Why Explore Seaweed-based Construction Materials

The construction and operation of buildings account for approximately 40 percent of global carbon emissions, with 11 percent of global emissions coming specifically from embodied carbon emissions; defined as the greenhouse gas emissions required to extract the materials and to manufacture, transport, maintain (excluding operational energy emissions such as from heating and cooling), and dispose of building components (World Bank, 2023).

Seaweed-based construction materials are worth exploring for emissions reduction through two main pathways: Carbon Sequestration/Storage and Emissions Avoidance (Displacement).

1. Carbon Sequestration and Long-Term Storage

Seaweed-based materials store carbon dioxide (CO₂). This CO₂ can be locked away for centuries, especially when used in material to construct long-lived products such as buildings. While the focus of this program is on reducing emissions, this is a critical component of the climate impact of seaweed-based materials.

2. Emissions Avoidance (Displacement of GHG-Intensive Materials)

Seaweed products can mitigate emissions to the extent that they replace more GHG-intensive products. For example, limited studies show that alginate (a biopolymer derived from macro-algae), can be used as a stabilizing additive in unfired clay bricks or adobe materials. The unfired clay bricks were found to have a lower embodied carbon footprint than fired clay bricks with equivalent mechanical performance. (Galán-Marín et al., 2015).

Construction materials also offer a possibility for more efficient use of resources; for example, by using waste seaweed left over from alginate extraction or biostimulant production in a cascading biorefinery setting as feedstock for the construction materials. Another possibility is using beach-cast seaweed-this is demonstrated commercially in Mexico, where companies use Sargassum (which cause  problematic inundation events) to make building blocks (Sargablocks) and concrete (SargaCreto). Utilizing this biomass prevents the algae from returning carbon or excess nutrients to the ocean, which aligns with a circular approach intended to minimize or eliminate waste while providing social and environmental benefits.

Construction Materials Incorporating Seaweed

Seaweed’s diverse properties such as binding, fiber reinforcement, flame suppression, and thermal insulation make it a candidate across a wide range of construction applications.

Table 1: Range of construction materials that incorporate seaweed.

Figure 1: Example of processing flow for seaweed-based construction materials. Source: World Bank (2023)

Species Selection

Species selection is driven by a combination of requirements for performance and local availability.

• Construction applications requiring binding or stabilizing agents, such as additives for unfired clay bricks, and often use brown seaweed for their sources of alginate (for their binding properties).
• A key focus, especially in the Caribbean and Mexico, is utilizing the excessive blooms of pelagic Sargassum (a brown seaweed) for materials.

Species like Cladophora sp. Kützing, Kappaphycus alvarezii, and Gracilaria sp. Greville have been tested as fiber, additive, or ash components in Portland cement composites (Albright & Fujita, 2023).

Cultivation

The companies currently building seaweed construction materials overwhelmingly rely on wild collected and beach-cast seaweed. Cultivated seaweeds have not been incorporated into the construction material supply chain (World Bank, 2023).

See the Cross Cutting: Cultivation section for details on approaches to cultivate seaweed. (Note: Insert link to the Cross Cutting: Cultivation section)

Harvesting

The logistics of harvesting vary significantly based on the seaweed source. For example, in areas dealing with invasive blooms (e.g., Quintana Roo, Mexico), the Sargassum biomass washes up on beaches and is collected. Collection of wild Sargassum often uses heavy machinery, such as loaders and dump trucks, due to the massive quantities involved. Companies such as Dakatso contract with beach owners to prevent Sargassum wash-up on shore using offshore barriers.

Figure 2: Collection of sargassum using a loader (Image Credit: Elizabeth Ruiz/Cuartoscuro)

Figure 3: Dakatso Sargassum Collector Vessel (Image Credit: Dakatso)

Other wild species are collected manually on foot or by boat in case of small operations or using mechanical systems (for example, a boat equipped with a rake-like device or a rotating mechanical hook is used to cut kelp species like Laminaria hyperborea). See the chapter, “Cultivation and Drying Considerations“, for details on approaches to harvest wild and cultivated seaweed. (Note: Insert link)

Pre-processing

Most pre-processing involves some cleaning to get rid of impurities, sand and to reduce salt content. Salt content is typically reduced through repeated freshwater rinsing or soaking, followed by sun-drying. Residual chloride content must be monitored for structural applications, as levels above threshold concentrations accelerate corrosion of adjacent steel reinforcement in composite applications.

