Renewable construction with lightweight concrete – Reclaimed recycled material systems with CO2-absorption
Timo Haller, Sebastian Scherb, Nancy Beuntner, Karl‐Christian Thienel
Abstract
The conservation of natural resources and the effective reduction of CO 2 emissions are critical goals for the cement and concrete industries. This study addresses the end-of-life scenario for lightweight concretes by presenting a strategy to recycle the most challenging type, Infra-Lightweight Concrete. The current version of the German standard for concrete, DIN 1045 (2023), does not permit the use of recycled materials in Lightweight Concretes. The objective of this study is to investigate the potential of Infra-Lightweight Concrete elements to be recycled into Recycled Lightweight Concrete Aggregates through mechanical processing and screening. Subsequently, these Recycled Lightweight Concrete Aggregates are used to produce Recycled Infra-Lightweight Concrete, which aims to replicate the properties of the original Infra-Lightweight Concrete. Key testing methods were employed to characterize Recycled Lightweight Concrete Aggregates and Recycled Infra-Lightweight Concrete, including density, water absorption, compressive strength, thermal conductivity, and CO 2 absorption. The study shows that Recycled Lightweight Concrete Aggregates exhibit an agglomerate structure, which significantly affects key parameters like density and water absorption, both essential for successful integration into new concrete mix designs. Recycled Lightweight Concrete Aggregates exhibited consistent strength potential across different batches of recycled material within a simple and reproducible method, particularly suitable for recycling Lightweight Concretes. Additionally, Recycled Lightweight Concrete Aggregates demonstrated substantial CO 2 absorption potential, with maximum CO 2 uptake values ranging from 123 to 138 kg per ton of Recycled Lightweight Concrete Aggregate after 10 days of conditioning in a controlled environment containing 0.5 % CO 2 by volume. Recycled Infra-Lightweight Concrete produced from Recycled Lightweight Concrete Aggregates exhibited similar strength, modulus of elasticity, and thermal conductivity as the original Infra-Lightweight Concrete. Notably, despite a 32 % increase in dry density, the thermal conductivity of Recycled Infra-Lightweight Concrete only increased by 3.3 %, indicating nearly identical performance properties to Infra-Lightweight Concrete. In conclusion, monolithic wall elements can be constructed using only Recycled Lightweight Concrete Aggregates while maintaining similar performance parameters. This approach promotes material circularity, reduces CO 2 emissions, and validates the structural performance of recycled lightweight concrete, thereby contributing to more sustainable construction practices. • Novel approach for recycling lightweight concrete, supporting circular economy. • Recycled lightweight concrete matches performance of original lightweight concrete. • Recycled lightweight concrete is made with recycled lightweight aggregates only. • RLCA showed significant CO 2 absorption, reducing construction's carbon footprint.