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Large numbers of soil-cement block masonry buildings exist in India and many other countries. The paper deals with an experimental study on the influence of soil grading on the characteristics of soil-cement blocks and shear-bond strength of soil-cement block masonry triplets. Influence of clay content of the soil-cement block on strength, absorption and durability characteristics, and interfacial mortar-block bond strength has been examined. Some of the major conclusions of the study are: (1) optimum clay content leading to maximum strength is in the range of 14-16%; (2) saturated water content of the blocks increases with increase in clay content of the block; (3) initial rate of absorption decreases with increase in clay content of the block; (4) weight loss after ASTM wire scratch test is minimum when the clay content of the block is about 16%; and (5) optimum clay content for the highest modulus for the blocks and for highest shear-bond strength is about 16%. DOI: 10.1061/(ASCE)0899-1561(2007)19:2(139) CE Database subject headings: Soil-cement; Compressive strength; Durability; Soil stabilization; Bonding strength; Stress strain relations.

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 diaineter of approximately 8.4 A in aggregates are prominent in both untreated and treated expansive soil samples; (2) mesopores with the diameter of greater than 30 [Angstrom] are mainly distributed in four ranges of 30-40, 70-75, 90-95, and 450-500 [Angstrom], and the stabilization agent has significant effect on the structure of mesopores with the diameter of greater than 200 [Angstrom]; 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 to 10 mm. DOI: 10.1061/(ASCE)0899-1561(2007)19:1(99) CE Database subject headings: Aggregates; Structures; Soil stabilization.

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 to 10 g/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 to 200 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 g/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 nm for PALM A (molecular weight =4 X [10.sup.6]) and PAM B (molecular weight=7 x [10.sup.6]) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of 4 g/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 g/L as an effective stabilization agent for expansive soils. DOI: 10.1061/(ASCE)0899-1561(2007)19:1(84) CE Database subject headings: Soil stabilization; Swelling; Polymers; Expansive soils; Clays.

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 ppm, or at a rate of 1 to 2 kg [ha.sup.-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 kg [ha.sup.-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. DOI: 10.1061/(ASCE)0899-1561(2007)19:1(58) CE Database subject headings: Erosion; Runoff; Polymers; Soil stabilization.

Efficacy of stabilizing Ce, Co, and Pb by adding apatite and zero-valent Fe(Fe(0)) 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 [less than or equal to] 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. Fe(0) and combined Fe(0) and apatite additions tended to increase the in situ desorption [K.sub.d] values more than apatite-only additions. DOI: 10.1061/(ASCE)0899-1561(2007)19:1(49) CE Database subject headings: Contamination; Lead; Coefficients; Soil pollution.

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. DOI: 10.1061/(ASCE)0899-1561(2007)19:1(33) CE Database subject headings: Liquefaction; Soil stabilization; Grouting; Colloids.

It is well known that Ca[Cl.sub.2] and Mg[Cl.sub.2] can been used for dust control and soil stabilization in many fields. However, solutions of Ca[Cl.sub.2] and Mg[Cl.sub.2] are slightly acidic and their application is often forbidden in the area where acid is restricted. Furthermore, in wet seasons, Ca[Cl.sub.2] and Mg[Cl.sub.2] can be partly leached away by water and result in other pollution. In order to solve such problems, CaO, 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: CaO, 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 CaO, MgO, and sodium silicate are added, the less its water absorption rate of the chlorides will be. At the same time, CaO, MgO, and sodium silicate can react with the chlorides, some ions on the surface of soil and dust particles, water and C[O.sub.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. DOI: 10.1061/(ASCE)0899-1561 (2007) 19:1 (10) CE Database subject headings: Chlorides; Dust; Absorption; Soil 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. CE Database subject headings: Soil stabilization; Arid lands; Agriculture; Fly ash.

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. CE Database subject headings: California bearing ratio; Compaction; Compressive strength; Durability; Expansive soils; Laboratory tests; Lime; Tropical soils.

The objective of this paper is to assess the potential use of the geogauge and the light falling weight deflectometer (LFWD) as quality control/quality assurance ([Q.sub.c]/[Q.sub.A]) devices for testing subgrades, base courses, and compacted soil layers. A comprehensive laboratory experimental program was conducted on compacted layers of silty clay, clayey silt, cement-treated clay, sand, gravel, recycled asphalt pavement, and limestone aggregates. The geogauge, LEWD, static plate load test (PLT), and the dynamic cone penetration (DCP) measurements were acquired for the constructed layers. The geogauge elastic modulus and the LEWD dynamic modulus were correlated with the PLT initial and reloading elastic moduli and with the DCP penetration rates. The results of this study show that the geogauge and the LEWD can be used to calculate the elastic modulus/stillness characteristics of compacted layers. Whereas the geogauge and the LEWD determined the initial modulus of the cement-treated clay, they did not yield accurate measurements of strength gain with time. Good statistical correlations were found between elastic moduli measured by the devices used in this investigation. CE Database subject headings: Falling bodies; Weight; Laboratory tests; Construction methods; Control methods; Quality control; Compacted soils; Base course; Subgrades.

