Pond Ash Research Articles

Effect of compaction water on strength and hydraulic properties of bentonite-based liner

The abundance of pond ash and its resemblance to natural sand encourages its use as a substitute for sand in sand–bentonite (SB) liner material. Compaction water content influences the geoengineering properties of cohesive soil to a great extent. Accordingly, the compaction, strength, permeability and shrinkage characteristics of both pond ash–bentonite (PAB) and SB mixes are investigated at standard and modified Proctor compaction energies at various water contents to support the recommendation of the PAB mixture as an alternative landfill liner. At similar compaction conditions, the PAB mix exhibits higher unconfined compressive strength (UCS) and hydraulic conductivity than the SB mix. The UCS values of mixes compacted on the dry side of optimum are higher than those of mixes compacted on the wet side. Dry-side compacted mixes exhibit a reduction in hydraulic conductivity with permeation time, whereas no substantial reduction in hydraulic conductivity is noticed for wet-side compacted mixes. Furthermore, the volumetric shrinkage of both PAB and SB mixes is within the permissible value of 4%, for a wide range of water variation from the dry to the wet side of optimum. The observed mechanical properties are correlated to the shape of coarse fraction particles and the corresponding microstructural arrangements of the compacted specimens.

Predicting the mechanical strength of coal pond ash based geopolymer concrete using linear regression method

Geopolymer concrete (GPC) is an innovative alternate material that can replace traditional Portland cement concrete. Generally, GPC requires heat or steam chamber during curing for optimal geopolymerization response on concrete specimens, which is tedious and a time-consuming process. Modified GPC is introduced to overcome these limitations as well as to improve the characteristics of specimens. This study goal was to assess and examine the mechanical strength of GPC when mixed with slaked lime, ground granulated blast furnace slag (GGBS), and pond ash (PA) at various proportions. Slaked lime was added at a rate of 1%, 2%, 3%, 4%, 5%, and 6% by combined weight of PA and GGBS. Concrete specimens were casted and cured for 7, 28, 56, and 90 days at ambient environmental condition. Experimental test results showed that PA and GGBS based GPC significantly gained mechanical strength than conventional GPC at 7, 28, 56, and 90 days. The admixtures PA and GGBS not only increased the strength of GPC but also reduced the curing time. In addition, it was found that the improvement in properties was the result of densification of microstructures over curing time.

Assessing the strength characteristics of PACACRETE by destructive method

The aim of this research is to examine the usage of GPA as supplemental material in the manufacture of coarse aggregate and concrete. Studying pond ash appropriateness as a silica substitute for coarse aggregate in concrete is the primary goal of this effort. The properties test such as., the crushing test, impact test, and abrasion test were conducted on the conventional and pond ash aggregate to obtain the optimum level. 14MPA combination shows better performance than other mixes. Additionally, an effort is being made to create concrete that satisfies the various structural features of concrete, such as compressive strength, by employing pond ash as source material for the coarse aggregates [PACACRETE]. From all of the experiments and investigations, it has been determined that the offered mix [M20 + GPA100% & M30 + GPA 100%] is the optimal combination, providing good compression strength over standard concrete with a potential modest drop in tensile and flexural strength.

Influence of coal ashes on fired clay brick quality: Random forest regression and artificial neural networks modeling

