Soil Fly Ash Mixtures Research Articles

Stabilizing cohesive soils with Micro- and Nano- fly ash as Eco-friendly Materials: An experimental study

Soil stabilization is a popular technique for improving soil properties and creating sustainable and green buildings using rammed earth walls. Nano materials are a new type of additive that can enhance soil performance. Laboratory tests were performed to examine the geotechnical properties of clay mixed with nano fly ash. Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray powder diffraction (XRD) were used to analyze the nature and changes of the particles before and after the grinding process. The effect of time and different dosages of nano fly ash (3%, 5%, and 7%) on the curing behavior was also investigated. The test results showed that the optimal amount of nano fly ash and fly ash added to soil was 7% by weight of soil after 28 days. This increased the unconfined compression strength of clay from 50 kPa to 410 kPa (8.2 times) and the triaxial strength of clay from 65, 80, and 90 kPa to 520, 640, and 720 kPa (8 times) respectively. The results showed that nano-fly ash as a nano soil-improvement suspension significantly improved the strength and stiffness of the soil-fly ash mixture by forming gel that filled the pores and bonded the soil particles. Nano-fly ash also acted as a nucleation site, enhancing the durability and strength of the mixture.

Environmental impact and mechanical improvement of microbially induced calcium carbonate precipitation-treated coal fly ash–soil mixture

Reuse of coal fly ash (CFA) as construction materials is one of the sustainable methods for mitigating its environmental impacts. However, the potential leaching of heavy metals and the limited effect on mechanical improvement impede the reuse of CFA. The objective of this research was to investigate the effects of environmental impact and mechanical improvement of the microbially induced calcium carbonate (CaCO3) precipitation (MICP) process on the CFA–soil mixture. Two resources of CFA, named CFA1 and CFA2, were used. CFA1 is classified as off-specification fly ash, and CFA2 is classified as class F-type fly ash. Experimental results showed that the unconfined compressive stress (UCS) of MICP-treated soil increased significantly with the addition of CFA. The MICP-treated 3% CFA1–soil mixture obtained the highest UCS of 2200 kPa, which was much higher than that of the MICP-treated soil (798 kPa). The maximum UCS of the MICP-treated 3% CFA2–soil mixture was 1398 kPa. X-ray diffraction analysis indicated that the main mineral crystal pattern present in the MICP-treated samples was calcite. Scanning electron microscopy images revealed that the formed calcium carbonate worked as a bridge to connect soil particles together, attached to the surface of soil or located in the pore side of soil particles. In addition, the batch leaching test indicated that cadmium (Cd), copper (Cu), magnesium (Mg), nickel (Ni) and zinc (Zn) were detected in the MICP-treated soil. With the addition of CFA, there was no metal exceeding the maximum contaminant level from the MICP-treated CFA1–soil mixture.

The Triaxial Test of Polypropylene Fiber Reinforced Fly Ash Soil.

Recently, soil reinforcement using arranged or randomly distributed fibers has attracted increasing attention in geotechnical engineering. In this study, polypropylene (PP) fibers with three lengths (6, 12, and 24 mm) and three mass percentages (0.5%, 1%, and 1.5%) were used to reinforce a coal fly ash soil (FAS) mixture. Unconsolidated, undrained triaxial tests were carried out in order to study the mechanical properties of the polypropylene fiber-reinforced FAS mixture and evaluate the impact of fiber on the shear strength of the FAS mixture. It is found that the fiber length of 12 mm could significantly improve the shear strength of the polypropylene fiber reinforced FAS mixture, and little effect is shown on the shear strength while using a fiber length of 24 mm. Additional fibers enhance the energy absorption capacity of the FAS specimens and therefore the highest energy absorption capacity occurs when the fiber content is 1% and the fiber length is 12 mm. The peak deviator stress enhances impressively with the addition of polypropylene fiber. The impact of fiber on the peak deviator stress is the largest when fiber content is within 1.0%. The fiber length has little effect on the peak deviator stress when it exceeds 12 mm.

