The test with double flat jacks assesses the deformability, the elastic modulus and the masonry resistance to compression by means of the load-compression curve.
Two parallel, horizontal cuts of about 3-4 mm are carried out at a distance of about 30 cm on the masonry to be investigated by means of a diamond disk. Then, two oleodynamic, half-oval flat jacks are placed into the cuts. They are properly activated by a manual, oleodynamic pump. Three couples of crack monitoring gauge bases are inserted into the masonry to be investigated. The latters allow to read the dispacements thanks to a crack monitoring gauge.
Once mounted inside the cuts, “pressure is put onto the jacks” by subsequent loading steps thus compressing the part of the masonry being investigated. The pressure from which the cracks start to arise is the masonry maximum compressive tension. Thanks to a crack monitoring gauge, the deformation at the loading steps, which took place following the relative dispacement of the measuring bars, is recorded. Thus, it is possible to get the masonry elastic modulus being investigated as the ratio between the applied pressure increase and the average specific deformation detected at each loading step, for three loading-unloading cycles. The bigger the contrast created by the upper masonry weight is, the more reliable the calculated parameters are.
- Measuring the resistance to monoaxial compression and the masonry elastic properties (elastic modulus) at local level.
ASTM C 1197-91