Tesis sobre el tema "Class F fly ashes"

In this thesis, characterization of two class F fly ashes (FA) from Ç
atalagzi and Sugö
zü
thermal power plants were carried out and their utilization potentials in three different fields were examined. Characterization of sintered samples and determination of their utilization potentials in ceramic industry is the first research area in this thesis. For this purpose, the class F fly ash samples were first pressed into cylindrical specimen without the addition of any organic binders or inorganic additives, and then sintered to form ceramic materials. Effects of sintering temperature and time on sintering characteristics were investigated. In the experiments, the cylindrical specimens were first preheated to 300oC for 1 h to remove moisture and any other gases. The specimens were then fired at the temperatures of 1000oC, 1050oC, 1100oC and 1150oC for the sintering times of 0.5, 1.0, 1.5 and 2.0 hours. Heating rate of 10oC/min was kept constant throughout the experiments. Quality of sintered samples was evaluated in terms of ceramic specifications such as density, water absorption, porosity, shrinkage and splitting tensile strength. In addition, mineralogical and microstructural changes during sintering were determined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. According to literature data, better microstructure, the highest density and strength with the lowest porosity, water absorption and shrinkage values are the indications of the optimum sintering conditions. Based on these specifications, Sugö
zü
fly ash gave better results compared to Ç
atalagzi fly ash, and the optimum conditions were achieved at the sintering temperature of 1150oC for the sintering time of 1.5 hours for both samples. Pozzolanic reactivity of the fly ashes and their utilization potentials in civil engineering applications were also examined in detail during this study. For this purpose, Ç
atalagzi (CFA) and Sugö
zü
(SFA) fly ashes were first subjected to a specific hydraulic classification process developed at CAER (University of Kentucky, Center for Applied Energy Research) to recover ultrafine fly ash particles. The overflow products with average particle sizes of 5.2 &mu
m for CFA and 4.4 &mu
m for SFA were separated from the respective as-received samples with average particle sizes of 39 &mu
m and 21 &mu
m. After the classification stage, the pozzolanic activities of these ultrafine fly ash fractions (UFA) and as-received samples were examined by preparing a number of mortar (mixture of Portland cement (PC), FA or UFA as partial cement replacement, sand and water) and paste (mixture of PC, FA or UFA as partial cement replacement and water) specimens. Control samples containing only PC were also prepared and tested through the experiments for the comparison of the results. In the mortar experiments, three different PC replacement ratios by FA and UFA (10%, 20% and 30%) were used to examine the effects of FA and UFA samples on the fresh and hardened mortar properties such as water requirement, compressive strength, drying shrinkage and water expansion. These mortar tests indicated that ultrafine fractions of Ç
atalagzi (CUFA) and Sugö
zü
(SUFA) fly ashes provided more than 10% reduction in water demand compared to the control sample for 30% PC replacement. The mortar cubes containing CUFA and SUFA samples exhibited also higher strength development rates after 14 days compared to the ones with as-received samples and PC only. At the end of the curing age of 112 days, both CUFA and SUFA provided more than 40% increase in compressive strength compared to the control sample for the PC replacement ratios higher than 20%. As a comparison, SUFA gave better results than CUFA in both water demand and compressive strength tests. The mortar bars prepared with the both FA and UFA samples exhibited very low shrinkage and expansion values. These values decreased generally with increasing PC replacement ratio especially after 14 days. In the paste experiments, thermogravimetric analyses (TGA) of the paste specimens prepared by using only with 20% PC replacement were carried out to determine pozzolanic reactivity of the samples. The difference between the remaining Ca(OH)2 (portlandite) contents in the paste specimens containing the fly ashes and the reference PC paste was used as a measure of pozzolanic reactivity. After 112 days, 68.56% and 62.68% Ca(OH)2 content of PC only pastes were obtained with the pastes containing CUFA and SUFA samples, respectively, corresponding to 11% and 13% more Ca(OH)2 consumptions in reference to the respective as-received samples. X-ray diffraction (XRD) analyses were also performed for comparison of main portlandite peak intensities in the paste specimens containing FA or UFA with those in the PC only paste during cement hydration. According to these XRD analyses, portlandite content in PC/UFA pastes decreased significantly after 14 days compared to the PC only paste. All of these tests and analyses showed that a highly reactive lower cost pozzolan with very fine particle size and higher surface area compared to regular fly ash pozzolans can be produced from both Ç
atalagzi and Sugö
zü
fly ashes using a relatively simple hydraulic classification technology. Cenosphere recovery potentials from Ç
atalagzi and Sugö
zü
fly ashes were also studied in this thesis. Determination of cenosphere content was done under optical microscope by particle counting on the basis of point and area. Based on the point-counting data, CFA and SFA samples originally contain 11.30% and 4.50% cenospheres, respectively. Variations of cenosphere contents in the fly ash samples were examined by using float-sink, screening and air classification tests. The results pointed out that cenosphere contents decreased with decreasing size and increasing density for both samples. According to the float-sink tests, Ç
atalagzi fly ash has much more floating products and more cenospheres than Sugö
zü
fly ash for the same density interval. Based on the air classification results, cenospheres were concentrated in the underflow products, and cenosphere contents increased with increasing air pressure and decreasing motor speed for both samples. The most efficient cenosphere separation technique among the examined methods was screening. Cenosphere contents of CFA and SFA increased to 21.65% and 11.83%, respectively by only using simple screening through 38 &mu
m.