Assessing the Capability of Chemical Ameliorants to Reduce the Bioavailability of Heavy Metals in Bulk Fly Ash Contaminated Soil.

In-situ rehabilitation of fly ash at dumping sites has rarely been addressed for crop production due to growth-related constraints, largely of heavy metal (HM) contamination in soils and crops. Current communication deals with a novel approach to identify a suitable management option for rejuvenating the contaminated soils. In this background, a 60-days incubation experiment was conducted with different fly ash-soil mixtures (50 + 50%, A1; 75 + 25%, A2; 100 + 0%, A3) along with four ameliorants, namely, lime (T1), sodium sulphide (T2), di-ammonium phosphate (T3), and humic acid (T4) at 30 ± 2 °C to assess the ability of different fly ash-soil-ameliorant mixtures in reducing bio-availability of HMs. Diethylenetriaminepentaacetic acid (DTPA)-extractable bio-available HM contents for lead (Pb), cadmium (Cd), nickel (Ni), and chromium (Cr) and their respective ratios to total HM contents under the influence of different treatments were estimated at 0, 15, 30, 45, and 60 days of incubation. Further, the eco-toxicological impact of different treatments on soil microbial properties was studied after 60 days of experimentation. A1T1 significantly recorded the lowest bio-availability of HMs (~49–233% lower) followed by A2T1 (~35–133%) among the treatments. The principal component analysis also confirmed the superiority of A1T1 and A2T1 in this regard. Further, A1T1 achieved low contamination factor and ecological risk with substantial microbial biomass carbon load and dehydrogenase activity. Thus, liming to fly ash-soil mixture at 50:50 may be considered as the best management option for ameliorating metal toxicity. This technology may guide thermal power plants to provide the necessary package of practices for the stakeholders to revive their contaminated lands for better environmental sustainability.

Influence of Fly Ash Addition on Behavior of Soft Clayey Soil

This paper investigates the impact of the fly Ash addition on the Geotechnical properties of soft soil as well as chooses the optimum percentage added of fly ash. To understand the behavior of fly ash mixed with soil, a number of laboratory experiments testing conducted on clayey soil-fly ash mixture in several percentages (5,10,15,20,25, and 30%) as Atterberg test, Specific gravity test, compaction test, California Bearing Ratio (C.B.R) Test, Unconfined Compressive Strength (UCS) Test, Consolidation Test. Test results indicate rising in plastic limit and liquid limit as fly ash adding. Specific gravity decreased essentially by adding fly ash. Whereas there was falling on the Dry unit weight value with the contract to the decreasing in the water content. The CBR and UCS values were increased with increasing fly ash content. 20% was the optimum fly Ash content. This study also benefits the effective use of fly ash and thus a cost-effective method for improving the soil properties.

Effect of incorporating multifilament polypropylene fibers into alkaline activated fly ash soil mixtures

Soil stabilization is a well-known methods for the treatment problematic soils. Its advantages over soil replacement include low cost and fast implementation. The alkaline activation of soft soils is a new technique that has been proposed recently to stabilize soft soils. However, its strengthening mechanism and the final product in terms of stiffness and brittleness resemble those observed in cemented soils. In other words, the residual strength which emerges when approaching failure is very low, and this results in immediate damage to building structures. These shortcomings need to be overcome, particularly in places where seismic loading can be expected. In the case of cemented columns under heavy embankments, horizontal displacement is likely to occur under seismic loading. This will result in the failure of stabilized material due to frail bending moments, making greater residual strengths more important than higher peak strengths. To address this problem, a fix fly ash content of 40% and polypropylene fibers in the range of 0.5%, 0.75%, 1%, and 1.25% were considered. Compressive, flexural and indirect tensile strength test results revealed the feasibility of polypropylene fibers to improve post-peak behavior, thus allowing for higher residual strength after failure.

