engleski

Effect of silica fume on the durability of Portland cement mortars exposed to magnesium sulphate attack

The deterioration of concrete structures due to the presence of sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended cements incorporating materials, such are: natural pozzolans, fly ash or silica fume, have an important role in the long-term durability of concrete exposed to sulfate attack. In this work, the partial replacement (2-15 mass %) of commercial bended Portland cement (Type CEM IIA-S 42.5N) with silica fume (SF) is investigated in terms of resistance of SF mortars to magnesium sulfate (MgSO4) solution ( (SO4)2-=2.5% ; exposure time up to 6 months at 20oC). The changes in length of mortars due to expansion, as well as changes in the elasticity modulus and mechanical strengths loss, as a function of silica fume replacement were determined. Structural changes in mortars because of magnesium sulfate attack were also evaluated by the differential thermal analysis (DTA) and by the X-ray diffraction analysis (XRD). Results show that the replacement of SF in most cases has a positive effect on the magnesium sulfate resistance. Mortars containing more than 8 mass % of SF replacement are characterized by a good sulfate resistance and show lower expansion than the control mortar on the basis of the sulfate-resisting Portland cement, due to the absence of the gypsum and ettringite, detected by XRD analysis. It is also shown that elastic modulus is proportional to the compressive strength, but higher compressive strength does not necessary correlate with better durability to sulfate attack.

blended cement; silica fume; sulfate attack; durability; elastic modulus

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