Published Article
Fly Ash is a by-product at thermal power stations, also otherwise known as residues of fine particles that rise with flue gases. An industrial by-product may be inferior to the traditional materials used construction applications, but, the lower the cost of these inferior materials make it an attractive alternative if adequate performance can be achieved. The objective of this study is to evaluate the chemical and physical effectiveness of self-cementing fly ashes derived from thermal power stations for construction applications with combined standards. Using laboratory testing specimens, suitable types of Fly Ashes namely: Kendal Dump Ash, Durapozz and Pozzfill, were tested to the required standards to evaluate the potential properties. All three Fly Ashes have been classified as a Class F Fly Ash, which requires a cementing agent for reactions to take place and for early strength gains in the early stages of the reaction processes. The Fly Ashes conformed to the combination of standards and have shown that the proper reactions will take place and will continue over period of time. The use of fly ash is accepted worldwide due to saving in cement, consuming industrial waste and making durable materials, especially due to improvement in the quality fly ash products.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.
"June 2013." Cataloged from PDF version of thesis.
Includes bibliographical references (pages 36-37).
Approximately 62.8 trillion kJ are consumed annually worldwide in the manufacturing process of traditional clay tiles. With this in mind, the goal of this project was to develop an eco-friendly alternative to clay tiles that maintain the ASTM building code standards. Through experimentation, a fly ash tile was produced that consumes 99% less energy in the manufacturing process than commercial clay tiles. The final product is a fly ash tile composed of two classes of fly ash, water, and several additives to strengthen the material. Standard ASTM tests were conducted. This fly ash tile is an energy efficient clay-tile alternative that excels in many mechanical properties.
by Jaclyn Schein.
S.B.

On-going research at Texas A&M University indicated that soil stabilization using calcium chloride filter cake along with Class F fly ash generates high strength. Previous studies were conducted with samples containing calcium chloride filter cake and both Class C fly ash and Class F fly ash. Mix design was fixed at 1.3% and 1.7% calcium chloride and 5% and 10% fly ash with crushed limestone base material. Throughout previous studies, recommended mix design was 1.7% calcium chloride filter cake with 10% Class F fly ash in crushed limestone base because Class F fly ash generates early high and durable strength. This research paper focused on the strength increase initiated by greater than 1.7% pure calcium chloride used with Class F fly ash in soil to verify the effectiveness and optimum ratio of calcium chloride and Class F fly ash in soil stabilization. Mix design was programmed at pure calcium chloride concentrations at 0% to 6% and Class F fly ash at 10 to 15%. Laboratory tests showed samples containing any calcium chloride concentration from 2% to 6% and Class F fly ash content from 10% to 15% obtained high early strength however, optimum moisture content, different mix design, and mineralogy deposit analysis are recommended to evaluate the role and the effectiveness of calcium chloride in soil stabilization because of the strength decreasing tendency of the samples containing calcium chloride after 56 days.

