Pure Fly Ash Research Articles

Compensating for Concrete Shrinkage with High-Calcium Fly Ash

Shrinkage of concrete during hardening is a serious problem in attempts to maintain the integrity of concrete structures. One of the methods of combating shrinkage is compensating for it using an expansive agent. The purpose of this work is to develop and study an expanding agent to concrete, including high-calcium fly ash and calcium nitrate as an expansion activator. The content of Ca(NO3)2 can be used to regulate the degree of expansion of the additive itself during hydration and, accordingly, to control shrinkage, thus obtaining shrinkage-free or expanding concrete. Shrinkage–expansion deformations of concrete can also be regulated by the amount of expanding additive replacing part of the cement. With the Ca(NO3)2 content of fly ash being 10% or more, concrete experiences expansion in the initial stages of hardening. The transition of deformation through 0 to the shrinkage region occurs depending on the composition and content of the additive after 8–15 days of hardening. It has been established that replacing cement with pure fly ash with a curing period of 90 days or more has virtually no effect on the strength of concrete, either in bending or in compression. The use of an expanding additive containing 5–15% Ca(NO3)2 reduces the strength of concrete by an average of 9%, despite the fact that calcium nitrate is a hardening accelerator.

Low-carbon high-strength engineered geopolymer composites (HS-EGC) with full-volume fly ash precursor: Role of silica modulus

In this study, the influence of the silica modulus of alkaline activators on the overall performances of pure fly ash (FA)-based High-Strength Engineered/Strain-Hardening Geopolymer Composites (HS-EGC/SHGC) was comprehensively studied. The developed HS-EGC successfully presented simultaneous high compressive strength (over 90 MPa) and high tensile ductility (over 6.0 %) for the first time. Tensile strain-hardening and over-saturated cracking phenomena were observed for all the HS-EGC mixes. It was found that the increase of the silica modulus from 1.0 to 2.0 reduced the tensile strength and strain energy density of HS-EGC, but the most distinguished overall mechanical index was achieved in the mix with the silica modulus of 1.5. Additionally, the underlying mechanism behind the mechanical performances was explored by Back Scattering Electron and Energy Dispersive Spectroscopy (BSE-EDS) tests. According to the data comparison from literature review, the good sustainability and market potential of the developed material were successfully demonstrated, and the developed HS-EGC pushed the performance envelope of pure FA-based EGC materials. The findings could help promote the future development and practical applications of this strain-hardening geopolymer material with both good sustainability and high mechanical performances.

Smart composite based on fly ash cenospheres and transformer oil with switchable electrical conductivity

Fly ash cenospheres serve as an inexpensive filler for various composites. Coating their surface with metal significantly alters the properties of the resulting composites. In this study, aluminosilicate cenospheres receive a copper coating using a plasma method with magnetron sputtering. Based on these copper-coated cenospheres, composites are created, and their dielectric properties are investigated in a parallel plate capacitor cell under isotropic pressures ranging from 1 to 75 atm. Composites based on pure fly ash cenospheres exhibit pressure-invariant properties, including the dielectric constant and loss factor. However, for composites based on copper-coated fly ash cenospheres, an abrupt increase in electrical conductivity is observed as the pressure increases. Interestingly, significant changes in electrodynamics characteristics are not detected under the influence of anisotropic stress. The methodology tested in this work can be utilized for creating smart materials based on cenospheres.

Preparation and mechanism of fly ash based composite fillers with different morphologies and its application in filling polyamide 6

In order to realize the high value-added utilization of coal-based solid waste fly ash (FA) and enhance the performance of polyamide 6 (PA6), three kinds of core-shell structure FA-based composite fillers with different shell morphologies (nano-flake, spherical and rod-like particles) were prepared using FA as raw material, MgSO4, MgCl2, Mg(NO3)2 and NaOH as coating agents, which were noted as composite powder 1 (CP1), composite powder 2 (CP2) and composite powder 3 (CP3). The specific surface areas were enhanced to 97.41, 58.59 and 20.21 m2 g−1 from 1.71 m2 g−1 (FA), while the corresponding pore volumes were increased from 0 to 0.31, 0.22 and 0.06 cm3 g−1. Si-O-C-O-Mg and Si-O-Mg-OH bonds were formed between Si-O-Si, Si-O bonds on the surface of FA and hydrated MgCO3 (MCH), Mg(OH)2 (MH). Three types of CPs were filled into PA6, respectively. After filling, CP2 caused silver grain effect when the material was damaged, which had better toughening effect on the matrix. Compared with pure PA6, the limiting oxygen index of pure MH, FA, CP1, CP2, and CP3 increased by 0.60, 0.70, 1.30, 2.30 and 4.10%, respectively. The thermal deformation temperature was increased by 29.10, 46.20, 53.70, 31.90 and 42.00°C respectively. The melting index decreased by 1.05, 0.70, 0.49, 0.17 and 0.47 g/min, respectively.

