W.A.FERGUSON, Building Research Establishment.

The screw pull-out test is being developed to provide a simple, inexpensive method of assessing the quality of both building mortar and units used in masonry. The test measures the shear strength of a small cylinder of the test material by finding the load required to withdraw a helical tie that has been driven into it. The pull-out load is related to the compressive strength of the material. The method appears suitable for materials of strengths ranging from 2 to 10 N/mm2. The system has potential, particularly for determining the compressive strength of AAC blocks, and it is hoped that modifications will enable it to test both units with higher densities and mortars.