Load Settlement Behaviour of Fly ash Mixed with Waste Sludge and Cement

One of the effective utilization strategies for fly ash and waste sludge is to use it as a fill material to raise low lying areas. Bearing capacity and settlement are the required input for the design of foundations on such fills. To determine the bearing capacity, plate load tests were carried out on the compacted beds of fly ash, fly ash-waste sludge and fly ash-waste sludge–cement. The tests were conducted by keeping 90, 95 and 100 % relative compaction, fresh and fresh submerged conditions, aged (28 days) and aged (28 days) submerged conditions as variables of the tests. The load-settlement curves were plotted for fly ash and mix blends. The minimum load was obtained for fly ash under submerged condition, further the test results show that the fly ash becomes flowable on submergence. On the other hand when the fly ash was mixed with waste sludge and cement, the load carrying capacity was found to improve to a greater extent. Test beds prepared with fly ash–cement-waste sludge under as compacted condition (fresh) show very high load carrying capacity (1600–2180 kN/m²). An analytical method has also been validated for fly ash–cement-waste sludge mix which was developed to estimate the settlement of footing resting on fly ash taking into account the pre-consolidation stresses. The non linearity of load-settlement behavior was appropriately modeled, on the basis of available plate load test data incorporated in the method. The method requires as input, the pre-consolidation stress and Young’s modulus of compacted mix of fly ash-waste sludge–cement. A comparison of load-settlement values observed in plate load tests and predicted values for the mix 47 %FA + 45 %S + 8 %C, using the proposed method shows good agreement. Hence, this relationship may also be useful to the field engineers to check the reported load-settlement values for such types of mixes in the field.     

Potential environmental pollution hazards by coal based power plant at Jhansi (UP) India

Coal, a fossil fuel, is the largest source of energy for the generation of electricity in India. In order to study the potential environmental hazards by coal based power plants, particulate matters were collected using Stack Monitoring Kit and gaseous pollutants by Automatic Flue Gas Analyzer. The morphological and chemical properties, mineralogical composition and particle size distributions have been determined by SEM–EDX, XRD and CILAS. The data revealed the presence of particulate matters, SO₂, NOx in the range of 236–315, 162–238, 173–222 mg/Nm³ respectively. The emission of CO₂ was in the range of 43,004–60,115 Nm³/h with an average of 52,830 Nm³/h. Among the elements, Fe > Mn > Al > Zn > B > Ni > Cr > Cu were present in substantially higher proportion than Pb > Mo > Cd > Se > As > Hg. It was found that most of the elements were concentrated on fly ash surface rather than coal, bottom ash and pond ash. This variation may be attributed to the fineness of fly ash particles with large surface ratio to mass. Mineralogical studies of coal and fly ash by X-ray diffraction revealed the presence of mullite, quartz, cristobalite and maghemite. Presence of mullite and quartz found in fly ash indicate the conversion of complex minerals to mullite and quartz at high temperature. Transfer Coefficient was calculated to determine the ratio of the enrichment of trace elements in fly or bottom ash with respect to coal and pond ash.     

Geotechnical characterization of fly ash composites for backfilling mine voids

Backfilling of mine voids is mandatory to avoid subsequent ground stability problems in the form of subsidence. River sand and mill tailings have been widely used since a long time as backfilling materials. However, with a strict regulation banning river sand mining in India, research for developing alternative engineering materials substituting sand has gained importance. In the present study four fly ash composite materials (FCMs) was developed from the fly ash obtained from a captive thermal unit of Rourkela Steel Plant (RSP). The main constituent of the composite were fly ash, lime and gypsum. Detailed physical, and engineering properties were determined for the FCMs. Significant increases in the compressive strength were obtained after 56 days of curing time. A detailed SEM studies was undertaken to account for the increase in strength with time. The fly ash composite developed from RSP has potential to be used as substitute to sand for backfilling the mine voids.     

