The present invention relates to a (meth)acrylic mixture for impregnating a fibrous substrate, characterized in that it comprises: a) a first dispersion comprising at least one (meth)acrylic polymer obtained by emulsion polymerization of one or more (meth)acrylic monomers, b) a second dispersion comprising at least one flame retardant. The invention also relates to a method for impregnating a fibrous substrate with a (meth)acrylic mixture of this kind, and to a method for manufacturing mechanical parts or structured elements, or articles, from the (meth)acrylic mixture. Another objective of the invention is a mechanical part or a structured element or an article made of composite material, obtained by the implementation of the manufacturing method.