Sustainable roller compacted concrete: integrating ferrochrome slag and reclaimed asphalt pavement with cost and life cycle analysis

This research centres on the complete replacement of coarse aggregates in roller-compacted concrete with ferrochrome slag (FCS) and reclaimed asphalt pavement (RAP) waste aggregates. A total of six mixes, along with the control mix, were formulated containing varying proportions of RAP and FCS and tested for fresh, hardened, and durability properties. Further cost analysis and life cycle assessment were executed to identify the economic and environmental effects of replacing the coarse aggregates with sustainable materials. The mix with 25% RAP and 75% FCS demonstrated mechanical properties similar to that of the control mix, and it reached 37.7 MPa in compressive strength, 4.82 MPa in flexural strength, and 3.65 MPa in splitting tensile strength at 90 days. The 50% RAP and 50% FCS blend satisfied the minimum strength specifications for RCC pavements, with a compressive strength of 33.9 MPa, flexural strength of 3.96 MPa, and splitting tensile strength of 3.17 MPa. The 75% RAP and 25% FCS blend had a 32.3% decrease in compressive strength due to the high RAP content compared to the control mix. On the other hand, the 100% FCS mixture surpassed the control mixture with a compressive strength of 42.4 MPa, a flexural strength of 6.4 MPa, and a splitting tensile strength of 4.57 MPa, highlighting the enhanced mechanical properties of FCS. A Life Cycle Assessment using a cradle-to-gate approach for roller-compacted concrete revealed that incorporating sustainable materials significantly reduced greenhouse gas emissions. The mixes using 100% RAP and 100% FCS as substitutes for natural coarse aggregates achieved a 7.1% reduction in greenhouse gas emissions. The 100% RAP, 100% FCS, and 25RAP + 75FCS blend Global Warming Index (GWI) was 340,441.931 g, indicating a decrease of 6.35% relative to the control mix (363,555.956 g). The 50% RAP + 50% FCS blend had the lowest GWI value of 340,294.525 g, reporting the greatest environmental advantage. The global warming index (GWI) pattern reinforced that incorporating more sustainable material lowered environmental load. From a cost perspective, substituting natural aggregates with RAP and FCS resulted in a 9% saving in material costs compared to the control mix, with all sustainable mixes having the same cost. At the outset, the study uniquely adds value to previous literature by offering a broad understanding of mechanical, durability, economic, and environmental aspects involved in the incorporation of RAP and FCS in RCC pavements, elucidating their potential as good substitute alternatives to the use of natural aggregates.