EVALUATION OF THE ENGINEERING VALUE OF RECLAIMED ASPHALT PAVEMENT (RAP) AGGREGATE FROM SELECTED REGION IN KLANG VALLEY

J. AHMAD
R. RAZALI
Postgraduate Student

ASSOC. PROFESSOR
M. Y. ABDUL RAHMAN
Z. MOHAMED
Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam

INTRODUCTION 

There has been tremendous amount of effort and innovative ideas to incorporate the use of recyclable materials in highway construction which when appropriately addressed can maximize economic benefits.  One good example is the reclaimed asphalt pavement (RAP), which is old pavement that is reclaimed for use.   The RAP has great potential not only for preserving valuable resources, but also for controlling escalating construction costs (Mokwa and Peebles, 2005).  Recycling in pavement industry has been known to offer environmental benefits which can reduce extraction of primary aggregates, disposal of existing materials and reduce haulage and fuel of construction materials.  The service life of pavement, although designed for 20 years normally do not reach the expected life.  It was noted that some pavements may only lasts for merely two years before experiencing permanent deformation and therefore, the need to rehabilitate. 

Currently in Malaysia, the maintenance allocation of the road network length for both Federal and State roads have increased gradually from year 1994 to 2002 as shown in Figure 1.  Obviously tonnes of waste which is 100% recyclable is produced from rehabilitation and maintenance of these existing roads.  Therefore, large volume of RAP material is disposed and new construction of wearing course will need good quality aggregates from quarrying production (Shahid, 2000). 

Figure 1:  Maintenance per Kilometer since 1994 for Federal and State Roads

(Source: Joseph Lim Chan San and Zulakmal Hj. Sufian, 2002) 

Common practice today is the use of recycled hot-mix, a process in which reclaimed asphalt pavement is combined with new asphalt or recycling agents, and new aggregates to produce hot-mix paving mixtures.  Since aggregate constitutes the bulk weight of asphaltic mixtures, the quality of aggregates is vital to ensure good pavement performance because aggregates are primarily responsible for the load supporting capacity of the asphalt mixtures which may lead to serviceability problems.  The physical properties of aggregates are meant for pavement characterization and other important properties which include toughness and abrasion to resistance.  The aggregates should be tough and hard enough to resist degradation and disintegration during process of handling, stockpiling, placing and compaction.  As reported in NCHRP Digest, 2001, RAP materials when use with new asphaltic mixtures are found to perform well and still valuable even when the pavements have reached the end of their service lives.  The RAP aggregate still retain some considerable value and may be used to restore pavement profile, improve skid resistance, and rectify cracking caused by binder hardening (Austroads and Asphalt Pavement Association, 1977). 

However, the engineering values of aggregates extracted from reclaimed asphalt pavement have not been fully investigated to bench mark RAP aggregate to virgin/source aggregate with respect to the engineering characteristics.  The RAP aggregate when recycled into hot-mix should still have engineering values and treated like any other aggregate stockpile in developing an HMA mix design (Pennsylvania Asphalt Pavement Association, 2005).   

PURPOSE AND SCOPE

This study is a preliminary investigation of the usefulness of the RAP aggregate which are normally recycled in hot-mix asphalt.  Unfortunately, the service life of the RAP materials used in this study is not available, however, this study is intended to give a general understanding and evaluation of the toughness and resistance to abrasion and skidding of RAP aggregates to quantify the quality of the aggregate after being in service for several years.  Study on the degradation and abrasion effect of RAP aggregates have proven that with proper evaluation, the RAP aggregates are still workable and have good resistance to degradation and abrasion (Ahmad et al., 2004).  The reclaimed asphalt pavement stockpiles were collected from various locations in Klang Valley i.e. Shah Alam, Kepong, Klang and Rawang area.  The Asphalt Content Tester or ignition oven is used to extract all the aggregate from reclaimed asphalt pavement. 

