Figure 24. Area of contact [𝑚𝑚2] vs. 𝐹𝑚𝑎𝑥[𝑁] of the quartzite and marble samples texturized through sandblasting

method.

From Figure 20, it can be observed that in the group of samples that were texturized by means of

the sandblasting method there is no clear relationship between the contact area of the aggregate with

the asphalt binder and the maximum load at failure 𝐹𝑚𝑎𝑥 for the quartzite or marble samples.

Figure 25. The Area of contact [𝑚𝑚2] vs. 𝑊𝑓[𝐽] of the quartzite and marble samples texturized through sandblasting

method.

Similarly, from Figure 21, it can be observed that in the group of samples that were texturized by

means of the sandblasting method there is not a clear relationship between the contact area of the

aggregate with the asphalt binder and the work of fracture 𝑊𝑓 obtained from the mechanical

adhesion test.


Similar to the previous section, Table 4 presents the results of 𝐹𝑚𝑎𝑥, 𝑊𝑓 and the Area of contact of

the aggregate surface with the asphalt binder for the serpentinite and marble samples that were

texturized by means of the scalpel method are presented in Table 4. In addition, the mechanical

0

200

400

600

800

1000

1200

570 580 590 600 610

F m

ax [N]

AC [mm2]

Quartzite

Marble

0.00

0.10

0.20

0.30

0.40

0.50

0.60

570 580 590 600 610

Wf[J]

AC [mm2]

Quartzite

Marble

29

performance of a quartzite and a marble sample without any texture in the surface was presented in

order to have control samples. The mechanical results of these samples were obtained by a previous

work presented by Cala et a (2019).The Load vs. Displacement curves for all the samples of

serpentinite can be seen in Figure 22, and in Figure 23 for the marble samples. The obtained

relationships between Ra and 𝐹𝑚𝑎𝑥 for both rocks can be observed in Figure 24. Additionally, the

relationship of Area of contact of the aggregate sample with the asphalt and 𝐹𝑚𝑎𝑥, and of the Area

of contact and 𝑊𝑓 for both rocks can be seen in Figure 25 and Figure 26, respectively.

Table 4. The maximum load at failure and the work fracture results of samples of serpentinite and marble texturized by

means of the scalpel method.

Serpentinite

Marble

Sample Ra

[𝝁𝒎]

𝑭𝒎𝒂𝒙

[𝑵]

𝑾𝒇

[𝑱]

Area

[𝒎𝒎𝟐]

Sample Ra

[𝝁𝒎]

𝑭𝒎𝒂𝒙

[𝑵]

𝑾𝒇

[𝑱]

Area

[𝒎𝒎𝟐]

0Spt1 1.68 557.60 0.62 501.19 0Mrb1 1.18 200.45 0.03 504.88

1Spt1 12.29 842.04 0.70 521.41 1Mrb1 14.61 781.34 0.54 531.07

1Spt2 10.55 702.29 1.02 523.10 1Mrb2 6.85 635.94 0.31 516.49

1Spt3 11.06 1118.02 0.71 517.08 1Mrb3 11.94 798.28 0.40 525.26

2Spt1 9.03 755.93 0.53 513.72 2Mrb1 20.02 376.91 0.32 540.45

2Spt2 9.04 452.43 0.66 512.69 2Mrb2 11.33 179.98 0.09 519.18

2Spt3 12.23 599.95 1.26 520.43 2Mrb3 13.19 544.89 0.63 526.53

3Spt1 12.74 739.70 1.10 522.67 3Mrb1 15.76 715.00 0.21 533.27

3Spt2 19.32 821.57 0.99 536.10 3Mrb2 19.43 306.33 0.15 545.17

3Spt3 14.57 854.75 1.67 530.81 3Mrb3 26.11 616.18 0.20 550.26

Mean 11.25 744.43 0.93 519.92 Mean 14.04 515.53 0.29 529.26

STD 4.5 185.65 0.35 9.72 STD 7.02 233.51 0.19 13.83

COV 40.0% 24.9% 38.2% 1.9% COV 50.0% 45.3% 66.3% 2.6%

Figure 26. Load[N] vs. Displacement [mm] curves of serpentinite samples textured by means of the scalpel method.

0

200

400

600

800

1000

1200

0.0

0

0.1

7

0.3

3

0.5

0

0.6

7

0.8

3

1.0

0

1.1

7

1.3

3

1.5

0

1.6

7

1.8

3

2.0

0

2.1

7

2.3

3

2.5

0

2.6

7

2.8

3

3.0

0

3.1

7

LOA

D [

N]

DISPLACEMENT [mm]

Spt Control Sample

0Spt1

1Spt1

1Spt2

1Spt3

2Spt1

2Spt2

2Spt3

3Spt1

3Spt2

30

Figure 27. Load[N] vs. Displacement [mm] curves of marble samples textured by means of the scalpel method.

