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This perspective article describes the past, present, and future directions on TiO2 photocatalysis, 3D concrete printing, and recycling for developing innovative building envelope components from façade skins. Using a methodology consisting of three phases, first the historical evolution of TiO2 photocatalysis, 3D concrete printing, and recycling policies was investigated. Second, the rationale and positioning with regard to the state of the art were developed. Third, the cementitious mix design assessment for 3D printing of the building envelope components, evaluation of the photocatalytic activity, evaluation of the self-cleaning and air-purifying properties, and environmental and health assessment of the building envelope components were identified and discussed as major issues in developing innovative building envelope components that have the potential to mitigate urban air pollution, reduce building maintenance activities, and reduce building embedded carbon while, for example, recycling significant amounts of construction and demolition waste. [ABSTRACT FROM AUTHOR]

Cold in-situ recycling with foamed bitumen has become one of the most cost-effective and sustainable technologies due to working with low heating energy, less transport, and decreasing the use of new materials. This paper presents a benchmark laboratory study of the volumetric and mechanical properties of cold recycled foamed bitumen mixes blended with 100% reclaimed asphalt pavement (RAP) in the granular base layer. The air void content, indirect tensile strength, and resistance to moisture damage are tested to evaluate the impact of active filler, compaction technique, and geopolymer. It was found that the addition of active filler, regardless of the type, increased the moisture resistance between 30% and 35% compared to the mixture with no active filler. Moreover, the addition of slag-based geopolymer resulted in a substantial increase in tensile strength from 434 kPa to 823 kPa while leading to a sharp decrease from 70% to 38% in moisture resistance. [ABSTRACT FROM AUTHOR]

Addressing urban air pollution is a pressing challenge, prompting the exploration of mitigation strategies such as urban greening. However, certain innovative greening approaches, while promising, may inadvertently incorporate unsustainable elements that undermine their eco-friendly philosophy. In this context, our research focuses on addressing the replacement of a petroleum-based filter substrate in an existing 'green' outdoor air purification system that utilizes 'moss filters', known as a 'moss wall'. This initiative is driven by concerns about microplastic leakage from the substrate and the need to optimize the moss wall system in terms of circularity. This preliminary study presents a crucial first step, aiming to assess the feasibility of developing a circular, bio-based plate as a replacement for the existing microfiber filter substrate. The focus is on the potential of this plate to recycle moss from the system itself as raw material, ensuring structural integrity and the ability to support its own weight. To achieve this goal, a series of controlled experiments were conducted in a laboratory setting using cellulose, corn starch, and metakaolin binders. Our findings indicated that cellulose was crucial for the structural integrity, starch significantly enhanced the sample strength, and metakaolin improved the water resistance. These insights culminated in the creation of a laboratory-scale moss-based composite prototype, with moss constituting more than half of the total mass. This prototype demonstrated promising results as a starting point for a more environmentally friendly and bio-based moss wall substrate. Subsequent research efforts will concentrate on optimizing the binder and fiber composition, evaluating and improving the bioreceptivity and filter properties, conducting outdoor testing, and scaling up the prototype for practical implementation. [ABSTRACT FROM AUTHOR]