(722b) Innovating a Bendable Concrete Railroad Tie with Enhanced Fatigue Durability Via CO2 Utilization

The concrete industry is a significant CO₂ emitter, with one of its primary components, Portland cement, accounting for 8% of anthropogenic CO₂ emissions through its production. As the global construction market is continuously expanding, effective strategies for mitigating concrete CO₂ footprint are much needed. In this study, we propose a novel approach that utilizes and sequesters CO₂ to create a highly durable bendable concrete (technically known as engineered cementitious composites, ECC) through precast carbonation curing of ECC rail ties. Our goal was to examine the potential for this production strategy to enhance rail tie service life and reduce overall lifecycle CO₂ emissions in railroad tie applications. To do this, we verified fatigue resistance of the CO₂-sequestered ECC with respect to conventional concrete, as this is a critical criterion for railroad tie service life prediction, and developed a comprehensive lifecycle assessment for the CO₂-cured ECC ties.

Preliminary results suggest that CO₂-sequestered ECC can achieve >30% CO₂ uptake per cement mass after 24-hour carbonation curing. Carbonation curing increased ECC’s flexural strength by 20% and promoted crack width control capability with maximum post-fatigue crack width being reduced from 128µm to 79µm. The flexural strength of carbonated ECC reached 12.03 MPa, exceeding the American Railway Engineering and Maintenance-of-Way Association (AREMA) requirement of 5.89 MPa for rail seat positive, negative, and center bending tests. Moreover, carbonation curing significantly improved the fatigue life of non-reinforced ECC to pass the standard-required 3 million cycles under flexural loading, with comparable performance to traditional prestressed railroad ties. This eliminates the need for the costly and time-consuming prestressing process for traditional tie production. Carbonation curing can also increase the fatigue life by 20% (under 0.5 stress level) and 12% (under 0.4 stress level). The enhanced fatigue life through CO₂ utilization is anticipated to improve the railroad safety, resiliency, and sustainability, while mitigating CO₂ emissions both at concrete manufacture and through infrastructure lifetime.