CENTER FOR TRANSPORTATION RESEARCH THE UNIVERSITY OF TEXAS AT AUSTIN Project Summary Report 7-1993-S Center for Transportation Research Project 7-1993: Evaluation of Nontraditional Soil and Aggregate Stabilizers The University of Texas at Austin Authors: Alan F. Rauch, Lynn E. Katz, and Howard M. Liljestrand May 2003 EVALUATION OF NONTRADITIONAL SOIL AND AGGREGATE STABILIZERS: A SUMMARY and at ten times the recommended tography (GPC), UV/Vis spectroscopy, Introduction application rates. These tests failed to and nuclear magnetic resonance (NMR) Proprietary chemical products are show significant, consistent changes spectroscopy. In some cases, we syn- marketed by a number of companies for in the engineering properties of the thesized the stabilizer components in stabilizing pavement base and subgrade test soils following treatment with the the laboratory or purchased them from soils. Usually supplied as concentrated three selected products at the applica- other chemical supply companies to liquids, these products are diluted in tion rates used. verify our conclusions. water on the project site and sprayed The three stabilizer products were on the soil to be treated prior to mix- What We Did... then reacted with three reference clays ing and compaction. If effective, these We began by selecting three and five native Texas clay soils. We products might be used as alternatives commercially available, liquid soil tested samples of the well-character- for treating sulfate-rich soils, which are stabilizer products for evaluation. ized, reference clays (kaolinite, illite, susceptible to excessive heaving when Although no effort was made to as- and montmorillonite) to increase the treated with traditional, calcium-based semble and classify a comprehensive likelihood of observing subtle physi- stabilizers such as lime, cement, and fly list of available products and suppliers, cal-chemical changes. The five mixed, ash. However, the chemical composi- it appears that the most readily available native clays were all highly plastic, fat tion, stabilizing mechanisms, and per- liquid soil stabilizers can be classified clays; one had a high sulfate content. formance of these liquid products are as one of three types: Because the test results are influ- not well understood. In this study, we (1) Ionic stabilizers, reported to enced by details of how the test speci- investigated the mechanisms by which work through cation exchange mens are prepared, we developed and clay soils are modified by these liquid within the clay mineral followed a detailed, rational protocol chemical agents. We also attempted to for preparing the soil test samples. quantify changes in the engineering (2) Enzyme stabilizers, described The same water content was used to properties of different clays following as consisting of various organic prepare untreated and treated specimens treatment. catalysts of a given soil, so that the effect of the We selected three representative (3) Polymer stabilizers, comprised stabilizer on the measured soil proper- commercial products for study: an of various organic and inorganic ties could be distinguished from the ef- ionic product, an enzyme product, and a polymers fects of varying the moisture content. polymer product. The chemical compo- A representative product of each For the same reason, the samples were sition of each was characterized using type was chosen and samples were ob- maintained at a constant water content a variety of chemical test methods. The tained from the suppliers. We have not during a seven-day curing period. The three products were then reacted with identified the specific product names specimen preparation protocol was sent three reference clays (kaolinite, illite, to avoid endorsement of particular to a number of industry and TxDOT and montmorillonite) and several native products and to avert disclosure of the representatives for comment, from Texas soils. chemical components of proprietary which a final, thirteen-step protocol In the “micro-characterization” materials. was developed. study, we studied the mechanisms of Next, we analyzed the selected In the micro-characterization soil modification at the particle level products to identify the primary or ac- study, we characterized the soils at the using physical-chemical analyses of tive ingredients and quantify the physi- particle level before and after treatment, untreated and treated soil samples. cal and chemical characteristics of each. in an effort to observe the clay/stabilizer Extremely high product application The analytical techniques included pH, interactions. The clay materials were rates were used so that possible soil conductivity, ion chromatography (IC), characterized using BET surface area modifications could be observed. potentiometric