Cement-stabilized Fly Ash Research Articles

Durability, Capillary Rise and Water Absorption Properties of a Fiber-Reinforced Cement-Stabilized Fly Ash–Stone Dust Mixture

The management of unutilized fly ash poses challenges due to concerns about storage and its potential groundwater contamination. Within the road industry, where the bulk utilization of fly ash is feasible, its unsuitability for use in the base and sub-base layers of pavements due to its low strength and a high proportion of fine particles has been a limitation. The incorporation of stone dust alongside fly ash, treated with lime or cement, yields superior strength and stiffness. Apart from strength, the stabilized mix’s durability, capillary rise, and water absorption properties are crucial for determining its suitability for pavement applications. Observations from this study reveal that fiber-reinforced cement-stabilized fly ash–stone aggregate specimens treated with 4% and 6% cement, with and without fibers, met the limiting mass loss of 20%, as specified in IRC SP: 89. The mass loss decreases with an increase in cement and fiber content. However, the capillary rise in the mixes increases with a higher percentage of fly ash and fiber content but decreases with increased cement content. Cement addition results in a reduction in water absorption; however, the addition of fibers results in an increase in water absorption. A linear correlation has been established between mass loss and UCS and IDT, which can be used to evaluate the suitability of materials for the structural layer without conducting a wet–dry durability test, which typically takes one month. This study proposes that cement-stabilized fly ash and stone aggregate mixtures with 4% and 6% cement can be used as the subbase and base of pavement based on wet–dry mass loss criteria and water absorption criteria. Observations from this study reveal that fiber-reinforced cement-stabilized fly ash–stone aggregate specimens treated with 4% and 6% cement, with and without fibers, met the limiting mass loss of 20%, as specified in IRC SP: 89. The mass loss decreases with an increase in cement and fiber content. However, the capillary rise in the mixes increases with a higher percentage of fly ash and fiber content but decreases with increased cement content. Cement addition results in reduction in water absorption. However, the addition of fibers results in increase in water absorption. A linear correlation is established between mass loss and UCS and IDT, which can be used to evaluate the suitability of materials for the structural layer without conducting wet–dry durability tests, which take one month. This study proposes that cement-stabilized fly ash and stone aggregate mixtures with 4% and 6% cement can be used as the subbase and base of pavement based on wet–dry mass loss criteria and water absorption criteria.

Strength and Stiffness Evaluation of a Fiber-Reinforced Cement-Stabilized Fly Ash Stone Dust Aggregate Mixture

The utilization of waste fly ash in road construction is primarily confined to its use in embankment filling or as a stabilizer when combined with lime and cement. Its application in structural pavement layers, such as the base and subbase, faces a challenge due to the high volume of fine particles, which renders it brittle when stabilized. In this study, fly ash was blended with stone dust and aggregated to enhance its gradation. Subsequently, it was stabilized with cement to bolster its strength, rendering it suitable for pavement use. Additionally, polypropylene (PP) fibers were introduced to mitigate the brittleness of the mixture. An extensive experimental investigation was conducted to assess the strength and stiffness properties, including compressive strength, indirect tensile strength, flexural strength, cyclic indirect tensile modulus, and flexural modulus of fiber-reinforced cement-stabilized mixtures of fly ash, stone dust, and aggregate. The experimental results reveal that the addition of PP fibers up to 0.25 wt.% enhances compressive strength, but any further increase in fiber content leads to a reduction in strength. However, indirect tensile strength and flexural strength show improvement, with an increase in fiber percentage up to 0.5 wt.%. It was observed that cement content plays a dominant role in stabilizing these materials. Appropriate relationships have been established between strength and modulus parameters for stabilized mixtures. Based on the strength and stiffness study, a combination of 70% fly ash and 30% stone dust aggregate with 6% cement can be considered for the base layer. Regarding the behavior of indirect tensile strength and flexural strength, an optimum fiber percentage of 0.35% is recommended.

