## 2 Materials and Methods
### Lightweight Aggregate (LWA) Preparation and Characterization  
Expanded clay is a product resulting from the firing of clay at around 1200 \({}^{\circ}\)C in a rotary kiln that is obtained as a pellet [18] and commercialized under different brand names, such as LECA (Light Expanded Clay Aggregate) and LIAPOR (Porous Lias Clay). It retains its characteristics over time; does not release toxic substances, disperse fibres or particles or require stabilizing treatments; and is used in the agricultural, construction and road sectors and as a material with sound-absorbing properties and fire, mechanical and thermal resistance [19]. The UNI EN 206-1: 2006 standard [20] defines lightweight aggregate as an \"aggregate of mineral origin having a density of granular particles dried in a stove \(\leq\) 2000 kg/m\({}^{3}\) determined according to UNI EN 1097-6 or a density dried in a kiln \(\leq\) 1200 kg/m\({}^{3}\) if determined according to UNI EN 1097-3\". In this work, samples were produced based on 85 parts clay and the remaining 15 weight-lightening agents, such as pyrolysis char obtained from the carbonization of cork waste at 420 \({}^{\circ}\)C. These percentages were optimized in a previous work [21]. Some samples were produced starting from clay, char and spent coffee grounds (Sample 1, Char 7.5%), which have been previously studied in the formulation of this type of material [22], or from clay and char (Sample 2, Char 15%). In detail:  
1. Char 7.5%: 1. 85 wt% clay (<1000 \(\mu\)m); 2. 7.5 wt% char from pyrolysis at 420 \({}^{\circ}\)C of the cork scrap (<1000 \(\mu\)m); 3. 7.5 wt% powder from exhausted, dried and sieved spent coffee grounds (<250 \(\mu\)m). 2. Char 15%: 1. 85 wt% clay (<1000 \(\mu\)m); 2. 15 wt% char from pyrolysis at 420 \({}^{\circ}\)C of the cork scrap (<1000 \(\mu\)m). In the first composition, the lower amount of char was compensated with SCGs (post-consumer residue) with good performance as a porous agent. In both formulations, char from pyrolyser cork waste was used but not as it was received because in the first attempt we had problems when making prototypes that resulted in cracks, particularly following the introduction of 15% cork powder [8]. The clay, first suitably ground with a fast ball mill, was then mixed in an agate mortar along with the two pouring agents mentioned above by means of a spatula, with distilled water carefully added, in order to obtain a workable paste. It was important in this phase to ensure semi-plastic behaviour in the compound, so as to be able to create a row that could be positioned on a mechanism that would allow it to be separated into balls [23]. Small spheres with weights varying between 1.5 g and 2 g were then obtained manually from the dough, with the samples intended to be similar in weight and shape to commercial LWAs (diameter 0.6-1.0 cm). Once the LWAs spheres were produced, they were first dried in the oven at 105 \(\pm\) 5 \({}^{\circ}\)C for 24 h in order to remove the excess water used in the dough preparation process and then fired inside ceramic crucibles in an electric static oven preheated to a temperature of 1000 \({}^{\circ}\)C for 1 h in an air atmosphere. This process subjected the aggregates to a thermal shock similar to that which they would undergo in industrial processes; these latter, however, occur at higher temperatures (from 1200 \({}^{\circ}\)C to 1400 \({}^{\circ}\)C) [23]. Finally, some important parameters for the use of the aggregates were evaluated, as described below. * **Shrinkage after firing (SF%):** this was calculated based on two measurements of diameter, post-drying (D\({}_{\text{d}}\)) and post-firing (D\({}_{\text{f}}\)), for ten LWA samples per formulation.