Effects of inorganic ions, organic polymers, and fly ashes on the sedimentation characteristics of kaolinite suspensions

The effects of inorganic ions, organic polymers, and fly ashes on the sedimentation characteristics of kaolinite suspensions, which include the particle associations, sedimentation mode, initial settling rate, final sediment height, and soil formation time, were systematically investigated through the batch sedimentation tests. The addition of salt and polymers were found to change the microfabrics of kaolinite and influence the sedimentation modes and settling rate of kaolinite suspensions. Due to the effects of charge neutralization and polymer bridging, cationic polymers such as cationic polyacrylamide (CPAM) and chitosan were found to facilitate flocculatation and aggregation of kaolinite, therefore, increased the settling rate and decreased the final sediment height. On the other hand, anionic polymers, for example, the polyacrylic acid (PAA), was found to relatively delay the process of settling and prolong the soil formation time due to the pseudoplastic nature and large repulsive forces among negatively charged polymers and negatively charged kaolinite particles. Fly ash hydration increased the ionic strength, which changed the the kaolinite from dispersed free settling to flocculated zone settling. In addition, fly ash particles were found to collide with the kaolinite particles during settling and form large agglomerates, therefore the settling rate of fly ash-soil mixture increased with the addition of fly ashes.

Experimental Investigation of Mechanical Behaviors of Fiber-Reinforced Fly Ash-Soil Mixture

In recent years, applications of different types of solid waste in fiber-reinforced soil are developed to improve the strength of soil. This study presents an experimental investigation of mechanical properties of polypropylene fiber-reinforced fly ash-soil mixtures. A series of direct shear tests and unconfined compression tests were carried out. The effects of fly ash content and fiber content on compaction characteristics, shear strength, strength parameters, and unconfined compressive strength of the reinforced soil are investigated and discussed. Results reveal that when the fly ash content of the specimen exceeds 20% and the curing period exceeds 14 days, specimens become more brittle in the unconfined compression tests. It can be deduced that 30% fly ash and 1% fiber provide the optimum content, and the inclusion of fiber reinforcement has positive benefits on the mechanical properties of the reinforced soil to a certain extent.

Alkaline Activation of Clayey Soil Using Potassium Hydroxide & Fly Ash

In this paper the potential of introducing alkali activated fly ash to a clayey soil as stabilizing agent was investigated. As alkaline activator Potassium hydroxide of 12 M was introduced to the soil fly ash mixtures. Unconfined compressive strength tests were carried out. Four different fly ash/solid ratios were proposed to be 10 %, 20 %, 30 % and 40 % at two curing regimes of 7 & 28 days. The greatest unconfined compressive strength was of 40 % mixture recorded at 3.68 Mpa after 28 days. Microstructural analyses including SEM, EDS and FTIR were conducted to detect and confirm gel formation. Alkaline activation of clayey soil using KOH solution as an activator proved to be a feasible alternative for soft soil stabilization.

Investigation of Strength Parameters of PVA Fiber-Reinforced Fly Ash-Soil Mixtures in Large-Scale Direct Shear Apparatus

Soil reinforcement is an old and still efficient technique in improving soil strength and stiffness properties. Current paper aims at quantifying the effects of different inclusions on mechanical behavior of fiber-reinforced cemented soil. An experimental program was conducted to study simultaneous effects of randomly oriented fiber inclusions and cement stabilization on the geotechnical characteristics of fly ash-soil mixtures. Chamkhaleh sand, polyvinyl alcohol (PVA) fiber, cement and fly ash with some water were mixed and compacted into large scale direct shear apparatus with three equal layers. PVA fibers were randomly distributed in three compacted layers at predetermined weight contents. Direct shear tests were carried out on fly ash-soil specimens prepared with different cement, fly ash and polyvinyl alcohol contents, and 7 different curing periods. Results show that cement increases the strength of the raw fly ash-soil specimens. The fiber inclusion further increases the strength of the cemented and uncemented soil specimens and transforms their brittle behavior to ductile behavior. The fiber reinforcement and distribution throughout the entire specimen results in a significant increase in the strength of fly ash -soil- cement mixtures.

