This project explores pathways towards a carbon-neutral life cycle for monolithic lightweight concrete structures by investigating repeated recycling of lightweight concrete materials. The aim is to improve the understanding of how lightweight concrete can be reused across multiple recycling loops and how its material properties, carbonation behaviour, and environmental performance may change over successive cycles.

A central objective is to examine the feasibility of a 100% material reuse strategy. In the first stage, recycled lightweight concrete (RLC) will be used as recycled lightweight concrete aggregate (RLCA) in newly designed recycled concretes. At later stages, finer fractions will be processed into recycled lightweight concrete powder (RLCP) to evaluate its potential as a reactive or resource-efficient supplementary cementitious material (SCM) with additional CO₂ binding capacity.

The experimental programme begins with the production and characterisation of three representative lightweight concretes covering common strength and density classes. After production, the concretes will undergo mechanical processing in an industrial facility, where crushing behaviour, particle size distribution, and morphology will be analysed.

All RLC materials will be evaluated with respect to fresh properties, mechanical characteristics, durability, and CO₂ absorption potential. Special attention will be given to how the starting concrete type influences CO₂ uptake of both recycled aggregates (RLCA) and powder (RLCP). Accelerated carbonation experiments in a glovebox will be performed to quantify sequestration potential and optimise the process for maximum CO₂ binding.

Data from all recycling loops, including performance criteria such as strength, density, and conversion factors, will be combined with recarbonation measurements to feed a net-zero production model. This model will help estimate the number of recycling cycles required to achieve climate-neutral criteria and support the development of a closed-loop sustainability model for lightweight concrete.

The project seeks to explore the potential for lightweight concrete recyclability and reusability, contributing to sustainable and low-carbon construction practices while providing insights into circular material use.

Applicants: Karl-Christian Thienel, Univ.-Prof. Dr.-Ing.