titrations, total organic analysis, cation exchange capacity In a paired “macro-characteriza- carbon (TOC) analysis, Fourier trans- (CEC), environmental scanning elec- tion” study, we performed standard geo- form infrared (FTIR) spectroscopy, gas tron microscopy (ESEM), scanning technical laboratory tests on untreated chromatography/mass spectrometry electron microscopy (SEM), energy PROJECT SUMMARY REPORT and treated compacted soil specimens. (GC/MS), high performance liquid dispersive X-ray spectroscopy (EDX), The products were mixed at the sup- chromatography/mass spectrometry and X-ray diffraction (XRD). For most pliers’ recommended application rates (HPLC/MS), gel permeation chroma- Project Summary Report 7-1993-S – 1 – of the tests in this part of the study, we used following conventional treatment with 6% stabilizer is reported to act in several ways, a product application mass ratio of 1:2 (mass hydrated lime. including the breakdown of clay minerals of concentrated stabilizer to mass of dry soil), with expulsion of water from the double layer, which is much higher than the application What We Found… the binding of clay particles by aggregation, rates suggested by the manufacturers. The Chemical analysis of the liquid products, internal or external adsorption to clay layers extremely high application rates were used coupled with the results from the micro-charac- preventing water absorption, or interlayer to maximize any chemical changes in the terization study, allow us to suggest the mecha- expansion with subsequent moisture entrap- structure and morphology of the clay miner- nisms by which these selected products may ment. The XRD results from clays treated at als and increase the likelihood of observing affect a clay soil. the high application ratios were consistent with the underlying stabilizer mechanisms. The main ingredient of the ionic stabilizer interlayer expansion. In addition, the surface In the macro-characterization study, we was sulfonated limonene, which we were able area results following the enzyme treatment used standard geotechnical laboratory tests to to synthesize in our laboratory. The hypoth- generally showed the largest decrease in sur- assess whether the engineering properties of esized mechanism for the ionic stabilizer was face area of all of the stabilizers tested. For the the test soils were altered by chemical treat- cation exchange with subsequent alteration in nonexpanding clay minerals, the hypothesized ment. Tests included measurement of the At- the clay mineral lattice. It was hypothesized mechanism of providing an adsorbing surface terberg limits (liquid limit, plastic limit, and that the sulfonated limonene could preferen- complex on the edges of clay particles was plasticity index), compaction characteristics tially extract aluminum from a clay mineral. supported by surface area measurements, pore (evaluated by comparing the compacted However, even at the high application ratios size distributions, ESEM images, and EDX density of untreated and treated specimens), we employed, significant changes in clay Al:Si ratios. undrained shear strength (measured using un- mineralogy were not apparent in the ESEM We identified sodium silicate as the prin- consolidated undrained triaxial compression images, the d-spacings measured in XRD tests cipal component of the polymer stabilizer. The tests), and free swell potential (determined indicated the continued presence of expansive hypothesized mechanism involved formation of from one-dimensional swell tests). Tests on clay minerals, and decreases in Al:Si ratio were a strongly adhesive, aggregated material. Fur- the three reference clays and two of the na- not significant in many cases. Examples of this thermore, the polymer stabilizer was alleged tive soils were conducted using the suppliers’ test data are presented in Figure 1. to coat the surface of soil particles rather than recommended application rates. These tests For the enzyme stabilizer, we identified chemically altering the clay inner layers. The failed to show conclusive results, so follow- polyethylene glycol as the principal ingredi- results of polymer treatment for all soils tested up tests were conducted on three other native ent, but it appears that polyethylene glycol is supported the proposed mechanism of surface clays with the stabilizers applied at ten times used only as a protein/enzyme deactivator. It coating and aggregation. This was confirmed the recommended application rates. To better is likely that the active ingredient is micro- consistently by the ESEM images and BET judge the efficacy of the liquid stabilizers, biological in nature, which is why it wasn’t analysis. No changes in d-spacing or Al:Si ratio we also tested the soils in this last test series