## 2 Materials and Methods
### Laboratory Agglomeration Tests and Recipes  
For the agglomeration tests in the laboratories of RWTH Aachen University and the University of Oulu (UOulu), two different presses were used (Figure 14). The Gabbrielli L-4 stamp press located at RWTH and the vibrating stamp press located at UOulu were used to produce full-sized bricks with different agglomeration parameters.  
In the pretests, a number of binders were tested, including sodium silicate, polyethyleneylcol (PEG), carboxymethylcellulose (CMC), different types of starch, molasses, copolymer binders and superabsorbers. In addition to these different binding systems and agglomeration parameters, such as pressing force, pressing time, aging condition and so forth, additives were also investigated. CaCO\({}_{3}\), bentonite, SiO\({}_{2}\) and sodium silicate hardener were used with a sodium silicate binder. Fibres from paper recycling were also tested to increase the strength of the produced agglomerates.  
Based on these pretests, starch was selected as the binder for the agglomerates and fibres from paper recycling were chosen as the additive to increase the strength of the agglomerates. Table 12 shows the recipes used for the laboratory production of the agglomerates. The press parameters SC and BC denote the use of two different upper stamps in the Gabbrielli stamp press at RWTH resulting in a clearance between mould and upper stamp of 50 (SC) and 500 (BC) \(\upmu\)m, respectively. The mould itself was of round geometry and 73 mm in diameter.  
After the mixing of the components, the pressing procedure was carried out. Since the manufacturing pressure (MP) is the most important parameter of the pressing process, it was varied for each of the first four recipes at RWTH, except MA604B SC, between 10 and 40 N/mm\({}^{2}\) in steps of 10 N/mm\({}^{2}\). MA604B SC was produced with only two MPs of 10 and 40 N/mm\({}^{2}\). For each step, four briquettes were press  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**PEAK TEMPERATURE (\({}^{\circ}\)C)** & **MASS LOSS (\%)** & **TRANSFORMATION** \\ \hline
177 & 0.334 & Zeolite dehydroxylation \\
690 & 1.551 & Calcite calcining \\
1120 & 2.759 & Melting \\ \hline \hline \end{tabular}
\end{table}
Table 11: Transformation temperature from TG-DSC of combustion chamber thermal analysis.  
Figure 14: Gabbrielli L-4 stamp press (RWTH Aachen University, left) and vibrating stamp press (University of Oulu (UOulu), right).  
The samples manufactured at RWTH showed sufficient green strength for further handling. In order to allow for further hardening, the samples were placed on wooden pallets in ambient atmosphere and ambient temperature for a minimum of 10 days in order to imitate a possible later industrial production (curing) process without further drying/heat treatment.  
The recipe UO was used to produce a total of 10 briquettes with a Carver vibrating press. The maximum vibration was 50 Hz and the MP was 20 N/mm\({}^{2}\). The produced briquettes were used to carry out drop and compression tests after 2 and 7 days of curing in ambient conditions. Since the grinding sludge contained a high water content, recipes that incorporated GS did not require more water during mixing. Throughout the curing time, the dimensions and mass of the produced briquettes were measured on a daily basis. On average, briquette size remained virtually unchanged and exhibited less than 1.5% mass loss. Mass loss was likely due water evaporation from briquettes during curing.