Hideo Koide

TENSILE BEHAVIOR OF A RECYCLED CONCRETE

ABSTRACT Tensile behavior of such a recycled concrete in which all the components were reused fine and coarse aggregates after simple crushing was studied. For compressive strength and durability the recycled concrete was already confirmed to be almost equivalent to the original concrete when the water to cement ratio was by 5% lower than original one. The uniaxial tension test showed that tensile strength and fracture energy were reduced considerably in the case of the recycled concrete even though it had the same level as the original concrete in compression and durability

Size Effect of Concrete in Uniaxial Tension

In order to investigate the size effect of concrete, four sizes of rectangular prisms were tested in uniaxial tension. The cross sections of the prisms were 50x100mm, 100x100mm, 200x100mm and 400x100mm. The concrete was an ordinary one with the compressive strength of 34 MPa and the maximum aggregate size of 20mm. Notches were applied on four side faces and secondary flexure was completely eliminated during the test in order to obtain the exact nominal tensile strength. The size effect was analyzed by four factors, namely tensile strength, fracture energy, critical crack opening displacement and tension softening curves. Clear size dependence was observed in critical crack opening displacement and initial convexity of tension softening curves, and a slight size dependence was observed in tensile strength. On the other hand, size effect was unclear in fracture energy and other part of tension softening curves because of their scatters.

Discussion on Secondary Flexure in Uniaxial Tension Test of Concrete

Abstract The fracture process of concrete is analyzed by using a finite element model combined with the tension softening curve of the concrete. The curve is obtained exactly by only a uniaxial tension test. However, there are still four misunderstandings about secondary flexure that inevitably occurs in the test. They are the followings. 1. secondary flexure is avoided by avoiding load eccentricity 2. secondary flexure appears after peak load 3. uniform stress distribution is realized by a simple load-control loading system 4. secondary flexure is avoided by adopting fixed boundaries Those misunderstandings are obstacles to establish a standard test method for the uniaxial tension of concrete. In addition, there are still papers based on those misunderstandings even recently. In this paper, those misunderstandings are discussed, cleared and confirmed to be erroneous by experimental results and theoretical considerations.

Characteristics of secondary flexures in uniaxial tension test of concrete

In the uniaxial tension test of concrete, inevitably some secondary flexures occur. However the characteristics of the secondary flexures are not well understood among others because of the complexity of performing the uniaxial tension test without the flexures. In this paper the uniaxial tension test in which secondary flexures are minimized, by a specially developed device, are compared to the tests where secondary flexures are left to develop freely. Experimental results and theoretical calculations are shown for the influence of secondary flexures on load-deformation curves, tensile strength and strain energy of the specimen. Plural flexures which grow finally plural cracks were also analyzed concerning to an experimental result. It is concluded that secondary flexures should be minimized, because they produce considerable error to the load-deformation curve and tensile strength. Furthermore, secondary flexures should be controlled continuously during the test because the minimized state is an unstable equilibrium of strain energy in the specimen. And the flexures can only be minimized by using a notched specimen because plural flexures occur in an un-notched specimen.