Case Studies of Thaumasite Formation


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Title: Case Studies of Thaumasite Formation

Author(s): H. Justnes and E. Rodum

Publication: Special Publication

Volume: 234


Appears on pages(s): 521-538

Keywords: chloride; concrete; deterioration; guano; manure; seawater; thaumasite

Date: 3/22/2006

Condition survey of cementitious composites serving under three widely different environments revealed that thaumasite; Ca3Si(OH)6(SO4)(CO3) 12H2O, had contributed to the general degradation of the material. The first case was a concrete beam from a manure cellar at a farm. There was severe degradation of the outer parts due to sulfate attack under conditions of high degree of water saturation. The binder was cracked and substantial amounts of thaumasite were identified. The source of carbonate for the thaumasite formation may be carbonation or urea-cement interaction, while the required sulfate comes from the manure as such or oxidized sulfides. The second case was a bridge where seagulls have nested on the lower I-beam for a few years. It was heavily polluted by guano from the birds containing chlorides, phosphates, sulfates and nitrogen compounds (urea, nitrates etc). Degradation of the microstructure started in the outer layers with deposition of a number of odd compounds along with thaumasite. The third case was a cooling water pipe made of asbestos reinforced cementitious binder (no aggregate). The cooling water was seawater and the 30 years old tubes had started to break occasionally when pumps were started. About 15 mm of the totally 36 mm wall thickness was affected chemically by seawater from both sides. Thaumasite layers were found parallel with the tube length along with cracks. The sulfate source is likely to be seawater.