## 3 Results and Discussion
### Reaction Products  
The XRD patterns for clay MA157 and the three (4, 6 and 8 M) pastes are reproduced in Figure 3. The precursor exhibited a significant amorphous component at 20 values of 20\({}^{\circ}\) to 40\({}^{\circ}\). The crystalline phases detected in MA157 included quartz, calcite, illite/muscovite, K-feldspar (orthoclase, albite and anorthite) and plagioclase. With the exception of calcite, the intensity of these diffraction lines barely varied after alkaline activation, an indication that the respective phases were inert. The patterns for all the pastes showed a slight shift in the hump located in the precursor at 20 = 20\({}^{\circ}\) to 40\({}^{\circ}\) to around 20 = 30\({}^{\circ}\) to 40\({}^{\circ}\) (the hump is a characteristic of amorphous and/or glassy phases) denoting a reaction between the amorphous phases in the clay and the formation of new, low structural order phases, primarily cementitious gels [4]. The lines attributed to the presence of calcite were more intense in the paste activated with 4 M NaOH. Although less calcite was formed at higher alkali concentrations (6 and 8 M), sodium carbonates or calcites such as natron (Na\({}_{2}\)CO\({}_{3}\)-10H\({}_{2}\)O (PDF # 00-015-0800)) and gaylussite (Na\({}_{2}\)Ca(CO\({}_{3}\))\({}_{2}\):5H\({}_{2}\)O) (PDF # 00-021-0343)) were detected on their diffractograms. Unlike other alkali-activated binders made with dehydroxylated clay as precursors [25; 26; 27], the pastes prepared here contained no zeolite crystals. That absence was attributed in part to the fairly low (13.4%) aluminium content in MA157 and/or to ambient temperature curing which would lower Al solubility. A number of authors have reported that zeolite formation as a secondary product in alkaline  
Figure 3: XRD patterns for anhydrous MA157 clay and 28 days, 4, 6 and 8 M NaOH-activated pastes Legend: I/Ms = illite/muscovite; Qtz = quartz; Pl = plagioclase, Kfs = K-feldspar, Cal = calcite; Na = natron; Pa = para-alumohydrocalcite/hemicarboaluminate. cements depends on both the reactive aluminium content and the synthesis parameters, primarily activator type and concentration [11; 12; 36], and curing conditions (time, temperature, humidity) [4; 37]. A small hump was observed at 20 = 10\({}^{\circ}\) to 11\({}^{\circ}\), possibly associated with the formation of para-alumohydrocalcite (CaAl\({}_{2}\)(CO\({}_{3}\))\({}_{2}\)(OH)\({}_{4}\)6H\({}_{2}\)O (PDF# 00-030-0222)), a hydrotalcite group mineral, or hemicarboxoluminate (Ca\({}_{4}\)Al\({}_{2}\)O\({}_{7}\)CO\({}_{2}\):11H\({}_{2}\)O (PDF# 00-036-0377)). These phases are often present as secondary reaction products in calcium-high alkaline cements such as alkali-activated blast furnace slag [38] or limestone-metakaolin blends [39]. The FTIR spectra for clay MA157 and the two and 28 days pastes are reproduced in Figure 4. The spectrum for the starting material exhibited a wide band at approximately 1079 to 1086 cm\({}^{-1}\), associated with the asymmetric stretching vibrations generated by the Si-O-T (T = Si, Al) bonds possibly present in the amorphous component of the material [40]. It also contained vibration bands characteristics of quartz at 1084, 796, 694 and 463 cm\({}^{-1}\)[41], a low intensity band at 1438 cm\({}^{-1}\) attributed to the presence of calcium carbonate and another at 1635 cm\({}^{-1}\) to the bending vibrations generated by the OH groups in water [41]. The Si-O-T (T = Si, Al) stretching band in the pastes was shifted to lower frequencies and its signal grew narrower at longer reaction times. That band appeared at 1010 cm\({}^{-1}\) in the two days and at 1014 cm\({}^{-1}\) in the 28 days pastes. Further to the literature [4; 9; 40; 41], these variations stem from the initial alkaline-mediated dissolution of the amorphous/reactive component in the clay and the ensuing precipitation of a cementitious gel with a fairly high aluminium content (intermediate reaction product, band at 1010 cm\({}^{-1}\)).