**Geopolymer Technologies for Stabilization of Basic Oxygen Furnace Slags and Sustainable Application as ConstructionMaterials**

#### **Wei-Hao Lee 1,\*, Ta-Wui Cheng 1, Kuan-Yu Lin 1, Kae-Long Lin 2, Chia-Cheng Wu 3 and Chih-Ta Tsai 4**


Received: 15 May 2020; Accepted: 9 June 2020; Published: 18 June 2020

**Abstract:** The basic oxygen furnace slag is a major waste by-product generated from steel-producing plants. It possesses excellent characteristics and can be used as a natural aggregate. Chemically, the basic oxygen furnace slag encloses free CaO and free MgO, which is the main reason for the expansion crisis since these free oxides of alkaline earth metals react with water to form their hydroxide yields. The objective of the present research study is to stabilize the basic oxygen furnace slag by using innovative geopolymer technology, as their matrix contains a vast quantity of free silicon, which can react with free CaO and free MgO to form stable silicate compounds resulting in the prevention of the basic oxygen furnace slag expansion predicament. Lab-scale and ready-mixed plant pilot-scale experimental findings revealed that the compressive strength of fine basic oxygen furnace slag-based geopolymer mortar can achieve a compressive strength of 30–40 MPa after 28 days, and increased compressive strength, as well as the expansion, can be controlled less than 0.5% after ASTM C151 autoclave testing. Several pilot-scale cubic meters basic oxygen furnace slag-based geopolymer concrete blocks were developed in a ready-mixed plant. The compressive strength and autoclave expansion test results demonstrated that geopolymer technology does not merely stabilize the basic oxygen furnace slag production issue totally, but also turns the slags into value-added products.

**Keywords:** basic oxygen furnace slag; autoclave test; geopolymer technology; expansion behavior; recycling
