Analytical tests to evaluate pozzolanic reaction in lime stabilized soils

Pavan Akula,Dallas N Little

doi:10.1016/j.mex.2020.100928

Abstract

Shrink-swell soils are predominant in various parts of the parts of the world. Lime has been extensively used to reduce the shrink-swell mechanism as it chemically reacts with soil minerals forming pozzolanic products such as calcite and calcium-silicate-hydrate (C-S-H). Conventionally, whether chemical treatment of soils results in effective pozzolanic stabilization reactions is determined anecdotally through engineering tests including unconfined compressive strength, plasticity index (PI), and pH tests. This study builds on existing literature regarding how more direct quantification of pozzolanic products can be obtained through tests that directly identify and quantify pozzolanic products, specifically in lime-treated clay soils. Specifically, x-ray diffraction (XRD) and differential thermogravimetric analysis (DTA) are used for this testing. Expansive soils with plasticity indices above 25% were selected for this study. Engineering tests on these lime-treated soils indicated significant improvement in strength and reduction in PI. In XRD analysis, pozzolanic products are assessed by the location and intensity of x-ray peak(s). The XRD data show a decrease in the intensity of alumio-silicate minerals such as kaolinite and smectite; silica and alumina are dissolved at a high pH and converted to pozzolanic products such as calcium-silicate-hydrate (C-S-H). DTA indicates the presence of C-S-H with the characteristic weight loss from 140°C to 250°C.The methodology describes the following:● Sample preparation steps for XRD and DTA analysis.● Analysis of XRD results and DTA analysis.

Highlights

Expansive clay minerals are prevalent in many parts of the western and southwestern U.S Soils containing such expansive minerals are referred to as shrink-swell soils due to their swelling characteristics in the presence of moisture and shrinking characteristics during moisture loss
Calcium based chemical additivities including lime, cement, and other cementitious materials are effective in stabilizing expansive soils
Unconfined compressive strength, pH and plasticity index (PI) of the treated and untreated soil was determined in accordance to ASTM D2166 [32], ASTM D4872 [33], and ASTM D4318 [34], respectively

Summary

Introduction

Expansive clay minerals are prevalent in many parts of the western and southwestern U.S Soils containing such expansive minerals are referred to as shrink-swell soils due to their swelling characteristics in the presence of moisture and shrinking characteristics during moisture loss. Calcium based chemical additivities including lime, cement, and other cementitious materials are effective in stabilizing expansive soils. Several researchers have studied the change in physical and engineering properties for limetreated soils [2,3,4,5,6,7,8]. Bell [9] determined that addition of a small percentage of lime to soil enhanced the engineering properties and improved constructability. In addition to improvement of physical and engineering properties, studies have identified mineralogical and geochemical changes in limetreated soils [10,11,12]. Investigations [14,15,16,17,18] have shown that soils treated with supplementary cementitious materials such as fly-ash and cement-kiln dust produce similar strength enhancing pozzolanic products

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