Finding a solution to the problem of the large buildup of coal ashes is a vital necessity. Although the use of coal ashes in fired clay bricks has been thoroughly investigated, there is insufficient information on their industrial utilization and researchers do not agree on whether or not this addition improves the quality of the final products. Therefore, a database has gathered 20 years of research containing key factors related to the quality of the bricks (i.e., chemical composition, firing temperature, soaking time, open porosity, water absorption and compressive strength). Then, random forest regression and artificial neural networks (ANN) modeling were used to separately predict the parameters concerning the quality of the final products. The overall conclusions were that the compressive strengths were the highest when using fly ashes and that class F ashes were highly suitable to be used in the brick industry as a replacement material for brick clay. In addition, the ANN models showed higher coefficients of determination and an overall better fit to the experimental data. By changing the chemical makeup of the initial materials and their proportions, the particle size of the ashes, the firing temperature and soaking time, as well as the size of a product, the created models can be used to estimate the quality of the brick containing coal ash. That is crucial because the inconsistent chemical composition of ash is generally the main obstacle to its utilization. The local sensitivity analysis revealed the highest influence of the content of the alkali oxides in the initial clay on the fired clay bricks due to their fluxing effect. In the case of ash-clay bricks, the decisive factors were the type of furnace used, the ashes' class, the Na2O content in raw clay, and the K2O introduced with the ash. The F class ashes containing about 2–3% of K2O and <5% of CaO gave the highest compressive strength in bricks fired at 1000–1100 °C.Additional analyzes were made for 50% pond ash and 50% clay bricks to test the best-suited model and fill in the knowledge gap. The results obtained in this study are important for supporting the decision in the selection of materials and process parameter values that will increase the quality of the ash-clay-fired bricks.

Performance evaluation of nano-material stabilized pond ash as subbase layer material for roadway pavement

The power capacity of India is heavily coal based. In the session 2021–22 the overall country’s coal production has been 777.31 million tons, with 8.55% positive growth. However, the Indian coal is of lower grade with higher ash content of 24–63%. This results in the generation of 240.27 million tons of Coal Combustion Ash (CCA) during 2021–22. This huge quantity of industrial byproduct mixed with water and stored in ash lagoons in the form of Pond Ash (PA). From this stored ash deposit only 79.18% finds utilization, which by far falls short of the 100% utilization target as strictly recommended by the Ministry of Environment Forest and Climate Change (MoEF & CC). This high volume generation compounded with lower utilization of PA has been consuming about 65,000 acres of valuable land. Moreover the prolonged disposal of PA in ash lagoons causes serious environmental and health hazards. Besides, the extensive use of Conventional Granular Material (CGM) has been alarming, thus necessitating it to be condemned and strict regulations imposed in construction. Emphasis being laid on the utilization of Non-Conventional Granular Materials (NCGM) like CCA. On the basis of the above mentioned circumstances the PA can be converted into a meaningful wealth for the subbase construction of pavement foundation. Therefore, this paper primarily addresses the potential of PA as subbase layer material for roadway pavement foundation. This study utilizes virgin PA as well as in partial replacement of CGM 10%-100% by weight, being stabilized with lime 0%-14% by weight and Nano-Material (NM) 1:1:150–1:1:400 by dosage as a subbase material for the foundation of pavement. Experimental work was carried out in stages to determine the chemical composition of PA, Lime and NM, characterize the PA samples by FTIR and FESEM followed by understanding the behavior of PA with and without any addition of additives as stabilizers. The c and φ ranges 0.88–40.02 kg/cm2 and 32°-53° The soaked CBR is of 19% to as high as 79% for optimum stabilized PA mix. Terrasil and Zycobond whose pH showed alkalinity, were used as nanomaterial, which provided little to zero permeability for the mix. Slake durability test provided medium to high to very high durability for the optimum mix. A comparative analysis was performed to determine the optimum mix providing the best stability. Light Falling weight Deflectometer (LFWD) showed satisfactory deflection. The values obtained satisfied the Ministry of Road Transport and Highways (MoRTH), Government of India.

Utilizing pond ash as fine aggregates in sustainable green concrete pavement – A case study

