Laboratory Comparison of Crushed Aggregate and Recycled Pavement Material With and Without High Carbon Fly Ash

In-place recycling of asphalt pavement materials is a sustainable rehabilitation method. Existing hot-mix asphalt (HMA) layer is pulverized and blended with some or the entire base course and possibly some subgrade to form a broadly graded material referred to as recycled pavement material (RPM). The RPM is then compacted as the new base course and overlaid by a new layer of HMA. In some occasions, additives are added to increase the strength of RPM base course, such as cement, emulsion, fly ash. It is plausible to utilize high calcium high carbon fly ash, as the high level of carbon prevents fly ash from being used in concrete. A series of laboratory tests were conducted to evaluate the performance of these materials, including crushed aggregate, untreated RPM, and treated RPM with high carbon fly ash. The tests included compaction, California Bearing Ratio, resilient modulus, and unconfined compressive strength for treated RPM. The engineering properties of these materials were compared.     

Deformation Modulus of Fly Ash Modified with Lime and Gypsum

Deformation modulus of fly ash is one of the most important mechanical properties generally used in different design problems and also as an input parameter to sophisticated numerical techniques employed to assess the response of different structures resting on fly ash fill or embankment made of fly ash. Deformation modulus is usually expressed in terms of compressive strength. This paper presents the deformation modulus of fly ash modified with lime alone or in combination with gypsum at different strain levels. The values of deformation modulus obtained from both unconfined compression test and unconsolidated undrained triaxial test results are presented herein. The specimens for unconfined compression test and for undrained triaxial tests were cured up to 90 and 28 days, respectively. The effects of addition of lime (4–10%) and gypsum (0.5 and 1.0%) on the deformation modulus of class F fly ash are highlighted. With addition of lime and gypsum, the class F fly ash achieved the deformation modulus in the range of 190 MPa in UCS test and up to 300 MPa in triaxial test specimens tested under all round pressure of 0.4 MPa. Based on the present test results empirical relationships are developed to estimate deformation modulus of modified fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus at different strain levels are also developed.     

绢云母片岩粗粒料改性试验研究

绢云母片岩属极软岩,强度低,直接作为路基填料难以压实,易造成路基沉陷、路面开裂等不良工程现象。通过对绢云母片岩及其4种改性方案进行表面振动压实试验、室内重型击实试验、室内CBR试验以及回弹模量试验研究,探讨绢云母片岩经改性后用作高速公路路基填料的适用性。试验表明,绢云母片岩最大干密度采用室内重型击实与表面振动压实试验结果相差较大,采用表面振动压实时为1.92 g/cm3,采用室内重型击实时为2.01 g/cm3。主要原因是由于绢云母片岩颗粒破碎的结果。绢云母片岩及其4种改性粗粒土的在最优含水率附近的较宽范围内的变动对压实效果的影响不大,有利于填料的压实。绢云母片岩的回弹模量E较低,小于32 MPa,经改性后的土料的回弹模量均有显著提高,均达到50 MPa以上。添加20%红砂岩和20%黏性土的试料CBR值均只有3.7,添加3%水泥和5%水泥的试料CBR值上升明显。绢云母片岩经添加3%、5%的水泥化学改性后可用于高速公路上路堤及路床填筑。     

Effect of Matric Suction on Resilient Modulus of Compacted Aggregate Base Courses

