Modification of Asphalt Cement by Natural Rubber for Pavement Construction

Transcription

1 Modification of Asphalt Cement by Natural Rubber for Pavement Construction Nopparat Vichitcholchai*, Jaratsri Panmai* and Nuchanat Na-Ranong* * Rubber Products Industry Group, Post-harvest and Product Processing Research and Development Office, Department of Agriculture, Ministry of Agriculture and Co-operatives, Bangkok, Thailand Abstract ARTICLE INFO Article history: Revise: 1 January 2012 Revise: in revise International Rubber Conference 2005, October 2005, Yokohama Japan Accepted: 12 January 2012 Available online: 5 January 2012 Improvement the quality of asphalt for pavement construction is practical to prolong lifetime of roads. Polymer Modified Asphalt or PMA is one of such improvement by mixing polymers in asphalt. Natural rubber is an interested polymer that can be efficiently used. The distingue quality of natural rubber is its high stability, elasticity, and fatigue resistance. The aim of the study is to find the appropriate ratio of asphalt and rubber, which can achieve specifications required. The experiments were carried on by adding Ribbed Smoked Sheet (RSS) of 0, 2, 4, 6, 8 and10% by weight in asphalt and using high shear mixer. Asphalt qualities were investigated in penetration, softening point, penetration index, ductility, torsional recovery, toughness-tenacity, and viscosity. It was found that 6% by weight of natural rubber in asphalt is the most effective ratio to develop low penetration, high softening point, high penetration index, high torsional recovery, and high toughness - tenacity. The road using this mixing rate shows high strength and resistance, whilst increasing of viscosity does not cause the problem in aggregation of asphalt-concrete.

2 Introduction Road construction is currently paved with asphalt owing to its good flexibility apart from the price that is lower than that of concrete. Materials for asphalt paving and standard structures must be complied with the requirements of standard specified by Highway Department in order to be sure that it s suitable to utilize and last long whilst highly safe for the users. However, asphalt paving roads shows limitation on temperature, soften when the temperature is high and cracked when the temperature is low. In addition, hard traffic and high loading weight will damage the roads earlier than usual and cause expenses to repair and maintenance. Therefore, it is necessary to improve the quality of asphalt by the material which can play the role as a binder to achieve the following properties ; - 1. increasing viscosity and elasticity 2. diminution of temperature susceptibility 3. higher softening point and aging resistance 4. ameliorate of cohesion The improvement of asphalt to have those properties with various methods is continually carried on, and the practical one is using polymers to mix in asphalt that is called Polymer Modification Asphalt. Rubber is a kind of polymers using for modifying the asphalt properties. Some properties that are advantages such as stability, elasticity and fatigue resistance will be the better supplementary to asphalt properties and to extend aging of roads which can be help to save budget of maintenance. One of polymers used to improve asphalt property is Styrene Butadiene Styrene, SBS. Mixing asphalt with rubber has been testing for a long time. Nair, N.R., Mathew, N.M., Thomas, S., Chatterjee, P. and Siddqui, Ma (1992) had studied on improvement asphalt properties using fumigated rubber to reduce molecule by dissolving rubber into Fluxing oil until it became to Liquid Natural Rubber, LNR, and had been mixed with asphalt cement by heating. Two kinds of asphalt cements were investigated those are penetration grade and blown grade. Another factor was the ratio of rubber to asphalt used to mix. The properties experimented were penetration, ductility, softening point and viscosity. It was found that adding LNR provided reduction of ductility and increased the softening point. On the other hand, Fermando, M.J. Nadarajah, M (1992) had carried on improvement asphalt properties by various kinds of natural rubber latex such as field latex, concentrated latex, and skim latex. They used heating mixture method by spraying natural rubber latex into asphalt at the temperature of O C and stirring continuously for 20 minutes after adding natural rubber latex. The results showed the same tendency that the penetration value had been reduced whilst the softening point was increased. Shelburne, T.E. and Sheppe, RL used powdered natural rubber, powdered reclaimed rubber mixed into asphalt. The properties studied were the nature of road surface compare to the roads of natural asphalt constructed by the agency of Virginia State (Virginia Department of Highway). The visual observations on damaged area showed that the road surface improved with polymer had less rough and crack. However, it took for years to investigate the difference between the road surface improved with powdered natural rubber and that of non-improvement with natural rubber. 33

3 The study in the past provided a useful technical information that rubber is an interested polymer mixing with asphalt to improve its properties resulted extending of the durability of roads. In addition, as Thailand is a biggest producing country of natural rubber, it is a good opportunity to increase amount of NR domestic consumption. Therefore, it is reasonable to study on suitable kind of rubber, ratio mixed in asphalt, and mixture technique. Experiments Masticate RSS with two-roll mill at the temperature of 70 O C for 30 minutes, then cut into small pieces. Add them to asphalt by using high shear mixer at the ratio of 2, 4, 6, 8 and 10% by weight at O C for 2 hours, then incubate at 120 O C for 1 day. 1. Properties of asphalt and asphalt mixed with rubber are tested in Penetration value, measuring from depth of standard needle of Penetrometer sank into asphalt under pressed weight of 100 grams at 25 O C for 5 minutes, the higher in hardness the lower of penetration value. 2. Softening point, the critical temperature that the asphalt becomes softens which affects the asphalt surface in bleeding. 3. Penetration Index (PI), sensitivity owing to changing of temperature of asphalt, the PI value shall be specified into 3 level; - over +1 referred to low sensitivity, under 1 high sensitivity of temperature changing. and in between - 1 and Torsional recovery, a test to investigate the elasticity of asphalt using steel cylinder placed in the middle of sample in cylinder cup with a specified size, twist the axis to 180 degree and left for 30 minutes then measure degree of recovery Toughness-tenacity - the toughness means energy used to make test piece broken completely under the force - Tenacity means work provided from maximum force to tear the sample The test is made by sinking halfcircle head of test equipment into the sample and stretch with constant velocity of 500 ± 5 mm. per minute until the sample torn separately from each other, record value of force and elongation. 6. Viscosity value measured with Thermal Brookfield Viscometer at 135 O C and 165 O C. Results and Discussion Viscosity The viscosity of the mixtures of asphalt and RSS at the ratio of 2, 4, 6, 8 and 10% by weight by Thermal Brookfield Viscometer at 135 O C and 165 O C are investigated. It is found that the viscosity becomes higher than that of non-modified asphalt as shown in Figure 1 and 2 34