Characterization of activated carbon obtained from Saudi Arabian fly ash

This study investigated the potential application of heavy oil burning fly ash as a precursor to prepare activated carbon. The raw fly ash obtained from a power plant is cleaned by nitric acid/hydrochloric acid and activated at 550–800 °C with hold times of 30 and 60 min to obtain fly ash activated carbon. The phosphoric acid is used as a chemical agent to improve the surface characteristics of the cleaned fly ash. The effects of process variables such as amount of chemical reagents, activation time and temperature were investigated according to two-levels full factorial design. The resultant activated carbons were characterized in terms of Brunauer, Emmett and Teller surface area and total and pore volume. The maximum specific surface area was found of 148.30 m²/g at 800 °C temperatures with 60 min holding time. The test showed that the surface area and pore volumes of the material are also significantly enhanced by the activation process.     

Effect of lime and fly ash on swell,consolidation and shear strength characteristics of expansive clays: a comparative study

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content (weight of lime/weight of dry soil) was varied as 0%, 2%, 4%?and 6%?and fly ash content (weight of fly ash/weight of dry soil) as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

An experimental investigation into the compaction characteristic of granulated gangue backfilling materials modified with binders

Solid backfill mining has apparent technical advantages in extracting coal resource under sensitive surface structures such as buildings and roads; meanwhile, as an effective method of disposing mining wastes, it works well in solving some environmental problems caused by mining activities. In addition, the controlling effect of solid backfill mining is directly related to the compaction characteristic of backfilling materials. The present study aims to modify the backfilling materials by assessing the effect of binders (cement, fly ash, and lime) on the compaction characteristic of granulated gangue backfilling materials. The compaction test was performed with rock mechanic test system equipped with a self-made circular cylinder apparatus. From the results obtained, cement is not the suitable binder for modifying the gangues backfilling materials, while fly ash or lime, when the dosage is up to 20 wt%, is beneficial to the compaction characteristic of backfilling materials. The relationship between strain behavior and micro-structure of backfilling materials was investigated by SEM and the effect of fly ash or lime on the strain behavior of backfilling materials could be associated with its cementation and gap-filling effect.     

Coupled consolidation model for negative skin friction on piles in clay layers

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content was varied as 0%, 2%, 4%?and 6%?and fly ash content as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.     

Effect of Pozzolanic Reactivity on Compressibility Characteristics of Stabilised Low Lime Fly Ashes

This paper presents the effects of addition of lime and lime along with gypsum on the compressibility behavior of two class F fly ashes. Since the fly ashes develop strength and exhibit lower compression, consolidation testing with conventional duration of load increment may not be appropriate. Hence, an attempt has been made to assess the minimum duration of load increment necessary to study the compressibility characteristics of such materials. Thus compressibility behavior of fly ashes with additives has been studied using conventional consolidation test with different durations of load increments varying from 30 min to 48 h. The results obtained indicated that 30 min of duration of load increment can be used to assess the compressibility behavior of such materials. The effect of lime which reduces the compression is seen to be maximum from the results obtained with the duration of load increment of 30 min but gradually reduces with higher durations of load increment. It has also been observed that the rate of decrease in the compressibility is maximum up to 2.5% lime and gradual thereafter. The compressibility of lime treated fly ashes further reduces when gypsum is incorporated, the optimum gypsum percentage being 2.5. This reduction in the compressibility of fly ashes enhanced by incorporating lime and gypsum makes them versatile in the construction of embankments and for structural fills, particularly reducing the time required in between laying of each lift.     

