Cementitious mixtures, compositions for use in cementitious mixtures, and methods of producing cementitious mixtures wherein the compositions are suitable for modifying or improving certain properties of the cementitious mixtures. The compositions include a superabsorbent polymer (SAP) hydrogel having a macromolecular network structure, and at least one pozzolanic material that is chemically incorporated into the macromolecular network structure of the SAP hydrogel.