Volume change observations from giant direct shear box tests on recycled 6F5 aggregates

Recycled 6F5 aggregate consists of crushed hardcore materials, predominantly concrete, along with other demolition waste. It is a sustainable, cost effective and versatile material commonly used in major infrastructure and civil engineering projects. It has a range of applications including load distribution platforms, capping layers, sub-bases and general backfill. Knowledge and understanding of the material properties of recycled 6F5 aggregate is required to ensure economical and safe construction. The main parameter needed for geotechnical design is the angle of friction and it is usually obtained using shear apparatus such as the direct shear box. Specifications of 6F5 state that the maximum particle diameter be 125 mm, which is too large for standard shear box apparatus. However, City St George’s, University of London has a Giant Shear Box facility with a shear plane area 2.25 m² and this has been used successfully to obtain a representative angle of friction of material with particles at this scale. In this paper the details of the development of shear and volume change of recycled 6F5 material when sheared at a relatively low vertical effective stress (50 kPa) is presented. The results show consistency with observations of geomaterials tested using conventional shear apparatus.