## 2 Material and Methods
### Experimental Methods  
GS sample was submitted to physical-chemical characterisation at the Department of Materials and Ceramic Engineering of the University of Aveiro (PT). The sample was characterised for (i) moisture content, (ii) particle size distribution, (iii) shrinkage, (iv) colour coordinates, (v) chemical and mineralogical composition by X-ray diffraction (XRD) and X-ray fluorescence (XRF), and (vi) Loss on Ignition (LOI).  
The moisture content was obtained by heating the sample at 110 \({}^{\circ}\)C (AE Adam Equipment Co, AMB 310, Milton Keynes, UK) until constant weight. The particle size distribution was determined by laser scattering (Coulter LS230 analyser, Miami, FL, USA). To estimate melting/fluxing characteristics and colour coordinates, pressed pellets of GSwith 25 mm diameter were fired at different temperatures, and their shrinkage and colour coordinates were measured. Shrinkage was measured as a percentage of reduction from the initial diameter of the pellets after firing, whereas the colour coordinates were measured in a portable colourimeter (Konica Minolta Chroma Meter CR-400, Tokyo, Japan), using DC illuminate and 10 standard observers (Y: 94.0, x: 0.3130, y: 0.3191) according to the Commission Internationale de l'Eclairage (CIE). CIEL*a*b*d data are expressed as brightness L*, changing from 0 (black) to 100 (white), a* (+ red, \(-\) green), and b* (+ yellow, \(-\) blue) [23].  
Crystalline phases present on the granite sludge were analysed via X-ray diffraction (XRD- Panalytical, Almelo, The Netherlands) with Cu K\(\alpha\) radiation, 10-80\({}^{\circ}\) 20, scanned from 0.02\({}^{\circ}\) 20 intervals and 10 s per step, using PANalytical X'Pert HighScore Plus PRO3 software. X-ray fluorescence (XRF, Philips X'Pert Pro MPD, Malvern Panalytical,  
Malvern, UK) was performed to evaluate their chemical composition. LOI was determined at 1000 \({}^{\circ}\)C during XRF analysis.  
For the assessment of the technical suitability of GS incorporation as a partial substitute for fine-medium inert materials in structural concrete mixtures, 25 L of concrete paste was prepared at the central laboratory of BETAO LIZ (CIMPOR Group, Coimbra, Portugal). Fine inert materials present in the concrete reference composition (Concrete C30/37.S4.D22.Cl0,40) were substituted by 5% \(w\)/\(w\) GS. The mixing was performed at a temperature from 22.3 \({}^{\circ}\)C to 22.8 \({}^{\circ}\)C. Table 1 shows the compositions of both the new formulation (concrete 5% \(w\)/\(w\) GS) and the reference structural concrete (concrete C30/37.S4.D22.Cl0,40). The concrete 5% \(w\)/\(w\) GS mixture was prepared by predicting an additional water requirement of about 15 L to keep the slump value close to the reference concrete mix value; thus, the final volume of the sample has been adjusted, reducing the amount of medium sand by 40 kg/m\({}^{3}\).  
Concrete monoliths were prepared and characterised for (i) apparent density, (ii) slump test according to NP EN 12350 [24], (iii) compressive strength test after 24 h, 2 days, 7 days, and 28 days of curing in a Universal Testing Machine (UTM). Compressive strength was performed according to the Portuguese Standard NP-1383 and the National Laboratory of Civil Engineering (LNEC), Specification number E-226. The characteristic values were obtained from the Portuguese regulation RBLH [25].