SizeEffectinHardenedCementPasteandHighStrengthConcrete

This paper will report on an experimental investigation into the size effect in the strength of Dardened cement paste (HCP, nominal compressive strength 40 MPa) and high strength concrete (HSC, mminal compressive strength 110 MPa) as measured in three point bending. The aim of the investigation is to judge the range of applicability of the various size effect formulae available in the literature. With this aim in mind, the failure loads have been analysed according to the size effect formulae ofBazant and ofKarihaloo h the notched beams and according to those of Bazant and of Carpinteri for the unnotched beams. The c:sults of this analysis will be presented. Improvements to Karihaloo's size effect formula will also be proposed. l INTRODUCTION where Ai and 82 are constants. This formula also reduces to the LEFM limit as W ~ oo. It is, The fracture mechanics size effect, as opposed to the however, unlikely to be applicable when W is small, Weibull statistical size effect, is a controversial topic which is a consequence of several approximations in the fracture of concrete. Yet, it is fracture and assumptions made in its derivation. These will mechanics which alone can illuminate the hitherto be touched upon later. mexplained size effect observed in the strength of Many quasi-brittle structures are known to fail at concrete structures. It would therefore seem crack initiation, although the process zone is well appropriate to conduct dedicated experiments in developed. For such structures the nominal failure order to establish the range of applicability of the stress was found to approach the LEFM limit for W several fracture mechanical size effect formulae -+ oo from above available in the literature (Bazant, 1984, 1997; Carpinteri, l 994a; Karihaloo, 1999). (3) Bazant ( 1984 ), using the energy release rate amcept, proposed the formula Here, A and B are positive constants. This formula 3 3 '7J ).