Fly Ash Mixtures Research Articles

Synthesis and characterization of geopolymers derived from coal gangue, fly ash and red mud

Abstract There is a growing need to utilize large stockpiles of the industrial byproducts including coal gangue (CG), fly ash (FA) and red mud (RM) which can pose potential environmental problems. The CG, FA and RM contain aluminosilicates which can be precursors for the synthesis of geopolymers. This research studied the utilization of CG, FA and RM by silicate activation into geopolymers. Binary mixes of CG and RM and ternary mixes of CG, FA and RM were prepared and cured at temperatures ranging from 80 to 800 °C. The unconfined compressive strength tests were performed on the specimens to determine their mechanical strength. Nitrogen adsorption, mercury intrusion porosimetry, Fourier transform infrared spectroscopy and scanning electron microscopy were used to study the textural, structural and morphological characteristics of the end products. At lower curing temperatures, the ternary mixtures of CG, FA and RM showed higher strength gains when compared to the binary mixtures of CG and RM. The textural characteristics revealed that the reduction in pores and specific surface area do not necessarily result in higher compressive strength values. Furthermore, the cementitious gels formed at high temperatures resulted in well-bonded geopolymers with homogenous structures.

Influence of randomly mixed coir fibres and fly ash on stabilization of clayey subgrade

This paper discusses the stabilization of clayey subgrade when mixed with coir fibres (CF) randomly and fly ash (FA). The tests were carried out on the locally available clay soil with different proportions of randomly mixed CF and FA. The CF and FA proportions used in the study are expressed in percentage by dry weight of soil. The CF and FA proportions used in the present study are 1%, 1.5% and 2% and 0%, 5%, 10%, 20% and 30% respectively. The tests results revealed that the clayey subgrade stabilized with FA resulted in improvement of strength and California bearing ratio (CBR). Further, it is observed that randomly mixed 1% CF and 20% FA mixture resulted in improvement of CBR of subgrade as compared to clay subgrade treated with 20% FA alone and this increase is noticed as 1.5 times. Overall, it is concluded that 20% FA + 1% CF resulted in improvement of subgrade in terms of CBR.

Mechanical behaviour of fly-ash-treated expansive soil

A major source of electrical energy is thermal power, which results in large quantities of coal ashes. Fly ash, which is produced from the combustion of pulverised coal, has an important place among industrial by-products. Currently, in India, more than 180 Mt of fly ash is being generated annually, posing the dual problem of environmental pollution and difficulty in disposal. This calls for establishing strategies to use the product as an engineered construction material in geotechnical applications for which the mechanical behaviour of soil–fly-ash mixes is an important consideration. In this study, high-calcium (class C) and low-calcium (class F) fly ashes in different proportions by weight were added to expansive soil to evaluate the effect of fly ashes on the strength behaviour of soil–fly-ash mixtures. Compacted clay–fly-ash samples were cured for 7 and 28 d and subjected to unconfined compression tests. It was found that 20% of class C fly ash is the optimum quantity to improve the characteristics of expansive soil, compared with 60% of class F fly ash. The main objective of the study was to illustrate the beneficial effects of fly ashes on the mechanical behaviour of fly-ash-treated expansive soil.

Synthesis of a novel core-shell-structure activated carbon material and its application in sulfamethoxazole adsorption.

The increasing release of pharmaceutical and personal care products (PPCPs) into water poses serious threats to human beings. In this study, a novel core-shell activated carbon (CSAC) material with a high-mechanical-strength porous ceramic shell was synthesized and tested by adsorbing sulfamethoxazole (SMX) from aqueous solutions. An activated carbon core (AC core) was synthesized from a mixture of powder AC (92%) and cassava waste splinters binder (8%). Moreover, a shell with a high thickness of 0.13 cm and compressive strength (2.92 MPa) was generated from the mixture of coal fly ash and clay at ratio of 60:40. It demonstrated high protection of the AC core. The adsorption efficiency of SMX by CSAC attained 99.0% and 97.9% at initial concentrations of 5 and 10 mg L-1, respectively. Furthermore, 77.0, 68.6 and 60.4% of SMX were adsorbed at higher concentrations of 30, 50, and 100 mg L-1, respectively. The kinetics study demonstrated that the adsorption of SMX followed pseudo-second-order kinetics. Moreover, the sorption isotherm was better fitted to Freundlich isotherms. Finally, SMX adsorption on CSAC simultaneously depended on the pore texture of CSAC and the hydrophobic properties of SMX, as well as the π-π bonds and electrostatic interactions between them.

Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures

Studies on shredded waste tires mixed with sand for fill applications are well documented. In this study, a new composite material from mixture of shredded tires and fly ash as fill material is explored. Shredded waste tires with nominal size equal to 9.5 mm (granulated rubber), and fly ash generated from two thermal power plants are used in the study. The composite material is obtained by mixing different proportions of granulated rubber and fly ash. Granulated rubber content equal to 0%, 10%, 30%, and 60% (by weight of fly ash) in the mixture are tested. Compaction characteristics, optimum mixing ratio, and shear strength properties of the mixtures are determined. The maximum dry unit weight and the optimum water content values ranged between 15%–22.5% and 12.6–14.6 kN/m3, and 10%–27% and 10.5–11.6 kN/m3 for mixtures prepared with fly ashes from two sources. Large-size direct shear apparatus is used to obtain the angle of shearing resistance and apparent cohesion of mixtures at both peak state and at near end-of-test. The shear strength of fly ash and granulated rubber mixture is found to be higher than that of fly ash alone or granulated rubber alone, and the maximum shear strength of the composite material is observed for granulated rubber contents equal to about 60% (by weight of fly ash). The peak shear strength parameters of mixtures, apparent cohesion and friction angle, are found to be in the range 14.9–46.0 kPa and 37.5°–50.1°, respectively. Based on minimum void ratio, optimum mix proportions of granulated rubber and fly ash from two sources ranges between 54%–100% and 81%–185% (by weight of fly ash). Based on shear strength testing, fly ash-granulated rubber mixtures are found to perform better than sand-granulated rubber mixtures.

Laboratory experiments on the improvement of rockfill materials with composite grout

Dam deformation should be strictly controlled for the construction of 300m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.

Pengaruh Limbah Keramik dan Abu Terbang Terhadap Kuat Tekan dan Daya Serap Air Bata Beton

The growth of development sector in Indonesia lead a high demand for cement and sand. The research was conducted from February to July 2018 with objectives of analyzing and knowing the influence of mixture of ceramic waste and fly ash on compressive strength and water absorption of paving block. The research was started from preparation of tools and materials, manufactured of specimens and also tested the compressive strength and absorption of paving block. Quality standardwere based on SNI 03-0691-1996. Based on the analysis result, the highest compressive strength of 26.56 Mpa was obtained from paving block with 9% fly ash and 6% ceramic waste and was classified as class B. The highest water absorption of 18.29% was paving block with 15% mixtured of ceramic wastes and the lowest water absorption of 9.65% was normal paving block. Brick concrete with 6% mixture of ceramic waste and 9% fly ash had several advantages, i.e. cheaper cost, had a higher compressive strength and higher water absorption compared to normal paving block, more environmental friendly, had lighter weight and ease of installation. Key words: ceramic wastes, compressive strength, fly ash, paving block, water absorption

Discussion on the cause of scaling in wet desulfurization system of large coal-fired power plants

The flue gas desulfurization method of large coal-fired power plants is generally limestone/gypsum wet method. But many equipments of this wet desulfurization system during daily operation often cause scaling problems. At present, more literature think s this scale is caused by the mixing of desulfurized gypsum and fly ash in flue gas. However, this paper analyzes the scale composition and appearance of several power plants in China, which shows that the scale is not a simple mixture of gypsum and fly ash, and is a smelting reaction of fly ash in a complex environment and forms a hard scale of gypsum/limestone-fly ash gel. This kind of scale will endanger the safe and stable operation of the desulfurization system, specific operational and maintenance recommendations are proposed for reference.