According to a recent estimate, more than 75 major accidents related to coal ash ponds have been reported between 2010 and 2020 which have resulted not only in loss of life and property, but also in extensive pollution of land, water, and air around the accident sites. In order to promote mass consumption in lieu of disposal, this study was aimed at utilizing the unused coal ash as fine aggregates in concrete pavements. In this regard, a pilot study was undertaken at NTPC Mouda wherein M25 grade pavement quality concrete (PQC) was used for casting a 500 m stretch of road inside the power plant premises. The mix design was prepared at VNIT Nagpur utilizing coarse and fine pond ash from NTPC Mouda as fine aggregates. OPC 43 grade of cement along with locally procured crushed stone aggregates were used. A compatible hyper-plasticizer was also used to maintain the workability and rheology of the concrete. The concrete was laid manually and was observed to attain its final setting within 600 min. The segment was cured for 28-days and finally, cores were extracted to evaluate the in-situ compressive strength of PQC and ascertain its durability. A 28-day compressive strength of 29.3 MPa along with reduced chloride ion permeability and abrasion loss indicate that the suggested approach of utilizing pond ash as fine aggregates in concrete roads is a sustainable alternative to conventionally used mix designs. Hence, the said approach will be a “greener” approach towards PQC construction reducing the dependency on natural river sand. Owing to the abundance of coal ash available in ash dykes, it is also expected that the suggested approach will prove cost-effective in terms of unit cost of concrete production.

Kinetics of mixed binder strength gain

Introduction. The storage of pond ash at ash dumps has a negative impact on the environmental situation in the nearby settlements, dumps constantly dust and pollute water sources. To solve this problem, it is proposed to use ash from pond ash as a component of mixed binder. Since the specific surface area of pond ash is different throughout the dump, it is necessary to study its influence on the strength set of mixed binder under different curing conditions.Materials and methods. The equipment on which the experiment was carried out is listed. To determine the specific surface ПСХ-12 device was used, ash drying was carried out in a desiccator. The samples were stored in a normal solidification chamber. The chemical composition of pond ash from TPP-5 of Omsk was presented.Results. Experimental data on the strength of samples of mixed binder at the age of 1,3,7,14,21,28,90 days of normal hardening and data on the strength of samples after heat and humidity treatment are presented. Durability of mixed binder composition with specific surface of hydraulic ash of 460-490 m2/kg under normal hardening conditions amounts to 42.57 MPa which corresponds to natural strength. The composition with the use of pond ash 460-490 m2/kg after water removal increased strength by 12% in comparison with the control composition. Compositions with specific surface of wet pond ash 220-250, 340-370, 650-700 m2/kg show durability results lower than the control ashless composition irrespective of hardening conditions.Discussion and conclusions. It is proved that the use of pond ash with a specific surface of 460-490 m2/kg is rational. Its strength under normal conditions of hardening is 42,57 MPa, which corresponds to the strength of the concrete. The composition with the use of wet pond ash 460-490 m2/kg after heat and moisture treatment has an increase in strength by 12% compared to the control composition. Increased strength of mixed binder compositions is associated with acceleration of pozzolanic reaction in them, the products of which have a positive effect on the strength of the products.

Effect of Underreamed Pervious Concrete Columns on Load-Carrying Capacity of Loose Cohesionless Soils

Weak confinement governs the bulging failure of granular columns. Pervious concrete columns have granular columns like drainage with stiffness of concrete column are thus independent of the confinement from the weak surrounding soil can be treated as an alternative solution. Moreover, it is well established that under-reaming bulb enhances the bearing resistance to the pile shaft. Therefore, the present experimental and analytical study investigates circular pervious concrete column (CPCC) and under-reamed pervious concrete column (UPCC) in improving the bearing capacity of loose pond ash fill. CPCC and UPCC are constructed in a model pond ash fill subjected to vertical loading. The load-carrying capacity, settlement failure mechanism, and consolidation parameters were examined. Theoretical analysis for evaluating the load-carrying improvement factor (LCF) with nondimensional parametric variation of area replacement ratio (Ra), underreamed bulb ratio (Br), and length ratio of the column (RL) was also done. Efficacy of CPCC was also numerically studied (Plaxis 3D). Experimental results show that the vertical settlement is reduced by 52.8% with CPCC and UPCC. UPCC renders higher load-carrying capacity than CPCC. Both CPCC and UPCC undergo deformation at depth of 4D during failure. For the same area replacement ratio (Ra), the experimental and theoretically computed values are found in good agreement. The rate of consolidation is reduced from 53 to 23 days by using CPCC signifying its drainage potential.

