Low-carbon cementitious paving systems with ladle furnace slag and fine recycled aggregate: a multi-scale experimental study

Reusing and recycling wastes and byproducts in construction materials is seen a circular economy practice efficient to preserve natural resources and address environmental issues. Cement-base urban architectural pavements -extensively used in cities- are the focal point of attention of this research due to the elevated CO2 footprint of Portland cement (PC) production, and the massive consumption of natural resources. In this context, ladle furnace slag—an industrial byproduct of refining/secondary steel treatment—, limestone powder, and fine recycled aggregate derived from construction and demolition waste have been incorporated in the cementitious matrices to examine the feasibility of producing paving blocks. The literature review indicates a lack of comprehensive research on the simultaneous replacement of both cement and natural aggregates in paving applications using ladle furnace slag and fine recycled aggregates. Mechanical performance and drying shrinkage of matrices with various slag dosages (50–75¿%) and sizes up to 2¿mm were characterized in laboratory. Further, the weathering resistance of the samples was characterized through water absorption and accelerated wet-dry cycles. Microstructural and chemical analysis techniques, including SEM, BSEM, XRD and XRF, were applied to complete the tests. Taking as reference 100¿% PC paving blocks produced by vibro-compaction in industrial facilities, the samples with 50¿% slag as PC substitution achieved 28-day average compressive and flexural tensile strengths of 11.4¿MPa and 5.8¿MPa, respectively. These represent a 55¿% and 30¿% reduction respect to the reference samples. The 50¿% slag sample exhibited ~15¿% higher water absorption than the control, with no strength degradation after wet-dry cycles. These results allowed concluding that this low-impact material—achieving approximately 45¿% and 25¿% reductions in embodied carbon and energy, respectively, compared to the control—can be used for urban paving in areas with moderate service loads, such as pavements designed for light-load vehicles or pedestrians.

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