The investigation of long-term performance of crumb rubber modified warm mix asphalt under environmental effects

Use of additives has become indispensable for bituminous mixtures to serve for a longer time. Mostly, polymer-type additives are used as additives. These additives' additional expenses, lack of energy efficiency and higher emission rates have raised the topic of using waste vehicle tires, which emerges at an increasing rate each year, as additives in many countries. However, while these additives improve performance and they provide more economic benefits in polymer modification, they affect the workability of the mixture negatively and decrease the binder viscosity. Recently, warm mixture additives have been widely used to improve the workability properties of the mixtures and to improve the binder viscosity as well. Nevertheless, not many comprehensive studies were conducted regarding the performance of binders and mixtures with these additives against long-term aging. Aging is a significant parameter that determines the service lives of pavements. In laboratories, various tests, mainly rolling thin film oven test (RTFOT) and pressure aging vessel (PAV), are used to represent the bitumen's aging. The standards of AASHTO R30 method, which is regarded as the method to age mixtures in laboratories, are questioned by researchers. Thus, many researchers used various aging methods to determine the field aging of mixtures. However, the aging methods vary in terms of the additive used, environmental conditions and mixture design. In this study, a total of 7 test methods, 4 binder and 3 mixture tests, were evaluated. The effects of 3 different modification (%10 Crumb rubber (CR), %10 CR+%3 Sasobit and %10 CR+%0.7 Evotherm) on binders and bituminous mixtures were investigated by considering various aging periods both in laboratory (at 60 °C for 1, 2, 3, and 4 weeks) and in the field (for 12 months with 2-month intervals). In the binder tests, binders obtained from the aged bituminous mixtures by using extraction and distillation method were used. As the binder tests, Fourier transform infrared spectroscopy (FTIR), dynamic shear rheometer (DSR), rotational viscometer (RV) and softening point tests were conducted. Indirect tensile fatigue, indirect tensile strength modulus (ITSM) and indirect tensile strength (ITS) mixture tests were conducted on laboratory and field-aged Marshall specimens, which were prepared with pure and modified binders. The variances in aging indexes from each test were investigated in order to evaluate the sensitivity of both binder and mixture tests in predicting aging as well as the efficiencies of CR modification and using warm asphalt additives with CR modification. It was determined that a minor change in the aging rate of bituminous mixtures could cause significant changes in the number of repetitive loads in the fatigue test, and fatigue test was determined to be the most sensitive test for aging in pure and modified mixtures. In terms of the sensitivity in evaluating aging, DSR, ITSM, RV, ITS, FTIR and softening point test follow the fatigue test, respectively. As a result of the tests conducted on the bitumen obtained from laboratory and field aging, it was determined that 10% CR + 3% Sasobit modified binder was aged the least compared to all other binders while 10% CR modified binder was aged the most. Also with these aging methods, 10% CR + 0.7% Evotherm modified binder was aged less than the pure binder was. According to these aging methods, sole use of CR had negative effects in terms of aging while its use with warm-mix asphalt additives substantially increased aging resistance. It was also determined that standard short-term aging method was not a suitable method for the aging of CR modified mixtures. In terms of binder and mixture tests, both CR modification and CR + warm-mix asphalt additives modification demonstrated significantly superior performances compared to pure binder and mixtures.