Converting industrial waste into valuable Zn2SiO4/SiO2 nanosheets for highly effective organic dye removal

As a common industrial waste, fly ash is conventionally used as a concrete additive, resulting in the wastage of silicon and aluminium materials and environmental pollution. In this study, we innovatively utilize fly ash waste to synthesize Zn2SiO4/SiO2 nanosheets, which are employed as effective adsorbents for purifying organic dyes such as methylene blue, rhodamine B, and congo red. The Zn2SiO4/SiO2 nanosheets, with a large specific surface area of approximately 81.21 m2 g−1, exhibit enhanced adsorption capacity for organic dyes, in contrast to pure fly ash with a specific surface area of only ∼1.06 m2 g−1. Notably, the Zn2SiO4/SiO2 nanosheets demonstrate a remarkable adsorption capacity of 124.50 mg g−1 for methylene blue, which is ∼120 times higher than pure fly ash. The adsorption kinetics are analyzed using Langmuir and Freundlich models, shedding light on the adsorption mechanism of the Zn2SiO4/SiO2 adsorbent. This study presents an efficient ‘waste-to-treasure’ approach, advocating for the secondary utilization of industrial waste to alleviate environmental pollution.

In Situ Synthesis of Zeolites in Solidified Fly Ash/Cement Matrices with High Na Content: Products, Pore Structure, and Leaching Behavior

Due to its high retention capacity and well durability, fly ash-based geopolymers rich of zeolites are considered to be potential solidified materials for low- and intermediate-level radioactive waste stream. This study mainly focused on the phase transformation, pore structure, and leaching characteristic of Sr2+ and Cs+ in solidified fly ash/cement matrices under different sodium hydroxide contents or sodium nitrate concentrations after thermal curing of 28 d. The results obtained from the experiments indicated that the geopolymers prepared from pure fly ash had the potential to transform into ordered structures at high temperatures of 90°C instead of room temperature, such as Na-P1 zeolite and chabazite. With the increase in sodium hydroxide contents, more sodium nitrate participated in the reaction to form a zeolite phase in solidified fly ash/cement matrices, while the coexistence phenomenon of chabazite and Na-P1 zeolite appeared under the condition of high sodium hydroxide contents of more than 5%. Just a proper number of zeolites can effectively inhibit the leaching of radionuclides Sr2+, as too many zeolites would lead to the increase in porosity, which was harmful to the retention of radionuclides. Solidified fly ash/cement matrices at a sodium hydroxide content of 5% or at a sodium nitrate concentration of 300 g/L obtained the lowest cumulative leaching fraction of Sr2+. Moreover, sodium hydroxide increased the cumulative leaching fraction of Cs+ which reversely decreased significantly with the increase in sodium nitrate concentrations.

Cyclic resistance of fly ash influenced by anisotropic stress condition, sand contents, and gravel content

A series of cyclic triaxial tests were performed to study the effect of anisotropic stress, sand content (in a fly ash-sand mixture), and addition of gravel on the cyclic resistance of fly ash. The results indicated that the failure mode of pure fly ash in the presence of isotropic stress was cyclic mobility and that the cyclic resistance of pure fly ash was significantly lower than that of clean Nakdong River sand for given test conditions. The cyclic resistance of pure fly ash decreased when the effective confining stress increased from 100 to 200 kPa, as expected. The failure of pure fly ash conducted in the absence of stress reversal was due to the initial axial strain accumulation and subsequent sudden runaway deformation, and this failure mode differed dramatically from that of fly ash conducted under symmetrical stress reversal. An increase in the anisotropic ratio resulted in a decrease in the cyclic resistance of pure fly ash. Nakdong River sand and gravels were added to pure fly ash and it was examined whether the cyclic resistance of fly ash increased. Addition of sand was observed to decrease the cyclic resistance for 10% and 20% sand content by volume, regardless of the amount of increase in the dry density of the samples. Furthermore, the cyclic resistance of fly ash-gravel mixtures was greater than that of pure fly ash by approximately 17%.