This research was conducted to investigate the effect of matric suction on resilient modulus of unbound aggregate base courses. The study characterized the water characteristic curves and resilient modulus versus matric suction relationships of aggregate base courses that were compacted at different water contents and between 98 and 103 % of the modified Proctor density. The soil–water characteristic curve (SWCC) and the relationship between resilient modulus (M _r ) and matric suction (ψ) were established for different unbound granular and recycled asphalt pavement materials. This relationship is important for predicting changes in modulus due to changes in moisture of unbound pavement materials. Resilient modulus tests were conducted according to the National Cooperative Highway Research Program (NCHRP) 1-28A procedure at varying water contents, and the measured SWCC was used to determine the corresponding matric suction. Three reference summary resilient moduli (SRM) were considered: at optimum water content, optimum water content +2 % and optimum water content ?2 %. The Bandia and Bargny limestones are characterized by a higher water-holding capacity which explains why the modulus of limestone was more sensitive to water content than for basalt or quartzite. Limestones tend to be more sensitive to changes in water content and thus to matric suction. The shape of the SWCC depends on the particle size distribution and the cementation properties from dehydration of the aggregates. Material properties required as input to the Mechanistic-Empirical Pavement Design Guide (M-EPDG) to predict changes in resilient modulus in response to changes in moisture contents in the field were determined for implementation in the M-EPDG process. Results show that the SRM was more correlated with matric suction than with compaction water content (for resilient modulus testing). The empirical models commonly used to predict the SWCC such as the Perera et al. (Prediction of the SWCC based on grain-size-distribution and index properties. GSP 130 Advances in Pavement Engineering, ASCE, 2005) and the M-EPDG (NCHRP in Guide for mechanistic-empirical design of pavement structures. National cooperative highway research program. ARA, Inc., ERES Consultants Division, Champaign, IL, 2004) models tend to underestimate the SWCC and cannot provide reasonable estimation. SRM normalized with respect to the SRM at the optimum water content varied linearly with the logarithm of matric suction. Empirical relationships between SRM and matric suction on semi-logarithmic scale were established and are reported.     

Effects of Testing Conditions on Intact Rock Strength and Variability

The strength of intact rock is a fundamental and integral part of many aspects of engineering and geologic practice. It is necessary to understand how testing conditions influence this strength and its variability, especially for use in reliability-based design. In this study, the effect of sample diameter and moisture content on the strength and its variability was examined in detail. Correlations are given for assessing the effect of sample diameter on the laboratory uniaxial compressive strength (q_u), Brazilian indirect tensile strength (q_t-Brazilian), and point load strength (I_s), and the associated direct correlations among these tests. Correlations also are given for assessing the effect of sample moisture content on q_u, q_t-Brazilian, and I_s. The statistics of data scatter suggest these correlations can introduce large uncertainties. The effect of sample diameter and moisture content on the coefficients of variation was examined subsequently, and it was found to be relatively minor.     

Coal fly ash and steel slag valorisation throughout a vitrification process

The aim of this research was to evaluate the feasibility of using the vitrification process as an alternative solution to the disposal of a coal fly ash and metallurgical slags in landfills. The starting wastes were characterised in terms of chemical, granulometric, mineralogical, and microstructural analysis. A selected batch composition composed by 58.5% fly ash, 31.5% metallurgical slag and 10.0 Na₂O% (wt%) was melted at 1450 °C and poured to obtain monolithic glass samples. The environmental behaviour of the starting wastes and the resulting glass was evaluated by standard leaching tests, which shows that vitrification leads to a stabilisation process in which the inorganic components of the wastes are immobilised throughout their incorporation into the glass structure. Moreover, vitrification transforms those hazardous wastes into a new non-hazardous glass. A preliminary study shows that the new glass is suitable for developing glass–ceramic tiles appropriate for floor pavement and wall covering.     

Parameters influencing the variation in mercury emissions from an Alberta power plant burning high inertinite coal over thirty-eight weeks period

