Large Volumes Of Fly Ash Research Articles

Geotechnical Characteristics of Fine-Grained Soils Stabilized with Fly Ash, a Review

Fly ash is a waste material obtained from burning of coal in thermal power plants. Coal consumption is still very high and is expected to remain above 38% globally. Therefore, large volumes of fly ash are produced every year that need to be managed as waste. Improper disposal of fly ash can lead to surface water and ground water pollution and adversely affect human health and environment. The use of fly ash as an agent to stabilize soil has recently become popular in geotechnical engineering due to its many benefits such as being eco-friendly and cost-effective, and improving the geotechnical characteristics of the soil. This paper presents a review of the geotechnical properties of fly ash-stabilized fine-grained soils. Several features of fly ash, including classification, physical, geotechnical, chemical, and mineralogical properties, health concerns, disposal, availability, and cost are analyzed. The effects of fly ash in improving a wide range of mechanical properties of soils including unconfined compressive strength, shear strength, CBR value, consolidation and/or swelling characteristics, and permeability are reviewed in detail. It is shown that fly ash can be a substitute material for use in soil stabilization, leading to substantial economic and environmental benefits.

Performance of alkali-activated cementitious composite mortar used for insulating walls

There are large volumes of fly ash, slag and silica fume produced in the world. The waste disposal to the landfill is problematic and causes many environmental issues. The objective of this work is to demonstrate how fly ash, slag and silica fume can be used to produce alkali-activated cementitious composite mortar (AACCM) used for insulating walls. The combination of both polymers and alkali-activated cementitious material (AACM) made from fly ash, slag powder and silica fume enables a full composite action. The polymers include Methyl Cellulose Ether (MCE), Polyvinyl Alcohol (PA), and Calcium Formate (CF). The thermal insulating aggregates were cemented into insulating mortar under the composite action. The ratio of fly ash, slag powder and silica fume in the AACM is 5:5:1. The experimental results show that the compressive strength, dry density and thermal conductivity of cement-based thermal insulation mortar (TIM) decrease significantly with the increase of MCE content. MCE has an obvious air-entraining effect on cement-based mortar. When the percentages of MCE, PA, and CF are 1%, 1.6% and 1%, the compressive strength, dry density and thermal conductivity of the TIM are 0.50 MPa, 398.7 kg/m3, and 0.0932 w/(m·k) respectively. MCE has a weak air-entraining effect on AACM. When the percentages of MCE, PA, and CF are 3%, 2% and 1%, the compressive strength, dry density and thermal conductivity of the TIM are 0.28 MPa, 328.7 kg/m3, and 0.0775 w/(m·k) respectively. The simulation results of heat transfer performance show AACCM can be used for insulating walls.

Influence of Limestone Powder and Fly Ash on the Freezing and Thawing Resistance of Roller-Compacted Concrete

Roller-compacted concrete (RCC) comprises the same raw materials used in conventional concrete, but with different proportions. It is dry and has a low paste volume. Large volumes of fly ash are commonly used in the construction of roller-compacted concrete dams (RCCD) and pavements (RCCP). However, it is not as abundant as limestone powder. The latter is also cheaper and environment-friendly. This study aims to investigate the optimal amount of limestone powder that can be used in RCC to reduce both cement and fly ash. The effects of limestone powder and fly ash on the water absorption, compressive strength, and freeze-thaw resistance of RCC were evaluated. Eight different combinations of the mineral admixtures were tested, with limestone powder and fly ash contents up to 35% and 30%, respectively. A decline in density was observed when the cement replacement level was greater than 30%. This also led to an increase in porosity and permeability. Two mix designs denoted as LS30 and LS30FA10, demonstrated satisfactory results after 100 freeze-thaw cycles with relative dynamic modulus of elasticity (RDME) values of 73% and 70%, respectively. Their corresponding mass loss was 3.05% and 3.72%, which were below the code specified limit (5%).

