The deposition of metal particles onto polymer-based substrates via thermal spraying technology presents an effective approach to enhance the thermal and electrical properties of polymer coating systems. However, the selection of materials often profoundly impacts the mechanical performance of metallized polymeric coatings. This study focuses on optimizing material selection through microstructural characterization and evaluating the mechanical performance of various metallized polymeric coatings. Two distinct polymer materials, MIL-DTL24441 epoxy polyamide (applied through two coating techniques: dip and air spray) and coal tar C-200A, were employed as primer coatings for atmospheric and immersion harsh environments, respectively. Three different metal compositions, including pure Zn, Al-15Zn alloy, and Al-Zn pseudo alloy, were deposited as metallization layers. The obtained results indicated that polymer-pure Zn coating system exhibited inadequate hardness that made it unsuitable for metallization. SEM cross-sectional analysis revealed noticeable defects such as material clumps and voids within the polymer layer and delamination at the interface in the case of dip coating-based metallization that significantly impacting its hardness and adhesion performance. Through comprehensive analysis and comparison of microhardness and adhesion strength, air spray coating-based Al-Zn pseudo alloy metallization and coal tar-based Al-Zn pseudo alloy metallization emerged as promising candidates with excellent overall mechanical properties for atmospheric and immersion harsh environments, respectively.

Climate change significantly impacts transportation infrastructure, particularly asphalt pavements. Similarly, the heat absorption of paved surfaces, especially conventional black pavements, significantly intensifies the urban microclimate. Paved surfaces, including asphalt pavements, account for over 30% of the covered surfaces and are vulnerable to rising temperatures, which cause not only pavement distress, such as rutting and cracking, but also urban heat islands (UHI). Sustainable pavement solutions, specifically colored pavements, have been investigated for their potential to mitigate these effects. This review presents an extensive overview of current pavement technologies, emphasizing conventional asphalt’s economic, environmental, and functional characteristics. A discussion of the benefits and challenges of colored pavements is also provided, including their ability to reduce UHI, enhance safety, and contribute to sustainable urban growth. This paper discusses advancements in pavement material science, the use of recycled materials, and the application of reflective coatings, providing insights into sustainable infrastructure development. Transitioning from conventional black pavements to sustainable colored alternatives is not merely a matter of material choice but a strategic transition toward resilient urban planning. Increasing demand for environmentally friendly infrastructure could prompt the construction industry to adopt colored pavements as a tool to promote environmental stewardship.

Pavement construction practices have evolved due to increasing environmental impact and urban heat island (UHI) effects, as pavements, covering over 30% of urban areas, contribute to elevated air temperatures. This study introduces heat-reflective pavements, by replacing conventional black bitumen with a clear binder and pigment-modified clear binders. Titanium dioxide white, zinc ferrite yellow, and iron oxide red pigments are used to give asphalt corresponding shades. The asphalt and bitumen specimens were subjected to thermal analysis in heat sinks, under varying solar fluxes. The pigment dosage was maintained at 4%, according to the weight of the total mix, for all pigment types. The samples were heated and cooled for 3 h and 2 h, respectively. Mechanical testing was conducted to ascertain the impact of temperature variations on both the neat clear binder (C.B) and pigmented C.B and asphalt mixture samples. Wheel tracking and dynamic modulus tests were conducted to evaluate their performance under high temperatures. The results indicate that non-black asphalt mixtures exhibit significant temperature reductions, up to 9 °C, which are further enhanced by pigmented binders, up to 11 °C. It was found that asphalt with a clear or transparent binder demonstrated lower temperatures and faster heat dissipation in extreme conditions. Moreover, C.B asphalt mixtures displayed a rut resistance of 15%, with the pigmented C.B asphalt mixture showing a remarkable rut resistance of 73%, outperforming conventional asphalt. Non-black mixtures, especially C.B + zinc ferrite, showed improved resistance to permanent deformation in dynamic modulus tests.

Non-black pavement surfaces may be more vulnerable to distress associated with high temperatures due to the high surface temperatures of conventional black asphalt. Since asphalt is viscoelastic and temperature sensitive, it is more likely to be damaged by traffic loading at higher temperatures. This contributes to the urban heat island (UHI) effect, thus necessitating the use of coloring or cooling additives to help lower pavement surface temperatures. In response to these issues, iron oxide red, titanium dioxide white-modified bituminous mixtures, and clear asphalt binder were thermally investigated under different heat fluxes and compared with a conventional binder. In addition, the corresponding asphalt mixtures were prepared and compared with conventional asphalt mixtures. Each combination has also been observed for the rate of heating and cooling. Compared to traditional black bitumen, the clear binder and pigment-modified binder absorb up to 15% less heat. In addition, asphalt made with a clear asphalt binder and pigmented asphalt takes more time to heat and less time to cool than conventional asphalt.

