Journal of Materials in Civil Engineering

Dry stacking is an improved method of storing bauxite residue mud, a by-product of the Bayer process in the alumina industry. Stacking has the potential to increase the density and stability of the residue deposit, reducing the costs associated with the construction of impoundment areas. Minimizing the land area exposed to the residue mud also reduces the possibility of groundwater contamination. The stored residue is alkaline and carries the potential for environmental impacts over the long term. Carbonation is being evaluated at Alcoa World Alumina Australia’s (Alcoa’s) Kwinana Refinery in Western Australia, as a means of neutralizing residue alkalinity. This paper details the physical characteristics exhibited by bauxite residue following treatment with carbonation and/or the addition of bitterns. The impact of residue carbonation and bitterns addition on the initial drainage and drying behavior of bauxite residues was evaluated. The long term consolidation properties of the residues and the impact of these chemical treatments on the overall stability of the deposit was also determined.

It is well known that ${\mathrm{CaCl}}_2$ and ${\mathrm{MgCl}}_2$ can been used for dust control and soil stabilization in many fields. However, solutions of ${\mathrm{CaCl}}_2$ and ${\mathrm{MgCl}}_2$ are slightly acidic and their application is often forbidden in the area where acid is restricted. Furthermore, in wet seasons, ${\mathrm{CaCl}}_2$ and ${\mathrm{MgCl}}_2$ can be partly leached away by water and result in other pollution. In order to solve such problems, $\mathrm{CaO}$ , $\mathrm{MgO}$ and sodium silicate were individually mixed to the chlorides to reduce their acidity in the investigation. Based on a large number of experiments, the principal results are as follows: $\mathrm{CaO}$ , $\mathrm{MgO}$ , and sodium silicate cannot only reduce effectively the acidity of the solutions but also decrease greatly the water absorption capacity of the chlorides. The more $\mathrm{CaO}$ , $\mathrm{MgO}$ , and sodium silicate are added, the less its water absorption rate of the chlorides will be. At the same time, $\mathrm{CaO}$ , $\mathrm{MgO}$ , and sodium silicate can react with the chlorides, some ions on the surface of soil and dust particles, water and ${\mathrm{CO}}_2$ in atmosphere, and their formation products can also bind dust and soil effectively. The binding principles of dust and soil are also explained in detail in this paper.

The potential of woodash to stabilize clay soil was evaluated. The evaluation involved the determination of the geotechnical properties of clay soil in its natural state as well as when mixed with varying proportions of woodash. The parameters tested included the particle size distribution, specific gravity, Atterberg limits, compaction characteristics, California bearing ratio (CBR) and the compressive strength. The CBR and strength tests were repeated after 28-day curing of the treated samples. Results showed that the geotechnical parameters of clay soil are improved substantially by the addition of woodash; plasticity was reduced by 35% and CBR and strength increased by 23–50% and 49–67%, respectively, depending on the compactive energy used. The highest CBR and strength values were achieved at 10% woodash. Results also showed that curing improved the strength of the woodash-treated clay. However, the strength gain was short lived as the strength quickly decreased after 7–14 days of curing. These results imply that although woodash provides some of the beneficial effects of lime in soil stabilization, such as plasticity and swell reduction, improved workability, and strength increase, it is unlikely to be a substitute for lime as strength gain is short lived.

Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of ${\mathrm{CaCl}}_2$ in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and ${\mathrm{CaCl}}_2$ treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the ${\mathrm{CaCl}}_2$ could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples.

