Epoxy 21

There are certainly technical and theoretical reasons determining whether an anchorage should be realized with resin or grout. However, in the practical application it is not so easy to define such limit, because of many factors, such as the compatibility with the original materials or simply feasibility problems during the execution. Significant parameters for choosing the type of anchors are type of substrate anchorage length hole diameter setting time and fixing mode waiting times for the loading of the anchorage The thixotropic consistency of the resin, that is useful to prevent from excessive spreading in the interstices of historical buildings, complicates the deep extrusion stage and limits the anchorage length in comparison with the application where the injection is realized with grouts.

Cooperation with the designer The characteristics of Bossong anchorages are defined on the base of the specific parameters of each single project, as well as the dimensions of the hole they must be embedded in, that depend on the type of material constituting the substrate. The change of information relating to the knowledge of the building’s state of preservation and of the aims of the provided interventions, drawings and pictures, the pattern of cracks and deformations, as well as the design of interventions, are very important to define the type of anchor that better fits the application and also to evaluate the intervention from the economic point of view. Tests in place The need to give to design engineers the possibility of an assessment of the behaviour of injected anchors in a particular application and in a specific setting has lead Bossong to equip its technician with a mobile instrumentation that allows the execution of onsite tests.

The need to begin studies in the field of injection anchors is testified by the stronger and stronger request by the designers for instruments and guidelines for the design of anchors and their application in the strengthening of masonry structures. One of the main aims of research is just that of supplying design recommendations which may be of help for designers and technicians working in this field. Laboratory tests In collaboration with the Civil Engineering Department (DICATA) of the University of Brescia a set of laboratory tests were carried on masonry samples in order to check the capacity of the injection anchors with sock in terms of adherence and mechanical interlocking with the substrate. The execution, during the research activity, of a great number of tests has lead to the definition of parameters that are fundamental for the design of injected anchors with sock, as the bond strength at the steel barinjected grout interface an at the injected groutsubstrate interface.

Bossong anchors are embedded into boreholes made in the masonry to be strengthened through drilling machines with diamond bits, that work only with rotation movement in order to avoid vibration and percussion effects on the masonry. Depending on the type of masonry and on the particular setting of the site drilling works can be done with water or air cooling or with techniques that help to avoid the spread of cooling liquids. The choice of the drilling technique is decisive when works are done in unique and precious settings where painting, ancient plasters and stuccoes are present and have to be saved and preserved. The borehole diameter is designed according to anchors size it is usually about three times the steel bar diameter; the length of the anchor is another parameter to be evaluated for the right choice of the borehole diameter.