Although the absence of portland cement (PC) in alkali-activated slag (AAS) lowers its carbon footprint, conventional alkaline activators like sodium silicate are expensive and have large environmental impacts. Soda solid waste (SSW) is an alkaline waste of the glass industry, and its disposal poses environmental problems. This study investigated the use of SSW to activate ground slag at 60 degrees C-120 degrees C. Strength development of mortars and heat evolution of pastes were evaluated. Hydration products were studied using X-ray diffraction and thermal analysis. Strength gain, rapid in the first 3-7 days, is attributed to formation of amorphous phases and partly crystalline calcium silicate hydrate (C-S-H). Increasing SSW content causes a weaker and broader rate of heat evolution peak in the first few hours and evolves greater total heat in the first day. SSW-activated slag pastes evolve significantly less heat up to 7 days than a typical room-temperature-cured PC paste but similar when heat is normalized by compressive strength. Mortars containing 40% slag and 60% SSW reach similar to 20 MPa after 7 days of curing at 120 degrees C. (c) 2019 American Society of Civil Engineers.