Leaching characteristics of fly ash

The disposal of fly ash as a byproduct of thermic power stations, results in significant environmental problems. The leaching of coal fly ash during disposal is of concern for possible contamination, especially for the aquatic environment when ash is in contact with water. The aim of this study was to investigate the leaching behaviour of fly ashes currently disposed in Kemerkoy Power Plant (Turkey) fly-ash-holding pond. The studies were conducted with fly ashes from the electrostatic precipitators (fresh fly ash) and from the fly ash pond (pre-leached fly ash). The fly ashes has alkaline in nature and pH ranges between 11.9 to 12.2. The pre-leached fly ash exhibited lower EC values (7,400 µS) than the fresh fly ash (10,300 µS). In contrast to Fe and Pb, the elements such as Cr, Cd, Cu and Co did not leach from the fly ash. The Ca and Mn concentrations decreased with increasing temperature whereas, Na and K concentrations increased. The results showed that the most important effects of fly ash leaching were pH, Na, Ca, K, Fe, Mg, Mn and Pb.     

粉煤灰填筑高速公路路堤的可行性研究

粉煤灰具有自重轻、抗剪强度高、抗压性能好、渗透性能好固结快、容量大技术要求低等优点。作为高速公路路基填料可同时解决其存放占地及高速公路路堤填土需征地的问题。此项施工中应充分利用粉煤灰的活性、在最佳含水量下压实及采用相应措施加强排水.     

粉煤灰处理软土地基的试验研究

利用淤泥质粘土掺入不同比例的粉煤灰, 分别进行了渗透、固结、直接剪切及三轴剪切试验, 详细研究了粘土掺入粉煤灰后其工程力学性能变化的特征以及粉煤灰加固软土的机理。试验结果证实, 利用粉煤灰处理软土地基是-种所需投资较少且有明显效果的方法, 并可带来良好的环境效益和社会效益。     

Numerical analysis of a pile–slab-supported railway embankment

This paper presents a numerical analysis of a well-monitored pile–slab-supported embankment for the Beijing–Tianjin high-speed railway in China. Cement–fly ash–gravel piles were used in this project. A coupled two-dimensional mechanical and hydraulic numerical model was used for this analysis and the results are compared with the field measurements including settlement, load distribution between soil and pile, and excess pore pressure. The numerical model calculated the settlement profile close to that measured in the field. The proportion of the load carried by the soil was small thus significantly reducing the settlement. The stress transfer from the soil to the piles reduced the excess pore pressure effectively. A parametric study was conducted to investigate the influence of three key factors on the performance of the embankment. The parametric study indicated that the existence of a cushion reduced the shear force in the slab. The increase in slab thickness and pile stiffness increased the shear force and bending moment in the slab. An increase in pile stiffness reduced the settlement and lateral displacement of the embankment.     

软土次固结特性试验研究

对广州南沙原状软土进行了一系列的固结试验,探讨了应力历史、加荷比、超载预压对软土次固结的影响。试验结果表明：软土的主次固结的划分与加荷比有关,加荷比对次固结系数C?也有影响;次固结系数主要受到先期固结压力pc的影响,当ppc时,次固结系数表现出不同的变化规律;经预压处理后土样的次固结系数与压缩指数Cc之比近似为一常数：C?/Cc≈0.03,试验成果所揭示的次固结特性对先期固结压力的依赖,为降低地基工后沉降提供了明确的思路。     

粉煤灰增强回填碱渣工程特性的试验研究

碱渣与饱和卤水混合制成浆体回填到盐矿废弃盐腔可同时解决碱渣处理问题和地下废弃盐腔存在的地质隐患。回填碱渣强度是影响充填效果的重要因素。因此,为了提高回填碱渣强度,采用掺入粉煤灰制成复合碱渣对其强度特性进行改良。针对不同粉煤灰掺合比的碱渣开展了组成、力学和细观试验。研究结果表明：（1）掺入粉煤灰能明显改善碱渣的强度,使其黏聚力、内摩擦角都大幅提高,抗剪强度大幅增加;（2）粉煤灰掺合比越大,增强效果越明显,但强度并非随掺合比呈线性变化,对黏聚力而言,在0～20%内的掺合比下增加速度最快,而对内摩擦角则在20%～30%的掺合比区间增加最快,对抗剪强度而言,0～20%的掺合比内增加最明显;（3）粉煤灰掺入还可显著改善碱渣的压缩固结特性,使其固结系数大幅提高,从而提高碱渣固结速度,缩短充填工期,其中在0～10%的掺合比内对压缩固结特性改善最显著;（4）矿物组成分析表明,粉煤灰掺入改变了矿物组成,使得亲水性矿物含量急剧锐减,进而改变了其沉积特性。而细观分析则表明,粉煤灰掺入使碱渣从絮凝团细观结构变成了粉煤灰充当骨架的充填结构,且粒间支撑和拉联效应明显。从增强效果提高、压缩固结特性增强、控制成本和工期综合分析表明,最优掺合比为20%左右,建议工程中以不高于20%的掺合比作为实用掺合比即可取得较为理想的充填增强效果。该研究为揭示碱渣增强机制及废弃盐腔碱渣充填工艺优化提供了有益参考。     

