Recycled Ultra High Performance Concrete (UHPC) as a Way to Reduce the Cement Demand in New UHPC

Abstract

The work reported in this paper aims at assessing the performance of Recycled Ultra High Performance Concrete (R-UHPC), produced using different fractions of recycled aggregates and fines obtained from crushed Ultra High Performance Concrete (UHPC), as a substitute of the both the natural aggregates, as customary in recycled aggregate concrete, and of cement. Three different (R-UHPC) mixes were designed and manufactured with a reference mix based on natural aggregate and two mixes with the natural aggregate totally replaced by recycled UHPC and 30% cement replacement either with recycled UHPC fines or with recycled UHPC aggregates as well, under the assumption of exploiting the paste halo around the recycled interface particles as a binder since it can consist of significant quantity of uh-hydrated cement. The possibility of totally replacing new fibres with recycled ones, reclaimed after UHPC crushing, was also addressed. This supports the cradle-to-cradle approach in life cycle engineering applications. The research confirmed the effective regeneration of new UHPC based on recycled aggregate obtained from crushed UHPC, attaining the required rheological, mechanical (compressive, flexural strength and toughness) and durability performance (chloride penetration resistance, chloride migration, water capillary suction and resistivity) as well as the capacity to maintain the overall performance upon the recycling process. This work is intended as the first step towards the sustainability assessment of the potential of R-UHPC for new and retrofit structural applications. The work has been conducted as a follow up of the activities of the H2020 ReSHEALience Project. One key objective of the project was to formulate the concept and experimentally validate the performance of UHPC for structures and infrastructures exposed to extremely aggressive scenarios, employing functionalizing micro- and nano-scale constituents especially added to deliver high durability in the cracked state under extremely aggressive exposure conditions”. In this context, the research was conducted to investigate the potential of recycling the UHPCs, developed and validated in previous research and employing them as a partial or even total replacement of natural fine aggregate in the production of a new UHDC.