Birger Gigla1
1 Dr.-Ing., Full Professor, University of Applied Sciences Lübeck
Mönkhofer Weg 239, 23562 Lübeck, Germany
Keywords: Strenghtening, injection anchor, design, pull-out test, grouting, water absorption.
Abstract. Supplementary injection anchors are used as a repairing-system inside masonry for
transferring tensile-forces that cannot be transmitted by the masonry itself or for new connections.
They have been utilised since the 1920s and are applied within a core philosophy of
minimum intervention. Design recommendations have been developed in Karlsruhe and
Lübeck since 1998. Basic design parameter is the compressive strength of the injected grout.
Recent test series of 50 pull-out tests in laboratory are focussing on the influence of water absorption
and climate exposure. During grouting inside absorptive stone material, a significant
amount of water is extracted through the borehole surface. Hereby, the water/cementratio
is decreased, resulting in a significant stronger compressive strength of the grout body.
The increase of bond strength inside water absorptive stone material might be considered
within the current design recommendations. The paper describes investigations of the bond
strength of injection anchors inside two different stone materials after one year of climate exposure
and the implications for the design recommendations. The design recommendations
are compared to the latest European specifications for the execution of tension tests on geotechnical