This research study aimed to assess the influence of different particle sizes of crumb rubber modifier on phase separation when mixed with virgin asphalt binder (PG 64-22). Both Superpave and multiple stress creep recovery (MSCR) tests were conducted to determine the optimal particle size. Three sizes of crumb-rubber particles (≤0.5 mm, ≤1 mm, and 1–2 mm) were individually incorporated into the binder at a weight proportion of 10%. The findings revealed that an increase in particle size resulted in higher viscosity, which reduced workability. However, the use of particles with a size of ≤0.5 mm effectively decreased viscosity. Furthermore, larger particle sizes enhanced resistance to rutting and improved the lifespan of the pavement. Multiple shear creep recovery (MSCR) tests confirmed that larger crumb-rubber particles exhibited a higher load-bearing capacity. Additionally, phase separation studies demonstrated that larger particle sizes were associated with increased phase separation. Notably, particles with a size of ≤0.5 mm performed exceptionally well in reducing phase separation across all combinations. In conclusion, crumb-rubber particles with a size of ≤0.5 mm were identified as the most effective in minimizing phase separation when blended with virgin asphalt binder. These findings provide solid scientific evidence related to the effects of crumb-rubber particles on the storage stability of rubberized asphalt binder and have significant implications for future research in this field.

This study presents a laboratory evaluation on rutting resistance of Open Graded Friction Course (OGFC) mixes made with different polymer modifiers and coarse aggregate sizes. For this research work, six mix designs for three polymer modifiers (3% SBS modified, 6% LDPE modified, and 12% rubber modified) and two aggregate sizes (13 mm and 10 mm) were carried out to determine the optimum asphalt contents. The OGFC specimens were fabricated using the Superpave gyratory compactor at a compaction level of 50 gyrations. The air void contents and final rut depths of the mixtures were measured by the Corelok system and the Asphalt Pavement Analyzer (APA), respectively. In general, the results indicated that the polymer modifier plays an important role in the rutting resistance of the OGFC mixes used in this study. With respect to the coarse aggregate size, it was found to have little effect on the rutting potential.

The use of intelligent compaction (IC) in asphalt overlay includes the use of double-drum IC rollers, a roller measurement system, global position system (GPS) radio/receiver/base station, infrared temperature sensors, and an onboard computer reporting system. GPS based mapping and optional feedback control help to overcome the drawbacks associated with conventional compaction such as identifying soft spots, achieving consistent roller patterns, and monitoring asphalt surface temperature and levels of compaction with adequate quality control or quality assurance (QC/QA). Cost-effectiveness of both compaction types was measured in terms of initial and roadway lifecycle cost based on the cost inputs received from South Korea and other published literatures. Roadway lifecycle cost was reported based on the improvement in in-place density, smoothness, and fatigue life. The results of this study showed that: (1) with IC an approximate 4.1% initial cost reduction can be achieved compared to conventional compaction; (2) QC/QA cost is found to have the most significant effect on the higher initial cost of conventional compaction compared to other associated costs whereas intelligent roller cost is the vital cost category for IC; (3) improvement of in-place air voids and density due to the IC has shown that at 97% field density (or at 3% air void content) the State Highway Agency can save approximately 44% over a 20-year service period; and (4) agency cost is observed to be reduced by approximately 62% with the IC method based on the 25-year analysis period due to the increase in fatigue life.

A number of warm mix asphalt (WMA) technology has been developed to allow asphalt mixtures to be produced and compacted at a significantly lower temperature. This eco-friendly technology has been spread so quickly in the world. Recently, an innovative WMA additive has been developed to reduce mixing and paving temperatures applied in asphalt paving process by Korea Institute of Construction Technology (KICT) and Kumho Petrochemical in Korea. It is named low energy and low carbon-dioxide asphalt pavement (LEADCAP), which is an organic additive of a wax-based composition including crystal controller and artificial materials. In this study, WMA mixtures using LEADCAP additive along with the control hot mix asphalt (HMA) mixtures were evaluated with respect to their moisture susceptibility and rutting resistance in the laboratory. The WMA pavement using LEADCAP additive along with a conventional HMA pavement were evaluated with respect to their density and air void in the field trials. Based on the limited laboratory and field test results, WMA mixtures using LEADCAP additive is superior to HMA mixtures in the moisture susceptibility and rutting resistance. The LEADCAP additive is found effective in producing and compacting WMA mixtures that are comparable to HMA mixtures.

Cold In-place Recycling (CIR) has been widely used in the world since it is easy to apply it in the field at a low cost. However, it is not normally used as a surface layer as a result of its inconsistent quality due to an excessive amount of fine aggregates pulverized during the milling process. Hot In-place Recycling (HIR) can retain the original shape of the aggregates, but it often produces a large amount of Volatile Organic Compounds (VOCs). Therefore, a third in-place recycling technique is introduced in this paper: Warm In-place Recycling (WIR). The WIR technique overcomes the limitations of both CIR and HIR techniques by lowering a heating temperature while adding a Tetraethylenepentamine (TEPA)/Soybean/SBS additive. To identify the effect of the additive on the RTFO-aged binder, viscosity and dynamic modulus values were measured at different temperatures. Based on Hamburg Wheel Tracking (HWT) and Disc-Shaped Compact Tension (DCT) tests, the additive improved the moisture susceptibility and low temperature cracking resistance. The indirect infrared heating equipment reduced the emission by lowering the pavement surface heating temperature by 20 °C from 140 to 120 °C. Compared with the heating at 140 °C, the LPG usage for heating at 140 °C was lowered by 21%. The proposed WIR equipment with an additive would revolutionize the in-place recycling practices.