AN ABSTRACT OF THE DISSERTATION OF RAJNISH PURI, for the Doctorate of Philosophy Degree in ENGINEERING SCIENCE WITH CONCENTRATION IN CIVIL AND ENVIRONMENTAL ENGINEERING, presented on APRIL 15, 2015 at Southern Illinois University Carbondale TITLE: DEVELOPMENT OF HIGH PERFORMANCE CONCRETE COMPOSITES USING CLASS F FLY ASH AND PCC BOTTOM ASH, AND A STATISTICAL MODEL TO PREDICT COMPRESSIVE STRENGTH OF SIMILAR CONCRETE COMPOSITES ADVISOR: Dr. Sanjeev Kumar It is a common knowledge that the use of concrete is as old as the evolution of human civilization. People have always dreamed beyond the dotted lines and so does the usage of concrete. With the rapid industrialization and globalization, the journey from ordinary concrete to high performance concrete (HPC) has been swift and remarkable. The diversification and utilization of high performance concrete has given the tool in the hands of engineers and architects who can now design and execute buildings of any shape and size deemed impractical a few decades ago. The aim of this research was to develop high performance concrete composites having different percentages of Illinois Class “F” fly ash and bottom ash by replacing the appropriate proportions of Type 1 portland cement and fine aggregate, respectively. The target was to develop high performance concrete composites that have compressive strength of 8,000 psi (55 Mpa) after 28 days of curing in water with a slump of 4±½” (102mm ± 13mm) and air content between 4 and 6 percent. In order to achieve the targeted air content, an air entraining agent DARAVAIR 1400 was used. The water-cement ratio of 0.3 was maintained throughout the research and to achieve the targeted slump, high-range water reducer ADVA 140M was used. The engineering parameters of the high performance concrete composites and an equivalent control mix were evaluated by conducting a detailed laboratory study which included several tests, e.g., slump, fresh air content, compressive strength, splitting-tensile strength, flexural strength, resistance to rapid freezing and thawing, sealed shrinkage and free swelling, and rapid chloride permeability. The results presented show that all high performance concrete composites developed in this study achieved the targeted compressive strength of 8,000 psi (55 MPa) after 28 days of curing in water. The results of the durability tests show that the concrete composites developed in this study have trends similar to that of an equivalent conventional concrete. Based, on the results of this study, it was concluded that the concrete composites have potential to be used on real world projects and thus help the environment by substantially reducing the amount of fly ash and bottom ash going to ash ponds or landfills. Based on the experimental test result data, a detailed statistical analysis was conducted to develop an empirical model to predict compressive strength of similar concrete composites for a given amount of fly ash, bottom ash, and curing period. Additional laboratory tests were performed to validate the mathematical model.

Thermal power station in most countries is saddled with the problem of fly ash disposal and unless suitable avenues are found for its proper use, this would pose a gigantic problem to the power sector. Disposal of huge quantities of fly ashes without proper care causes considerable impact on the environment particularly the one leading to soil and groundwater contamination. On the other hand, fly ashes have many desirable properties which can find applications in civil engineering, especially in geotechnical engineering. The pozzolanic reactivity is one of the important properties of fly ashes that enhance its application. Thought the fly ashes with self – pozzolanic property are well utilized, fly ashes with insufficient free lime, such as class F fly ashes are being grossly underutilized and they form a considerable portion of fly ashes that are disposed. Yet another factor restricting the use of fly ash is the concern about the leachability of lime under field conditions particularly under saturated or partially saturated conditions. Hence an attempt is made in this thesis, to reduce the lime leachability of class F fly ashes with different additives. Thus, selection of right amounts of additives to reduce the lime leacability is an important aspect studied in this thesis. Effect of such as strength, compressibility, and CBR value is also investigated. Another simple way to reduce the problem of disposal of fly ash is to utilize it for the construction of waste disposal sites particularly for lining solid waste disposal facilities in place of the natural clay materials which are very often procured by excavating and transporting from far off places. Also, the capacities of fly ashes to sorb heavy metal that are likely to be present in the leachates generated from the industrial wastes have been studied. Of the other factors limiting the generous use of fly ashes is the leachability of several trace elements present in them. Hence the leachability of trace metals from fly ashes under different practical situations, before and after incorporating the selected additives for improving the engineering properties of fly ashes, has been studied. The thesis is presented in 10 chapters. The relevant background for the studies and scope of the work is given Chapter 1. Sources of the fly ashes collected for the investigating along with their physical and chemical properties are presented in chapter 2. Two low line fly ashes are collected directly from the electronic precipitators of the thermal power plants located at Neyvelli town of the Tamil nadu and Maddanur town of Andhra Pradesh, India, named NFA and MFA respectively. MFA has greater finer particle content than NFA. The particles of MFA Have rougher surface compared to those of NFA. Both of fly ashes have predominantly quartz and mullite phase in them. The silica, total lime and carbon contents which have major influence on the pozzolanic reactivity of fly ashes vary considerably in the both the fly ashes. Lime leachability is taken as the amount of lime that is converted into soluble form (by dissociation into calcium and hydroxyl ions) under a standardized condition. It can be used to asses the long term sustainability of the strength achieved in fly