In the construction and maintenance of asphalt pavement, reclaimed asphalt pavement (RAP) is being widely used as a cheaper alternative to the conventional hot mix asphalt (HMA). HMA incorporated with a high RAP content (e.g., 40%), which is the most commonly used, may have prominent adverse effects on life cycle, performance properties, and related costs. Thus, before utilizing RAP, it is essential to investigate whether it is still economical to use under the local climate by taking into consideration the life cycle performance. Therefore, for this paper, a case study was conducted using 20% RAP, assessed in terms of materials related to cost analysis. The results of the analysis showed that, from the total life cycle costing measurement, a total of 14% cost reduction was reported using RAP as compared to conventional materials. Moreover, the two materials (conventional HMA and RAP) are manufactured in different types of manufacturing plants. Thus, in analyzing the cost difference between the two chosen manufacturing plants for virgin materials and RAP, a total of 57% cost reduction was observed for a RAP manufacturing plant. Besides this, no cost difference was observed in the rest of the phases, such as manpower, materials transportation, and construction activities, as the same procedures and types of machinery are used. Furthermore, assessing the carbon dioxide impact and cost, the transportation and machinery emissions were considered, while the plant’s operation emission was omitted due to the unavailability of the data.

The utilization of waste polyethylene terephthalate (WPET) as aggregate substitutes in pavement has been extensively promoted because of its environmental advantages. However, previous studies have shown that a high percentage of WPET reduces the performance of the pavement. To increase the durability of pavement and mitigate the environmental issues caused by WPET, WPET is treated with gamma-irradiation as a component in asphalt mixtures. The study objectives were to investigate the feasibility of using WPET granules as a sustainable aggregate on asphalt mixture stiffness and rutting and predict the asphalt mixture performance containing irradiated WPET via an RSM-ANN-framework. To achieve the objectives, stiffness and rutting tests were conducted to evaluate the WPET modified mixtures’ performance. The result indicated that samples containing 40% irradiated WPET provided a better performance compared to mixtures containing 20% non-irradiated WPET, increasing the stiffness by 27% and 21% at 25 °C and 40 °C, respectively, and rutting resistance by 11% at 45 °C. Furthermore, both predictive models developed demonstrated excellent reliability. The ANN exhibited superior performance than the RSM. The utilization of WPET as aggregate in asphalt mixtures represents a way to addressing related recycling issues while also improving performance. With gamma-irradiation treatment, the utilization of WPET can be increased with improved asphalt mixture performance.

In this study the effect of irradiated and non-irradiated waste polyethylene terephthalate (PET) as replacement of cement and fly-ash in ordinary Portland cement (OPC) and geopolymeric cement (GPC) based cementitious grouts on flexural strength of semi-flexible pavement specimens were evaluated. The porous asphalt gradation was selected based on Malaysian specifications for semi-flexible pavements with a target of 30% air voids. The cement content in the OPC grouts and the fly-ash content in the GPC based grouts were partially replaced with 1.25% PET (using both irradiated and non-irradiated PET). Beam specimens were prepared and tested for flexural strength properties using center point loading configuration. The grouts modified with recycled waste plastic (PET) showed approximately the same results as obtained from the control specimens. Although the replacement amount was low (1.25% by weight of cement), nonetheless, significant impact on reducing CO₂ emissions is expected when preparing grouts for mass construction of semi-flexible pavement surfaces. Similarly, effective recycling of waste plastics in road construction and replacing OPC with plastic and geopolymers will have a positive effect on the environment and will furthermore contribute to sustainable pavement construction.