Synthesis and characterization of geopolymeric refractory bricks using blends of indigenous fly ash and metakaolin

High sintering temperature, is required for the production of refractory bricks which is an energy-intensive operation and utilizes expensive raw material. Geopolymerization is a chemical process that produces a class of inorganic binders of geopolymers. This technique is an energy efficient technique for the geopolymer refractory bricks (GPRB) synthesis because it utilizes low sintering temperature and uses raw material such as fly ash (FA) and metakaolin (MK) which is more economical as compared to conventional raw materials for refractory bricks. As the FA has a high thermal resistance and is available as abundant waste while the metakaoline possesses high compressive strength compared to the FA. In the current study, GPRB were prepared through geopolymerization by blending FA and metakaolin in different weight percents. The six samples have been designed and prepared with various compositions of FA and metakaoline. The compressive strength and thermal conductivity for pure metakaoline based GPRB were 24.15 MPa and 0.78 W/mK, respectively at 28 days, while these were 3.06 MPa and 0.54 W/mK for pure FA based at room temperature. By increasing the amount of FA in the samples increases the thermal resistance, however it reduces the compressive strength of the samples. The optimum blending ratio can be selected for different applications according to the minimum mechanical strength requirements with the desired thermal resistance considering the synthesis of specific refractory.

Effects of ladle slag on Class F fly ash geopolymer: Reaction mechanism and high temperature behavior

Due to its low hydraulic reactivity, ladle slag is currently underutilized with nearly 80% of annual generation is either landfilled or dumped. This work investigates the joint activation of LS with Class F fly ash, and the impact of ladle slag on fly ash geopolymer with the focus on activation, hydrates assemblage, conversion process, and thermal behavior. Results reveal that the unique reaction process of ladle slag in alkali activation system shows a positive influence on fly ash geopolymers. Within an alkaline system rich in soluble Si, the initially hydrated CAH phases transform into C-A-S-H, which not only hinders the conversion and enhances the mechanical strength but also retains the geopolymerization. The hybrid geopolymer system exhibits superior thermal performance to pure fly ash geopolymers, especially under high temperature exposure. With increasing ladle slag substitution, more stable crystalline phases are formed at high temperatures. After 800 °C exposure, a high residual compressive strength of 64.7 MPa is achieved with 25 wt% ladle slag addition compared to 55.2 MPa in pure fly ash geopolymers.

Resistance of blended alkali-activated fly ash-OPC mortar to mild-concentration sulfuric and acetic acid attack.

The traditional cementitious product is prone to suffer from a high degree of deterioration in the case of exposure to acid solutions because of the decomposition of the binder network. However, the degradation of concrete structures in service by mild concentrations of acid under conditions involving sewage, industrial waters, and acid rain is more common and results in a significant environmental problem. The utilization of alkali-activated materials has been seen to potentially offer an attractive option with regard to acceptable durability and a low carbon footprint. With the aid of visual observation, mass loss, compressive strength tests, X-ray diffraction, Fourier transform infrared spectroscopy, and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, the acid resistance of alkali-activated fly ash mortars in which the precursor was partially replaced (0-30% by mass proportion) with ordinary Portland cement (OPC) was evaluated after 180 days of exposure to mild-concentration sulfuric and acetic solutions (pH = 3). A conventional cement mortar (100% OPC) was used as a reference group. The results demonstrate that the addition of OPC into the alkali-activated system causes a significant increase in compressive strength (around 16.08-36.61%) while showing an opposite influence on durability after acid attack. Based on a linear mean value and nonlinear artificial neural network model simulation, the mass losses of the specimens were evaluated, and the alkali-activated pure-fly ash mortar demonstrated the lowest value (i.e., a maximum of 5.61%) together with the best behavior in the aspect of discreteness at 180 days. The results from microstructure analysis show that the coexistence of the N-A-S-H and C-S-H networks in the blend system occurred by both OPC hydration and FA. However, the formation of the gypsum deposition within the fly ash-OPC blend systems at sulfuric acid was found to impose internal disintegrating stresses, causing a significant area of delamination and cracks. In addition, alkali metal ion leaching, dealumination, as well as the disappearance of some crystalline phases occurred in specimens immersed in both types of acids.

