- Start small - The first time trying a low-carbon material, don’t use it for the whole project — start with a low-stakes component that requires only minimal load bearing, such as rat slabs, temporary access mats, curbs or landscaping walls, said
Lindsey Maclise
e, licensed structural engineer and principal with
City and County of San Francisco
FORELL ELSESSER
. Use these test projects to gain an understanding of how the material behaves, and to win over more skeptical members of the project team.
- Make time for testing - Low-carbon concrete typically uses less cement by substituting some percentage for supplementary cementing materials such as fly ash, slag and silica fume — all industrial byproducts that can perform a similar binding role. SCMs can be used individually with Portland or blended cement and in different combinations, according to the @Portland Cement Association. Do more test cylinders when first using a new cement, said Maclise. Try a few different types of low-carbon mixes and see what works best for your needs.
- Find the right client - Contractors should be selective about the clients they partner with to first attempt a more elaborate low-carbon concrete project, according to
Jessie Buckmaster
, director of sustainability at San Francisco-headquartered
Hathaway Dinwiddie
. Some owners put greater value in reducing the carbon footprint of their project than others and are more willing to experiment — and to pay for the cost of experimentation. As the market goes through the process of adjustment to this flood of new options, low-carbon concrete continues to cost more than Portland cement. Fifty years ago, fly ash mixes similarly were new and came at a premium, but have now become commonplace, Maclise said. Prices vary but are going down, and sometimes green mixes qualify for carbon offsets, said Buckmaster. Work with the owner to set bid-leveling criteria to account for low-carbon concrete.
- Talk to your supplier - There are now at least dozens of types of low-carbon cements on the market, but not all are in mass production or available in every region. Talk with your supplier about what green mixes can service a given project, said
Juan Gonzalez
, manager of strategic development and sustainability at
Central Concrete Supply Co
in San Jose, California. Some useful questions to ask your supplier include:
- Collaborate with team members - The GC, concrete supplier and structural engineer should all meet up front to ensure mixes are optimized to minimize global warming potential and to discuss how to manage the project timeline to accommodate the new formulations, said Maclise. The structural engineer should be involved throughout the process to make the experiment successful, said Maclise, and it’s also important to collaborate with the design and preconstruction teams.
- Be prepared for push back - Sometimes, engineers who are not yet familiar with low-carbon mixes are resistant to change, but contractors can sometimes nudge engineers out of their comfort zone, said Buckmaster. Let them know that reducing the carbon footprint is a priority, and connect them with other engineers who have used the material to answer questions and offer advice.
- Know the standards - Note that new low-carbon tech and mixes may need approval from governmental authorities. The
GSA
, which directs the federal government’s procurement efforts, released standards for low-carbon concrete in 2022 that are being tweaked based on industry feedback. In the meantime, contractors could use these federal benchmarks to guide their maximum embodied carbon limit, or carbon budget, for their project, said
Prateek Jain
, senior environmental designer at
Atelier Ten
USA in San Francisco.
- Adjust the project schedule - Expect low-carbon mixes to behave differently from Portland cement, Maclise said. Green concrete mixes may take longer to set and have a slower strength gain, so contractors should adjust project schedules accordingly. Coordinate work hours and form work rotation, considering longer cure times as well as season and expected extreme temperatures.? Ask for mix design submittals early to allow for testing, as well as sample environmental product declarations, Buckmaster advised.?
- Have a backup plan - Get used to assumed overstrength in design, or strength in excess of seismic code requirements, said Maclise, and don’t be nervous about not hitting over strength numbers. Know the local building codes and their true requirements, she said, and know your “outs,” or alternative ways to add strength and still meet requirements for a given part of a project if the concrete doesn’t set as anticipated.?
This is fantastic article as it highlights the challenges and what is required to moved forward with green cement.
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