Airport pavements deteriorate with age due to the impacts of environmental factors and air traffic. There is a dearth of studies on the scheduling of airport pavement maintenance and the importance of assessing the different scheduling strategies using Life-Cycle Cost Analysis (LCCA). An analysis of the cost–benefit study of a delay in maintenance alternatives should be done to determine whether a one-year delay is beneficial. This study concerns airport pavement management systems and the significance of a delay in several maintenance and preservation strategies depending on the analysis of inputs and outputs based on data from the Rocky Mountain Metropolitan airport in Jefferson County, United States. Herein, four preventive maintenance strategies were reviewed: three of the strategies involve crack treatment, namely crack sealing, patching, and a slurry seal, while the review of surface treatment only looks at the overlay method, which is done based on two Pavement Condition Indices (PCI 90 and PCI 80), and the resulting improvement in service life. The novel integrated LCCA + LCA program, namely PAVECO, is introduced in this research to compare alternatives from perspectives that are not purely economic, by considering direct costs, indirect costs, and salvage values. Results show that a one-year delay in preventive maintenance increases the deterministic life cycle cost by 16%. Based on the sensitivity analysis of the discount rate, the total cost shows more than a 10% decrease as the discount rate increased by 1%. Additionally, the uncertainty in PCI 80 is higher than that in PCI 90. The probabilistic model provides stakeholders with the opportunity to consider the alternative which is most suited to the allocated budget. It can be concluded that, based on the simulation of the effects of maintenance activities during the pavement life-cycle, preventive maintenance should start when the roads are in good condition to prompt managers and stakeholders to analyze the costs during the life-cycle. Postponing the preventive maintenance of airport pavement could raise the cost by 50%. The maintenance of airport pavements in developing countries is still one of the main challenges of pavement management due to the maintenance only being done when it is necessary.

Peat is a well-known problematic soil associated with poor engineering properties. Its replacement with an expensive competent foundation material is practiced for road embankment construction which is costly and causes greenhouse gas emissions. Therefore, this paper investigated the effectiveness of a byproduct from a metal industry (silica fume) to stabilize peat along with ordinary Portland cement (OPC) through a series of experimental tests. After peat-indexed characterization, a number of standard compaction and mechanical tests were performed on the stabilized and parent peat. For this purpose, nine designated mixes were prepared possessing various combinations of silica fume (SF) and 10–20% OPC. Unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests were carried out after 7, 14, and 28 days of curing to assess strength enhancement and binder effectiveness, and the microstructural evolution induced by the binders was examined with scanning electron microscopy (SEM). The analysis revealed a substantial improvement in mechanical properties with the incorporation of SF and OPC, ultimately meeting the minimum strength requirement for highway construction (i.e., 345 kPa). A peak UCS of 1063.94 kPa was recorded at 20% SF, and an unsoaked CBR value of 42.95 was observed using 15% SF and 15% OPC after 28 days of curing. Furthermore, the increasing percentage of hydraulic binders exhibited brittle, collapsible failure, while the microstructural study revealed the formation of a dense matrix with a refined pore structure in the treated peat. Finally, a significant statistical analysis was carried out by correlating the test parameters. In this way, rather than stockpiling and dumping, an industrial byproduct was implemented in peat stabilization in an eco-friendly manner.

Semi-flexible pavement surfacing, or grouted macadam, is an alternative to conventional flexible and rigid pavement. It is constructed by injecting cementitious grout into the voids of an open-graded asphalt surfacing. The cement used in cementitious grouts has adverse environmental effects because of the carbon dioxide emission in cement production. The objective of this study was to investigate the potential of using irradiated waste polyethylene terephthalate (PET) and fly ash (FA) as a (partial) cement replacement in cementitious grouts for semi-flexible pavement surfacing. This study sought to assess the stiffness modulus and fatigue properties of the semi-flexible specimens prepared with control grout, regular PET (2.57% PET + 10% FA) and irradiated PET (4.75% PET + 10% FA)-based grouts and compares the stiffness modulus and fatigue properties of semi-flexible specimens with the conventional hot mix asphalt (HMA) concrete. The semi-flexible surfacing specimens showed superior performance, higher stiffness modulus, and better fatigue life than the hot mix asphalt. The difference in fatigue cycles was apparent at lower stress ratios of 25 and 30%. The semi-flexible pavement mixtures exceeded 100,000 cycles at the lowest stress ratio of 25%, while the HMA fatigue cycles were less than 100,000 cycles. Furthermore, the semi-flexible specimen with irradiated PET (which contain a higher amount of waste PET than the regular PET) showed similar stiffness modulus and fatigue life as the specimens with regular PET and control grout. The irradiation technique offers a sustainable solution for recycling higher amounts of waste PET in highway materials for semi-flexible pavement surfacing.