Crack formation behavior of composite fly ash – bentonite (FAB) in landfill liner system

This study aims to investigate the influence of different mixtures on the phenomenon of desiccation cracking in bentonite-fly ash mixtures as a landfill liner system. Fly ash is quite potential to be used as a landfill liner mixture because it has a low hydraulic permeability or conductivity value. This study uses class F fly ash from the Paiton power plant production process, Indonesia, which has been distributed commercially. Desiccation test was conducted in this study. The composition of fly ash and bentonite which is used are pure fly ash (FAB0), fly ash and bentonite 15% (FAB15), fly ash and bentonite 20% (FAB20) and fly ash and bentonite 25% (FAB25). The smallest CIF value is found in the pure fly ash layer. However, the pure fly ash cannot be used as landfill liner because the high permeability value. Therefore, the addition of bentonite will increase the possibility of crack formation. This study reveals that the addition bentonite in the fly ash composite will increase the crack. However, determining appropriate mixture composition is critical when working on the landfill liner system.

Evaluation of flexural properties and characterisation of 10-mm thin geopolymer based on fly ash and ladle furnace slag

The formulation and flexural properties of thin fly ash geopolymers with thickness of merely 10 mm and replacement of ladle furnace slag to fly ash in thin geopolymer were presented. The formulation was discussed in terms of NaOH molarity, solid aluminosilicates-to-liquid alkali activator (S/L) mass ratio, and alkali activator (Na 2 SiO 3 /NaOH) mass ratio. Thin fly ash geopolymers with flexural strength and Young's modulus of 6.2 MPa and 0.14 GPa, respectively, were obtained by using 12 M NaOH, S/L ratio of 2.5 and Na 2 SiO 3 /NaOH ratio of 4.0. A high Na 2 SiO 3 /NaOH ratio was implemented for thin geopolymer synthesis to produce a more viscous slurry which helped to retain the shape of a thin geopolymer. The incorporation of ladle furnace slag up to 40 wt.% reported an increment of 26% in flexural strength up to 7.8 MPa as compared to pure fly ash geopolymers and the stiffness was increased to 0.19 GPa. Denser microstructure with improved compactness was observed as the ladle furnace slag acted as the filler. New crystalline phases of calcium silicate hydrate (C–S–H) were formed and coexisted with the geopolymer matrix, which consequently enhanced the flexural strength of thin fly ash geopolymer. This proved that the ladle furnace slag has the potential to be utilised in geopolymer synthesis and will enhance the flexural properties of thin geopolymers. The flexural performance of thin geopolymers in this study was considerably good as the thin geopolymers exhibited comparatively similar flexural strengths, but a higher strength/thickness ratio as compared to geopolymers with thickness greater than 40 mm.

Development of artificial one-part geopolymer lightweight aggregates by crushing technique

The production method of geopolymer lightweight aggregates (GLAs) is explored in this study through crushing technique, which has a good prospect for massive industrial production. Geopolymer cubes with the dimension of 100 mm × 100 mm × 100 mm were firstly produced using one-part geopolymer technology and then crushed into coarse aggregates with angular shapes. Coal fly ash (FA), ground granulated blast-furnace slag (GGBS) and anhydrous sodium metasilicate particles in industrial grades were utilized for the one-part geopolymer in this study. Results showed that the produced GLAs with different mixes were all lightweight with a loose bulk density below 800 kg/m3 and an apparent density of 1450–1750 kg/m3. The produced GLAs were further used as coarse aggregates to produce geopolymer aggregate concrete (GAC). It was found that for GLAs, the increase in alkalinity and the addition of GGBS resulted in a higher one-day compressive strength, which would make better aggregate shapes, but need higher crushing energy and might cause initial damage to the aggregates. The highest cylinder compressive strength was obtained in GLAs with pure fly ash as the precursor and the activator to precursor ratio of 14%. However, the highest compressive strength of geopolymer aggregate concrete (GAC) was obtained using GLAs with 20% GGBS addition and the activator to precursor ratio of 12% although the cylinder compressive strength of this type of aggregates was not the highest. It was found that the addition of GGBS in GLAs resulted in stronger aggregate-matrix interface in GAC. Finally, the embodied carbon and material cost of GLAs were analyzed. The findings in this study are useful for future production and application of GLAs in concrete industry.

