Title: Testing High-Strength Concrete Compressive Strength

Author(s): Michel Lessard, Omar Challal, and Pierre-Claude Aticin

Publication: Materials Journal

Volume: 90

Issue: 4

Appears on pages(s): 303-307

Keywords: caps (supports); compressive strength; eccentricity; tests; grinding (materials removal); high-strength concrete; test equipment; Materials Research

DOI: 10.14359/3876

Date: 7/1/1993

Abstract:
Testing high-strength concrete (HSC) for compressive strength puts into doubt a certain number of concrete testing practices. First, most testing laboratories are equipped with loading capacity machines inadequate for testing 150 x 300-mm (6 x 12-in.) specimens, thus limiting HSC specimens to 100 x 200 mm (4 x 8 in.) in size. As most designers rely on compressive strengths derived from larger specimens, they must be given relations between the different values obtained when smaller specimens are used. Comparative testing reveals that HSC compressive strength values are greater by 5 percent when measured on 100 x 200-mm specimens. Moreover, the coefficient of variation on one set of three 100 x 200-mm specimens is as small as, or smaller than, that for 150 x 300-mm specimens. Furthermore, a high-performance capping compound testing 60 to 70 MPa using 50-mm cubes has proved to be effective when used for testing HSC up to 120 Mpa due to the confinement of the capping compound between the platen and the specimen, but the capping layer must be less than 3 mm thick. Under these conditions, the results are similar to those obtained when the ends are faced by grinding. Nevertheless, it is safer to grind the specimen ends when the strength of the concrete exceeds 100 Mpa. Finally, it is shown that eccentricity of less than 4 mm between the testing machine and specimen axis does not affect the compressive strength values.