Comparison of different post-demolition autoclaved aerated concrete (AAC) recycling options

Abstract

Autoclaved aerated concrete (AAC) is used as masonry blocks and prefabricated reinforced elements preferably in residential buildings. Due to its porous structure and mineral composition, it combines low thermal conductivity and fire resistance properties. Consequently, the popularity of AAC increases. However, due to significant AAC production volumes in many European countries since the 1960s and 1970s and given building lifetimes, strongly increasing post-demolition AAC waste volumes can be expected in the following decades. Recycling these post-demolition AAC wastes could protect primary resources and landfill capacities and reduce greenhouse gas emissions. But, recycling of post-demolition AAC is not yet established. The majority of the waste is landfilled even though landfill capacities have decreased and the legal framework conditions in Europe regarding a circular economy are becoming stricter. Therefore, new recycling options are needed. Current research approaches propose different open-loop recycling routes for post-demolition AAC, e.g. lightweight aggregate concrete, lightweight mortar, no-fines concrete, floor screed, animal bedding, oil- and chemical binders, and insulating fills for voids and interstitial spaces. Additionally, closed-loop recycling is possible and under research. Finely ground post-demolition AAC powder can be directly used in AAC production or can be chemically converted to belite (C2S) clinker to substitute primary cement in AAC production. These promising recycling options are compared regarding environmental and economic aspects. We find that the resource consumption is lower in all recycling options since post-demolition AAC helps to save primary resources. Furthermore, greenhouse gas emissions associated with the substituted primary resources are saved - especially when substituting primary cement in closed-loop recycling. In economic terms, increasing landfill costs could be avoided, which leaves a considerable margin for the cost of pre-processing, transport and recycling. The results can help decision-makers to implement circular management for AAC by fostering post-demolition AAC recycling and reducing its landfilling.

Roles of carbonated recycled fines and aggregates in hydration, microstructure and mechanical properties of concrete: A critical review

“…and enforced carbonation [93,94], and glass production via thermal treatment and fast quenching [95,96].…”

Energieeinsparungen durch das Recycling von Bauabfällen?

“…Bilanzierungen werden bewusst nicht angestellt, weil dadurch Genauigkeiten suggeriert werden, die nicht existieren und die wiederum zu falschen Schlüssen führen können. Für sortenreinen Porenbeton wurde eine Reihe von baustoffl ichen Anwendungen untersucht, die von der Herstellung von Leichtsteinen über die Herstellung von Werktrockenmörteln oder Estrichen bis zum erneuten Einsatz für die Porenbetonherstellung reichten [29]. In allen Fällen war eine Bindemittelzugabe erforderlich, sodass keine Energieeinsparungen erwartet werden können.…”

Belite cement clinker from autoclaved aerated concrete waste fines with high sulfate content

“…Through high‐quality recycling, natural resources such as mineral raw materials, groundwater, and the natural environment can be used responsibly and energy‐efficiently. If AAC is produced without recycling from primary raw materials, many sustainability indicators and in particular the emission of greenhouse gases are strongly negatively influenced by the upstream chain (cement, lime) [1]. In closed‐loop recycling, the secondary material is valorized within the AAC processing, which significantly reduces greenhouse gas emissions.…”

“…Closed-loop recycling is common practice for production-related AAC waste. In contrast, direct recycling of AAC waste from demolition (pd-AAC) in production is only possible after pre-processing and only to a limited extent due to contamination with impurities such as gypsum, plastics, metals, and so forth [1]. One new approach is the utilization of pd-AAC as a component of a raw meal for the process- An even higher yield of 92%-94% could be reached for the sample with high sulfate content by the addition of 3 to 5 wt% Na 2 CO 3 as mineralizing agent (Figure 3).…”