# Mechanical and Physical Characterization of Papercrete as New Eco-Friendly Construction Material
## 3 Results
### Capillary Water Absorption Tests  
Water absorption is a crucial property for construction materials because it influences their durability. Water absorption coefficient C, expressed in [kg/(m\({}^{2}\)\(\times\) min\({}^{0.5}\))], corresponds to the line slope joining the representative points measurements and represents the absorbent capacity of the material [27]. After 28 days of wet curing, the four long faces of the prismatic specimens were sealed with the paraffin and then they were broken into two halves. Hence, they were oven-dried up to constant mass at 60 \({}^{\circ}\)C and finally immersed in a shallow bath of water at a temperature equal to 20 \({}^{\circ}\)C and at a depth of about 6 mm. For a more efficient evaluation of the coefficient C, tests were performed in a more complete procedure [28] with respect to the protocol indicated in Reference [27], taking into account more points for the linear regression representing the material adsorbent capacity. In particular, the uptake of water by capillary absorption was calculated through each specimen resulting weight, measured at the following times after the immersion beginning: 10, 30, 45, 90, 120 min. It should be noted that in Reference [27], only weighing at 10 and 90 min are indicated. The equation used to model the absorption of water due to capillary action is the following:  
\[A=\left(St^{0.5}+a_{0}\right) \tag{1}\]  
where \(A\) [mg/mm\({}^{2}\)] is the water absorbed by the area unit since it is immersed in water; \(S\) [mg/(mm\({}^{2}\)\(\times\) min\({}^{0.5}\))] is the material absorptivity; \(t\) [minutes] is the elapsed time; \(a_{0}\) [mg/mm\({}^{2}\)] is the water initially absorbed by the pores in contact with water. Figure 5 shows the measured relationships between the water absorbed by the immerged specimen per unit area (measured as total weight at a certain time divided by 1600 mm\({}^{2}\)) and the time square root [27]. In particular, Figure 5a,b shows the results of 'PAPER' and 'PULP' specimens, respectively. In the same graphs, the linear regressions of the experimental values are reported, together with the correlation coefficient \(R^{2}\). In this way, the capillarity absorption coefficient \(S\) is calculated, summarized in Table 4 together with the absorption variation percentage calculated with respect to the 'REF' specimen [(S\({}_{\text{PAPER/PULP}}\)-S\({}_{\text{REF}}\))/S\({}_{\text{REF}}\)\(\times\) 100]. As regards the waste paper, it is easy to note that the percentage of water absorption drastically increases as the recycled paper content increases. This is due to the fact that the spaces in the lower density samples are larger, allowing water to penetrate more easily into the specimen matrix. Water absorption is inversely proportional to the fiber cement density [29], and the presence of cellulose materials facilitates water absorption. This demonstrates the necessity to provide waterproofing behavior or an additional coating to the paper mixture in order to contrast the water absorption. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **REF** & **PAPER2** & **PAPER5** & **PAPER10** & **PULP2** & **PULP5** & **PULP10** \\ \hline S [mg/(mm\({}^{2}\)\(\times\) min\({}^{0.5}\))] \(\times\) 10\({}^{-1}\) & 2.95 & 4.06 & 4.32 & 8.59 & 1.05 & 1.87 & 3.54 \\ \% variation & - & 37.6 & 46.4 & 191.2 & \(-\)64.4 & \(-\)36.6 & 20.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Capillarity water absorption coefficient values and percentage variation. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Thermal Conductivity \(\lambda_{10}\) [W/mK]** & **Thermal Resistance [m\({}^{2}\)K/W]** \\ \hline REF & 0.396 & 0.064 \\ PAPER2 & 0.283 & 0.089 \\ PAPER5 & 0.221 & 0.114 \\ PAPER10 & 0.206 & 0.124 \\ PULP2 & 0.381 & 0.065 \\ PULP5 & 0.297 & 0.086 \\ PULP10 & 0.314 & 0.082 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of thermal tests. On the contrary, as regards the pulp, different behaviors are observed.