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Characterization of the reactivity of mineral additions by different microstructural and mechanical approaches

Bouglada M. S., Naceri A., Baheddi M.

Mining Science

2018

Vol. 25

129--146

This paper presents an experimental study aimed at evaluating the reactivity of natural and industrial local mineral additions (pozzolan, slag and limestone) by different microstructural and mechanical approaches. Binary, ternary and quaternary cement compositions were prepared with partial replacement of the clinker by additions limited to 20%, according to CEM II / A cement specifications. The reactivity during the hydration process is characterized by the hydraulic power of the additions to react with the water and the hydrates of the cement and the pozzolanic capability of fixing the portlandite to form new mineral phases which contribute to the resistance as much as the hydrated products of cement. An experimental methodology was established for the reactivity illustration of the additions by a microstructural approach based on a study of the physicochemical and microstructural properties realized by X-ray diffraction (XRD), the scanning electron microscopy (SEM) on pastes. Further, thermogravimetric analysis (TGA), mercury microporosity (MIP) on mortars at 28 days of age was performed. A mechanical approach based on compressive strength at 2, 7 and 28 days to determine the activity index according to ASTM C 618 has been undertaken. The results obtained show a good correlation between the microporosity, X-ray diffraction and the resistance activity index, in particular for the slag, as for the thermogravimetric analysis that clearly confirms the pozzolanic activity of the pozzolan addition. As for mechanical performance, a binary mortar with 20% slag showed a better compressive strength at 28 days (49.40 MPa) with a reactivity index (87.90%) compared to the control mortar. Further, the slag developed better resistance (49.53 MPa) in combination with the other additions for quaternary mortars (pozzolan, limestone and slag) with an optimal rate of 5, 5 and 10%, respectively. Nevertheless, the pozzolan showed better compressive strength values compared to the slag for the binary mortars at young age 2 and 7 days of 25.67 and 32.07 MPa, respectively.