Understanding Type IL Cement
Type IL cement (ASTM C-150), also known as Portland-Limestone Cement (PLC), is produced using a similar process to the production of ordinary portland cement (OPC), with some modifications to incorporate limestone as a supplementary cementitious material (SCM). The entire production process consists of crushing and grinding limestone, clay, shale, and other raw materials, and carefully proportioning them to achieve the desired chemical composition of the cement. The raw mix is fed into a rotary kiln, where it undergoes high-temperature calcination (exceeding 1400 C). This process results in the formation of clinker, a chemical reaction responsible for the release of carbon footprint (CO2). The increase in raw limestone in Type IL cement results in a reduction of clinker, which leads to a significant reduction in carbon footprint, estimated to be around 10% compared to OPC.
Durability and Cost Benefits
Research studies have demonstrated the superior durability of concrete pavements constructed with Type IL cement. Incorporating limestone as an SCM enhances resistance to sulfate attack and alkali-silica reaction, common causes of deterioration in concrete structures. The use of Type IL cement in concrete pavements has also been associated with lower permeability compared to OPC. This reduced permeability helps prevent the ingress of moisture and harmful substances, thereby enhancing the durability of the pavement structure.
While initial costs may vary slightly, the long-term economic benefits of Type IL cement in concrete paving are substantial. The enhanced durability of pavements leads to reduced maintenance requirements and lower life cycle costs. A study developed by the Federal Highway Administration (FHWA) determined that the use of Type IL cement, when used appropriately, has the potential to increase cost savings over the lifespan of the concrete pavement, making it a cost-effective solution for transportation agencies and infrastructure owners.
Performance Challenges and Recommended Strategies
While the incorporation of Type IL cement provides many durability and environmental benefits for concrete pavements, there have been reports of some performance issues associated with setting time and workability. Variations in setting time lead to challenges for concrete paving operations that require precise scheduling and coordination. Similarly, concrete mixtures containing Type IL cement may exhibit different workability characteristics compared to OPC, impacting placement and finishing processes. There also exist concerns associated with its long-term performance during freeze-thaw cycles, extreme hot weather conditions, and other environmental stressors.
There has been, however, many recorded adjustments in construction practices and techniques that can help mitigate those issues. Engineers and concrete producers can optimize mix designs by proportioning aggregates and incorporating chemical admixtures to achieve desired workability and setting time while maintaining performance standards. Quality control measures and regulatory testing, of fresh and harden concrete, are essential to ensure compliance with project specifications and performance requirements. Continuous monitoring and evaluation of concrete pavements constructed with Type IL cement are crucial to assess their long-term performance and durability. And, proactive maintenance practices, already performed in conventional concrete pavements, can help extend the pavement service life and mitigate deterioration.
Industry Adoption and Future Outlook
The adoption of Type IL cement in concrete paving projects is steadily increasing, driven by a combination of environmental initiatives, regulatory mandates, and cost considerations. Major paving projects, such as highway expansions and airport runways, are increasingly specifying Type IL cement to meet sustainability goals. The Cement Council of Texas has been actively involved in promoting sustainable construction practices, including the use of Type IL cement, in various paving projects. Additionally, as sustainability initiatives continue to grow, more projects incorporating alternative cementitious materials are likely to emerge.
Conclusion
Type IL cement holds immense promise for advancing sustainability in concrete paving applications, offering a viable alternative to ordinary Portland cement with reduced environmental impact (about 10% reduction in CO2). However, its utilization comes with inherent performance challenges that demand careful attention and proactive management. By leveraging optimized mix designs, rigorous quality control protocols and testing, and adherence to best practices, stakeholders can overcome these challenges and pave the way for a more sustainable infrastructure.
References
Cement Sustainability Initiative (CSI). "Life Cycle Inventory of Portland Cement and Concrete." World Business Council for Sustainable Development, 2017.
Shi, C., et al. "Alkali–silica reaction mitigation by limestone in blended cements." Cement and Concrete Research, vol. 32, no. 6, 2002, pp. 943-947.
Bentz, D.P., et al. "Influence of limestone on the hydration of Portland cements." Cement and Concrete Research, vol. 34, no. 1, 2004, pp. 127-131.
Ghafoori, N., et al. “Long-Term Performance of Concrete Pavements with Portland Limestone Cement.” Journal of Materials in Civil Engineering, vol 30, no. 1, 2018, doi:10.1061/(ASCE)MT.1943-5533.0002053.
Federal Highway Administration (FHWA). "Evaluation of the Use of Portland-Limestone Cement in Concrete Pavements." FHWA-HIF-16-012, 2016.
American Concrete Pavement Association (ACPA). “Sustainable Concrete Pavements: A Manual of Practice.” ACPA, 2020.
