Journal of Materials in Civil Engineering

The shear strength of an arsenic bearing sludge derived from gold mining was evaluated as a function of lime content. Lime was used as a physico-chemical stabilization agent of this waste to enhance slope stability and increase site storage capacity. Shear strength characteristics of the sludge before and after lime stabilization were obtained through unconsolidated undrained triaxial tests performed at lime content weight percentages of 0, 5, 10, and 20%. The shear strength testing results show an increase in cohesion from 5 kPa at 0% lime content, to 27 kPa at 20% lime content. Slope stability analysis indicates that stabilization of the sludges improves storage capacity by 43%. This represents an increase from $\mathrm{3,487.5}{\mathrm{m}}^3∕\mathrm{m}$ (0% lime content) to $\mathrm{4,987.50}{\mathrm{m}}^3∕\mathrm{m}$ (20% lime content). Thus the addition of lime is effective in improving the shear strength and storage capacity of arsenic bearing sludge.

A site-specific study on stabilizing acid-generating mine tailings from Sudbury Mine using a coal fly ash from Nanticoke Generating Station is presented in this paper. The objective of the study is to evaluate the feasibility of codisposal of the fly ash and mine tailings to reduce environmental impacts of Sudbury tailings disposal sites. The study includes three phases, i.e., characterization of the mine tailings, and coal fly ash, oxidation tests on the mine tailings and kinetic column permeation tests. The results of the experiments indicate that when permeated with acid mine drainage, the hydraulic conductivity of Nanticoke coal fly ash decreased more than three orders of magnitude (from $1\times {10}^{-6}$ to $1\times {10}^{-9}\mathrm{cm}∕\mathrm{s}$ ), mainly due to chemical reactions between the ash solids and acid mine drainage. Furthermore, the hydraulic gradient required for acid mine drainage to break through the coal fly ash is increased up to ten times (from 17 to 150) as compared with that for water. The results also show that the leachate from coal fly ash neutralizes the acidic pore fluid of mine tailings. The concentrations of trace elements in effluents from all kinetic column permeation tests indicated that coplacement of coal fly ash with mine tailings has the benefit of immobilizing trace elements, especially heavy metals. All regulated element concentrations from effluent during testing are well below the leachate quality criteria set by the local regulatory authority.

With little mining information, old abandoned coal workings were grouted beneath a proposed building site. Mine stabilization was found necessary after an investigation of subsidence potential was performed. The investigation indicated that the 67 m deep abandoned mine, although old, still had not collapsed and consequently presented a significant risk of subsidence in the future. Further, based on the history of subsidence over old mines in the area, mine grouting was recommended. To stabilize the mine, about $\mathrm{11,468}{\mathrm{m}}^3$ of grout were pumped. The grouting was designed to account for the significant amount of rubble which existed in the mine. There were three grout mixes of different flowability characteristics specified. The 1,725 kPa grout was batched at a slump of 10 and 20–22 cm and at a efflux flow rate of 30–40 s. Permeation, squeeze (or intrusion), and compaction grouting was performed per the project specifications. Also, to economize on the amount of grouting necessary, subsidence resistant features were incorporated into the design of the building.

This paper examines the compressibility and strength characteristics of high water content cement-admixed clay in deep mixing applications. During curing time, both cement content and total clay water content of the clay–water–cement mixture significantly affect the strength and compressibility of the resulting stabilized clay. To ensure optimum improvement, the selection of an appropriate total clay water content for a mixture with a certain cement content is crucial. Furthermore, the fundamental parameters such as the ratio of after-curing void ratio $\left(e_{\mathrm{ot}}\right)$ and cement content $\left(A_w\right)$ have been found sufficient to characterize the strength and compressibility of cement-admixed clay. The results of unconfined compression and consolidated–undrained tests have proven that the ratio $e_{\mathrm{ot}}∕A_w$ combines together the influences of clay water content, cement content, and curing time as well as curing pressure on the strength of cement-admixed clay. In addition, useful empirical relationships on deep mixing application are presented.

The results of a laboratory study on the influence of standard Proctor and West African Standard (WAS) compactive efforts on the compaction and strength characteristics of tropical black clay with a maximum of 8% lime and 10% slag (by dry weight of soil) is presented. Lime stabilized soil was admixed with slag in order to establish its soil improving potentials. Unconfined compressive strength and California bearing ratio tests on the soil-lime-slag mixtures yielded peak values at 8% lime and 7.5% slag concentrations in all the cases considered. The soil-lime-slag mixtures can be used as subbase and base courses of lightly trafficked roads when compacted at the energies of the standard Proctor and WAS, respectively.

