EMBEDDING SUSTAINABILITY
IN PAVING
WITH A VIEW ON IMPROVING SUSTAINABILITY IN THE PAVING SECTOR, ROADS & INFRASTRUCTURE LOOKS AT SOME OF THE LATEST SOLUTIONS ON OFFER, FROM THE DISCUSSIONS AT THE AFPA 2021 INTERNATIONAL PAVEMENTS SYMPOSIUM.
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ustralia still has over half a million kilometres of unpaved roads and over 350,000 kilometres of paved roads which will require ongoing maintenance – that’s why it’s important the pavements sector continues to optimise the materials used in roads and refines the production methods to deliver safer and more sustainable solutions to the roads network and wider communities. Sustainable paving solutions were the focal points of discussions at the Australian flexible Pavement Association’s AfPA 2021 Symposium in August. From biosourced additives for binder improvement to reviving graded seals with lower environmental impact binders, a range of solutions were presented to help achieve more sustainability in the pavement sector. TRACKLESS BOND COATS Iulian Man, Technical Service Manager at SAMI Bitumen Technologies talked about how trackless bond coats can provide longer lasting asphalt pavements. A tack or bond coat is a very light application of bitumen emulsion used to
promote the bond between the existing surface and the new asphalt application. Conventionally in Australia, the standard CRS60 has been used as a tack coat. SAMI Bitumen has developed a trackless polymer modified tack coat emulsion, the SAMIbond 007, which improves bond strength between asphalt layers, allowing the pavement to act as a monolithic structure under very high stresses. Due to its good bonding characteristics, SAMIbond 007 is expressly designed to withstand the high shear stresses that develop under aircraft traffic loadings. It has been successfully used in Western Australia’s Solomon Airport and on the main runway at Sydney Airport. Road trial at Mamre Road in New South Wales’ Mount Vernon has proven a quicker curing time and higher shear strength of the SAMIbond 007 compared to the conventional CRS60, with the emulsion showing a track-free behaviour 40 minutes after spraying. ENCAPSULATED BIOCHAR AS BITUMEN Alexandru Let, Technical Manager at State
Asphalt NSW, talked about the properties of asphalt with binders containing various percentages of plastic encapsulated biochar. Biochar is a carbon rich material produced from the slow pyrolysis (heating in absence of oxygen) of any biomass, where all of the cellulose, lignin and other non-carbon materials gasify and are burned away. According to Let, biochar has already been used as part of the mix design in a collaboration with the Austrian Road Authority, where biochar was encapsulated within recyclable plastic to prevent any dust inhalation of the biochar. The plasticised biochar was then added to the asphalt mix in a dry mix process. State Asphalts NSW has conducted lab trials of modified bitumen samples by mixing base bitumen with plastic encapsulated biochar and asphalt mix by dry and wet procedure. Due to its carbon nature and morphology, the plastic encapsulated biochar has shown to have a twofold impact on the properties of bitumen, namely: it acts as an antioxidant thus retarding the ageing properties of bitumen and, secondly, it stiffens the
SAMI Bitumen technologies’ SAMIbond 007 trackless bond coat was successfully used in Western Australia’s Solomon Airport. 20
ROADS OCTOBER 2021