ashes with lime. Lime leachability studies have been conducted on the fly ashes stabilized with different additives in specially designed moulds. Results presented in Chapter 3 showed that leachability of lime in fly ashes increases with the increase in lime content though it is not in proportion to the increase in lime content. This is because the solubility of lime is less and is independent of the total lime present. The marginal reduction in leachability is mainly due to cemented matrix of fly ash inhibiting the leaching of time. The higher the strength of the matrix the lower is the leachability. Further it is made clear that at any lime content presence of gypsum reduces the time leachability which has been attributed to the transformation of pozzolanic compounds into less soluble form than the compounds formed with lime alone. With the increase in curing period, the amount of lime that leaches from the lime-stabilized fly ashes as well as those treated with gypsum to a considerable extent. The nature of alteration does not seem to change with time as revealed by a good correlation between lime leachability ratios obtained after 7 days and 14 days of curing periods. Chapter 4 presents the results of unconfined compressive strength tests carried out on fly ashes with varying lime and gypsum contents, before soaking and also soaking in several heavy metal solutions, along with the durability to the cycle of wetting and drying. The results revealed that the strength of low lime fly ashes increases with lime content significantly up to the optimum lime content of about 2.5 – 5% and gradually thereafter. Addition of gypsum of 1 – 2.5% increases the strength of fly ashes further at any lime content. Increase in strength with gypsum, which is quite significant at lower lime contents initially, is observed for a considerable period (up to 180 days) at higher lime contents. The increase in strength is as high as 40-fold in some instances. This increase in strength which is also more durable has been attributed to the formation of calcium – sodium – aluminium - silicate hydrate along with calcium silicate hydrate. Further, it is observed that fly ash which responds better to lime stabilization shows accelerated gain in strength due to the addition of gypsum at early curing periods than the fly ash that responds solely to lime. Decrease in lime leachability ratio is a good indication of the increased strength along with the increased durability. California Bearing Radio (CBR) values are of great significance in the utilization of fly ashes in bulk quantities for the construction of road and railway embankments and pavements. Studies conducted to determine the CBR values of fly ashes with different lime and gypsum contents after curing for different time periods are described in chapter 5. The CBR values are observed to increase with lime alone significantly up to 2.5% and only marginally beyond. But the increase in CRB values is considerable with gypsum at any lime content. The increase in CBR value is particularly more with 2.5% gypsum for fly ashes with 2.5% lime. The CBR values of stabilized fly ashes are generally higher for 5 mm depth of penetration than those for 2.5 mm one due to the high stiffness of the matrix formed even at low strain levels. The loss in CBR values with soaking is relatively more at lower curing the periods due to the improper cementation of particles. Even after this significant loss in CBR values, fly ashes with 2.5% lime and 2.5% gypsum register the maximum values after curing under soaked condition. Unlike in the case of unconfined compressive strength, lime leachability values could not be well correlated with the CBR values of fly ashes with different lime and gypsum contents since many more factors influence the CBR values than those of unconfined compressive strength alone. Chapter 6.brings out the effects of addition of lime alone and lime along with gypsum on the compressibility behaviour of the fly ashes. Since the fly ashes when treated with additives develop strength and exhibit lower compression with the passage of time, consolidation testing with conventional duration of load increment may not be appropriate. Hence an attempt has been made to assess the minimum duration of load increment necessary to study the compressibility characteristics of such materials. Thus the compressibility behaviour of fly ashes with additives has been studied using conventional consolidation test with different durations of load increments varying from 30 minutes to 48 hours. The results indicated that 30 minutes of duration of load increment can be used to assess the compressibility behaviour of such materials. The effect of lime which reduces the compression is seen to be maximum from the results obtained with the load duration increment of 30 minutes but gradually reduce with higher duration of load increment. It has also been observed that the rate of decrease in the compressibility is maximum up to 2.5% lime and thereafter gradual. The compressibility of lime –treated fly ashes further reduces when gypsum is incorporated, the optimum gypsum percentage being 2.5. This reduction in the compressibility of fly ashes enhanced by incorporating lime and gypsum makes them versatile in the construction of embankments and for structural fills, particularly reducing the time required in between laying of each lift. It has been brought out that decrease in the lime leachability decreases the compressibility of fly ashes. Fly ash has potential application in the construction of base liners of waste containment facilities. While most of the fly ashes improve in the strength with curing, the ranges of hydraulic conductivities they attain may often not meet the basic requirement of a liner material. Attempts to reduce the hydraulic conductivity by adding lime as gypsum along with lime to both the fly ashes are presented in chapter 7. Hydraulic conductivities of the compacted specimens have been determined in the laboratory using the falling head methods. It has been observed that the addition of gypsum reduces the hydraulic conductivity of the lime treated fly ashes. The reduction in the hydraulic conductivity of the fly ashes containing gypsum is significantly more of sample with high amounts of lime contents (as high as 