A prediction study of hydroxyapatite entrapment ability in concrete

✍ Scribed by D.M. Bastidas; V.M. La Iglesia; M. Criado; S. Fajardo; A. La Iglesia; J.M. Bastidas

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 268 KB
• Volume: 24
• Category: Article
• ISSN: 0950-0618
• DOI: 10.1016/j.conbuildmat.2010.04.060

✦ Synopsis

The entrapment ability of phosphates containing OH À , such as hydroxyapatite (HAP) (Ca 5 (PO 4 ) 3 (OH)), was investigated as a means for chloride removal from a concrete pore network solution. The chloride uptake by HAP was found to be very low, of the order of 32-44 ppm after 28 days immersion in a 0.5 M sodium chloride (NaCl) solution at pH 9. A thermodynamic study was performed on the chemical equilibrium of HAP, whitlockite (Ca 3 (PO 4 ) 2 ), and hilgenstockite (Ca 4 O(PO 4 ) 2 ), indicating that the contribution of PO 3À 4 ion activity to the concrete is very low to justify the crystallization of chlorapatite (Ca 5 (PO 4 ) 3 Cl). In contrast, the precipitation of a solid phase such as FePO 4 Á2H 2 O to act as a physical barrier inhibiting steel corrosion is thermodynamically favoured, which means that HAP and other phosphates may be used as a corrosion inhibitors.