DETAILED DESCRIPTION OF BEST MODE AND PREFERRED EMBODIMENTS OF THE INVENTION More particularly according to the present invention, by the term "cement" are intended compositions comprising the aforesaid first and second constituents, together with, if required, the usual cement additives, and compositions based on said two constituents indicated above and, optionally, conventional cement additives, and also comprising aggregates.
The constituent elements of the phosphomagnesia cement will first be described.
The cements of this invention thus comprise a binder phase including a first, phosphorus based constituent and a second, magnesium based constituent.
Any phosphorus compound can be used, provided that it includes phosphorus pentoxide, either directly or in the form of a precursor thereof.
Exemplary phosphorus based compounds include phosphorus pentoxide, phosphoric acid or derivatives thereof, such as orthophosphoric acid, pyrophosphoric acid, or polyphosphoric acid, or salts of these acids, such as the phosphates, hydrogen phosphates, orthophosphates, pyrophosphates, polyphosphates, tripolyphosphates or tetrapolyphosphates of aluminum, calcium, potassium, magnesium or ammonium, or mixtures thereof.
It should be noted that phosphorus-containing effluents from the fertilizer manufacturing industry or from steelworks (steel pickling, corrosion reduction treatment) can be used as the phosphorus based constituent.
Green phosphoric acid can also be used.
Salts of the phosphorus based acids indicated above are employed in one particular embodiment.
The phosphates and hydrogen phosphates of potassium, magnesium or ammonium, or mixtures thereof, are preferably used.
Ammonium dihydrogen phosphate is the most preferred.
The phosphorus based constituent can be used in either a liquid or solid form.
Preferably, said constituent is used in the solid form.
In a first embodiment, the constituent is in the form of particles, in particular in which the granulometry is at most 300 .
mu.
m.
It will be appreciated that this value is not critical and that, if constituents are used which have a particle size of more than 300
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