1000 times) than those with lower amounts of lime. However, there is relatively more increases in the strengths of the samples with the inclusion of gypsum to the fly ashes even at lower lime contents. This is due to the fact that excess lime added to fly ash is not effectively converted in to pozzolanic compounds. Even the presence of gypsum is observed not to activate these reactions with excess lime. On the other hand the higher amount of lime in the presence of gypsum is observed to produce more cementitious compounds which block the pores in the fly ash. Amount of lime leached in the found to be directly related to the hydraulic conductivity inspite of many –fold variations in the hydraulic conductivity achieved by curing fly ash with lime and gypsum. The consequent reduction on the hydraulic conductivity of fly ash would be beneficial in reducing the leachability of trace elements in the fly ash when used as base liner. Fly ash contains trace metals and other substances in the sufficient quantities which may leach out over a period of time. The study has been extended to examine the leachability of a few selected trace metals viz., Cd, Cu, Cr, Mn, Pb and Zn from fly ash before and after incorporating additives has been reported in chapter 9. The standard laboratory leaching test for the combustion residues developed by Van der Sloot et al. has been employed to study the leachabilities of trace elements as a function of liquid to solid (L/S) ratio and pH. The leachability test were conducted on the powdered fly ash samples obtained from unconfined compressive strength tests, conducted after a curing period of 28 and 180 days. It observed that, there is a marked reduction in the relative leachabilities of trace elements present, at the end of 28 days which reduced only marginally at the end of 180 days. Chapter 9 reports the retention capacities of fly ashes for copper, lead and zinc metals ions. Various parameters like contact time, initial concentration and pH have been varied and their effect on retention mechanism studied. The retention order of metals ions, Cu+ 2 > Pb+2>Zn+2, is observed to be the same for both the fly ashes at all pH values. The dominant mechanisms responsible for the retention are precipitation at higher pH’s as hydroxides and adsorption at lower pH’s Due to presence of silica and alumina oxide surface in fly ash. First order kinetic plots have revealed that the rate constant value increases with increase in initial concentration and pH. Langmuir adsorption isotherms have been plotted to study the maximum adsorption isotherms have been plotted to study the maximum adsorption capacities for metal ions under different conditions. The older indicates that the adsorption is predominantly by silica surface than that by alumina or iron oxide surfaces. This thesis demonstrates that incorporation of gypsum along with lime in the optimal proportions not only reduces the lime leachability but also greatly enhances the strength and CBR values, reduces the compressibility and minimizes the leaching of trace elements present in them enhancing the potential of fly ashes for many applications. Detailed conclusions are presented in chapter 10. The study greatly helps in promoting the use of fly ashes for many geotechnical and geo-environmental applications.

Fly ash and blast furnace slag are the two major industrial solid by-products generated in most countries including India. Although their utilization rate has increased in the recent years, still huge quantities of these material remain unused and are stored or disposed of consuming large land area involving huge costs apart from causing environmental problems. Environmentally safe disposal of Fly ash is much more troublesome because of its ever increasing quantity and its nature compared to blast furnace slag. Bulk utilization of these materials which is essentially possible in civil engineering in general and more particular in geotechnical engineering can provide a relief to environmental problems apart from having economic benefit. One of the important aspects of these waste materials is that they improve physical and mechanical properties with time and can be enhanced to a significant level by activating with chemical additives like lime and cement. Class-C Fly ashes which have sufficient lime are well utilized but class-F Fly ashes account for a considerable portion that is disposed of due to their low chemical reactivity. Blast furnace slag in granulated form is used as a replacement for sand to conserve the fast declining natural source. The granulated blast furnace slag (GBS) is further ground to enhance its pozzolanic nature. If GBS is activated by chemical means rather than grinding, it can provide a good economical option and enhance its utilization potential as well. GGBS is latent hydraulic cement and is mostly utilized in cement and concrete industries. Most uses of these materials are due to their pozzolanic reactivity. Though Fly ash and GGBS are pozzolanic materials, there is a considerable difference in their chemical composition. For optimal pozzolanic reactivity, sufficient lime and silica should be available in desired proportions. Generally, Fly ash has higher silica (SiO2) content whereas GGBS is rich in lime (CaO) content. Combining these two industrial wastes in the right proportion may be more beneficial compared to using them individually. The main objective of the thesis has been to evaluate the suitability of the class-F Fly ash/GGBS mixtures with as high Fly ash contents for Geotechnical and Geo-environmental applications. For this purpose, sufficient amount of class-F Fly ash and GGBS were collected and their mixtures were tested in the laboratory for analyzing their mechanical behavior. The experimental program included the evaluation of mechanical properties such as compaction, strength, compressibility of the Fly ash/GGBS mixtures at different proportions with GGBS content varying from 10 to 40 percent. An external agent such as chemical additives like lime or cement is required to accelerate the hydration and pozzolanic reactions in both these materials. Hence, addition of varying percentages of lime is also considered. However, these studies are not extended to chemically activate GBS and only GGBS is used in the present