Mechanical, Durability, Carbon Footprint, and Economic Assessment of Sand-Gravel-Gneiss Aggregate Mixtures for Sustainable Road Construction.

This study evaluates the influence of different crushed gneiss contents on the mechanical, durability, environmental, and economic performance of sand-gravel/gneiss mixtures for sustainable road construction. Natural sand-gravel aggregate was blended with crushed gneiss at three proportions (10%, 30%, and 50% by mass). The experimental program included grain size analysis, compaction characteristics, California Bearing Ratio (CBR), deformation modulus, and freeze-thaw durability tests. Environmental performance was assessed using a cradle-to-site carbon footprint approach based on Life Cycle Assessment principles according to ISO 14040, ISO 14044, and ISO 14067, with the analysis focused on Global Warming Potential (GWP100), combined with a Total Cost of Ownership analysis. Increasing gneiss content improved mechanical performance, with CBR increasing from 45% to 95% and deformation modulus from 110 to 185 MPa. The 70/30 sand-gravel/gneiss mixture provided the most balanced performance among the investigated compositions, combining high bearing capacity, satisfactory freeze-thaw resistance, and favorable environmental and economic characteristics. Its carbon footprint was 3.90 kg CO2 eq./t, with diesel consumption during aggregate handling identified as the dominant emission source (69%), followed by gneiss transportation (20%) and electricity consumption (12%). Higher gneiss contents and longer transport distances increased environmental impacts and production costs. The results indicate that selecting an appropriate aggregate composition and reducing transport-related emissions can support lower-carbon construction materials while maintaining required engineering performance.