SENSE 600®: Achieving Significant Embodied Carbon Reduction in Mirvac’s 55 Pitt Street Project

SENSE 600® is a high-strength reinforcing steel bar that has contributed to a significant reduction in embodied carbon in the concrete elements of Mirvac’s 55 Pitt Street, a 55-storey commercial and retail building currently under construction in Sydney.

Mirvac’s design vision for 55 Pitt Street includes premium commercial and retail spaces, underscored by a commitment to sustainability. The developers, Mirvac, are targeting 25% recycled content in major materials and for the building’s upfront carbon emissions to be at least 40% less than those of a reference building.

SENSE 600®: Technical Overview and Sustainability Benefits

SENSE 600® is a range of 600 MPa reinforcing bars, produced to Australian Standard AS/NZS 4671. The bar’s unique specification allows it to achieve the same load capacity as traditional 500 MPa bars, despite being 16.7% lighter. This smaller diameter, high-capacity bar offers structural performance equivalent to 500 MPa bars, which simplifies substitution for designers, steel processors, steel fixers, and contractors, without compromising strength.

In addition to its material efficiency, SENSE 600® is manufactured entirely from scrap steel at InfraBuild’s steel mills in Melbourne and Sydney. This not only contributes to the high recycled content of the product but also ensures it remains highly recyclable at the end of its lifecycle, aligning with circular economy principles.

Integration of SENSE 600® into 55 Pitt Street’s Design and Construction

The initial design for 55 Pitt Street, which began in January 2021, predates the availability of SENSE 600® by several years. When the project was first conceived, 500 MPa bars were specified for the columns, and construction was set to begin. However, upon introduction to SENSE 600®, it became evident that the substitution could be made with minimal impact on the existing design.

A CodeMark certificate, recognised by the National Construction Code, facilitated the substitution of the 500 MPa bars with equivalent capacity SENSE 600® bars. As a result, 112 tonnes of 500 MPa column fitments were replaced with 93 tonnes of SENSE 600® fitments, resulting in significant material savings.

While the longitudinal bars required a design review, the equivalent capacity of the SENSE 600® bars meant the bar arrangement could remain unchanged, simplifying the redesign and documentation process.

Material and Embodied Carbon Savings

Due to project scheduling and design variations, the substitution of SENSE 600® for 500 MPa bars began at level B2, which affected the total material savings. Nonetheless, the material savings for the longitudinal column bars were calculated at 15.4%, approaching the potential 16.7% savings. The actual embodied carbon savings achieved in the column reinforcement was calculated at 38.6%, based on material take-offs and InfraBuild’s Environmental Product Declarations, close to the anticipated 39%* reduction.

Expanding the Use of SENSE 600®: Redesigning Beams

The success of the SENSE 600® substitution in the columns led to its further integration in the design of the building’s beams. Engineers from Arup and ADG were commissioned to redesign the post tensioned beams on the typical floors, from level 15 upwards, using SENSE 600® reinforcing bars. This redesign is expected to result in a further reduction of 270 tonnes in reinforcing steel mass, with an associated embodied carbon saving of 800 tonnes.

Further Technical Details

For an in-depth analysis of the material savings and technical considerations when substituting SENSE 600® for 500 MPa bars, refer to the paper: D. Drevon, M. Holt-Smith, A. Ng, J. Brown, “600 MPa Prefabricated Column Cages to Improve Sustainability,” Australasian Structural Engineering Conference: ASEC 2024, Melbourne, Australia.

*Editor’s note: The 39% reduction reflects the SENSE 600® Environmental Product Declaration (EPD) available at the time of the project. Based on the current SENSE 600® EPD, the equivalent reduction is now 60% compared with the NABERS average for reinforcing steel (v2026.2).