Structural Fill Material Research Articles

Effects of Roller Compacted Concrete Incorporating Coal Bottom Ash as a Fine Aggregate Replacement

Coal bottom ash (CBA) is a by-product generated in the coal furnaces of thermal power plants. It has adverse effects on the environment and requires additional landfill storage. However, the physical appearance of CBA is similar to that of sand, with particle sizes ranging from fine to coarse aggregates. Hence, many previous studies have focused on its application instead of sand for conventional concrete and structural fill materials considering natural sand depletion. Roller compacted concrete (RCC) is a zero-slump concrete with better compressive strength than conventional concrete because of the aggregate interlock achieved due to the compactness. It uses a low cement content but requires a large amount of sand. However, the applicability of CBA to RCC is limited. The properties of CBA may vary depending on the location. Therefore, this study aims to evaluate the effect of CBA as a sand replacement in RCC in terms of strength and long-term performance by conducting an empirical experiment under given conditions. Initially, a comprehensive literature review of various concrete strengths using CBA as sand replacement is provided. Thereafter, details related to the experiments on the strength and durability of the given CBA are presented. The results show that the RCC strength improves when CBA increases owing to the good gradation and low percentage of calcium oxide. Furthermore, the samples displayed acceptable freeze–thaw resistance values, but the scaling resistance values were small, owing to the high-water absorption. Therefore, CBA can be used in RCC as sand for improved structural performance, while additional research should be conducted to improve its long-term performance.

A Soil-Structure Interaction Study using Sustainable Structural Fill below Foundations

Structural fill is utilized to improve the bearing capacity and reduce settlement below foundations supported on weak soils or when foundations are supported on filled up soil. The present study evaluates the potential application of municipal solid waste finer fraction (MSW-FF) as a sustainable structural fill material. The finer fraction constitutes significant proportion of old landfill waste in cities, and do not easily find applications as compared to the other fraction of old waste. The present work determines the engineering properties of MSW-FF. A detailed assessment has also been carried out to evaluate the bearing capacity, settlement and modulus of subgrade reaction for the shallow foundation of different sizes and shapes resting on (a) soil with low subgrade modulus and (b) soil improved with a layer of MSW-FF as structural fill. A soil-structure interaction analysis has also been carried out by utilizing STAAD Pro. software, to understand the effect of soil and foundation stiffness on the foundation design parameters, viz., base pressure, settlement, bending moment and shear stress in shallow foundations for both cases (natural soil and with MSW-FF as structural fill). The comparison of different foundation systems resting on soil improved with MSW-FF structural fill layer and soil with low subgrade modulus has been presented to demonstrate the efficacy of MSW-FF as a suitable structural fill material. From the soil-structure interaction analysis, it is observed that the effect of soil subgrade modulus on foundation base pressure and settlement is prominent, while having a negligible effect of bending moment and shear stress in the foundation. Further, the relative stiffness of foundation and soil has a significant effect on the foundation design parameters. The study results are quite encouraging with respect to the potential of utilizing MSW-FF as a sustainable structural fill and put forward a new and promising alternate material for application in different infrastructure projects.

Extraction and characterization of microplastics in Landfill-Mined-Soil-like-Fractions: A novel methodology

Utilization of Landfill-mined-soil-like-fractions (LFMSF), a major constituent of landfill mined residues and resembles organic soil, is essential for landfill mining activity to be a sustainable practice. In this context, the potential utilization schemes of LFMSF such as compost, buffering material, landfill biocover, road subbase, and structural fill material were explored by earlier researchers. However, as the LFMSF originates from unscientifically created landfills/dumpsites (UCLDs) and/or engineered landfills (ELFs) that contain microplastics (MPs), there exists a school of thought that its utilization might contaminate the geoenvironment in the long run. Hence, it becomes mandatory to investigate their presence in LFMSF which unfortunately has not been attempted. In this context, to estimate the presence of MPs in LFMSF, it would be prudent to adopt the methodologies applied for their extraction and characterization in the organic-rich solid matrices (ORSMs). However, limitations associated with the existing protocols of (i) organic matter removal and (ii) ultrasonication in their extraction and characterization call for developing appropriate methodologies. Keeping this in view, a novel methodology for extraction and characterization of MPs in ORSMs by incorporating modifications to the existing protocols was developed and the details are presented. Further, the efficacy of the proposed methodology when employed for extracting MPs from the standard ORSMs and LFMSF has been verified. Subsequently, this methodology was adopted to estimate the concentration of MPs present in the LFMSF samples obtained from four different UCLDs/ELF. It was observed that the concentration of MPs in LFMSF samples varies between 23361.11 ± 1927.77 and 42066.67 ± 1713.02 particles/kg. Moreover, light-density polymer (i.e., polyethylene and polypropylene) based MPs amount to ≈50 % of their total concentration. In authors’ opinion, the proposed methodology should be applied to (i) extract and characterize the MPs present in other ORSMs and (ii) develop protocols/guidelines for utilizing LFMSF for different sustainable development applications.