For this method, Figure 22 and Figure 23 show that there are two types of Load vs. Displacement

curves. The first type of curve exhibits an increment of load with a constant slope and in the

maximum load at failure the slope and load fall immediately (e.g., 1Spt3 curve). The second type

of curve exhibits an increment of load with a constant slope and in the maximum load at failure the

load maintains constant for a certain period and finally at failure the slope and load fall immediately

(e.g., 1Mrb1 curve). As it happened in the previous graphs (Figure 18 and Figure 19), it is difficult

to know at this time what is the cause in the differences in this mechanical behavior among samples.

It is speculated that the lack of control over the thickness of the asphalt film between samples and

the different values of Ra among them could partially explain this behavior since a higher thickness

of the asphalt film tend to promote cohesive failure, lower values of the maximum load at failure

(𝐹𝑚𝑎𝑥) and different mechanical performance in the test.

The average maximum load at failure for the serpentinite samples is 745 N, while the average

maximum load at failure for the marble samples 515 N, this value is considerably different for both

types of rocks with a difference of 44% between them. Nevertheless, the result of the average

maximum load at failure of the samples of marble texturized through sandblasting is very similar to

the value of the average maximum load at failure of the samples of this same type of rock texturized

by means of the scalpel method, with a difference of only 1.76% between their values. The behavior

of the of Load vs. Displacement curves of both samples of marble also had similar behavior

independently of the method used to texturize the samples (i.e., difference in the average maximum

load at marble of 1.76% between the two texturing methods).

0

200

400

600

800

1000

1200

0.0

00

.10

0.2

00

.30

0.4

00

.50

0.6

00

.70

0.8

00

.90

1.0

01

.10

1.2

01

.30

1.4

01

.50

1.6

01

.70

1.8

01

.90

LOA

D [

N]

DISPLACEMENT [mm]

Mrb Control Sample

0Mrb1

1Mrb1

1Mrb2

1Mrb3

2Mrb1

2Mrb2

2Mrb3

3Mrb1

3Mrb2

31

Figure 28. Ra [μm] vs. (𝐹𝑚𝑎𝑥)[N]] curves of serpentinite and marble samples textured by means of the scalpel method.

From Figure 24, it can be observed that the of serpentinite and marble samples texturized by means

of the scalpel method does not present a clear relationship between Ra and 𝐹𝑚𝑎𝑥. However, if the

serpentinite samples are analyzed individually, a small tendency of a direct relationship between Ra

and 𝐹𝑚𝑎𝑥 (i.e., increase of the Ra value as the 𝐹𝑚𝑎𝑥 increases) can be seen. Similarly, if the marble

samples are analyzed individually, the same slight increasing relationship between Ra and 𝐹𝑚𝑎𝑥 can

be observed. Nevertheless, this trend is not strong enough to obtain conclusions about a relationship

between these two variables.

Figure 29. The Area of contact [𝑚𝑚2] vs. 𝐹𝑚𝑎𝑥[𝑁] graph of the serpentinite and marble samples texturized by means

of the scalpel method.

Similar to the sandblasting method, Figure 25 shows that the results for the samples texturized using

the scalpel method do not present a relationship between the contact area of the aggregate with the

binder and 𝐹𝑚𝑎𝑥, although the data suggests a weak positive tendency between the contact area of

the aggregate and 𝐹𝑚𝑎𝑥 for both aggregates.

R² = 0.2312

R² = 0.4287

0

200

400

600

800

1000

1200

0 5 10 15 20 25

Fmax

[N]

Ra [μm]

Serpentinite

Marble

Expon.(Serpentinite)Poly. (Marble)

0

200

400

600

800

1000

1200

500 505 510 515 520 525 530 535 540

Fmax[N]

AC [mm2]

Serpentinite

Marble

32

Figure 30. The Area of contact [𝑚𝑚2] vs. 𝑊𝑓[𝐽] graph of the serpentinite and marble samples texturized by means of

the scalpel method.

Finally, Figure 26 shows that the samples texturized by means of the scalpel method present a weak

positive relationship between the contact area of aggregate with the asphalt binder and 𝑊𝑓 for the

serpentinite samples. On the contrary, no clear relationship was observed between these parameters

for the marble samples.

5.3.3 Types of failure

The testing procedure consisted of applying tensile forces on the AAS systems under a control

displacement condition of 10mm/min until reaching the failure of the system. This failure could be

adhesive, cohesive or substrate failure. Adhesive failure occurs when there is a debonding at the

asphalt-aggregate interface, while the cohesive failure occurs on the asphalt film itself. Finally,

substrate failure occurs when the substrate, in this ca se, the rock sample, fails prior to bond failure.