Trend of settlement in primary and secondary consolidations

The trend/rate of settlement of any load on clay can be measured at any time without knowing the past history of load increment. It can be a source of some useful information like quick evaluation of consolidation characteristics, time-compression data of the present, past and future, type and stage of consolidation, drainage conditions, time of load increment, etc. Basic mathematical/graphical properties of vertical, radial, 3D and secondary consolidations are studied from this angle. Two types of 3D consolidations are discussed. First is the combined vertical and radial consolidation with vertical drains. Second is the general 3D consolidation in Cartesian co-ordinates where drainage occurs through all the six phases of a parallelopipe-shaped sample. But the settlement in both cases is allowed in the vertical direction only. It is shown that primary compression after 60% consolidation, with whatever simple or complicated drainage conditions, essentially gives a straight line on a linear plot of settlement versus rate of settlement while secondary consolidation is a straight line on semi-log plot of settlement versus rate of settlement.     

Adsorptive removal of pharmaceuticals and personal care products from aqueous solutions by chemically treated fly ash

This study investigated the removal efficiency of pharmaceuticals from aqueous solutions supported on chemically treated fly ash. The coal fly ash was supplied by the electric power station in Krakow, Poland. There are plenty of studies showing the utilization of fly ash as a low-cost adsorbent for wastewater containing heavy metals or dyes. Adsorption and immobilization of pharmaceuticals and personal care products on fly ash is a relatively new method but it is a very promising one. In this study, the adsorptive removal of diclofenac, ketoprofen, carbamazepine, bezafibrate, bisphenol A, 17α-ethinyl estradiol and estriol by HCl- and NaOH-treated fly ash was assessed. Chemical treatment of fly ash changed structures of particles and enhanced specific surface areas. HCl-treated fly ash was characterized by the highest BET specific surface area 47.9 m² g^?1 and unburned carbon content 8.1%. Isotherms for all compounds except for 17α-ethinyl estradiol (EE2) and estriol (E3) were linear. Higher linear regression coefficients (R ²) obtained for isotherms of EE2 and E3 show that the Freundlich model better describes their sorption. Adsorption coefficients K _d varied between 109.5 (L kg^?1) for bisphenol A and 471.5 (L kg^?1) for bezafibrate. Freundlich constants (K _F) for EE2 and E3 were 62.3 and 119.9 (µg^1?1/n L^1/n kg^?1), respectively. Acid treatment of fly ash increased adsorption of diclofenac, ketoprofen, carbamazepine, bezafibrate and bisphenol A. Comparison of the octanol–water partitioning coefficients (log K _OW) with the partitioning coefficients normalized on unburned carbon content (log K _UC) revealed similarities but no strong correlation. The increasing of unburned carbon increased sorption of compounds to fly ash.     

水热条件下利用微波加热从粉煤灰合成沸石研究

着重选用NaOH水溶液为反应前驱物, 通过改变反应温度、NaOH浓度与合成时间等参数, 在水热条件下利用微波加热直接对粉煤灰进行晶化, 合成得到了浊沸石、菱沸石、NaP1沸石3种沸石.粉煤灰转化为沸石率约15%~40%.研究表明: (1) 反应体系在15min左右即有合成沸石产生, 30min左右合成沸石转化率达到最佳; (2) 为保证沸石晶核生成和晶体的生长, 反应体系的溶液/粉煤灰比不应低于2.5; (3) 在溶液/粉煤灰比为2.5时, 应控制加热时间在30min左右.      

