Macrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both 27Al and 31P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO3. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue.

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