Synthesis of Floral-Shaped Nanosilica from Coal Fly Ash and Its Application for the Remediation of Heavy Metals from Fly Ash Aqueous Solutions

Every year a large amount of coal fly ash (CFA) is generated and dumped in fly ash ponds. Fly ash has numerous toxic heavy metals, which leads to water pollution due to the percolation of these heavy metals. Heavy metal toxicity has become a major issue for the whole globe. Moreover, CFA has several value-added minerals, such as silica, alumina, and ferrous in large amounts. Therefore, the synthesis of silica nanoparticles from CFA and their application for the removal of toxic heavy metals from fly ash aqueous solution will prove to be an economical and efficient approach. Here, in the present research work, investigators synthesized nanosilica from CFA by alkali dissolution and sol-gel methods and applied them for heavy metal removal. Firstly, CFA was treated with high molar NaOH, along with stirring and heating. Further, the sodium silicate leachate from CFA was treated with dilute HCl till the formation of a white gel at neutral pH. Purification of the nanosilica was achieved by treating with 1M HCl along with stirring followed by calcination at 400 °C for 4 h. The synthesized nanosilica was characterized by UV-Vis, Fourier transform infrared (FTIR), particle size analyzer (PSA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electron diffraction spectroscopy (EDS), and high-resolution transmission electron microscope (HR-TEM). The sizes of the floral-shaped nanosilica particles were 20–70 nm, and the purity was 90–95%, as confirmed by microscopy and EDS, respectively. The XRD and FTIR revealed the amorphous nature of nanosilica. Finally, the potential of the nanosilica was assessed for the removal of heavy metals from 20% CFA aqueous solutions in batch experiments. The nanosilica showed about 40–90% removal of heavy metals (Al, Pb, Cd, Cu, Cr, Ni, Co, Zn, Mn) from the fly ash aqueous solution.

Dynamic Behaviour of Pond Ash Mixed with Coir and Crumb Rubber

An experimental program was conducted to determine the dynamic properties of pond ash (PA) and pond ash mixed with admixtures like crumb rubber (CR) and coir fiber (CF) which are wastes of different industries. Additives CR and CF were mixed separately with pond ash in a percentage ranging from 0%–20% at an interval of 5% and 0%–2% at an interval of 0.5% by weight of pond ash, respectively. Dynamic properties (Shear modulus, Number of cycles to initiate liquefaction, Degradation index and Damping ratio) for pond ash mixes were determined using strain-controlled cyclic tri-axial apparatus. The shear strain was kept constant at 1.2% and the frequency varied from 0.4 to 1 Hz. Liquefaction resistance improves when crumb rubber is added to pond ash, however adding Coir fiber to pond ash has essentially no effect on the number of cycles required to initiate liquefaction. The dynamic shear modulus decreases when crumb rubber was mixed in pond ash whereas when coir fiber is added to pond ash, the dynamic shear modulus increases significantly. A mix of PA, CR, and CF was also tried to balance the number of cycles required to initiate liquefaction and shear modulus. The mixed sample in the proportion of PA (84%) + CR (15) + CF (1%) can be termed a balanced mix as the number of cycles to initiate liquefaction was more than all PA-CF mixes and also the shear modulus was more than all PA-CR mixes. Damping ratio increases with increasing frequency of loading (0.4 to 1 Hz).

