Effect and mechanism of nano-Ca10(PO4)6(OH)2 additive on compressive strength of calcium aluminate cement at high temperature

Calcium aluminate cement (CAC) is widely used as a binder for refractory materials, and thus the improvement in compressive strength is of vital importance for CAC applied at high temperature. For this purpose, nano-Ca-10(PO4)(6)(OH)(2) additive with a ratio of 0.5-1.5 mass% was added with the water-cement ratio to be 0.4. X-ray diffraction and isothermal calorimetry analysis demonstrate that nano-Ca-10(PO4)(6)(OH)(2) additive can shorten the hydration process and promote the formation of main hydrates of CaAl2O4 center dot 10H(2)O (CAH(10)) and Ca2Al2O5 center dot 8H(2)O (C(2)AH(8)). In addition, scanning electron microscopy results suggest that nano-Ca-10(PO4)(6)(OH)(2) can protect CAH(10) and C(2)AH(8) from being destroyed during the calcination, guaranteeing that these thin lamellar crystals are intertwined to form the denser microstructure. Benefited from above effects, nano-Ca-10(PO4)(6)(OH)(2) can obviously improve the compressive strength of the CAC mortar samples cured for 7 d after calcination at 1100 degrees C, while the improving effect is dependent upon its contents. Especially, compared with the one without the additive, the compressive strength of the sample with 1.0% nano-Ca-10(PO4)(6)(OH)(2) is increased by 14%.