Drying: Since fresh seaweed is composed of 80–90% water, drying is crucial for economical use, as shipping wet seaweed is generally uneconomical. The most energy-efficient method is sun-drying or air-drying on beaches. Companies making Sargassum-based concrete (Dakatso) utilize ‘UV dehydration’—which appears to be sun-drying on plastic sheets (Albright and Fujita, 2023).

See the “Cultivation and Drying Considerations” chapter for details on approaches to clean and dry seaweed.

Processing

The processing requirements generally depend on the final product, but in most cases, the seaweed only needs to be shredded to the correct size and mixed with other ingredients in the right proportion, often following industry standards.

Table 2 Processing methods for current commercial products made from seaweed. Sources: Albright and Fujita (2023), The World Bank Group (2023)

Other Approaches under Research

Seaweed Based Aerogels: Aerogels are promising candidates in thermal super-insulation applications. Cellulose nanofiber (CNF) based aerogels offer a potentially non-toxic alternative for flame-retardant insulation.  Berglund et al. described a process for a seaweed-based CNF aerogel. In this process, the seaweed stipe is purified to remove pigments and impurities. This was done by bleaching in Sodium Hypochlorite in an acetate buffer and then washing until a neutral pH is achieved. After purification, the seaweed is ground with coarse Silicon carbide grinding stones to separate the cellulosic part into very fine nanofibers. The aerogel is then created through a process called ice templating, where the seaweed gel is mixed with water and then frozen in a mold. The ice-crystals grow and push aside the solid materials. This is then freeze-dried to form a porous CNF aerogel structure because ice is removed by sublimation and leaves gaps where the ice crystals used to be, Finally, this aerogel is treated with Calcium Chloride solutions in ethanol to generate a crosslinked structure, improving mechanical properties.

Seaweed Inclusion in Concrete

Several research initiatives are being undertaken to include seaweed in different form factors to improve the performance of cement and concrete. For example, seaweeds can be burnt/pyrolyzed (thermal decomposition of a material in the absence of oxygen) and the ash can be used as a partial replacement for a mineral component.

Researchers at the University of Washington and Microsoft developed low-carbon concrete by mixing dried, powdered seaweed with cement and found a 21% reduction in global warming potential (Lin et al., 2025).

The Technology Readiness Level (TRL) or Development Stage for seaweed-based construction products varies widely, ranging from niche but commercial products that utilize waste biomass to materials that are still in the early research and development phase. Construction materials are generally categorized as a long-term emerging market opportunity projected to reach a potential market value of $1.4 billion by 2030 (World Bank, 2023).

Table 3: Technology Readiness Level for Seaweed-based Construction Products

Context

Cement manufacturing accounted for 1.6 gigatons CO₂e in 2022 so addressing these emissions have significant impact.  Comprehensive Life Cycle Analyses (LCAs) do not yet exist for many seaweed construction products, making it difficult to quantify the long-term benefits and environmental impact of the processing operations required. Lin et al. (2025) performed a closed loop optimization driven by machine learning with feedback from real-time experiments on Ulva sp. inclusion in cement to reduce global warming potential (GWP) while reaching a target compression strength. The result of the analysis was a 21% drop in GWP while achieving the target compression strength. A 21% reduction in emissions from cement manufacturing would equal about 330 million tons CO₂e per year. If real-world cement manufacturing processes can achieve these results, there’s a potential for meaningful emissions reductions (even at 5% adoption).

Evidence Base

Chaurasiya et al. (2026) reviewed approximately sixty published LCA studies across diverse seaweed product categories which included construction materials. Here’s a summary of the hotspots where emissions are largest and their relevance to seaweed construction products, with a focus on the current commercial case of using Sargassum blooms in materials such as Sargablocks.

