Lime stabilization is a common technique used to improve the engineering properties of clayey soils. The process of lime stabilization can be split into two parts. First, the mobilization and crowding of [Formula: see text] ions or [Formula: see text]molecules from hydrated lime at net negative surface charge sites on expansive clay colloids. Second, the formation of pozzolanic products including calcium-silicate-hydrate (C-S-H) because of reactions within lime-soil mixtures. The pozzolanic reaction is generally considered to be more durable, while the [Formula: see text] adsorption has been associated with more easily reversible consistency changes. This study offers a protocol to assess whether the stabilization process is dominated by durable C-S-H (pozzolanic) reactions or a combination of cation exchange and pozzolanic reactions. Expansive clays with plasticity indices >45% from a major highway project in Texas are the focus of lime treatment in this study. The protocol consists of subjecting lime-soil mixtures to a reasonable curing period followed by a rigorous but realistic durability test and investigating the quality and quantity of the pozzolanic reaction product. Mineralogical analyses using quantitative X-ray diffraction (XRD) and thermogravimetric analysis (TGA) indicates the formation of different forms of C-S-H. In addition, geochemical modeling is used to simulate the lime-soil reactions and evaluate the effect of pH on the stability of C-S-H. The results indicate C-S-H with Ca/Si ratio of 0.66 as most the stable form of C-S-H among other forms with Ca/Si ratio ranging from 0.66 to 2.25. The effect of reducing equilibrium pH on C-S-H is also evaluated. A reduction in pH favored dissolution of all forms of C-S-H indicating the need to maintain a pH ≥ 10.
The soils across Lake Texcoco (LT) basin are notorious for the presence of highly compressible salt-affected lacustrine clays. The geological formation of the area accompanied by the unmonitored flow of water from Mexico City region has resulted in a unique sodium-rich clay that is highly plastic (plasticity index~200), and impermeable ( k~1.5 × 10−9 m/s) and possesses low compressive strength (unconfined compressive strength < 10 kPa). Over the last few decades, the entire basin has settled at an average of 13.2 cm per year and will continue further with increased loads as a result of rapid urbanization. In planning a solid foundation for the airport, as well as developing the surrounding area, trial sections were built to analyze the effect of quicklime (CaO) on the natural clay s physical, chemical, and engineering properties through laboratory testing. The lab-scale investigations were accompanied with field measurements using the variable energy dynamic cone penetrometer (DCP) and plate load tests. Additionally, a numerical analysis of the effect of deep mixed columns (DMC) to reduce consolidation settlement was performed. The numerical analysis comprised of various DMC stabilizers, loading pressures, column lengths, and area replacement ratios. DMC lengths were observed to be the most dominant parameter to reduce consolidation settlements. Settlement reduction was more sensitive to the area replacement ratio for end-bearing columns, and to the loading pressures for floating columns. Based on the stabilizers evaluated, a combination lime and Portland cement performed the best across all loading pressures and column lengths. Other stabilizer combinations also had a remarkable effect on limiting the consolidation settlement.
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