Stabilising compressed earth materials with untreated and thermally treated recycled concrete: A multi-scale investigation

This paper presents a novel process to recycle the fine fraction of ground concrete waste as a construction binder. The fine fraction of ground concrete is rich of partly hydrated cementitious products, whose binding capacity is further enhanced by treatment at relatively moderate temperatures. The viability of the recycled binder has been demonstrated through the stabilisation of two earth building materials with kaolinitic and illitic clay fractions, respectively. At the microstructural level, X-ray diffractometry tests, mid-infrared spectroscopy tests and thermogravimetric tests have been performed to investigate the mineralogical composition and chemical bonds of the stabilising phase. At the macrostructural level, unconfined compression tests have been performed to evaluate the influence of stabilisation on the elastic modulus, peak strength and energy at failure. Results show that the addition of untreated recycled concrete to both earth types induces an average increase of 4% in apparent elastic modulus, 52% in compressive strength and 108% in failure energy relative to the unstabilised material. The addition of thermally treated recycled concrete induces an even larger increase of 30% in apparent elastic modulus, 93% in compressive strength and 187% in failure energy relative to the unstabilised earth. This is due to the higher hydration capacity of the thermally treated recycled concrete and the consequent formation of stronger inter-particle bonds. These preliminary results indicate a promising way to recycle concrete waste into earth stabilisers, which would ease difficulties associated to the disposal of demolition waste while, at the same time, improving the sustainability of current building practices.