# Mechanical and Physical Characterization of Papercrete as New Eco-Friendly Construction Material
## 4 Masonry Panels Strengthened with External Papercrete Layers  
The experimental results show that the new mortar produced using waste paper or paper pulp is capable of reaching mechanical strengths comparable with the ones provided by classical structural mortars applied in the masonry panels. For instance, for structural applications [31, 32], mortars having compressive strengths higher than 1.0 and 2.5 N/mm\({}^{2}\) are required, respectively. Moreover, compressive strengths higher than 20 N/mm\({}^{2}\) may be reached. In this work, the results obtained from mechanical tests show that concrete with different volumetric percentages of paper/pul reaches a compressive strength between 6.92 N/mm\({}^{2}\) and 14.11 N/mm\({}^{2}\), so it is suitable for structural applications. In addition, due to its not negligible strength values, the papercrete should be applied also as external jacketing of masonry walls, alternatively to the traditional strengthening interventions steel jackets. To this scope, one may calculate the contribution of the external papercrete layers with the following analytical expression, as follows [33]:  
\[f_{t,mn}=\beta\cdot f_{t,um}+2\cdot\left(f_{t,plast}\cdot\frac{t_{plast}}{t_{ lum}}+\frac{EA_{r}\cdot\overline{\epsilon}}{t_{um}\cdot p}\right) \tag{2}\]  
where \(f_{t,m}\) is the reinforced masonry equivalent tensile strength; \(f_{t,um}\) is the unreinforced masonry tensile strength; \(f_{t,plast}\) is the papercrete plaster tensile strength; \(t_{um}\) is the masonry thickness excluding reinforcement; \(t_{plast}\) is plaster thickness; \(p\) is the reinforcing mesh size (if any); \(EA_{r}\) is axial stiffness of a mesh wire (having transversal area \(A_{r}\)); \(\overline{\epsilon}\) is the mortar deformation in the uncracked condition, given by \(\overline{\epsilon}=\frac{f_{t,plate}}{E_{plant}}\), where \(E_{plast}\) is the plaster elastic modulus; \(\beta\) is the coefficient taking into account the efficiency of the papercrete plaster on the tensile strength depending on the type of masonry, conservatively assumed in this study equal to 1. The previous equation has been derived by assuming that the external papercrete jacketing is applied on both faces of the masonry panel and that the maximum tensile strength of the reinforced masonry panel is attained at the first cracking of the external papercrete plaster. Figure 5: Capillary absorption vs. time square root: (**a**) ‘PAPER’ specimens, (**b**) ‘PULP’ specimens. Equation (2) reveals that the tensile strength of reinforced masonry panel is ideally provided by three terms: the tensile strength of unreinforced masonry, the one of the external layers, and the one offered by the additional reinforcing mesh. If this external reinforcement is not applied, then the third term of Equation (2) may be assumed equal to zero. For instance, Figure 6a shows the equivalent tensile \(f_{t,mn}\) plotted as a function of the papercrete jacketing \(t_{plast}\), by referring to the case of a brick masonry panel strengthened on the two faces with a papercrete layer, by assuming a \(f_{t0}=0.2\) N/mm\({}^{2}\), and a compressive strength \(f=3.45\) N/mm\({}^{2}\).\(f_{t,mn}\) is calculated with Equation (2) where, according to the References [31; 32], the unreinforced masonry tensile strength \(f_{t,um}\) may be calculated starting from the \(f_{t0}\), that is the masonry shear strength, as \(f_{t,um}=1.5f_{t0}\). It should be pointed out that in the case analyzed, \(f_{t0}\) refers to the shear strength associated with stair step cracks for masonry of good texture. According to the formulation adopted, it should be noted that the higher the \(t_{plast}\), the higher the \(f_{t,rm}\). For sake of completeness, in Figure 6b, the ratios \(f_{t,rm}\)/\(f_{t,um}\) are illustrated. It is clear to note that, in the range analyzed, due to the papercrete applied the tensile strength, \(f_{t,rm}\) may be higher than 4 times the \(f_{t,um}\) in the case of PULP5 specimen.