The effects of alkali-activated slag on the engineering properties of clayey soil were investigated. The mix proportion parameters were chosen by using Taguchi's experimental design methodology. Four factors (groundgranulated blast-furnace slag content, concentration of sodium hydroxide solution, sodium hydroxide-to-sodium silicate weight ratio and alkaline solution-to-slag weight ratio) were assessed in order to obtain the greatest compaction properties, uniaxial compressive strength and California bearing ratio (CBR). Significant improvements were observed in the mechanical properties (unconfined compressive strength (UCS) and CBR) of the clayey soil with addition of the stabilisers. Optimal values (15% slag content, sodium hydroxide concentration of 6 M, sodium hydroxide-to-sodium silicate ratio of 0•5 and alkaline solution-to-slag ratio of 2•5) increased the UCS of the compound from 8 to 100 kg/cm 2 at 7 d. The excessive addition of alkaline solutions weakened the strength parameters of the soil. The results showed that the most influential factor was the alkaline solution-to-slag weight ratio. The Taguchi method is an effective and suitable experimental method for optimising alkali-activated slag parameters. NotationA alkaline liquid-to-slag ratio M concentration of sodium hydroxide solution R sodium hydroxide-to-sodium silicate solution ratio S ground-granulated blast-furnace slag content 17 Cite this articleDavari Algoo S, Akhlaghi T and Ranjbarnia M (2021) Engineering properties of clayey soil stabilised with alkali-activated slag.