Explanation

Steel slag, an industrial by-product obtained during the pyrometallurgical separation of molten steel from impurities, has diverse applications across civil engineering and agronomy:

– 1. Base road construction (Correct): Due to high mechanical durability, angular friction, and load-bearing capacity, processed slag aggregate is widely used as a sub-base material in highway construction and asphalt pavements.
– 2. Improvement of agricultural soil (Correct): Rich in calcium oxide (CaO), magnesium oxide (MgO), and silica, ground steel slag serves as an effective soil conditioner to neutralize soil acidity, correct pH levels, and supply essential micronutrients to crops.
– 3. Cement production (Correct): Granulated blast-furnace and steel slag can replace clinker in the production of Portland Slag Cement (PSC), reducing kiln emissions and energy expenditure.

Hence, steel slag can be utilized across all three domains — Option D.