A study of the tensile strength of concrete across construction joints

In this report are discussed the relative merits of various types of treatment to an existing concrete surface before fresh concrete is placed against it to form a construction joint. Results of tests of the tensile strength of joints made in various ways are given, and they show that, contrary to modern practice, old concrete should be left dry when the new concrete is placed against it. They also show that surfaces cleaned by abrasive methods such as wire brushing and sandblasting, are slightly superior to scabbled surfaces.

The results of a second series of tests are given which show that the age of the hardened concrete at the time of placing the new has little effect on the strength of the joint.