History of Magnesium in Hydraulic Cements

Fortunately there is a history of magnesium in hydraulic cements and this is helping TecEco overcome dogmatic hurdles such as standards.

Magnesium has been found in high percentages in many Roman concretes, and it is thought to have got there either as a contaminant in the lime that was burnt or contained in Pozzolan which is a siliceous volcanic dust containing on analysis essentially iron oxide, aluminium oxide, calcium oxide and magnesia and deriving its name from Pozzuoli, near Naples, where it was first utilized and afterwards found in great beds on the Roman Campagna. It was never deliberately added to our knowledge.

Roman cements containing magnesium are stronger and more enduring. According to the classic encyclopedia based on the Britannica of 1911[1], "Cements containing magnesia are pronounced both by Vicat and Chatoney to resist the dissolving action of sea-water better than those in which no magnesia is present, and it is pretty well established by experience that cements derived from argillo-magnesian limestones furnish a durable cement for construction in the sea."

The cements referred to by Vicat and Chatoney were calcined with magnesia included. It is important to note that TecEco cements and in particular our Tec-Cement require the later addition of a highly reactive form of magnesia and are not thus not anticipated by Roman prior art in which the magnesia was calcined along with the lime or argillaceous lime.

The early American experience with magnesium in cements was similar to that of the Romans. For most of the 19th century and more than half of the 20th, natural cement from Rosendale New York state, USA was a prominent binder used in the construction of many buildings, monuments and structures (See links on Rosendale cements). The Rosendale natural cement was rich in magnesium because the rock from which it was made was a dolomitic limestone. On analysis Rosendale cements contain 14-30% magnesium determined as the oxide present mainly as brucite, carbonates of magnesium and iron like sjoegrenite and biotite. The magnesium minerals have resulted in extreme durability and this has caught the attention of many modern researchers such a Laura Powers[3].

Rosendale cements were made in shaft kilns and the periclase that formed was generally sufficiently fine grained to hydrate rapidly enough so that dimensional distress was not an issue although sometimes problems occurred[4]. Around 1937 Rosendale cements were considered so good than "every road built of concrete in New York State had to have one bag of Rosendale cement to every three bags of Portland cement."[5].

The Chinese have also been using magnesia in concretes, particularly for Dam manufacture since the 70’s. The type of magnesia used is much less reactive than recommended by TecEco and no more that 5% is added. The Chinese strategy was to match the expansion from the delayed hydration of the finely ground periclase they used with the drying shrinkage in large structures and at this they have been very successful.[2] See also The Use of MgO by the Chinese.

Magnesium minerals are also present in most ground granulated blast furnace slag, are in a form which does not cause dimensional distress and that adds to the durability of concrete. See Other Magnesium Minerals in Concretes

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