Concrete Parameters And Double K-parameter Model Is A Comparative Study

With the successful application of linear fracture mechanics in some fields, some researchers were inspired to apply fracture mechanics to concrete. However, it was found even at the first that in concrete Krc is size-dependent and sub-critical propagation exists. From that on , many models have been set up, in which double-parameter model and double-k model are included, to find a parameter without size effect.Double-parameter model is one based on corrected linear fracture mechanics and double-k model is based on fictitious crack model. Both double-parameter and double-k models need to achieve the critical effective crack length a* to further calculate other parameters. And they both determine a* though the relation between a and the compliance C', but differ on which compliance should be used.In this article tests including two kinds of specimens are carried: standard three-point bend beam and wedge splitting specimen . It is found that KK in two-parameter model and KKm in double-k parameter model, CTODc in both models are nearly size-independent. It is also found that a in double-parameter is larger than that in double-k parameter, which naturally leads to the fact : KK and CTODc in double-parameter larger than those in double-k parameter.In double-parameter model, because of the difficulty of unloading at the exact peak load, Shah suggested to unload at about 95% of the peak load after the load passes the maximum load. However, in our tests it is found that since the unrestorable displacement develops dramatically after load passes the peak load, the parameters calculated through compliance of the 95% peak load are remarkably larger than those calculated through compliance of the peak load . So it is unsuitable to unload at about 95% of the peak load.