Table 4: Hotspots in the seaweed-based product development lifecycle and relevance to seaweed-based construction products

The current processing of sargassum for Sargablocks , avoiding the major hotspots suggest products may already have a better emissions profile than the academic LCA literature implies for seaweed products generally, though without published LCAs this cannot be confirmed. The key question for scalable climate impact would be if the inclusion of seaweed in cement can result in reduced emissions (as promised from the modeling and experimental study performed by Lin et al. (2025)) when a cradle to grave LCA is performed in real-world settings

While Sargablocks meet Mexican federal regulations for construction and MDF boards meet international standards, limited real-world long-term performance data exists for most seaweed-based construction materials, restricting widespread adoption. For example, there are no detailed studies on the properties of the blocks made out of Sargacreto (Miranda et al., 2021).

Table 5: Performance metrics for seaweed-based construction products

In addition, companies are exploring products that use the fire-retardant properties of biopolymers in seaweed. Seaweed inclusion can also reduce thermal conductivity, making its use attractive in insulation for homes (Affan et al., 2023).

The demand for green construction materials is a potential impetus for the use of seaweed in construction. This demand is driven by policy, but also by increasing interest from consumers, architecture firms and construction companies in the concept of environmentally friendly construction and the use of bio-based materials. In the Caribbean, hotels and governments have been adversely impacted by Sargassum blooms, prompting their collection and use in construction.

Costs

Currently, cultivated seaweed is too expensive to be processed into materials to replace or even be incorporated in traditional bulk- commodity materials such as wood, cement, bricks and blocks. The use of Sargassum in adobe blocks in Mexico is however currently viable. See the costs below in Table 5 for comparison.

Algae bioplastic panels are being adopted in more luxury settings where they are cost-competitive with incumbent materials. These tend to be materials used mainly as artistic elements.

Table 6 Cost comparison between seaweed-based construction products and their incumbent alternatives. Source: World Bank (2023)

As a result of challenges to adoption (see section “Knowledge and Development Gaps”), the seaweed-based construction material market is expected to remain relatively small (approximately 0.2% of the $670B market) by 2030.

Table 7: Projected market size of seaweed-based construction materials. Source: World Bank (2023)

Co-benefits

• The deployment of macroalgae in construction provides a method for valorizing waste seaweed. Utilizing massive, expanding volumes of stranded algae, such as the Sargassum drifting over to the Caribbean, converts a severe ecological threat into a viable economic asset by eliminating substantial cleanup costs and reduces the life cycle emissions relative to cultivated products. (Amador-Castro, 2021) Similarly, producers can use waste seaweed leftover from alginate extraction or biostimulant production as a low-cost feedstock.
• Materials like earth masonry and seaweed-based materials are easier to recycle than fired bricks or concrete. If Sargablocks break, they can be ground up and re-used to make new ones, supporting a circular approach.

Risks

Co-benefits

• Companies utilizing massive invasive Sargassum blooms (e.g., Sargablocks) create an alternative income source for residents in regions heavily reliant on tourism (which is negatively affected by the blooms). For example, the profit derived from collecting the abundant and cheap feedstock often allows manufacturers (like BlueGreen in Mexico) to donate the bricks to low-income families free of charge (Albright and Fujita, 2023)
• Enhanced seaweed production and value chains can contribute to meeting U.N. Sustainable Development Goals (SDGs) such as SDG5 (Gender Equality) and SDG8(Decent Work and Economic Growth). In emerging nations, women have played a significant leadership role in the growth of the seaweed industry and seaweed farming has the potential to employ women
• Natural, inert materials like unfired earth, stabilized with alginate, exhibit superior hygroscopicity. This moisture buffering can help regulate indoor humidity levels, leading to improved air quality, reduced requirements for mechanical ventilation, and potential energy savings (Dove, 2016)

Risks

• While seaweed is generally non-toxic, if materials are made from poorly purified or contaminated seaweed (such as is possible in the case of beach-cast Sargassum), there is a potential risk of exposure to heavy metals and pollutants (Lopez Miranda et al., 2021)

The limited current adoption of seaweed-based construction products is primarily driven by mandates and targets related to environmental performance and the reduction of conventional materials, particularly in Europe, as well as economic necessity in regions dealing with invasive seaweed blooms.

Table 8: Policy Drivers that support the adoption of seaweed-based construction materials