Study on Strength Behavior of Organic Soil Stabilized with Fly Ash.

The aim of this study is to investigate the effect of fly ash on the consistency, compactness, acidic properties, and strength of organic soil. The presence of organic content in the soil has detrimental impacts on the physical and strength behavior of soil. To investigate the effectiveness of fly ash in the stabilization of organic soil, two types of fly ashes (Type I and Type II) at different percentages were used. It is found that fly ash significantly reduces the plasticity index of the organic soil, whereas the liquid and plastic limits increase. The dry density of the fly ash-soil mixture increases significantly, while the water requirement reduces due to the addition of fly ash. The increase of dry density compromises higher strength. The increase of qu with the increase of fly ash content is mainly due to the pozzolanic reaction of fly ash, although the reduction in water content results from the addition of dry fly ash solid. Moreover, Type I fly ash contributes a higher value of qu compared to Type II fly ash. This is attributed to the characteristics of fly ash including CaO and CaO/SiO2 ratio.

Prediction of Consolidation and Shear Behavior of Fly Ash–Soil Mixtures Using Mixture Theory

AbstractFly ash is the most generated coal combustion by-product (CCP) and causes the most substantial disposal issues. The current practice of landfilling these materials is costly and ultimately ...

Evaluation of Cohesive Soil Mixed With Fly Ash and Reinforced With Nylon Fibre

Black cotton soil is a expansive soil. And mostly found in Vidarbha region of Maharashtra, this soil is highly unstable and it should be stabilize for carry out construction work. Materials like fly ash, rise husk, nylon fiber are used to make soil stable. Addition of such material will increase the physical, chemical and engineering properties of soil. Some of the properties which are improved are CBR value, shear strength, liquidity index, plasticity index, unconfined compressive strength (UCS) and bearing capacity, etc. The main objective of this study was to evaluate the effect of fly ash in stabilization of Black cotton soil. Mainly UCS and other properties of soil were calculated. The tests were conducted on Soil-Fly Ash mixtures, by increasing the Fly Ash percentage in Black cotton soil like 25%, 50%, 75%, and 100%, and then the soil was tested on Soil-Fly Ash - Fibre mixture by adding the fiber in increasing order like 0.5%, 1%, 1.5%. Results were obtained for mixed proportion of 75% soil and 25% fly ash which has unconfined compressive strength of 173 KN/m2. And by adding 1% of nylon fiber in same proportion of soil – fly ash the unconfined compressive strength increased to 243.12 KN/m2. Increase in UCS value can help in reducing the thickness of earthen roads and pavements and increase the bearing capacity and shear strength of soil. With analysis of results it was found that the fly ash along with nylon fiber has good potential to be used as an additive for improving engineering properties of expansive soil.

NUMERICAL MODELING OF CALIFORNIA BEARING RATIO VALUE OF FIBRE REINFORCED FLY ASH STABILIZED EXPANSIVE SOIL

nExpansive soils causing significant damage to civil engineering structures. It has become a worldwide problem. In United States during 1973, the annual cost of damage was $2.3 billion due to expansive soil movement. A more up-to- date it has reached up to $9 billion annual damages to different structures. This paper presents experimental study of California bearing ratio values of soil-fly ash mixtures and randomly distributed Nylon fibres. The effect of addition of Nylon Fibres on California bearing ratio values (CBR) is studied. The percentage of HT Nylon 66 Fibres content is considered as 0.25 %, 0.75% and 1.25 % by stabilize soil- fly ash mixtures. Samples were cured in the laboratory under controlled conditions with optimum moisture content (OMC) and maximum dry density (MDD). The mathematical modelling is done to correlate California bearing ratio values with different parameters. The model is adequately useful to predict the strength. Adequacy has been tested by conducting different verification experiments on the developed model. It is found that difference of predicted and observed value is lying within 10%.

