Living building material

A living building material (LBM) is a material used in construction or industrial design that behaves in a way resembling a living organism. Examples include: self-mending biocement, self-replicating concrete replacement, and mycelium-based composites for construction and packaging. Artistic projects include building components and household items.

History The development of living building materials began with research of methods for mineralizing concrete, that were inspired by coral mineralization. The use of microbiologically induced calcite precipitation (MICP) in concrete was pioneered by Adolphe et al. in 1990, as a method of applying a protective coating to building façades. In 2007, "Greensulate", a mycelium-based building insulation material was introduced by Ecovative Design, a spin off of research conducted at the Rensselaer Polytechnic Institute. Mycelium composites were later developed for packaging, sound absorption, and structural building materials such as bricks. In the United Kingdom, the Materials for Life (M4L) project was founded at Cardiff University in 2013 to "create a built environment and infrastructure which is a sustainable and resilient system comprising materials and structures that continually monitor, regulate, adapt and repair themselves without the need for external intervention". M4L led to the UK's first self-healing concrete trials. In 2017 the project expanded into a consortium led by the universities of Cardiff, Cambridge, Bath and Bradford, changing its name to Resilient Materials 4 Life (RM4L) and receiving funding from the Engineering and Physical Sciences Research Council. This consortium focuses on four aspects of material engineering: self-healing of cracks at multiple scales; self-healing of time-dependent and cycling loading damage; self-diagnosis and healing of chemical damage; and self-diagnosis and immunization against physical damage. In 2016 the United States Department of Defense's Defense Advanced Research Projects Agency (DARPA) launched the Engineered Living Materials (ELM) program. The goal of this program is to "develop design tools and methods that enable the engineering of structural features into cellular systems that function as living materials, thereby opening up a new design space for building technology... [and] to validate these new methods through the production of living materials that can reproduce, self-organize, and self-heal." In 2017 the ELM program contracted Ecovative Design to produce "a living hybrid composite building material... [to] genetically re-program that living material with responsive functionality [such as] wound repair... [and to] rapidly reuse and redeploy [the] material into new shapes, forms, and applications." In 2020 a research group at the University of Colorado, funded by an ELM grant, published a paper after successfully creating exponentially regenerating concrete.

Self-replicating concrete

Self-replicating concrete is produced using a mixture of sand and hydrogel, which are used as a growth medium for synechococcus bacteria to grow on.

Synthesis and fabrication The sand-hydrogel mixture from which self-replicating concrete is made has a lower pH, lower ionic strength, and lower curing temperatures than a typical concrete mix, allowing it to serve as a growth medium for the bacteria. As the bacteria reproduce they spread through the medium, and biomineralize it with calcium carbonate, which is the main contributor to the overall strength and durability of the material. After mineralization the sand-hydrogel compound is strong enough to be used in construction, as concrete or mortar. The bacteria in self-replicating concrete react to humidity changes: they are most active - and reproduce the fastest - in an environment with 100% humidity, though a drop to 50% does not have a large impact on the cellular activity. Lower humidity does result in a stronger material than high humidity. As the bacteria reproduce, their biomineralization activity increases; this allows production capacity to scale exponentially.

Properties The structural properties of this material are similar to those of Portland cement-based mortars: it has an elastic modulus of 293.9 MPa, and a tensile strength of 3.6 MPa (the minimum required value for Portland-cement based concrete is approximately 3.5 MPa); however it has a fracture energy of 170 N, which is much less than most standard concrete formulations, which can reach up to several kN.

Uses Self-replicating concrete can be used in a variety of applications and environments, but the effect of humidity on the properties of the end material (see above) means that the application of the material must be tailored to its environment. In humid environments the material can be used as to fill cracks in roads, walls and sidewalks, sipping into cavities and growing into a solid mass as it sets; while in drier environments it can be used structurally, due to its increased strength in low-humidity environments. Unlike traditional concrete, the production of which releases massive amounts of carbon dioxide to the atmosphere, the bacteria used in self-replicating concrete absorb carbon dioxide, resulting in a lower carbon footprint. This self-replicating concrete is not meant to replace standard concrete, but to create a new class of materials, with a mixture of strength, ecological benefits, and biological functionality.

Calcium carbonate biocement

Biocement is a sand aggregate material produced through the process of microbiologically induced calcite precipitation (MICP). It is an environmentally friendly material which can be produced using a variety of stocks, from agricultural waste to mine tailings.

Synthesis and fabrication Microscopic organisms are the key component in the formation of bioconcrete, as they provide the nucleation site for CaCO3 to precipitate on the surface. Microorganisms such as Sporosarcina pasteurii are useful in this process, as they create highly alkaline environments where dissolved inorganic carbon (DIC) is present at high amounts. These factors are essential for microbiologically induced calcite precipitation (MICP), which is the main mechanism in which bioconcrete is formed. Other organisms that can be used to induce this process include photosynthesizing microorganisms such as microalgae, cyanobacteria, and sulphate reducing bacteria (SRB) such as Desulfovibrio desulfuricans. Calcium carbonate nucleation depends on four major factors:

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