*Article* **MSWI Bottom Ash Application to Resist Sulfate Attack on Concrete**

#### **Yongzhen Cheng \*, Yun Dong, Jiakang Diao, Guoying Zhang, Chao Chen and Danxi Wu**

Faculty of Architecture and Civil Engineering, Huaiyin Institute of Technology, Huai'an 223001, China; dyunhyit@hyit.edu.cn (Y.D.); 201861228007@njtech.edu.cn (J.D.); 18351888629@163.com (G.Z.); 201861228005@njtech.edu.cn (C.C.); 201861228010@njtech.edu.cn (D.W.) **\***Correspondence:230139226@seu.edu.cn

Received: 28 October 2019; Accepted: 21 November 2019; Published: 25 November 2019

**Abstract:** This research provides a strategy for partially replacing cement with municipal solid waste incineration (MSWI) bottom ash (BA) to improve the performance of concrete against sulphate attack. Mortar strength tests were performed firstly to evaluate the hydration activity of the ground BA. Concrete specimens were cured in standard conditions and immersed in a solution that contained 10% sodium sulfate. Then, the compressive strength of these specimens was measured to investigate the mechanical properties and durability of the concrete. Next, the capillary porosity of the concrete was determined from the volume fractions of water lost in specimens. Finally, the transport of the sulphate solution in concrete was analyzed using capillary rise, crystallization rate, and solution absorption tests. The results indicated that BA had a certain hydration activity. The equivalent replacement of cement by BA decreased the compressive strength of the specimens but increased the durability of the concrete. There was an excellent correlation between capillary rise height, sulfate solution absorption amount, crystallization rate, and coarse capillary porosity. The addition of BA can decrease the coarse capillary porosity and further slow the capillary transport and crystallization of sulfate solution in concrete. Overall, the replacement of cement with BA can improve the durability of concrete and actualize the utilization of MSWI residues as a resource.

**Keywords:** MSWI bottom ash; concrete; sulfate attack; capillary transport; crystallization
