Performance and Leaching Assessment of Flowable Slurry

This project was conducted to evaluate the performance and leaching of controlled low strength materials (CLSM) incorporating fly ash and foundry sand. Two different CLSM (or flowable slurry) reference mixtures (equivalent to available production CLSM mixtures) were proportioned for unconfined compressive strength levels in the range of 0.3–0.7 MPa (50–100 psi), at 28 days, using two sources of ASTM Class F fly ash. For each reference mixture, other mixtures were proportioned using two sources of foundry sand (molten metal-casting mold sand) as a replacement for fly ash in the range of 30–85%. The ingredients of the slurry mixtures—fly ash, clean foundry sand, and used foundry sand—were tested for their physical and chemical properties and their leachate characteristics. Portland cement used as the primary binder was also tested for its properties. All CLSM mixtures made with and without foundry sand were evaluated for settlement, setting and hardening characteristics, compressive strength, permeability, and leachate characteristics. The leachate results of these CLSM-making materials were below the enforcement standards (ES) of the Wisconsin Department of Natural Resources (WDNR) ground-water quality standards (GWQS). They also met practically all the parameters of the drinking water standards. A number of CLSM mixtures incorporating fly ash and foundry sand are recommended for construction applications.     

Forensic Investigation of Pavement Premature Failure due to Soil Sulfate-Induced Heave

Current practice does not recommend stabilizing high sulfate-bearing soils using calcium-based stabilizers due to high potential swell and low retained unconfined compressive strength. In this technical note, a series of tests has demonstrated that a combination of lime and fly ash (Class F) proved to be the most suitable stabilizer for a high sulfate-bearing soil, and a combination of lime and slag seemed to be the most effective stabilizer for a moderate sulfate-bearing soil in terms of retained unconfined compressive strength and three-dimensional free swell potential.     

Strength Characteristics of Class F Fly Ash Modified with Lime and Gypsum

This paper presents the shear strength characteristics of a low lime class F fly ash modified with lime alone or in combination with gypsum. Unconfined compression tests were conducted for both unsoaked and soaked specimens cured up to 90 days. Addition of a small percentage of gypsum (0.5 and 1.0%) along with lime (4–10%) enhanced the shear strength of modified fly ash within short curing periods (7 and 28 days). The gain in unsoaked unconfined compressive strength (qu) of the fly ash was 2,853 and 3,567% at 28 and 90 days curing, respectively, for addition of 10% lime along with 1% gypsum to the fly ash. The effect of 24?h soaking showed reduction of qu varying from 30 to 2% depending on mix proportions and curing period. Unconsolidated undrained triaxial tests with pore-pressure measurements were conducted for 7 and 28 days cured specimens. The cohesion of the Class F fly ash increased up to 3,150% with addition of 10% lime along with 1% gypsum to the fly ash and cured for 28 days. The modified fly ash shows the values of Skempton’s pore-pressure parameter, Af similar to that of over consolidated soils. The effects of lime content, gypsum content, and curing period on the shear strength parameters of the fly ash are highlighted herein. Empirical relationships are proposed to estimate the design parameters like deviatoric stress at failure, and cohesion of the modified fly ash. Thus, this modified fly ash with considerable shear strength may find potential use in civil engineering construction fields.     

In-Place Stabilization of Pond Ash Deposits by Hydrated Lime Columns

Abandoned coal ash ponds cover up vast stretches of precious land and cause environmental problems. Application of suitable in situ stabilization methods may bring about improvement in the geotechnical properties of the ash deposit as a whole, converting it to a usable site. In this study, a technique of in-place stabilization by hydrated lime columns was applied to large-scale laboratory models of ash ponds. Samples collected from different radial distances and different depths of the ash deposit were tested to study the improvements in the water content, dry density, particle size distribution, unconfined compressive strength, pH, hydraulic conductivity, and leachate characteristics over a period of one year. The in-place stabilization by lime column technique has been found effective in increasing the unconfined compressive strength and reducing hydraulic conductivity of pond ash deposits in addition to modifying other geotechnical parameters. The method has also proved to be useful in reducing the contamination potential of the ash leachates, thus mitigating the adverse environmental effects of ash deposits.     

