MICROSTRUCTURAL STABILIZATION OF SUSTAINABLE EARTH-BASED MATERIALS: EXPERIMENTAL CHARACTERIZATION AND MODELLING

Earthen structures constructed from soil-based materials are extensively recognized as an environmentally sustainable building solution. The fight against climate change has delineated new objectives, among which one of the most crucial is the replacement of high-energy intensity materials (cement) in the construction sector with more sustainable, thermally efficient, high mechanical strength and excellent hygroscopic characteristics. Consequently, the thermal properties of materials assume fundamental importance. In this regard, the large-scale use of earth represents a promising option, not only due to its widespread availability but especially for its minimal embodied energy making them a significant area of study in sustainable building research. This thesis investigates the efficiency of bio-based polymers, S-BAR and D-UAR, along with the natural biopolymer Opuntia ficus-indica (OFI), as stabilizers for enhancing the properties of earthen construction materials. As a preliminary step, an experimental campaign was carried out to examine the mechanisms of natural and bio-based polymer stabilization and optimize its application in earthen construction materials. The results demonstrate that the strength of bio-stabilized soils arises from a synergistic interaction between soil and hydrogel formation. This study analyses experimental systems based on earth stabilized with natural and bio-based polymers to evaluate their thermal properties and how these vary depending on the selected mix design. Experimental measurements have shown thermal properties comparable to conventional materials. However, the data obtained for individual systems may vary depending on the topological characteristics, which were analysed through a model for granular materials. The modelling suggests correlations between microstructures and thermal behaviour, which can be useful to develop tools for mix-design procedure. Statistical analysis was conducted on thermal conductivity data using ANOVA with a significance level of 0.05. The experimental and statistical findings reveal environmental samples of mix designs show improvement in thermal performance in the dry conditions. In a subsequent phase of experimental research, the capability absorption and mechanical properties of bio-stabilized soils were investigated to measure their structural performance and functional efficacy. Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), colourimetry and X-ray Diffraction (PXRD) analyses of natural and bio-based polymer-stabilized earthen materials yielded positive results, confirming enhanced structural integrity and compositional stability.