Low Carbon Road Pavement by Maximising Material Circularity and Adopting Sustainable Materials

Description

Road pavements are important infrastructures for surface transportation, and they not only consume enormous amount of natural resources, but their construction and maintenance could also lead to substantial carbon emissions. Despite the development of various decarbonation solutions in the construction sector, low carbon pavement design and construction is a much overlooked topic. Pavement systems that can maximise the reutilisation of locally available resources and sustainable materials can help decarbonise the road pavement of Hong Kong. This study aims to develop low carbon road pavement systems by adopting the closed-loop and open-loop based material circularity strategies according to the specifications of pavement systems of Hong Kong. The closed-loop design includes the use of recycled concrete aggregates in rigid pavement, and recycled asphalt pavement (RAP) and RCA in flexible pavement. As for the open-loop design, it strives to incorporate locally available waste glass and highly sustainable natural pozzolan as potentially alternative supplementary cementitious materials in rigid pavement, and to integrate locally available waste tyre in flexible pavement. By using both the closed-loop and open-loop strategies for rigid pavement system design, it is expected that the emission intensive ordinary Portland cement for building the concrete pavement structure can be reduced by 25-55% based on 5-15% of glass powder and 20-40% of natural pozzolan substitution, with sacrificing the mechanical performance and durability. This could result in at least 25% of carbon reduction in rigid pavement construction. Laboratory tests including the compressive strength, transverse strength, tensile strength, flexural strength, drying shrinkage, chloride penetration, sulphate attack, alkali / acid attack, etc., will be carried out to verify the performance of the designed low carbon rigid pavement system. As for flexible pavement, apart from employing recycled concrete aggregates as subbase materials, a higher percentage of recycled asphalt pavement (30-40%) and waste tyre (5-15%) will be used to replace the use of asphalt. Through which, it is hoping to reduce the carbon footprint of flexible pavement by at least 25%. A series of laboratory tests not least the moisture sensitivity, water permeability, standard Marshall stability test, wheel tracking test, immersion Marshall test, indirect tensile strength test, indirect tensile fatigue test, etc. Finally, field tests will be conducted for both low carbon rigid and flexible pavement systems by implementing the proposed designs in typical road pavement sections at the university sites to analyse the long-term performance. The environmental performance including the carbon emissions would be comprehensively evaluated to ascertain and benchmark the carbon-friendliness of the proposed design systems. On the basis of the laboratory and field test results as well as the carbon reduction potential, a practical guideline will be prepared by considering various influential like including the traffic patterns, weather condition, etc. to facilitate the practical use of the proposed low carbon pavement systems in Hong Kong. The proposed low carbon pavement systems would not only help resolve the waste disposal and material scarcity problems of Hong Kong, but they could also contribute significantly to meeting the carbon neutral target while supporting the ambitious development plan of Hong Kong.