Feed coals and fly ashes from a coal-fired power station burning Alberta subbituminous coal were examined for a period of thirty-eight weeks to determine the variation in emitted mercury. Feed coal samples were analyzed for proximate, calorific value and Hg content, while fly ash samples were examined for C and Hg contents. The maceral content of the feed coal was also determined. The emitted mercury was calculated and compared to mercury emitted from the stack according to a mass-balance calculation from a previous study for the same station.Mercury contents ranged from 0.029 to 0.066 mg/kg for feed coal, and from 0.069 to 0.112 mg/kg for fly ash. The carbon/char in fly ash was separated into reactive (vitrinitic/bimacerate) and less reactive (inertinitic) chars using ZnBr₂ at specific gravities of 1.7, 2.0, and 2.25 to 2.4. The result shows that there is a positive correlation between the carbon and mercury content of the fly ash. The reactive char particles in the fly ash may be responsible for the capture mercury in fly ash. The percentage of estimated captured mercury by fly ash increases with increasing carbon content (%) in fly ash. The percentage of emitted mercury for the period of 38 weeks is estimated to be within the range of 49% to 76% of the total input of mercury.     

粉煤灰基地聚物加固土的强度及抗冻融性能试验研究

粉煤灰基地聚物作为一种低碳胶凝材料,在地基处理中的应用越来越受到关注。但是目前关于碱激发胶凝材料加固土在冻融极端气候条件下的工程特性尚不清楚,有必要进一步开展冻融循环条件下加固土的强度、变形特征及其影响因素研究。通过室内试验研究了原材料硅铝比、碱激发剂模数及碱溶液浓度对粉煤灰基地聚物固化土的强度与抗冻融性能的影响及微观...     

Leachate studies on fly ash-stabilised expansive clay liners

This paper presents leachate studies on fly ash-stabilised expansive clay liners. Fly ash in different contents (0%, 10%, 20% and 30%) by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a compacted lateritic clay layer. Deionised water (DIW) and calcium chloride (CaCl₂) solutions of varying concentration (5 mM, 10 mM, 20 mM, 50 mM, 100 mM and 500 mM) were used as the permeating fluids in the leachate studies. Chemical analysis of the leachate was performed. For a given CaCl₂ concentration, the concentrations of both calcium ion and chloride ion in the leachate decreased up to a fly ash content of 20%, and thereafter they increased when the fly ash content was increased to 30%. Further, for a given fly ash content, concentrations of calcium ion and chloride ion increased with increasing CaCl₂ concentration.     

武汉地区粉煤灰和膨润土双掺合剂水泥土性能改良试验研究

近年来,水泥土被广泛应用于土体加固工程,其强度与加固效果密切相关。为研究膨润土和粉煤灰掺量对水泥土性能的影响,对25组不同膨润土和粉煤灰掺量的水泥土进行基本力学性能试验。通过抗压强度试验,发现当粉煤灰和膨润土掺量分别为40%和11%时,28 d的水泥土抗压强度最大,为7.30 MPa;当粉煤灰和膨润土掺量分别为20%和7%时,90 d的水泥土抗压强度最大,为7.19 MPa。通过室内直接剪切试验,发现当粉煤灰和膨润土掺量分别为20%和11%时,28 d的水泥土抗剪强度参数粘聚力c最大,为1144.8 kPa;当粉煤灰和膨润土掺量分别为30%和5%时,90 d的水泥土抗剪强度参数粘聚力c最大,为1753.71 kPa。研究成果可以为武汉地区的粉煤灰和膨润土双掺合剂改良水泥土的现场施工提供参考依据。     

粉煤灰水泥土变形特性实验研究

水泥土中掺入粉煤灰能在一定程度改善其性能,而变形特性是实际工程应用的重要指标。因此,研究粉煤灰和龄期对水泥土变形特性的影响对实际工程具有较大的参考价值。通过粉煤灰掺量为0和8%的水泥土无侧限抗压强度实验,研究发现养护龄期的增长与粉煤灰的掺加有利于水泥土变形模量的增长,尤其是粉煤灰的掺加有利于后期变形模量的增长。进一步对比分析两种粉煤灰掺量时的无侧限抗压强度和平均变形模量,发现它们之间基本上呈线性关系,随后通过拟合得出了它们之间的换算公式。最后,考虑应力-应变曲线模型特征以及对试验数据回归分析,推导出了一定条件下的水泥土应力-应变上升段表达式,为实际工程设计提供参考。     

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.     