study. Unconfined compressive strength tests have been carried out on various Fly ash/ GGBS mixtures at different proportions at different curing periods. The test results demonstrated rise in strength with increase in GGBS content and with 30 and 40 percent of GGBS addition, the mixture showed higher strength than either of the components i.e. Fly ash or GGBS after sufficient curing periods. Addition of small amount of lime increased the strength tremendously which indicated the occurrence of stronger cementitious reactions in the Fly ash/GGBS mixtures than in samples containing only Fly ash. Improvement of the strength of the Fly ash/GGBS mixtures was explained through micro-structural and mineralogical studies. The microstructure and mineralogical studies of the original and the stabilized samples were investigated by scanning electron microscopy (SEM) and X-Ray diffraction techniques respectively. These studies together showed the formation of cementitious compounds such as C-S-H, responsible for imparting strength to the pozzolanic materials, is better in the mixture containing 30 and 40 percent of GGBS content than in individual components. Resilient and permanent deformation behavior on an optimized mix sample of Fly ash and GGBS cured for 7 day curing period has been studied. The Resilient Modulus (Mr) is a measure of subgrade material stiffness and is actually an estimate of its modulus of elasticity (E). The permanent deformation behavior is also important in predicting the performance of the pavements particularly in thin pavements encountered mainly in rural and low volume roads. The higher resilient modulus values indicated its suitability for use as subgrade or sub-base materials in pavement construction. Permanent axial strain was found to increase with the number of load cycles and accumulation of plastic strain in the sample reduced with the increase in confining pressure. Consolidation tests were carried on Fly ash/GGBS mixtures using conventional oedometer to assess their volume stability. However, such materials develop increased strength with time and conventional rate of 24 hour as duration of load increment which requires considerable time to complete the test is not suitable to assess their volume change behavior in initial stages. An attempt was thus made to reduce the duration of load increment so as to reflect the true compressibility characteristics of the material as close as possible. By comparing the compressibility behavior of Fly ash and GGBS between conventional 24 hour and 30 minutes duration of load increment, it was found that 30 minutes was sufficient to assess the compressibility characteristics due to the higher rate of consolidation. The results indicated the compressibility of the Fly ash/GGBS mixtures slightly decreases initially but increase with increase in GGBS content. Addition of lime did not have any significant effect on the compressibility characteristics since the pozzolanic reaction, which is a time dependent process and as such could not influence due to very low duration of loading. Results were also represented in terms of constrained modulus which is a most commonly used parameter for the determination of settlement under one dimensional compression tests. It was found that tangent constrained modulus showed higher values only at higher amounts of GGBS. It was also concluded that settlement analysis can also be done by taking into account the constrained modulus. The low values of compression and recompression indices suggested that settlements on the embankments and fills (and the structures built upon these) will be immediate and minimal when these mixtures are used. In addition to geotechnical applications of Fly ash/GGBS mixture, their use for the removal of heavy metals for contaminated soils was also explored. Batch equilibrium tests at different pH and time intervals were conducted with Fly ash and Fly ash/GGBS mixture at a proportion of 70:30 by weight as adsorbents to adsorb lead ions. It was found that though uptake of lead by Fly ash itself was high, it increased further in the presence of GGBS. Also, the removal of lead ions increased with increase in pH of the solution but decreases at very high pH. The retention of lead ions by sorbents at higher pH was due to its precipitation as hydroxide. Results of the adsorption kinetics showed that the reaction involving removal of lead by both the adsorbents follow second-order kinetics. One of the major problems which geotechnical engineers often face is construction of foundations on expansive soils. Though stabilization of expansive soils with lime or cement is well established, the use of by-product materials such as Fly ash and blast furnace slag to achieve economy and reduce the disposal problem needs to be explored. To stabilize the soil, binder comprising of Fly ash and GGBS in the ratio of 70:30 was used. Different percentages of binder with respect to the soil were incorporated to the expansive soil and changes in the physical and engineering properties of the soil were examined. Small addition of lime was also considered to enhance the pozzolanic reactions by increasing the pH. It was found that liquid limit, plasticity index, swell potential and swell pressure of the expansive soil decreased considerably while the strength increased with the addition of binder. The effect was more pronounced with the addition of lime. Swell potential and swell pressure reduced significantly in the presence of lime. Based on the results, it can be concluded that the expansive soils can be successfully stabilized with the Fly ash-GGBS based binder with small addition of lime. This is also more advantageous in terms of lime requirement which is typically high when Fly ash, class-F in particular, is used alone to stabilize expansive soils. Based on the studies carried out in the present work, it is established that combination of Fly ash and GGBS can be advantageous as compared to using them separately for various geotechnical applications such as for construction of embankments/fills, stabilization of expansive soils etc. with very small amount of lime. Further, these mixtures have better potential for geo-environmental applications such as decontamination of soil. However, it is still a challenge to activate GBS without grinding.

