Due to changes in climate, cities and urban areas are more and more tormented by issues such as the Urban Heat Island Effect and extreme precipitation. One way to tackle these issues is the implementation of green spaces, found to control local climate and improve water management. However, densification within cities threatens the space for green envelope. The application of moss, a type of plant that can adapt to many habitats, directly on the concrete surface of buildings could provide a solution. This requires the concrete to possess certain characteristics that allow and promote moss growth. The general term for a material’s ability to be colonized by biological growth is called its bioreceptivity. Surface roughness, surface pH, chemical composition, porosity and water retention have been documented to be strong predictors for bioreceptivity of concrete.

In this thesis, the bioreceptivity of 3D printed concrete (3DPC), an upcoming and promising concrete manufacturing technique with near prospects in urban context, is aimed to be improved by incorporating lightweight aggregates (LWA). A starting 3DPC mixture was adopted. Samples were 3D-printed with sand partially replaced by 30% Crushed Expanded Clay (CEC), Expanded Glass (EG), Expanded Vermiculite (EV), and Pumice (PU). Additionally, a separate set of samples incorporated a 45% replacement using only pumice.

Moss was planted on the specimens and allowed to grow in a climate controlled glass house. After 7 weeks, the green coverage on all specimens had severely decreased. The maximum quantum yield measured by Pulse Amplitude Modulation Fluorometry (PAM-F) suggested decreasing plant health as well. Improper environmental conditions and watering regime were held accountable for this. The results yielded insufficient information to discuss the impact of added LWA on bioreceptivity.

The samples were evaluated on their bioreceptivity factors, compressive and flexural strength. Surface roughness was similar across all the variants. All samples had a surface pH that exceeded 12. Samples withg with 30% replacement of expanded vermiculite (EV30) showed highest porosity, but lowest water retention. Mechanically, EV30 showed weakest compressive and flexural strength, but this can be partially allocated to its curing conditions. Contrarily, CEC30 and PU30 samples showed similar or higher values for compressive and flexural strength than the reference samples without any treatment.

The findings in this research implied that 3DPC open porosity increases with increasing aggregate porosity, and implied a reduced ability to retain water with increasing open porosity, although both these characteristics are reliant on the pore microstructure as well. Of all the LWAs, implementation of EV showed to be most promising in terms of habitat provision for moss growth. However, due to the marginal sample size the statistical significance is questionable.