The concrete industry ended 2023 with a bang, with the American Concrete Institute offering a first look at what is believed to be the world’s first code defining low-carbon concrete. The highlight of the new year so far has been the World of Concrete show, which celebrated its 50th anniversary. With one of the premier annual construction events now in the rearview, let’s take a look at some of the biggest news from the show and what concrete and cement industry stakeholders should be monitoring for the rest of the year.
A big victory in post-tensioning
In the first quarter of the year, the International Code Council will release the 2024 International Residential Code, which comprises all building, plumbing, mechanical, energy conservation and electrical requirements for one- and two-family housing units and townhomes no higher than three stories. During World of Concrete, the Post-Tensioning Institute unveiled its Stronger Standards, Exceptional Structures campaign to highlight its work that will be reflected in the 2024 IRC. Specifically, the code will include a major update related to the design and construction of post-tensioned, slab-on-ground floors. The update, noted in a new section of the code, Section R506.2, stipulates that post-tensioned concrete slab-on-ground floors placed on expansive or stable soils must be designed in accordance with PTI’s latest guidance, PTI DC10.5.
The update could improve the quality of post-tensioning system materials and subsequent installation. As PTI Executive Vice President Tim Christie explains, post-tensioning materials used in this type of construction will now need to be supplied by PTI-certified plants or an accepted equivalent facility, and the installation and stressing of these materials will need to be performed by PTI-certified field personnel. With the best personnel overseeing installation, the institute believes there will be fewer troubleshooting incidents for licensed contractors and designers that are more commonly encountered when using non-certified personnel.
“In general, if something is installed incorrectly, and a post-tension anchor might have a blowout or something in the concrete or something else might slip, other people could be subjected to danger,” Christie says. “When they stress those tendons, it’s a very high force – 33,000 pounds of tensioning force. With the equipment they use to stress those tendons, if you don’t know what you’re doing, it’s a very unsafe situation.”
The update should also improve structural durability and lead to lower life-cycle costs. From a risk management perspective, it could also result in fewer homebuilder warranty issues.
Transparency around PLC and EPDs
One of the most notable ways the concrete and cement industries have fostered sustainability in recent years is by slowly phasing out production of ordinary portland cement and ramping up production of more environmentally friendly portland limestone cement. Holcim, for example, has made that transition at 12 of its 13 plants in the US. According to Patrick Cleary, senior vice president of cement sales at Holcim US, that’s just the first step in the transformation of the market. The next step is transparently answering the tough questions from their customers who want to help municipalities and project owners simultaneously lower the embodied carbon of their projects without compromising strength and durability.
“We’re seeing our customers being asked to provide not only 4000, 5000, 6000, 7000 psi mix designs, but also a side-by-side comparison of the embodied carbon of that material as well,” says Cleary. “So there’s a desire for transparency and a desire for more EPDs – something that [Holcim US has] had for five or six years now.”
The demand for EPDs isn’t new, especially from federal contractors, and Holcim has been among the major material suppliers who have supported pilot programs for lower-embodied-carbon materials for federal projects.
“With the federal government incentivizing transparency and low-carbon construction through its Buy Clean initiatives, we’re hearing from customers, architects and engineers who want to learn how to meet the moment,” says Michael LeMonds, chief sustainability officer and vice president, ESG, at Holcim US. “Holcim US has been an in-demand resource in that area since the General Services Administration published its low embodied concrete standard for all GSA projects.”
However, Cleary says there’s also been more centralized demand from certain regions of the US that previously were not seen as hotspots for low-carbon concrete.
“The biggest transformation in the last year in a bit has been an influx of questions and demand from Middle America, as opposed to just the coasts, where you usually see the ‘green’ movements,” says Cleary.
AI for performance-based design
Another way concrete customers are looking to foster sustainability is by avoiding overdesign. Cleary feels the industry has been “spinning its wheels” when it comes to getting DOTs to accept performance-based design, but that’s starting to change.