Geopolymer concretes synthesised from composite class F fly ashes and a mixed alkaline activator were optimised by use of Taguchi orthogonal design method. The optimised mix achieved a compressive strength at the age of 28 days of 70 and 58 MPa after initial curing at 70??C for 12 hours and at 23??C for 24 hours, respectively. The resultant Geopolymer has an amorphous aluminosilicate structure. Efflorescence and the potential risk of alkali-silica reaction for the Geopolymer used in this study are both very low. The research confirmed that the Geopolymer concrete developed in this study is far superior to Portland cement concrete when exposed in a sulphuric acid environment. The standard immersion tests finally selected for this research were in 10% sulphuric acid for 56 days and in 1% sulphuric acid for one year. Geopolymer concrete samples retained their shape without softening though they experienced a mass loss of about 5% and a strength loss of some 30%. Portland cement concrete recorded a mass loss of some 40% in a 10% sulphuric acid for 28 days. The penetration rate of sulphuric acid into the Geopolymer concrete was found to approximately follow Fick’s first law of diffusion and a linear relationship between the neutralisation depth and the square root of immersion time (in day) was established. The degradation processes of Geopolymer concrete in sulphuric acid environments were intensively studied. The first stage involved the preferential liberation of alkali ions. The tetrahedral aluminium in the Si-O-Al configuration was removed and converted to octahedral aluminium. Consequently, the original units of Si(1Al) degraded to a silica polymorph structure in the corroded Geopolymer, which continued to serve a cementitious role. In contrast, in the case of Portland cement concrete, the acid solution dissolved the hydration products of the cement paste. The residual reaction products were found to be soft and have no structural strength. Geopolymers with alkaline activators of mixed sodium hydroxide and sodium silicate did not exhibit any cracking problems. Class F fly ash with low calcium content was found to be suitable for developing a Geopolymer binder able to withstand sulphuric acid attack.

Most concrete produced today utilizes pozzolans or supplementary cementitious materials (SCMs) to promote better long term durability and resistance to deleterious chemical reactions. While other pozzolans and SCMs are available and provide many of the same benefits, Class F fly ash has become the industry standard for producing quality, durable concrete because of its low cost and wide-spread availability. With impending environmental and safety regulations threatening the availability and quality of Class F fly ash, it is becoming increasing important to find viable alternatives. This research aims to find natural, lightly processed, alternatives to fly ash that perform similarly to Class F fly ash with regards to pozzolanic reactivity and provide comparable compressive strength, workability, drying shrinkage, thermal expansion properties and resistance to alkali-silica reaction, sulfate attack, and chloride ion penetration. Eight fly ash alternatives from the US were tested for compatibility with the governing standard for pozzolans used in portland cement concrete and various fresh and hardened mortar and concrete properties. The results of this research indicate that six materials meet the requirements for natural pozzolans set by the American Society for Testing and Materials and many are comparable to Class F fly ash in durability tests. The primary concern when using these materials in concrete is the increase in water demand. The spherical particle shape of fly ash provides improved workability even at relatively low water-to-cement ratios; however, all of the materials tested for this research required grinding to achieve the appropriate particle size, resulting in an angular and rough surface area that requires more lubrication to achieve a workable consistency. So long as an appropriate water reducing admixture is used, six of the eight materials tested in this study are appropriate and beneficial for use in portland cement concrete.
text

Thesis (M.S.)--University of Wisconsin--Madison, 1996.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 114-116).

South Africa is a country with very little prime farmland. A large percentage of this high agricultural capability land is generally acidic and nutrient poor, and situated in areas where large coal mining activities occur. Coal mining and agriculture are important industries in South Africa. They impact extensive land areas, and often compete for the same land. The surface mining of coal seriously damages the surface soil, local flora and fauna. Mining wastes viz. overburden, discards and mine effluents, have also created land degradation problems. Three of the most common factors that characterize degraded substrates are soil acidification, nutrient depletion and loss of biological activity. To ensure a healthy and productive vegetation, disturbed soils need to be ameliorated effectively. Using conventional methods is costly and is often not sustainable. The challenge is, therefore, to use potential alternative ameliorants in an economically, ecologically and socially sustainable manner. Fortunately, South Africa has plenty of industrial and organic by-products, which might be used as alternative ameliorants. There is an enormous amount of international literature on the use of class C fly ash, (Sub bitumious or lignite CCB – [Coal combustion byproduct]), and to a lesser extent class F fly ash (Bitumious CCB), as opposed to South African class F fly ash, which is predominantly produced in this country. Fly ash, either by itself, or together with other wastes such as biosolids, can serve as a soil ameliorant by providing a good source of micro-, macronutrients and organic material for the reclamation of land. Previous research has shown that when sewage sludge is mixed with class F fly ash and a suitable source of reactive lime in a specific ratio, sewage sludge pasteurization will occur. The SLudgeASH (SLASH) mixture has been extensively