Singh, Bhupendra

While significant research efforts have been devoted to the rejuvenation of aged bitumen using bio-rejuvenators, a universally recognised approach for dosage optimisation is still yet to be established. Aiming to develop standardised methods to determine the optimal dosages of six types of bio-rejuvenators, this study validated the use of a rheology-based rejuvenation index as a potential universal method. Rheological properties of rejuvenated binders, determined through frequency sweep tests, multiple stress creep and recovery tests, linear amplitude sweep tests, and bending beam rheometer (BBR) tests were carried out with the properties of virgin binder as reference targets. The results indicated that the applied rheology-based rejuvenation index is a feasible approach. This index can ensure improved low- and intermediate-temperature (fatigue) performance of aged bitumen while maintaining high-temperature performance within acceptable limits. Further characterisation of the binders by Fourier Transform Infrared Spectroscopy (FTIR) analysis suggested that the bio-rejuvenation processes will commonly only involve physical softening rather than a chemical reversal of ageing. Therefore, the use of chemistry-based indices is likely not feasible.

This study investigates the utilization of recycled concrete aggregates (RCA) in waste low-density polyethylene (LDPE)-bonded, non-traffic cementless paver blocks. RCA is incorporated at varying percentages (0%, 25%, 50%, 75%, and 100%) to replace virgin coarse aggregates. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and melt flow index (MFI) were performed to characterize the thermal and physical properties of LDPE. RCA was treated using a 2-phase treatment technique to incorporate its efficient utilization. Four types of LDPE-to-aggregate mixes, namely, A (1:2.5), B (1:3), C (1:3.5), and D (1:4), were prepared to determine the optimal ratio and the quality control parameters through trial mixes. Paver blocks were evaluated based on their compressive strength, density, water absorption, and thermal strength stability. The results indicate that performing a double-treatment on RCA, optimized mix ratios, and identifying quality control parameters enhances the overall performance of paver blocks. A 35 MPa strength is achieved with 75% replacement, 1:3.5 LDPE-to-aggregate ratio, 30:70 coarse to fine aggregate ratio, and 50 mm depth, with a melt mixing temperature of 180–210°C. Microstructure analysis reveals a strong inter-transition zone (ITZ) for 75% replacement. The ANOVA, followed by a post-hoc analysis, was performed to validate the significance of these results.

Quartzite aggregates have poor adhesion with asphalt binder due to the higher silica content present in the mineral composition. Apart from conventional asphalt mixture testing methods, the surface free energy (SFE)-based adhesion evaluation method is most widely used in recent times to predict compatibility between aggregate and asphalt binder and moisture susceptibility in asphalt mixtures. This study tried to improve quartzite aggregates' adhesion properties by modifying the aggregates' surface with a nano-organosilicon (NOS), and two silane coupling agents (SCA) were used in modifying the aggregates' surface. Results showed that surface modifications by chemical treatments reduced the aggregate's SFE by increasing the aggregate nonpolar components to make a better bond with asphalt binder, which is also a non-polar material. From tensile strength ratio (TSR) results, it is found that the asphalt mixtures prepared with surface-modified aggregates showed better resistance to moisture damage with a 12%-15% increase in TSR. SFE indices like adhesion energy and energy ratio (ER) also showed significant improvement in adhesion between aggregates and asphalt binder, even in the presence of moisture. The ER values were above acceptable limits after surface treatments and showed a 100% increase compared with control mixes. SCA-1 and SCA-2 treatments effectively improved moisture damage in hot-mix asphalt with quartzite aggregates. One-way ANOVA was used to predict the effect of treatment methods and aggregate types on conventional TSR values and advanced SFE indices. The statistical results proved significant improvements in TSR and ER after the treatment of aggregates, but aggregate types do not make significant changes.