Migration of ions from lime piles to bring about improvements in clay soils, into which the lime piles have been installed, has been observed by several researchers. Specific measurements have been taken to show how effective the improvement has been (in terms of distance, time, and magnitude of the physical change), and yet the observations have yet to be adequately explained. This paper aims to examine, via a series of controlled laboratory experiments, the physico-chemical phenomena in London clay brought about by the ion migration from a lime pile having the same initial water content as the clay. Ion migration was shown to occur under a combination of three drivers (chemical, electrical, and hydraulic gradients), the importance of each being discussed. Changes in the clay’s properties were determined by shear strength, using a novel fall cone technique, and plasticity measurements, while measurement of pH, conductivity, and ion concentrations proved vital to understanding the processes taking place, notably in relation to the cation exchange and clay mineral dissolution effects of classic stabilization.

Soil and water conservation is essential for sustaining food production and for preserving the environment. This review considers the potential of four types of soil amendments, namely gypsum, organic polymers, organic matter waste materials, and fly ash, as soil stabilizers. Addition of gypsum to soil can limit clay swelling and dispersion, and thus improve soil structural stability, by both soil solution electrolyte effects and cation-exchange effects. Synthetic organic polymer addition to soil surface aggregates leads to their stabilization, improved bonding between adjacent aggregates, and clay flocculation. Organic matter, also used for promoting aggregate stabilization, enhances soil microbial activity that transforms the newly added organic matter into polysaccharides and long chain aliphatic compounds capable of binding and stabilizing aggregates. Fly ash additives can improve soil physical characteristics including texture, structure, water holding capacity, hydraulic properties, and aeration. However, fly ash has a number of inherent qualities that under certain circumstances may limit its usefulness for soil stabilization, and which may even result in increased erosion and soil loss.

To effectively use recycled geomaterials in earthwork and pavement base/subgrade construction, engineering properties, design values, proper construction practices, and long-term behavior must be known. Recent experience in Iowa reveals that reclaimed hydrated fly ash (HFA) can be designed and constructed to meet performance objectives as demonstrated by three field test projects where HFA materials were used in construction of structural pavement base layers. In addition to construction operations and field performance monitoring, this paper summarizes HFA engineering properties determined from laboratory tests including: compaction characteristics, shear strength parameter values, hydraulic conductivity, freeze–thaw durability, and microstructural features. Results are also presented for HFA materials activated with high calcium stabilizers including hydrated lime, cement kiln dust, Class C fly ash, and atmospheric fluidized bed combustion residue. Successful use of these materials follows 10 years of research and field performance monitoring in Iowa.

This study investigates the roles of contaminant-grout and contaminant-soil interactions on the effectiveness of grouting gasoline-contaminated soil for minimizing contaminant migration by substantially decreasing the permeability of the grouted mass and/or encapsulating contaminant residuals. Experiments were conducted to determine the bleed capacity, unconfined compressive strength, and microstructure of neat microfine grout at three water:cement ratios with up to 20% of gasoline contamination. The gasoline was found to significantly reduce sedimentation, lower the compressive strength, and become encapsulated in the grout matrix. To quantify the effects of various interactions in the contaminant-grout-soil system and the effectiveness of contaminant containment, microfine cement grouts were injected into three gradations of Ottawa sand subjected to six different pregrout scenarios to physically model different degrees of residual saturation. The contaminated sands were determined to have higher permeability and lower strength due to more porous interfacial zones and adsorbed contaminant layers on the sand surfaces. These microstructural features and encapsulated contaminant entities were documented by microscopy. A first approximation of the apparent mass of contaminant residual that may migrate from grouted sand was determined by leaching tests and gas chromatography; results were typically 50% greater in cases where gasoline saturated initially dry sand.

The uses of byproducts such as blastfurnace slag and steel slag [electric arc furnace slag and basic oxygen steel (BOS) slag, and ground granulated blastfurnace slag] have long been established in a number of applications in the civil engineering industry. However, the use of ground BOS slag fines in the area of soil stabilization has not been fully investigated and developed despite having similar chemical composition and mineralogy to that of Portland cement. This paper describes a laboratory investigation for English China clay and Mercia mudstone, which are stabilized with three BOS slag fines from three different steel production sites in the United Kingdom. The investigation also included using mixture of BOS slag fines and two different activators: quicklime and sodium metasilicate. The results indicate that the use of BOS slag fines produce improvements in strength and durability, and also reduction in expansion. However, to achieve significant improvements in strength soils required a high percentage (15–20%) of BOS slag fines and a long curing period.

