Rapid and Simple Identification of Free Magnesia in Steelmaking Slag Used for Road Construction Using Cathodoluminescenc
- PDF / 1,201,460 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 85 Downloads / 177 Views
ION
THE reuse of by-products and/or industrial wastes has been tackled aggressively in various manufacturing industries globally to realize an improved sustainability.[1,2] Huge amounts of steelmaking slag, which is a by-product from the conversion of carbon-rich molten iron to steel in basic oxygen and an electric arc furnaces, are produced globally. The reuse rate of steelmaking slag is close to 100 pct in developed countries such as USA, Japan, Germany, and France,[3,4] where almost half of the reused steelmaking slag has been used in road constructions, such as road base and asphaltic concrete.[1,3–6] Steelmaking slag contains free lime (f-CaO) and free magnesia (f-MgO) that can result in volumetric instabilities because f-CaO and f-MgO double their volumes by reaction with water.[7,8] Before it is used for road construction, steelmaking slag is exposed in air for a year or is sprayed with hot water or steam for a week,[9] which is termed aging, to accelerate the hydration reactions of f-CaO and f-MgO. Subsequently, an SUSUMU IMASHUKU, HIROKI TSUNEDA, AND KAZUAKI WAGATSUMA are with the Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Contact e-mail: [email protected]. Manuscript submitted June 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
expansion test is normally performed for aged steelmaking slag by measuring the linear expansion of aging-treated steelmaking slag immersed in hot water for several days in a cylindrical vessel.[9] Only final products with linear expansions below a specified value (e.g., 1 pct in Japan[10]) are used for road construction. However, f-CaO and f-MgO may remain in the aged steelmaking slag that passes the expansion test because the test cannot detect f-CaO or f-MgO directly. The residual f-CaO and f-MgO may create serious problems, such as road expansion and cracking.[6] In particular, f-MgO is the main expansive component in aged steelmaking slag because the hydration reaction of f-MgO occurs much more slowly than that of f-CaO.[9] Therefore, the detection and determination of f-MgO is important to use steelmaking slag for road construction efficiently and safely. Unlike the determination of f-CaO content, no reliable analytical method exists to determine the f-MgO content in steelmaking slag,[9] although several methods have been presented; for instance, selective extraction into a liquid phase followed by analysis of f-MgO (e.g., titration,[11] combined analysis of inductively coupled plasma-atomic emission spectrometry and thermogravimetry[12,13]), 25Mg nuclear magnetic resonance (NMR),[14] and X-ray diffraction (XRD).[11] However, these methods have the following drawbacks: magnesium compounds other than f-MgO may be extracted, several days are required to quantify f-MgO
by NMR, and it is difficult to detect f-MgO with a low crystallinity and quantify f-MgO with a high crystal orientation by XRD. Owing to these drawbacks, even a qualitative method to detect f-MgO rapidly has not been established well. In t
Data Loading...
