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Abstract

A composition of hydraulic cement is disclosed, having low water demand, high strength and low fragility. The cement comprises finely ground Portland cement clinker, calcium sulfate and a dry modifier containing an organic water reducing component in a weight percent ratio of 91 to 97:2 to 7:0.085 to 4, respectively. The clinker particles comprise three fractions, I, II and III chemically bonded with the organic water reducing component and having respective particle sizes: I--0.05 to 10 mkm in a weight percent of 15.3 to 34.3; II--10.1 to 30 mkm in a weight percent of 37.2 to 77.5; III--30.1 to 80 mkm in a weight percent of 4.2 to 19.6; plus a fraction IV--having a particle size more than 80 mkm in a weight percent less than 4.9 and free of the modifier. The calcium sulfate comprises a fraction of particles of a size 0.5 to 15 mkm, free of the modifier. The dry modifier is chemically bonded with the three clinker fractions in the following weight percent quantities: I--0.045 to 1.7; II--0.02 to 2.1; and III--0.01 to 0.2. The modifier includes a hardening accelerator: an alkali sulfate or a gel-former. The water reducing component comprises, for example, water soluble salts of: the condensate with formaldehyde of sulfated aromatic compounds, or sulfated, condensed heterocyclic compounds, or sulfated condensed monocyclic aromatic hydrocarbons, or sulfated condensed polycyclic aromatic hydrocarbons, or a condensate of .beta.-naphthalenesulfonic acid with formaldehyde, or a sulfomethylised melamine resin, or a lignosulfonate, or a lignosulfonate compound modified with a carbamide-formaldehyde resin. The modifier covers the particles of franctions I-III.

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