All the lithologies presented cohesive failure (i.e., the failure occurred within the asphalt binder),

as shown in Figure 27. Nevertheless, some of the lithologies texturized through the sandblasting

method presented a cohesive failure in combination with a substrate failure. It means that most of

the failure was cohesive but, in some areas, there was a substrate failure in which parts of the rock

remained attached to the metallic stub, as shown in Figure 28. Some explanations for this behavior

are explored in the following section.

Figure 31. Quartzite 80Qtz4 sample with a cohesive failure in the interface.

0.00

0.50

1.00

1.50

2.00

500 505 510 515 520 525 530 535 540

Wf[J]

AC [mm2]

Serpentinite

Marble

33

Figure 32. Quartzite 60Mrb2 sample with a cohesive failure and substrate failure in the interface.

5.4 Comparison of results among rocks and texturing methods

In order to establish the relative performance of these three lithologies, texturized by means of two

different methods, a comparative analysis of the results presented previously was evaluated. As

expected, the AAS systems with all the lithologies texturized through both methods exhibit a small

tendency of the improvement of the bonding quality with the increase of the roughness parameter

Ra. Nevertheless, some lithologies (i.e., Quartzite) presented better adhesive qualities and a clearer

tendency of this relationship than others.

All the lithologies presented cohesive failure, and some of the lithologies texturized through the

sandblasting method had a combination of cohesive failure and substrate failure (i.e., Quartzite and

Marble). One explanation for this result could be that the sandblasting texturing method is an

aggressive method that consists of a system of launching abrasive materials with pressurized air, in

which the rock samples are pre-fractured, which could in turn contribute to a substrate failure.

Additionally, when analyzing the type of texture obtained through both methods based on the results

of the roughness profiles, it is found that the area of contact of the aggregate surface with the asphalt

binder is 8% higher in the rocks texturized through the sandblasting method than the rocks

texturized with the scalpel method. Thus, the samples texturized through the sandblasting method

had more contact with the asphalt binder and a thicker asphalt layer than the samples texturized by

means of the scalpel method. The thicker asphalt layer between the rock sample and the metallic

hub contributes to a cohesive failure due to an increase in the quantity of asphalt.

The marble lithologies that were texturized with both methods had very similar behavior in the

mechanical results. Nevertheless, the samples that were texturized by the second method present

more frequently a behavior in which the curve exhibits an increment of load with a constant slope

and in the maximum load at failure the load maintains constant for a certain period and finally at

failure the slope and load fall immediately. These results serve to conclude that the technique used

to texturize the samples affect the mechanical performance of the asphalt-aggregate system. The

Load vs. Displacement curves were similar and the value of the maximum load at failure 𝐹𝑚𝑎𝑥 was

only about 1.76% different. The marble samples texturized through sandblasting reached higher

loads at failure with a difference of 1.76% between the two texturing methods.

The lithology that exhibited the highest maximum load at failure values 𝐹𝑚𝑎𝑥 was the serpentinite

texturized by means of the scalpel method. The average maximum load at failure for this group of

samples was 745 N, while the average value for marble samples was about 520 N and for quartzite

34

samples was 467 N. In general, both samples, serpentinite and marble texturized by means of the

scalpel method had higher values of maximum load at failure 𝐹𝑚𝑎𝑥 than the samples of quartzite

and marble texturized through sandblasting method. The reason why the lithologies texturized by

means of the scalpel method reached higher values of 𝐹𝑚𝑎𝑥 than those texturized through the

sandblasting method is attributed to the pre-fractured condition of the sample with the sandblasting

method, and the increase in the asphalt layer in the AAS system. A thinner asphalt layer between

the rock sample and the metallic hub contributes to a higher maximum load at failure. As this layer

of asphalt in the system increases, the maximum load at failure decreases.

The lithologies texturized by means of the scalpel method showed a direct relationship between the

area of contact of the aggregate surface with the asphalt and 𝐹𝑚𝑎𝑥, as expected. A bigger contact

area of the aggregate surface with the asphalt binder has an improvement in the adhesion quality.

Also, the serpentinite samples of this group showed a relationship between the aggregate contact

area and 𝑊𝑓, as expected. Nevertheless, some lithologies did not present a relationship between the

area of contact and 𝐹𝑚𝑎𝑥, and in the contact area with 𝑊𝑓.

The group of samples texturized by the sandblasting method had a COV of the Ra value of 14.02%

while the group of samples texturized by the scalpel method had a COV of the Ra value of 45%.

Similarly, the COV of the contact area AC of the samples texturized by the first method, 1.68%, is

smaller than the COV of the contact area AC of the samples texturized by the second method, 2.24%.

This means that the first technique of texture provides a more homogeneous and less variable texture

between the samples.