Effect of Nano Iron Oxide on Strength and Durability Characteristics of High Volume Fly Ash Concrete for Pavement Construction

Cement is the principal component of cement concrete used for construction of rigid pavements and is produced by an energy intensive process. Large scale production and its subsequent utilization detrimentally contributes towards global warming. In order to cater for sustainable development, there is a need to utilize waste materials having cementitious properties as a partial substitute for cement. Fly ash is one of such waste which is being extensively used for the production of cement concrete. Concrete produced by utilizing fly ash more than fifty percent of cement is termed as high volume fly ash concrete (HVFAC). Although HVFAC facilitates utilization of large volume of fly ash, it however has the disadvantage of delayed gain in strength which limits its usage as pavement quality concrete (PQC). Contemporary literatures show the usage of various types of nanomaterials to overcome this disadvantage. The present study was carried out to investigate the influence of nano iron oxide on strength and durability properties of HVFAC. The HVFAC used in the study was prepared by replacement of fifty five percent ordinary Portland cement with F-type fly ash obtained from thermal power plant. Nano iron oxide was utilized in different percentages to improve the strength and durability characteristics of HVFAC. The strength properties of the concrete was evaluated by flexural, compressive and split tensile strength tests, whereas the durability characteristics were evaluated by density, permeability, sorptivity, ultrasonic pulse velocity and rapid chloride penetration tests. The tests were carried out at 28, 56 and 90 days age of concrete. The test result showed that HVFAC modified with 0.75% nano iron oxide by weight gave the optimal strength and durability results which were comparable with that of normal cement concrete used for construction of rigid pavements.

Effect of M/P and Borax on the Hydration Properties of Magnesium Potassium Phosphate Cement Blended with Large Volume of Fly Ash

The effect of the borax content and magnesia to phosphate ratio (M/P) on the hydration properties of the magnesium potassium phosphate cement (MKPC) with large volume of fly ash was investigated, and a five-hydration-stage for MKPCs was proposed. The results show that MKPC sets rapidly with less than 8% of borax, which is unfavorable to the application of MKPC on construction. Adding more than 8% (including 8%) of borax results in a secondary hydration peak for MKPC, in which the process of hydration can be divided into five stages, namely, pre-induction period, induction period, acceleration period, deceleration period and stable period. M/P ratios could not change the multi-step reactive stages but higher M/P ratios could accelerate the hydration. Borax tends to impact the formation of Mg-containing hydrated products.

Influence of Accelerators on cement replacement by large volumes of Fly ash to achieve early strength

The chemical admixtures named as accelerators improve the early setting and strength of cementations products whereas theh Cement prepared with large volumes of Fly ash (Pozzolana) fetch the durability and better sustainability. Achieving High early strength as well as durability in cementations products is a tough and challenging job which provokes the idea of the addition of accelerators to cement prepared with large volumes of Fly ash (pozzolana). The present study investigated the early setting and strength enhancement of Ordinary Portland Cement (OPC) replacement with 30, 40 and 50% of Fly ash when mixed with the accelerating admixtures such as Calcium nitrate (Ca(NO3)2) and Calcium nitrate (Ca(NO3)2) combination with Triethanolamine (C6H15NO3) at temperature of 25 ± 5 °C and 58±5 % relative humidity. In early ages, the maximum compressive strength was noted for 30 % Fly ash with 1% of Ca(NO3)2 in combinations with 0.05 % of C6H15NO3 and the achieved percentages noted as 18.23% and 54.29% for 1 and 3 days. The microstructural property (SEM) was also determined for OPC replacement with 30% of Fly ash at 1 and 3 days for 1% of Ca(NO3)2 in combination with 0.05, 0.1, 0.15 and 0.2% of C6H15NO3.

Manufacture of hybrid cements with fly ash and bottom ash from a municipal solid waste incinerator

Concerns about the large volume of fly ash and bottom ash generated by the incineration of municipal solid waste (MSW) have induced the scientific community to seek ways to reduce their environmental impact. One of the proposals that has been researched most intensely is their valorisation as supplementary cementitious materials and aggregates in Portland cement-based pastes, mortars and concretes. The present paper proposes an alternative use for this waste: as a raw material in alkali-activated hybrid cements. A hybrid cement developed for that purpose by blending 60wt% clinker and 40wt% incinerator bottom ash and fly ash exhibited good 28-day mechanical strength (upward of 32.5MPa). The leaching of potentially toxic metals present in the hybrid cement as a result of the inclusion of MSW fly ash and bottom ash was tested with different leaching procedures. The findings and the results of the analysis of the leaching parameters measured (Li, Fij…) showed that the hybrid cement proposed can effectively immobilise the potentially hazardous metals present in MSW fly ash and bottom ash.