Compaction and strength behavior of Kaolin clay stabilized with Pond ash

In India 75% electricity is produced by thermal power plants using coal. Because the majority of the nation's coal reserves are of a lower non-cooking quality, more ash will be created as a result. One of the main causes of increased ash generation is the average 35% ash content of Indian coal. Fly ash makes up a relatively minor portion of the total amount of ash produced, with pond ash and bottom ash making up the rest. Therefore, there is a need to manage this material to avoid any environmental concerns. Another issue is the presence of problematic soil, in particular, expansive clays. Their presence at any site is a challenging task for geotechnical engineer. It is because they show high signs of volume change. To tackle this issue, engineers can go with either of the two available solutions: a) replacement and b) soil modification. Keeping this in view, the present investigation focuses on the utilization of Pond ash (PA) as an admixture in Kaolin clay (KC) as a soil modification method. Hence, in this paper, strength and compaction behaviour of KC stabilized with Pond ash PA was studied. For strength characteristics, unconfined compressive strength (UCS) and split tensile strength (STS) tests were carried out. Similarly, for compaction characteristics, modified proctor compaction tests were carried out. From the test results, it was observed that the inclusion of PA in KC significantly affected its compaction and strength characteristics. The optimum Pond ash content was observed to be 30% where, OMC, MDD, UCS and STS values were 17.30%, 1.60 g/cc, 360 kN/m2 and 88.70kN/m2, respectively.

Economical and environment friendly self-compacting concrete

A rapid industrialization and urbanization resulted in the increased demand for usage of electricity at an alarming rate. At the same time, coal ashes are produced in coal based thermal power plant in large quantity. Fly ash is being used as an alternative material in construction industries while pond ash is disposed-off on huge land areas resulting in environmental pollution through soil, water and air. This research emphases on the study of performance of pond ash as a fine aggregate in self-compacting concrete (SCC). Fine aggregate is substituted by pond ash in percentages of 10, 15, 20, 25, 30. The fresh state properties of SCC like flowability, passing ability of all mixes have been checked by conducting inverted slump cone and L-box according to IS code of practice. The cost analysis of SCC has been conducted to establish the relative cost savings. From the experimental investigation, cost analysis and life cycle assessment, it is concluded that SCC with 20% fine aggregate replaced by pond ash can be economical and environment friendly self-compacting concrete.

Prediction of the cementing potential of activated pond ash reinforced with glass powder for soft soil strengthening, by an artificial neural network model

The effect of Pond Ash (PA) activated with sodium chloride (NaCl) solution and reinforced with glass powder on the mechanical properties of soft clay soil, which comprise of the California bearing ratio (CBR) and the unconfined compressive strength (UCS) has been studied in this research work. The PA requires pozzolanic improvements to meet the ASTM C618 requirements for pozzolanas. In the present research paper, further emphasis has been on the machine learning prediction of CBR and UCS of the soft clay soil stabilized with a composite of PA. Generally, the studied soft clay soil properties, which were the microstructure, microspecter/micrograph, oxide composition, Atterberg limits, compaction behavior, free swell index (FSI), CBR and UCS significantly improved due to the enhanced cementitious ability of the activated and reinforced PA. The multiple data collected from this general stabilization result were used to predict the soil’s CBR and UCS by the artificial neural network (ANN) technique. The results showed high performance of the model in terms of the sum of squares error (SSE) of 1.5% and 2.0% and the coefficient of determination (R2) of 0.9979 and 0.9973 for the CBR and UCS models, respectively. The models also outclassed the performances of other models from the literature.

Strength and compaction characteristics of kaolin clay blended with industrial wastes

The long-term stability of the construction over soil depends significantly on the strength of the ground. Swelling and shrinkage characteristics of expansive fine-grained soil causes volumetric changes followed by distress and damage to the structures resting on it. One of the most popular and cost-effective methods of improving soil is adding admixtures. Utilization of industrial wastes in soil stabilization is a cost effective and environment friendly solution. In this study, two types of industrial wastes, copper slag and pond ash, are used with the aim of improving the strength and compaction characteristics of subgrade. So, the work is focused on evaluating the compaction and strength characteristics of Kaolin clay (KC) blended with Copper Slag (CS) and Pond Ash (PA). For the compaction characteristics, modified proctor compaction tests were conducted and to study the strength characteristics, Unconfined compressive strength (UCS) and split tensile strength (STS) tests were conducted. In Total, 14 different mix combinations were used in this study. From the test results, it has been observed that blending KC with PA and CS not only improved its compaction characteristics but strength too.