Adhesion and moisture damage are significant factors in the early failure of pavements. This study examined the adhesion and moisture resistance of three types of binders (40-50, 60-70, and 80-100 pen bitumen) modified with paraffin wax (PW), hydrated lime (HL), and low-density polyethylene (LDPE) at dosages of 1% and 2% by weight of the binder. The Bitumen Bond Strength (BBS) test was performed using the Pneumatic Adhesion Tensile Testing Instrument (PATTI) to measure Pull-Off Tensile Strength (POTS) and determine the type of failure following dry and wet conditioning. Additionally, the mixture was tested for moisture susceptibility using the Rolling Bottle Test (RBT). The RBT results showed that adding LDPE and HL to the control binder increased bitumen coverage, indicating greater resistance to moisture damage. In contrast, adding PW reduced bitumen coverage, indicating higher susceptibility to moisture damage. Based on the BBS test, LDPE and HL-modified bitumen developed greater bond strengths as POTS values increased, while PW-modified bitumen developed decreased bond strengths as POTS values decreased.

Incorporation of high content of Reclaimed Asphalt Pavement (RAP) into fresh asphalt mixtures make them prone to thermal cracking and fatigue failure. Rejuvenators are usually recommended to overcome this problem by restoring the aged asphalt binder properties. This study aims to investigate the feasibility of using Mustard oil as a rejuvenator and to evaluate its effectiveness as a rejuvenator by determining the extent to which it restores the chemical and physical properties of aged asphalt binder extracted from RAP. The effect of Mustard oil on physical, rheological, chemical and thermal properties of aged asphalt binder was studied by employing Rotational Viscometer, Dynamic Shear Rheometer, Bending Beam Rheometer, Fourier Transform Infrared Spectroscopy, Thermogravimetric analysis, Gas-Chromatography-Mass Spectrometry and Rolling bottle equipment. Results indicated that Mustard oil effectively restores the properties of aged asphalt binder and can be used as a suitable rejuvenator. Ten per cent of Mustard oil is recommended as an optimum dose for rejuvenation of aged asphalt binder. This dose is based on restoring the RAP binder to match the properties of neat binder having PG64 and is specific to the stiffness of RAP material being used.

Lower thermal conduction and higher specific heat of conventional black pavement result in extreme surface temperatures during summers. Asphalt being highly temperature-dependent and viscoelastic, is more vulnerable to damage under vehicular loading at these temperatures. It also contributes towards Urban Heat Island (UHI) effect, hence demanding for non-black pavement surfaces by use of coloring additives which could help in the surface temperature reduction. Iron oxide red and Titanium dioxide white pigments are used to decolor the black mixes. Asphalt and bitumen samples were thermally investigated in heat sinks at three different solar fluxes. Pigment dosage was kept at 4% by weight of total mix for all the types of pigments. Samples were heated and cooled for 3 and 2 h, respectively. The effect of change in temperature of pigmented samples was also verified through performance testing. Cooper wheel tracking and dynamic modulus tests were performed to assess the high-temperature performance while fatigue parameters were assessed with a four-point bending beam fatigue test. Rheology of binder was assessed using Dynamic Shear Rheometer (DSR). Moreover, Rolling Bottle Test and Bitumen Bond Strength Test were also performed to check moisture sensitivity. Results showed that pigmented binder remain 8-10 degrees C cooler while pigmented asphalt mixtures remain 4-5 degrees C cooler as compared to unmodified samples. Performance tests reflected higher permanent deformation resistance at higher temperatures without compromising the fatigue property at lower temperatures. Rheology also depicted an increase in stiffness of pigmented binder, indicating better performance at higher temperatures. Use of pigments also enhances the moisture resistance/adhesion of the binder.

Asphalt binder is a temperature dependent material and is more susceptible to damage at higher temperatures. During summers, low thermal conduction and high specific heat of conventional asphalt results in extreme pavement surface temperatures and increased vulnerability. The situation demands for use of additives/modifiers that could help reduce pavement surface temperature. Thermal conduction of pigment modified/non-black asphalt mixtures is investigated in this research. Study focuses both on heating and cooling phase w.r.t time. Asphalt mixtures were evaluated for thermal conduction using larger heat sink with internal dimensions of 100 x 100 x 50 mm(3). However, bituminous mixtures were examined in smaller heat sink with internal dimensions of 60 x 60 x 25 mm(3). Both heat sinks were subjected to 800,1000, and 1200 W/m(2) heat flux and measurements were recorded accordingly. DC power supply was used as a heating source and silicon heater as a heating surface. Sinks were connected with data logger via calibrated K-type thermocouples. Iron oxide red and Titanium dioxide white pigments are used to decolour the black mixes. 4% by weight of total mix of each pigment is used to colour the black binder. Results have shown that at the end of 3 h of heating phase, pigment modified samples remain 8-10 degrees C cooler in case of bitumen binder and 4-5 degrees C cooler in case of asphalt mixtures. At the end of 2 h of cooling phase, a difference of 3-4 degrees C was noted between pigmented and conventional asphalt. Results also show that pigmented mixtures not only conduct more heat but also cool faster. Quantitatively, pigmented mixtures conduct 10%-15% more heat in comparison to the unmodified/black asphalt mixtures. The reduction in temperature susceptibility of pigmented mixtures may also help improve their high temperature performance. (C) 2020 Elsevier B.V. All rights reserved.