Laboratory tests, field application and carbon footprint assessment of cement-stabilized pure coal solid wastes as pavement base materials

Solid wastes from coal industry, such as coal gangue (CG), coal bottom ash (CBA) and fly ash (FA) from coal-fired power plants, pose a significant impact on the environment. Thus, it is essential to fully study the potential values of these coal solid wastes (CSW) as construction materials. In this study, cement-stabilized FA, CBA and CG were performed as pavement base materials, and the mechanical properties and environmental benefits were systematically investigated in order to achieve the utilization of CSW in road construction. The unconfined compressive strength (UCS) test, splitting tensile strength (STS) test, ultrasonic test, triaxial test, and field application were conducted. The results show that CBA exhibits a negative effect on the early strength of the mixtures. However, the negative effect gradually decreases with the extension of the curing age. In addition, the relationship models between UCS and STS, between UCS and amplitude, between peak stress, peak strain and confining pressure with different CBARR and cement content were proposed. Based on the Mohr-Coulomb (M-C) failure criterion, the unified function expression and parameter-related function expressions with various CBARR and cement content of the shear stress τ were established. The laboratory tests indicate that the mixture with CBARR of 50% exhibits preferable mechanical performance. Field application and carbon footprint assessment verify that the mixture has great potential to be used as a new eco-friendly pavement base material and meets the technical requirements for heavy traffic of class II highways in China.

Valorization of Crushed Glass as a Potential Replacement for Sand in Cement Stabilized Fly Ash Bricks

Abstract The present study involved the utilization of crushed glass as an auxiliary additive in the manufacture of cement stabilized fly ash (CSF) bricks. The bricks were made with 1:1 proportion of fly ash and sand stabilized with 20 % cement. Crushed glass was used as replacement for the fine aggregate in increments of 10 % up to 40 % wherein the sand was completely replaced with crushed glass. The various mix proportions were then moulded into bricks with the addition of water by hand moulding method of forming the bricks and sun dried followed by sprinkle curing over a period of 21 days. The bricks were then subjected to compressive strength, water absorption and efflorescence tests to gauge its performance. The investigation revealed that the addition of crushed glass to the brick mix resulted in an increase in strength of the bricks, however, the maximum strength achieved could not achieve the strength of the control specimen. But the strength was higher than the minimum strength recommended by Bureau of Indian Standards (BIS) for stabilized blocks as well as burnt bricks. It also reduced the water absorption marginally while no efflorescence was seen in any of the combinations. A cost comparison revealed that the optimal combination with crushed glass was able reduce the cost of the brick by 20 %.

Use of cement-chelated, solidified, municipal solid waste incinerator (MSWI) fly ash for pavement material: mechanical and environmental evaluations

As a by-product from the incineration of municipal solid waste (MSW), fly ash usually contains mobile heavy metals that may engender severe pollution when reused. In this study, fly ash was solidified with cement and a chelating agent to immobilize these polluting elements. The possibility of using the solidified fly ash for pavement materials was also assessed through mechanical and environmental perspectives. According to the results, the strength of solidified fly ash was found proportional to both the cement/fly ash ratio and curing time. This indicated that the increase of fly ash loading reduced the concentration of products from cement hydration, and thus destroyed the structure of the products of hydration. With the increase of freeze–thaw cycles, the compressive strength of cement-stabilized fly ash decreased between days 7 and 14, and then increased between days 14 and 28. Subsequently, the finite element analysis showed that placing the solidified fly ash layer as a pavement material between an unbound base course and subgrade was beneficial to prolong fatigue life and reduce rutting distress of asphalt pavements. Finally, leachability of metals from the mixtures was tested, which showed that leaching concentration decreased as the cement/ash ratio, curing time, and chelating agent content increased.

