Research Paper

Journal of Engineering and Technological Sciences

Structural Analysis and Service Life Prediction of Rubberized Thin
Surfacing Hot Mix Asphalt
\\\\\\\\

Sebastianus Kristianto Nugroho*, Ary Setyawan & Arif Budiarto
Department of Civil Engineering, Faculty of Engineering, Sebelas Maret University, Jalan Ir. Sutami No 36,
Surakarta 57126, Indonesia
Corresponding author: sebastianknugroho@gmail.com

Abstract
Rubberized thin surfacing hot mix asphalt (RTSHMA) is a type of flexible pavement that is currently being developed. It can
provide the same good performance as asphalt concrete–wearing course (AC-WC). Based on previous research, the use of
crumb rubber in the asphalt mixture can provide several advantages, such as increasing the flexibility of the mix so that the
pavement is more resistant to cracking. Based on research showing the advantages of rubberized asphalt, the idea emerged
to apply it in the field, namely on the Palur–Sragen City Boundary section as wearing course. The method of analysis in this
study was modeling the pavement structure with the KENPAVE and BISAR 3.0 programs. The analysis results showed that
the AC-WC model and RTSHMA model have the same good performance because both of them have a service life of more
than twenty years, which is the standard for flexible pavements. However, RTSHMA has an advantage, i.e., the thickness
layer is 25% thinner than AC-WC’s. With a thinner layer than AC-WC but the same good performance, RTSHMA is worth
considering as an alternative pavement, especially for overlays.
Keywords: BISAR 3.0; KENPAVE; overlay; rubberized asphalt; service life.

Introduction
The Palur–Sragen City Boundary section is a national arterial road in Indonesia, located in the province of Central
Java. This road segment is 20.01 km long and connects the cities of Solo and Sragen. The increase in vehicles
passing through arterial roads is directly proportional to population growth, resulting in premature damage
characterized by cracks and deformation [1, 2]. This needs to be addressed immediately to prevent further
damage, and one way is to overlay it.
So far, the pavement mixtures for overlay commonly used in Indonesia are asphalt concrete–wearing course
(AC-WC) and hot rolled sheet–wearing course (HRS-WC). AC-WC pavement is a type of tightly graded pavement,
while HRS-WC is a type of gap-graded pavement. Both have in common that the minimum thickness is 4 cm.
Apart from these two types of pavement mixtures, a different kind of pavement is now widely used in Indonesia,
especially for overlays, namely thin surfacing hot mix asphalt (TSHMA).
TSHMA is a mixture that has hybrid characteristics between AC and HRS mixture. TSHMA can provide exemplary
performance in terms of stability and flexibility. Therefore, this mixture generally has a long service life [3]. The
main advantage of TSHMA mixture is its thin thickness. Where the mixture of AC and HRS requires a thickness
of 4 to 5 cm for the surface layer, TSHMA only requires a thickness of 2 to 3 cm to provide the same good
performance [4]. This offers many benefits, especially from an economic and environmental perspective [5].
Many studies on TSHMA have been carried out, one of which is known as rubberized thin surfacing hot mix
asphalt (RTSHMA).
RTSHMA is a TSHMA mixture that utilizes crumb rubber as an added ingredient or as a substitute for aggregate
or asphalt. Adding crumb rubber to the asphalt mixture can increase the stability, ductility, skid resistance, and
softening point of the mixture [6-9]. Using crumb rubber in combination can also reduce the amount of asphalt
used. By adding crumb rubber at 0.5% of the total weight of the mixture, the optimum asphalt content (KAO)

Copyright ©2023 Published by IRCS - ITB
ISSN: 2337-5779

J. Eng. Technol. Sci. Vol. 55, No. 5, 2023, 538-547
DOI: 10.5614/j.eng.technol.sci.2023.55.5.3

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can decrease by 29.6% [10]. In the HRA mixture, using crumb rubber as a substitute for all fine aggregates makes
the mixture more flexible, durable, and impermeable [11].
So far, studies on rubberized asphalt only focused on the characteristics of the mixture. Little attention has been
paid to using rubberized asphalt as a road pavement layer and how it performs under traffic loads. Therefore,
this study tried to close this research gap by applying RTSHMA as a layer of the pavement structure and studying
it under traffic loads. This research used modeling with the help of the KENPAVE and BISAR 3.0 programs. These
are often used to evaluate the performance of pavement structures based on fatigue, rutting, and permanent
deformation criteria [12, 13].

