AbstractLarge amounts of waste products have been and most probably will continue to be produced with urbanization, industrialization, and technological developments. The study presented herein is devoted to using blast furnace slag in cement-based composites as much as possible. For this purpose, the mechanical properties and microstructural differences of alkaline (sodium hydroxide and sodium silicate solutions)-absorbed mortars that contain 25%, 50%, and 75% (by mass) ground granulated blast furnace slag were investigated. According to the test results, it was found that a positive effect of sodium hydroxide curing on strength development started to be seen as the slag content in the mortar specimens increased. In addition, in order to see the effect of the curing time, 3-day and 7-day cured mortar samples were kept in air for 25 and 21 days, and then strength tests were conducted. Twenty-eight-day–cured samples had a compressive strength value close to that of samples with 7 days of curing plus 21 days of resting period. In addition, in the case of substitution of ground granulated blast furnace slag (GBFS) in mortar, curing mortar samples in sodium silicate is the most effective way to alter compressive strengths compared with the other curing conditions.