A coupled model of freezing–thawing of saturated porous materials, such as soils and rocks, is presented. The formulation is based on fundamental laws of continuum mechanics, i.e., conservation of mass, momentum, energy, and on mixtures theory. The problem is first tackled by ignoring irreversible phenomena like soil or rock damage. Therefore it is assumed that the phenomenon of freezing or thawing is governed by the theory of thermodynamics of reversible processes. It is shown that under certain assumptions the energy balance equation may be simplified to an equation with the unknown temperature only. This is a significant result since temperature is an easily measured parameter during an experiment. Subsequently, the heat flow equation is implemented into a one-dimensional finite element code that takes into account the change of phase of pore water during freezing. Finally, it is shown that the model may be used for the analysis of preliminary thawing experiments on a porous sandstone.

A statistical study of the effects of compaction delays on properties of lime-stabilized lateritic soil was conducted using two-way analysis of variance and multiple regression analysis. The reductions in mavimum dry density (MDD) and optimum moisture content (OMC) associated with compaction delays are statistically significant at the 5% level, regardless of the compactive effort employed (i.e., standard Proctor or West African Standard). The effects of compaction delays on unconfined compressive stength (UCS) are statistically significant for different compactions, lime contents, and curing. Compaction delay effects on California bearing ratio (CBR) of soil–lime mixtures are statistically significant. The $t$ -statistics from regression analysis show that compaction delays significantly influence the measured values of MDD, OMC, UCS, and CBR. It is believed that the findings of this study will be helpful in controlling the compaction delay for lime-treated soils.

This paper aims to show that the addition of lime and lime/cement can significantly improve both the stiffness and the resistance to permanent deformation of clay soils even under adverse, though realistic, curing conditions. The AASHTO Guide for Design of Pavement Structures incorporates a method of calculating subgrade resilient modulus $\left(M_R\right)$ , using repeated load triaxial testing, with respect to seasonal variations of the soil’s moisture content and temperature, while the equivalent British specifications adopt a “soaked California bearing ratio” approach. In practice 8°C is a realistic worst case curing temperature in situ and a (necessarily) wetter underlying clay will allow water to be drawn into the chemically treated layer during curing as a result of suctions, while the material will experience a small degree of confinement after compaction. These conditions have been replicated in a series of repeated load triaxial tests on lime and lime/cement stabilized, predominantly kaolinitic clay and the results compared with those from sealed samples, which were also cured at 8°C. All samples were subjected to 100 cycles of stresses representing 20, 40, 60, and 80% of the relevant undrained shear strength. This paper concludes that allowing the samples access to water is necessary if field performance is to be replicated.

Contaminant migration from polluted sites that are excessively permeable to fluids can be minimized by ground stabilization through grouting with cementitious materials. Analyses of the long term drying process of 2.75 mm diameter samples of cement–bentonite grouted soils from Dover, Del. in an environmental chamber maintained at a temperature of 25°C and relative humidity of 30% indicate that for most samples, the water-filled porosity (0.02–0.033) varied in a quasi-sinusoidal pattern with respect to drying time. Measurements of ultrasonic wave transit time with a James V-Meter correlated in time, with moisture loss determinations by weight loss measurements, show that in the initial 0–65 day drying period, the escape of moisture and consequent increase in air-filled porosity is responsible for the decrease in ultrasonic pulse velocity. Thereafter, increases in pulse velocity values ranging from 50 to $260\mathrm{m}∕\mathrm{s}$ observed for the reaction products at sustained drying at 25°C, provide enough activation energy for continuation of cement hydration and cement–bentonite reactions. Continuation of drying beyond reasonably complete moisture loss, to 200 days, generally produced decreases in pulse velocity that are herein attributed to microcracking. These observations are significant with respect to long-term barrier integrity in the vadose zone where variations in moisture content and temperature increase the opportunity for the desiccation of subsurface barriers of waste containment systems.

Cement stabilization of metallurgical residues is a frequently implemented option to reduce the associated environmental risks and thus simplify residue disposal procedures. As chemical stabilization is the first and main purpose of the process, physical testing of these stabilized residues is usually kept simple with unconfined compressive strength, permeability, and durability as the most frequently employed control tests. These tests are, however, unable to deliver a true image of the potentially complex mechanical behavior after stabilization of some important residues. One example is treated sludge. Stabilizing agents and fine residues are usually mixed at high water contents, resulting in a very porous microstructure, with fragile bonds. Under loading, rapid destructuration and compaction is possible and this process may be prone to material instabilities. These phenomena are experimentally and theoretically illustrated herein. The experimental illustrations are brought from a microstructural study and undrained triaxial campaign on a stabilized jarosite. The theoretical explanations are obtained from an elasto-plastic model previously employed for soft rocks.

