**Preface to "Temperature Reduction Technologies Meet Asphalt Pavement: Green and Sustainability"**

Temperature reduction technologies have been used worldwide over the last two decades in asphalt pavement engineering [1,2]. The aim of these technologies is to use a lower temperature throughout production processes without affecting the performance of asphalt materials. Currently, different temperature reduction technologies, including warm mix asphalt, half-warm mix asphalt and cold mix asphalt, can be used with varieties of organic/chemical additives and foaming/emulsion techniques. The comparable ad even better overall performance properties and durability were achieved in the temperature reduction technologies compared to the conventional hot mix asphalt [3,4,5,6]. Significant economic, social, and environmental benefits can be achieved, including but not restricted to energy, greenhouse gas and fume emissions reduction, and increased field workability [1,3,7]. However, there are still several knowledge gaps to overcome. For example, the incomplete drying of aggregates caused by the lower production temperature may ultimately lead to serious rutting and moisture damage. These limitations hinder the mega-scale application of temperature reduction technologies in asphalt pavement constructions [8,9].

In this respect, the aim of this collection of papers is to report recent innovative studies and practices based on the use of temperature reduction technologies in asphalt industries. It includes twelve original research articles from five different countries and regions: China, Finland, Germany, Taiwan, and U.S.A., with international distribution accepted for this purpose. Various subjects related to advanced temperature reduction technologies in bituminous materials are covered. We believe that this Special Issue could help civil engineers and material scientists to better identify underlying views for sustainable pavement construction.

In the paper by Gao et al. [10], the fracture properties of a cold recycled mixture (CRM) were investigated via the designed rotary test device and Finite Element Method (FEM). It was found that the mixed-mode fracture test method can effectively evaluate the cracking resistance of CRM by the proposed fracture parameters, while the notch length on the initial crack angle and the crack propagation process of the CRM are mainly related to the distribution characteristics of its meso-structure. Jin et al. [11] experimentally evaluated the performance properties of Cold In-Place Recycling (CIR) asphalt mixtures over a wide range of temperatures. The results indicated that the CIR technology could significantly improve the low temperature and fatigue cracking properties. Mechanistic–empirical (M-E) pavement design methods show that the accompanied moisture damage accelerates the rutting and low-temperature fracture when distressed; however, such behaviors are acceptable for low-volume roads. Yan et al. [12] attempted using the Graphite Nanoplatelets (GNP) and/or aggregate packing technology to reduce the asphalt materials'compaction temperatures. The results show that the combined use of these two technologies could significantly reduce the compaction temperatures, while only optimizing the aggregate has the least impact.

For the purpose of mitigating the urban heat island (UHI) effect, Yang et al. [13] used different types of permeable road pavements to improve heat storage and dissipation efficiency. It was found that a fully permeable pavement has a higher efficiency than a semi-permeable pavement and a reasonable design depth of permeable road pavement could be 30 cm. Lai et al. [14] also worked on porous asphalt materials; the noise reduction properties were characterized by the sound pressure level sensors. Different mix designs showed a significant impact on the noise reduction responses; however, such an effect was mitigated with the increase in the wheel and decrease in the road structure depths. In particular, this was found for the open-graded friction courses. In Wang et al.'s [15] work, water-retentive and thermal-resistant cement (WTC) materials were developed, and their cooling effect was experimentally evaluated. The WTC was prepared with water-retentive material and a high aluminum refractory aggregate (RA) with porous cement concrete (PCC). The experimental results indicated superior cooling effects, and this material has the potential to mitigate the UHI effect under medium-traffic roads. Liu et al. [16] attempted to use numerical methods to study the temperature field effect on the mechanical properties of conventional and cool roads with a reflective coating. Cool pavement shows the potential to improve the rutting resistance, while only leading to limited benefits on the fatigue properties.

The road surface functions were studied by Yu et al. [17] and Guo et al. [18]. Yu et al. [17] focused on the effect of texturing parameters on road skid-resistance performance and driving stability. The width of the groove group can be adjusted to balance these two requirements. The optimal width, depth, spacing, and groove group width were defined in this study and validated by the actual engineering construction. Guo and his co-authors [18] use a Molecular Dynamics (MD) simulation to evaluate the adhesion properties and moisture effect between the interface of binder and aggregates. To balance the dry adhesion and moisture resistance, the energy ratio (ER) is an option to select the optimal SBS additive.

