Guidelines for Use of Iron, Steel and Copper Slag in the Construction of Rural Roads
2018 Edition

The recommended proportions for incorporating copper slag into embankments include mixing 10% to 75% by weight of copper slag with local soils—whether clayey, expansive, or non-expansive—and similarly 10% to 75% with fly ash or other waste materials. Laboratory testing to optimize these mixes is essential to ensure they meet design requirements such as Plasticity Index (10-20), adequate dry density, and CBR values specified by MoRD. Fly ash should be sun-dried and conditioned to 1-2% moisture before blending to minimize dust. These mixtures enhance gradation, compaction, shear strength, and bearing capacity, ensuring stable embankment performance.

Mechanical stabilization of copper slag addresses its natural lack of cohesion and poor grading by blending it with local soil or pond ash, resulting in improved particle distribution, higher dry density, and increased shear strength (cohesion and friction angle). This process elevates the California Bearing Ratio (CBR), essential for embankment stability. Additionally, stabilization helps maintain Plasticity Index below 45, complying with MoRD standards. Incorporating 3-6% cement can further stabilize mixes containing up to 75% copper slag, achieving Unconfined Compressive Strengths of 1.7 MPa for sub-base and 3 MPa for base layers. Laboratory evaluations of 7-day cured samples ensure design compliance, producing durable, compactable materials suitable for embankment construction.

Key properties of slags pertinent to pavement applications include high specific gravity (copper slag: 3.2-3.6; steel slags: approximately 3.3-3.5; blast furnace slag: 2.45-2.65), low loss on ignition, and chemical compositions featuring significant Fe2O3 (40-45% in copper slag), SiO2 (28-35%), Al2O3, CaO, MgO, and controlled sulfur content. Engineering properties such as water absorption (1-7%), dry and wet strength (ranging from about 130 MPa for blast furnace slag to over 400 MPa for steel slags), abrasion resistance, polished aggregate friction values (around 53-63), and soundness tests confirm durability and skid resistance. These characteristics make the slags suitable as aggregates in base and sub-base pavement layers, providing strength, stability, and environmental compatibility.

Steel slags, including Basic Oxygen Furnace Slag (BOFS), Electric Arc Furnace Slag (EAFS), and Air Cooled Blast Furnace Slag (ACBFS), are recommended for bituminous surface courses. Blast Furnace Slag (GBFS) is generally unsuitable for bituminous layers. Copper slag is limited to coarse or combined fractions and should not be used in fine form for bituminous pavements. Slag aggregates should replace 15-20% of fine aggregates in mixes. The gradation requirements must comply with MoRD Table 500.4, which specifies percentage passing ranges for sieve sizes from 20 mm down to 0.075 mm to ensure proper particle distribution. Additionally, binder content should be increased by 0.5% compared to normal specifications due to the vesicular texture of slag aggregates, promoting better adhesion and durability.

Quality control for slag-based pavement materials includes several critical tests: Iron unsoundness tests are conducted when FeO content exceeds 3% and sulphur content is over 1%, involving immersion of sample particles in distilled water for 14 days with acceptance criteria that less than 1% show disintegration or cracking. Volumetric expansion ratio tests limit swelling to 2% to prevent instability. Free lime content is monitored using petrographic or X-ray diffraction methods, especially for new slag sources, requiring weathering if free lime is excessive. Additional tests per IS:383-2016 include assessments of particle shape, density, strength, abrasion resistance (ASTM D6928), polished aggregate friction (ASTM D3319), sodium sulphate soundness (ASTM C88), and maximum dry density and optimum moisture content per IS/IRC standards. These tests ensure that slag materials meet the mechanical and durability requirements for safe, long-lasting pavement construction.