METHOD 

Six sources of reclaimed asphalt pavement were selected for the study located in the Klang Valley.  The bulk of wearing course disposal was collected and the aggregate physical properties were carried out in accordance with the American Society of Testing Materials (ASTM).  The RAP samples were collected from sites which undergo rehabilitation works carried out by Roadcare Sdn. Bhd. and random sampling was used to get the best representation of the materials.  The sample was carefully brought back to laboratory and placed under shelter in open space condition.  Two common methods can be used to extract aggregates from RAP which are the solvent method and ignition method.  However, solvent method is widely banned due to hazardous solvent such as the dichloromethane to man and environment.  Hence, the ignition oven method was used in this study.  To avoid any segregation, the samples are carefully extracted by quartering on a large tray.  RAP samples extracted are first broken down to avoid lumps of aggregates bounded together.  The RAP aggregate was extracted in accordance to ASTM D6307 at a temperature of 540⁰C and after completion of the burning process in the ignition oven, only aggregates are left in the tray as shown in Figure 2.  

Figure 2:  RAP specimen (a) before and (b) after extraction from the ignition oven

 The aggregates extracted from the ignition oven are then tested to evaluate the abrasion or crushing effect to determine the toughness of the aggregates.  These aggregates should be completely cooled naturally before handling in the laboratory for further investigation.  The resistance to disintegration is carried out to determine the strength when subjected to loading.  This test is important because the properties of RAP depend on the properties of the constituent materials and type of asphaltic mix.  Aggregates used for wearing course should be of high quality and high resistance to friction compared to aggregates used in base or subbase of the pavement layers.    Figure 3 shows the various types of equipments used to carry out the tests.

 Figure 3: (a) Aggregate Crushing Value and (b) Aggregate Impact Value Apparatus

The first phase of this study examines the physical properties of RAP aggregates with respect to the strength and also flakiness.  Next, these aggregates were evaluated for their skidding resistance properties measured using the Polished Stone Value (PSV) and portable skid resistance tester in laboratory.  There are numerous factors known to affect skid resistance and the concept is based on the fact that pavement skid resistance is attributed mainly to the texture of the aggregates (Kokkalis et al., 2002).

RESULTS AND DISCUSSIONS 

All six locations of reclaimed asphalt pavement showed different variations of optimum asphalt content at different locality depending on the mix design of the pavement.  The mix design of the RAP samples acquired was designed by the Marshall method which typically has asphalt content ranging between 4.0 to 6.5 percent.  Results showed that the optimum asphalt content (OAC) of the RAP mixtures are within the limits and ranges between 4.74 to 5.14 percent.  The optimum asphalt content of the RAP specimens from all six locations is tabulated in Table 1.  

 TABLE 1: Asphalt Content of RAP from Selected Klang Valley Locations

In a previous study on randomly chosen virgin/source aggregates from few quarries i.e. Rawang, Puchong, Cheras, Hulu Selangor and Shah Alam, some typical values of virgin/source aggregate in terms of the strength and flakiness index was examined as tabulated in Table 2.  The result from the previous study was compared to RAP aggregate in this study to evaluate the level of deterioration or degradation of the aggregate.   

Table 2 :  Aggregate Properties of Source Aggregate (Source : Ahmad et al. 2004) 

Aggregate Crushing and Impact Value

 To ensure good pavement performance, aggregates must be resistance to crushing under gradually applied compressive load, abrasion effect, sudden shock and also particle shape element.  The crushing value gives value of hardness of aggregate when subjected to 400 kN load in accordance to BS 812: Part 3.  In this test, RAP aggregate was compacted and subjected to crushing action to a degree that is dependent on the crushing resistance of the material. Aggregates with crushing value less than 10 are regarded as strong and anything above 35 are normally too weak for use in road surfaces.  Figure 4 indicates that all the RAP aggregates showed acceptable crushing values in the range of 25 to 28 percent.  Comparing to the virgin/source aggregate from the same quarry source, the aggregate crushing values (ACV) are much lower, which implies that the virgin/source aggregate are more resistant to crushing effect.  The RAP aggregate from KEP, KLG, and PJW and RAW showed an increment of approximately 35 percent more crushing values from the source/virgin aggregate.  RAP aggregate originated from Hulu Langat quarry source degrade at a much higher value of 54 percent than the virgin/source aggregate.  This implies that although all RAP aggregates are within the maximum limits of the ACV, the resistant to crushing value it affected within the range of 54 to 35 percent.                            

