Rehydration reactivity of recycled mortar from concrete waste experienced to thermal treatment

It is desirable to completely recycle concrete waste in order to protect the natural resources and reduce the environment pollution. The coarse recycled concrete aggregates (CRCA) from crushed concrete waste have been successfully applied in new concrete and road base. However, the use of fine recycled concrete aggregates (FRCA) is generally limited due to its detrimental effects on the mechanical property and durability of concrete. In this paper, it is intended to alternatively use FRCA subjected to thermal treatment as the main component of building mortar. Techniques of thermogravimetric-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) were used to identify the formation of dehydrated and transformed phases of preheated FRCA. The rehydration of preheated FRCA was then evaluated by the mechanical properties of mortar, together with the microstructure and chemical compositions of rehydration products. The results show that the preheated FRCA can take on the rehydration reactivity. The addition of fly ash and Portland cement to preheated FRCA can significantly enhance its rehydrated strength.