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The hydration of High alumina Cement (HAC) in the presence of sodium polyphosphate (sodium hexametaphosphate -Na6P6O18) was investigated under normal and hydrothermal condition. Reference sample and modified one were submitted to long-term hydration (365 days). It was found out that sodium hexametaphosphate has increased the compressive strength. The main hydration products of HAC (C3AH6 and gibbsite) were found stable over time. However, when submitted to hydrothermal curing conditions of 20 bars (corresponding to 220 °C) during 7 days, binder has lower compressive strength values, but increasing with time. Thermal analysis method, X-ray diffraction and Scanning electronic microscopy were used to characterize the reaction products. Under hydrothermal curing (220 °C/ 20 bars), the main hydration products were hydroxyapatite (Ca5(PO4)3OH) and nordstrandite (A(OH)3), known as chemically bond ceramics formed by acid-base reaction between HAC and sodium hexametaphosphate.
Palou et al. (Fri,) studied this question.