Evaluation of the effects of intrinsic soil calcium carbonate and iron oxides on the properties of earthen building materials by means of engineered soils
2025
Nikiforos Meimaroglou | Charalampos Mouzakis
Abstract In the context of sustainable development, earthen building materials could be a viable alternative to conventional, energy-intensive materials if the constraints to their general acceptance and widespread use are mitigated. A key challenge is the limited understanding of how intrinsic soil properties influence the performance of these materials. This study investigates the role of intrinsic iron oxides and calcium carbonate, components that are believed, yet not conclusively proven, to exert a strong influence on earthen materials by increasing strength and reducing shrinkage through aggregation and cementation mechanisms. Engineered soils based on kaolin powder, bentonite powder, and a natural clayey soil were prepared and combined with ferric oxide, iron powder, and fine limestone powder to produce mortars. Mortars with iron and iron oxides exhibited no significant improvement in compressive strength, a finding attributed to the high crystallinity and low solubility of the oxides used, as well as to the alkaline pH of the soils. In contrast, mortars containing limestone powder exhibited remarkable strength gains across all soil types, demonstrating that intrinsic CaCO3, particularly its finer and more reactive fraction, can positively impact strength development. Further analysis, including pH cation exchange capacity (CEC) and exchangeable calcium measurements, revealed that limestone powder actively interacts with the soil’s exchangeable complex, driven by its significant active calcium carbonate (ACC) content. These results underline the importance of soil chemistry in the performance of earthen building materials.
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