Hasanain Radhi Radeef al dulaimi

The use of waste polymers for modifying asphalt has remarkable environmental and economic advantages. However, limitation still exists in the resistance of these mixtures against moisture damage and ageing. This paper aims to explore the impact of ageing and moisture damage on the mechanical properties of modified asphalt mixtures with polymer wastes (plastic waste and crumb rubber). Asphalt mixtures designated asphalt concrete (AC14) were prepared using granite aggregate, 60/70 PEN asphalt, and filler (hydrated lime). The properties of indirect tensile strength, resilient modulus, dynamic creep, and rutting were calculated to examine the effect of short-, long-term ageing and moisture damage. The results of the mechanical tests for the modified mixtures were compared to the conventional dense-graded asphalt mixture. The findings showed that asphalt mixtures containing both polymers presented superior properties after short-term ageing. In contrast, long-term ageing has enhanced the control and plastic waste mixtures’ bonding properties while negatively impacting the rubberised asphalt. Long-term ageing has reduced the resistance of rubberised mixture against permanent deformation by about 33%. The moisture conditioning has significantly deteriorated the mixture’s resistance to cracking and permanent deformation, particularly for the control and rubberised mixtures. The modulus and rutting resistance of the asphalt mixtures modified by crumb rubber and waste plastic has decreased by up to 9% and 17% after moisture conditioning.

Asphalt pavements undergo ageing and moisture damage over the service life. The ageing and moisture process resulted in more cracking susceptibility and lowered pavement serviceability. Recently, the semi-circular bending (SCB) test has been widely utilised to characterise the fracture resistance of asphalt mixtures. In this study, the Illinois Flexibility Index Test (I-FIT) were utilised to investigate the impact of long-term ageing and moisture damage on the cracking resistance of asphalt mixtures modified by crumb rubber and plastic waste. This test is currently being adopted as a routine test in Illinois and has shown good correlations with the field cracking performance of asphalt mixture. For the Semi-Circular Bending (SCB) test, a sample width of 50 mm and a notch length of 15 mm was used for conducting the fracture test using a constant loading rate of 50 mm/min and a test temperature of 25 °C. The fracture energy-based crack mouth opening displacement of the control and modified mixtures was also evaluated using Digital Image Correlation (DIC). The results showed that the flexibility index (FI) values from the I-FIT are sensitive to the modifier type (elastomers or plastomers) and long-term ageing while underestimating the impact of moisture conditioning on the fracture performance of asphalt. Fracture energy results were higher for the rubberised mixture compared to the control and plastic waste modified asphalt mixture. Ageing condition has noticeably decreased the flexibility index (FI) of the rubberised mixture and consequently reduced the fracture performance.

Asphalt mixtures behave as linear viscoelastic materials when subjected to loading conditions that are similar to pavement operating conditions. Thus, this study proposed a novel method for extracting the linear viscoelastic properties of asphalt mixture at 25 °C using digital image correlation and repeated-load semi-circular bending (SCB) test. Digital image correlation was utilised successfully for extracting creep compliance using semi-circular samples under repeated loading conditions. A fractional time-dependent viscoelastic element converted the creep compliance data into relaxation modulus. The extracted relaxation modulus data were verified by simulating the viscoelastic response of control and modified asphalt mixtures using the extended finite element model (XFEM). The findings presented in this paper showed that digital image correlation has a high potential for bridging the gap between experimental and simulation work. The strain map provided by the prediction model was compatible with the DIC strain.

Characterising the fracture properties of asphalt mixtures is a critical step toward a better pavement design. This study aims to investigate the mechanical response of asphalt mixtures modified with crumb rubber and plastic waste. These modified mixtures have been introduced in road construction based on the basic understanding of their mechanical properties. The R-curve based cumulative fracture energy and digital image correlation (DIC) technique were used to assess the fracture behaviour of the modified asphalt. The asphalt mixtures were examined under a monotonic semi-circular bending test for unconditioned, aged- and moisture-conditioned samples. The digital image analysis technique was used to construct the resistance curve based on the cumulative fracture energy. The DIC technique was used to capture the sample’s strain field for the control and modified mixtures. Results showed that the rubberised asphalt promoted crack propagation, whilst plastic waste resisted cracking by prolonging the crack initiation phase compared to the conventional asphalt. Strain fields derived by DIC demonstrated different mechanical contributions for both modifiers under the fracture test.

In recent years, the proliferation of plastic waste has become a global problem. A potential solution to this problem is the dry process, which incorporates plastic waste into asphalt mixtures. However, the dry process often has inconsistent performance due to poor interaction with binder and improper distribution of plastic waste particles in the mixture skeleton. This inconsistency may be caused by inaccurate mixing method, shredding size, mixing temperature and ingredient priorities. Thus, this study aims to improve the consistency of the dry process by comparing the control asphalt mixture and two plastic waste-modified asphalt mixtures prepared using the dry process. This study used crushed granite aggregate with the nominal maximum aggregate size of 14 mm whereas the shredded plastic bag is in the range of 5-10 mm. Quantitative sieving analysis and performance tests were carried out to examine the effects of plastic waste added into the asphalt mixture. The volumetric and performance properties combined with image analysis of the modified mixtures were obtained and compared with the control mixture. In addition, the moisture damage, resilient modulus, creep deformation and rutting were evaluated. This study also highlighted in detail the distribution of plastic particles in the final skeleton of the asphalt mixture. Based on the analysis, an enhanced dry process of mixing procedure was proposed and evaluated. Results showed that the addition of plastic particles using the conventional dry process leads to the deviation in the aggregate structure as high plastic content is added. Furthermore, the enhanced dry process developed in this study presents substantial enhancement in the asphalt performance, particularly with plastic waste that accounts for 20% of the weight of the asphalt binder.

The utilisation of plastic waste as a modifier in asphalt mixtures has inflicted significant impacts on the cracking resistance of the produced mixtures. Whilst many studies have evaluated the cracking resistance of asphalt mixtures incorporating plastic waste using wet method, limited studies have used the dry method are available. The current study aims to evaluate the effect of plastic waste incorporation on the fracture properties of conventional asphalt mixture. In addition, the impact of ageing and moisture damage on the fracture properties of modified asphalt was also investigated. Indirect tensile strength test was carried out to assess the CT-index, tensile strength, and fracture energy of the asphalt mixtures before and after exposure to ageing and moisture conditioning. The finding revealed that the asphalt mixture incorporating plastic waste demonstrated superior resistance to thermal and fatigue cracking compared to the control mixture, thus proving the capability of plastic waste in increasing the resistance of asphalt against ageing and moisture damage.