Reducing Ettringite- and Thaumasiteformation in damaged sulfate containing Masonry

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During the maintenance of sulfate containing masonry still serious mistakes are made today. One reason for this is the fact, that for many of those measures practicable solutions for maintenance are missing. So for example the inserting of water by conventional injections in those masonries does not only show that damaging reaction cannot be stopped, but also lead to less capacity of the masonry. Preliminary tests have shown that it is possible to suppress a further volume expansion by inserting silica acid ester. The silica acid ester will be inserted in its liquid form without adding water, which ensures that neither slide can take place nor loss of resistance will occur caused by a moisture penetration of the sulfate containing material. The exact mechanisms of action of the silica acid ester as well as the essential parameters for its effectiveness are not known yet. It is expected that due to the polycondensation of the silica acid ester reactive silicon is available, which allows the formation of secondary C-S-H phases with the existing calciumhydroxid. They stabilize the structure and reduce the Portlanditcontent (Ca/Si-ratio) of the hydraulic material. As a result of this a higher sulfate resistance is expected. In the work program chemical/mineralogical and physical aspects of the silica acid ester usage are investigated to prepare the use of those materials in practice. The usage of optimized silica acid ester-material on a test object is planned.