About point #3

Hamza Algazra
CHAPTER 3. USING RAP IN ROAD APPLICATIONS

The RAPs are used in road applications of low-specification, such as the

construction of roadbed layers. Hack and Bryan [28] stated that recycled
asphalt materials can be utilized as a base-course material, also, it can be
used in unpaved-roads as a road surfacing. In such applications, the use of
recycled asphalt materials has benefits such as road performance
improvement, and prevent dust. Papp et al. [29] stated that RAP can provide
a good application as a granular base material. Taha et al. [23] showed that
the mixture of RAP-natural aggregates provides good roadbed layers. They
mixed the natural aggregate with five different contents of RAP (from 20% to
100%). The properties of RAP used are asphalt content 5.5%, and CBR value
11%. They were concluded that the maximum RAP contents required for the
construction of the sub-base layer and base layer are 60% and 10%
respectively.

While, According to McGarrah [30], the maximum RAP content required for
the construction of the sub-base layer is 50%. On the other hand, 25%, 50%,
75%, and 100% RAP was used by Cooley [31] to improve the properties of
two types of aggregate (surrounded and angular). This author found that the
CBR values are inversely proportional with RAP content. Gregory and Halsted
[32] investigated the possibility of the RAP full-depth reclamation to produce
a new base layer.

Several studies recommended the use of unbound RAP in asphalt

pavement layers. The typical content of RAP in such construction is between
20% and 50% [21]. RAP material can be treated with different additives. RAP
properties can be restored using some types of additives like soil/lime,
cement, bitumen emulsion, etc. The use of these additives is not aimed only
at restoring the RAP properties, but it has many environmental benefits.
Mohammad et al. [24] used foamed asphalt to treat RAP and studied the
potential of the RAP treated as a roadbed layer.
 Also, RAP can be used for road shoulders as embankment, back-filling
material, retaining walls, slope protections, landfill capping systems, pothole
filler material, and drainage works [4, 10, 11, and 12]. The environmental
impact of RAP has been investigated by Yang et al. [12]. The engineering
possibility of using RAP in an unbound road, also investigated. The result of
this investigation proved that the RAP can be utilized as an unbound material
even in acidic environment [12]. An economical solution was stated by
Troeger and Widyatmoko [33] to reuse and recycle the "distressed asphalt
surface courses".

Available research showed that the lightly traveled roads, footways, and
other rural and urban sites are possible sites to recycle and reuse of these
materials. The solution includes pulverizing the existing roads to a suitable
depth, producing a uniformly-graded material, milling broken up and leveling
the surfacing layers, applying bitumen emulsion, then rolling the surface and
completing the surface layer.

Using RAP in HMA Layers

One of the most difficult challenges for the development of any road network is to execute
projects in harmony with the concept of sustainable development. The road industry is
therefore looking forward for alternative materials and construction technology, which are
environment friendly, energy efficient and cost effective for the construction and maintenance
of roads

Use of high RAP content in hot mix asphalt

The use of RAP in road construction can provide savings from 14% to 34% for RAP
percentages varying from 10% to 50% of the total mix,[3]. Although it is generally accepted that
the utilization of RAP in HMA can reduce cost, the percentage of RAP to be used in conventional
HMA mixesis still debated. When using high RAP content in HMA, it is still unclear as how the
aged asphalt binder from RAP interacts with virgin asphalt binder. It is generally assumed that
the RAP material will not act like a black rock in the new mix and it will blend well with virgin
binder during mixing[4], but the question remains as to what extent will it blend. A constant
effort is being made by the DOTs to adopt a higher RAP percentage for regular HMA production
so as to reduce the consumption of virgin aggregates, cost and conserve energy.
Please add a section for RAP usage in any other layers of the road not
mentioned earlier or in maintenance and rehabilitation applications.

• Using RAP in soil stabilization

• Different efforts have been directed to investigate the possibility of

RAP to stabilize soil. Some efforts studied the potential of using RAP
alone, while other efforts used admixtures with the RAP [20, 38, 50,
and 51]. The cohesive soil stabilized with RAP and cement was
studied [18]. These authors showed that the stabilized soil with 2%
cement satisfies the requirement of pavement layers. One
problematic lateritic soil (clayey sand) from Thailand has been
stabilized by adding RAP and cement with different content [19].
The content of RAP used is 20%, 40%, 60%, and 80%. It was noted
that the RAP (up to 50%) decreases the optimum water content of
the soil. The strength of soil-RAP is increased with cement content
and curing period. An attempt to stabilize clay soil was carried out
[52]. In this attempt, the RAP and bagasse ash have been used to
stabilize the soil for pavement construction. It was noticed that 40%
of RAP increased the dry density of the soil from 1.77 g/cm3 to 1.79
g/cm3. The addition of 4% bagasse ash to the mixture increased the
density to 1.82 g/cm3. The content of bagasse ash required to
improve the bearing value of the mixture of soil and RAP is 6% to
8%. Kamel et al. [5] evaluated the California bearing ratio for
subgrade soil mixed with different proportions of RAP material (from
0% to 100%). The content of bitumen in RAP used is about 5%.