Cementitious stabilization is a common method of ground improvement when weak foundation soils are encountered in practice, and marginal or nonstandard materials such as recycled aggregates are used in civil engineering construction. Long-term durability of stabilized materials becomes an issue, especially when it involves one or more recycled materials with unknown and often questionable properties. The study presented herein investigates the fatigue durability, endurance limit, and damage accumulation process in recycled crushed concrete aggregate stabilized with cement–fly ash mixtures. Results show that the $2\text{million}\text{cycles}$ fatigue endurance limit for the stabilized recycled aggregate was nearly 53% of the static modulus of rupture, indicating that the fatigue strength of this material is quite similar to or better than other traditional cementitious composites. It was also found that the accumulated permanent deformation and the expended fatigue life can be related by a nonlinear power law, and the fatigue damage in this material approximately follows Miner’s rule for cumulative damage. Finally, the importance of developing innovative testing methods for durability assessment are highlighted, which include coupled mechanical and environmental loadings to simulate the most damaging field conditions, and accelerated aging and life prediction processes using the Arrhenius time–temperature superposition methods.

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. It is based on the concept of slowly injecting colloidal silica at the edge of a site with subsequent delivery to the target location using natural or augmented groundwater flow. Colloidal silica is an aqueous dispersion of silica nanoparticles that can be made to gel by adjusting the pH or salt concentration of the dispersion. It stabilizes liquefiable soils by cementing individual grains together in addition to reducing the hydraulic conductivity of the formation. Centrifuge modeling was used to investigate the effect of colloidal silica treatment on the liquefaction and deformation resistance of loose, liquefiable sands during centrifuge in-flight shaking. Loose sand was successfully saturated with colloidal silica grout and subsequently subjected to two shaking events to evaluate the response of the treated sand layer. The treated soil did not liquefy during either shaking event. In addition, a box model was used to investigate the ability to uniformly deliver colloidal silica to loose sands using low-head injection wells. Five injection and two extraction wells were used to deliver stabilizer in a fairly uniform pattern to the loose sand formation. The results of the box model testing will be used to design future centrifuge model tests modeling other delivery methods of the grout.

The present study focuses on investigating the effect of freeze–thaw (FT) cycles, referred to as environmental effect in this paper, on aggregates stabilized with various stabilizing agents, namely, cement kiln dust (CKD), Class C fly ash (CFA), and fluidized bed ash (FBA). Cylindrical specimens were compacted and cured for $28\text{days}$ in a moist room with a constant temperature and controlled humidity. After curing, specimens were subjected to 0, 8, 16, and 30 FT cycles, and then tested for resilient modulus $\left(M_r\right)$ . Results showed that $M_r$ values of stabilized specimens decreased with increasing FT cycles up to 30. The reasons for such changes are explained by the increase in moisture content during thawing and the formation of ice lenses within the pores during freezing, causing distortion of the matrix of particles. It was also found that the decrease in $M_r$ values varied with the type of stabilizing agents. The CKD-stabilized Meridian and Richard Spur aggregates exhibited a higher reduction in $M_r$ values than the corresponding values of CFA- and FBA-stabilized specimens. The CFA-stabilized Sawyer specimens performed better than their CKD- and FBA-stabilized counterparts.

Efficacy of stabilizing Ce, Co, and Pb by adding apatite and zero-valent $\mathrm{Fe}\left(\mathrm{Fe}\right(0\left)\right)$ to contaminated wetland sediments was quantified under oxidizing and reducing conditions. The redox status and the general water chemistry of the oxidized and reduced treatments differed greatly, yet the influences of the amendments on contaminant stabilization were quite similar; both amendments significantly $(p⩽0.05)$ reduced aqueous contaminant concentrations. Based on resin sorption studies and thermodynamic calculations, Ce is believed to exist primarily as cationic species and Co as cationic, neutral, and organically complexed species. Based on a series of selective extractions, almost 50% by weight of the Co and Pb were already strongly bound to the sediment, thereby limiting the potential (and need) of affecting additional immobilization through the use of amendments. $\mathrm{Fe}\left(0\right)$ and combined $\mathrm{Fe}\left(0\right)$ and apatite additions tended to increase the in situ desorption $K_d$ values more than apatite-only additions.