Figure 4: Comparison of ACV of RAP and Source Aggregate

Next, the aggregate impact value (AIV) measures the resistance of aggregate to sudden shock or impact, which differ from their resistance to a slowly applied compressive load.  Impact value of an aggregate test gives ‘an idea’ of toughness of the aggregate to resist fracture under the impact of moving load and BS 812 recommended that the AIV should be less than 30.  Figure 5 shows the aggregate impact value for PJW, SA8, SA14, KEP and KLG only showed slight increment of AIV and ranges between 17 to 26 percent compared to source/virgin aggregate with lower impact values of less than 15 percent.  This simply means that the RAP aggregate from these locations showed slight degradation and have good resistant to sudden impact.  However, the AIV of RAP from SA8 and SA14 has the highest percent increment of impact values between 55 and 63 percent compared to their respective virgin/source aggregate.  This obviously shows that aggregate from SA8 and SA14 is least resistant when subjected to sudden impact load. 

                    Figure 5: Comparison of AIV of RAP and Source Aggregate

            Results in Figure 6 showed that there seemed to be a relationship and trend of deterioration for both crushing and impact values of the RAP aggregate.  It was obvious that RAP aggregate from both SA8 and SA14 showed the highest ACV and AIV and it is also evident that when the ACV decreases, the AIV also showed a decline in value.  Regardless of the types of test conducted, both crushing and impact tests exhibits the strength evaluation of the aggregate. 

Flakiness Index 

In terms of flakiness of aggregate, RAP aggregate are not much affected but this test is important because flakiness of an aggregate will affect the stability and workability of mixture and surface dressing treatments.  Aggregate particles are classified as flaky when the single-sized aggregate has a thickness (smallest dimension) of less than 0.6 of their mean sieve size.  Separating the flaky particles and expressing their mass as a percentage of the mass of the sample tested find the flakiness index of an aggregate sample.  The test conducted on RAP aggregates still conformed to the flakiness index criteria.  RAP aggregate from PJW, RAW and KEP showed slight increment in flakiness with an average of 16.2 percent.  RAP aggregate from SA8 and SA14 showed higher flakiness value averaged at 35 percent while, KLG showed the highest percent increment in flakiness of the RAP aggregate.  However, generally the RAP aggregates still maintain its flakiness despite several years of service life and are still favourable for reuse.

Figure 7: Comparison of Flakiness Index of RAP and Source Aggregates

 Resistance to Polishing Action 

The skidding resistance is very important to ensure safe maneuvering and friction between pavement and tyre contact.  Results showed that there is no obvious change in behaviour for both RAP and source aggregates as depicted in Figure 8.  The skidding resistance of the RAP aggregate does not deteriorate for both wet and dry conditions.  The decline of PSV for RAP averaged at 8.1 percent which showed very minimal degradation of the RAP aggregate.  This could be due to good quality Malaysian granite aggregates. Geologically, granite is known to be strong, durable and has good bonding matrix of mineralogy which relates to the intrusive formation of the rock. 

Figure 8: Comparison of PSV of RAP and Source Aggregate

 Research by UK Road Research Laboratory showed there is a significant relationship between polishing of aggregate used in road surface and skid resistance.  Factors affecting skid resistance are numerous and the concepts are based on the fact that pavement skid resistance is attributed mainly to the texture of the aggregates (Kokkalis et al., 2002).  This friction is dependent on the microscopic and macroscopic roughness of the pavement surface, the polish-wear characteristics of the aggregates and the ability of the surface to drain (Beaton, 1976).  This simply means that the higher the PSV values, the greater resistance the aggregate has to polishing, and the greater the ability the aggregate has to retain its inherent very fine surface texture, i.e. micro-texture.

CONCLUSION 

The initial findings has provide a better understanding of the quality and potential deterioration characteristic of RAP aggregates from the study location in Klang Valley area.  The RAP aggregate are still valuable, within the acceptable limits and showed acceptable resistance to degradation due to sudden shock and gradually imposed loading from traffic.  Results also showed that there seemed to be a relationship between crushing effect and sudden impact of the aggregate.  Since both tests are related to strength, the percent range of degradation for crushing and impact values showed some similarity in trend.  The good polishing values also indicate the polish wear characteristics of the aggregates will definitely contribute to the friction of pavement surface and is dependent on the macroscopic and microscopic roughness of the aggregates.  However, further study to identify the disintegration of mineralogy within the aggregates after long years in service is useful to evaluate how much degradation has or has not occurred within the aggregate mineral structure.  Finally, recycling of these aggregates with proper evaluation will definitely reduce cost and conserve environment because the RAP aggregates are still valuable and workable.