Gate-to-gate life cycle assessment with primary plant data estimates greenhouse gas emissions for Australian bitumen grades

The study notes that around 800,000 metric tonnes of bitumen in various grades are used across Australia annually for pavement construction, and that almost 100% of bitumen is imported from other countries.

The study, published in Case Studies in Construction Materials, was conducted by Quddus Tushar, Joao Santos and Filippo Giustozzi. Rather than relying on proxy inventory data, the team developed a life cycle inventory directly from an operating plant, tracking electricity, industrial oil, liquefied natural gas and cooling water through every stage of production. Their gate-to-gate analysis covers the moment imported straight-run bitumen arrives at a storage tank held at 160 degrees Celsius until a finished viscosity grade is loaded onto a truck bound for an asphalt plant.

The functional unit was one tonne of bitumen, and the system boundary included two 600-tonne storage tanks, a 150-tonne feeding tank, a 50-tonne oxidation tank, three selling tanks and two 150-tonne mixing tanks. Crude oil extraction, base bitumen production, ocean shipping and capital infrastructure were deliberately excluded, because the researchers wanted to isolate the emissions of the plant-level conversion process itself. That boundary choice matters enormously when comparing results with other datasets, since the Eurobitume and AusLCI inventories include substantial upstream contributions that this study does not.

Imported bitumen arrives in Australia as a C170-equivalent straight-run product, maintained at roughly 160 degrees Celsius during maritime transit. At the plant, it is heated to about 165 degrees in storage. If a client orders standard C170, the material flows directly through heated pipelines at approximately 180 degrees to the selling tanks and onto trucks. For higher viscosity grades, the bitumen must first pass through a feeding tank heated to around 220 degrees, then into an oxidation tank at roughly 240 degrees, where compressed air is bubbled through the bitumen in the presence of a catalyst to blow it into a far more viscous product the industry informally labels C20000. Gases from that oxidation step are combusted in an incinerator fuelled by liquefied natural gas.

The blown C20000 bitumen is then cooled to about 200 degrees and blended with straight-run C170 in the mixing tanks to create the grades Australian roads actually use. C600 contains roughly 35 percent C20000 and 65 percent C170, C450 roughly 25 percent and 75 percent, and C320 roughly 15 percent and 85 percent. These proportions shift constantly depending on how the blowing process runs, since shorter blowing times and lower temperatures produce less viscous bitumen than longer, hotter cycles. The plant manager adjusts the blend continuously, and the study treats this variability as a sensitivity case rather than a fixed assumption.

Using the ReCiPe 2016 impact assessment method in SimaPro 9.4 with the AusLCI database, the researchers calculated eighteen midpoint environmental impact categories. The headline finding is that producing one tonne of blown C20000 bitumen emits a mean of 19.389 kilograms of carbon dioxide equivalent, while straight-run C170 comes in at 12.201 kilograms per tonne, a 37.07 percent reduction. The intermediate grades fall neatly in between: C600 at 14.716, C450 at 13.998 and C320 at 13.279 kilograms of carbon dioxide equivalent per tonne. Electricity from the Australian national grid accounts for 79.08 percent of the total carbon footprint, with industrial oil contributing a further 20.38 percent.

Those plant-level figures are not directly comparable with the established reference datasets because the system boundaries differ. Eurobitume reports approximately 149.6 kilograms of carbon dioxide equivalent per tonne of paving-grade bitumen when infrastructure is excluded, rising to about 207.5 kilograms when it is included, with crude oil production alone contributing 102.1 kilograms. The AusLCI dataset reports roughly 236.75 kilograms per tonne. The difference reflects the boundary: the Eurobitume and AusLCI inventories cover a cradle-to-gate chain including crude oil extraction, base bitumen production, refining and shipping, whereas this study assesses only the plant-level conversion of imported bitumen into variable grades in Australia.

To test how robust these numbers are, the team ran Monte Carlo simulations with ten thousand iterations, scoring data quality through a pedigree matrix covering reliability, completeness, temporal, geographical and technological correlation. The probabilistic results show a 5th to 95th percentile confidence interval of 18.685 to 20.128 kilograms of carbon dioxide equivalent for blown C20000, with a full minimum-to-maximum spread of 17.906 to 20.876. For the conventional grades, the confidence intervals overlap considerably: C600 spans 14.338 to 15.116, C450 spans 13.618 to 14.411, C320 spans 12.882 to 13.711 and C170 spans 11.755 to 12.675 kilograms per tonne. The authors note that the differences among the intermediate classes are therefore not statistically significant, though at a national scale of 800,000 tonnes per year even small per-tonne gaps accumulate into meaningful totals.

Sensitivity analysis on the blending ratios reinforces that picture. Shifting the C20000 share by five percentage points in either direction changes the carbon footprint of the final grade by only about 2.44 to 2.71 percent. Electricity is identified as the most influential input driving emissions. Pearson correlation analysis shows a strong relationship between electricity consumption and carbon emissions, with a coefficient of 0.93 and an adjusted R-squared of 0.881, meaning electricity explains 88.1 percent of the variation in the carbon score. Industrial oil shows only a weak correlation at 0.34, while liquefied natural gas and water contribute little variability at this facility.

The authors state that decarbonization in grid electricity production is a feasible solution for decreasing carbon footprints in the industrial and manufacturing sectors. Australia generated 76 percent of its electricity from fossil fuels in 2022, with renewables supplying just 24 percent. National targets aim for 36 percent fossil and 64 percent renewable by 2030, and 6 percent fossil and 94 percent renewable by 2050. The authors also flag practical site-level measures: optimising tank insulation to cut heat loss, recovering thermal energy from the oxidation process for feedstock preheating or hot-water generation, shifting pumping and mixing to periods of lower electricity demand, and integrating on-site photovoltaic generation. The authors note that whether higher-viscosity grades justify their extra emissions depends on pavement-specific performance, and that a hypothetical analysis assumes a 20-year service life for C170-grade bitumen, with C600 requiring approximately a 20.61% service-life extension to offset its higher GHG emissions; whether this threshold is achievable requires project-specific investigation outside the scope of the study.

Subject of Research: Life cycle assessment of greenhouse gas emissions from producing multiple viscosity grades of paving bitumen at an Australian plant using primary operational data

Article Title: Quantifying greenhouse gas emissions for the production of various bitumen grades: A comparative life cycle assessment (LCA) study using primary plant data

Article References: Tushar, Q., Santos, J., & Giustozzi, F. (2026). Quantifying greenhouse gas emissions for the production of various bitumen grades: A comparative life cycle assessment (LCA) study using primary plant data. Case Studies in Construction Materials, 25, Article e06676. https://doi.org/10.1016/j.cscm.2026.e06676

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06676

Keywords: bitumen, life cycle assessment, greenhouse gas emissions, Australia, pavement construction, carbon footprint, electricity decarbonisation, blown bitumen, viscosity grades, Monte Carlo simulation, ReCiPe 2016, industrial energy use