Accepted Manuscript
The effects of fibers on the performance of bituminous mastics for road pavements
Cristina Bonica, Emanuele Toraldo, Luca Andena, Claudia Marano, Edoardo Mariani
PII: S1359-8368(16)30157-3
DOI: 10.1016/j.compositesb.2016.03.069
Reference: JCOMB 4170
To appear in:
Composites Part B
Received Date: 30 July 2015
Revised Date: 8 March 2016
Accepted Date: 25 March 2016
Please cite this article as: Bonica C, Toraldo E, Andena L, Marano C, Mariani E, The effects of fibers on
the performance of bituminous mastics for road pavements, Composites Part B (2016), doi: 10.1016/
j.compositesb.2016.03.069.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.
MANUS CRIP T
ACCEP TED
ACCEPTED MANUSCRIPT
1
The effects of fibers on the performance of bituminous mastics
for road pavements
Cristina Bonica
a
, Emanuele Toraldo
a
*, Luca Andena
b
, Claudia Marano
b
, Edoardo
Mariani
a
a
Department of Civil and Environmental Engineering, Politecnico di Milano, Piazza
Leonardo da Vinci 32, 20133 Milan, Italy. Email: cristina.bonica@polimi.it;
emanuele.toraldo@polimi.it; edoardo.mariani@polimi.it
b
Department of Chemistry, Materials and Chemical Engineering "Giulio Natta",
Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy. Email:
luca.andena@polimi.it; claudia.marano@polimi.it
*Corresponding author: Tel: +39 02 2399 6618, email address:
emanuele.toraldo@polimi.it
Abstract
The experimental investigation herein described is aimed at understanding the effects
of cellulose-based fibers on the mechanical properties of bituminous mastics for
paving applications. Three bitumen (two of which modified with SBS polymers), a
calcareous filler and four different types of fiber with varying content were used to
prepare the investigated mastics. The filler to bitumen ratio was maintained constant.
The laboratory investigations were focused on empirical tests (Needle Penetration and
Ring and Ball - R&B - Temperature) and dynamic-mechanical tests, the latter
performed in a wide range of temperatures. Results suggest that fibers improve the
MANUS CRIP T
ACCEP TED
ACCEPTED MANUSCRIPT
2
behavior of mastics for hot mix asphalts, particularly with respect to the prevention of
rutting phenomena at high service temperatures.
Keywords: A. Bituminous mastics; A. Fibers; B. Rheological properties; C. Dynamic
Mechanical Analysis.
1. Introduction
Hot Mix Asphalts (HMAs) are the materials most used for road pavements through the
world. They are composed of aggregates, bitumen and filler [1]; different types of
additives are also frequently used for both processing and performance purposes.
Aggregates, generally deriving from rock quarries, are the skeleton of a HMA. Bitumen
and filler together form the so-called mastic which, when mixed with the aggregates,
acts as an effective binder for the lithic skeleton. Thus mastics have a crucial role in the
HMAs’ performance during a pavement service life [2-5] because they have to bear
both traffic loads and climatic changes.
Polymers and natural or synthetic fibers are often used as HMAs’ additive to improve
their performance in the field. They can be added either to the bitumen (modified
bitumen) or directly to the final HMAs; the latter option is of particular interest in
areas of the world in which bitumen modification plants are not available or too far
from the construction site.
The main effects of an additive on the HMA’s behavior are related to its interaction
with the mastic: this is true for both a polymer-based additive, due to its affinity to the
bitumen, and an additive based on fibers, whose specific area is significantly higher
than that of typical aggregates.
MANUS CRIP T
ACCEP TED
ACCEPTED MANUSCRIPT
3
Consequently, the role of fiber-based additives on preventing failure in the HMA
pavements, such as rutting or thermal cracking [6-8], can be more easily studied at a
small scale on the bituminous mastics rather than on the complete asphalt system
(standard, porous, or other HMA compositions).
Short fibers are often used as reinforcement of HMA for road applications. In this
context several studies have been conducted, as demonstrated by recent scientific
literature review papers [9, 10]. In particular, some recent papers focused on the use
of both natural (i.e. coir) [11, 12] or waste/recycled (i.e. textiles, tires, carpets) [13, 14]
fibers into HMA. Several studies have addressed the use of fibers to improve the HMAs
performance: a few of them focused on the specific performance related to
environmental, water and temperature effects [15, 16], while other experimentations
were carried out to highlight HMAs’ mechanical performance, e.g. stiffness [17],
fatigue [18] and rutting [19]. Another line of research has been devoted to investigate
the whole performance of fiber-reinforced HMAs [20, 21], their mix-design [22], or
their performance related to the effects of fibers during compaction [23].
In this context, few researches have been focused on binder reinforcement due to
fibers, taking into account the specific interaction with the bitumen. These researches
concern the study of rheological properties [24, 25] and fiber dispersion into the
bitumen blends [26], not considering the effect of filler which, in turn, is crucial to
determine the mastic’s final behavior.
Given this scenario, the main goal of the research described in this paper is to study,
through laboratory tests, the effect of fiber addition on the mechanical behavior of
bituminous mastics. The mastics considered in this research are composed by bitumen
(three different bitumen were considered, two of them modified with the addition of a
MANUS CRIP T
ACCEP TED
ACCEPTED MANUSCRIPT
4
Styrene-Butadyene block copolymer, SBS), a calcareous filler (a single ratio of filler to
bitumen was considered in this research) and a short- cellulose fiber-based compound
(four different types of compound were used). Different contents of the reinforcing
fiber additives were considered. As for the mechanical tests, both empirical
measurements (Needle Penetration and Ring and Ball tests) and dynamic-mechanical
analyses (DMA) were carried out [27-32]. Temperature sweep DMA tests were carried
out in a range of temperatures (which reproduce the typical climatic conditions of
Mediterranean countries) to investigate the associated changes in bitumen stiffness. In
particular, the research was focused on the role of mastics in preventing high
temperature rutting phenomena and low temperature cracking that typically occur in
road pavements during their service life.
Finally, the paper describes some details of the specific protocols developed during the
research project and it provides an overview of the obtained results.
2. Materials, experimental plan and test methods
The basic constituents of the materials used in the research described in this paper are
summarized in Table 1 and more details about bitumen and fibers are given in Table 2
and Table 3 respectively.
The bitumen and the fiber compounds used in this work are commercial products
available on the Italian market. As for the fiber compounds (in Figure 1 their general
appearance is shown), their exact composition has not been disclosed by the producer.
Data shown in Table 3 were taken from the supplier’s technical data sheets.
Starting from these basic constituents, 67 combinations of fiber reinforced mastics
were prepared in the laboratory, using a filler-bitumen ratio equal to 1.20 by weight,
as required by the most common Italian Standard Technical Specifications (filler