This paper reports the findings of experimental studies with regard to some common engineering properties (e.g., grain size, specific gravity, compaction characteristics, and unconfined compression strength) of both low and high calcium fly ashes, to evaluate their suitability as embankment materials and reclamation fills. In addition, morphology, chemistry, and mineralogy of fly ashes are studied using scanning electron microscope, electron dispersive x-ray analyzer, x-ray diffractometer, and infrared absorption spectroscopy. In high calcium fly ash, mineralogical and chemical differences are observed for particles, >75 [micro]m and the particles of CE Database subject headings: Fly ash; India; Grain size; Soil compaction; Compression strength.

The mineralogy of a soil susceptible to sulfate attack was investigated in detail, with particular attention paid to the sulfate and clay minerals. The soil from north Louisiana suffered sulfate attack when stabilized by Type I portland cement. A number of analytical techniques, such as x-ray diffractometry, thermal analysis (thermogravimetry and differential scanning calorimetry), Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray absorption near edge structure (XANES), were used. Thermogravimetry showed that 7.8% gypsum (CaS[O.sub.4]x2[H.sub.2]O) was present in the soil from the average of four samples. Quantitative x-ray diffractometry yielded a value of 12.9 [+ or -] 1.1% for one soil. XANES indicated that all the sulfur in the soil was present as sulfate phases. Gypsum was found in all size fractions. The clay minerals, kaolinite (highest concentration), illite (intermediate concentration), and smectite (lowest concentration) could be identified with certainty only after the clay fraction was concentrated by removal of gypsum by acid dissolution followed by centrifugation. Kaolinite (5%) could be easily quantified by thermogravimetry but not other clay minerals. DOI: 10.1061/(ASCE)0899-1561 (2004) 16:4(375) CE Database subject headings: Soil stabilization; Mineralogy; Mineral analysis; Calcium sulfate; Clays; X-ray analysis; Thermal analysis; Microscopy.

Sabkha soils are known for their low-bearing strength in their natural condition. Moreover, the collapse potential of sabkhas presents an unacceptable risk in normal practice and calls for the improvement of their mechanical properties prior to any construction. A review of the literature indicates that research on the stabilization of sabkha is scanty despite the extensive distribution of sabkha soils worldwide. Moreover, since the sabkha is a highly variable material, there is a need to formulate a 'data bank' by stabilizing as many sabkhas as possible. In this study, a 'selected' sabkha soil from Al-Qurayyah, eastern Saudi Arabia, was researched for improving its properties using cement and lime at five different dosages ranging from 0 to 10%. The load-bearing capability of plain and chemically stabilized sabkha mixtures was evaluated using the CBR, unconfined compressive strength, and Clegg impact value at different moisture contents. The results indicated that cement improved the performance of stabilized sabkha much more than lime, particularly at high moisture contents. Further, the 7% cement addition has satisfied the strength requirements so that sabkha soil can be used as a base course in rigid pavements and a subbase in flexible pavements. CE Database keywords: Salinity; Stabilization; Cement; Lime; Moisture content; Correlation.

Expansive clay soils--those that change significantly in volume with changes in water content--are the cause of distortions to structures that cost taxpayers several billion dollars annually in the United States. Much has been learned about their behavior over the past 60 years, and relatively successful methods have been developed to modify and stabilize them. This paper reviews some of the key advances developed over the past 60 years in improving our understanding of the nature and methods of modifying and stabilizing expansive clay soils. The state of the practice in stabilization is presented, and practical and research needs to help improve the state of the practice are discussed. CE Database keywords: Stabilization; Clays; Expansive soils; Earth structures; Distortion.

In recent years, considerable research has been conducted in the construction of pavement layers incorporating foamed asphalt (FA). Development of improved foaming techniques has enabled both effective and economical stabilization of marginal quality pavement materials. This paper explores the ability of using FA to stabilize local sebkha soils to be used as a base or subbase material in asphalt structures under the relatively high temperature conditions in eastern Saudi Arabia. For the sake of relative performance and cost comparison, three types of treatment were used to stabilize the low quality sebkha soil: FA, emulsified asphalt, and sulfate-resisting (type V) portland cement. Marshall stability, indirect tensile, and unconfined compressive strength tests were performed to evaluate the properties of Marshall-prepared samples. Properly designed FA sebkha soil with as little as 2% cement displayed significant improvement in the strength properties, as compared with those of emulsified and cement-treated sebkha mixes. From cost perspectives, the FA-sebkha-2% cement mixture exhibited a superior rating as compared with the other stabilizing agents.