Three relatively new applications for controlling wind and water erosion using polyacrylamide copolymers are described that take advantage of their ability to stabilize and add structure to soil. In the first application, low concentrations of anionic, high purity polyacrylamide (PAM) eliminates sediment in runoff water by more than 90% when added to irrigation water at $10\mathrm{ppm}$ , or at a rate of 1 to $2\mathrm{kg}{\mathrm{ha}}^{-1}$ per irrigation. Lab-furrow tests were utilized to characterize the role of molecular weight, charge, and ion concentrations in applying PAM during irrigation. In the second application, PAM is applied at construction sites and road cuts at rates of $22.5\mathrm{kg}{\mathrm{ha}}^{-2}$ (tenfold higher rates than in irrigation control) resulting in reduction in sediment runoff by 60–85% during (simulated) heavy rains. Finally, a formulation of PAM mixed with aluminum chlorohydrate and cross-linked poly(acrylic acid) superabsorbent at a ratio of (6:1:1) has been applied to create helicopter landing pads that minimize dust clouds during helicopter operation. This formulation was specifically developed to minimize dust clouds during landing of helicopters in fine, arid soils such as those potentially encountered in the Middle East. A biodegradable alternative to PAM, acid-hydrolyzed cellulose microfibrils, was tested in lab-scale furrows and was less effective than PAM at similar concentrations, but show promises. Microfibrils reduce sediment run-off in lab-furrow tests by 88% when applied at eight- to tenfold the concentration of PAM.

This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content.

The field of groundwater remediation needs cost effective and time efficient technologies. Recent developments in the field of chaotic advection in low Reynolds number flows have led to the belief that a system of wells that oscillate between injection and extraction with time-dependent, randomly constrained flow rates could cause substantial mixing in an aquifer. This could have significant effects when combined with the advection and dispersion and biodegradation aspects of natural attenuation, especially in the context of mixing rate-limiting electron acceptors with contaminants that are serving as substrate for microbes. Chaotic advection enhanced remediation could possibly turn decades into years, while reducing both exposure risk and clean up costs. In this research work, we use flow and transport modeling to study the mixing phenomena created in groundwater by oscillating wells. To quantify mixing, an index is developed using the concept of average interparticle distances and implemented along with the dilution index, presented in the literature before.

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from $0.5\text{to}10\mathrm{g}∕\mathrm{L}$ , as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from $120\text{to}200\mathrm{h}$ , and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below $2\mathrm{g}∕\mathrm{L}$ . Data from x-ray diffraction and batch sorption tests on dried Na-montmorillonite samples indicate that postsorption/swelling interlayer spacings of 0.74 and $0.78\mathrm{nm}$ for PAM A (molecular $\text{weight}=4\times {10}^6$ ) and PAM B (molecular $\text{weight}=7\times {10}^6$ ) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of $4\mathrm{g}∕\mathrm{L}$ . Test results for CMC (the anionic polymer) and PEO (the neutral polymer) show that swelling is not significantly reduced relative to that of distilled water. PAM can be used at aqueous concentrations between 0.5 and $4\mathrm{g}∕\mathrm{L}$ as an effective stabilization agent for expansive soils.

The low-viscosity stabilizer, colloidal silica (CS), is extensively used as a grouting material in the construction of grout curtains to prevent fluid movements. It is a low viscosity and nontoxic material, which is suitable for injection to stabilize/solidify fine grained soils. It is also used in the in situ treatment of hazardous waste as a stabilizer/solidifier. Once the CS solution is injected into contaminated soil, it moves through the pores inside the soil matrix and initiates the stabilization/solidification process. The viscosity of the CS mixture increases while it moves until complete solidification occurs. In this paper, the transport of CS during injection was simulated at the microscopic level to understand the stabilization/solidification process. The microscopic behavior/movement of CS stabilizer inside anisotropic granular soil during grouting was simulated by numerically solving the Navier-Stokes equation. The change in gel viscosity with time was used to model the movement of CS during injection. A model parameter $v_{\min }$ , the minimum velocity for CS to become a solid, was introduced. The simulation showed that during the grouting of fine sands, solidification starts at the soil surface and expands to fill the majority of voids within $1.2\mathrm{h}$ . The simulation of CS grouting of different soil types, soil compaction levels, and soil anisotropies showed the impact of soil parameters such as grain size distribution, void ratio and anisotropy on velocity contours and the final solidification. This microscopic model can be further improved to be used in the design of grout curtains, especially for the determination of the ability to grout soils and the size of stabilizer plume in such stabilization projects.

