## 4 Conclusions  
The thermal properties and microstructures characterizations of new insulating materials based on Juncus martimus mortar composites were investigated. The thermal properties measurement was performed using boxes method and the microstructures characterization was studied using scanning electron microscope (SEM) and micro computed Tomography (\(\mu\)CT) techniques. The results presented herein point out that the crushed Juncus martimus fibers present low thermal conductivity, close to insulating materials such as wood shaving, date palm fibers (DPF). They could be used to replace the traditional reinforcement (such as glass fibers). A specific attention is put on the influence of Juncus maritimus fibers content.  
It is shown that the increasing of the Juncus maritimus fibers content in the mortar induces increasing of porosity of mortar composite, porosity is almost two times higher than the reference mortar. Subsequently, the overall thermal conductivity is reduced by up to 67% for 10% of JM mass fraction in the mortar matrix; the thermal diffusivity is reduced by about 37% compared to reference mortar. Furthermore, the use of the Juncus maritimus particles as reinforcement in the mortar matrix decreases its density by up to 44%. As a result, these new lightened composites are shown to present efficient thermal performance materials. Thus the use of the natural material \"Juncus maritimus\" in the construction materials is promising. In future work the mechanical properties could be investigated and improved using chemical treatment of Juncus maritimus fibers.  
We investigate also thermal conductivity analytical models of composites. The thermal conductivities of each solid phase constitutive of the materials are required. Such local conductivities are difficult to measure directly. The solid thermal conductivity of dense mortar is determined by fitting Hadley model results and experimental measurements of the effective thermal conductivity of the porous mortar samples without fibers. This method leads to the identification of the solid thermal conductivity of dense mortar, \(k_{s}\) = 2.868 W/m\(\cdot\)K. Hence, the effective thermal conductivity of porous mortar is deduced theoretically by Hadley model for different porosities.  
On the other hand, the local thermal conductivity of Juncus maritimus is particularly difficult to determine, such data are not available in literature. It is identified by fitting experimental effective conductivity of samples and analytical modeling results. Effective thermal conductivity measurements are performed on packed bed of crushed fibers but also on mortar composites samples. Both measurements are complementary and are recommended in order to analyze the results, to guide the identification of local thermal conductivity of Juncus maritimus and to choose the most appropriate analytical models.  
Indeed, measurement of effective thermal conductivity performed on packed bed of crushed fibers permit to obtain a first estimation of \(k_{J\mathrm{MS}}\). We have shown that this value \(k_{J\mathrm{MS}}\) = 0.76 W/m\(\cdot\)K could be overestimated due to the radiative contribution. Thus, we can deduce that the value of \(k_{J\mathrm{MS}}\) identified from mortar composites samples must be lower than the first estimation of \(k_{J\mathrm{MS}}\). It was deduced that the Glicksman model is the most appropriate model and an estimated value of 0.472 W/m\(\cdot\)K for local thermal conductivity of Juncus maritimus is obtained.  
Investigation and writing-original draft Z.S.; Methodology, Z.S.; D.B. and A.J.; Supervision and validation, D.B., A.J., N.N. and N.B.  
This research received no external funding.  
The authors declare no conflict of interest.