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.     

利用湖泊底泥和粉煤灰制备瓷质砖的实验研究

将湖泊底泥引入瓷质砖的生产, 既可消除污染, 又能减少传统的瓷质砖生产中所需的粘土.以武汉市东湖底泥和湖北黄石电厂粉煤灰为主要原料, 辅以伟晶花岗岩、石英为添加剂, 设计4个底泥含量分别为4 0 %、5 0 %、6 0 %和70 %的配方, 每一配方压制6片生坯, 分别在1 190, 1 175, 1 160, 1 130, 1 115和1 100℃下烧成.XRD分析显示瓷坯中的莫来石晶相随烧成温度的升高而增加.在1 160~1 175℃烧成的瓷坯的吸水率和断裂模数测试结果分别为0.0 8%~ 0.2 0 %和39.36~ 51.0 8MPa, 表明利用湖泊底泥和粉煤灰作为主要原料可以烧制瓷质砖, 二者的总用量可达75 %~ 80 %.      

Strength characteristics of compacted pond ash

Strength properties of compacted ash layers depend to a great extent on the moulding conditions. This paper focuses on the effects of compaction energy and degree of saturation on strength characteristics of compacted pond ash. The pond ash sample, collected from the ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 kJ/m³ to 3488 kJ/m³. The optimum moisture content and maximum dry densities corresponding to different compactive energies were determined by conventional compaction tests. The shear strength parameters, unconfined compressive strengths (UCS) and California bearing ratio (CBR) values of specimens compacted to different dry densities and moisture content were assessed and reported. The effects of compaction energy and degree of saturation on shear strength parameters i.e. unit cohesion (c_u) and angle of internal friction (Ф) values and also the UCS values are evaluated and presented herein. The results indicate that the dry density and strength of the compacted pond ash can be suitably modified by controlling the compactive energy and moulding moisture content. The strength achieved in the present study is comparable to the good quality, similar graded conventional earth materials. Hence, it may be safely concluded that pond ash can replace the natural earth materials in geotechnical constructions.     

Physical and Compaction Behaviour of Clay Soil–Fly Ash Mixtures

At present, nearly 100 million tonnes of fly ash is being generated annually in India posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent usually used in combination with soils. In the present study, high-calcium (ASTM Class C—Neyveli fly) and low-calcium (ASTM Class F—Badarpur fly ash) fly ashes in different proportions by weight (10, 20, 40, 60 and 80 %) were added to a highly expansive soil [known as black cotton (BC) soil] from India. Laboratory tests involved determination of physical properties, compaction characteristics and swell potential. The test results show that the consistency limits, compaction characteristics and swelling potential of expansive soil–fly ash mixtures are significantly modified and improved. It is seen that 40 % fly ash content is the optimum quantity to improve the plasticity characteristics of BC soil. The fly ashes exhibit low dry unit weight compared to BC soil. With the addition of fly ash to BC soil the maximum dry unit weight (γ_dmax) of the soil–fly ash mixtures decreases with increase in optimum moisture content (OMC), which can be mainly attributed to the improvement in gradation of the fly ash. It is also observed that 10 % of Neyveli fly ash is the optimum amount required to minimize the swell potential compared to 40 % of Badarpur fly ash. Therefore, the main objective of the study was to study the effect of fly ashes on the physical, compaction, and swelling potential of BC soils, and bulk utilization of industrial waste by-product without adversely affecting the environment.     

On the Ratios between Elastic Modulus and Uniaxial Compressive Strength of Heterogeneous Carbonate Rocks

The ratios M _R = E/σ _c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ _c < 100 MPa) and very strong (σ _c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus (E = 6100–82300 MPa), uniaxial compressive strength (σ _c = 14–273.9 MPa), Poisson's ratio (ν = 0.13–0.49), and dry bulk density (ρ = 1.7–2.7 g/cm³). The observed range of M _R = 60.9–1011.4 and mean value of M _R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20, 1968) for limestones and dolomites, and the statistical analysis of M _R distribution is performed. Mutual relations between E, σ _c, ρ, M _R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ _c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus and M _R in very strong carbonate samples are more correlated with ρ−σ _c combination and ε _a max, respectively, than in weak to strong samples. The relation between M _R and maximum axial strain (ε _a max) for all studied rock samples (weak-to-strong and very strong) is discussed.     

