Mechanical Properties of Sprayed SFRC

1. Introduction

Steel fiber reinforced concrete (SFRC), as a composite material by compounding the short steel fibers in concrete or mortar uniformly and being considered to improve the resistance against the defect of crack and toughness in plain concrete, is now getting more and more popularity in the application field of construction [1]. A lot of studies on the SFRC made by placing have been carried out [2] and its properties have been becoming clear, only few studies, however, have been published on the sprayed SFRC. It is well known, on the other hand, SFRC can be sprayed easily and quickly on the wall of tunnel or the surface of a slope for protection, so it is suitable for excavating and/or protecting skill of today's mechanization and automation. Therefore it is considered important to obtain more knowledge concerning mechanical properties of sprayed SFRC.

1.1 Background

To prevent from the disaster of, for example, landslide, a construction of spraying SFRC on a steep slope was performed in April 1994, at Shizuoka, Japan, beside a highway road. Fig. 1 shows a scene of the SFRC spraying process of the construction. To verify the steel fiber reinforced effect, also a plain concrete, in which mix proportions are completely the same with the SFRC, was sprayed on the slope next to the SFRC area. Further, to investigate steel fiber reinforced effect in SFRC more precisely, as well as sprayed SFRC's basic mechanical properties, specimens with the same mix proportions were made by similar sprayed method (as shown in fig.2) for laboratory experiment. 

1.2 SFRC material used in tests

As shown in Table1, the SFRC material used as specimens have four kinds of contents of Steel fiber (SF). The volume fractions of steel fiber (Vf) are 0, 0.5, 1.0, and 1.5% respectively. After sprayed to panel, 2 or 3 days wet curing and then air curing was performed.

1.3 Steel fiber

The steel fiber used in the specimen SFRC was made by wire cutting method [3]. Its characteristics are shown in Table2. The shape of the steel fiber is shown schematically in Fig.3. It is indented for improving the adhesion as shown by shade and white parts alternatively.

1.4 Orientation of the steel fiber in the sprayed SFRC

It has been pointed out that there are evident orientation of the steel fiber in SFRC, especially in sprayed ones [4]. For the purpose of making clear of this, X ray photographs were taken from the SFRC block parallel and normal to the sprayed plane. Fig.4 is an example of the photographs in which we can see almost all the steel fibers are oriented in plane parallel to sprayed planes.