Investigation on Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures incorporating Nanosilica Modified Binder
Ahmad Kamil Arshad1,2, Khairil Azman Masri2*, Juraidah Ahmad1,2 and Mohamad Saifullah Samsudin2
1Institute for Infrastructure Engineering and Sustainable Management, IIESM, Faculty of Civil Engineering, Universiti Teknologi MARA (UiTM), 40200 Shah Alam, Selangor, Malaysia2Faculty of Civil Engineering, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia
ABSTRACT
This paper presents the outcome of a laboratory investigation on mix design, resilient modulus, moisture susceptibility and rutting resistance of Stone Mastic Asphalt (SMA) and Dense Graded Asphalt (AC) that is incorporated with Nanosilica (NS) modified binder. Penetration Grade 60-70 (PEN60-70) types of binder were mixed with nanoparticles (NS) using concentration of 0wt%, 2wt%, 4wt% and 6wt% by weight of asphalt binder. The mixtures were tested for resilient modulus, indirect tensile strength and rutting, in order to evaluate the performance of NS-SMA and NS-AC. The results show that the existence of NS is capable of enhancing the performance of both asphalt mixtures, and the addition of NS decreases the susceptibility of moisture damage and provides better resistance against permanent deformation. Furthermore, the addition of 4wt% NS appears to be the most effective amount for the performance enhancement in AC and SMA mixtures.
Asphalt mixture especially hot mix asphalt (HMA) is usually regarded as having stripping and permanent deformation problems. Temperatures of around 30-35o together with frequent rain exposes asphalt pavement to moisture susceptibility and rutting. Both issues are usually inter-related and the existence of moisture leads to stripping and severe rutting, leading to low ride-ability,
Ahmad Kamil Arshad, Khairil Azman Masri, Juraidah Ahmad and Mohamad Saifullah Samsudin
comfort-ability, general performance and motorist safety. There are several advantages of using Stone Mastic Asphalt. First, it provides more resistance towards permanent deformation or rutting (30% - 40% less than dense graded asphalt). Second, SMA relies on stone to stone contact in terms of mechanical properties, so they are less sensitive to binder variations than the conventional mixes (Brown et al., 1996). But, the costs related to producing SMA is higher due to its higher binder content and fibres additive. It is also high in filler content, thus resulting to productivity reduction, Furthermore, there is a possible delay in opening the road to traffic as SMA mixtures must be cooled to below 40°C in order to prevent flushing of the binder surface (Nejad et al., 2012). However, this may be overcome by suitable modifications. Figure 1 shows rutting phenomena that usually occurred on the asphalt pavement.
INTRODUCTION
Asphalt mixture especially hot mix asphalt (HMA) is usually regarded as having stripping and
permanent deformation problems. Temperatures of around 30-35o together with frequent rain
exposes asphalt pavement to moisture susceptibility and rutting. Both issues are usually inter-
related and the existence of moisture leads to stripping and severe rutting, leading to low ride-
ability, comfort-ability, general performance and motorist safety. There are several advantages of
using Stone Mastic Asphalt. First, it provides more resistance towards permanent deformation or
rutting (30% - 40% less than dense graded asphalt). Second, SMA relies on stone to stone
contact in terms of mechanical properties, so they are less sensitive to binder variations than the
conventional mixes (Brown et al., 1996). But, the costs related to producing SMA is higher due
to its higher binder content and fibres additive. It is also high in filler content, thus resulting to
productivity reduction, Furthermore, there is a possible delay in opening the road to traffic as
SMA mixtures must be cooled to below 40°C in order to prevent flushing of the binder surface
(Nejad et al., 2012). However, this may be overcome by suitable modifications. Figure 1 shows
rutting phenomena that usually occurred on the asphalt pavement.
