Changes in the phase assemblage of concrete exposed to sea water

• Published in: Cement & concrete composites Vol. 47; pp. 53 - 63
• Main Authors: De Weerdt, Klaartje, Justnes, Harald, Geiker, Mette R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2014
• Subjects: Chloride ingress; Chlorides; Concretes; Cracks; Exposure; ICP-MS; Magnesium; Marine; Phase transformations; SEM–EDS; Slaked lime; TGA; Thermodynamic modelling; Thermodynamic models; XRD; SEM–EDS; XRD; ICP-MS; Thermodynamic modelling; Chloride ingress; TGA
• ISSN: 0958-9465; 1873-393X
• DOI: 10.1016/j.cemconcomp.2013.09.015

In the present study the phase changes in an ordinary concrete standing for 10years in a tidal zone were investigated with a range of techniques. From the exposed surface and inwards different zones had formed. SEM–EDS analysis of a polished section of the surface near region, showed a Mg rich layer with a thickness of 10–20μm, as well as the filling of cracks leading from the surface with a Mg rich phase, most likely brucite. In the outermost 2mm, an increase in the calcium carbonate content was identified by XRD and TGA. In the same zone SEM–EDS analyses indicated enrichment in ettringite and thaumasite. In the first 20mm calcium hydroxide leaching was observed using XRD and TGA. Chlorides appeared to have penetrated up to approx. 70mm from the surface. Part of the chlorides were found to be bound in alumina containing phases and in the C–S–H by SEM–EDS. These experimentally observed phase changes generally agreed with the predictions of a thermodynamic model.