This research examines the feasibility of using excavated soil (clay content of 44 %) as 25 % and 50 % replacement of natural sand in 3D printable formulations. A combination of ordinary Portland cement (OPC) and fly ash (FA) are used as binders for stabilization. The development of engineering properties subject to two curing conditions - normal curing and CO2 curing (5 % concentration for 5 h) are investigated. Experimental findings suggest that a combination of FA and clay (mainly kaolinite) in the used soil reduces plastic viscosity and improves flow retention, thus enhancing the extrusion quality and stability. The flocculation of clay at rest accelerates the evolution of static yield stress after extrusion, imparting 18-30 % better thixotropy. As a result, OPC-FA-soil mixes could be stacked to a height of 1.20 m compared to 0.48-0.54 m for OPC-sand and OPC-FAsand mixes. Carbon sequestration via CO2 curing leads to an increase in wet compressive strength of OPC-25 % soil and OPC-FA-25 % soil by 29-38 % and 26-47 % respectively at 1-day age, which is ascribed to the densification effect of mineral carbonates. This is also reflected in the reduction in water sorptivity through the interlayer zones and total shrinkage by 20 % and 16 % respectively. Due to reduced shrinkage and capillary sorption, inter-layer bond strengths in CO2-cured OPC-25 % soil are also improved by 20-50 % than the normally cured counterpart. In summary, the research demonstrates a feasible pathway to develop carbon-sequestering earthbased materials (CO2 uptake of 9-11 wt% of OPC) for additive manufacturing of masonry building and infrastructural members.

This article investigates the hygrothermal properties of earth-based materials by analyzing experimental data from 88 articles spanning 32 countries worldwide. The focus is determining effective techniques for leveraging the use of excavated soil in construction, particularly emphasizing enhancement of hygrothermal comfort in specific climates. Based on statistical analysis, the study presents a comprehensive classification of earth production techniques, incorporating additives, and examines their impacts on hygrothermal properties of excavated soils. Additionally, it explores the intricate relationship between the climatic conditions of a region and the chosen earth-material production techniques. The analysis aims to propose standard parameters for earthen materials and identify gaps in both methods and experimental studies. Therefore, this study will provide valuable insights by proposing new design tools (ternary diagrams) to maximize the use of excavated soils in construction practices. The proposed diagrams illustrate the intricate relation linking either hygrothermal properties, the climate zone, and manufacturing techniques, or the relation between the most studied manufacturing techniques (compaction, fibered, and stabilization) and expected dry thermal conductivity. Thereby, results from this meta-analysis and critical review will contribute to advancing sustainable construction practices.