Investigation on geomechanical behaviour and microstructure of cement-stabilized fly ash

Present laboratory study investigated the geomechanical behaviour of cement-stabilised fly ash. Class F fly ash collected from two different power plants in India was used in the study. Fly ash was stabilised with varying proportions of cement up to 10%, added in the ratio of dry weight of fly ash. Effects of addition of cement were evaluated on compacted fly ash–cement mix at optimum moisture content for rest period of 7, 14, 21 and 28 days. Results showed that the hydraulic conductivity of both the fly ash samples decreased by an order in magnitude when added with 10% cement. Effects of rest periods on hydraulic conductivity of cement-stabilised fly ash were found to be insignificant. Unconfined compressive strength of the cement-stabilised fly ash samples increased with increase in the cement content and rest periods, while the compression index of the stabilised samples decreased with increase in cement content. Different geomechanical behaviour was correlated with the microstructural changes in cement-stabilised fly ash, obtained through Field Emission Scanning Electron Microscope (FMSEM). Test results showed that cement stabilisation improved the engineering behaviour of both the fly ash, which may aid in their application as resource geomaterial.

Unconfined Compressive Strength of Fly Ash Mixed With Lime Precipitated Waste Sludge and Cement

For an effective disposal of fly ash, avoiding environmental pollution, it is necessary to utilize it on a continuous basis for some beneficial purposes. The present study investigated the feasibility and effectiveness of the fly ash along with lime precipitated waste sludge and cement. The Unconfined Compressive Strength (UCS) tests were carried out on the specimens comprising of fly ash (FA), (5 to 35%) lime precipitated electroplating waste sludge (S) and (2-20%) cement at 7 and 28 days of curing periods. The results of UCS tests indicated that the strength of fly ash increases substantially on addition of lime precipitated sludge and cement. It has been observed that compressive strengths of cement stabilized fly ash were smaller than the cement-sludge stabilized mix. It has also been observed that the strength was increasing upto 20% sludge addition to fly ash-cement mix, however, the strength started decreasing on further addition of sludge beyond 20% to the fly ash-cement combination. The most effective percentage of fly ash-cement-sludge was found as 72%FA+20%S+8%C. The UCS of this mix was found as 18 and 25 MPa at 7 and 28 days of curing respectively. This is substantially higher than the UCS of plain fly ash (1.0 and 2.5 MPa) at the same curing periods respectively. The X-ray analyses of some selected samples using EDX technique were also carried to study the elemental analyses of the various mixes. The EDX data showed that the experimental results obtain by UCS tests were in conformity with the chemical findings of EDX

Behavior of expansive soils under stabilized fly ash cushions during cyclic wetting and drying

Structures built in expansive clays are likely to be damaged due to the strains caused in them by alternate swelling and shrinkage. Variations in the moisture regime during monsoon and summer are the cause of this alternate swelling and shrinkage. Several innovative foundation techniques have been suggested to overcome the problems associated with expansive soils. Belled pier and under-reamed pile are some of the foundation practices adopted in these soils. Besides, overburden in the form of a sand cushion or a cohesive non-swelling soil (CNS) cushion has also been tried for arresting heave. But, most of them suffer from one shortcoming or the other. In order to overcome the drawbacks of the existing foundation practices, fly ash cushion, stabilized with lime or cement, has been tried by the authors. The principle of this technique is the same as that of a CNS cushion. This proved to be very effective in arresting heave. However, its efficacy over a few cycles of wetting and drying needs to be established since CNS cushion, which was found to be effective in arresting heave during the first cycle of wetting and drying was ineffective during the subsequent cycles. The present study relates to the behavior of expansive clays under lime- or cement-stabilized fly ash cushion subjected to several wetting and drying cycles.

