Mechanical and Microstructural Comparison of Improved Sand with Guar Gum and Cement

Research on sustainable alternatives to conventional soil stabilization has promoted the use of natural biopolymers as partial substitutes for cementitious binders. This study presents a mechanical and microstructural comparison between poorly graded Colombian sand stabilized with guar gum (GG) and Type III Portland cement. GG was incorporated at 0.25–1.00% with curing periods of 28 and 90 days, while cement contents ranged from 3 to 9% with 7 days of curing. A total of 108 cylindrical specimens were tested using unconfined compressive strength (UCS) and SEM–EDS analyses. Results show that both binders significantly improve soil strength, although cement exhibits a steeper strength gain due to hydration processes. GG-treated samples reached a maximum UCS of 470 kPa at 90 days, representing an increase of approximately 40% compared to 28 days and showing comparable performance to 5% cement. The porosity/binder index (η/Biv) demonstrated a strong correlation with UCS (R2 > 0.91), confirming its predictive capability. Microstructural analysis revealed the formation of C–S–H and ettringite in cement-treated samples, while GG-treated soils exhibited hydrogel bridges and the presence of pores that may influence particle bonding. Overall, the results demonstrate the technical feasibility of GG as a sustainable soil stabilization alternative.