Toughness study on fly ash based fiber reinforced concrete

The objective of the present investigation is to study the toughness of steel fiber-reinforced fly ash concrete based on the Japan Society of Civil Engineers (JSCE) approach. Fly ash is also considered as a hazardous waste due to the probable leaching of potentially toxic substances into the surface water, ground water, and soil. The ash content of the Indian coal (30% to 50%) contributes to these large volumes of fly ash. This paper highlights about the behavior of concrete when fly ash and steel fiber are added in concrete. Fiber-reinforced concrete is a concrete containing fibrous material which increases its structural integrity. The addition of random fibers to concrete considerably improves its structural characteristics such as static flexural strength, impact strength, tensile strength, ductility, and flexural toughness (Qian and Stroeven, Cem. Concr. Res. 30:63–68, 2000). Fly ash has been used by replacing cement in percentages, and steel fibers are added by volume of concrete in different percentages. Grooved type of steel fibers of aspect ratio 50 was used in this study. Flexural strength test was carried out for the specimens, and its results were highlighted. The toughness factor as measured by the JSCE approach is reported, and there is a good correlation between the steel fibers added in various percentages such as 1.5%, 2%, and 2.5% and the calculated toughness factor.

Effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing class F fly ash

Sustainability of concrete can be improved by using large volume of fly ash as a replacement of cement and by ensuring enhanced durability of concrete. Durability of concrete containing large volume of class F fly ash is dependent on the design of mixture proportions. This paper presents an experimental study on the effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing large volume of local class F fly ash. Concrete mixtures were designed with and without adjustments in the water to binder ratio (w/b) and the total binder content to take into account the incorporation of fly ash up to 40% of total binder. Concretes, in which the mixture proportions were adjusted for fly ash inclusion achieved equivalent strength of the control concrete and showed enhanced properties of drying shrinkage, sorptivity, water permeability and chloride penetration as compared to the control concrete. The improvement of durability properties was less significant when no adjustments were made to the w/b ratio and total binder content. The results show the necessity of the adjustments in mixture proportions of concrete to achieve improved durability properties when using class F fly ash as a cement replacement.

Flyash Based Geopolymer Concrete – A State of t he Art Review

Concrete usage around the world is second only to water. Ordinary Portland Cement (OPC) is conventionally used as the primary binder to produce concrete. But the amount of carbon dioxide released during the manufacture of OPC due to the calcinations of lime stone and combustion of fossil fuel is in the order of 600 kg for every ton of OPC produced. In addition, the extent of energy requires to produce OPC is only next to steel and aluminum. On the other hand, the abundant availability of fly ash worldwide creates opportunity to utilize (by ‐ product of burning coal, regarded as a waste material) as substitute for OPC to manufacture concrete. Binders could be produced by polymeric reaction of alkali liquids with the silicon and the aluminum in the source materials such as fly ash and rice husk ash and these binders are termed as Geopolymer. In Geopolymer Concrete, fly ash and aggregates are mixed with alkaline liquids such as a combination of Sodium Silicate and Sodium Hydroxide. United Nation’s Intergovernmental panel on Climate Change (IPCC) prepared a report on global warming during April 2007 which enlists various methods of reduction of CO2 emissions into atmosphere. As per that report, unmindful pumping of CO2 into the atmosphere is the main culprit for the climate change. Large volume of fly ash is being produced by thermal power stations and part of the fly ash produced is used in concrete industry, low laying area fill, roads and embankment, brick manufacturing etc. The balance amount of fly ash is being stored in fly ash ponds. Hence it is imperative on the part of Scientists and Engineers to devise suitable methodologies for the disposal of fly ash. Disposal of fly ash has the objective of saving vast amount of land meant for ash pond to store fly ash. Further, use of fly ash as a value added material as in the case of geopolymer concrete, reduces the consumption of cement. Reduction of cement usage will reduce the production of cement which in turn cut the CO2 emissions. Many researchers have worked on the development of geopolymer cement and concrete for the past ten years. The time has come for the review of progress made in the field of development of geopolymer concrete. Consequently 102 papers pertaining to the ingredients and technology of geopolymer concrete have been reviewed in this state of the art paper.