Development of low-calcium fly ash-based geopolymer mortar using nanosilica and hybrid fibers

Fly ash has been widely explored in alkali-activated concrete technology as a precursor; however, it suffers sudden brittle failure and requires heat activation for early-strength development. Previous studies have demonstrated that these shortcomings can be overcome by adding nanosilica and various types of fibers. However, they were mainly focused on improving the mechanical properties, but there is no clear understanding of the durability and microstructural changes. Therefore, this study systematically addresses the effects of nanosilica sol and hybrid fibers (steel and polypropylene fibers) on the workability, porosity, flexural/compressive strength development, flexural toughness, crack resistance, and durability (subjected to sulfuric acid of pH = 1, 5% sodium sulfate, and 3.5% seawater attacks) of fly ash-based mortars cured at ambient environments. The results demonstrate that nanosilica and hybrid fibers have acceptable simultaneous effects on the properties of mortar. Although they both reduce fluidity, nanosilica improves the pore enlargement caused by fiber materials; thus, it greatly improves the mechanical properties of mortar. The flexural toughness of the mortar with nanosilica and hybrid fibers was approximately 200% higher than that of the pure-fly ash. Only approximately 58.25 mm2 microcracks were observed during the early crack detection, and the residual strength also improved under chemical solution attack. The microstructures were studied by field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction/Rietveld method, and nanoscale 3D X-ray microscopy. The nanosilica enhanced the reactivity of the precursors and refined the pore structure of the mortar due to the changes in the crystalline and amorphous phases, and the hybrid fibers produced composites with good internal characteristics and strong fiber/matrix interfacial bonding.

Fly Ash Utilisation in Mullite Fabrication: Development of Novel Percolated Mullite

Fly ash is an aluminosilicate and the major by-product from coal combustion in power stations; its increasing volumes are major economic and environmental concerns, particularly since it is one of the largest mineral resources based on current estimates. Mullite (3Al2O3·2SiO2) is the only stable phase in the Al2O3-SiO2 system and is used in numerous applications owing to its high-temperature chemical and mechanical stabilities. Hence, fly ash offers a potential economical resource for mullite fabrication, which is confirmed by a review of the current literature. This review details the methodologies to utilise fly ash with different additives to fabricate what are described as porous interconnected mullite skeletons or dense mullite bodies of approximately stoichiometric compositions. However, studies of pure fly ash examined only high-Al2O3 forms and none of these works reported long-term, high-temperature, firing shrinkage data for these mullite bodies. In the present work, high-SiO2 fly ashes were used to fabricate percolated mullite, which is demonstrated by the absence of firing shrinkage upon long-term high-temperature soaking. The major glass component of the fly ash provides viscosities suitably high for shape retention but low enough for ionic diffusion and the minor mullite component provides the nucleating agent to grow mullite needles into a direct-bonded, single-crystal, continuous, needle network that prevents high-temperature deformation and isolates the residual glass in the triple points. These attributes confer outstanding long-term dimensional stability at temperatures exceeding 1500 °C, which is unprecedented for mullite-based compositions.

Designing of a nanoscale zerovalent iron@fly ash composite as efficient and sustainable adsorbents for hexavalent chromium (Cr(VI)) from water.

The present study encompasses a unique concept involving the formation of core-shell particles with surface-activated fly ash (FA) as core and nanoscale zerovalent iron (nZVI) particles as shell, which not only imparts high adsorption efficiency for Cr(VI) but also contributes to fruitful utilization of FA while overcoming the drawbacks associated with ZVI nanoparticles (aggregation, rapid oxidation and less durability). The otherwise inert surface of FA has been modified and activated to achieve a uniform and stable layer of nZVI over FA. The functionalized particles were studied using FE-SEM/EDAX, HR-TEM, XRD and FT-IR studies for its physical, functional and morphological characteristics. The results indicate the strong adsorption ability of nZVI@FA particles, with 100% removal efficiency within 10 min at low initial concentrations of Cr(VI), which is appreciably higher than that of pure fly ash (26%) after 60 min of reaction. Besides, the so-formed structure of composite aids to improve its life, as the synthesized nZVI@FA particles could be efficiently regenerated and reused up to 5 subsequent adsorption-desorption cycles, which is in contrast with the ability of fly ash considering its low desorption potential. Hence, the composite material proves to be an effective and sustainable alternative for treatment of a waste using a waste.