“We’re finally getting people to listen,” Cleary says. “We can show you the industry has matured. We can give you the test data and show you that you can produce this high-quality concrete that you’re asking for with a lower carbon footprint if you give us the opportunity to build performance based mixes.”
In recent years, AI has emerged as a valuable tool that allows producers to adjust the proportions of their concrete mixes, such as the use of chemical admixtures and amount of cement, based on copious amounts of data. Those optimized mixes could allow DOTs to move away from prescriptive methods and physical testing, and instead adopt performance-based mixes tailored for specific projects that meet sustainability goals like reduced carbon emissions.
“I think there’s a huge opportunity for AI to … really accelerate the adoption of performance-based mixes, which would then reduce the embodied carbon of all of our projects,” says Cleary.
The market for fly ash and slag
One of the biggest areas of opportunity for sustainable concrete has been the increased acceptance of mixes that incorporate fly ash from pulverized coal in electric power generating plants. Putting fly ash in concrete mixes reduces the need for disposal in landfills and promotes the recycling of this industrial byproduct. Additionally, fly ash can improve concrete’s workability and can help in reducing the heat generated during the early stages of concrete curing. It’s also typically less expensive than ordinary portland cement.
However, as many power stations are being retired, the market for fly ash has taken a “significant hit” over the past five years, says Cleary. He adds that as this happens, the market is starting to shift toward beneficiated fly ash. Beneficiation technology allows fly ash stored in ponds to be processed and utilized, providing years’ worth of consumption. Cleary notes that Holcim subsidiary Lafarge Canada and energy provider TransAlta recently reached a deal to recover and process fly ash from a decommissioned coal-fired power plant in Edmonton, Alberta. Fly ash will be processed via a special beneficiation technology that will replace as much as 25% of cement for low-carbon concrete production.
Another industrial byproduct of interest, ground-granulated blast furnace slag, is generating interest from clients due to performance and sustainability, Cleary says. He notes that “there’s not a lot of new US-based granulation,” but he’s hearing “rumblings of a couple new granulation projects being dusted off to introduce more US domestic granules.”
Gaining market share in paving
In highway paving projects, asphalt is king, primarily due to its relative cost-effectiveness. Given the US’ high inflation market, it’s easy to see why asphalt might be attractive to a project manager.
However, the American Concrete Paving Association feels a little competition among materials never hurts. In fact, during World of Concrete, the association released a report outlining the benefits of encouraging competition between paving materials. The report cites research performed by the MIT Concrete Sustainability Hub that explores how the split of DOT paving expenditures between industries affects paving unit costs. Specifically, the report argues:
“As inter-industry competition increases, unit costs of both concrete and asphalt paving materials fall significantly—particularly those of concrete. For example, if a state with a low concrete market share (e.g., 1 %) were to increase its concrete market share to 25%, it would lower concrete and asphalt paving material unit costs by around 29% and 8%, respectively.”
The report also notes that some state DOTs, such as Florida, Texas, Wisconsin, Michigan and Minnesota, have found different ways to integrate both asphalt and concrete into their road construction projects. Florida and Texas set specific targets, with the former targeting roughly 40 miles of concrete pavement annually, while the latter puts out bids for around 5 million square yards of concrete annually. Wisconsin and Michigan adopt a metric-driven strategy, ensuring a balance between asphalt tonnage and square yards of concrete pavement on a yearly basis. This facilitates the involvement of both industries during periods of ample funding and commensurate adjustments during times of reduced funding. Another method involves the utilization of traffic or road classifications to assign separate markets for each material, with factors like equivalent single axle load (ESAL) values influencing material choices. Minnesota has made material decisions based on ESAL values, utilizing asphalt for projects with less than 1 million ESALs, concrete for those exceeding 7 million ESALs, and conducting life cycle cost analyses for projects falling between one and seven million ESALs.
If you enjoyed this article, click here to subscribe to ACI SmartBrief.