Performance evaluation of cement stabilized fly ash–GBFS mixes as a highway construction material

Fly ash and granulated blast furnace slag (GBFS) are major by-products of thermal and steel plants, respectively. These materials often cause disposal problems and environmental pollution. Detailed laboratory investigations were carried out on cement stabilized fly ash-(GBFS) mixes in order to find out its suitability for road embankments, and for base and sub-base courses of highway pavements. Proctor compaction test, unconfined compressive strength (UCS) test and California Bearing Ratio (CBR) test were conducted on cement stabilized fly ash-GBFS mixes as per the Indian Standard Code of Practice. Cement content in the mix was varied from 0% to 8% at 2% intervals, whereas the slag content was varied as 0%, 10%, 20%, 30% and 40%. Test results show that an increase of either cement or GBFS content in the mixture, results in increase of maximum dry density (MDD) and decrease of optimum moisture content (OMC) of the compacted mixture. The MDD of the cement stabilized fly ash-GBFS mixture is comparably lower than that of similarly graded natural inorganic soil of sand to silt size. This is advantageous in constructing lightweight embankments over soft, compressible soils. An increase in percentage of cement in the fly ash-GBFS mix increases enormously the CBR value. Also an increase of the amount of GBFS in the fly ash sample with fixed cement content improves the CBR value of the stabilized mix. In the present study, the maximum CBR value of compacted fly ash-GBFS-cement (52:40:8) mixture obtained was 105%, indicating its suitability for use in base and sub-base courses in highway pavements with proper combinations of raw materials.

Efficacy of Cement-stabilized Fly Ash Cushion in Arresting Heave of Expansive Soils

Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage. Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves, unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction in the amount of heave is as high as 99.1%.

Analysis and design of a stabilized fly ash as pavement base material

The main objective of this study is to utilize a class F fly ash as base material in road pavements. Since class F fly ashes do not manifest desirable engineering properties for this purpose, it was decided to stabilize the material with cement. Fly ash may be utilized with or without aggregate as a pavement layer. It should be noted that, in this research only aggregate free stabilized mixtures (fly ash and cement only) were used since the aim was to utilize high volumes of this waste material. Cement content in the stabilized, laboratory prepared samples were between 2%, 4%, 8%, and 10% by total weight. Initially, Texas triaxial test was carried out to justify the suitability of the fly ash as pavement material. Then, mechanical tests were performed to obtain the fundamental properties of the cement stabilized material in order to analyze the pavement structure. Under repeated wheel loading, fatigue cracking is the primary mode of failure of stabilized materials in which cracks initiate due to the repeated tensile stresses. Utilizing an accelerated full scale road test data for the fatigue performance of cement stabilized fly ash and performing a mechanistic-empirical design procedure, required layer thickness for different lives were obtained for different amount of cement content.

Hydraulic conductivity of compacted cement–stabilized fly ash

When combined with portland cement and compacted, fly ash is a high-strength material. In some instances, it may also be desirable to control the hydraulic conductivity ( k) of the compacted mixture. Therefore, a study was performed to assess the effects of water content ( w), cement content, curing time, and compaction effort on the hydraulic conductivity of compacted cement–stabilized fly ash. When compacting relatively dry mixtures ( w < 20%), k is independent of compaction effort, and is on the order of 10 −5 cm/s. When compacting between w of 20% and optimum water content ( w opt), compaction effort affects k, and, at a given w, k decreases by about an order of magnitude when increasing from standard to modified proctor effort. When wet of w opt, k is on the order of 10 −6 cm/s regardless of compaction effort or water content. With respect to curing time, extended curing time has relatively little effect on k within a 60-day time frame. Based on the results of this study, an approach to construction quality assurance testing can be applied to estimate k based on in situ measurement of dry density ( ρ d) and w.

Behavior of Fiber-Reinforced Cement-Stabilized Fly Ashes

A laboratory experimental study was carried out on two Indian fly ashes to investigate their compressive strength and flexural behaviors as cement-stabilized and fiber-reinforced base course materials. The cement content was chosen to comply with the criteria specified by the Electric Power Research Institute. The fiber reinforcement was in the form of randomly oriented polymeric fibers. Unconfined compression tests and flexure tests were conducted on specimens stabilized with cement alone and with both cement and fibers. The experimental program included the determination of the chemical composition of the raw fly ashes, and scanning electron microscopy and x-ray diffraction tests of the raw and stabilized fly ashes. The study showed that, in general, the fiber inclusions improved the performance of the cement-stabilized fly ash specimens.

