Abstract:
The presence of MgO is a problem in lime, as it has slower hydration with marked swelling. But when in aggregate MgO is not in free form, but combined with other elements such as silicon and calcium in the crystal lattice of the mineral constituents of the rock. Thus the presence of MgO is not indicative of any aggregate performance problem in concrete. The only situation in which the MgO content is relevant occurs when applying the standards of Canada and the USA for assessing the potential for alkali-carbonate reaction. For this application, limited to limestone, the ratio of the CaO and MgO contents is compared with the percentage of Al2O3 in a graph divided in areas where the aggregate is considered potentially expansive or not. This approach, although has the advantage of speed in getting the results should be applied only in limestone, which is a sedimentary carbonate rock and should not be used in aggregate carbonate metamorphic origin, such as marbles. For silicate aggregates as granites, gneisses and basalts determining the MgO content is useless. There is no practical need for determining Mg or MgO levels for the majority of Brazilian aggregates. When more in depth studies of the aggregate are carried out, the important thing to know is what are de the Mg bearing minerals, because the mineralogy is the key factor to any kind of pathology related to the aggregate.
Reference:
QUITETE, Eduardo Brandau; LEAL, Priscila Rodrigues Melo; SANTOS, Rafael Francisco Cardoso dos; BALI, Mikaella; MEDINA, Gabriel Sapata Soares. A relevância da presença de magnésio em agregados. In: CONGRESSO BRASILEIRO DO CONCRETO, 58., 2016, Belo Horizonte. Anais… 8 p.
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