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.

Rheological behavior of high volume fly ash mixtures containing micro silica for digital construction application

Digital construction has recently become the subject of very rapidly growing research activities all over the world. In this regard, our current research demonstrates the possibility of using high volume fly ash mortar, modified with micro silica for 3D concrete printing application. To assess the effect of the micro silica on rheological performance, a rotational rheometer was used to measure yield stress, viscosity and reversible stiffening behavior of ternary blends of fly ash–cement–micro silica. Since, the disposal of fly ash from coal power plants has increased rapidly due to the feed-in tariff established by the government, this research will pave a way to utilize high volume of fly ash for digital construction application.

Setting, Strength, and Autogenous Shrinkage of Alkali-Activated Fly Ash and Slag Pastes: Effect of Slag Content.

The engineering properties of alkali activated materials (AAMs) mainly depend on the constituent materials and their mixture proportions. Despite many studies on the characterization of AAMs, guidelines for mixture design of AAMs and their applications in engineering practice are not available. Extensive experimental studies are still necessary for the investigation of the role of different constituents on the properties of AAMs. This paper focuses on the development of alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) paste mixtures in order to determine their suitability for making concretes. In particular, the influence of the GBFS/FA ratio and liquid-to-binder (l/b) ratio on the slump, setting, strength, and autogenous shrinkage of the alkali activated pastes is studied.It is shown that fresh properties largely depend on the type of precursor (GBFS or FA). The slump and setting time of GBFS-rich pastes was significantly reduced. These pastes also have higher compressive strength than FA-rich pastes. The study identifies important practical challenges for application of the studied mixtures, such as the behavior of their flexural strength and high amplitudes of autogenous shrinkage of GBFS-rich mixtures. Finally, the optimum GBFS/FA ratio for their future use in concretes is recommended.

Waste-based geopolymeric mortars with very high moisture buffering capacity

In this study, lightweight waste-based geopolymeric mortars were evaluated for the first time regarding their potential to passively adjust indoor relative humidity (RH) levels. Geopolymer mortars were prepared using a mixture of fly ash (FA) and metakaolin (MK) as a binder, in a proportion of 75:25 wt% (FA:MK), construction and demolition waste as the fine aggregate and a pore forming agent in varying amounts. The results showed that the addition of a pore-forming agent to the compositions considerably increased the moisture buffer value (MBV) of the mortars, that is, from 0.80 (reference mortar) to 5.61 g/m2 Δ%RH (mortar with highest porosity). The moisture buffering capacity shown by these eco-friendly mortars is higher than values reported for other binder materials and can be classified as excellent (MBV > 2 g/m2 Δ%RH). The porous FA-based mortars also presented low thermal conductivity (as low as 0.19 W/m∙K), which suggests that these innovative binders could be simultaneously used for indoor moisture buffering and as low thermal conductivity materials.

Investigation of the hydration kinetics and microstructure formation mechanism of fresh fly ash cemented filling materials based on hydration heat and volume resistivity characteristics

