*Article* **Experimental Study on the Effect of Compound Activator on the Mechanical Properties of Steel Slag Cement Mortar**

**Junfeng Guan <sup>1</sup> , Yulong Zhang <sup>1</sup> , Xianhua Yao 1,\* , Lielie Li <sup>1</sup> , Lei Zhang <sup>2</sup> and Jinhua Yi <sup>3</sup>**


**Abstract:** In this study, activator, metakaolin, and silica fume were used as a compound activator to improve the activity of steel slag powder. The influence of activator, steel slag powder, metakaolin, and silica fume on the resulting strength of steel slag cement mortar was investigated by orthogonal experiments. For four weight fractions of steel slag powder (10%, 20%, 30%, 40%), the experimental results indicate that the compressive strength of mortar can reach up to more than 85% of the control group while the flexural strength can reach up to more than 90% of the flexural strength of the control group. Through orthogonal analysis, it is determined that the activator is the primary factor influencing the mortar strength. According to the result of orthogonal analysis, the optimal dosages of activator, steel slag powder, metakaolin, and silica fume are suggested. The GM (0, *N*) prediction model of compressive strength and flexural strength was established, and the compressive strength and flexural strength of mortar with the optimal dosage combinations were predicted. The prediction results show that by using the optimal dosage combination, the mortar strength can reach the level of P·O·42.5 cement. Considering the different strength and cost requirements of cementitious materials in practical engineering, the economic benefits of replacing cement with steel slag powder activated by compound activator in various proportions and equal amounts were presented. The results show that the method proposed in this study can reduce the cost of cementitious materials.

**Keywords:** steel slag powder; compound activator; mortar strength; orthogonal experiment; GM (0, *N*) model