Development of a Test Procedure for Freeze-Thaw Durability of Geomaterials Stabilized With Fly Ash

Abstract The objective of this research was to develop a freeze-thaw cycling test procedure and to investigate how the volume, moisture content, resilient modulus (Mr), and unconfined compressive strength (qu) of geomaterials, including soils and recycled materials, stabilized with fly ash change after freeze-thaw cycling. Three different types of materials (fine-grained and coarse-grained soils and recycled pavement materials) and five different fly ashes were used at different percentages (10, 12, 14, and 20 % by dry weight). Both one-dimensional and three-dimensional freezing of the specimens were considered. Freezing in three-dimensional was faster in terms of completing the freeze-thaw cycling and provided very similar results to the ones prepared in one-dimensional. Thus, three-dimensional freezing was adopted in this study without access to water (i.e., closed system). The results of this study indicated that the volume of all soil-fly ash mixtures tended to increase after freeze-thaw cycling; however, the volume change was not significant. Resilient modulus tests were conducted on all unstabilized materials, as well as on their mixtures with fly ash, while qu tests were conducted only on fine-grained soil and their fly ash mixtures. The Mr of all mixtures with one exception decreased by an average of 28.5 % when specimens were subjected to freeze-thaw cycling. The drop in the Mr of the specimens leveled off after 5 freeze-thaw cycles. A general trend of higher Mr of materials stabilized with fly ash (from 3 to 168 %), even after freeze-thaw cycles compared to unstabilized material was observed. In general, a reduction in unconfined compressive strength (qu) after freeze-thaw cycles up to 70 % was obtained. However, results showed that qu of stabilized soils that were subjected to freeze-thaw cycles were still higher (from 6 to 157 %) than the qu of unstabilized soils.

Engineering behavior of clay soils stabilized with class C and class F fly ashes

Abstract Damages and economical losses due to problematic soils have caused researchers to conduct many studies for the stabilization of these soils within years. Especially, the use of fly ashes in soil stabilization provides great benefits in contributing to the economy, as well as decreasing the environmental pollution. In the present study, the stabilization characteristics of soil-fly ash mixtures were evaluated in terms of Atterberg limits, compaction characteristics, swell potential and unconfined compressive strength with curing effect. To determine these effects, Catalagzi and Soma fly ashes obtained from Turkey were used in different proportions by weight for stabilization of clay soil samples. It was found that the plasticity index of the soils decreased considerably with the addition of fly ashes, while the strength improved and swell potential decreased. The decreasing trend in the swell percentage and swell pressure values decelerated especially after 25% fly ash additive content and negligible changes occurred. Similar behavior was observed in strength tests. Experimental results show that swelling and strength properties of the soils could be improved by using fly ash and Soma fly ash is far more effective than Catalagzi fly ash.

Influence of burnt ash additives on stabilisation of soft clay soils

Abstract This paper discusses the results of the improvement in compaction, consolidation and shear strength parameters of soft clay when stabilised with burnt ash additives those derived from a furnace in the thermal power industry. Different combinations of soil–ash mixtures are prepared with the addition of ash in the range of 10–40 % by weight of soil to arrive the optimum dosage of ash which one exhibiting maximum UCS. Herein the ash additives including both the fly ash and bottom ashes are used as the stabilising agents. The influence of curing time is also studied on UCS strength property of various soil combinations. Results indicate that the stabilisation of soft clay with ash additives is improving the UCS up to certain level of ash amounts, and further the strength is decreased. The strength of soil–fly ash mixture is much more than the strength of soil–bottom ash mixture, and it was found to be 4.86 times the strength of soft clay. The mixing of ash additives in the soil could lead to speed up the time required to consolidate the clay soil and become more permeable.