Alluvial soils as subgrade material: Laboratory and statistical evaluation

In India, rural roads are constantly being constructed. To ensure proper design of rural roads, it is desirable to have an appropriate selection of design parameters. The California bearing ratio (CBR) method of pavement design is the most commonly used method employed for the foundation design of rural roads. In the CBR method, the CBR value of the subgrade soil is critical in deciding the overall thickness of the pavement. Additionally, for good drainage, a typical specification for the pavement foundation design requires the value of permeability coefficient of the subgrade material to be specified. Thus, permeability and CBR constitute two important parameters in the design and assessment of long-term performance of the pavement. In this study, laboratory investigation has been carried out on a number of soil samples procured from a roadwork project site. Preliminary tests, such as index tests and particle size distribution tests, useful for soil classification, were followed by light compaction, CBR and variable head permeability tests. Further, observations from the laboratory investigation are statistically analysed to study correlations among various parameters. Because the predominant soil type found in the study area is alluvial, this study also highlights the suitability of alluvial soils as pavement subgrade material.     

Heave Studies on Fly Ash-Stabilised Expansive Clay Liners

Clay liners or compacted earthen barriers are important barrier materials used for preventing contaminant transport through soils. A low hydraulic conductivity (k) is a significant parameter that governs the design and construction of clay liners. Compacted expansive clays, which are montmorillonite clays, also have a very low hydraulic conductivity (k). When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity (k) further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as a unique clay liner material. As expansive clays undergo heave when they come into contact with water, it is necessary to study the heave behaviour of fly ash-stabilised expansive clay liners. This paper presents heave studies on fly ash-stabilised expansive clay liners. Fly ash in different contents by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a natural field soil layer. Compacted lateritic clay was used for simulating the natural field soil into which contaminants migrate. Calcium chloride (CaCl₂) solution of varying concentration (5, 10, 20, 50, 100 and 500 mM) was used as the permeating fluid in the heave studies. The rate of heave and the amount of heave of the fly ash-stabilised expansive clay liners were monitored. Deionised water (DIW) was also used as inundating fluid for comparative study. Heave (mm) decreased with increase in solute concentration for all fly ash contents. For a given solute concentration, heave decreased up to a fly ash content of 20 % and thereafter it increased when the fly ash content was increased to 30 %. Heave of the fly ash-stabilised expansive clay liners was correlated with their permeability, liquid limit (LL) and free swell index (FSI) pertaining to the respective fly ash content and CaCl₂ concentration.     

Effect of the dilution process on the attenuation of contaminants in aquifers

This paper discusses the effects of the dilution process on levels of aquifer contamination attenuation, developing analytical equations for application in theoretical and practical cases. The key finding is that, in aquifers, the dilution process causes a reduction of the contaminant concentration. Analytical equations for the assessment of the contaminant attenuation capacity, by means of the dilution process in an aquifer, are put forward. In particular, the attenuation of the contaminant concentration in an aquifer, and thus the dilution, is described by the volumetric flow rate per unit width perpendicular to the flow direction (q _u). Moreover, a classification of q _u was developed, considering six classes of attenuation capacity due to dilution. For the equations validation, nitrate contamination attenuation due to dilution was analysed in two sample areas in Piedmont (North-West Italy). The results confirmed the hypothesis, evidencing high nitrate concentrations in areas with low q _u values, connected to low dilution rate of the contaminant in the groundwater; vice versa, low nitrate concentrations were evidenced in areas with high q _u values, due to a high nitrate dilution rate.