4 % RSS in sphalt by weight Figure 1. Viscosity of mixed asphalt by RSS at C RSS in asphalt by weight Figure 2. Viscosity of mixed asphalt by RSS at C The viscosity of the mixtures shows the value of 1.7, 3.7, 6.6, 14.5 and 19.2 times of non-modified respectively. A consideration of increasing viscosity, the ratio of 2, 4 and 6 % revealed lower tangent slope than that of 6 to 8 and 10%. The sudden high viscosity shall affect asphalt mixture with aggregate as the mixer will be unable to spray the asphalt being mixed with aggregate and it may cause the mixture system clogged. Penetration value In term of penetration value, the asphalt used to test is AC 60/70 Grade that its penetration value is 64. Improving asphalt property by RSS at the ratio of 2, and 4% by weight provided lower penetration value of 55, and 49 respectively revealed in Figure 3, which is shown the tendency of strength. 35

5 Figure 3. Penetration Values of asphalt improved with Ribbed Smoked Sheet. At 6% by weight, the penetration value shows return point to the value of 51. Increasing the ratio of RSS to 8 and 10% by weight the penetration value is increased to 76 and 78 respectively. It was shown that excess of RSS affected the dispersion of rubber in asphalt causing mixed asphalt with higher penetration value that is the asphalt would be softer. Softening point Test results on softening point showed that the ratio of 2, 4, 6, 8 and 10% by asphalt weight caused softening temperature higher at the beginning point and then gradually reduced respectively as shown in figure 4. The values are at 47.5 for non-modified to 50.0, 60.0, 61.0, 59.5 and C. The suitable explanation is that as RSS is a macromolecule with long chain and three-dimensional network, mixing it into asphalt composed of polar aromatic material which is hard, large molecule and dispersed in saturated paraffin materials, will cause difficulty to soften the mixture. The higher softening point is practical for the tropical countries. Figure 4. Softening point of asphalt improved with Ribbed Smoked Sheet 36

6 Penetration Index (PI) Improvement on asphalt properties with RSS will make asphalt more strength and softer at higher temperature. The penetration indexes shows sensitivity to temperature changing and figure 5 revealed that PI value has increased to positive value when increasing amount of natural rubber. The advantage of higher index is that the roads have sensitivity to temperature changing and can be indicated the trend on durability of the roads. % RSS in asphalt by weigh Figure 5. Penetration Index Value of asphalt improved with Ribbed Smoked Sheet Torsional Recovery Adding RSS in asphalt at higher ratio affected gradually on Torsional Recovery since RSS which is a polymer has a characteristic of elasticity, can be deformed under force and returned to the original shape after released that force. But excess ratio resulted that this property would descend (figure 6) because the dispersion of RSS in asphalt is not enough homogenized, make level separation and finally reduction of torsional recovery. Figure 6. Torsional Recovery of asphalt improved with Ribbed Smoked Sheet. 37

7 Toughness-Tenacity The ratio of 2, 4 and 6% by weight of asphalt ameliorate Toughness -Tenacity of mixed asphalt but the ratio of 8 and 10% values are increased very rapidly shown in figures 7 and 8. In this case It can be explained that increasing RSS to 8 and 10% make high viscosity mixture, so the strength of modified asphalt provides higher values of toughness and tenacity. Figure 7. Toughness of asphalt improved with Ribbed Smoked Sheet Figure 8. Tenacity of asphalt improved with Ribbed Smoked Sheet 38

8 Conclusion The most effective ratio of Ribbed Smoked Sheet (RSS) to improve properties of asphalt is 6% by weight of natural rubber in asphalt. The results from experiments show low penetration, high softening point, high penetration index, high torsional recovery, and high toughness tenacity. These properties can indicate that the roads paving with NR-modified asphalt shall have more strength and durability than using nonmodified asphalt. Addition of polymer causes increasing viscosity but it will not affect mixing process. However, this process needs high efficiency mixer that can be further applied to pilot scale. Shelburne, T.E., and Sheppe, R.L. Field Experiments with Powdered Rubber in Bituminous Road Construction. Rubber Age. Vol.66(5). p References Fernando, M.J.,and Nadarajah, M Use of Natural Rubber Latex in Road Construction. Polymer Modified Asphalt Binders. ASTM STP 1108, Kenneth R. Wardlaw and Scott Shuler, Eds., American Society for Testing and Material, Philadelphia. Nair, NR., Mathew,N.M.,Thomas,S., Chatterjee, P. and Siddqui, M.A Physical and Rheological Characteristics of Liquid Natural Rubber Modified Bitumen. Polymer Modified Asphalt Binders. ASTM STP 1108, Kenneth R. Wardlaw and Scott Shuler, Eds., American Society for Testing and Material, Philadelphia. 39