_Applied sciences_  
_Article_  
Influence of Particle Size on Compressed Earth Blocks Properties and Strategies for Enhanced Performance  
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production of which involves high energy consumption. However, modern applications require building materials to meet specific functional requirements. Despite the advantages listed above and the long tradition of earthen construction, many aspects related to the functional performance of these blocks are still unclear. This is especially the case with hygrothermal performance. In fact, while the numerous studies on mechanical aspects make it possible to affirm that the compressive strength of soil samples varies approximately between 1 and 2 MPa, the same cannot be said of thermo-hygrometric parameters [6]. The data available in this area are much less and more scattered. Although an inverse linear correlation with bulk density is attributed to the thermal response [7], this has not yet been established with a reasonable degree of certainty. Indeed, it depends on many factors and the inherent variability of soils in nature, combined with the lack of experimental data, makes their characteristics unpredictable.  
When evaluating the performance of the material, the influence of particle size is an aspect that is often overlooked [8]. Some studies addressed this aspect in compacted earth-based materials (e.g., hyper-compacted earth [8; 9] or cement-stabilised soil cylinders [10]), but they tend to focus on (hygro-) mechanical or durability aspects. Such investigations reveal that finer-textured soils exhibit superior strength and durability than coarser soils. However, there is a gap in evaluating thermophysical attributes such as thermal conductivity and thermal capacity. Understanding these properties is crucial for assessing and optimising energy efficiency and overall thermal performance at the building scale. To the authors' best knowledge, there is only a study from 2019 [11] involving cement-stabilised rammed earth walls that found that grading differences can bring variations in the R-value. To study these grading differences, the authors of this research created a range of three subsoils by mixing a selection of gravel, sand, and silty clay in different proportions. The problem under consideration is also particularly interesting from a practical point of view. When it comes to earth as a building material, the natural soil grain distribution is often amended to obtain new, well-graded soil with desired characteristics. This is to guarantee the homogeneity of the mixture, which is essential to ensure a good porosity and porous structure, as well as stability. The addition of sand is the most common example, as it allows for better water permeability in the case of clayy soils [8; 9]. On the contrary, sandy soils may lack cohesion and be weak or unstable [12]. In these cases, the addition of mineral stabilisers (time or cement) is common [13]. Alternatively, soils can be collected from various sites [10]. Other less conventional approaches found in the literature are (i) the addition of lime-cement blend [13], (ii) the reduction of clay and silt content via washing [14], and (iii) the addition of a mix of river sand and construction and demolition waste [15]. These studies investigate the effect of grain size curve corrections on the quality of the newly obtained soils, mainly through mechanical and durability tests. However, these corrections bring microstructural, mineralogical and, more generally, physical changes, which inevitably interfere with the thermo-hygrometric attributes.