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Portland cement is one of the most used materials on earth. Its annual production is responsible for approximately 7% of global carbon dioxide (CO2) emissions. These emissions are primarily associated with (1) the burning of fossil fuels to heat cement kilns and (2) the release of CO2 during limestone calcination. One proposed strategy for CO2 reduction includes the use of functional limestone fillers, which reduce the amount of portland cement in concrete without compromising strength. This study investigated the effect of using renewable, CO2-storing, biogenic CaCO3 produced by E. huxleyi as limestone filler in portland limestone cements (PLCs). Biogenic CaCO3 was used to synthesize PLCs with 0, 5, 15, and 35% limestone replacement of portland cement. The results substantiate that the particle sizes of the biogenic CaCO3 were significantly smaller and the surface areas significantly larger than that of reagent grade CaCO3. X-ray diffraction indicated no differences in mineralogy between reagent-grade and biogenic CaCO3. The use of biogenic CaCO3 as a limestone filler led to (i) increased water demand at the higher replacements, which was countered by using a superplasticizer, and (ii) enhanced nucleation during cement hydration, as measured by isothermal conduction calorimetry. The 7-day compressive strengths of the PLC pastes were measured using mechanical testing. Enhanced nucleation effects were observed for PLC samples containing biogenic CaCO3. 7-day compressive strength of the PLCs produced using biogenic CaCO3 were also enhanced compared to PLCs produced using reagent-grade CaCO3 due to the nucleation effect. This study illustrates an opportunity for using CO2-storing, biogenic CaCO3 to enhance mechanical properties and CO2 storage in PLCs containing biologically architected CaCO3. 

Sustainable earthen building materials provide a pathway to mitigating the environmental impacts of the modern construction sector. While the application of these materials has been limited due to the inherent heterogeneity, erosivity, and weak mechanical properties of soil, the physical and thermal properties can be improved through the addition of ubiquitous, non-toxic, sustainable biopolymers. Yet, the fundamental understanding of the physiochemical bonding mechanisms between clays and biopolymers in this system is limited. In this work, a ‘micro to macro’ methodological approach was applied to investigate the bonding characteristics of common clays and clay-stabilizing biopolymers. At the micro-scale, fundamental interactions of clays (i.e., kaolinite, bentonite) with biopolymer additives (i.e., xanthan gum, guar gum, sodium alginate, microcrystalline cellulose) were assessed through mineral binding characterization techniques, including Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The findings were used to interpret unconfined compressive strength (UCS) tests results for macro-scale soil-biopolymer composites samples (1% biopolymer by soil mass). The results from this study illustrate the utility of understanding the mechanisms of clay-biopolymer interactions for improving the design of strong and durable earthen materials and structures. 

Natural earth-fiber building assemblies such as light straw clay, hempcrete, and clay-plastered straw bales incorporate vegetable by-products that are mixed with geological binders, traditionally used as an insulative infill in building construction. As a geo- and bio-based insulative infill method composed mostly of fiber, heat transfer coefficients are lower than mass materials, making it a compatible assembly that meets energy code requirements. Furthermore, due to their permeability, these materials exhibit high hygric capacity, providing regulated indoor temperatures and relative humidity levels, thus showing a promising future for socially just and healthier built environments. Despite these advantages, the use of earth-fiber building materials in digital construction is still underdeveloped. In the past few years, 3D-printed earth has gained an increasing interest, however, high contents of fibers in earth mixtures have yet to be fully tested and characterized. This paper presents an experimental workflow to characterize fiber-earth composites for 3D printed assemblies, using natural soils infused with natural fibers. The paper begins with a literature review of a range of fibers: straw, hemp, kenaf, sisal, and banana leaves, as well as naturally occurring biopolymer additives. The experimental setup includes manual extrudability and buildability tests, to identify optimal mix designs that are then tested for their printability and buckling using clay 3D printers. As a final deliverable, first pass geometric studies showcase the lightweight and structural possibilities of each material. The significance of this research lies in the development of a methodology for identifying novel mix design for digital fabrication, by increasing carbon storing vegetable fiber content within digital earth, and by creating a range of natural 3D printed assembly types: from mass-insulation walls to paper-thin lightweight partition assemblage.