An integrated approach combines hydrothermal chemical and biological treatment to enhance recycle of rare metals from coal fly ash

Coal fly ash rich in rare metals accounts for a large amount of solid waste released from coal-fired power plants. However, rare metals, the components of coal fly ash with the highest economic value, are not fully recycled due to the lack of an effective, low-cost approach. Therefore, it is urgent to develop a new approach, aiming at increasing the recycling efficient, decreasing the cost and strengthening the high economic value of fly ash. Here, we developed an integrated approach combines hydrothermal chemical treatment process (HTCP) and biological leaching process (BLP) to improve recycle of rare metals from coal fly ash. The results showed that the one-step bioleaching method could obtain more kinds of rare metals and dramatically improve bioleaching rate after hydrothermal-alkali treatment (HAKT) using Acidithiobacillus thiooxidans. After HAKT, the leaching rates of metals V, Sr, Y, La, and Ce were higher than those of the untreated pure fly ash (UPFA) with the maximum values of 51%, 70.52%, 37.48%, 64.77%, and 76.37%, respectively; after hydrothermal-acid treatment (HTAT), the bioleaching rates of rare metals Ni, Sr, and Y, were higher than those of the UPFA with the maximum values of 70.24%, 20.26%, and 34.54% respectively. The results also showed that, for most rare metals, the recovery rate following HAKT was higher than that following HTAT. This result can be demonstrated via analyzing adsorption quantity, adsorption kinetics and diffusion model of fly ashes for A.thiooxidans. Our study provides an important pathway for recycling rare metals from coal fly ash.

Physical, chemical, and geotechnical properties of coal fly ash: A global review

In 2015, fly ash utilization rates were 70% for China, 62% for India, and 50% for the US. This leaves substantial potential for increased utilization. This article summarizes available literature concerning physical and chemical and geotechnical properties of fly ash which affect its options for re-use. Fly ashes are broadly classified worldwide into two chemical types for their industrial applications, mostly in cement industries, namely class C and class F. Class C fly ash, with its higher levels of calcium oxide, generally has self-cementing properties. In terms of global fly ash composition, fly ash from India on average contains higher levels of silicon dioxide than that from the US and China. In terms of particle size, studies report that fly ash more often is poorly graded than well-graded; fly ash from India in particular tends to be poorly graded. Optimum moisture content (OMC) values for fly ashes vary from 11 to 53%, and maximum dry density values range from 1.01 to 1.78 g/cm3. Country-specific trends in terms of fly ash OMC and maximum dry density values are not readily apparent. Fly ash tends to be non-plastic, meaning it will not swell if used as a foundation material for structures. Reported fly ash shrinkage limits range from 38 to 65. Permeability of pure fly ash generally varies from 10−4 to 10-7 cm/sec, and angle of friction varies from 25° to 40°.

Abrasion resistance behaviour of fly ash based geopolymer using nanoindentation and artificial neural network

Abstract This study presents the investigation of the abrasion resistance of fly ash based geopolymer via the application of nanoindentation. Nine fly ash based geopolymer mixes with four variables: silica fume (SF), sand to cementitious ratio (s/c), liquid to solid ratio (l/s) and superplasticizer (SP) were investigated with statistical methods to obtain the plasticity index of the four fly ash based geopolymer phases. The results suggest that the pure fly ash based geopolymer paste with no SF, no SP, no sand and l/s ratio of 0.60 provides the highest abrasion resistance. Artificial neural network (ANN) is also adopted to predict the abrasion performance of the fly ash based geopolymer where good correlation is found. With the application of deconvolution method, it is reported that the plasticity index of N-A-S-H, partly activated slag and non-activated slag phases show a decreasing trend of plasticity index with increasing hardness or modulus. The non-activated compact slag phase shows no clear trend with changes in hardness and modulus. The relationship between degree of activation versus plasticity index (PI) is also studied, it was found that high degree of activation leads to formation of high volume fraction of N-A-S-H which this correlates with increased compressive strength and improved abrasion resistance. The application of nanoindentation with deconvolution method is suitable in quantifying the PI of the phases and abrasion resistance of the fly ash based geopolymer mortar.

Effects of Fly Ash on Liquefaction Characteristics of Ottawa Sand

This paper presents the results of effects of non-plastic fines (Class F fly ash) on liquefaction behavior of Ottawa sand. Stress-controlled cyclic triaxial tests were performed on clean Ottawa sand, fly ash, and sand–fly ash mixtures containing 10, 20, 25, 30, 50, and 70% of fly ash. For the evaluation of the effects of confining pressure on liquefaction resistance, three series of tests were conducted at 34.48, 68.96, and 103.42 kPa initial effective confining pressures, except for pure fly ash. In the case of pure fly ash, tests were conducted only at an effective confining pressure of 34.48 kPa. The reversible shear stress was applied systematically by varying Cyclic Stress Ratio from 0.1 to 0.5. Addition of fly ash to sand resulted in decrease in liquefaction resistance initially and then increase in liquefaction resistance for fly ash contents up to about 20–25%. Increase in fly ash content beyond 25% was seen to decrease the liquefaction resistance.