Resilient modulus can be used to determine the mechanical characteristics and provides empirical approached in designing the pavement structure and predicting the rutting roughness. Asphalt mixture behaves elastically and plastically when a load is applied (El-Shafie et al., 2012). Resilient modulus is important for evaluating the performance of asphalt mixtures subjected to repeated loads. This parameter is used as an input parameter to evaluate the response of pavement under traffic loading. Venudharan and Biligiri (2015) also defined resilient modulus as the ratio of deviator stress to the recoverable strain at any particular temperature and frequency. Resilient modulus values are determined via laboratory tests which subjecting the cylindrical specimen to loads using Universal Testing Machine (UTM). This test helps to measure the elasticity of the asphaltic specimens, evaluate the quality of the materials, and provide input for pavement design. According to Shafabakhsh and Tanakizadeh (2015), the asphaltic layers can be considered elastic if the load applied is small compared to the strength of material. It involves subjecting the specimen to a large number of load applications and the deformation under each load recorded. The factors that can influence resilient modulus are water, dry density and stress level. The value of resilient modulus can decrease when the water content increases and increase with increases in dry density, confining and deviator stress.
Besides rutting, another primary cause of distress in asphalt mixture is moisture susceptibility. If the internal bonds between aggregates and asphalt are weakened in the presence of water, the asphalt mixtures may be considered susceptible to moisture. Moisture susceptibility
Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures
is a major reason for the premature failure of asphalt mixtures. Moisture susceptibility is also known as moisture damage, or the degradation of the material’s mechanical properties that attribute to the presence of moisture in its microstructure (Kumar & Anand, 2012). The factors that can affect moisture susceptibility in asphaltic mixtures are the type of aggregates, type of source of crude oil and refining process in asphalt cement manufacturing, asphalt mixtures properties which are influenced by the degree of compaction, asphalt film thickness and environmental condition and traffic (Ebrahim & Behiry, 2013). The chief means by which moisture enters the pavement structure are infiltration of surface water, the capillary rise of subsurface water, and the diffusion of water vapor.
Studies done to enhance the performance of asphalt mix suggest the use of binder modification. One type of binder modification is the use of nanotechnology, nanosilica (NS), which shows a promising result in improving binder properties. This study utilizes colloidal NS to enhance the properties of asphalt binder. SMA and AC asphalt containing different amounts of NS are studied by subjecting them to resilient modulus, rutting resistance and moisture susceptibility tests.
METHOD
Materials
The binder used in this study was PEN 60/70 grade. Asphalt binder was blended with 2wt%, 4wt% and 6wt% of nanosilica. The quantity of each additive was selected based on the weight of the asphalt binder and mixed in a binder mixer. To conduct the mixing process, an aluminium can was filled with 250 – 260 g of binder and placed in a mixer. After reaching a temperature of 160°C, a specified amount of nanosilica was added to the asphalt binder and mixing process was continued for one hour at 1800 rpm. Nanosilica should be fully added into the binder in the first 30 minutes of the mixing process (Arshad et al., 2016).
Marshall Mix Design
The Optimum Binder Content (OBC) for SMA20 and AC14 were determined based on Marshall Mix Design Method. This process was carried out in accordance with the Malaysian Public Works Department JKR/SPJ/2008, 2008.
Three specimens were prepared for each binder content within the range of 5-7% for SMA20 and 4%-6% for AC14 with the increment of 0.5%. The bulk specific gravity of each test specimen was determined in accordance to ASTM D 2726, as soon as the freshly compacted specimens cooled to the room temperature. The stability and flow values of each test specimen was obtained in accordance with ASTM D 1559. Specific gravity and void analysis was carried out for each test specimen after the completion of the stability and flow test in order to determine the percentage air voids in mineral aggregate (VMA) and the percentage air voids in the compacted mix (VIM). The average values of bulk specific gravity, stability, flow, VFB and VMA obtained above was plotted separately against the binder content and a smooth curve was drawn through the plotted values. Table 1 lists the properties of NS while Table 2 shows the aggregate gradation for SMA20 and AC14.
Ahmad Kamil Arshad, Khairil Azman Masri, Juraidah Ahmad and Mohamad Saifullah Samsudin
The Indirect Tension was used to determine resilient modulus of bituminous mixtures by applying compressive loads with a haversine waveform. The resilient modulus value was obtained by the elastic modulus based on the recoverable strain under repeated loads. The results were shown in the total resilient axial deformation response of a specimen using Universal Testing Machine (Figure 2). Three Marshall Specimens for each mixture (SMA and AC) and NS content (0wt%, 2wt%, 4wt%, and 6wt%) were tested. This test was conducted in accordance to ASTM D4123-82. All the samples were tested at fixed temperature (25°C), two positions and three different pulse repetitions (1000ms, 2000ms and 3000ms).