Fly ash cemented filling materials (FCFM) have received a great deal of attention in recent years as more sustainable solutions to the large-scale utilization problems of fly ash and coal gangue. Based on the hydration heat and the volume resistivity characteristics, this study examined the changes in the fresh FCFM properties from the thermodynamic and electrical perspectives, which reflected the characteristics of the hydration kinetics and microstructure formation mechanism of the FCFM. The results showed that the hydration exothermic process of the FCFM exhibited a rapid reaction stage, an induction stage, an acceleration stage, a deceleration stage and a stable stage. Compared with cement, the mixture of fly ash and coal gangue resulted in a substantially lower hydration heat. The volume resistivity of the FCFM changed over time, initially increasing, then decreasing, then increasing again. The hydration kinetics of the FCFM could be described by three processes: nucleation and crystal growth (NG), interactions at the phase boundaries (I) and diffusion (D). The NG process dominated in the early stage of hydration, and the I and D processes gradually became dominant as the hydration degree increased. Compared with cement, changing the hydration kinetics required a higher degree of hydration in the mixture of fly ash and coal gangue. The improvement in the hydration reaction rate of FCFM due to additives was primarily reflected in the early hydration stage. The calculated data on the C-S-H gel content of the FCFM paste agreed well with the changes in the uniaxial compressive strength (UCS) and plane porosity over time. Remarkable negative correlations between the plane porosity and the UCS and between the plane porosity and the C-S-H gel content were found, along with a significant positive correlation between the C-S-H gel content and UCS. A microstructure formation mechanism model of the FCFM was constructed, and the hydration process of the filling material was divided into a dissolution period, a hydration period and a flocculated-structure formation and growth period. These findings provide new insights into the hydration kinetics and microstructure formation mechanism of fresh FCFM.

Research on the performance and application of low traffic hardened lime-fly ash pavement materials in rural areas

By means of curing agent hardening technology applied for lime-fly ash road surface, the performance of unconfined compressive strength, water stability and freezing stability of hardened fly ash mixture has been tested, and the feasibility of the technology has been verified. At the same time, combined with the indoor test results, the test road has been paved which achieved good results, and the construction technology is simple, economical and reasonable, so it has a good value of popularization and application.

Chemical Stability and Leaching Behavior of One-Part Geopolymer from Soil and Coal Fly Ash Mixtures

Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.

Use of anthropogenic soils in securing unstable road embankment

In the article the problem of anthropogenic soils from thermal treatment of waste in terms of their use in road construction is discussed. As part of the research, the basic physical and mechanical properties of the anthropogenic soils were determined. PN-S-02205: 1998, the analyzed ground material (fly ash and slag mixture) qualifies as useful for embedding into the lower layers of the embankment below the freezing zone, provided they are in dry places or are insulated from water. The next step was to model an exemplary, unstable road embankment in the MIDAS GTS NX. The results point out that the strength and physical properties of the anthropogenic soils may be used to secure unstable road embankments with simple soil and water conditions. It should be remembered that analysed anthropogenic soils should also be subjected to rigorous testing for their chemical composition. The obtained results will allow us to determine the possibilities of their use in road construction in terms of their strength properties.

Assessment of tracing element characteristics of F-type fly and bottom ash mixture

ABSTRACTPresently, fly ash–water slurry is transported to ash disposal site at very low solid concentration of approximately 15–20% (by weight), resulting in huge water and energy wastage which leads to several environmental and health problem. The production of a large amount of the toxic metal elements in the ash disposal system of the thermal power plants can pose negative environmental effects on human health and on plants. In the present study, an attempt has been made to investigate the leaching characteristics of fly ash at higher concentrations. The bottom ash was taken as an additive in the proportion of 10, 20, and 30% (by weight) to enhance the leaching characteristics of fly ash. The solid concentration of fly ash suspension was taken in the range of 40 to 60% (by weight). The addition of additive helps to reduce the tracing metal concentration of fly ash. Leaching experiment data show that leachate concentration of all tracing elements present in fly ash reduced maximum with 20% addition of bottom ash (by weight). The present study helps to improve the ash disposal system of the thermal power plant and to minimize the environmental impact.

