HB 34-1992

This handbook provides information on three methods for the near-to-surface testing of hardened concrete, as follows:(a) Break-off number - by determination of the force required to break off a cylindrical portion from a completed concrete structure by cantilever loading.NOTE: This method is generally applicable to concrete with a maximum nominal aggregate size of 20 mm and a thickness of at least 100 mm, although some users claim satisfactory results have been obtained with a nominal aggregate size of up to 25 mm.(b) Rebound number - by determination of the rebound distance from a concrete surface using a spring-driven steel hammer.NOTE: The testing of concrete by surface hardness methods is not generally recommended except as a useful preliminary or as a complementary method. Hardness measurements provide information in the quality of the surface layer (about 30 mm depth) of the concrete only.(c) Pull-out strength - by determination of pull-out force required to remove an embedded metal insert. Each of these tests can be carried out in the field without the need to remove a sample for laboratory testing.NOTES:1 Additional information on near-to-surface testing of hardened concrete is available in BS 1881, Parts 201 and 207.2 Information on ultrasonic testing of concrete and on the use of the electromagnetic covermeter is available in BS 1881, Parts 203 and 204 respectively.

First published as HB34-1992.