Phosphate Bonding: A New Method for Using Large Volume of Fly Ash

Magnesium phosphate cements (MPC) with larger volume of fly ash were studied in the present work. Dead burned magnesia, phosphates and fly ash were the components of MPC. The volume of fly ash in MPC was 70%, 75% and 80%, respectively. Three phosphates, monosodium phosphate (MSP), monopotassium phosphate (MPP) and monoammonium phosphate (MAP) were used. Compressive strength of the three MPC mortars with different fly ash content was determined. Results show that the compressive strength reduced with the proportion increase of fly ash, increased with the curing time. After cured 28 days in the lab air, the compressive strength of cement mortar can reach 14MPa, when the fly ash dosage was 80% by weight of cement. The reaction product is struvite of potassium (KMgPO4•6H2O) in potassium phosphate based MPC, and hydrated sodium phosphate (Na2HPO4•17H2O) in sodium phosphate based MPC. The results indicate that MPC has capacity to bond large volume of fly ash. A new way to utilize fly ash in a large scale can be realized by phosphate bonding.

Magnesium Phosphate Cement with Large Volume of Fly Ash

The accumulation of fly ash leads to severe problems in ecological environments. Various ways to excite the activity of fly ash in Portland cement based cementitious materials have been carried out for many years. In the present study, effect of large volume of fly ash in phosphate cement was studied. Dead burned magnesia, two phosphates (monoammonium phosphate and monosodium phosphate), and fly ash were used. The fabricated cement mortar specimens with different fly ash dosages were cured for 28 days in the lab air. Compressive strength was determined in 1d, 3d, 7d and 28d respectively. It is showed the compressive strength reduced with increase of fly ash content and increased with the curing time. After cured 28 days, the compressive strength of cement mortar developed to14MPa, when 80% fly ash was used. The reaction product, Na2HPO4•17H2O was found by X-ray diffraction analysis in sodium phosphate based cement. No ammonia gas was emitted and large volume of fly ash can be used in cement prepared from sodium phosphate. It is a new environmentally friendly cement material.

Effect of polyester fibres on the compressive strength and abrasion resistance of HVFA concrete

Approximately 95 million tones of fly is generated in India yearly, and most of the fly ash is of Class F type. Out of which only around 15–20% is utilized in cement production and cement/concrete related activities. Since large scale utilization of large volumes of fly ash in various concrete applications is a becoming a more general practice, an investigation was carried out to investigate the compressive strength and abrasion resistance of high volume fly ash concrete (HVFA) concrete with polyester fibres.In this paper, abrasion resistance of high volume fly ash (HVFA) concretes made with 30%, 40%, and 50% of cement replacement was evaluated in terms of its relation with compressive strength. Comparison was made between ordinary Portland cement and fly ash concrete. Test results indicated that abrasion resistance of concrete having cement replacement up to 30% was comparable to the normal concrete mixture with out fly ash. Beyond 30% cement replacement, fly ash concretes exhibited slightly lower resistance to abrasion relative to non-fly ash concretes. Inclusion of polyester fibres in HVFA concretes improved the abrasion resistance of concrete. Test results further indicated that abrasion resistance of concrete is closely related with compressive strength, and had a very good correlation between abrasion resistance and compressive strength (R2) value between 0.9208 and 0.804 depending upon fly ash content, testing age, and percentage of polyester fibres.