Fundamental Aspects and Research Method
Fatigue Cracking
Fatigue cracking is a type of pavement damage in the form of a series of cracks that occur in the surface layer
14, 15]. Basically, fatigue is caused by elastic and viscoelastic behaviors of asphalt mixture [16]. Various factors,
including time, loading time, loading speed, loading mode, temperature, moisture, resting period, stress level,
and aging, have an effect on the deformation behavior and performance of flexible pavement [17-19]. To
calculate number of load repetitions that cause fatigue cracking, the following equation approach from the
Asphalt Institute can be used:
= 0.0769(ɛht)-3.921|E|-0.845

(1)

where:
Nfg
ɛht
E

= number of repetitions of the fatigue criteria, ESAL
= horizontal tensile strain
= modulus elasticity, kPa

Permanent Deformation
Permanent deformation is a type of damage caused by repetitive traffic loads and is characterized by a
permanent decrease/deformation of the road pavement structure [20-22]. The location of permanent
deformation is below the sub-base course layer or above the subgrade layer. The following equation approach
from the Asphalt Institute can be used to calculate the number of load repetitions that cause permanent
deformation:
=
where:
Ndp
ɛvc
fa
ft

(ɛvc)-ft

(2)

= number of repetitions of the permanent deformation criteria, ESAL
= vertical compressive strain
= 1.365 x 10-9
= 4.477

Service Life
Service life is the length of time a pavement structure can achieve in serving traffic loads until damage occurs
[23]. The road pavement structure will experience a decrease in its service life along with its ability to withstand
traffic loads. It is necessary to maintain the road pavement structure to achieve its planned life, as shown in
Figure 1 below.

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Sebastianus Kristianto Nugroho et al.

Figure 1 Graph of the relationship between pavement structural condition and service life. Source: [23]
In this study, service life was calculated by substituting the value of the number load repetitions based on fatigue
(Nfg) or the number load repetitions based on permanent deformation (Ndp) as the CESAL value in Equation 3
below.
= ∑(LHRTjk x FVD) x 365 x FL x FD x
where:
CESAL
LHRTjk
FVD
FL
FD
q
SL

(

( .

) )

( .

)

(3)

= cumulative equivalent standard axle load
= average daily traffic in one year
= factor of vehicle damage
= lane distribution factor
= directional distribution factor
= traffic growth rate
= service life

Research Method
The research method used in this research was modeling by using the KENPAVE and BISAR 3.0 programs. An
overview of the pavement structure model to be analyzed in this study can be seen in Figure 2.
replace surface layer

(a)

(b)
Figure 2 (a) Existing AC-WC model (b) RTSHMA model.

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KENPAVE
KENPAVE is a program that is often used in the modeling of road pavement structures. In the KENPAVE program,
there are two modeling menus : KENSLABS, which is used for modeling rigid pavement structures, and
KENLAYER, which is used for modeling flexible pavement structures [24]. This study focused on the KENLAYER
menu because the pavement structure model to be modeled was a flexible pavement type. The steps for
modeling pavement structures using KENPAVE program are:
1. Input thickness and Poisson’s ratio
The first step in making a model is creating a frame, In the KENPAVE program, the frame can be described
according to the thickness of each layer in the pavement structure. The thickness data are secondary data from
the construction design of the Palur–Sragen City Boundary section, which were obtained from the National Road
Implementation Center of Central Java – DIY. The existing AC-WC model and the RTHSMA model only differed
in the thickness of surface layer, used which was 4 cm in the existing AC-WC model and 3 cm in the RTSHMA
model. Apart from inputting the layer thickness, in the initial steps the Poisson’s ratio value was also specified
which was the typical Poisson’s ratio of the materials obtained from literature. The thickness (TH) and Poisson’s
ratio (PR) that were used can be seen in Figure 3.