• BENEFITS OF RAP
*Economic Benefits
According to Babashamsi et al. 2006 the life cycle cost analysis of
pavements incorporated with RAP showed that a saving of $58,000/km
can be achieved for asphalt mixtures containing 30 to 50% RAP. This
saving consists of the savings in material cost due to the replacement
of a part of the binders‟ virgin aggregates with RAP and the lower
 transportation cost. Conventional crushed stones are generally more
expensive than recycled materials. According to Edil [22] a saving of
up to 30% was achieved by using RAP as base material for pavements.
The most expensive component of asphalt pavement construction is
the asphalt binder. The use of RAP material in pavement construction
means that less asphalt binder is required. As such, it has been
proposed that the most economical use of RAP in asphalt mixtures is in
the immediate and surface layers of flexible pavements [22].

* Environmental Benefits
Amongst the many environmental benefits of using RAP are reduced
demand for non-renewable resources; less landfill space is required for
the disposal of used pavements; reduced fuel consumption and
emissions since the materials do not have to be transported; and less
extraction of virgin materials [24]. Previous studies have proven these
benefits. For instance, one study has shown that the incorporation of
15% RAP into warm-mix asphalt mixtures was able to reduce the total
cumulative energy requirement, climate change and use of fossil fuels
by 13 to 14% [23].

* Engineering Benefits
A survey was carried out in the United States to compare the Long-
Term Pavement Performance of virgin mixes and mixes containing RAP.
Results show that, in terms of all aspects of pavement performance,
the performance of mixes containing a minimum of 30% RAP is
equivalent to those containing virgin materials. Another study has
shown that the base layers containing RAP have higher strength than
those containing conventional aggregates. The use of RAP has also
been demonstrated to be suitable for the construction of pavements in
areas with low traffic and freezing temperatures; areas with high traffic
and non-freezing temperatures; and areas with medium traffic and
freezing temperatures as well as low moisture levels [24]

• Potential disadvantages of WMA include increased rutting, moisture

sensitivity, and a lack of long-term field performance results. In the
case of the chemical and foaming groups, mixture stiffness may be
reduced such that rutting resistance. In contrast, organic additives may
increase stiffness such that pavement cracking potential increases. The
 lack of long-term WMA performance data in the field of practice also
affects WMA use in the United States; the technology has only been in
place for approximately 8 years. As a result, laboratory performance
tests continue to fulfill a critical role in the design and deployment of
existing and emerging WMA technologies.

• Disadvantages arise with the use of RAP as well. RAP is an inherently

stiff material due to the oxidizing effect of sunlight and the
atmosphere. According to Xiao et al. (2007), the presence of as little as
15% RAP has the ability to significantly stiffen an asphalt mixture.
Wagoner et al. (2005) found that the fracture resistance of asphalt
mixtures was reduced through the use of an increased asphalt grade.
Consequently, the addition of RAP, according to NCHRP 9-12, increases
the PG grade of the asphalt binder. Therefore, the increased stiffness
increases the brittle nature of the asphalt concrete and the probability
of brittle failure at low temperatures. Variability among RAP stockpiles
is also a significant issue.

• Dave (2003) studied the recovered asphalt binder of 16 different RAP

stockpiles in Illinois through the use of the Dynamic Shear Rheometer.
The complex modulus, G*, of each RAP stockpile was calculated and
they found that the complex moduli differed significantly. Therefore,
RAP stockpiles must be considered on a case-by-case basis because
the stiffness of a given RAP stockpile may require different
considerations from a stockpile in a different location.

Advantage Disadvantage
• Reduction in construction costs Limited Application
• Less disposal materials. Material Quality Variability
• Reduced transportation cost Aging of Binder
• Conservation of aggregates and Moisture Sensitivity
binders
• Conservation of energy
• Preservation of environment Durability and Service Life
(reduction in toxic and greenhouse
gas emissions)
• Preservation of existing pavement Environmental Impact leaching of
geometrics hazardous materials, such as heavy
metals and carcinogenic organic
compounds, from the RAP
• Reduction in user delay and The quality of the final mix depends
Reduction in road wears due to less on the properties and condition of
transport of materials. the reclaimed asphalt.

References
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