粉煤灰改性高水材料力学性能试验研究及机理分析

为解决矿山高水充填材料成本较高、粉煤灰等工业废料大量剩余造成资源浪费、环境污染等问题,借助微机控制电子万能试验机(ETM)力学试验系统、扫描电镜扫描装置和X射线衍射分析仪,研究粉煤灰掺量对高水材料物理力学性能的影响规律,并通过物相和微观结构分析探讨其影响机理.结果表明:随着粉煤灰掺量的增加,高水材料的凝结时间逐渐延长,含水率逐渐降低,容重基本不变;掺杂粉煤灰前后高水材料均是一种弹塑性材料,其变形破坏过程可以分为孔隙压密阶段、弹性阶段、屈服阶段和破坏阶段;高水材料的峰值强度、弹性模量和变形模量均随粉煤灰掺量的增加略有降低,残余强度却有所提高;综合考虑高水材料的强度、模量和成本,粉煤灰掺量a为15%是最优掺量,此时峰值强度、弹性模量和变形模量仅分别降低了25%、8.6%和10%,残余强度却提高了50%.物相和微观形貌分析结果表明:粉煤灰的掺量影响了β-C₂S的水化进程,导致钙矾石生成量减少,其他水化产物生成量增多,进而破坏了钙矾石结构的整体性和均匀性,最终降低了高水材料的抗压强度.      

地聚合物混凝土配比及力学性能研究

混凝土是巷道支护过程中的重要建筑材料,然而混凝土在巷道施工中常常出现质量问题,为了不影响正常生产,需要对其进行修补。地聚合物混凝土凝结时间快,早期强度高,界面结合能力强,耐高温性和抗冻性强,耐腐蚀性良好,具有用作修补材料的潜力。以粉煤灰和矿粉为原料,Na₂SiO₃溶液和NaOH为碱激发剂制备地聚合物胶砂,研究不同的碱激发剂模数（1.0、1.2、1.4）和掺量（10%、15%、20%）对不同龄期胶砂力学性能的影响。结果表明：当碱激发剂模数为1.2,碱掺量为15%时,胶砂强度达到最大值。设计正交试验,研究了不同水胶比（0.45、0.50、0.55）、粉煤灰掺量（30%、50%、70%）和砂率（30%、35%、40%）对不同龄期地聚合物混凝土的工作性能和力学性能的影响。结果表明：粉煤灰掺量对抗压强度影响最为显著,水胶比次之,而砂率对强度发展几乎没有影响。最优的配合比为水胶比为0.50,粉煤灰掺量为50%,砂率为35%。     

Effects of Kiln Ash on the Compressibility of Residual Lateritic Soils

The potential for the use of kiln ash as an additive to Lateritic soils to improve their engineering characteristics as road construction material was experimentally investigated. The results of laboratory tests indicate that no significant improvement of the soil properties occurred until after several weeks of curing time. In general, as the content of kiln ash in the soil was increased, the soil pH increased from 5.5 to 11.8; the maximum unconfined shear strength increased from 340 to 423 kPa (corresponding to 0–8% kiln ash content), the soil liquid limit reduced from 59 to 49% (corresponding to 0–20% kiln ash as content). No significant change in the plasticity limits of the lateritic soil was observed, in the range of 0 to 8% kiln ash content. Relative to the compressibility of the natural soil (measured in terms of the total strain), a decrease of about 3% occurred for kiln ash contents of 5, 10, and 20% within 1 to 7 days; and that this decrease reached about 19% for 20% kiln ash content as time progressed (to more than 177 days). These results imply that significant and desirable changes in soil compressibility can be achieved after a few months if the soils are admixed with kiln ash. Soil solution pH changes cause a time-dependent increase in soil strength, where calcium cations combine with silica and aluminum of the soil to form insoluble cementitious materials.     

Neural Network Modeling of Resilient Modulus Using Routine Subgrade Soil Properties

Artificial neural network (ANN) models are developed in this study to correlate resilient modulus with routine properties of subgrade soils and state of stress for pavement design application. A database is developed containing grain size distribution, Atterberg limits, standard Proctor, unconfined compression, and resilient modulus results for 97 soils from 16 different counties in Oklahoma. Of these, 63 soils (development data set) are used in training, and the remaining 34 soils (evaluation data set) from two different counties are used in the evaluation of the developed models. A commercial software, STATISTICA 7.1, is used to develop four different feedforward-type ANN models: linear network, general regression neural network, radial basis function network, and multilayer perceptrons network (MLPN). In each of these models, the input layer consists of seven nodes, one node for each of the independent variables, namely moisture content (w), dry density (γd), plasticity index (PI), percent passing sieve No. 200 (P200), unconfined compressive strength (Uc), deviatoric stress (σd), and bulk stress (θ). The output layer consists of only one node—resilient modulus (MR). After the architecture is set, the development data set is fed into the model for training. The strengths and weaknesses of the developed models are examined by comparing the predicted MR values with the experimental values with respect to the R2 values. Overall, the MLPN model with two hidden layers was found to be the best model for the present development and evaluation data sets. This model as well as the other models could be refined using an enriched database.     