Environmental effects of using copper mine tailings in various geotechnical applications

On the basis of the available literature, this paper evaluates the environmental effects of copper mine tailings (CMT) when used as a structural fill material in various geotechnical applications. Leaching of heavy metals from the CMT is considered as the vital factor hindering its wider acceptability among researchers and engineers. Therefore, apart from physical and chemical characteristics, due consideration was given to assess the leachability of CMT when used as structural fill in various geotechnical applications such as subgrade, embankment, fill and reclamation. From the literature review, it was found that CMT seems to be satisfying the criteria meant for structural fills. Results of leachability tests show that only a very few elemental concentrations exceeded the limits in un-stabilised form. Stabilised CMT performed better by bringing down the concentration well below the permissible limits in all the application types. This encourages the utilisation of CMT in structural fills and shows that environmental impacts are within the limits prescribed in standards.

Recycling of End-of-Life Tires (ELTs) for Sustainable Geotechnical Applications: A New Zealand Perspective

End-of-life tires (ELTs) are tires, unusable in their original form, which go into a waste management scheme (for recycling and energy recovery purposes), or otherwise are disposed. In New Zealand, the annual disposal of 3.5 million ELTs is posing critical environmental and socio-economic issues, and the reuse of ELTs through large-volume recycling engineering projects is a necessity. In this study, gravel and recycled granulated rubber were mixed to explore the possibility of obtaining synthetic granular geomaterials (with adequate geotechnical and environmental characteristics) that are suitable as structural fills for geotechnical applications including foundation systems for low-rise light-weight residential buildings. Moreover, an original framework with a set of geo-environmental criteria is proposed for the acceptance of gravel–rubber mixtures (GRMs) as structural fills. It is shown that when gravel-size like rubber particles are used, GRMs with volumetric rubber content of 40% or less have adequate strength (ϕ’ > 30°), low compressibility (εv ≤ 3%), excellent energy adsorption properties, and acceptable leachate metal concentration values (e.g., Zn < 1 mg/L), making them ideal synthetic structural fill materials for many sustainable geotechnical applications.

Coal combustion residue as structural fill material for reinforced soil structures

Coal combustion residue (CCR) has gained considerable acceptance in civil engineering applications, mainly in the cement industry and brick manufacturing. However, despite an increasing application of CCR, a large proportion remains unutilized globally. This research focuses on the feasibility of using fly ash, bottom ash, and their mixtures as a filling material in reinforced soil structures (RSS). The physical, mechanical characterization of the materials, along with the pullout resistance behavior of the interface between the CCR and a uniaxial polyester geogrid was studied. The grain size distribution tests showed the presence of 80% silt particles in fly ash and 7% in bottom ash. All the CCR samples were non-plastic in nature, and direct shear test results revealed that well compacted CCR samples offer similar shear strength as that of natural soils used as backfill in RSS. The leachability tests of CCR were carried out as per EN 12457–4 (2002) for the assessment of environmental risk. The results revealed that the leachable toxic contents in CCR remained quite below than the standard prescribed limits defined by the European Council Decision 2003/33/EC. The interaction coefficient values for a bottom ash-geogrid interface, obtained from the pullout test, match well with the results of natural/conventional fill material. The interaction coefficient value for the fly ash-geogrid interface was the lowest amongst the materials tested i. e 0.28 at 80 kPa, which is greater than the value recommended by JTJ015-91. The finding of the study demonstrated the suitability of using CCR as an economical, environmentally safe and sustainable structural fill material behind RSS.

