Ibrahim KAMARUDDIN Madzlan NAPIAH
University Technology PETRONAS Faculty of engineering
USING RICE HUSKS POWDER TO UPGRADE THE RHEOLOGICAL PROPERTIES OF BITUMEN BINDER
Keywords: aging, oxidation, rheology, cracking, rutting
A b s t r a c t
Oxidative aging is one of the main concern issues in the asphalt binder technology nowadays. Oxidation drives the bitumen to be harder and eventually cracked under high loads. Many researches have been tried to improve the resistance of asphalt pavement to rutting and cracking. The objective of this study is to investigate the influence of adding rice husks powder to the asphalt binder, on its physical and rheological properties. Three percentages (5%, 10% and 12%) of rice husks were used as modifiers. The influence of rice husks on the conventional properties, complex modulus (G*), cracking parameters and rutting parameters were investigated. Therefore penetration and rheological tests using a dynamic shear rheometer (DSR) were carried out to characterize the rice husks- modified bitumen. Based on the results obtained from the conventional properties tests and rheological tests, rice husks reduces the temperature susceptibility and increases the viscosity, stiffness and elastic behavior of the rice husks-modified bitumen. Rice husks enhanced rutting resistance and fatigue resistance of the bitumen at high temperatures and low temperatures. The best results were recorded for rice husks-modified bitumen containing 10% of rice husks.
Introduction
Aging due to oxidation cause bitumen to be harder and more susceptible to cracking, therefore oxidation is considered as the main cause permanent deterioration in asphalt pavements [1, 2, 3]. Most of the asphalt aging occurs during the road construction as the asphalts heated up to 165°C [4, 5]. Nowadays, Biomass has been used widely in many researches and industries as its cheap, effective and environmentally friendly materials. Rice husks are one of agriculture wastes and it is widely available in Malaysia. The purpose of choosing rice husks in this
study is due to the high content of lignin wish is can be up to 43%. Lignin is well known as antioxidant.
Materials
The bitumen grade of 80/100 pen is mostly use in the road construction in Malaysia, thus it has been used in this study. The bitumen were supplied by PETRONAS refinery in Melaka. Rice husks are widely available in Malaysia as agriculture waste.
Few steps of preparation were carried out to produce the final fine powder to be blended with asphalt binder. The biomass (rice husks) dried in the drying oven at temperature of 40°C for 10 days to get rid of any moisture content in it. Furthermore, biomass has grinded by using grinding machine until it gets to powder form. Finally, the powdered biomass sieved using 75 micron sieve machine. Only the fine particles that passed the 75 micron sieve has been collected to be used in this study as modifier.
Preparations Of The Modified Binders
Three Rice Husk modified bitumen were produced by mixing Rice Husks (5%, 10% and 12% content
By weight of bitumen) with base bitumen. All the modified bitumen was prepared using a high shear mixer at 160 °C under 4000 rpm of speed for one hour. The bitumen was preheated in the oven at 160°C before the blending processes to get the bitumen in to liquid form.
Conventional Binder Tests
Penetration test is used to measure the grade of the bitumen and to measure the temperature susceptibility, according to ASTM standards.
The higher values of penetration indicate the softer bitumen and higher temperature susceptibility and vice versa. The bitumen sample was melted and poured to cups then preconditioned by cooling it to 25°C.
Standard needle was applied to the sample in the penetration cup at a temperature of 25°C and penetration value was measured by using penetrometer [6].
In the softening point test, two horizontal samples of bitumen, placed in shouldered brass rings, are heated at a controlled rate in a water bath while a steel ball was placed on the center top of each sample. The softening point value is the mean temperatures at which the two disks
soften sufficiently to allow each ball, enveloped in bitumen, to fall 25 mm [7].
Temperature Susceptibility
Penetration index (PI) was calculated to investigate the influence of adding rice husks on the temperature susceptibility of the bitumen. Higher penetration index values refer to lower temperature susceptibility of bitumen and vice versa. Penetration value from penetrometer at 25 °C was used to measure the temperature susceptibility of the binders.
Penetration index is calculated using an equation, shows as follows [8]:
PI= (1952-500 log Pen-20S.P) / (50 log Pen-S.P-120)
Where Pen is the penetration test at 25 °C and S.P is the softening point.
Dynamic Viscoelastic Properties
KINEXUS Pro+ is the dynamic shear rheometer (DSR) used in this study. It was used to determine the asphalt binder’s rheological properties. Frequency sweep was applied between 1 and 100 rad/s.
frequency sweep tests were conducted at temperatures ranged from 10 to 40 °C. One plate was used in DSR, namely an 8 mm diameter spindle with a gap of 2 mm. The rheometer apparatus were preheated to the test temperature to get the temperature stabilized the bitumen sample poured on the top of the bottom plate [9].
The trimming will be conducted after the top and bottom plate get close to each other by a 10% more than the designed gap. The test will be stated after trimming and the plate reaches the target gap. The smallest possible stain control chosen to ensure that the tests done in the linear area and it must be large enough to obtain sufficient torque readings at low frequencies and high temperatures and sufficient strain at high frequencies and low temperatures. Dynamic viscoelastic properties analysis, using a dynamic (oscillatory) type test, has been used as a fundamental rheological testing method for bitumen. In this study, sinusoidal shear strains were imposed on binder samples. Binder samples were placed between two parallel plates under a dynamic shear rheometer instrument and applied various frequencies under several temperatures [10].
