# Clinker-Free Cement: A New Reality
## 3 Results and Discussions
### Cementitious Mixtures Results  
The results of the specific surface, alkalinity and setting times of the cement mixtures are shown in Figure 1.  
The cement mixtures produced in the study had particles with a specific surface area of approximately 550 m\({}^{2}\)/kg. This ensured that the cement had a similar water demand, as observed in the results of the normal consistency paste, as they all remained within the range of 29%. Although the cement mixtures in this study had particles with a similar specific surface area, the hydration speed resulted, in addition to the cement's fineness, from the solution's alkalinity and the chemical composition of the cement mixtures [5]. The hydration process of these cements relies on the decomposition conditions of the GBFS. It is essential to have an alkaline reaction environment as the slag dissolution occurs through a hydroxyl attack. This environment allows for the dissolution of aluminum, calcium, and silicon ions, to react with the sulfate calcium, forming ettringite, hydrated calcium aluminates, and silicates (C-A-H and C-S-H). In that sense, it has been confirmed (Figure 1A) that the cement blends with BOF slag have higher alkalinity levels when compared to M0. This is due to the high basicity of BOF slag caused by its alkaline oxides. As a result, when these oxides dissolve, the environment becomes more alkaline. The M0 mixture had a low hydration rate, which made it impossible to characterize setting times. The other mixtures, however, performed well within normative limits for CPIIE and CPIII cements, except for M10, which had a longer final setting time than the normative limit for CPIIE, a behavior attributed to the highest content of BOF slag and the slower slag dissolution and hydrated product formation reaction. Figure 1: (**A**) Alkalinity and (**B**) setting times of cement mixtures. Note: The cement mixtures were compared to the standardized Brazilian cement CPIII and CPIIE, which have the highest GBFS content, despite being composed of Portland clinker. The alkalinity influence effect is also noticeable when evaluating the pozzolanic activity of cement blends. The result of the pozzolanic test, exhibited in Figure 2, determined that all cement exhibit pozzolanic behavior, as Ca(OH)\({}_{2}\) is fixed by the formation of C-S-H, reducing the total alkalinity and CaO content in the solution, especially for cements M3, M6 and M10, which demonstrates that the mixtures with BOF slag had greater availability of Ca(OH)\({}_{2}\) to react with the silica from GBFS. The impact of the alkaline activation of BOF slag was also verified through mechanical tests. As shown in Figure 3, the setting time results of M0 are supported by the fact that compressive strength results could not be obtained until after 3 days of curing for the M0 mixture. This is because the specimens did not possess sufficient mechanical resistance to be unmolded. The mechanical performance of cement mixtures, evaluated by compressive strength, is shown in Figure 4 and compares them to the normative limits of cement CP III-32 and CPII E-32 [19], and CSS 32.5 N [20], as these may be considered the normalized types of cement most similar to the mixtures produced. Figure 3: Fragmentation of the specimens during demolding of M0 after 24 h of curing. Figure 2: Pozzolanicity of the pastes of the cement mixtures. Unlike M0, all mixtures containing BOF slag showed the development of mechanical strength at the initial curing ages (Figure 4). Additionally, at all ages evaluated, the cementitious mixtures exhibited a mechanical behavior superior to the M0 cement mixture. The results demonstrate the chemical activating action that the BOF slag provided to the environment through the effect of alkalinity and pozzolanicity.