Interface between construction materials and soils play an important rolein many geotechnical systems, including retaining walls, shallow and deepfoundations. Interface behavior is studied using split samples consistingof concrete block at the bottom half and soil at the top half of the direct shear. The objective of this research is to assess the effect of aggregate crushing at the concrete-soil interface. To be able to control the large number of parameters affecting the interface behavior, granular soil was manufactured using fly ash by cold-bonding pelletization technique with predetermined shape, size, grain size distribution, surface roughness, water absorption, unit weight and crushing strength. The physical and mechanical properties of these aggregates were investigated by using conventionalsoil mechanics tests. Interface tests between lightweight aggregates and concrete showed that the effects of grain crushing, particle shape and thesurface roughness of aggregates play an important role in the interface behavior between granular soils and concrete. At low normal stress values, the crushing strength of aggregates did not affect the interface behavior.For the synthetic aggregates studied, the ratio of interface to internal friction angle decreased with increasing crushing strength.
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