Characterization of ferrochrome slag as a controlled low-strength structural fill material

Development and utilization of controlled low-strength material (CLSM), a flowable self-compacting material using industrial wastes is an effective way of sustainable infrastructure development. In the present study, an effort has been made to characterize ferrochrome slag, a less explored industrial waste as a construction material in general and FS as a base material with cement and fly ash for CLSM material, in particular. Different tests such as scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscope image, compaction, electrical conductivity, total dissolved solids (TDS), thermal conductivity are conducted to characterize ferrochrome slag as an alternate construction material. Then the properties of developed CLSM are discussed in terms of its flowability, fresh density, bleeding, unconfined compressive strength (UCS), settlement analysis and California bearing ratio (CBR) values. Based on the above results it was observed the FS can be used as a structural fill material with cement and fly ash for infrastructure development thereby conserving the natural resources, utilizing the industrial wastes and helping in sustainable development.

Effect of Crushing and Strain Rate on Mechanical Behavior of Type-F Fly Ash

Fly ash is a by-product of coal combustion from thermal power plant. It comprises of hollow spherical silt size particles with low specific gravity. The increased use of fly ash in highway/railway embankment construction as a structural fill material raises the need to study its mechanical behavior in detail. Although it has been reported that fly ash particles are susceptible to breakage, the effect of crushing on mechanical behavior of fly ash is yet to be explored. The current experimental research was conducted on type-F fly ash to study the following: (a) effect of crushing of fly ash particles on its macroscopic and microscopic behavior and (b) effect of strain rate on pore pressure evolution and stress-strain response of fly ash (uncrushed). Macroscopic (shear strength, compressibility, compaction behavior) and microscopic (particle’s shape and size using SEM images) tests were performed on fly ash to study the crushing effect. Strain rate effect on pore pressure and stress-strain response of uncrushed fly ash was studied by performing CU triaxial tests at different loading rates (0.005–9% per min). Macroscopic response of fly ash exhibited that higher crushing reduced shear strength and compressibility of fly ash and improved its compaction behavior. Microscopic response indicated deformation and breakage of fly ash particles due to crushing. Strain rate study showed large negative pore pressure generation along with brittle stress-strain response of uncrushed fly ash at 9% per min as compared to lower strain rates.

Long-term leaching prediction of constituents in coal bottom ash used as a structural fill material

Purpose This study is aimed to assess the long-term leaching of inorganic constituents from structural fills composed of reused coal bottom ash in Korea and identify key parameters that affect the amount of the constituents leached.

Characterization of red mud as a structural fill and embankment material using bioremediation

Red mud (Bauxite residue), a by-product of aluminum industry possess very serious and alarming environmental concern. Globally, 120 million tonne of red mud is generated per year. Disposal of red mud requires huge land, abundant earth material, high cost and further monitoring. And also, it has a potential to pollute nearby water, air and land due to its high toxicity. The most important barrier to remediate, re-use and long term red mud/bauxite residue management is its high alkalinity having pH range of 10–13. Hence, in the present study, bio-neutralization, an eco-friendly approach on red mud is attempted using various indigenous and non-indigenous microbes. In this study, the effect of bio-neutralization on morphological, physical and geotechnical properties of red mud due to the biogeochemical reactions are investigated and compared with raw red mud. Results indicated that reduction in pH value to nearly 7.5 from high alkalinity value of 10.06 is achieved by adding dairy waste product, sugar molasses and rice water in red mud, which act as a cost effective source of microorganism's nutrient. Further, geotechnical characterization as consistency of the red mud is improved in terms of plasticity index. The compaction characteristic is improved in terms of low optimum moisture content and compressive strength after bio-treatment increased marginally. The unconfined compressive strength (UCS) value of bio-treated red mud increased up to 298.6 kPa compared to 136.5 kPa for untreated red mud. The observation made is not only an option to neutralize red mud but also assist in effective utilization of the bauxite residue and various industrial wastes as dairy waste, sugar molasses and etc. The present study shows that bio-treatment of red mud provides an ample opportunity to use it in huge quantities as a structural fill and embankment material.

