Theoretical Evaluation of the Break Off Test for Concrete

THEORETICAL EVALUATION OF THE BREAK OFF TEST FOR CONCRETE by Arjuna Priyara Ranasinghe Strength of concrete is normally m easured using the standard cylinder or cube. The m easured s treng th is used for design. The accuracy of concre te strength is frequently challenged, particularly in large concrete s truc tures where size effect of the te s t specim ens is attributed for the differences. Many nondestructive te s ts were developed to evaluate concrete s treng ths . In recent years, it w as obvious th a t th ese te s ts are unreliable. As the infrastructure decays , more nondestructive te s ts are required to evaluate the existing s truc tures . The Break Off Test is a recently developed nondestructive test. Although substantial am ount of experimental investigations have been carried out on this te s t, no in-depth theoretical evaluation has yet been done to date . In this study the behavior of the break off te s t specim en was investigated and the potential theoretical basis of this te s t explored. Based on linear elastic fracture m echanics, a model to predict the com pressive strength of concrete-m anom eter reading relationship of the break off te s te r w as proposed and com pared with experimental results with good correlation. Both flexural and shear failure m odes were considered and the effect of aggregate interlock w as investigated. The s tress distribution of the deep-beam cantilever core was obtained using finite elements. It also confirmed the experimentally established minimum thickness of structural m em bers for which this te s t m ethod could be used. The study also found th a t the American Concrete Institute 's recom mendation on the modulus of rupture is an extremely conservative value, especially for m em bers with widths less than 6". The modulus of rupture of a rectangular beam is different from that observed from a circular cross section such as the break off te s t specim en. These findings s trengthen the concerns over the size effects on various recom mended concrete strength param eters. In this study, new modulus of rupture values were suggested for small rectangular beam s and m em bers with circular cross sections. The study confirmed the existence of a theoretical basis for the break off te s t and show ed th a t it can be a simple and reliable nondestructive te s t for measuring the com pressive strength of concrete . THEORETICAL EVALUATION OF THE BREAK OFF TEST FOR CONCRETE by Arjuna Priyara Ranasinghe A Dissertation Submitted to the Faculty of New Je rsey Institute of Technology in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Departm ent of Civil and Environmental Engineering January 1 9 9 4 Copyright© 1993 by Arjuna Priyara Ranasinghe ALL RIGHTS RESERVED