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This paper proposes the induction of an acid-base reaction during the formation of silico-aluminophosphate (SAP) geopolymer. Such reaction is promoted by dead burnt magnesia (DBM) and phosphate activating solution to synthesize a DBM-doped silico-aluminophosphate (DBM-SAP) geopolymer with enhanced early-age properties. The reaction mechanisms and chemistries between DBM and mono-aluminum phosphate (MAP) in aqueous solution were firstly investigated at four Mg/Al ratios. Conductivity and pH evolutions of the solution systems, in addition to X-ray diffraction (XRD) and scanning electron microscopy (SEM) results of the final precipitations indicated that the crystalline phase (i.e., Newberyite) started to precipitate at a pH of 3 approximately. Besides, the reaction between DBM and MAP produced an amorphous aluminum magnesium phosphate (Al₂O₃·3MgO·2P₂O₅) phase. The rate of such …