| Popis: |
Foamed Bitumen Stabilisation (FBS) is well-established as a beneficial technology for the improvement of existing pavement materials and for expedient pavement construction or rehabilitation. Foamed Bitumen Base (FBB) can be produced in-situ, by a specialised stabilising train, or ex-situ in a pugmill. However, regardless of the production process used in the field, the same laboratory production process and accelerated curing regime is applied for mix design and characterisation purposes. Although foamed bitumen technology has been used in Australia since the 1960s, there remain numerous areas of the mix design and stabilisation process that require development and better understanding. This partly reflects the fact that the mix design for FBS in Australia differs from processes used internationally. Two key areas requiring further development for Australian applications of FBS are; understanding the differences that occur between laboratory production, insitu field production and ex-situ field production processes and evaluating the representativeness of the curing methodology applied to laboratory produced foamed bitumen stabilised materials. This is particularly important for foamed bitumen stabilised materials in Australia where the mix design process is commonly required to achieve a minimum material modulus that is relied upon for structural pavement design. In this case, measuring laboratory modulus values that are representative of field conditions is critical. This research produced otherwise nominally identical FBB using laboratory, in-situ and ex-situ processes and identified significant differences in the Indirect Tensile Modulus (ITM) values and other material properties. For example, the laboratory produced materials achieved cured ITM values of approximately 10,000MPa, while the field mixtures achieved cured ITM of just 3,600MPa to 5,000MPa for the same curing period and conditions. Additionally, compared to ex-situ production, the in-situ process produced material was more variable across a production run. The research also compared the same FBB characteristics after accelerated laboratory curing to a simulated in-pavement curing regime. It was concluded that accelerated laboratory curing was more representative of 20-30 days of in-pavement curing, rather than the intended medium (3-6 month) term curing condition. It is therefore recommended that further research focus on adjusting laboratory production and curing protocols to ensure that field conditions are adequately represented. These findings benefit the pavement industry by highlighting that the Australian laboratory characterisation process for FBS is not representative of field conditions, and as such, there are process changes required to ensure that future FBB is fit for purpose, efficient and sustainable. |