Efficacy of Pond Ash as a Cover Material in Single and Dual Capillary Barriers

In this paper, numerical study results that highlight the capability of using pond ash as a cover material in covers with capillary barrier effects are succinctly summarized. A model was exclusively developed and calibrated using commercial software SEEP/W for this study. After calibration, the efficiency of pond ash as a coarse-grained layer (CGL), fine-grained layer (FGL), unsaturated drainage layer (UDL), and seepage control layer (SCL) was investigated using various combinations. The CCBE made of pond ash obtained from the output and input points of an ash pond as alternate fine- and coarse-grained layers were observed to perform well. The performance of pond ash as UDL and SCL was also observed to be good. The approach presented in this study is valuable in assessing likely slope failures of coal ash storage facilities that may be triggered by rainfall events. The study aids in significantly reducing rainfall infiltration, improving the overall stability of the slopes, and promoting sustainability by utilising the concept of “waste covering waste”. The approaches used in this study can be extended in the rational design of slopes to address the future challenges anticipated with unprecedent rainfall events and its negative impacts associated with climate change effects.

Predicting groundwater contamination to protect the storm-exposed vulnerable

Domestic wells provide drinking water to 44 million people nationwide. Many of these wells, which remain federally unregulated and rarely tested for pollutants, serve rural populations clustered near surface-contaminated sites (e.g., hazardous waste sites, animal agriculture operations, coal ash ponds, etc.). The potential for natural disasters to deteriorate drinking water quality is well documented. Less understood is whether opportunistic post-disaster sampling might underrepresent vulnerable populations. When disaster strikes, well water sampling campaigns offer a glimpse into the quality of water for exposed residents. We examined over 8,000 well water samples from 2016 and 2017 to measure Hurricane Matthew’s impact on the presence of indicator bacteria. Bacteria presence was predicted at the household level following Hurricane Matthew’s landfall. The residential addresses associated with birth records as well as clinically estimated dates of conception and birth dates were used to predict the likelihood of indicator bacteria in drinking water sources that were unsampled but likely to have served pregnant women. We estimate that opportunistic well water sampling captures the average predicted contamination rates among households with pregnant women. Our approach documents a distribution of contamination risk where 2.7% of the vulnerable sample (670 unsampled households) have a 75% likelihood of total coliform presence. The predicted likelihood of indicator bacteria is elevated for a small share of households nearby swine lagoons that experienced the most torrential rainfall. However, the gap between sampled and unsampled households cannot otherwise be explained by the storm event or proximity to surface-contaminated sites. Findings suggest that sophisticated and holistic water quality prediction models may support post-disaster sampling campaigns by targeting individual households within vulnerable groups that are likely to experience higher risks from groundwater contamination.

An insight into failure of iron ore mine tailings dams

ABSTRACT Mine tailings dams are surface impoundment structures consisting of raised embankments that are built to contain mine tailings and mill effluents. In the past, many failures of these iron ore mine tailings storage facilities/dams have been reported worldwide in different forms. In this paper, an attempt has been made to review the failure modes, mechanisms and possible solutions to enhance the stability and safety of iron ore tailings dams. A comprehensive investigation has been carried out on 16 failure cases of such dams that were reported from 1917 to the current period. Additionally, mineralogy of iron ore tailings has been provided. The analysis of the past failures shows that most failures took place as a result of slope instability, overtopping, liquefaction-related instability, foundation movement and some form of structural failure. It has been found that 31.25% of iron ore mine tailings dams collapsed due to slope instability, 18.75% due to overtopping, 6.25% due to liquefaction-related instabilities, 6.25% due to foundation failure, 6.25% due to erosion, and 6.25% due to structural failure. In 25% of the failure cases, the causes have been unknown. An attempt is also made here to present prevention and remediation measures for avoiding failures and the associated negative environmental impacts in future.

Sustainable utilization of industrial wastes in controlled low-strength materials: a review.

