The bond adhesion strength tests the tensile force per unit area and there are two different stage tests: one is a laboratory pull-off test; the other is a construction site pull-off test. Laboratory Pull-off test Laboratory Pull-off test can test bond adhesion strength for both joint mortar and bedding mortar acting with stone element. The characteristic of the bond adhesion strength is confirming the performance of material in order to achieve continuous pavement structure in horizontal and vertical direction. The minimum requirement of bond adhesion strength for both joint and laying course are stating in BS 7533-7:2010, Clause C2.

Construction site Pull-off test Construction site Pull-off test determines bond adhesion strength between the stone element and the laying course material only and it shall carry out on construction site. The characteristic of bond adhesion strength is confirming the performance of construction in order to achieve continuous pavement structure in the vertical direction. The test follows the theory of BS EN 1015-12 2000: determination of adhesive strength of hardened rendering and plastering mortars on substrates, and DIN 18555 Part 6 1987: Testing of mortars containing mineral binder-determination of bond strength of hardened mortar. The stone element shall be pre-drilled with two 20mm diameter, 70mm depth holes at central surface and each hole should apart 70mm. Then it shall be laid on bedding mortar and isolated by cut bedding mortar around the edge of stone. The bond agent will apply if necessary. A steel base plate shall firmly attach on the surface of stone by expansion screw, and then the pull-off kit shall connect with the steel base. The pressure jig should apply gently and constant load till the test sample fails and the maximum fail load should be recorded from measure gauge. It shall be recorded in kN. The bond adhesion strength is calculated by the maximum fail load dividing the contact area; the unit of shear is N/mm2.