For the purpose of understanding the influence of stabilizing agents on the internal structure of aggregates in treated soils, seven soil samples were prepared for tests according to type and quantity of stabilization agents, as well as sampling location. In nitrogen adsorption and desorption tests, HK and BJH methods are, respectively, adopted to analyze the diameter distributions of micropores and mesopores within aggregates in samples with diverse treatment. The results indicate that: (1) micropores with the diameter of approximately $8.4\mathrm{\AA }$ in aggregates are prominent in both untreated and treated expansive soil samples; (2) mesopores with the diameter of greater than $30\mathrm{\AA }$ are mainly distributed in four ranges of 30–40, 70–75, 90–95, and $450–500\mathrm{\AA }$ , and the stabilization agent has significant effect on the structure of mesopores with the diameter of greater than $200\mathrm{\AA }$ ; and (3) both lime and cement are able to decrease the volumes of micropores while increasing those of mesopores and macropores in expansive soils. The scanning electron microscope images of the samples were presented to interpret the difference in micropore structure between lime-treated soils and cement-treated soils and further validate the results from adsorption tests. In addition, energy-dispersive X-ray spectrometer (EDX) analysis was employed to determine the composition of some points on the individual aggregate and migration of calcium ions in the aggregates in lime treated soils. Through the EDX analysis, it is shown that lime usually concentrates in pores or on the surface of aggregates and has few effects on the inner of aggregates with size ranging from $5\text{to}10\mathrm{mm}$ .

In this study, samples treated with aluminum, lime, and fly ash technology were subjected to different leaching tests per the toxicity characteristics leaching procedures (TCLP). The leachants were simulated groundwater, acid rain, sulfuric acid solution (modified TCLP), and 0.1 molar acetic acid solution (TCLP). The leachate solutions were analyzed by atomic absorption spectroscopy for the metal concentrations. The success of the treatment was evaluated based on results of leachability combined with X-ray diffraction analysis. The results of the experiments indicate that upon availability of aluminum for reaction, ettringite, and ettringitelike minerals are formed and precipitated as stable minerals. Moreover, the high hydrogen ion concentration environment of the samples, produced by lime and fly ash addition, and the stabilization effect of ettringite had contributed significantly to the reduction of the solubility of heavy metals. The X-ray diffraction analysis indicated that ettringite remained stable during the testing period of 660 days.

Activation methods and their effects on strength development of nonclinker cements made with 50% cement kiln dust (CKD) and 50% Class F fly ash (FA) were investigated. These activation methods included (1) ball mill cogrinding; (2) chemical (2 and 5% $\mathrm{NaOH}$ ) addition; and (3) elevated temperature curing (38 and $50°\mathrm{C}$ ). Particle size distribution, hydration products, and compressive strength of the CKD-FA binders were studied. Soluble alkali and chloride content as well as pH value of the CKD-FA pastes were evaluated. The results indicate that all activation methods improved binder strength development. The strength improvement was more significant at the early age than that at the later age. Curing at elevated temperature appeared to be the most effective activation methods compared with grinding and $\mathrm{NaOH}$ addition. Combined activation methods provided the binder with higher activation effectiveness than any single activation method. The CKD-FA pastes had much higher alkali and chloride contents but slightly lower pH value than the corresponding portland cement paste.