The Effect of Particle Size on Fracture Properties and Size Effect of Concrete.
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The Effect of Particle Size on Fracture Properties and Size Effect of Concrete. Erik Schlangen1, Heng Soon Lim1, Jaap Weerheijm1,2 1 Delft University of Technology, CiTG, Microlab, P.O. Box 5048, 2600 GA Delft, The Netherlands [email protected] 2 TNO Prins Maurits Laboratory, P.O. Box 45, 2280 AA Rijswijk, The Netherlands ABSTRACT In the study the effect of scaling the material structure on the fracture behaviour of concrete is investigated. Next to this the size effect of concrete fracture strength and fracture energy is studied. The fracture mechanism of concrete made with different size aggregates are tested numerically. A lattice type fracture model is adopted to simulate the fracture mechanisms in concrete. The heterogeneity of the concrete is implemented using a regular pattern of circular particles on top of the lattice of beams. The results obtained show that with the model a structural size effect is obtained, which his however partly an artefact of the model. Furthermore a dependency of strength, fracture energy and brittleness of the aggregate size is found.
INTRODUCTION Experimental research and theoretical investigations showed that concrete structural behaviour (compression, tension, shear etc) is greatly influence by its specimen size, see for instance [1]. This phenomenon that is observed in a heterogeneous material like concrete is termed as “size effect”. Numerous compression, bending, and tensile tests on geometrically similar concrete specimens were carried out. Larger compression specimens exhibit steeper softening paths [2] while larger beams are weaker in bending, shear and torsion. Various theories were proposed for the size effect phenomenon. For example, it could be due to boundary layer or so-called wall effect, or due to rates of diffusivity, or due to heat of hydration or due to statistical fact based on number of defects per unit volume or related to energy dissipation during the evolution of fracture and damage. In the size effect study of concrete, the size of aggregate play an important role. Various studies and experiments showed that aggregate maximum size and aggregate distribution influence the post peak (strain softening) behaviour of concrete. This has implication in the scaled modelling of concrete. Consider this example: a researcher has to conduct an experiment for a scaled model with a length scale factor of 10. Ideally, the behaviour of the scaled concrete specimen and the full scaled specimen should be the same. The question is therefore should we scale the aggregates as well so that their properties remain approximately equal. If we decide to scale the aggregates, what is a suitable scale factor for the aggregates? The ultimate aim of this study is to determine a suitable aggregate size when a model specimen is scaled down. To achieve this aim, it is important to understand the effect of
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aggregate size on the strength, modulus, strength softening and other mechanical properties. Numerical simulations were carried out of tensile tests for
