Performance Evaluation of Waste Polymers Modified HMA using Superpave Mix Design

Abstract

Transportation infrastructure plays a substantial role in the everyday life of social beings. The preservation of this vast infrastructure needs appropriate and cost-effective material and design technique. Several distresses are associated with pavement structure but more severe include Rutting, fatigue cracking and stripping Etc. Due to these severe kinds of distresses; pavement fails before completing its service life. In 1987, strategic highway research program (SHRP) put substantial effort to introduce new mix design procedure and in 1993 SHRP introduced SUPERPAVE system that is purely based on performance based specifications. Much work has been done on Superpave around the world but it is yet to be implemented in Pakistan. In this research HMA is characterized by two testing protocols as Asphalt Mix Performance Tester (AMPT) and Universal Testing Machine (UTM-25P). The three candidate tests for AMPT include dynamic modulus |E*|, flow number (FN) and flow time (FT) tests and Three candidate test for UTM-25P includes Indirect tensile strength (ITS), Resilient Modulus (Mr) and Tensile Strength Ratio (TSR). All these tests are conducted on two Polymers (LDPE and HDPE) and conventional mixes. Bitumen binder used is of ARL 60/70 grade and aggregate source is of Margalla Quarry. Optimum binder content was determined by means of Superpave Mix design method and based on the 4.36% OBC optimum polymer contents were determined incorporating stability and flow test. Samples for performance testing were prepared and then cored and trimmed to the specified dimensions. Dynamic modulus (E*) test was directed on 4 different temperatures i.e. 4.4°C, 21.1°C, 37.7°C and 54.4°C and 6 different frequencies i.e. 25Hz, 10Hz, 4Hz, 1Hz, 0.5Hz and 0.1 Hz. The |E*| test results were subjected to non-linear optimization technique to develop stress-dependent master curves which revealed that Polymers significantly influence the stiffness of mixtures 2-level factorial design of experiment technique was utilized to find the simultaneous effect of independent variables and their interaction on the response. Three factors were found to have a significant effect on the values of dynamic modulus i.e. temperature, frequency and Modifiers. Mixture prepared using LDPE showed better stiffness. Fatigue parameter was calculated using xvii the dynamic modulus and phase angle values and the results revealed that fatigue parameter value is low for LDPE mixtures at 4.4°C and at higher frequencies of 25HZ at 21.1°C which means that LDPE mixtures are less fatigue susceptible. Flow Number and Flow Time tests were conducted at temperature of 54.4ºC and a stress level of 300 Kpa. Flow number and flow time results were also analyzed to determine the rutting susceptibility of mixes. The mixtures prepared by LDPE accumulated less strains as compared to HDPE and conventional mixtures making it less rut susceptible. ITS test was carried out at 25ºC temperature both in dry and wet condition to determined tensile strength ratio which is a measure of moisture damage all mixes possess more than 0.9 TSR value .out of those LDPE showed 5.6% better resistant against moisture damage. Resilient Modulus (Mr) test was also performed at 25ºC temperature and 20% of Peak force obtained in indirect tensile strength test. Resilient modulus results also confirm the trend observed by dynamic modulus test that LDPE has high stiffens value following by HDPE and conventional mixtures. Cost effectiveness analysis was also carried out keeping all the factors constant and calculating the cost of bitumen replaced by polymers. which shows that LDPE is 4.63% and HDPE is 0.53% cost effective than Conventional mixtures because both the waste polymers have less cost as compared to the bitumen.