This test was carried out in accordance to AASHTO TP-63 using Asphalt Pavement Analyzer (APA) Equipment. The APA machine was used to measure the rutting resistance of a modified and unmodified AC and SMA mixtures. Rutting resistance was evaluated by running a steel wheel over the pressurized tubing which rests on top of the specimens (Apeagyei, 2011). According AASHTO specification, asphalt mixes specimens that were used are 75 mm in height and 150 mm in diameter. The specimens had to be conditioned in the mould at the required temperature for 6 hours, when a concave wheel was used to run over pressurized rubber hosing that was set on top of three gyratory specimens in the temperature-controlled chamber. The rubber air lines on the load rack was pressurized to 0.69 ± 0.03 MPa and the wheel load was set up to 0.45 ± 0.02 KN. The asphalt mixture specimens were subjected to 8000 cycles of wheel loading in the chamber. The raw data was recorded on rut depth for each cycle, and the test repeated and to allow the mean of rut depth to be calculated. Figure 3 illustrates rut samples before and after testing.
applying compressive loads with a haversine waveform. The resilient modulus value was
obtained by the elastic modulus based on the recoverable strain under repeated loads. The results
were shown in the total resilient axial deformation response of a specimen using Universal
Testing Machine (Figure 2). Three Marshall Specimens for each mixture (SMA and AC) and NS
content (0wt%, 2wt%, 4wt%, and 6wt%) were tested. This test was conducted in accordance to
ASTM D4123-82. All the samples were tested at fixed temperature (25oC), two positions and
three different pulse repetitions (1000ms, 2000ms and 3000ms).
(a) (b)
Figure 2. (a) UTM machine; and (b) sample position
Rutting Resistance
This test was carried out in accordance to AASHTO TP-63 using Asphalt Pavement Analyzer
(APA) Equipment. The APA machine was used to measure the rutting resistance of a modified
and unmodified AC and SMA mixtures. Rutting resistance was evaluated by running a steel
wheel over the pressurized tubing which rests on top of the specimens (Apeagyei, 2011).
According AASHTO specification, asphalt mixes specimens that were used are 75 mm in height
Figure 2. (a) UTM machine; and (b) sample position
and 150 mm in diameter. The specimens had to be conditioned in the mould at the required
temperature for 6 hours, when a concave wheel was used to run over pressurized rubber hosing
that was set on top of three gyratory specimens in the temperature-controlled chamber. The
rubber air lines on the load rack was pressurized to 0.69 ± 0.03 MPa and the wheel load was set
up to 0.45 ± 0.02 KN. The asphalt mixture specimens were subjected to 8000 cycles of wheel
loading in the chamber. The raw data was recorded on rut depth for each cycle, and the test
repeated and to allow the mean of rut depth to be calculated. Figure 3 illustrates rut samples
before and after testing.
(a) (b) (c)
Figure 3. (a) Sample position; (b) sample after test; and (c) sample before test
Moisture Susceptibility
Moisture susceptibility also known as moisture damage is the most common concern for asphalt
pavements. In this research, moisture damage was evaluated in accordance with AASHTO T283.
Stripping samples for both SMA and AC were compacted to obtained 7 ± 1 % air voids
according to AASHTO T283 standard requirement. The indirect tensile strength test to determine
the tensile properties of cylindrical samples was performed by applying a compression load
along a diametrical plane of two opposite loading heads. For indirect tensile strength test, the
Figure 3. (a) Sample position; (b) sample after test; and (c) sample before test
Ahmad Kamil Arshad, Khairil Azman Masri, Juraidah Ahmad and Mohamad Saifullah Samsudin
Moisture susceptibility also known as moisture damage is the most common concern for asphalt pavements. In this research, moisture damage was evaluated in accordance with AASHTO T283. Stripping samples for both SMA and AC were compacted to obtained 7 ± 1 % air voids according to AASHTO T283 standard requirement. The indirect tensile strength test to determine the tensile properties of cylindrical samples was performed by applying a compression load along a diametrical plane of two opposite loading heads. For indirect tensile strength test, the samples were placed between the steel loading strips using an indirect tensile strength machine.