Fan et al. [19] evaluated the environmental benefits of low-emission mixed epoxy asphalt pavement. Overall, better anti-fatigue and rutting properties were found in the epoxy asphalt pavement compared to the conventional HMA, while a 30% reduction in carbon emissions was observed. Both Wei et al. [20] and Wang et al. [21] studied the rheological response of modified asphalt binders. Wei et al. [20] attempted to use polyphosphoric acid (PPA) as an alternative to Styrene-Butadiene-Styrene (SBS) and Styrene-Butadiene Rubber (SBR). It was found that the application of PPA could remarkably reduce the ratio of SBS and/or SBR; meanwhile, better anti-aging properties were found in the PPA-modified binders. Wang et al. [21] used polyphosphates acid and waste cooking oil (WCO) to enhance the conventional and rheological properties of asphalt binders. It was found that different components of WCO lead to a significant improvement in the low-temperature performance of PPA-modified binders. The solid–liquid phase change was observed at low temperatures.

## Funding

This research received no external funding.

#### Acknowledgments

We would like to thank all the authors, reviewers, and staff of the *Materials* Editorial Office for their great support during the preparation of this Special Issue. Special acknowledgments go to the contact editor, Ms. Emma Fang, for her continuous support during the organization of this Special Issue.

## Conflicts of Interest

The authors declare no conflicts of interest.

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10. Gao, L.; Deng, X.; Zhang, Y.; Ji, X.; Li, Q. Fracture Parameters and Cracking Propagation of Cold Recycled Mixture Considering Material Heterogeneity Based on Extended Finite Element Method. *Materials* 2021, 14(8), 1993. https://doi.org/10.3390/ma14081993

11. Jin, D.; Ge, D.; Chen, S.; Che, T.; Liu, H.; Malburg, L.; You, Z. Cold in-place recycling asphalt mixtures: laboratory performance and preliminary ME design analysis. *Materials* 2021, 14(8), 2036. https://doi.org/10.3390/ma14082036

12. Yan, T.; Turos, M.; Le, J. L.; Marasteanu, M. Reducing Compaction Temperature of Asphalt Mixtures by GNP Modification and Aggregate Packing Optimization. *Materials* 2022, 15(17), 6060. https://doi.org/10.3390/ma15176060

13. Yang, C. C.; Siao, J. H.; Yeh, W. C.; Wang, Y. M. A Study on Heat Storage and Dissipation Efficiency at Permeable Road Pavements. *Materials* 2021, 14(12), 3431. https://doi.org/10.3390/ma14123431

14. Lai, F.; Huang, Z.; Guo, F. Noise Reduction Characteristics of Macroporous Asphalt Pavement Based on A Weighted Sound Pressure Level Sensor. *Materials* 2021, 14(16), 4356. https://doi.org/10.3390/ma14164356

15. Wang, X.; Hu, X.; Ji, X.; Chen, B.; Chen, H. Development of water retentive and thermal resistant cement concrete and cooling effects evaluation. *Materials* 2021, 14(20), 6141. https://doi.org/10.3390/ma14206141

16. Liu, P.; Kong, X.; Du, C.; Wang, C.; Wang, D.; Oeser, M. Numerical Investigation of the Temperature Field Effect on the Mechanical Responses of Conventional and Cool Pavements. *Materials* 2022, 15(19), 6813. https://doi.org/10.3390/ma15196813

17. Yu, J.; Zhang, B.; Long, P.; Chen, B.; Guo, F. Optimizing the texturing parameters of concrete pavement by balancing skid-resistance performance and driving stability. *Materials* 2021, 14(20), 6137. https://doi.org/10.3390/ma14206137

18. Guo, F.; Pei, J.; Zhang, J.; Li, R.; Liu, P.; Wang, D. Study on adhesion property and moisture effect between SBS modified asphalt binder and aggregate using molecular dynamics simulation. *Materials* 2022, 15(19), 6912. https://doi.org/10.3390/ma15196912

19. Wei, J.; Shi, S.; Zhou, Y.; Chen, Z.; Yu, F.; Peng, Z.; Duan, X. Research on Performance of SBS-PPA and SBR-PPA Compound Modified Asphalts. *Materials* 2022, 15(6), 2112. https://doi.org/10.3390/ma15062112

20. Fan, Y.; Wu, Y.; Chen, H.; Liu, S.; Huang, W.; Wang, H.; Yang, J. Performance Evaluation and Structure Optimization of Low-Emission Mixed Epoxy Asphalt Pavement. *Materials* 2022, 15(18), 6472. https://doi.org/10.3390/ma15186472

21. Wang, W.; Li, J.; Wang, D.; Liu, P.; Li, X. The Synergistic Effect of Polyphosphates Acid and Different Compounds of Waste Cooking Oil on Conventional and Rheological Properties of Modified Bitumen. *Materials* 2022, 15(23), 8681. https://doi.org/10.3390/ma15238681

> **Markus Oeser, Michael Wistuba, Pengfei Liu, and Di Wang** *Editors*
