Jodok Waibel Nakahara

Biotechnologically modified sand as sustainable resource for construction industry S. Grüner1*, J. Waibel Nakahara1, A. L. Schuhmacher1, D. Koch2, T. Federrath3 1 Hochschule Weihenstephan-Triesdorf, 2 Koch Carbon Consulting GmbH, 3 Albert Hodel GmbH *sabine.gruener@hswt.deSand is the basis for inorganic building materials and the second-most used resource after water. However, not all sand sources are equally suitable for the construction industry. Variations in grain size, surface, bulk density, and water storage capacity, along with availability and the environmental impact of extraction, affect the usability of sand. Often, the particle surface of sand grains is too smooth for concrete production, the porosity of the bulk material is either too high or too low, or the flow behavior is not ideal. This research focuses on enhancing the usability of sand through biotechnological methods, specifically by using microorganisms, which modify particle surfaces and their interaction. The goal is to drive innovation and support a nature-positive transition, aligning with one of the five priority actions defined by the World Economic Forum. [1][2]    Figure 1. Microscopic view of G. resinaceum on an agar plate (a). Sand cube created through MICP using S. pasteurii (b).   The roughness of sand particle surface was improved through targeted measures. Microbially induced calcium carbonate precipitation (MICP), utilizing the bacterium S. pasteurii and the use of additives to modify the crystal structure of CaCO₃, effectively reduced porosity and water storage capacity. Fungal mycelium of G. resinaceum strengthened interparticle connections and increased surface roughness. [3][4] The growth of bacteria and fungi in sand bulk material was successfully implemented, resulting in the compaction of sand grains. The crystalline structure and associated strength of sand granules treated with microbially induced calcium carbonate precipitation (MICP) were influenced by specific additives. This effect can be demonstrated by compressive strength measurements using cubes created with MICP, as shown in Figure 1. Additionally, a successfully reduced water absorption capacity, an increased surface roughness as well as a corresponding reduction in flowability of the modified sand were achieved. These modifications open up new areas of application for sand raw materials that were previously difficult to utilize, enhancing the properties of sand for the construction industry. Future investigations will focus on optimizing the modification processes and scaling up the application.   References [1] World Economic Forum Nature Positive: Role of the Cement and Concrete Sector, 2023, insight report, No. 31 [2] Food and Agriculture Organization of the United Nations, Status of the World´s Soil Resources, 2015, Main Report [3] A. Van Wylick et al. Fungal Biology and Biotechnology, 2021, 8, No. 16 [4] M. S. Carter et al. Applied and Environmental Microbiology, 2023, 89 No. 8