Steel 10–4.75?mm were compared to each other to

Steel slag was collected from Electric Arc Furnace (EAF) of a medium scale steel industry, capacity of 360,000 tonnes per annum. It is producing mainly carbon steels, alloy steel, free & semi free cutting steel and stainless steel which is involved in the secondary stage of production.

Steel slag was obtained in the form of lumps or boulders. They were first broken into small pieces by the help of a hammer and then crushed in a crushing machine and sieved through to obtain two fractions of coarse aggregate according to BIS 383:1970 31. The first fraction was 20?mm to 10?mm and the second fraction was 10?mm to 4.75?mm as shown in Fig. 1 and the images of EAF steel slag aggregate are depicted in Fig. 2.

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It was noticed that slag aggregates had a very porous surface texture. The porosity of steel slag was enhanced by the presence of steam and other gases in EAF which resulted in highly porous aggregate 1. Basalt aggregate was used as natural coarse aggregate. The particle size distribution curves of basalt aggregate and steel slag aggregate of the fractions 20–10?mm and 10–4.75?mm were compared to each other to minimize the possible effect of the change of gradation on the properties of concrete and plotted in Fig. 3. The gradation of both natural and steel slag aggregates were found to be within the limits of BIS 383:1970 31.

The chemical compositions of steel slag and basalt aggregate were examined by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer model-S8 Tiger Bruker (Germany) and listed in Table 4. The value of Fe2O3 was found as 3.75%, the lesser value of iron content in steel slag obtained was due to the secondary stage of production of steel.

The amount of free CaO in steel slag was determined according to laboratory testing manual of Ministry of Transportation, Ontario (test method LS-622) 32 and it was obtained as 1.2%. The risk of expansion of EAF slag is negligible when free CaO content is <5% 33. Physical and mechanical properties of steel slag and basalt aggregate were evaluated in accordance with the provisions of BIS 2386 (part I–IV) – 1963 34 and reported in Table 5. Moreover, the slag aggregate were found as light weight aggregate as compared to basalt aggregate as it was obtained from secondary stage of steel production. Steel slag abrasion value was very high i.e.

53.73% (Table 5) because it was highly prone to fragmentation due to its special crystalline microstructure. This favors breakage and exfoliation during the initial mixing process, affecting the properties of the concrete. The water absorption capacity of this fine and powdered steel slag was also measured and reported in Table 5. The Mineral compositions present in the steel slag were determined through X-ray diffraction test and depicted in Fig. 4. The major minerals present in steel slag were dodecacalcium hepta-aluminate (Ca12Al14O33) or also known as mayenite, calcium fluoroaluminate (11CaO.

7Al2O3.CaF2 or C11A7CaF2) and yttrium aluminum garnet (Y3Al5O12). Mineral mayenite is highly reactive and responsible for accelerated hydration reaction.

It reacts rapidly with water and forms 3CaO·Al2O3·6H2O and Al(OH)3 gel with considerable heat evolution and contributes to strength developing phase of concrete 35. Mineral calcium fluoro-aluminate is a component of jet cement. The reactivity of this mineral is also very high like mayenite because of high CaO content leading to rapid hydration and shows rapid setting and early strength of concrete 36. Mineral yttrium aluminum garnet (Y3Al5O12) has no cementing property and it is mostly used in adhesive and coloring agents for enamel, field emission displays, cathode materials for alkaline batteries, pigments for ceramics and glasses; phosphors and electro-luminescent application and for the production of transparent ceramics etc. 37,38.


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