## 2 Current Situation of Olive Stones in Spain
### Economic Cost of Mortar Doped with Olive Stones  
Ground olive stones can be used as a mortar doping to reduce the thermal conductivity of the mortar and, consequently, reduce the energy demand for heating and air conditioning by reducing the thermal transmittance of newly constructed buildings. As such, one must bear in mind that increasing the percentage of olive stones also produces a decrease in the mechanical compressive strength that the different mortars are capable of withstanding. These characteristics limit its use in construction, since it is not capable of withstanding great stresses, and for this reason, mechanical specimens are made with a maximum percentage of olive stone of 30% [23]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Composition** & & **Percentage** \\ \hline \multirow{5}{*}{Chemical composition} & C (\%) & 50.2 \\  & O (\%) & 45.2 \\  & H (\%) & 7.02 \\  & N (\%) & 0.47 \\  & S (\%) & 0.04 \\ \hline \multirow{5}{*}{By component} & Lignin (\%) & 32.1 \\  & Hemicellulose (\%) & 34.8 \\ \cline{1-1}  & Cellulose (\%) & 26.9 \\ \cline{1-1}  & Soluble (\%) & 5.4 \\ \cline{1-1}  & Ash (\%) & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical analysis of ground olive stones. Figure 4: (**a**) Mortar specimens doped with ground olive stones. (**b**) Raw material of ground olive stones. (**c**) Surface image of the ground olive stone in the mortar specimen. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Mortar** & **Compression** & **Flexural** & **Thermal Conductivity** & **Density** \\
**Sample** & **Strength (MPa)** & **Strength (MPa)** & **\(\lambda\) (W/m-k)** & **(kg/m\({}^{3}\))** \\ \hline M-0 & 14.18 & 3.41 & 1.050 & 2080.42 \\ M-5 & 10.31 & 2.61 & 0.867 & 2021.67 \\ M-10 & 10.31 & 2.15 & 0.917 & 1978.13 \\ M-15 & 10.87 & 1.92 & 0.847 & 1918.34 \\ M-20 & 9.62 & 1.62 & 0.703 & 1854.79 \\ M-25 & 12.45 & 1.53 & 0.773 & 1803.34 \\ M-30 & 10.24 & 1.48 & 0.607 & 1796.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of mechanical and thermal properties of mortar with ground olive stones. Similarly, the addition of more than 15% of ground olive stone in the total weight of mortar has also been evaluated as unprofitable. The energy recovery of the incorporated residue exceeds 75 years compared to the energy that could be obtained by burning the stone with a useful yield of 75%. This is too long a period of time for the useful life of a building [24]. However, this period of time for doping between 5% and 15% does find a correct balance between the amount of olive stone provided and the reduction in demand. Thus, the time period for combustion energy recovery was established according to the different climatic zones by the Technical Building Code in Spain [41]:  
* Between 30 and 37 years for the 5% doped (mean value 34 years);
* Between 47 and 58 years for the 10% doped (mean value of 53 years);
* Between 59 and 72 years for the 15% doped (mean value of 65 years). These values, although high, are still within the useful life of a building (75 years), making it a cost-effective measure from an energy point of view. At an economic level, this substitution of materials has repercussions on prices since the price of fine aggregate is usually lower than that of ground olive stone residue. For the calculations, an average price for fine aggregate of 12 \(\epsilon/t\) (average price for 2021 supply according to the National Association of Aggregates Manufacturers--ANEFA [42]) and 167 \(\epsilon/t\) for ground olive stone (average price AveBiom 2021 [36]) is used. The price increases per m\({}^{3}\) of treated mortar are shown in Table 4.  
The m\({}^{3}\) of 5% doped mortar is 3.5 \(\epsilon/\)m\({}^{3}\) more expensive than undoped mortar. And this value increases to 7.41 \(\epsilon/\)m\({}^{3}\) for M-10 and 10.72 \(\epsilon/\)m\({}^{3}\) for M-15. It should be borne in mind that a m\({}^{3}\) of conventional fine aggregate mortar averages around 60-70 \(\epsilon/\)m\({}^{3}\).