## 3 Case Study--Description and Technical Assessment Results  
As mentioned, the implementation of the circular model allowed not only to use line ash as an alternative filler in the precast concrete industry but, at the same time, to avoid its landfilling in the pulp industry. The precast concrete industry produces a variety of products, such as the linear concrete elements (trusses and pillars) used in this study. In this industrial-scale trial, implementation of the circular model involved the following 12 steps (Figure 1): 1. Lime ash storage at waste producer; 2. Lime ash transportation to the precast concrete factory; 3. Concrete mixture ready for application; 4. Preparation of the reinforcement bars and moulds for beams and columns execution; 5. Internal sensors installation for future in situ monitorisation; 6. Concrete discharge into the form and execution of concrete samples for monitoring tests; 7. Curing and drying process; 8. Columns and beams for the frames; 9. Land preparation and direct foundations execution; 10. Columns assembly; 11. Beams and girders assembly; 12. Final frames structure. Figure 1: Implementation of lime ash in precast concrete (12 steps). To produce the precast concrete columns, the standard formulation shown in Table 1 was used. Each column consumes 2.1 m\({}^{3}\) of concrete and has a section of 0.5 \(\times\) 0.4 m\({}^{2}\) and 10.25 m in height, being its strength class the C30/37 one. In the case of concrete, the aggregate is based on the EN 12620 product standard, which identifies the minimum requirements that the aggregates must meet (particle size analysis) and the set of properties to be characterised (density and quality of fines). Thus, Table 2 shows the properties of lime ash and natural limestone filler (ref. Betocarb-OU), which were characterised in the laboratory. The results with lime ash are like those of the natural filler it replaced, representing, according to the formulation in Table 1, a filler percentage of 4.4 wt.% (104 kg per m\({}^{3}\) of concrete). Figure 2 shows lime ash and natural filler particle size distribution (EN 933-10). A filler usually presents 70% of particles below 63 microns and, as it is possible to observe, lime ash particle size is within the defined minimum limit for a filler, making it possible lime ash to be used as such. In step 6 of the implementation, 12 samples were collected from the circular (concrete with lime ash) and linear model (reference concrete) cases to evaluate the compressive strength, the concrete density in the hardened state at 7, 28, 180 and 365 days of curing (Figure 3), as well as three samples for water absorption and capillary coefficient (Figure 4) \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Standard** & **Natural Filler** & **Lime Ash** & **Units** \\ \hline Particle density & EN 1097-6 & 2.66 & 2.60 & Mg/m\({}^{3}\) \\ Fines quality & EN 933-9 & 0.1 & 0.2 & g/kg \\ Specific surface area & BET method & 0.786 & 1.156 & m\({}^{2}\)/g \\ Composition & XRD analysis & Calcite (100\%) & Calcite (96\%) and Lime (4\%) & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics for lime ash and natural filler. Figure 2: Particle size distribution of filler and lime ash. measurements with curing time (for 28, 180 and 365 days). Internal sensors placed for temperature and shrinkage control showed similar results during this time. The harmonised standard for precast concrete establishes a minimum compressive strength class for columns and, at the beginning of the pilot design, that was defined to be C30/37. The results in Figure 3b are according to the required class from the project design. Moreover, the standard deviations in the results shown in Figures 3 and 4 were so negligible that their respective statistical deviation bars would not appear in these figures scales. Regarding water absorption and capillarity coefficient, the behaviour of concrete containing lime ash is also like that of the reference concrete.