Effect of Fly Ash on Engineering Properties of Expansive Soils

This note presents a study of the efficacy of fly ash as an additive in improving the engineering characteristics of expansive soils. An experimental program has evaluated the effect of the fly ash content on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil. The plasticity, hydraulic conductivity and swelling properties of the blends decreased and the dry unit weight and strength increased with an increase in fly ash content. The resistance to penetration of the blends increased significantly with an increase in fly ash content for a given water content. Excellent correlation was obtained between the measured and predicted undrained shear strengths.     

Design of Compacted Lateritic Soil Liners and Covers

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.     

Variables Controlling Stiffness and Strength of Lime-Stabilized Soils

Lime treatment is an attractive technique for soil improvement in the construction of rail tracks and pavement layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as in the case of soil-cement technology, where the voids/cement ratio is shown to be a key parameter for the estimation of both strength and stiffness. The present study, therefore, was aimed at quantifying the influence of the amount of lime, porosity, and voids/lime ratio on the initial shear modulus (G0) and unconfined compressive strength (qu) of a lime-treated clayey sandy soil. From the results of unconfined compression tests and bender elements measurements, it was shown, for the soil-lime mixtures investigated, that the voids/lime ratio is an appropriate parameter to assess both initial stiffness and unconfined compressive strength. Also, a unique G0/qu versus voids/lime ratio relationship was established linking the soil-lime mixture initial stiffness and compressive strength.     

Use of Class C Fly Ashes for the Stabilizationof an Expansive Soil

Excessive heave associated with swelling of expansive soils can cause considerable distress to lightweight civil engineering structures. Several methods have been suggested to control this problem. The most commonly used method is addition of stabilizing agents, such as lime or cement to the expansive soil. In this study, high-calcium and low-calcium class C fly ashes from the Soma and Tuncbilek thermal power plants, respectively, in Turkey, were used for stabilization of an expansive soil. An evaluation of the expansive soil-lime, expansive soil-cement, and expansive soil-fly ash systems is presented. Lime and cement were added to the expansive soil at 0–8% to establish baseline values. Soma fly ash and Tuncbilek fly ash were added to the expansive soil at 0–25%. Test specimens were subjected to chemical composition, grain size distribution, consistency limits, and free swell tests. Specimens with fly ash were cured for 7 days and 28 days, after which they were subjected to oedometer free swell tests. Based on the favorable results obtained, it can be concluded that the expansive soil can be successfully stabilized by fly ashes.     

高铝粉煤灰钙矿相转化行为研究

从高铝粉煤灰的矿相特性入手,研究转化剂的种类及用量、温度、时间、液固比等对高铝粉煤灰钙矿相转化行为的影响及其反应机理,并提出了高铝粉煤灰制备铝硅合金新工艺。结果表明,高铝粉煤灰中Al2O3和SiO2含量之和达到70%以上,Ca元素主要以CaSO4形式存在,还有一部分以2CaO·Al2O3·SiO2形式存在。粉煤灰中钙矿相转化为碳酸钙后对后续酸浸除杂过程中氧化铝损失影响不大,但能够大幅度提高除钙率。高铝粉煤灰钙矿相转化最佳条件为:转化剂Na2CO3添加量为2倍理论值、转化温度60℃、反应时间1.5h、液固比4,在此条件下除钙率能够达到90%以上。     

铁尾矿粉制备高延性纤维增强水泥基复合材料

探索采用铁尾矿粉取代粉煤灰作为矿物掺合料制备高延性纤维增强水泥基复合材料（ECC）的可行性,重点研究铁尾矿粉掺量对ECC的拉伸特性和抗压强度的影响,并比较所研发的新型铁尾矿粉ECC与传统粉煤灰ECC的宏观力学性能.研究发现,采用铁尾矿粉作为矿物掺合料制备高延性纤维增强水泥基复合材料是可行的.在同等矿物掺合料掺量下,铁尾矿粉ECC的强度性能低于粉煤灰ECC,但表现出更强的拉伸延性.在所研制的铁尾矿粉ECC中,当铁尾矿粉与水泥质量比为1.2-2.2时,ECC的28 d抗压强度为36.7-54.2 MPa,满足一般混凝土结构对抗压强度的要求.此时,ECC的28 d极限拉伸应变为3.4%-4.3%,铁尾矿的总用量占固体基体原材料总质量的66.6%-77.0%.      

