**Sung Choi 1, Gum-Sung Ryu 2,\*, Kyeong-Taek Koh 2, Gi-Hong An <sup>2</sup> and Hyeong-Yeol Kim <sup>2</sup>**


Received: 5 September 2019; Accepted: 28 September 2019; Published: 11 October 2019

**Abstract:** In this study, a calcium sulfoaluminate-based expansive additive (0%, 2.5%, 5.0%, and 7.5% by the mass of the binder) was added to compensate for the shrinkage of alkali-activated material (AAM) mortar. Modulus of elasticity curves based on the ACI 209 model were derived for the AAM mortar mixed with the additive by measuring the compressive strength and modulus of elasticity. Moreover, autogenous shrinkage and total shrinkage were measured for 150 days, and drying shrinkage was calculated by excluding autogenous shrinkage from total shrinkage. For the autogenous and drying shrinkage of AAM mortar, shrinkage curves by age were obtained by deriving material constants using the exponential function model. Finally, shrinkage stress was calculated using the modulus of elasticity of the AAM mortar and the curves obtained using the shrinkage model. The results showed that the calcium sulfoaluminate-based expansive additive had an excellent compensation effect on the drying shrinkage of AAM mortar, but the effect was observed only at early ages when the modulus of elasticity was low. From a long-term perspective, the shrinkage compensation effect was low when the modulus of elasticity was high, and thus, shrinkage stress could not be reduced.

**Keywords:** alkali-activated material; calcium sulfoaluminate-based expansive additive; concrete shrinkage; modulus of elasticity; shrinkage stress
