1. Introduction
Blast Furnace Slag is a by product of the steel industry. It is defined as “the non-metallic product consisting essentially of calcium silicates and other bases that is developed in a molten condition simultaneously with iron in a blast furnace” [1]. It results in the production of gas compounds (blast furnaces gas), of liquid (slag cast-iron), and of solid (gas dust). The granulated blast furnace slag may be used to make blast furnace slag cement either by being interground with the Portland cement clinker or by grinding the blast furnace slag separately and then blending it with cement. Each ton of cast-iron is necessarily followed up by a certain quantity of slag, which is variable according to the nature of the product fed in the kiln whether it is ore or combustible. This slag gathers in a liquid form of residual ore element in addition to gas and gas dust: such elements originate from ore gangue, fuel dust, or flux additions of a siliceous, calcareous or magnesium nature. The quantity of slag taking shape varies between 300 and 900 kg per ton of cast-iron in proportion according to the richness of ore content. The floating slag in a liquid state splits under the melting iron-cast gravity is evacuated through a casting hole [2]. El Hadjar’s plant produces around 380 kg of slag per ton of cast-iron.
Following the method of solidification applied, the following products are obtained:
Vitrified slag, as a result of sudden cooling (by tempering), using water pressure leading to granular of a size varying between 0 and 5 mm.
Crystallized slag obtained through a slow air-cooling is a hard angular rubbing rock.
Construction industry is one of the areas of solid wastes can be used in large quantities. Especially large amounts of natural resources are used in concrete production. In addition, the production of Portland cement which is a basic component of concrete causes the greenhouses gases production which causes global warming and climate change [3].
Mechanically activated granulated blast furnace slag was used in the range of 20% - 75% to replace clinker in Portland slag cement. The slag and clinker were activated separately using a mill and mixed to prepare cement formulations [4].
Use of activated slag resulted in a remarkable increase in strength vis-à-vis slag cement. Both 2-day, 28-day and 90-day strength were found to increase with an increase in slag content up to 75%. The strength of the sample containing 20% - 75% slag was comparable to the commercial cement used as a reference. It was observed that mechanical activation of slag was more critical from the point of view of strength development.
2. Experimental Program
The main objective of this work is the characterization of the granular slag blast furnaces from El Hadjar, located in eastern Algeria, using various techniques [5,6] and its investigation in order to utilize it as a basic component of cement. This is achieved through a chemical analysis, which allows the calculation of hydraulic indices, X rays diffractometry, thermal analysis, spectrometry, and conductimetry. The binding formula on a weight basis is as follows:
X1% slag + (100 – X1)% clinker + 5% gypsum By varying:
The slag grinding degree such (2000 cm2/g, 3750 cm2/g and 6000 cm2/g).
The slag content such (20%, 30%, 40%, 50%, 60%, 80%).
The nature of the clinkers by using cement products used by the ERCEst (company of cement industry in Algeria).
The mechanical performances have been estimated by the use of the 4 × 4 × 16 cm3 mortar prisms.
3. Characterization of the Constituents
3.1. Slag Chemical Analysis
Slag is primarily made up of silica, alumina, calcium oxide, and magnesia. The exact concentrations of elements vary slightly depending on where and how the slag is produced.
When cement reacts with water, it hydrates and produces calcium silicate hydrate (CSH). When blast furnace slag is added to the mixture, it also reacts with water and produces CSH from its available supply of calcium oxide and silica. A pozzolanic reaction also takes place which uses the excess SiO2 from the slag source, Ca(OH)2 produced by the hydration of the Portland cement, and water to produces more of the desirable CSH making slag a beneficial mineral admixture to the durability of concrete [7]. Table 1 presents the chemical composition of the slag used in the present study.
3.2. Basicity Module
The calculation of the basicity module “p” can be obtained by applying the following formulas [3,4].
The symbol values are as follows:
C = %CaO; S = %SiO2; A = %AL2O3; M = %MgO P1 = C/S = 1.03 P2 = (C+M)/S = (37.22 + 3.55)/35.84 = 1.13 P2 = 1.13 We notice that: P1 > 1, P2 < 1.5.
So, the slag in question is basic which makes it appropriate for a possible use in the cements.
3.3. X Rays Diffraction
The vitrified slag diffractograms shows a diffuse area, which characterizes the vitreous phase as well as a few low intensity rays that constitute the crystallized components. Figure 1 illustrates fairly well that the identified major crystalline phase corresponds to carbonates (CaCO3), which confirmed by infrared analysis.
3.4. Infrared Spectrometry (IRTF)
Figure 2 shows the slag infrared spectrums for different specific blaine surfaces. The spectrum 1, 2, and 3 correspond respectively to specific Blaine surfaces of 2000 cm2/g, 3750 cm2/g and 6000 cm2/g. The spectrum shows identified bands such as the Ca-O, Si-O and the presence of carbonates characterized by the 876 cm–1. The peak determines this band, which tends to lose its shape and intensity in proportion to the increase of the Blain slaggrinding rate.