Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

Abstract

Calcium-based stabilizing materials (CBSMs) such as lime and fly ash are extensively used in subgrade primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in more durable roadway. The soluble sulfate phase contained in some soils, however, can react with CBSMs and form ettringite minerals. If the soil is compacted before the end of this reaction, large, unstable, and volumetric swelling can occur. Among several methods to control sulfate-induced swelling, a “mellowing” approach is typically used because of its efficient, economical, and practical benefits when dealing with calcium-based stabilization of soils with significant soluble sulfate contents. Although the mellowing method is one of the frequently used methods, little data is available on the characterization of the specified mellowing process in the high-sulfate-bearing soil during the mellowing period. A research program investigated key factors influencing the mellowing process during the mellowing period, explaining how stabilizer type and content, remixing interval, mellowing period, and temperature play a role in reducing soluble sulfate content. Moreover, for selected mixtures, the 3-dimensional volumetric expansion and retained strength were measured after the mellowing process. Laboratory test results have revealed that a single mellowing process with higher lime content and daily remixing at high temperature leads to the rapid reduction of sulfate content in the soil. Moreover, after the mellowing process, additional soil treatment with fly ash or a combination of lime and fly ash leads to lower expansion and higher retained unconfined compressive strength of the soil mixture.

Stabilization of High Sulfate-Saline Soil with Lime, Ground Granulated Blast Furnace Slag (GGBFS), and Basic Oxygen Furnace Slag (BOFS)

“…All soil mixtures combined with lime-and-slags (GGBFS and BOFS) experienced drying shrinkage behaviors for up to 12 days before experiencing an increasing trend at later ages. This phenomenon may be caused by the consolidation and hydration of lime and slag-based materials [22]. At 28-day, mixture [soil+4%lime+2%(50% GGBFS+50% BOFS)] presented the lowest expansion,…”

High Sulfate-Bearing Kaolin Clay Stabilization with Waste Glass Powder before and after Mellowing Process

“…At high sulfate concentrations and low voids ratio, the soil matrix cannot accommodate formed ettringite, which leads to soil swelling [9]. Compaction of the soil before forming ettringite in road construction can result in excessive soil expansion [10]. Expansions in the CBS-treated subgrades containing sulfates prompted the search for alternative stabilization methods.…”