Fracture Mechanics of Concrete

This special issue of Sādhanāis rightly dedicated to the fracture mechanics of concrete. In particular, the size effect is highlighted. As appropriately pointed out in the first international conference on fracture mechanics of concrete structures, FraMCos-I, organized by Z P Băzant, at Breckenridge, Colorado in 1992, fracture mechanics of concrete can be called the 3rd phase in the evolution of concrete structures. Since then the number of published papers on the topic have increased several-fold. Going back in the memory pipeline, it was M F Kaplan1 (in 1961) who tried to obtain the fracture toughness of concrete. It was observed later that there was no consistent value of fracture toughness of concrete. Therefore, towards the early eighties, nonlinear fracture theories were proposed. The process zone ahead of the crack tip was identified as having an important role to play in the nonlinear fracture mechanics of concrete. A little later, it led to the size effect, which as proposed in fracture mechanics is different from Weibull’s hypothesis for size effect. Later, there was a workshop on the size effect in concrete structures, organized by H Mihashi, H Okamura and Z P Bă zant, at Sendai, Japan in 1993. Various international committees were formed, the earliest one being the RILEM Committee chaired b y F H Wittmann. Several other important meetings took place at different places like the international workshop at Locarno, Switzerland in September, 1990 organised by Wittmann and Dungar, and the international workshop on concrete fracture, organised by A Carpinteri, at Torino in October 1991. In recent years, as high performance concrete is gaining importance, its fracture behaviour is being studied with great seriousness. High strength concrete is nearer to linear theories of fracture and is relatively more brittle. The challenge is whether one can make high strength concrete relatively more ductile by improving the cohesiveness of cracks. The next question is how to bring the size effect into codes of practice on the design of reinforced concrete structures, since large structures like dams, nuclear reactors, very tall towers, do contain large sized members. The issue to be addressed is whether it is in order to assume the same tensile strength as obtained in the laboratory for the full scale structure also. This special issue is intended to focus on the above features. Fracture mechanics of concrete has yet to go a long way. One may say that a complete textbook in the strict sense of the term came out only as recently as in 1995, written by B L Karihaloo. The contributors to this special issue , F H Wittmann, A Carpinteri and B Chiaia, V E Saouma and D Natekar, B Karihaloo and Q Z Xiao, Jin Keun Kim and Seong Tae Yi, and Vladimir Cervenkaet al, are all leading researchers in the field of fracture mechanics of concrete. This special issue will certainly be an important document relating to the latest research on the subject. It will also help active researchers to pursue further research on the topic.