Two sets of samples were prepared for each mixture, dry samples were tested without moisture conditioning while the second was conditioned by saturating with water at 70 – 80% degree of saturation. The conditioned samples were immersed in water for 24 hours at 60°C in a water bath and conditioned at 25°C. The samples were then subjected to indirect tensile strength test (Figure 4).
A constant rate of 50 mm per minute at 25°C was applied on the diameter of the specimens. The specimen usually fails by splitting along with the loaded plane when the loading acts perpendicularly to the applied load plane. The maximum load carried by a specimen at the point of failure can be calculated by equation 1;
[1]
Where;ITS = Indirect tensile strength P = Maximum load h = Thickness of specimen D = Diameter of specimen
The ratio of the average tensile strength of the dry conditioned and wet conditioned specimens or also known as Tensile Strength Ratio (TSR) is obtained using the following equation 2;
[2]
Where;TSR = Tensile strength ratioS1 = Average tensile strength of the dry subsetS2 = Average tensile strength of the conditioned subset
Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures
The value of Optimum Binder Content (OBC) is based on the volumetric properties values. Table 3 below shows the Marshall result for SMA20 and AC14. Results indicate all values were in the specified range.
Where;
TSR = Tensile strength ratio
S1 = Average tensile strength of the dry subset
S2 = Average tensile strength of the conditioned subset
(a) (b) (c)
Figure 4. ITS Test: (a) ITS machine; (b) sample position; and (c) wet conditioned samples
RESULTS AND DISCUSSION
Volumetric Properties
The value of Optimum Binder Content (OBC) is based on the volumetric properties values.
Table 3 below shows the Marshall result for SMA20 and AC14. Results indicate all values were
in the specified range.
Table 3
Properties Specification
JKR/SPJ/2008
SMA20 Status Properties Specification
JKR/SPJ/2008
AC14 Status
Figure 4. ITS Test: (a) ITS machine; (b) sample position; and (c) wet conditioned samples
Table 3 Marshall result for SMA20 and AC14
Properties Specification JKR/SPJ/2008
SMA20 Status Properties Specification JKR/SPJ/2008
AC14 Status
OBC, % 5-7 6.16 PASS OBC, % 4-6 4.85 PASSVTM, % 3-5 4.55 PASS VTM, % 3-5 3.9 PASSVFB, % Min 17 69 PASS VFB, % 70-80 74 PASSVMA, % - 26.8 PASS VMA, % - 15.8 PASSStability, N Min 6200 22563 PASS Stability, N Min 8000 18150 PASSFlow, mm 2-4 3.10 PASS Flow, mm 2-4 3.85 PASSDraindown 0.3 0.25 PASS Stiffness, N/mm Min 2000 5000 PASSSMA20 & AC14 volumetric properties
Resilient Modulus
For SMA20, the increment in the amount of NS will result in a higher value of resilient modulus. At 1000ms pulse period, the resilient modulus for 0wt% NS-SMA20 was 3138 MPa. The highest Mr value obtained at 4wt% NS-SMA20 was 4076 MPa. However, the results for resilient modulus values at different pulse period did not show any trend in uniformity. For AC14, the highest resilient modulus value was obtained at 4wt% NS-AC14 which was 8217 MPa at 1000ms pulse repetition. The lowest average value of resilient modulus obtained was
Ahmad Kamil Arshad, Khairil Azman Masri, Juraidah Ahmad and Mohamad Saifullah Samsudin
3849 MPa for 6wt% NS-AC14 at 2000ms pulse repetition. In general, higher pulse repetitive period loads the lower was the resilient modulus value. For instant, at 4wt% NS-AC14, the average resilient modulus was 8217 MPa at 1000ms, 6060 MPa at 2000ms and 5644 MPa at 3000ms. Table 4 shows the results of resilient modulus for both mixtures and how 4wt% NS can be considered the optimum amount for enhancing PA performance.
Table 4 NS-SMA20 & NS-AC14 resilient modulus
Sample Point Mean Pulse Repetitive Period (ms) SMA20
The objective of this test is to determine the rut depth of asphalt mixtures with the Asphalt Pavement Analyzer (APA). The Asphalt Pavement Analyzer counter was set to run at 8000 cycles. For this test, all the specimens were tested at 60oC. This test was conducted in accordance with AASHTO TP 63. The most effective amount of NS in enhancing the performance of asphalt mixtures i.e. 4wt% NS was used in both mixtures.
