*3.2. Soil Mixtures*

Figure 4 shows the optical images representing the soil consistence and grain-sizes of the different mixtures used. These mixtures contain 0.1% fibers and 35% water by dry soil weight. As it can be seen, the molasses concentration has an important role in the grain-size formation, since as its concentration increases the grain-size of the mix becomes larger. Figure 4a–g presents the different mixtures of soil with fibers, water, and molasses as summarized in Table 3.

Figure 5 shows the mixed soil grain-size probability distribution for each mixture prepared. The normal probability distribution represents the random nature of the grainsize forming process, and shows that as molasses content increases the statistical data dispersion and grain-size increase. Samples M0, M2, and M4 showed a distribution in a similar interval, see Figure 5a; while samples M6, M8, M10, and M12 were more diverse in the distribution values, see Figure 5b.

**Figure 4.** Optical images showing the soil consistence of mixtures.

**Figure 5.** (**a**) Mixed soil grain size probability distribution for samples M0, M2, M4; (**b**) probability distribution for samples M6, M8, M10, M12.

Figure 6 illustrates the XRD spectrum of soil. M0 red line corresponds to soil in its natural condition and the M12 blue line is the chemical composition of the soil after mixing the fibers, 35% of water and 12% of molasses by dry weight of soil. The MINCRYS database was consulted for mineral identification. Halloysite, kaolinite, illite, quartz, dickite, and goethite were identified as the crystalline phases constituting the clay. Kaolinite clay is the main plastic component of this soil, which is important as Colombia has plenty of kaolin-based soils. The particle size distribution via sieve method of the clay is presented before, were more than 80% of the soil is less than 0.1 mm (100 µm) in particle size.

**Figure 6.** XRD spectrum for the soil. H: halloysite, K: kaolinite, I: illite, Q: quartz, D: dickite, G: goethite peaks.