Behavior of Cement-Stabilized Fiber-Reinforced Fly Ash-Soil Mixtures

An experimental program was undertaken to study the individual and combined effects of randomly oriented fiber inclusions and cement stabilization on the geotechnical characteristics of fly ash-soil mixtures. An Indian fly ash was mixed with silt and sand in different proportions. The geotechnical characteristics of the raw fly ash-soil specimens and fly ash-soil specimens containing 1% randomly oriented polyester fiber inclusions were investigated. Unconfined compression tests were carried out on fly ash-soil specimens prepared with 3% cement content alone and also with 3% cement and 1% fiber contents, after different periods of curing. The study shows that cement stabilization increases the strength of the raw fly ash-soil specimens. The fiber inclusions increase the strength of the raw fly ash-soil specimens as well as that of the cement-stabilized specimens and change their brittle behavior to ductile behavior. Depending on the type of fly ash-soil mixture and curing period, the increase in strength caused by the combined action of cement and fibers is either more than or nearly equal to the sum of the increase caused by them individually.     

Key Parameters for Strength Control of Artificially Cemented Soils

Often, the use of traditional techniques in geotechnical engineering faces obstacles of economical and environmental nature. The addition of cement becomes an attractive technique when the project requires improvement of the local soil. The treatment of soils with cement finds application, for instance, in the construction of pavement base layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as exist in the case of the concrete technology, where the water/cement ratio plays a fundamental role in the assessment of the target strength. This study therefore aims to quantify the influence of the amount of cement, the porosity and the moisture content on the strength of a sandy soil artificially cemented, as well as to evaluate the use of a water/cement ratio and a voids/cement ratio to assess its unconfined compression strength. A number of unconfined compression tests, triaxial compression tests, and measurements of matric suction were carried out. The results show that the unconfined compression strength increased linearly with the increase in the cement content and exponentially with the reduction in porosity of the compacted mixture. The change in moisture content also has a marked effect on the unconfined compression strength of mixtures compacted at the same dry density. It was shown that, for the soil-cement mixture in an unsaturated state (which is usual for compacted fills), the water/cement ratio is not a good parameter for the assessment of unconfined compression strength. In contrast, the voids/cement ratio, defined as the ratio between the porosity of the compacted mixture and the volumetric cement content, is demonstrated to be the most appropriate parameter to assess the unconfined compression strength of the soil-cement mixture studied.     

Effect of Wetting on Unconfined Compressive Strength of Cemented Sands

A weakly cemented sand and gravel has been partly or entirely used in the construction of earth structures such as dams and retaining walls. Such cemented soils that are usually highly permeable can undergo repetitive wetting and drying during curing due to temporary rainfall or a change in the groundwater table. In this study, weakly cemented sand specimens with four different cement ratios were compacted at optimum water content and cured for 28 days. When the cemented sand specimens were exposed to repetitive wetting and drying during curing, their 28-day unconfined compressive strength was evaluated. Wetting for one day on the last day was found to decrease the unconfined compressive strength of cemented sand, whereas wetting for one day in the middle of curing resulted in an increase in strength. The strength reduction due to wetting on the last day decreases as the cement ratio increases. For a specimen under repetitive wetting and drying over 28-day curing, the strength increases as the number of wetting increases up to three cycles. After three cycles of wetting and drying, the strength either becomes constant or slightly decreases due to insufficient water for hydration and/or washing cementitious materials.     