Effect of fly ash on the kinetics of Portland cement hydration at different curing temperatures

This paper describes the effect of fly ash on the hydration kinetics of cement in low water to binder (w/b) fly ash-cement at different curing temperatures. The modified shrinking-core model was used to quantify the kinetic coefficients of the various hydration processes. The results show that the effect of fly ash on the hydration kinetics of cement depends on fly ash replacement ratios and curing temperatures. It was found that, at 20 °C and 35 °C, the fly ash retards the hydration of cement in the early period and accelerates the hydration of cement in the later period. Higher the fly ash replacement ratios lead to stronger effects. However, at 50 °C, the fly ash retards the hydration of the cement at later ages when it is used at high replacement ratios. This is because the pozzolanic reaction of the large volumes of fly ash is strongly accelerated from early in the aging, impeding the hydration of the cement.

Properties of sustainable concrete containing fly ash, slag and recycled concrete aggregate

The suitability of using more “sustainable” concrete for wind turbine foundations and other applications involving large quantities of concrete was investigated. The approach taken was to make material substitutions so that the environmental, energy and CO 2 -impact of concrete could be reduced. This was accomplished by partial replacement of cement with large volumes of fly ash or blast furnace slag and by using recycled concrete aggregate. Five basic concrete mixes were considered. These were: (1) conventional mix with no material substitutions, (2) 50% replacement of cement with fly ash, (3) 50% replacement of cement with blast furnace slag, (4) 70% replacement of cement with blast furnace slag and (5) 25% replacement of cement with fly ash and 25% replacement with blast furnace slag. Recycled concrete aggregate was investigated in conventional and slag-modified concretes. Properties investigated included compressive and tensile strengths, elastic modulus, coefficient of permeability and durability in chloride and sulphate solutions. It was determined that the mixes containing 50% slag gave the best overall performance. Slag was particularly beneficial for concrete with recycled aggregate and could reduce strength losses. Durability tests indicated slight increases in coefficient of permeability and chloride diffusion coefficient when using recycled concrete aggregate. However, values remained acceptable for durable concrete and the chloride diffusion coefficient was improved by incorporation of slag in the mix. Concrete with 50% fly ash had relatively poor performance for the materials and mix proportions used in this study and it is recommended that such mixes be thoroughly tested before use in construction projects.

Experimental study of chemical treatment of coal fly ash to reduce the mobility of priority trace elements

Coal fired electric power plants produce large volumes of fly ash and other coal combustion by-products (CCBs) every year. Although almost 50% of the fly ash produced in the US is recycled for beneficial use, most of the ash material is disposed in dry landfills and ash lagoon impoundments. Fly ash may contain hazardous leachable trace elements such as As, B, Cr, Mo, Ni, Se, Sr and V which have a negative impact on the environment due to potential leaching by acid rain and groundwater with time. Many of the older CCB disposal facilities are unlined and unmonitored and as a result the EPA is currently developing national standards for monitoring CCB disposal sites. The cost to the US electric power industry could exceed one billion dollars if existing and closed CCB disposal facilities come under regulation. Thus simple, low-cost and effective in situ chemical treatment techniques are needed to stabilize hazardous leachable trace elements in the coal combustion by-product (CCB) materials. This paper reports the results of experiments designed to chemically treat fly ash with ferrous sulfate solutions to immobilize hazardous leachable trace elements after disposal. The current study is focused on three acidic and one alkaline fly ash samples collected from electric power plants located in the southeastern United States that were treated with two ferrous sulfate treatment solutions. The first treatment solution contained ferrous sulfate (FS) to give 322 mg/L of dissolved iron, while the second treatment solution contained the same concentration of ferrous sulfate along with excess calcium carbonate (FS + CC) to buffer the pH. Fly ash treatment experiments were carried out at solid:liquid (S:L) ratios of 1:3 and 1:30. The effectiveness of the treatment methods was evaluated by sequentially leaching the treated and the untreated fly ash samples using a synthetic acid rain (SAR) solution (US EPA Method 1312B SPLP fluid) as the leachate. The best overall treatment result was shown by the unbuffered ferrous sulfate solution at the 1:30 S:L ratio, which substantially reduced the mobility of the oxyanion trace elements. The overall mobility reduction achieved for As was 23–72%, B mobility was reduced by 43–80%, Cr by 45–77%, Mo by 21–90%, Se by 41–85% and V by 41–53% The unbuffered ferrous sulfate treatment was not effective for immobilization of the cationic trace elements Ni and Sr.