Enhanced series-parallel model for estimating the time-dependent thermal conductivity of fly ash soil mixtures

An enhanced series-parallel (S-II) model of one-dimensional conductive heat flow through a unit cell was developed to estimate the time-dependent thermal conductivity of Class C fly ash stabilized soils. The unit cell is composed of three separate heat flow paths: a continuous path through solid contacts (soil contacts, fly ash contacts, and soil fly ash contacts) in parallel arrangement, a series-parallel path of solids in a series arrangement with a parallel arranged path of solid-miniscule pores (miniscule portion of solid water and miniscule portion of solid air), and a continuous path through water and air in parallel arrangement. The solid-miniscule pores volume fraction and the fluid/air volume fraction changes during pozzolanic reaction were modeled by estimating the interparticle pore water consumption rate. In addition, the time-dependent thermal conductivity characteristics of the fly ash soil mixtures were investigated by conducting experimental tests. Based on the test observations and parametric analysis, interparticle voids, fly ash percentage and degree of cementation, volume change of the interparticle liquids, and curing time were all found to play critical roles on the effective thermal conductivity of fly ash soil mixtures. The predicted thermal conductivity using the enhanced S-II model was compared with the experimental test data with good agreement, suggesting that the enhanced S-II model is a robust tool for estimating the global effective thermal conductivity of Class C fly ash stabilized soils.

Geochemical Analysis of Leached Elements from Fly Ash Stabilized Soils

AbstractLeaching controlling mechanisms of As, Ba, Ca, Cd, Mg, Se, and Sr from soil alone, fly ash alone, and soil-fly ash mixtures were investigated at a pH range of 1.5–14 through geochemical modeling. Results of the pH-static tests from previous studies indicated that As and Se concentrations increased at alkaline conditions, while Ca, Cd, Mg, and Sr concentrations increased when the pH of the aqueous solutions were acidic. Leaching of Ba tended to increase slightly at alkaline pH values. Effluent pH, oxidation-reduction (i.e., redox) potential Eh, and element concentrations measured from pH-static tests were used as input data in the geochemical model. Geochemical modeling results indicated that release of the elements, except As and Se, are controlled by the dissolution and precipitation of oxide, hydroxide, sulfate, and carbonate solids of the elements. For a given element, these solids controlling the leaching of elements were very consistent regardless of soil and fly ash types. Model-based predic...

Compaction and strength characteristics of fly ash and fiber amended clayey soil

An experimental program was undertaken to investigate the effects of discrete polypropylene fibers and Class C fly ash on the stress–strain and shear strength behavior of clayey soil. Two types of fiber (fibrillated polypropylene fiber and multifilament polypropylene fiber) in two different lengths (6.0mm and 19.0mm) and two fiber dosages (i.e. 0.5% and 1.0% by dry weight of soil) were considered. At first, compaction characteristics of the untreated soil and seven different fly ash–soil mixtures (2.5%, 5.0%, 7.5%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were evaluated at standard compaction energy. Considering compaction characteristics, unconfined compression tests of untreated soil and five different fly ash–soil mixtures (5.0%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were carried out after 1-, 7-, 14-, 28- and 90-day curing periods. According to the obtained test results, untreated soil and two different fly ash–soil mixtures (i.e. 10.0, and 30.0% by dry weight of soil) were mixed with fibrillated polypropylene fiber and multifilament polypropylene fiber in two different lengths and in two different fiber dosages, separately. A total of 17 different fiber–fly ash–soil mixtures were composed, and their unconfined compression tests were carried out after 28-day curing period. According to unconfined compression test results, 6 different fiber–fly ash–soil mixtures were selected for UU triaxial tests at the end of 28-day curing period. The obtained test results indicated that the effect of fly ash content on the stress–strain behavior is superior to the effect of fibers. The post-peak strength behavior is strongly affected by fiber type, length and dosage. The magnitude of the effect increases as the fly ash content increases. Inclusion of fiber alone without fly ash decreases unconfined compressive strength (UCS) of the compacted fiber–clay mixtures. On the other hand, when combined with fly ash, fiber inclusion increases UCS depending on fiber type, length and dosage. Moreover, for both fiber types and fiber lengths, the higher the dosage of fiber, the higher the UCS is. The increase in UCS becomes as much as 218% for 30% fly ash content and 1.0% 19mm long fibrillated polypropylene fiber.