Assessment of recycled low-carbon ultra-high performance concrete based on recycled UHPC

Abstract

Ultra-high-performance concrete (UHPC) is widely used in construction for its outstanding strength and durability. However, its high cement and steel fiber content leads to increased carbon emissions and environmental concerns. This study explores the use of sustainable materials in UHPC to reduce its overall environmental impact. The objective of the research is to develop a low-carbon Ultra High Performance Concrete (UHPC) and to assess the performance of recycled low-carbon ultra-high performance concrete (R-UHPC), produced from different fractions of recycled aggregate crushed from low-carbon UHPC. Low carbon UHPC based on a cement with low environmental impact (CEM IV) was first produced and optimised to ensure an improved performance in terms of fresh properties and mechanical properties including strength and durability. In the development process, UHPC with different types of fibres were assessed, including amorphous alloy and steel fibres. The Low Carbon UHPC developed, was then used as source material for the production of the Recycled Low-Carbon UHPC, based on recycled UHPC aggregate, as a substitute of the natural aggregates as is typical of recycled aggregate concrete. Different recycled UHPC mixes were designed and produced with a reference mix based on natural aggregate and three mixes with the natural aggregate replaced using recycled UHPC according to different percentage replacement values (50 and 100%). This supports the cradle-to-cradle approach in life cycle engineering applications. The research confirmed the effective regeneration of new UHPC based on the recycled UHPC, attaining the required rheological characteristics, mechanical properties, durability performance. This work supports the sustainability assessment of the end of life of Low Carbon UHPC materials and structures and the potential of recycled UHPC for new structures and retrofit structural applications.