Solidification/Stabilization of Hazardous Wastes Containing Metals and Organic Contaminants

The potential of solidification/stabilization (S/S) technology for the safe disposal of hazardous wastes has wide spread recognition. The purpose of this study was to investigate the effectiveness of portland cement-based S/S technology for the safe disposal of hazardous wastes containing toxic metals and organic contaminants. As hazardous wastes, metal enriched mining residue, adsorbable organic halogens (AOX) containing pulp and paper sludge, and polychlorinated biphenyl (PCB) oil-contaminated soil were used. For S/S of waste, portland cement as a binding agent was mixed with wastes at different ratios. For initial waste characterization, contaminant concentrations and some physical waste characteristics such as particle-size distribution, Atterberg limits, specific gravity, and moisture content yielding the maximum compacted dry density were determined. Waste and cement mixtures were cured for 28 days after compacting the desired waste-cement mixtures at their predetermined optimum moisture contents yielding the corresponding maximum dry densities in cylindrical molds having a height of 71 mm and a diameter of 36 mm. At the end of the 28-day cure period, unconfined compressive strength and hydraulic conductivity measurements were conducted on the solidified samples. Subsequently, solidified samples were crushed for fractionation into two different aggregate sizes (between 1–2 and >2 mm) and subjected to the U.S. Environmental Protection Agency Toxicity Characteristic Leaching Procedure (TCLP). The effectiveness of S/S was assessed by comparing the chemical composition of leachates obtained from TCLP tests of untreated and treated, i.e., S/S waste samples, and comparing values of strength and hydraulic conductivity of solidified waste samples with regulatory requirements. For mining waste, effective application of S/S was achieved for most cases. AOX containing sludge yielded acceptable results in terms of strength and hydraulic conductivity but leachate AOX concentrations were above regulatory levels. The effectiveness of S/S for coarse textured-soils contaminated with a PCB oil was not satisfactory, especially at a cement:soil ratio less than 35%.     

Age-hardening characteristics of aluminum alloy-hollow fly ash composites

The aging characteristics of aluminum alloy A356 and an aluminum alloy A356 containing hollow spherical fly ash particles were studied using optical microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, hardness tests, and compressive tests. The variation of hardness and compressive strength as a function of aging time for the composite have been reported. Since the density of the composite is lower than that of the base alloy due to the presence of hollow particles, the composites have a higher specific strength and specific hardness compared to the matrix. Even though the hardness of the as-cast composite was higher than that of the base alloy, no significant change in the aging kinetics was observed, due to the presence of spherical fly ash particles in the matrix. Aging times of the order of 10⁴ to 10⁵ seconds were required to reach the peak hardness (92 HRF) and compressive strength (376 MPa) in both the A356-5 wt pct fly ash composite and the matrix alloy. The possible effects of shape and hollowness of particles, the interface between the matrix and the particles, the low modulus of the particles, and the microcracks formed on the surface of hollow fly ash particles on the kinetics of the age hardening of aluminum alloy A356 are discussed.     

Stabilized Dredged Material. III: Mineralogical Perspective

The prior two papers in this series reported on the geoenvironmental and geomechanical properties of 20 stabilized dredged material (SDM) blends using dredged material (DM) from the U.S. Army Corps of Engineers Craney Island confined disposal facility. The pozzolans included lime, cement kiln dust (CKD), class F fly ash, and two cements (portland and slag cement). This paper reports on the mineralogical evolution of the SDM blends over a 6-month curing period using techniques new to mainstream geotechnical engineering: X-ray diffraction (XRD) with Rietveld quantification analysis which allows direct quantitative mineralogical comparisons between soil samples. Despite being classified as a high plasticity clay-organic clay (CH/OH soil), XRD showed that the DM contained no montmorillonite, illite or kaolinite, and was thus mineralogically unreactive. The quartz, feldspar, and mica contents were numerically tracked and were shown to remain stable 6 months after blending. The chlorite (in DM) content decreased over time and with the fly ash served as the sources of soluble silica and alumina for pozzolanic reactions especially in the lime-based SDM blends. Lime in the lime-based blends persisted in significant quantities (3%) as unreacted portlandite [Ca(OH)2] even at 6 months curing, indicating that the solubility of silica in the DM was the limiting factor for strength development. New (ettringite and hydrocalumite) mineral formation was quantified. CKD provided high early strength (7 and 28 days) when used in combination with small amounts of lime that provided prolonged pH buffering; CKD alone or in combination with fly ash did not maintain elevated pH (>10.8) over 6 months. Overall, the unconfined compressive strength, pH, and mineralogy results at 6 months were substantially different compared to the standard curing time of 28 days, confirming similar findings of previous long-term stabilization-solidification studies.