Role of crystalline silica admixture in mitigating ettringite-induced heave in lime-treated sulfate-rich soils

Abstract

A research study was designed and conducted to evaluate the applicability of using crystalline silica-rich material as a co-additive with calcium-based stabilisers to treat sulfate-rich expansive soils. Extensive laboratory tests were conducted on lime-treated sulfate-rich soils, with and without crystalline silica admixture, to evaluate the improvements in engineering properties, including swell strain, unconfined compressive strength and resilient moduli properties. The influence of co-additive dosage, curing period and duration of moisture exposure was studied to gain insights into the behaviour of treated soils. Supplementary mineralogical and microstructural studies including X-ray diffraction, scanning electron microscope imaging and differential scanning calorimetry studies were performed on the treated soils to detect the formation of ettringite mineral and cementitious gel compounds. Test results indicated that the use of crystalline silica facilitated enhancement of both the strength before and after capillary soaking, and the resilient moduli properties, while suppressing ettringite mineral formation and associated free swell strains in the treated soils. Mineralogical and engineering studies showed the dominance of pozzolanic activity between lime and crystalline silica over ettringite formation and hence contributed to the effective stabilisation of sulfate-rich soils. Overall, the paper provides a comprehensive understanding of the role of crystalline silica admixture for mitigating deleterious sulfate heaving in lime-treated soils.

Evaluation of Geopolymer for Stabilization of Sulfate-Rich Expansive Soils for Supporting Pavement Infrastructure

“…Ettringite, Ca 6 (Al(OH) 6 ) 2 (SO 4 ) 3 ċ26H 2 O), a calcium-alumino-sulfate mineral is precipitated when alumina available from the dissolution of clay in alkaline environments (pH > 10.5) reacts with Ca +2 from Ca-based stabilizers and soluble sulfates in the presence of water ( 1 , 12 , 13 , 16 ). Stoichiometrically, ettringite crystals could undergo a potential volumetric expansion up to 137% ( 7 , 17 ). Furthermore, the volumetric expansion could reach up to 250% in Ca-based stabilizer treated sulfate-rich soil layers from the hydration and growth of ettringite when exposed to water ( 18 , 19 ).…”

“…10.5) reacts with Ca +2 from Ca-based stabilizers and soluble sulfates in the presence of water (1,12,13,16). Stoichiometrically, ettringite crystals could undergo a potential volumetric expansion up to 137% (7,17). Furthermore, the volumetric expansion could reach up to 250% in Ca-based stabilizer treated sulfate-rich soil layers from the hydration and growth of ettringite when exposed to water (18,19).…”

“…Different treatment techniques, including precompaction mellowing, double lime application, and utilization of co-additives (e.g., Class F fly ash, ground granulated blast furnace slags, and crystalline silica-rich admixtures), have been investigated for stabilizing sulfate-rich soils (17,(20)(21)(22)(23). Even though some of these techniques have shown promising results, most techniques increase the overall construction time because of longer curing periods required for effective performance before moisture exposure (17,24). Moreover, the use of the majority of such co-additives involves the usage of a substantial amount of Ca-based stabilizers.…”

Resilient Characteristics of Polymer Emulsion-Treated Sandy Soil

“…The AASHTO MEPDG recommends the use of resilient modulus for characterizing the subgrade soils ( 14–17 ). Thus, the resilient modulus ( M R ) is a key design parameter for flexible pavement systems and offers a better characterization of the behavior of pavement materials under traffic loading ( 18–20 ). The resilient modulus is defined as the ratio of cyclic axial stress ( σ cyclic ) to resilient axial strain ( ϵ r ) as presented mathematically in Equation 1 ( 21 ).…”

Evaluating the Performance of Wicking Geotextile in Providing Drainage for Flexible Pavements Built over Expansive Soils

“…Flexible pavements constructed on these expansive soil subgrades experience rutting, cracking, and differential heaving resulting in long-term serviceability issues ( 2, 3 ). The failure of these pavements is predominantly attributed to seasonal variations in moisture levels within the subgrade layer ( 4 – 7 ). Annually, several million U.S. dollars of expenditure are incurred in Texas for the maintenance of such distressed pavements ( 8 ).…”