Novels patterns of hydration and new compounds in the ternary system of CaO-Al2O3-P2O5

 The patterns of hydrating and solidifying with the compositional variation of phosphorus-rich, phosphorus-calcium-rich and aluminum-calcium rich regions in ternary system CaO-Al₂O₃-P₂O₅ has been studied in detail, and two new ternary compounds L and H have been synthesized here. The results indicate that the region of 48–56% P₂O₅ doesn’t present cementitiousness, which contains mainly crystal phases of β-C₂P(2CaO·P₂O₅), α-C₃P(3CaO·P₂O₅) and AlPO₄; the phosphorus-calcium-rich region of 21–35% P₂O₅ exhibits substantial cementitiousness, which contains mainly crystal phase of α-C₃P and certain amount of CA(CaO·Al₂O₃) and new phases L/H; and the aluminum-calcium-rich region of 8–18% P₂O₅ is full of promise for cementitiousness. It contains mainly new crystal phase L and certain amount of α-C₃P and CA. The hydration and solidification mechanisms have been preliminarily analyzed by means of XRD, XPS and DTA. It appears that crystal phase CA might hydrate directly to the stable phase of C₃A·6H₂O in the phosphorus-rich case of 21–35% P₂O₅; new phase H has the behavior of rapid setting; and L, being a dominant phase, can prevent cement pastes from significant strength loss in long curing cycles. Received: 12 March 1998 / Accepted: 29 July 1998