High strength bio-concrete for the production of building components

Summary

Aggregate packing densityOne-dimensional compression strength tests have shown that in MICP-treated sand, at the micro level, the bonds between the calcium carbonate and the aggregates break first, followed by the destruction of calcium carbonate crystals and ultimately the breakage of aggregates20. Maximizing the aggregate content is therefore crucial for achieving high compressive strength of the biocemented material. Packing density optimization allows to increase the volume ratio of aggregates to voids in the mix, which also brings economical benefits due to the reduced consumption of the cementation solution.The packing density optimization was carried out with six different quartz sand fractions ([0.063–0.25 mm], [0.1–0.4 mm], [0.2–0.6 mm], [0.3–0.8 mm], [0.7–1.25 mm] and [1.0–2.0 mm] with the grain density 2.65 g/cm3, each), obtained from Holcim Kies und Beton GmbH. The Elkem Material Mix Analyser (EMMA) software was used to generate a grading curve with an optimized packing density based on the Modified Andreassen model. The grading curve was designed only with respect to the aggregate content disregarding the finer UACP particles. It was assumed that the low amount of UACP with particle sizes of 3 to 15 μm would not affect the aggregate packing density. The resulting grading curve is shown in Fig. 1A.Fig. 1: Aggregate packing density optimization.A Grading curve of the optimized sand mix with grain sizes of 0.063–2 mm (blue) in comparison to the theoretical Andreassen-curve (red). B Volume compositions of mixes with 1.5% (w/wdm) UACP in the compacted specimen.Subsequently, compaction experiments were carried out to compare the packing density of the optimized mix with homogeneous aggregates, along with UACP. The volume compositions of the mixes after compaction were determined based on their weights, the mass fractions of the mix components and the densities of the respective materials.Two parameters were employed to characterize the packing density in the ...