The objective of this study was to evaluate the effectiveness of self-cementing fly ashes derived from combustion of sub-bituminous coal at electric power plants for stabilization of soft fine-grained soils. California bearing ratio (CBR) and resilient modulus $\left(M_r\right)$ tests were conducted on mixtures prepared with seven soft fine-grained soils (six inorganic soils and one organic soil) and four fly ashes. The soils were selected to represent a relatively broad range of plasticity, with plasticity indices ranging between 15 and 38. Two of the fly ashes are high quality Class C ashes (per ASTM C 618) that are normally used in Portland cement concrete. The other ashes are off-specification ashes, meaning they do not meet the Class C or Class F criteria in ASTM C 618. Tests were conducted on soils and soil–fly ash mixtures prepared at optimum water content (a standardized condition), 7% wet of optimum water content (representative of the typical in situ condition in Wisconsin), and 9–18% wet of optimum water content (representative of a very wet in situ condition). Addition of fly ash resulted in appreciable increases in the CBR and $M_r$ of the inorganic soils. For water contents 7% wet of optimum, CBRs of the soils alone ranged between 1 and 5. Addition of 10% fly ash resulted in CBRs ranging between 8 and 17 and 18% fly ash resulted in CBRs between 15 and 31. Similarly, $M_r$ of the soil alone ranged between 3 and 15 MPa at 7% wet of optimum, whereas addition of 10% fly ash resulted in $M_r$ between 12 and 60 MPa and 18% fly ash resulted in $M_r$ between 51 and 106 MPa. In contrast, except for one fly ash, addition of fly ash generally had little effect on CBR or $M_r$ of the organic soil.

In this paper, class F fly ash, bottom ash, polypropylene fibers, and nylon fibers were evaluated as potential stabilizers in enhancing volume change properties of sulfate rich expansive soils. As a part of the research evaluation, a comprehensive laboratory experimental program was designed and conducted on two different subgrade soils from two locations in Texas. Four dosage levels of each stabilizer, two compaction moisture content levels, and 14 days curing period were investigated. Volume change behavioral tests including volumetric free swell, volumetric shrinkage strain, and vertical swell pressure tests were conducted on both isolated stabilizer treated and combined ash-fiber stabilized soils. Ash stabilizers showed improvements in reducing swelling, shrinkage, and plasticity characteristics by 20–80% whereas fibers treatments resulted in varied improvements. In combined treatments, class F fly ash mixed with nylon fibers was the most effective treatment on both Dallas and Arlington soils, where the soil property enhancements were considered average-to-moderate. Possible mechanisms that resulted in the soil property improvements are discussed along with the recommended stabilizers and their dosages for expansive soil treatments.

In order to understand the mechanism by which aqueous polymers improve the resistance of clayey barrier soils to stresses, it is important to precisely determine the quantity of polymer that is sorbed onto barrier soil from aqueous solution. Batch sorption test results performed to analyze polyacrylamide (PAM) sorption from aqueous solutions by Na-montmorillonite (Nammt) indicate that viscosity measurement provides higher sorption amounts of PAM ( $0.1539\mathrm{g}∕\mathrm{g}$ of Nammt) than thermogravimetric analyzer (TGA) measurement ( $0.0533\mathrm{g}∕\mathrm{g}$ of Nammt). Statistical analyses of sorption data for both methods performed at various concentrations ranging from 0.1 to $4.0\mathrm{g}∕\mathrm{L}$ show that in general, the thermogravimetry is more consistent than viscometry. The demerit of viscometry is that the amount of polymer sorbed on solids is estimated indirectly through measurements of polymer solution concentration. Some free polymer molecules may still exist within interparticle pores of the separated solid fraction and can impose higher levels of sorption than actual levels. In the case of TGA, freezing drying of samples, which is a part of the test protocol, extracts pore liquid containing polymer molecules by sublimation. This leaves behind polymer molecules that are actually sorbed on soil particles, thereby producing lesser and more realistic sorption data than viscometry can provide.

Dredged harbor sediments contaminated with harmful industrial chemicals need to be physically and chemically stabilized before being used in harbor developments. Solidification is often done using cement or lime additions but the performance of these materials is affected by the type and content of clay in the sediments. Two New Zealand harbor sediments, containing 18–27% clay and moderate levels of heavy metals, were investigated as part of marina developments in Nelson and Auckland harbors. Binding of these sediments was investigated using Portland cement, cement kiln dust, lime, amorphous silica, and diatomite. The effectiveness of physical binding of these systems was found to be dependent on the clay type, with montmorillonite clays producing higher compressive strength than kaolinite clays (cf. highest strengths of 1,320 and 630 kPa, respectively). Research findings indicate that effective solidification of contaminated harbor sediments is possible using a range of materials including waste products from the cement industry such as cement kiln dust that produced strengths of almost 800 kPa.