Centrifuge Model Tests on Failure of Cementstabilized Fly Ash Ground

ABSTRACT An experimental investigation was carried out to study the feasibility of using fly ash, the industrial residue of thermo-electric power plants, as a fill material for waterfront retaining structures. In the study, centrifuge model tests were performed on cement stabilized fly ash ground to investigate its failure pattern and active earth pressure acting on the retaining wall. The stabilized fly ash ground was brought to an acceleration field of 70 g and then the retaining wall was allowed to rotate about its bottom to cause ground failure. As a result of this study it was found that the failure pattern of fly ash ground mixed with a small amount of cement is characterized by a vertical tension crack and a straight shear failure which is much different from those of ordinary clay or sandy ground. It was also found that the active earth pressure of the cement stabilized fly ash ground was lower than ordinary sand fill and could be reasonably estimated by a proposed method incorporating the failure pattern of the ground.

Cement-stabilized fly ash base courses

Various demonstration projects have been carried out in The Netherlands with cement-stabilized fly ash as a base course. Usually these courses were made of 100 parts by mass of fly ash; 10 parts by mass of cement; 20 to 30 parts by mass of water. However, the projects were not quite successful since delamination was observed, and long-term strength, after a period of six years of performance, appears to be much smaller than expected on the basis of preliminary laboratory research. A model for pozzolanic reaction of fly ash recently developed by Fraay and Bijen pointed out that the reactivity of fly ash is influenced greatly by the pH value of the pore water. A pH of at least 13 is required to initiate fly ash pozzolanic reaction in a Portland cement environment. Pore water extraction measurements showed that the pH of cement-stabilized fly ash often has a substantially lower value. In this high-volume fly ash application the effect of the acidity of fly ash is much greater than in ordinary concrete with cement replaced by fly ash up to 30%. By addition of NaOH and/or sodium silicate to the mixing water, the pH value can be increased above the ‘threshold’ value. Tests were carried out with different types of class-F fly ashes and with different NaOH concentrations in the mixing water. The results show an increase in compressive strength of up to 300% depending on the type of fly ash, and a substantial decrease in the rate of water absorption.

Short and Long-Term Leaching Behavior of a Low-Calcium Fly Ash and Cement-Stabilized Fly Ash

ABSTRACTLow-calcium fly ashes from eastern Pennsylvania power plants, stabilized with Portland cement, have a potential application as a pipeline bedding material. A typical fly ash, and a cement-stabilized material made with this fly ash, were subjected to extensive physical and chemical characterization. Two procedures were used to investigate whether leachates from the bedding materials were nonhazardous according to the criteria of the regulatory agencies. The first was the short-term EPA test, used to define a hazardous waste under the RCRA regulations, and the second was a long-term flow-through test developed at MRL/PSU. In the second test, driving pressure, flow rate and permeability were monitored during the experiment. Calculations showed that this flow-through technique simulates rain water percolation in a similar sized bed for about 25 years. The leaching fluids in both methods were deionized water (EPA procedure) and simulated rain water. Analyses for seventeen metals by DC plasma emission spectrometry and for seven anions by ion chromatography were performed. Concentrations of the leachates from the two procedures were well below the levels that define a hazardous waste. Considerable insight into the long term leaching mechanisms of various elements was obtained from the flow-through experiments.

Flowable fly ash: a new cement stabilized backfill

Cement stabilized fly ash placed at a plastic fluid consistency is a new structural backfill material that flows into place, either above or below water, without using sophisticated construction methods and procedures. This cuts cost and time. It is primarily composed of fly ash, a byproduct made available in quantity from coal burning power plants. Usually 4% to 5% of cement is added along with the appropriate amount of water for the particular application. The advantages and disadvantages of this material—which tests have shown to have qualities and economies that equal or surpass those of conventional backfill materials—are described.