Rutting and Fatigue Parameters
The rutting parameter is calculated as the complex modulus divided by the sine of the phase angle, G*/sin while the fatigue parameter is calculated as the complex modulus multiplied by the sine of the phase angle, G*.sin [11]. The higher the rutting and fatigue parameters indicated higher rutting and fatigue resistance.
Results of Conventional Binder Tests
Table 2 shows the penetrations and softening points for the modified binders. All Rice Husk modified binders indicate decreased penetration with increasing Rice Husks content. The increase in binder hardness can be assigned to the addition of the Rice Husks to the virgin bitumen. The softening points, shown in Table 2, increased after the modification, thus indicating an identical increase in modified bitumen’s hardness. Relying on the results from these two conventional tests, the mechanism of modification would seem to correspond only to a stiffening of the base bitumen.
Table 1, conventional properties of the virgin bitumen and modified bitumen.
Binder Penetration @ 25°C (dmm)
Softening point (°C)
Penetration index (PI)
80/100 81 45.4 -1.19
5% Rice Husks 74 49.7 0.12
10% Rice Husks 58 55.3 39
12% Rice Husks 50 58.00 0.57
Results of Temperature Susceptibility
Temperature susceptibility of bitumen is used to be expected by calculating Penetration index (PI). For the virgin bitumen the PI value normally ranges from approximately -3 (for high temperature susceptible bitumen) to approximately +7 for highly blown (low temperature susceptible) bitumen [11]. The highest value of penetration index obtained in this study is (0.57) with the addition of Rice Husks. Thus,
temperature susceptibility of the bitumen decreases by the addition of Rice Husks.
Rheological Properties of the Modified Bitumen
Plots of complex modulus (G*) versus temperature at 10 rad/s of frequency are shown in Fig. 1.
Fig.1. Plots of complex modulus at 10 rad/s for the modified binders.
Increase in G* for virgin and modified binders is recorded. The addition of 12% of Rice Husks shows a higher increase in G* indicating a different compatibility between base bitumen and the Rice Husks. This behavior was also stated by previous studies for another elastomer modifier and SBS [12,13]. Moreover, the modified bitumen shows a more noticeable increase in G* and an improvement in the temperature susceptibility. In a previous study, isochronal plots for SBS modified bitumen show same minor increasing in G* at low frequency, 0.02 Hz, and low temperatures, less than 20°C. Another study was done with using natural rubber latex (NR) and shows same minor increasing in G* for high frequency which indicating improvement in term of temperature susceptibility [12, 14, 15].
1,00E+01 1,00E+02 1,00E+03 1,00E+04 1,00E+05
10 15 20 25 30 35 40
Complex Modulus (kPa)
Temperature °C
Virgin bitumen 5% Rice Husks 10% Rice Husks 12% Rice Husks
Rutting And Fatigue Parameters
The effect of temperature on the rutting parameter (G*/sin ) is shown in Fig. 2. The rutting parameter G*/sin is defined as the stiffness indicator to evaluate the rutting resistance the virgin and the modified. It was found that the rutting parameter G*/sin increased as the rice husks increases wich is shows an improvement in the rutting resistance of the modified bitumen.
Fig.2. Effect of temperature on rutting parameter (G*/sin )
The same results were recorded in previous studies, increasing NR latex content as a modifier with bitumen resulted increasing in stiffness where indicating improvement in rutting resistance [14]. The influence of temperature on fatigue resistance parameter (G*.sin ) are shown in Fig. 3.
Due to the increasing of cars on the roads nowadays, the repeated loads increases on the road pavements causing permanent damage known as fatigue. The cracks caused by fatigue allow water to flow inside the pavements causing further damages. Fig. 3 shows that the fatigue parameter decreased as the Rice Husks content increasing indicating an improvement in fatigue resistance.
1,00E+01 1,00E+02 1,00E+03 1,00E+04 1,00E+05
10 15 20 25 30 35 40
G*/sin (kPa)
Temperature C
Virgin bitumen 5% Rice Husks 10% Rice Husks 12% Rice Husks
Fig.3. Effect of temperature on rutting parameter (G*.sin )
Conclusions
This study was conducted to investigate the influence of rice husks on the conventional properties, complex modulus (G*), cracking parameters and rutting parameters of bitumen. Based on penetration and softening point results, the mechanism of modification seemed to entail a stiffening of the base bitumen. Moreover, the penetration index results show that adding Rice Husks to bitumen decreased its temperature susceptibility.
Furthermore, isochronal plots of G* showed that 10% rice husks- modified bitumen more noticeable increase in the complex modulus and hence improved temperature susceptibility. However, based on master curves, Rice Husks provides polymeric modification by means of a highly elastic network within the bitumen and this elastic network increases the viscosity, stiffness and elastic behavior of the modified bitumen. In addition, based on the rutting and fatigue parameters, adding Rice Husks decreased the rutting parameter for the binder and improved the fatigue behavior at temperatures. As a result, the rheological properties indicated that 10% Rice Husks content optimally modified bitumen.
Acknowledgment
The author(s) would like to acknowledge the supports that received form Universiti Teknologi PETRONAS.
G*.sin (kPa)
Temperature ( C)
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