(a)

(b)

Figure 3 (a) Thickness of existing AC-WC model (b) thickness of RTSHMA model.
2. Input load and elastic modulus
As the next step after setting the thickness and Poisson’s ratio, the load and elastic modulus were set. The
standard axle load in the models was set to a single axle load (dual wheels of 8.16 ton). The value of the elastic
modulus describes the hardness of each layer of the pavement structure. The elastic modulus in the existing ACWC model and the RTHSMA model only differed in the surface layer, with the existing AC-WC model using 2 x
106 kPa based on typical data and the RTSHMA model using 3.1 x 106 kPa based on previous research. The elastic
modulus value obtained from the literature was the typical elastic modulus of the materials. The elastic modulus
value used can be seen in Figure 4.

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Sebastianus Kristianto Nugroho et al.

(a)

(b)

Figure 4 (a) Elastic modulus of AC-WC model (b) elastic modulus of RTSHMA model.
3. Running the models
The last step of modeling with KENPAVE is running the models by clicking on the ‘Run Analysis’ command. The
output of the models are strain values. Then, the strain values were used to calculate the number of load
repetitions using Equation 1 and Equation 2.

BISAR 3.0
BISAR 3.0 is a program created by Shell that is often used to analyze road pavement models. This program is
very simple to use and can explore models with a multi-layer system [25]. Similar to the KENPAVE program, the

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BISAR 3.0 program also needs the layer thickness, Poisson’s ratio value, load, and elastic modulus to create
models. The steps for modeling a pavement structure using BISAR 3.0 program are:
1. Input thickness, elastic modulus, and Poisson’s ratio
The first step of making a model in BISAR 3.0 is inputting the thickness, elastic modulus, and Poisson’s ratio of
values for the model. The data required by the BISAR 3.0 program are same as for the KENPAVE program. The
thickness, elastic modulus, and Poisson’s ratio used can be seen in Figure 5.

(a)

(b)

Figure 5 (a) Frame of exisiting AC-WC model (b) frame of RTSHMA model.
2. Input load
The next step is inputting the load. The load of the models also described as the standard axle load, was defined
by choosing ‘Use Standard Dual Wheel’, which automatically sets the load. The load used shown in Figure 6.

Figure 6 Inputting the load for the models.
3. Running the models
The last step of modeling with BISAR 3.0 is the same as KENPAVE, i.e. running the models with the ‘Run Analysis’
command. The outputs of the models are also strain values. The strain values were used to calculate the number
of load repetitions using Eqs. (1) and (2). Then, the result of the number of load repetitions were compared to
the result of the number of load repetitions by the KENPAVE program.

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Result and Discussion
Flexible pavement is designed to be able to carry loads for twenty years, so the pavement structure must be
able to service the traffic loads without fatigue cracking or permanent deformation, occurring at least until the
planned age. Therefore, it is necessary to calculate the number of load repetitions the planned age, i.e. twenty
years for flexible pavements. This number of load repetitions based on planned age controlled the models in
this research.
The study case in this research was the Palur–Sragen City Boundary section, which is a national arterial road with
two directions. Each direction has two lanes, so based on the manual pavement design, the direction distribution
factor (DD) is 50%, and the lane distribution factor (DL) is 80%. The calculation of the number of load repetitions
can be seen in Table 1.
Table 1

Calculation Number of Load Repetitions Palur–Sragen City Boundary Section

Type of Vehicle
Category 1,2,3,4,8
Category 5A
Category 5B
Category 6A
Category 6B
Category 7A
Category 7B
Category 7C

LHRT
28,647
247
656
2,195
2,955
457
87
106

R
32.375
32.375
32.375
32.375
32.375
32.375
32.375
32.375
CESAL

DD
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5

DL
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8

VDF
0
0
1
0.5
9.2
14.4
18.2
19.8

ESA
0
0
3,100,748
5,187,608
128,501,426
31,105,796
7,484,336
9,920,503
185,300,417

Result of KENPAVE and BISAR 3.0 Programs
The outputs of the analysis using the KENPAVE and BISAR 3.0 programs are the values of the horizontal tensile
strain and the vertical compressive strain. These strain values were the basis for calculation of the service life of
the two types of models studied. The model analysis results can be seen in Table 2 below.
Table 2

