Rapid urbanization generates billions of tons of excavated soil waste annually from underground developments, presenting significant sustainability challenges. The objective of this study was to develop a sustainable recycling method for soil waste. Soil waste was calcined to transform its kaolin content into metakaolin. Then, the calcined soil, supplemented with ground granulated blast-furnace slag and uncalcined soil, was used to produce low-carbon alkali-activated construction materials. An optimal formulation of the alkali-activated materials was identified through strength, efflorescence, and microstructure testing, alongside preliminary carbon footprint and economic evaluations. Results showed that alkali-activated calcined soil alone exhibited middle-class strength and a high efflorescence risk. Adding slag altered the alkali-activated products from sodium aluminosilicate hydrate to a coexistence of sodium aluminosilicate hydrate and calcium aluminosilicate hydrate, reducing porosity and refining pore size due to the increased chemically bound water, thus enhancing strength and efflorescence resistance, as well as reducing CO