Feasibility study of copper slag as a structural fill in reinforced soil structures

Copper slag (CS) is a granulated cohesionless glassy material with the appearance of dark black coloured sandy size material. Copper slag is classified as poorly graded sand (SP) as per the Unified Classification System (USCS) and has a specific gravity of 3.6. Copper slag contains iron silicates, calcium oxide, and alumina, with small amounts of copper, lead, zinc, and other metals. The evaluated gradation, physical, shear strength characteristics and electrochemical properties of copper slag met the standard specifications for a structural fill material recommended for use in mechanically stabilized earth (MSE) walls and reinforced soil slopes (RSS). The angle of shearing resistance of copper slag varied between 35° and 49° for loose and dense states, respectively. Thereafter pullout tests were conducted to determine interface apparent coefficient of friction (μS/GSY) between the geogrid and copper slag at normal stresses of 7.3 kPa, 12.5 kPa, 25 kPa and 50 kPa and obtained results are then compared with those of geogrid in reference fill material, Yamuna sand (YS). The pullout tests were carried out as per ASTM Standard D 6706–01(2013) on an apparatus that was fabricated indigenously. This paper addresses the geogrid – copper slag interaction and geogrid – Yamuna sand interaction from pullout tests and demonstrates that copper slag can be effectively used as a structural fill for reinforced soil structures.

Geotechnical and Environmental Characterization of Boiler Slag as Fill Material

AbstractBoiler slag is a by-product that is derived from coal combustion in wet bottom boilers. Due to its low bulk density, in the compacted state it is an attractive alternative for use as structural fill material. Compared with other coal combustion by-products, the geotechnical and leaching properties of boiler slag are less known. This paper presents the results of laboratory and field investigation of boiler slag, produced in boilers where brown coal is used as fuel. Chemical and mineralogical composition, as well as mechanical properties were studied in the laboratory. A test embankment was constructed in order to identify compaction behavior and the achieved layer stiffness. A lysimeter was installed as part of the test embankment for the long-term monitoring of the quality and quantity of percolated water.

Use of crushed brick in reinforced earth railway structures

The Bermondsey Dive-Under (BDU) scheme is a fundamental part of UK's Thameslink Programme. The scheme involves extensive demolition of 900 m of masonry viaduct followed by the construction of 900 m of new structures, 200 m of reinforced earth structures and 200 m of embankment modifications. Crushed brick is typically not used as a structural fill material in the UK due to concerns over its friability and associated long-term performance. This paper describes a study undertaken in 2012 that examined the viability of recycling the demolished brickwork material into a crushed engineered fill material for use in the BDU permanent works. The overarching objective of the study was to seek to reduce the scheme's significant volumes of both imported fill and exported demolition material, with associated sustainability advantages in addition to the environmental and safety benefits resulting from the significantly reduced lorry movements from London's streets. The paper details the sampling and testing of brickwork that was undertaken and presents the findings from the study. The paper also discusses some of the issues associated with introducing innovation within major work programmes. The BDU scheme is currently under construction and is scheduled for completion in 2017.

Geochemical characterization of engineered coal-combustion byproducts (CCBs): Occurrence and mobility of trace elements, implications for interactions with acidic and ambient groundwater

Fixed scrubber sludge (FSS), is a coal-combustion byproduct composed of flue gas desulphurization sludge, fly ash, and quick lime. FSS has potential usages as structural fill and capping materials in mine land reclamation because of its low permeability and acid-neutralization capacity. Sediment cores extracted from an abandoned mine land reclamation site where FSS was used as a hydrologic barrier to groundwater recharge were analyzed in an effort to quantify the chemical phases (both primary and secondary) that constitute the FSS, and to evaluate any evidence of weathering that has occurred during the 18years since emplacement. The primary solid phase is amorphous spheroids. Four different types were identified and their quantitative compositions were obtained, with SiO2, Al2O3, and FeO being the primary components. Of special concern was the occurrence and mobility of trace elements within the solid phases. Sequential extractions using different chemical reagents were conducted to analyze the concentrations of As, B, Ba, Cd, Cr, Cu, Ni, Pb, and Zn in different fractions as indications of mobility. The highest concentration of the trace elements was contained in the residual fraction, which is consistent with the amorphous spheroids being very resistant to chemical weathering. The results also suggest that the mobility of the trace elements decrease in the following order: B, Cu>Cd, Zn, Pb, Cr>Ba>Ni>As. Comparison of samples collected from the weathered edges and unweathered portions of the FSS layer reveal that a more aggressive weathering environment exists at the upper boundary of the FSS, where it is in contact with oxygenated soil water. The quantitative chemical compositions, distribution of trace elements, as well as evidence of how trace elements are released provide background data for the development a reactive transport model to simulate long-term effects of placing FSS in the natural environment; and particularly in areas that are being subjected to abandoned mine land reclamation.

