## 4 Conclusions  
This paper presents the results of a study of mixtures whose particle size distributions were based on the particle size distributions of soil samples taken from traditional rammed earth houses in eastern Croatia. Additionally, lime, cereal straw and industrial hemp fibers were added to certain mixtures. Direct shear tests were carried out on those samples. Based on the results obtained from the direct shear tests, the following points were observed and can be concluded:  
* The shear strength of the samples increased with time. The aforementioned phenomenon can be connected to the drying of the samples over time. However, it is necessary to keep in mind that the tested samples were up to 28 days old, and it is possible to expect stabilization in the shear strength values, for samples exposed to the same conditions, over time. This needs to be further investigated in older samples. Figure 13: Cohesion and internal friction angle values change with specimen age, samples M4 and M7–M11 (influence of natural fibers): (**a**) cohesion; (**b**) internal friction angle. * In the case of samples tested on the day of installation, no significant differences in peak shear stresses were recorded for the observed samples. The influence of a lower content of cohesive soil, lime and natural fibers (cereal straw and hemp fibers) was seen with the aged samples. * Samples with a lower content of cohesive soil generally had higher shear strength. Further research is needed to determine the optimum grading curves, i.e., the soil composition for the area of eastern Croatia. * The samples with a lower lime content (4%) proved to be better than the samples with a higher lime content (8%). To determine the optimum lime content in the observed mixture, additional research is needed. An increase in strength was recorded in samples aged 7 days compared to samples tested on the day of installation. Further ageing of the sample (samples aged 28 days) did not record any further contribution of lime to the increase in the shear strength of the sample. * Adding natural fibers increased the shear strength of the samples. The best results were recorded for the sample micro-reinforced with rye straw. It is recommended to additionally investigate the optimum content of natural fibers in the mixtures with regard to the shear strength of the sample. * By comparing the values of cohesion and the internal friction angle, an increase of 138.5% (average value) in the cohesion value and 21.3% (average value) in the value of the internal friction angle was recorded when comparing the values of the strength parameters of samples aged 28 days and the samples tested on the day of installation. * The addition of lime to the base mixture did not significantly improve the shear strength, in contrast to the addition of cereal straw and hemp fibers, which can significantly contribute to the shear strength of the material even if added in very small fractions. * Although mixtures M2, M3 and M4 are similar in the context of granulometry, they do not behave similarly when subjected to shear loading. Thus, it can be concluded that granulometry has no significant influence on the shear properties of the material, which is why it is possible to conclude that the existing houses in eastern Croatia will behave similarly when exposed to external loads that cause shear stresses (e.g., earthquakes). Through this research, we obtained the results and conclusions that will be applied to draft norms and recommendations for the design of earthen structures in Croatia. In addition, this will enable the rehabilitation of existing structures, which are in a very poor condition and pose a threat to the environment or the people who still use them. In order to raise the level of understanding of the behavior of rammed earth, future research should cover particle breakage behaviors, following the methodology described in Refs. [44; 45]. Conceptualization, J.K. and I.K. ; methodology, J.K. and I.K. ; formal analysis, J.K.; investigation, J.K., I.K., A.P. and L.K.