evaluated as a soil ameliorant and has proven to be viable for the reclamation of poor and marginal soils. This study, has focused on the effect of soil ameliorants on the chemical-, physical- and microbiological properties of degraded agricultural land, mine land and other mining wastes (tailings and discards) requiring rehabilitation. This study also evaluated the affects of class F fly ash and SLASH amelioration of soils and substrates on plant production and revegetation, in comparison with conventional liming and fertilization methods currently in use. Species such as maize (Zea mays) and wheat (Triticum aestivum); pasture legumes such as lucerne or alfalfa (Medicago sativa); sub tropical grasses such as Foxtail Buffalo grass (Cenchrus ciliaris), Rhodegrass (Chloris gayana) and Smutsfinger grass (Digitaria erianthra) have been evaluated. The success of enhanced plant production, re- vegetation and sustainability of once degraded soils / substrates is an indication of the amelioration success achieved. Seed germination, root development, plant yield, plant density, botanical diversity and biological activity are parameters which can all be used to support the conclusion that alternative substrate amendment practices can improve the plant growth medium. Based on the results obtained in this study, it was concluded that fly ash and fly ash/organic material mixtures (SLASH) improved soil chemical properties such as pH, ammonium acetate extractable K, Ca, Mg and Bray 1 extractable P levels. All parameters measured were significantly influenced by the fly ash and SLASH. For example, the pH of soils impacted by acid mine drainage was improved by 240% by the use of SLASH. Other results illustrate improvements in soil physical properties such as texture, bulk density, water infiltration rate and hydraulic conductivity, by class F fly ash based soil ameliorants. In addition to the beneficial effects on soil physical properties, the microbial properties were also improved, as indicated by the beneficiation of symbiotic relationship of the Rhizobium bacteria and the important host plant Medicago sativa. Improvements in crop yields, such as: wheat yields on SLASH and fly ash treatments were 270% and 150% better than the control respectively; yields of maize and alfalfa were improved by 130 % and 450% respectively, were also registered. Fly ash and SLASH ameliorated soils resulted in approximately 850%, 266% and 110% higher dry matter production on gold mine tailings, AMD impacted soil and acidic mine cover soil, respectively, relative to the control treatments. Results also clearly illustrated that the abundance of certain species can be related to the higher fertility levels of the rehabilitated soil. Data collected over the past seven years, illustrates how the botanical composition has changed, and that soils receiving class F fly ash and sewage sludge had a higher dry matter production, whereas the control (no treatment) had a better biodiversity. With respect to the reclamation of coal discard materials, significant increases in yield, of up to 200%, were noted for soils and discards treated with class F fly ash, relative to the untreated control. The pH of cover soil was the most strongly affected soil parameter during the experimental period. Class F fly ash and SLASH have the potential to improve the chemical, physical and microbiological properties of degraded soils and substrates. From this experimental work it can be concluded that class F fly ash from Lethabo definitely has a much higher CaCO3 equivalent than what was originally assumed and that other SA sources probably have an even better neutralizing value. Class F fly ash and SLASH, are good sources of micronutrients and some macro nutrients, and may play a significant role in neutralizing acidity due to their residual alkalinity, and thus ability to continuously change the soil chemical balance so that nutrients become more available for plant uptake and use, thereby enhancing growth. Agricultural, domestic and industrial byproducts unfortunately, vary greatly in nutrient content, trace metals and liming potential, and these factors can affect both re-vegetation success and the environmental impact of reclamation. Co-utilization of by-products can often combine beneficial properties of the individual by-products to eventually have a more pronounced effect on the degraded soil or substrate.
Thesis (PhD(Pasture Science))--University of Pretoria, 2008.
Plant Production and Soil Science
PhD
unrestricted

碩士
國立成功大學
土木工程學系碩博士班
97
The Alkali-activated cementitious materials refer to each kind of silicates and aluminosilicates which adds the solid or liquid state of alkali activator to initiate a reaction and produce the material with cementitious property. Due to the differences between the composition of material and the process of manufacture, both the harden mechanism and type of hydrate of Alkali-activated cementitious material differ from these of Portland cement In recent years, this Alkali-activated cementitious material is considered to have fabulous performance, for instance, high compressive strength, corrosion resistance, permeation resistance, durability, etc., are much better than these properties of Portland cement. In this study, the industrial waste such as Circulating Fluidized Bed(CFB) byproduct lime and mechanical activated fly ash were investigated as basic ingredient of alkali-activated cementitious materials. Attrition milling is carried out to improve reactivity of fly ash through size reduction and Calcium in byproduct lime can support the reactions. According to different mixture of materials, we discuss the experiment results, and make the analysis from material mechanical properties, to internal microstructure completely. The compressive strength increases continuingly in 28 days. It is also with well fluidity as an appropriate water:gel ratio. Scanning electron microscopy was used to observe the end products of alkali-activated cementitious materials, geopolymer gel and calcium silicate hydrate gel are included. However, because of its well apparel and firm structure, it is the reason mechanical excel in its performance.