Despite being economically and environmentally friendly, the use of cold bitumen emulsion mix (CBEM) is still limited to minor repair work and construction of low volume roads. One of the reasons behind this underutilization is its poor cracking resistance. Fillers have significant effects on the cracking resistance of asphalt mixes. So, the present study aims at examining the effect of different fillers, i.e., stone dust, cement, lime, fly ash (FA), and ground granulated blast furnace slag (GGBFS) on the cracking resistance of CBEM. The cracking resistance of CBEM was examined by indirect tensile strength (ITS) and semicircular bending (SCB) tests. Results showed that the inclusion of active as well as waste fillers significantly improved the cracking resistance of all modified CBEM. However, the cracking resistance developed by FA and GGBFS modified CBEM were not comparable to cement modified CBEM. So for further modification, lime was added to FA and GGBFS modified CBEM, which further enhanced the cracking resistance of CBEM, making it comparable to that of cement modified CBEM. This experimental study was further extended to examine the effect of these fillers on the properties of cold bitumen emulsion mastic (CBEMa) by conducting scanning electron microscopy (SEM), X-ray diffraction (XRD), and linear amplitude sweep (LAS) tests. The SEM and XRD results confirms the presence of hydration products in the mastic phase of CBEM. In addition, a Pearson correlation analysis was carried out between the LAS parameters of CBEMa and the cracking resistance parameters of CBEM, confirming a linear association between both characteristics.

Hydrated lime (HL) has been used in asphalt mixtures to enhance the resistance to moisture damage in three ways, viz, as a filler, bitumen additive, and coating to aggregates. Quartzite aggregates are weaker in adhesion to asphalt binder due to higher silica content in chemical composition. This study compared three HL addition mechanisms to improve moisture-induced damage in hot mix asphalt made with high siliceous quartzite aggregates. Extensive experimental investigations were carried out, such as indirect tensile strength (ITS), tensile strength ratio (TSR), and fracture energy (FE), to compare the effects of HL addition with respect to conventional mixes. The ITS and TSR results found that HL-additive and HL-coating methods improved the resistance to moisture damage. Compared to control mixtures, HL-treated mixtures showed 20–25 percent higher TSR values. Meanwhile, the HL-filler method showed better resistance to fracture than the other two methods, offering better resistance to fracture in the field.

Application of Cold bituminous emulsion mix (CBEM) for the construction and maintenance of bituminous roads can offer several benefits toward environment and economic aspects over conventional hot mix asphalt due to its production at ambient temperature. However, its application is limited due to its lower early strength, which further affects its durability. To address these issues, many researchers have suggested to use fillers to improve the characteristics of CBEM. The present study utilized flyash as partial replacement of conventional filler, stone dust (SD) to modify the CBEM. This study is mainly aimed to examine the effect of flyash as a filler on the strength characteristics and moisture susceptibility of CBEM. The CBEM prepared by 100% SD as filler was considered as the control CBEM. The flyash modified CBEM was prepared by replacing SD with flyash at 20, 40, 60, 80, and 100% of the total weight of the filler. For further improvement curing was applied by keeping prepared specimens in oven at 40 °C for 1, 3 and 7 days before performing any tests. The Marshall stability and indirect tensile strength (ITS) were evaluated to analyze the strength characteristics of CBEM. The moisture susceptibility of CBEM was analyzed by evaluating retained stability and tensile strength ratio (TSR) tests. The results of these tests were compared to the control CBEM sample, and it was found that the inclusion of flyash improved the characteristics of CBEM. In addition, these properties were found to be further improved by increasing curing intervals. Based on the results, it was observed that 60 % flyash replacement meet the requirements after three days of curing.

In the current study, waste soybean oil (WSO) was utilized to retrieve the qualities of aged bitumen to that of virgin bitumen. The viscosity grade 30 (VG30) was employed as the control bitumen. Both rolling thin film oven tests (RTFOT) as well as pressurized ageing vessel tests (PAV) were used to replicate short-term and long-term ageing. The tests were performed at three ageing stages: no ageing, RTFO ageing, and RTFO + PAV ageing. A rejuvenator named WSO as mentioned above was introduced to both types of aged bitumen at varying weight-to-bitumen ratios of 2, 4, 6, 8, and 10%. Physical characteristics, viscosity, and rheology of virgin, short-term aged (STA), long-term aged (LTA), as well as rejuvenated bitumen were investigated. Performance-related tests such as multiple stress creep recovery (MSCR) and linear amplitude sweep (LAS) were also conducted at 60 °C and 25 °C respectively. The optimal dose of WSO necessary to rejuvenate both STA & LTA bitumen to the levels of virgin bitumen were found to be 4% and 8–10%, respectively. Furthermore, bitumen rejuvenated with WSO is less prone to long-term ageing, indicating their potential to extend the lifespan of asphalt pavements.