From Figure 5, for SMA20, it can be seen the rut depth increased rapidly at the beginning of the test which is between 0 to 6000 cycles and the critical part happened at the range between 0 to 1000 cycles and subsequently maintained at a range of 7000 to 8000 cycles. The result was still in the range of depth measurement (4 mm) complied with the AASHTO TP 63 specifications. Meanwhile, it can be stated that the sample for 4wt% NS-SMA20 is better because the rut depth recorded was lower than the control sample of 0wt% NS-SMA20. The percent changes were highest at 4000 cycles with 87.47% to decrease to 24.92% at 8000 cycles. On the other hand, for 4wt% NS-SMA20, the highest percentage change of 89.68% was also at 4000 cycles and the value decreased to 28.12% at the 8000 cycles.
For AC14, the modified asphalt mix specimen selected for this test was also 4wt% NS-AC14. From Figure 6, it can be seen that the percentage changes for the control specimen was higher than that of the modified specimen (4wt% NS-AC14). After 8000 cycles, rut depth
Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures
for the control specimen was 5.002 mm and for the modified specimen was 4.473 mm. The percentage change of rut depth of the control specimen changed to a high of 52.68% compared with the modified specimen which changed to 55.26%. This shows that, the presence of NS in AC14 can decrease the rut depth. Lower rut depth indicates that NS-AC14 provides better rutting resistance.
Figure 5. NS-SMA20 rut depth
Figure 6. NS-AC14 rut depth
Figure 5. NS-SMA20 rut depth
Figure 5. NS-SMA20 rut depth
Figure 6. NS-AC14 rut depth
Figure 6. NS-AC14 rut depth
Moisture Susceptibility
The objective of this test was to determine moisture susceptibility values for SMA20 and AC14 using the indirect tensile strength test. Samples were tested under dry and wet conditions in accordance to AASHTO T283.
For SMA20, the value of moisture susceptibility for dry condition was higher compared to the wet condition. The value of TSR increased roughly 10% for modified specimens. In addition, the TSR value for control sample which was 0wt% NS-SMA20 was 84% while 94%
Ahmad Kamil Arshad, Khairil Azman Masri, Juraidah Ahmad and Mohamad Saifullah Samsudin
for modified specimens. Both achieved the minimum requirement based on AASTHO T283 specification. If the TSR value is more than 80%, resistance towards moisture is higher and if the TSR value is below 80%, it is sensitive to moisture damage.
For AC14, dry ITS value for 0wt% NS-AC14 mixtures was only 499 Kpa while 537 Kpa for modified specimens. For wet conditions, the value of ITS for control specimen and modified specimen were 420 Kpa and 505 Kpa respectively. TSR value for both control sample and modified sample passed the minimum requirement which were 86% and 91% respectively. The result indicated the indirect tensile strength values of wet conditioned values were lower than that for dry conditioned, and the presence of NS in the bituminous mixes increased the mixtures strength to resist damage created by moisture. Figure 7 illustrates the result of ITS and TSR value for both asphalt mixtures.
(a) (b)
(c) (d)
Figure 7. (a) ITS SMA20; (b) ITS AC14; (c) TSR SMA20; and (d) TSR AC14
CONCLUSION
The findings of this study indicate that the existence of nanoparticle in particular 4wt% NS can
enhance the performance of SMA20 and AC14 in terms of mix design, resilient modulus, rutting
resistance and moisture susceptibility.
ACKNOWLEDGEMENTS
The authors would like to acknowledge FRGS Research Grant: FRGS/1/2015/TK08/UITM/02/3
Figure 7. (a) ITS SMA20; (b) ITS AC14; (c) TSR SMA20; and (d) TSR AC14
CONCLUSION
The findings of this study indicate that the existence of nanoparticle in particular 4wt% NS can enhance the performance of SMA20 and AC14 in terms of mix design, resilient modulus, rutting resistance and moisture susceptibility.
Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures
The authors would like to acknowledge FRGS Research Grant: FRGS/1/2015/TK08/UITM/02/3 and UiTM Shah Alam Malaysia for funding this study and to the IIESM UiTM Shah Alam Malaysia to allow this article to be written.
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