4 Invasive PlantBricks – Exploring the Potential of Ailanthus Altissima as a zero-waste building material

Faculty Mentor: Shundana Yusaf (School of Architecture, University of Utah)

Introduction

Ailanthus altissima, commonly known as Tree of Heaven, is widely recognized as one of the most invasive plant species globally (Weber and Gut, 2004), significantly impacting ecological and urban environments. Introduced to North America in 1784 as an ornamental tree, its rapid growth and adaptability have enabled it to extensively establish itself across disturbed and urban habitats worldwide (Sladonja, Sušek, and Guillermic 2015; WNWCB 2011). The species’ prolific seed production and aggressive root systems allow it to colonize and dominate landscapes quickly, posing considerable ecological threats through allelopathic interactions, biodiversity reduction, and infrastructure damage (McAvoy et al. 2012; Nature Conservancy 2025; Weber and Gut 2004).

This research addresses critical ecological and architectural challenges posed by invasive plants. Ailanthus altissima substantially reduces biodiversity and disrupts ecosystems through rapid growth, allopathic chemical release, and displacement of native species (Heisey 1990; Motard et al. 2011; Soler and Izquierdo 2024). Additionally, its aggressive root system damages urban infrastructure, leading to costly structural issues. Furthermore, the species exacerbates pest invasions, notably serving as the primary host of the spotted lanternfly (Uyi et al. 2021).

Recognizing these pervasive ecological, architectural, and economic threats, this research sought an innovative solution for a circular economy. Through collaboration, a method was developed to integrate Tree of Heaven fibers into a low-carbon, sustainable matrix composed primarily of clay, sand, and lime, to create unfired bricks. Bricks were selected specifically due to their ease of production, replicability through molding, and their suitability for mechanical studies without relying on carbon-intensive manufacturing processes. This approach also ensured accessibility and adaptability for all communities and scales.

Methods

Ingredient Proportions and Rationale

Wild Clay (~65%): Provides a binding matrix and compressive strength (Houben and Guillaud 1994; Norton 1997).

Sand (~25%): Enhances particle packing, reduces shrinkage, and increases compressive strength. Coarse sand acts as a rigid skeleton in fiber–clay mixtures, improving workability and limiting drying cracks (Minke 2009; Elahi et al. 2018).

Ailanthus Altissima Pulp (~5% dry weight): Organic fiber improves tensile strength, thermal insulation, and reduces shrinkage (Ismail and Al-Hashmi 2008; Binici et al. 2007; Júnior et al. 2020).

Hydrated Lime (~5%): Improves moisture resistance, pH stability, and longevity of organic fibers. Even small amounts of lime significantly enhance water resistance and inhibit microbial decay, extending brick durability (Walker and Heathcote 2002).

Material Sourcing and Preparation: Clay sourced from Rush Valley, Utah, identified via BLM maps and tested onsite for plasticity using standard ribbon tests. Fiber harvested from backyard-grown Ailanthus altissima, processed into chips, soaked, cooked with soda ash, and beaten into pulp using a Hollander beater.

Mixing, Mold Design, and Curing: The materials were mixed using a handheld concrete mixer until a homogeneous mixture was achieved. Bricks formed in molds designed for ease of removal and mortarless stacking, aiming for optimal brick dimension demonstration. Curing occurred at room temperature (78–83°F), with weight measurements recorded every 7 days for 28 days.

Repeatability and Scalability Considerations: For broader application, the methods outlined are intentionally designed to utilize low-tech, easily accessible materials and processes. Ensuring consistency in sourcing and preparation methods, alongside thorough documentation of environmental conditions, will facilitate repeatability and scalability in various geographic contexts.

Findings

Preliminary findings from this research indicate that bricks lost approximately 5-7% of their initial weight due to moisture evaporation during curing. While comprehensive mechanical testing remains for future research, the bricks showed promise for application in low-tech, sustainable building contexts. This project directly challenges conventional sustainable building practices by demonstrating the practical potential of repurposing invasive biomass. Through a low-tech, low-carbon methodology, this research promotes a resilient circular economy by transforming an ecological threat into an architectural resource. There is an ever-growing need for innovation in material experimentation in the broader construction industry, and this project highlights the synergy between ecological management and sustainable architecture.

Conclusions

Future research directions should focus on optimizing brick formulations and curing methods, alongside rigorous mechanical and durability testing, all to truly understand Ailanthus altissima’s applications in sustainable architecture. Additionally, expanding the application of invasive biomass to other building materials, such as insulation and composite panels, could further amplify ecological restoration and sustainability goals. Ultimately, the integration of invasive plant biomass into architecture fosters sustainable, economically viable, and ecologically restorative construction practices, marking a significant step toward a more resilient built environment.

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