In situ effect of combined utilization of fly ash and polyacrylamide on sand stabilization in North China

A field experiment was conducted to investigate the resistance to wind erosion of consolidated soil layer (CSL) on the edge of Ulan Buh Desert in Inner Mongolia, China under natural conditions during Aug. 2015–Apr. 2016. The CSLs consisted of sandy soil, fly ash (FA) (5%, 10% and 15% (w/w) soil) and polyacrylamide (PAM) (0.05% and 0.1% (w/w) soil). The experimental site was divided equally into Regions A and B where dry FA and PAM powder were applied in two ways in mid-Jul. 2015. In Region A, FA and PAM were mixed homogeneously with the 0–0.3 m depth topsoil. In Region B, FA alone was mixed homogeneously with the 0–0.3 m depth topsoil. PAM was then scattered uniformly on top of the surface layer. Finally, CSLs were formed by spraying an appropriate amount of water onto the surface to dissolve PAM fully and being equilibrated for one week to achieve a moisture content close to the initial soil moisture content (0.6%). It was found that during 2–26 Aug. 2015, the wind erosion rate (WER) was reduced most significantly by 77% in CSL (10%FA + 0.05%PAM) in Region A and by 58% in CSL (10%FA + 0.1%PAM) in Region B compared with control (CK) (WER = 10.2 kg/m2). However, during 3–27 Sep. 2015, there was no significant difference in WER between treatments in Regions A and B compared with CK (WER = 1.4 kg/m2). Whereas, during the following longer period of wind erosion (viz. 27 Sep. 2015–21 Apr. 2016), the WER was reduced most significantly by 69% in CSL (5%FA + 0.1%PAM) in Region A and by 32% in CSL (5%FA + 0.05%PAM) in Region B compared with CK (WER = 80.7 kg/m2). The resistance to wind erosion of CSL in Region A was much stronger than in Region B. The WER of CSL was influenced by wind conditions including wind speed and direction. Precipitation also had an impact on the WER of CSL as the cohesive effect of PAM can be influenced by precipitation. The CSL as a mixture of sandy soil, FA and PAM is recommended for wind erosion control.

Pemanfaatan Fly Ash dan Alkali Resistant Glass Fibre (ARG) dalam Pembuatan Paving Block

The paving block is an alternative to the use of pavement layer that is safe, strong and easy to installation and maintenance. Pavement paving block also can be produced both mechanically and manually. The added fly ash was a waste material from coal combustion in the steam power plant furnace in the form of fine, round, pozzolanic and fibre-resistant. Alkali Resistant Glass Fibre (ARG) which is shaped like a rope 18-36 mm long was added into the paving block with mixed compositions 1 Pc:10 Ps that aims to strengthen the compressive strength and flexibility of the paving block. This research was used 15 samples with mixture variation of fly ash 19% and fiber 0,25%, 0,5%, 0,75% and 1%. Based on the results of laboratory analysis, paving block (1 Pc: 10 Ps) with the addition of fly ash 19% and ARG 0.6% yielding a maximum compressive strength of 18.35 MPa. The addition of fibres with fly ash mixture was also able to increase the compressive strength of the paving block.

Synthesis of zeolite P1 from fly ash under solvent-free conditions for ammonium removal from water

In this work, zeolite P1 is synthesized from fluidized bed fly ash (FA) via a solvent-free process. The formation of zeolite P1 is investigated as a function of crystallization reaction time. The solid mixture of FA and Na2SiO3·9H2O with a mole ratio of Na:Al:Si = 1.5:1:1.7 can be converted to zeolite P1 at 80 °C for 24–96 h. XRF, XRD, SEM/EDS, FTIR, TG/DSC and BET techniques are used to test the properties of resultant zeolite products. The efficiencies of the resultant zeolite for ammonium adsorption are evaluated on factors including solution pH, NH4+ ions concentration, temperature and adsorption time. The kinetic data and adsorption equilibrium data fit satisfactory with the Ho's pseudo-second-order kinetic model and Langmuir model. The maximum ammonium adsorption capacity of zeolite P1 (22.9 mg/g) can be reached within 40 min at optimal pH of 6. The adsorption performance is higher than many of the natural zeolites and closely similar to the zeolites synthesized from fly ash through the conventional hydrothermal route. Our study not only provides new insights into the preparation of zeolite from fly ash, but also reveal that the zeolite P1 synthesized through solvent-free route is a promising material for ammonium removal.