*2.1. Materials*

In this research, the cement was Class 52.5 ordinary Portland cement (Shan Aluminum Cement Co., Ltd., Shandong, China). Fly ash was Class I fly ash (Shenhua Guohua Shoudian Electric Co., Ltd., Beijing, China). The chemical composition of cement and fly ash was tested according to GBT 176, 2017 "Chemical Analysis Method of Cement" [33], and the test results are shown in Table 1. The coarse aggregate was limestone macadam with 5–20 mm continuous grading. Its apparent density was 2.73 g/cm<sup>3</sup> , its bulk density was 1.48 g/cm<sup>3</sup> , its porosity was 46.7%, and its water absorption was 0.45%. The fine aggregate was river sand, with a fineness modulus of 2.94, apparent density of 2.63 g/cm<sup>3</sup> , bulk density of 1.54 g/cm<sup>3</sup> , porosity of 41.7%, and water absorption of 0.40%. The MgO expansion agent was produced by Wuhan Sanyuan Special Building Materials Co. LTD in China, and its activity was 115 s. The steel fiber was wave shaped steel fiber (SF, Shuanglian Building Materials Co., Ltd., Shandong, China), and its detailed parameters are shown in Table 2. The mix proportions are listed in Table 3.

**Table 1.** Chemical composition of cement and fly ash.



**Table 2.** Basic properties of steel fiber.



### *2.2. Experimental*