The construction industry is experiencing an increasing demand for sustainable alternative materials. There is huge scope for converting the industrial wastes as partial or complete substitution of cementitious materials and fine aggregates. This study focuses on exploring the performance of different industrial waste materials as possible substitutes for flowable fill or controlled low-strength materials (CLSM). The most commonly used waste materials are found to bebottom ash, pond ash, steel slag, alum sludge, waste glass powder, red mud, cement kiln dust, copper slag, treated oil sand waste, and waste oyster shells. In order to verify their suitabilitycompaas potential CLSM, the plasticproperties (flowability, hardening time, segregation, bleeding, and density), hardened or in situ properties (unconfined compressive strength, California bearing ratio, and ultrasonic pulse velocity), durabilityproperties(permeability and freezing-thawing effects), and microstructural properties (X-ray diffraction and scanning electron microscopy) are compared. It is observed that the addition of different industrial wastes could satisfy the provision of CLSM as per ACI standards. There is immense scope for improvising the present utilization through functional optimization as well as investigating the potential of many unused waste materials which are locally available in bulk.

Leaching and geochemical evaluation of oxyanion partitioning within an active coal ash management unit

Field monitoring combined with laboratory leaching characterization and geochemical speciation modeling were used to identify important geochemical parameters and controlling mechanisms for leaching of oxyanions from coal ash in a disposal site. The site consisted of dry stacked ash on top of a former surface impoundment. Constituents leached from the dry stacked ash served as sources for the soluble fractions of constituents in underlying impoundment ash. Weathering of field ash was evidenced by the identification of calcite and ettringite. Porewater concentrations of As, B, and V in the field pH range (9–11) and liquid-to-solid ratio (L/S) condition (∼0.6 L/kg-dry) were primarily controlled by Ca-bearing precipitates (Ca-arsenate, B-substituted carbonate solid solution, Ca-vanadate, and V-substituted ettringite solid solution). The leachable fraction of Mo as a function of pH was limited by the available content in the solid, with aqueous concentrations of Mo being a function of L/S. Leaching behavior of Cr and Se was sensitive to the redox changes (from suboxic to oxic conditions) during field ash collection and laboratory leaching tests, including oxidative dissolution of insoluble Cr(III)-oxides and conversion of Se(0) in the solid to dissolved Se(IV)/Se(VI). Oxidation resulted in increased Cr concentrations from < 0.00005 (in porewater) to 0.001–0.1 mg/L (in laboratory eluates). The identified geochemical parameters and leaching-controlling mechanisms provide the bases for understanding and estimating the partitioning of oxyanions in other disposal sites with alkaline and suboxic conditions. This case study also provides a typical example of laboratory test results interpretation and field leaching behavior estimation for other studies.

Sustainable cement alternatives utilizing geopolymer for use in full depth reclamation of asphalt pavements

ABSTRACT This laboratory study investigates the feasibility of using geopolymer-based stabilization of base soil and reclaimed asphalt pavements (RAP) to fully replace cement in road rehabilitation projects. Geopolymer is an environment-friendly material that is based on the alkaline activation of aluminosilicate precursors. The performance of Portland cement as a chemical stabilizer for the full depth reclamation (FDR) of asphalt pavements is well established. However, Portland cement manufacturing has a high carbon footprint and other significant environmental impacts. Furthermore, there is a shortage of cement available for FDR projects across many country regions. Simultaneously, there is a strong motivation to explore various industrial wastes such as ponded ash, slag, ground glass fibers, etc., as replacements for Portland cement in construction. Therefore, a geopolymer based on ground glass fibers (GGF), either separately or combined with ponded fly ash (PFA) or slag (S), was studied to replace cement in FDR. All mixtures were tested for unconfined compressive strength (UCS), flexural strength, and drying shrinkage, wetting/drying, freezing/thawing, and tube suction tests. The results showed promising performance of geopolymer-based stabilized mixtures as compared to control. However, some test methods related to FDR with cement need to be modified to suit the mixtures of FDR with geopolymer.