Retention of fly ash-derived copper in sediments of the Pandu River near Kanpur,India

A coal-based thermal power plant is situated on the bank of the Pandu River, which is a tributary to the Ganges near Kanpur. River sediments downstream from the ash pond outfall are contaminated by fly ash. In order to establish the role of soils and sediments in retaining fly ash-derived heavy metals, copper was investigated as a model metal. A maximum concentration of 70 ppm Cu could be leached from the fly ash, confirming that it is a major source of this metal. Soil samples and river sediments were examined for Cu adsorption in the natural state as well as after treatment with H₂O₂, EDTA, and H₂O₂ followed by EDTA. The organic fraction of the samples was determined, and it had a major control on removal of Cu from a solution with 10^–4 M initial concentration. Further characterization of organic matter indicated that with reference to natural samples, the humic acid fraction had a copper enrichment factor in the range 9.1–15.1. The factor for fulvic acids, in contrast, was between 3.5 and 5.5. This leads to the conclusion that river deposits rich in humic acids would withstand relatively high metal loads. Only when the metal input exceeds the maximum retention potential, would the metal be fractionated into the aqueous phase and act as a potential biocide.     

Compression Behavior of Mine Tailings Amended with Cementitious Binders

The objective of this study was to evaluate the effect of fly ash amendment on the compression behavior of mine tailings. Natural and synthetic (i.e., laboratory prepared) mine tailings were used to assess the effects of tailings composition and tailings solids content on compressibility. Three types of off-specification fly ashes and Type I–II Portland cement were used as cementitious binders. Tailings-fly ash mixtures were prepared at solids content of 60–75% (water content = 33–67%), water-to-binder ratios of 2.5 and 5, and were cured for 0.1 days (2 h), 7, and 28 days. Bi-linear compression curves on semi-log plots were observed in most of the binder-amended tailings specimens. The break in slope on the compression curve was identified as the breaking stress, whereupon cementitious bonds were broken. The breaking stress increased with an increase in fly ash content, which was attributed to a lower water-to-binder ratio and void volume-to-binder volume ratio that produced more effective particle bonding. Breaking stress also increased with an increase in CaO content and CaO-to-SiO₂ ratio of fly ash, which resulted in more effective bonding between particles. The effect of curing time on the breaking stress of fly ash amended specimens was characterized by (1) an increase in breaking stress via increase in curing time and cementitious bond formation or (2) a constant breaking stress with curing time due to competing mechanisms during loading. Specimens cured under a vertical stress showed an increase in breakings stress with applied load water removal prior to cementitious bond formation that reduced the water-to-binder ratio and led to more effective cementation.     

Municipal solid waste incineration fly ash sintered lightweight aggregates and kinetics model establishment

Municipal solid waste incineration fly ash blended with pine sawdust and shale, using a neotype trefoil rotary kiln to form lightweight aggregates, is an effective and a potential means method of fly ash disposal. The optimum sintering conditions of Trefoil rotary kiln were determined in terms of an orthogonal test by measuring the pellets’ bulk density, granule strength, 1 h water absorption. As far as the kinetics is concerned, an integral method of Coats–Redfern was introduced to analyze the kinetics characteristics of the mixture samples. Also, the kinetic triplets (apparent activation energy, pre-exponential factor and reaction order) were estimated by the reaction of kinetics model functions. It is shown that the optimum sintering conditions are as follows: (a) preheating temperature of 500 °C, (b) sintering temperature of 1130 °C, (c) holding time of 4 min. The optimum reaction models of the four stages are Avrami–Erofeev, Mample, Avrami–Erofeev and There-dimensional diffusion (Jander), respectively.