Self-cementitious property of steel slag powder blended with gypsum

• The self-cementitious property of steel slag with 5 wt% gypsum was revealed.
• The hydration and hardening properties of steel slag-gypsum and cement are compared.
• The hydration products of steel slag-gypsum are different from pure steel slag.
• The hydration degree or strength with ages conforms to a functional relationship.

In order to reveal the self-cementitious property of steel slag, the hydration and hardening characteristics of steel slag powder blended with 5 wt% gypsum were investigated from hydration heat, non-evaporable water (Wn) and Ca(OH)2 contents, hydration products, strength and so on. The results show that the hydration process of steel slag-gypsum also has two exothermic peaks, which is similar to cement, but it has a longer early hydration period and lower hydration exothermic rate. The second exothermic peak value of steel slag-gypsum is only about one eighth of that of cement. The hydration products of steel slag-gypsum mainly contain amorphous C-S-H gels, rod-like ettringite and a small amount of Ca(OH)2, while almost no ettringite is generated in hydration products of pure steel slag. Compared with pure steel slag paste, steel slag-gypsum paste has a more hydration products and more compact structure. The relationships of Wn contents or Ca(OH)2 contents with ages for steel slag-gypsum paste show a good exponential relationship, while both the paste and mortar strengths of steel slag-gypsum with logarithm of ages conform to the linear relationship. In addition, the Wn content and strength of steel slag-gypsum paste can be obviously improved by the simulated cement pore solution at 28 days and 90 days.