A novel chemically bonded phosphate ceramics derived from metakaolin and monocalcium phosphate monohydrate for restoration of stone relics

Choosing proper cementitious material for the restoration of stone relics with high strength is challenging. In this study, a novel chemically bonded phosphate ceramics (CBPCs) was prepared based on acid-base reaction adopting metakaolin (MK) and monocalcium phosphate monohydrate (Ca(H 2 PO 4 ) 2 ·H 2 O, MCPM). The reaction products mainly consist of brushite (CaHPO 4 ·2H 2 O) and phosphorus‑aluminum silicate gel phase. In which, the appropriate amount of brushite can fill the gap in the gel phase, favoring more densified microstructure and higher mechanical performance. Notably, the activated alumina in metakaolin is the key reaction component, and the P/Al molar ratios affect the compositions and properties. Besides, the physicochemical properties of the product are comparable to stone matrix. Further, the concentration of the undesirable soluble salt ions is less than 7 % of ordinary Portland cement, which can effectively avoid salt damage and guarantee the applicational safety of the stone relics.