Spent Coffee Grounds–Fly Ash Geopolymer Used as an Embankment Structural Fill Material

AbstractThe drinking of coffee forms a deep-rooted pastime in many communities worldwide. However, the culture of coffee drinking generates vast quantities of organic waste that ends up in landfills. Current research trends are inclined towards recycling of waste materials into alternative construction materials, hence the need to research sustainable uses for spent coffee grounds. Coffee grounds (CG) are highly organic with a very high percentage of biodegradable material. The objective of this research was to study the strength development of CG when used as a geopolymer stabilized embankment structural fill material aiming for a better understanding of geopolymer stabilization of highly organic material. Fly ash (FA), being a silica and alumina rich material, was used as a precursor. A liquid alkaline activator, L, being a sodium hydroxide-sodium silicate solution was used for alkali activation of FA in the CG-FA geopolymer. Factors found to affect strength development of the CG-FA geopolymer were: (1)...

Optimisation of coal wash–slag blend as a structural fill

Coal wash (CW) and basic oxygen steel slag fines (BOS) are by-products of the coal mining and steel industries, respectively. Their effective reuse and recycling through large-scale geotechnical projects, such as port reclamation, is economically beneficial and environmentally sustainable. In this study, CW and BOS were blended in order to explore the possibility to obtain synthetic fills having geotechnical properties similar or superior to conventional fills, therefore suitable as a structural fill for the Port Kembla Outer Harbour reclamation near Wollongong City, Australia. A framework with four levels of acceptance is proposed in this paper to select granular waste as structural fill materials. This framework was used for optimising the CW-BOS blend. It was found that for the Port Kembla Outer Harbour reclamation, a CW-BOS blend with a BOS content between 30 and 45% can meet most geotechnical specifications (i.e. high shear strength and bearing capacity, low swelling and particle breakage levels, and adequate permeability) required for a suitable structural fill above the high tidal level.

Properties and sustainability of alkali-activated slag foamed concrete

Abstract In the present study, 15 concrete mixes with dry density between 300 and 500 kg/m3 were tested for developing reliable mixing proportions, and establishing the significance of sustainable application of alkali-activated (AA) foamed concrete as a thermal insulation material in floor heating systems of buildings. Ground granulated blast-furnace slag (GGBS) was activated using the following three types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, 5% Ca(OH)2 and 6.5% Na2SiO3, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The unit binder content varied in the concrete mixes corresponding to each type of activator. All mixes were produced using the pre-formed foam procedure with no aggregate or filler. The test results revealed that AA GGBS foamed concrete has considerable potential for practical applications when the unit binder content is close to 400 kg/m3, achieving the minimum quality requirements specified in the KS F 4039 as well as ensuring economic efficiency. Furthermore, the tested AA GGBS foamed concrete developed higher compressive strength than ordinary Portland cement (OPC) foamed concrete with the same dry density. In particular, a lifecycle assessment demonstrated a reduction in the environmental impact profiles of all specimens relative to typical OPC foamed concrete as follows: 99% for photochemical oxidation potential, 85–93% for global warming potential, 73–85% for abiotic depletion, and 68–85% for both acidification potential and human toxicity. Overall, the developed AA GGBS foamed concrete can be enlarged to sustainable varieties of cast-in-place structural fill and precast masonry materials.