Output of KENPAVE and BISAR 3.0 Programs

AC-WC Model with KENPAVE Program
AC-WC Model with BISAR 3.0 Program
RTSHMA Model with KENPAVE Program
RTSHMA Model with BISAR 3.0 Program

Horizontal Tensile Strain
(ɛht)
7.894 x 10-5
8.844 x 10-5
8.678 x 10-5
9.186 x 10-5

Vertical Compressive Strain
(ɛvc)
1.278 x 10-4
1.319 x 10-4
1.285 x 10-4
1.330 x 10-4

Result of Load Repetition Calculation
The strain values based on the output of the KENPAVE and BISAR 3.0 programs was then used to calculate the
number of repetitions of the load. The horizontal tensile strain value (ɛht) was used to calculate the load
repetitions based on the fatigue criteria with Equation 1. The vertical compressive strain value (ɛvc) was used to
calculate the load repetitions based on the permanent deformation criteria with Eq. (2). The results of calculating
the number of load repetitions can be seen in Table 3.
Table 3
AC-WC Model with KENPAVE Program
AC-WC Model with BISAR 3.0 Program
RTSHMA Model with KENPAVE Program
RTSHMA Model with BISAR 3.0 Program

Calculation of Number Load Repetitions
Nfg
4,889,816,785 ESAL
3,131,734,358 ESAL
3,373,270,524 ESAL
2,698,831,852 ESAL

Ndp
368,293,470 ESAL
319,739,802 ESAL
359,396,091 ESAL
308,069,607 ESAL

Control
185,300,417 ESAL
185,300,417 ESAL
185,300,417 ESAL
185,300,417 ESAL

Note
Qualified
Qualified
Qualified
Qualified

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Result of Service Life Calculation
The number of load repetitions of the fatigue criteria was used to calculate the service life, while the number of
load repetitions of the permanent deformation criteria measured the permanent deformation. The number of
load repetitions was then used to calculate the service life with Eq. (3) by substituting the number of load
repetitions with the CESAL value. The results of the calculation of the service life can be seen in Table 4 below.
Table 4

Calculation of Service Life

AC-WC Model with KENPAVE Program
AC-WC Model with BISAR 3.0 Program
RTSHMA Model with KENPAVE Program
RTSHMA Model with BISAR 3.0 Program

Nfg
75 Years
66 Years
67 Years
63 Years

Ndp
27 Years
24 Years
26 Years
24 Years

Control
20 Years
20 Years
20 Years
20 Years

Note
Qualified
Qualified
Qualified
Qualified

The service life calculation results are also shown in the comparison graphs in Figure 7 below.

(a)

(b)

Figure 7 (a) Criteria for fatigue (b) criteria for permanent deformation

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Sebastianus Kristianto Nugroho et al.

Based on the results of the analysis and the calculations, it was found that the performance of the existing ACWC pavement is slightly better than of RTSHMA pavement. Still, both types of pavement meet the minimum
service life requirements for flexible pavement layers, which is twenty years. Therefore, with a thinner layer
thickness and using waste materials and still obtaining a good performance, the RTSHMA pavement is quite
feasible to be considered for overlays.

Conclusion
Based on the results of the analysis and discussion above, it can be concluded that:
1.
2.

The existing pavement on the Palur–Boundary Section of Sragen city performs slightly better than RTSHMA.
Still, both types of pavement meet the minimum service life standard when applied in the field.
RTSHMA can reduce the layer thickness by 25% compared to the existing pavement and provides equally
good performance. Therefore, RTSHMA is worth considering as an alternative pavement option.

The design of the RTSHMA structure in this research may be further developed by using variations of layer
thickness and loading so that it is possible to obtain a structural design with optimal performance.

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Manuscript Received: 19 September 2022
1st Revision Manuscript Received: 10 March 2023
2nd Revision Manuscript Received: 5 June 2023
3rd Revision Manuscript Received: 6 September 2023
Accepted Manuscript: 14 November 2023