Grantee Research Project Results

Final Report: Plient Recycled Steel Fiber Reinforcement to Achieve Ultra-Low Carbon Concrete Buildings

EPA Contract Number: 68HERC25C0025
Title: Plient Recycled Steel Fiber Reinforcement to Achieve Ultra-Low Carbon Concrete Buildings
Investigators: Donnelly, Charles
Small Business: Circle Concrete Tech, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: December 16, 2024 through June 15, 2025
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2025) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR)

Description:

Circle Concrete Tech, Inc, (“Circle”) has developed a sustainable, cost-effective alternative to traditional reinforcement agents for specific concrete applications. This technology consists of Plient fibers, an engineered recycled steel fiber product which can be used to achieve 7x – 19x lower carbon emissions compared to rebar, mesh, or manufactured steel fibers (MSF). Through 5+ years of research, Circle identified that high doses of Plient fibers (>1%) are required to achieve sufficient residual flexural strength for Plient to replace traditional reinforcement agents for certain applications. Since fibers are known to affect concrete workability, there was concern that these high doses would prohibit Plient concrete from being pumpable using conventional concrete boom pump trucks, which is required for typical industrial flooring applications. During an extensive customer discovery process, clients consistently expressed that Plient concrete must be placed and finished using conventional equipment and practices. The following key research questions were identified through this process: Q1) Can pumpable concrete mixtures be designed with high volume fractions (i.e., 1%) of Plient fibers? Q2) Can concrete with high volume fractions of Plient fibers be placed and finished using the same tools, equipment, and methods that are standard in the industry? These questions were successfully addressed through this EPA Phase I SBIR project.
The two key objectives of the study were as follows:

1. Experimentally evaluate the pumpability of typical industrial concrete floor mixture designs with high Plient fiber volume fractions and identify pumpable mixture designs.
2. Construct an industrial concrete floor slab prototype using a pumpable concrete mixture identified in O1 and finished using standard finishing tools, methods, and equipment.

Summary/Accomplishments (Outputs/Outcomes):

The project was divided into four successfully completed tasks which were designed to achieve the project objectives. The results from each task and the corresponding objectives are summarized in Table 1.

First, Tasks 1 and 2 were conducted to evaluate the pumpability of typical concrete mixture designs used for flooring with different doses of Plient fibers, and to identify pumpable Plient concrete mixture designs (O1). In Task 1, a total of 15 different pumpable concrete mixture designs were obtained from five different industry sources and used to develop a baseline concrete mixture that is representative of a typical pumpable concrete for flooring applications. Two additional concrete mixtures (medium paste, high paste) were developed by increasing the volume fraction of the cement paste of the baseline concrete mixture. In Task 2, the pumpability of the three mixtures (baseline, medium paste, high paste) was tested using a Sliding Pipe Rheometer (SLIPER). SLIPER testing was conducted using a full factorial analysis in which each mixture design was evaluated with three different volume fractions of Plient fibers equal to 0.5%, 1.0%, and 1.5%. The results were used to evaluate the trade-off between paste content and pumpability for typical concrete mixtures designs used for industrial flooring. The second component of the study consisted of developing a pumpable Plient concrete mixture design (Task 3) to be used to construct a Plient concrete prototype floor (Task 4). The product of these tasks was the construction of an industrial Plient concrete floor slab prototype using standard finishing tools, methods, and equipment (O2). Circle decided to use the construction of the prototype floor system in Task 4 as a showcase event to highlight Plient fibers to potential customers. This event took place on May 1st, 2025, at the RELLIS Campus of Texas A&M University. In addition to successfully completing Task 4, Circle demonstrated the potential of this technology to approximately 30 experts from the concrete industry. Attendees included contractors, engineering firms, ready-mix concrete producers, and representatives from municipal and county agencies.

This showcase event was a definitive success for Circle. As shown in Figure 1, a standard boom pump truck pumped Plient concrete from a ready-mix concrete truck to be placed in the forms. The concrete was successfully pumped and placed with no challenges or loss in quality. Conventional equipment was used to finish the surface of the floor system, as shown in Figure 2. The successful construction of this prototype satisfies the second objective of this project by demonstrating that Plient concrete can be pumped, placed, and finished using conventional construction methods.

The event was also a success because it provided an opportunity for open engagement between Circle and potential Plient customers. Experts in the concrete industry witnessed firsthand Plient concrete effectively implemented while learning about the advantages of this product. This event provided a forum during which engineers and contractors could provide feedback to Circle, which will improve our ability to address the specific needs of future customers. Because of this event several attendees have expressed interest in using Plient fibers for upcoming projects, which has led to ongoing discussions which may lead to successfully securing projects.

Conclusions:

The successful completion of this Phase I SBIR project has produced several critical results that will enable successful commercialization of Plient fibers for industrial flooring applications. First, the laboratory analysis effectively determined the pumpability of Plient concrete as a function of paste volume fraction and Plient fiber dosage. The laboratory results were then successfully translated into a full-scale prototype slab section that was constructed using standard pumping and finishing techniques. This success, along with feedback provided by the showcase event attendees, confirmed the viability of Plient fibers as a suitable alternative to traditional reinforcement.