Creep response of recycled asphalt shingles

Recycled asphalt shingles (RAS) mixed with granular materials or cementitiously stabilized to control their otherwise high compressibility provide a viable lightweight structural fill material in highway embankments or backfill behind retaining structures. In this research, deviator creep response of RAS mixed with bottom ash (BA) or stabilized with self-cementing fly ash (FA) was investigated. Systematic constant stress consolidated-drained triaxial tests were conducted on compacted RAS–BA and RAS–FA mixtures at ranges of confining pressures, deviator stresses, and temperatures expected in the field. Results showed that both compacted RAS–BA and RAS–FA mixtures represent classic creep response similar to soils. Creep rupture was observed at deviator stresses higher than 80% of deviator stress at failure. To prevent creep rupture, mobilized shear strength in the design of side slopes of highway embankments containing RAS should be limited to 80% of deviator stress at failure. Creep rate is affected by confining pressures. At a given stress level, the creep rate decreased and the time to creep rupture increased with increasing confining pressure. Temperature change also affects the creep strain and strain rate of compacted RAS–BA and RAS–FA mixtures. The strain rate of the compacted RAS–BA mixture exponentially increased with temperature. However, thermal pre-loading at summer field temperatures significantly reduced the strain rate of the compacted RAS–BA mixture from 64 × 10−6%/min to 3.6 × 10−6%/min and that of the RAS–FA mixture from 190 × 10−6%/min to 6.9 × 10−6%/min. To minimize creep strain and strain rate of structural fill materials containing RAS, construction is recommended during warm seasons. Creep models were developed to evaluate the time-dependent deformation of embankments constructed with RAS mixed with granular materials or stabilized with self-cementing fly ash.

Effect of Temperature on Shear Strength of Recycled Asphalt Shingles

The effect of seasonal variations in field temperature on the shear strength of recycled asphalt shingles (RAS) improved by mixing with bottom ash (BA) was evaluated for their use as structural fill material in highway embankments. Typical field temperatures ranging from 5°C to 35°C were induced to compacted mixtures of RAS:BA. An increase in temperature reduced the shear strength of compacted mixtures of RAS:BA, and therefore temperature effects should be taken into consideration in design. The friction angle of compacted RAS:BA mixtures, however, remained within the range suitable for stability of embankment fills. Thermal cycling induced thermal preloading to the mixtures containing RAS; this preloading in turn increased shear strength. From these results, to achieve optimum engineering behavior, construction of highway embankments made with granular materials containing RAS is recommended during warm seasons. The use of RAS in high-volume structural fill applications can contribute to more sustainable roadway infrastructure.

English

Coal combustion byproducts (CCBs) have potential as structural fill and capping materials in abandoned mine land (AML) reclamation because of their acid-neutralization capacity. However, the potential for these materials to leach constituents of potential concern (COPCs) into groundwater hinders their use by AML program managers. In 1996, the Midwestern AML site in southwestern Indiana was reclaimed using fixated scrubber sludge (FSS) cap composed of flue gas desulphurization sludge, fly ash, and lime. The cap was placed over a pyritic refuse deposit, an unreclaimed spoil ridge, and highwall lakes that were filled with ponded ash. Post reclamation analyses of groundwater chemistry showed that alkalinity and pH levels increased below the cap, indicating that the CCBs helped to neutralize the preexisting acid mine water. Concentrations of COPCs initially increased below the cap, but dropped back to near or below pre-reclamation values over the past 10 years. For example, boron that initially increased to 13,000 µg/L decreased to pre-reclamation values (300 μg/L) with time. X-ray diffractometry was conducted on core samples containing FSS and ponded ash collected from the site in 2011 to identify mineralogical changes since emplacement. Oxidation of hannebachite (calcium sulfite hemihydrate) produced gypsum and calcite in the upper 1 to 4 cm of the 1 to 3 m thick FSS cap. No oxidation zone was observed at the bottom of the cap. Sediment cores of ponded ash reveal little change with depth, possibly because leaching had already occurred as a result of stockpiling at the power plant. The results of this study indicate that FSS did contribute COPCs, including boron, molybdenum, chromium, and arsenic, to groundwater for short periods and in the immediate vicinity of emplacement. Nevertheless, a lack of significant oxidation and declining trends in groundwater contamination represent long-term favorable outcomes for use of CCBs in AML reclamation.