Optimization of properties of soil concrete with biologically active additives

This paper presents an experimental study on the modification of grouted soil (soil concrete) with biologically active additives, specifically mosses and algae, to improve material properties. Laboratory tests were conducted using three types of ultrafine cement (UFC) injected into medium sand, with and without biological additives. The results show that the inclusion of mosses and algae led to a modest increase in compressive strength, with the most notable effect observed for UFC Type 1, where strength increased from 2.4 MPa to 2.7 MPa at 180 days. Density of bio-modified samples was also slightly higher, which may be attributed to microbial-induced calcite precipitation filling pores and microcracks. Viability tests confirmed that microorganisms survived the injection and curing process when protective measures (buffering agents, hydrogels, low-heat cement) were applied. The proposed approach shows potential for self-healing properties, reduced carbon footprint, and lower long-term maintenance costs, while remaining compatible with existing construction practices. These findings position bio-modified grouted soil as a promising material for sustainable infrastructure applications.