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. The correct borehole diameter is important to guarantee the feasibility of the insertion of the anchor equipped with sock, couplers and feed pipes and, at the same time, the working principle of the anchoring system; the adherence surface is strictly influenced by the drilling diameter.
Assembling and installing
After drilling works it is necessary to insert, inside drilled boreholes, the special Bossong plastic sleeves BOS-TP, of the correct diameter, in order to make the insertion of anchors easier and to avoid the re-drilling work in case of boreholes obstruction. The anchors, supplied with the special sock, are assembled on site, if required lengths are over the transport limits, and then installed inside the holes. The connection between the different parts is obtained with full strength couplers and special turnbuckles in case of tendons designed to contain the drift of pushing elements such arch and vaults.
The special grout is a mixture especially designed to be injected into the fabric sock; the pre-packed product that consists of a binder added with different graded aggregates, when mixed with water, produce a pumpable grout that exhibits good strength without shrinkage. After mixing, the grout is introduced in a into a pressure pot with pressure limits between 3-5 bars: the admissible grouting pressure has to be adjusted according to the state of the masonry and the effective anchor’s length. The injection is done gradually until the anchor is fully injected.