Evaluation of the mechanical properties of class-F fly ash

Coal-burning power plants in the United States (US) generate more than 70 million tons of fly ash as a by-product annually. Recycling large volumes of fly ash in geotechnical applications may offer an attractive alternative to the disposal problem as most of it is currently dumped in ponds or landfills. Class-F fly ash, resulting from burning of bituminous or anthracite coals, is the most common type of fly ash in the US. In the present study, the mechanical characteristics (compaction response, compressibility, and shear strength) of class-F fly ash were investigated by performing various laboratory tests (compaction test, one-dimensional compression test, direct shear test and consolidated-drained triaxial compression test) on fly ash samples collected from three power plants in the state of Indiana (US). Test results have shown that despite some morphological differences, class-F fly ash exhibits mechanical properties that are, in general, comparable to those observed in natural sandy soils.

Influence of fly ash and its mean particle size on certain engineering properties of cement composite mortars

An experimental investigation on the effects of incorporating large volumes of fly ash on the early engineering properties and long-term strength of masonry mortars is reported. The effect of fly ash and its mean particle size (PD) on the variation of workability and strength has been studied. It was found that fly ash and its mean particle size play a very significant role on the strength of masonry mortars. It has been observed that the early-term strength, except the mortars incorporating coarse fly ash (CFA), was slightly influenced by the replacement with fly ash. The long-term strength (both the bond strength and the compressive strength) will significantly increase, especially for the bond strength of mortars incorporating coarse fly ash. It was also found that the bond strength significantly increased as the mean particle size of fly ash decreases after 28 days curing. However, the 7-day strength was little influenced by fly ash particle size. The fluidity of composite mortar enhanced due to replace cement and lime with fly ash, and the mean PD of fly ash significantly influenced the workability.

Chemical and Engineering Properties of Fired Bricks Containing 50 Weight Percent of Class F Fly Ash

The generation of fly ash during coal combustion represents a considerable solid waste disposal problem in the state of Illinois and nationwide. In fact, the majority of the three million tons of fly ash produced from burning Illinois bituminous coals is disposed of in landfills. The purpose of this study was to obtain a preliminary assessment of the technical feasibility of mitigating this solid waste problem by making fired bricks with the large volume of fly ash generated from burning Illinois coals. Test bricks were produced by the extrusion method with increasing amounts (20-50% by weight) of fly ash as a replacement for conventional raw materials. The chemical characteristics and engineering properties of the test bricks produced with and without 50 wt% of fly ash substitutions were analyzed and compared. The properties of the test bricks containing fly ash were at least comparable to, if not better than, those of standard test bricks made without fly ash and met the commercial specifications for fired bricks. The positive results of this study suggest that further study on test bricks with fly ash substitutions of greater than 50 wt% is warranted. Successful results could have an important impact in reducing the waste disposal problem related to class F fly ash while providing the brick industry with a new low cost raw material.

Reduction in water demand of non-air-entrained concrete incorporating large volumes of fly ash

This paper presents the results of an investigation dealing with the reduction in water demand of the non-air-entrained concrete incorporating large volumes of ASTM Class F and C fly ashes. The eight fly ashes investigated were from Canada and the USA, and the percentage replacement of fly ash in concrete was 55% by mass of Portland cement. No superplasticizer was used in the concrete mixtures. The test results show that the reduction in water demand of the concrete incorporating the fly ashes ranged from a low of 8.8 for Lingan fly ash from Nova Scotia, Canada to a high of 19.4% for Coal Creek fly ash from the USA. The 1-day compressive strength of the concrete ranged from 6.3 MPa for fly ash from Belews Creek, USA to a high of 13.9 MPa for fly ash from Thunder Bay, Canada. The 28-day compressive strength of the concrete ranged from 30.7 to 55.8 MPa.