Mechanical Properties of Sprayed SFRC

3. Uniaxial Compression Test

A 1,500kN capacity MTS servo-controlled testing machine was employed for uniaxial compressive testing of SFRC. Specimen and testing method are similar to the ones mentioned above in uniaxial tensile test except following difference: (@)the size of specimen was30~60 mm. (A)No epoxy resin was used between platen and end surface of specimen to affix the specimen. (B) The constant strain-rate was 10-5s-1. (C) The ages of SFRC were 18-19 months during the testing.

3.1 Complete stress-strain curves

The results of the test were shown in Table4. Similar to the tensile test, up to the strength failure point, there are no evident variations at strength, Young's modulus and Poisson's ratio, but the strain in the strength failure point become bigger with the increase of steel fibers, especially in the specimens of type b. The fact is considered that the reinforced effort caused by the mix of steel fiber does not occur before the inner crack width reached some extent. Fig.10 shows the complete stress-strain curves under the uniaxial compressive stress. Contrary to the tension test, it is hard to say, as shown in Fig.10(a), there are evident difference between plain concrete and SFRC in group of type a. The specimens of type b, on the other hand, see Fig.10(b), the curves changed by the increase of steel fibers. Before stress reached about 40 MPa, they showed as good straight, but then they began to curve to indicate the inner cracks growing up. From the strength failure point to the complete failure, the curves showed ductile and the ductility became larger with the increase of steel fibers contents.

3.2 An effect on the residual strength caused by steel fibers

Although the residual strength under the uniaxial compressive stress exists in the plain concrete, an effort on its rise cause by the increase of steel fibers is evident as shown in Fig.11. An experimental equation for describing the relationship between residual strength RE and steel fiber volume fraction Vf is given as:
RE (Vf) =RE(0) + b()EVf
here is strain, andRE(0) is the plain concrete's residual strength. b() = 0.8(7-)2 is a proportional coefficient.

3.3 A summary about the anisotropy of sprayed SFRC

As shown in fig.4, we have known the steel fibers in the sprayed SFRC are oriented in plane parallel to the sprayed plane. This fact led to anisotropy in sprayed SFRC and complete different mechanical properties as shown in the testing results mentioned above. A summary is made in Table5. It can be a reference for telling us how to take the advantage of sprayed SFRC and avoid its disadvantage in engineering application.