Low-Carbon Tilt Wall testing for Schedule-Driven Applications

Summarize the project's program, features and achievements?

In November 2023 a consortium of industry partners from Clayco Construction, Concrete Strategies, Wiss Janney Elstner, Ozinga Concrete, Kienstra Concrete, Amazon Web Services, Breakthrough Energy and Climate Works consulting came together to pour and evaluate three experimental concrete tilt-wall panels to compare strength gain and constructability performance between common and innovative concrete mixes, each achieving varying levels of embodied carbon reduction vs industry average benchmarks. Funding was provided by both the client and research/NGO groups listed above.

The goal was to prove the applicability of low-carbon concrete mixes for use in FAST-TRACK Tilt-Wall construction. Tilt-wall construction is typically schedule driven; the use of high early-strength concrete mixes to facilitate "tilting" or erecting of the panels within an aggressive construction schedule is often necessary. Panels are typically lifted 5-7 days after pouring, but sometimes as early as 3 days. Conversely, the use of Supplemental Cementitious Materials (SCMs) in low-carbon concrete mix designs can extend the traditional strength gain curve of traditional portland cement mixes.

The three mixes tested were: 1: Control mix - 100% Type 1L cement from Holcim St. Genevieve plant, 2: Blended cement - 25% blast furnace slag, 75% Holcim 1L, and 3: Ozinga proprietary blended type 1157 cement. Prior to site work, Wiss Janney Elstner performed laboratory testing in their Northbrook, IL facility to prove that the mixes could achieve the dual compression and bending strength criteria by day 3. In our case, the specific metrics evaluated to facilitate panel erection were: 1. Achieve 50% f'c (concrete strength) in compression at 3 days, and 2: achieve 10% f'c in bending at 3 days.

1. In laboratory settings, all three mixes achieved the dual compression/bending criteria in three days.
2. In the field, all three mixes were able to be pumped, placed and finished. Panels 1 and 2 attained adequate compressive and flexural strength to facilitate erection on day 3. Panel 3 was affected by cold temperatures during placement and attained strength on day 7.

1. Panel 2 represents the successful use of a high-early strength mix with approximately 40% embodied carbon reduction vs. the NRMCA 3.2 baseline. This mix can be implemented successfully in all weather conditions.
2. Panel 3 is a mix that aggressively reduces embodied carbon by 64% vs NRMCA 3.2 and can be implemented in warmer climates. Further testing will be completed to determine applicable temperature ranges.

This testing effort has continued with the client to fine-tune this mix as well as to test further innovative mix designs. The Ozinga mix was incorporated on a large data center site in Indiana for foundations, and the team is hoping to use it for slabs and tilt walls in the near future.

What obstacles were overcome related to the schedule, budget, program, specification, site, etc. on this project?

The team overcame many obstacles in order to fine-tune the program and present objective, recreatable results for the client. Funding from NGO's provided needed access to strain gages and smart rock maturity sensors, which became key in evaluating strength gain when original test cylinders were compromised. Knowing this was a project undertaken as a supplemental effort to traditional project work, every team member worked to adjust their own schedules to accommodate for meetings and travel. In the field, adjustments had to be made "on the fly" but yet still meticulously documented. Interpreting daily strength gain results from the laboratory in St. Louis which did not match the in-situ strength sensors required the team to consider various causes of non-aligning data and pivoting to address. The result was a tight-knit group which freely shares non-proprietary information and best practices with other industry stakeholders as a result.

Please communicate any engineering complexities or unique features of the panel design for this project?

The Concrete Strategies management and field teams, as well as the ready-mix partners, approached this testing with a heightened awareness of the impact and importance of the effort - knowing the significance of results for the client as well as an overall effort of disseminating best practices when evaluating novel concrete mixes in general. Specifically, the field teams worked around the presence of multiple strain/strength sensors which are not present in traditional construction, and took great effort to document the field crew's effort in pouring, placement and finishing of the various mixes. The project team has truly set the bar in terms of best practice in evaluating new mixes.

What is the potential for this project's impact on the community and/or environment?

Community impact was not evaluated, but the group largely feels there is value to the larger design and construction community, even though there is not a geographic community impact.

Demonstrate how Embodied Carbon was reduced through smart design and/or material innovation.

Other than demonstrating early strength gain, Embodied Carbon reduction was a main critieria of this testing program. In the construction industry we are slow to innovate and change, as this can lead to unplanned cost and schedule adjustments. EPDs to document the Global Warming Parameters from the mixes used will be submitted separately. Briefly, the Global Warming Potential in kcCO2e/yd3 was: 209 for Panel 1, 169 for Panel 2, and 99 for Panel 3. This was in comparison to the NRMCA V3.2 Great Lakes benchmark for 5ksi concrete of 277. As a result of this testing, the client can confidently say the 25% slag mix for Panel 2 is a mix that provides meaningful carbon footprint reduction with NO expected effects to cost or schedule. Panel 3 (1157 mix) does carry a small cost increase (low single digit percentages) vs traditional cement. This increase is only applied to the material cost, not the full package. This testing allowed enough comfort with the innovative material to incorporate it on a subsequent project - but for foundations, not tilt walls. The team is lookign to incorporate it on ground slabs and tilt walls in the near future.

Provide information on strategies implemented to minimize and reduce waste during construction, such as recycling or re-using materials.

Portions of the test panels were salvaged in order to evaluate extended weather exposure.

Provide information on innovative construction techniques which aided in achieving sustainable goals.

Gathering feedback from field crews pumping, placing, and finishing the panels was a key goal of the project. Regardless of how a mix performs "on paper", if it cannot be successfully pumped, placed and finished it will not take hold in the industry. During pouring and placing of all mixes comments from the crews were recorded. This was an EARLY prototype of the Ozinga 1157 mix which had not been deployed at scale. Field crews initially struggled to pump the mix, and it had a low slump value. Crews had to pivot, realizing that continuously vibrating the mix would provide the workabilty needed. This key finding led to efforts to further tweak the mix formulation. The result, several months and deployments later, is a mix that has been improved to the point where current field crews cannot tell a difference and actually prefer the 1157 mix in some cases vs traditional cement.

Provide information on the community impact of the project related to sustainability.

Community impact was not evaluated, but the group largely feels there is value to the larger design and construction community, even though there is not a geographic community impact.

Provide information on obtaining relevant sustainability certifications, such as LEED, Passive House, Living Building Challenge, or other green building certifications.

No certifications were attempted or achieved as this was a testing program.

Give examples of innovative materials, novel procurement or construction strategies, and using tilt wall design to showcase exceptional performance in any of the above categories.

This effort notably included companies who in many cases are direct competitors coming together for a testing effort which will assist the client and overall tilt-up construction industry. Donation of materials, time, and expertise drove collaboration and success. Most notably, the proprietary mix which was difficult to place in this trial has been significantly improved in subsequent efforts. At a recent test pour field crews did not notice a difference between the improved mix and a traditional mix, and even preferred the improved mix in some cases. This type of patience and innovation is rarely seen in our industry, and should be recognized and applauded. We have been able to build a solid relationship with the client, who now sees our group as one who will go above and beyond to successfully implement their environmental goals alongside cost, schedule and durability. Following this testing, the Clayco/Concrete Strategies group completed novel mix testing for both slabs on ground and tilt-wall panels using innovative Calcined Clay mixes. We continue to partner on efforts to prove applicability of low-carbon mixes in schedule-driven work.