# Formulation of Alkali-Activated Slag Binder Destined for Use in Developing Countries
## 2 Materials and Methods  
The BFS herein used was provided by Cementval SL (Puerto de Sagunto-Valencia, Spain). BFS was dry-milled in a ball mill for 30 min (450 g of BFS were milled with 98 alumina balls). The commercial reagents (NaOH and Na\({}_{2}\)CO\({}_{3}\)) were supplied by PANREAC QUIMICA SLU (Barcelona, Spain). Some characteristics of the used BFS are detailed using techniques like XRF (X-ray fluorescence) or FESEM (field emission scanning electron microscopy). The chemical composition of BFS was measured in a Magix Pro spectrometer (Philips) by the XRF technique. Table 1 provides the oxide composition per weight percent (wt %). The equipment used to measure granulometric distribution was a Mastersizer 2000 (Malvern Instruments, Malvern, UK). The technique followed by the equipment was laser diffraction. BFS was dispersed in water and stirred at 1200 rpm by applying a 1-min ultrasound before measurements. The milled BFS presented a unimodal curve with a narrower shoulder of particles below 1 \(\upmu\)m (Figure 1). Brucker AXS D8 (Billerica, MA, USA) Advance equipment was employed to carry out X-ray diffraction (XRD) analyses. The range went from 5 to 70 20 degrees using Cu K\(\alpha\) radiation at 20 mA and 40 kV, with a 2 s accumulation time and a 0.02 angle step. The XRD diffractogram of BFS is represented in Figure 2. The halo located within 20-35 20 degrees was attributed to the amorphous phase of BFS. A crystalline phase attributed to the presence of calcite (C, CaCO\({}_{3}\), PDF#050586) can also be observed. Finally, the morphology of the milled BFS was observed by FESEM. The equipment employed was ULTRA 55 ZEISS equipment. BFS was carbon-coated to observe it, and the image was taken at 2 kV. The micrograph of the BFS particle morphology is represented in Figure 3. The milled BFS presented an irregular morphology with different size particles as a result of the milling process. Two types of alkali activators were used: NaOH, Na\({}_{2}\)CO\({}_{3}\), and a mixture of both. The samples activated with only NaOH were called SH, and the chosen molarities were 3, 4 and 5 M. The samples activated with Na\({}_{2}\)CO\({}_{3}\) were named SC, and the chosen molarities were 1.5, 2, 2.5, 3 and 3.5 M. Finally, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **MgO** & **Na\({}_{2}\)O** & **SO\({}_{3}\)** & **Other** & \({}^{*}\)**LOI** \\ \hline
10.60 & 30.04 & 40.35 & 1.30 & 0.57 & 7.47 & 0.87 & 1.94 & 1.30 & 5.56 \\ \hline \hline \end{tabular} \({}^{*}\) LOI—loss of ignition determined at 950 \({}^{\circ}\)C for 1 h.  
\end{table} 
Table 1: Chemical composition of blast furnace slag (BFS) (wt %). Figure 1: Granulometric distribution of milled BFS. the samples that used the mixture of two reagents were called SHC, and the chosen molarities differed for both products. For example, the mixture named SHC 2/1 had molarity of 2 M for NaOH and a molarity of 1 M for Na\({}_{2}\)CO\({}_{3}\). All the combinations of activators are represented in Table 2. In this research, mortars were prepared at a BFS/sand weight ratio of 1:3 (450:1350 g) and at a BFS/water ratio of 0.4 (180 g of H\({}_{2}\)O). The humidity of the natural siliceous sand (from the company Caolines Lapiedra, Liria, Valencia, Spain) was less than 1% with a specific weight of 2.71 \(\pm\) 0.15 g/cm\({}^{3}\). Mortars were cast in 4 \(\times\) 4 \(\times\) 16 cm\({}^{3}\) molds. Mortars were cured in a conditioned chamber (at 20 \({}^{\circ}\)C, 100% RH), demolded after 24 h, weighed and returned to the conditioned chamber until mechanical testing commenced (7, 28 and 90 curing days), which was performed in a universal Instron Model 3382 machine with the charge rate set at 1 mm/min according to EN 196-1 [23]. Microstructural analyses were done only on some selected pastes (without sand) cured under the same conditions as mortars.