From the results presented in Figure 20, it can be observed that at low roughness levels (Ra between

8 𝜇𝑚 and 11 𝜇𝑚) marble samples had higher values of maximum load at failure 𝐹𝑚𝑎𝑥 than the

samples of quartzite, both texturized through the sandblasting method. Nevertheless, at higher levels

of roughness, quartzite samples had higher values of maximum load that the samples of quartzite.

These results imply that at low roughness levels the behavior of the system is strongly influenced

by the chemistry of the rock and conversely, at high roughness levels, what dominates the response

to adhesion is not the lithology chemistry but the rock surface roughness. Nonetheless, this behavior

is not evident in the results for the samples of serpentinite and marble texturized by means of the

scalpel method presented in Figure 25, in which the serpentinite lithology had higher values of

maximum load at failure 𝐹𝑚𝑎𝑥 at low and high roughness levels.

The control lithologies of quartzite, marble and serpentinite were samples that did not go through a

texturization process and the faces were polished. These samples exhibited a value of the maximum

load at failure 𝐹𝑚𝑎𝑥 of 1372.11 N, 1053.08 N and 1006.5 N respectively. These values are 65.96%,

50.6% and 25.98% higher from the values of maximum load at failure 𝐹𝑚𝑎𝑥 obtained for the

samples that were texturized by means of both methods. One possible reason for this result is that

in the lithologies that were not texturized (i.e., no roughness) it was possible to guarantee an asphalt

film of 0.20 𝜇𝑚 while in the samples that were texturized by means of both methodologies, a higher

thickness of the asphalt film was achieved (i.e., 35 𝜇𝑚) due to the valleys and peaks formed during

the texturization process. In this regard, a thicker asphalt film promotes a cohesive failure and a

failure at lower loads.

35

6 Conclusions

This work included a characterization of three different lithologies: i) Quartzite, ii) Marble, and iii)

Serpentinite, that were texturized using two different methods: i) Sandblasting and ii) Scalpel, in

order to evaluate the relationship between the aggregate surface roughness and the adhesion quality

of asphalt-aggregate systems. It was demonstrated that some rocks (i.e., Quartzite) with higher

roughness tend to have an increment in the adhesion quality of the asphalt-aggregate systems, as

concluded from the 𝐹𝑚𝑎𝑥, 𝑊𝑓, and Area of contact of the aggregate surface with the asphalt binder

obtained from the mechanical test and the analysis of the results. The main conclusions of this work

are as follows:

• Quartzite rocks with higher roughness in the aggregate surface have better adhesion quality

of the asphalt-aggregate system due to an increase in the contact area between the aggregate

surface and the asphalt binder contributing to better adhesion between them.

• Serpentinite and Marble samples do not present a clear relationship between the surface

roughness and the adhesion quality of the asphalt-aggregate system. Therefore, the surface

roughness of these aggregates does not have an influence on the adhesion quality of the

asphalt-aggregate system.

• Serpentinite rocks are more sensitive to the texturization process than the quartzite and

marble, having higher magnitudes in the roughness parameters than the other lithologies

and higher maximum load at failure values, supporting the conclusion that higher roughness

values contribute to better adhesion quality in the asphalt-aggregate system.

• The failure type presented in all the AAS systems was a cohesive failure.

• In some lithologies (i.e., 40Qtz1, 40Qtz3, 60Qtz1, 60Qtz4, 80Qtz1, 60Mrb3, 60Mrb2,

60Mrb4, 40Mrb3, 60Mrb1, 80Mrb1, 80Mrb2, 80Mrb5, 60Mrb5) texturized through the

sandblasting method, a substrate failure occurred which is attributed to the abrasive process.

• The similarity in the mechanical results for the marble lithology samples, texturized by both

methods, shows that the adhesion quality is more dependent on the lithology than on the

methods used to produce the texture.

• Depending on the roughness range, it was found that the rock chemistry had a stronger

influence on the mechanical response of asphalt-aggregate systems than the rock roughness.

Specifically, for samples prepared by the sandblasting method with Ra values below 12 𝜇𝑚,

quartzite samples had higher maximum load at failure values compared to marble samples.

In the case of samples prepared by means of the scalpel method, the serpentinite presented

better mechanical response in terms of maximum load at failure values for all the roughness

values, compared to those obtained for marble.

• It is necessary to find new and better texturizing methods in which a better control of the

asphalt film can be made in order to obtain a more homogeneous roughness on the whole

lithology surface.

• It is necessary to conduct more tests in a bigger number of samples and a larger number of

lithologies in order to obtain more clear results and make stronger conclusions about the

relationship between the aggregate surface roughness and the adhesion quality in the

asphalt-aggregate system.

36

• Finally, it would be important to assess in future studies if the rugosity plays a relevant role

in the durability of the aggregate-asphalt system under moisture conditions (i.e., conduct

the mechanical tests after subjecting the AAS samples to different moisture conditioning

processes).

37

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