Showing papers on "Fly ash published in 2013"
TL;DR: In this article, the authors present the results of comprehensive carbon footprint estimates for both geopolymer and OPC concrete, including energy expending activities associated with mining and transport of raw materials, manufacturing and concrete construction.
1,274 citations
TL;DR: In this article, the effects of chemical changes of alkaline activators on the compressive strength of mortar and analysis of the microstructure of the mortar through SEM, EDS, XRD, FT-IR and by porosity assessments were examined.
568 citations
TL;DR: In this paper, two distinct gels (C-A-S-H and N-A−S−H) are formed in activated fly ash/slag blends, and under accelerated carbonation, the N−A −S −H gel behaves comparably to fly ash-based systems, while the C-A -S -H gel is decalcified similarly to alkali activated slag.
541 citations
TL;DR: In this paper, a series of tests of the compressive strength, elastic modulus, splitting tensile strength, flow, setting time, and porosity of the alkali-activated fly ash/slag concrete were carried out.
453 citations
TL;DR: In this paper, the authors investigated the rheological properties of clay-modified cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles and nanosilica.
Abstract: This is a summary paper on the work being done at the Center for Advanced Cement-Based Materials at Northwestern University on the modification of cement-based materials with nanoparticles, specifically nanoclays, calcium carbonate nanoparticles, and nanosilica. The rheological properties of clay-modified cement-based materials are investigated to understand the influence of nanoclays on thixotropy. The influence of the method of dispersion of calcium carbonate nanoparticles on rate of hydration, setting, and compressive strength are evaluated. And an in-depth study on the mechanisms underlying the influence of nanosilica on the compressive strength gain of fly ash–cement systems is discussed. The motivation behind these studies is that with proper processing techniques and fundamental understanding of the mechanisms underlying the effect of the nanoparticles, they can be used to enhance the fresh-state and hardened properties of cement-based materials for various applications. Nanoclays can increase the green strength of self-consolidating concrete for reduced formwork pressure and slipform paving. Calcium carbonate nanoparticles and nanosilica can offset the negative effects of fly ash on early-age properties to facilitate the development of a more environmentally friendly, high-volume fly ash concrete.
422 citations
TL;DR: In this article, the authors investigated the properties of slag mortar and concretes with partial fly ash substitution and showed that the chemistry of the binding gels significantly controls the mass and ionic transport in chloride-containing environments.
373 citations
TL;DR: In this paper, a long-term study on the mechanical and durability properties of concrete prepared with 0, 50% and 100% recycled concrete aggregate that were cured in water or outdoor exposure conditions for 10 years was presented.
Abstract: This paper presents the findings of a long-term study on the mechanical and durability properties of concrete prepared with 0%, 50% and 100% recycled concrete aggregate that were cured in water or outdoor exposure conditions for 10 years. The recycled aggregate concrete (RAC) was prepared by using 25%, 35% and 55% class-F fly ash, as cement replacements. It was found that, after 10 years, the compressive strength and modulus of elasticity of the concrete prepared with 100% recycled concrete aggregate was still lower than that of the control concrete. Over this period, the highest gain in compressive strength and modulus of elasticity was recorded for the concrete mixture prepared with 55% fly ash. Fly ash improved the resistance to chloride ion penetration but it also increased the carbonation depth of the concrete.
360 citations
TL;DR: An extended overview of phase-mineral transformations of organic and inorganic matter that occur during biomass combustion was conducted in this article, where it was demonstrated that the phase composition of BA is polycomponent, heterogeneous and variable and includes: (1) mostly inorganic material (IM) composed of non-crystalline (amorphous) and crystalline to semiscale constituents; (2) subordinately organic matter (OM) consisting of char and organic minerals; and (3) some fluid matter associated with both IM and OM.
358 citations
TL;DR: In this article, the microstructural development and hardening rate of fly ash-slag geopolymers were investigated using SEM-EDS, and the reaction rate was monitored using semi-adiabatic calorimetry.
337 citations
TL;DR: In this article, the binding mechanism and properties of alkali-activated fly ash/slag (AAFS) mortars with various ratios of fly ash to slag were investigated by compressive strength test, flexural strength test and water absorption test, drying shrinkage test, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis.
289 citations
TL;DR: In this article, the role of influential factors on the strength development in a clay-fly ash geopolymer was studied and the relationship between the strength and heat energy was proposed.
TL;DR: In this article, the influence of red mud addition on the reaction, structure and properties of fly ash geopolymer was studied using isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR), electron probe microanalysis (EPMA), and mechanical testing.
TL;DR: In this article, the combined effects of colloidal nanosilica (CNS) and fly ash on the properties of cement-based materials were investigated, which revealed that CNS accelerates the setting of fly ash-cement systems by accelerating cement hydration while fly ash can offset the reduction in fluidity caused by CNS.
Abstract: The present study is aimed at investigating the combined effects of colloidal nanosilica (CNS) and fly ash on the properties of cement-based materials. The fresh and hardened properties of mixtures with CNS of 10 nm size and two Class F fly ashes were evaluated. Results revealed that CNS accelerates the setting of fly ash–cement systems by accelerating cement hydration, while fly ash can offset the reduction in fluidity caused by CNS. The early-age strength gain (before 7 d) of fly ash–cement systems was improved by CNS. However, the strength gain of mixtures with CNS diminished at later ages (after 28 d), where strength was eventually comparable to or exceeded by mixtures without CNS. Results showed that lack of Ca(OH)2, which results from the high pozzolanic reactivity of CNS at early ages, and the hydration hindrance effect of CNS on cement at later ages can be the critical reasons.
TL;DR: In this article, the effect of natural zeolite, silica fume and fly ash on the properties of fresh and hardened concrete is discussed. And the test results indicate that incorporation of mineral admixtures generally improve mechanical and durability characteristics of the mixes.
TL;DR: In this paper, the performance of fly ash/slag geopolymer binders was investigated in different forms of sulfate exposure, specifically, immersion in 5 ¾wt% magnesium sulfate or 5 ¼wt% sodium sulfate solutions, for 3 months.
Abstract: Sulfate attack is recognized as a significant threat to many concrete structures, and often takes place in soil or marine environments. However, the understanding of the behavior of alkali-activated and geopolymer materials in sulfate-rich environments is limited. Therefore, the aim of this study is to investigate the performance of alkali silicate-activated fly ash/slag geopolymer binders subjected to different forms of sulfate exposure, specifically, immersion in 5 wt% magnesium sulfate or 5 wt% sodium sulfate solutions, for 3 months. Extensive physical deterioration of the pastes is observed during immersion in MgSO4 solution, but not in Na2SO4 solution. Calcium sulfate dihydrate (gypsum) forms in pastes immersed in MgSO4, and its expansive effects are identified as being particularly damaging to the material, but it is not observed in Na2SO4 environments. A lower water/binder (w/b) ratio leads to a greatly enhanced resistance to degradation by sulfate attack. Infrared spectroscopy shows some significant changes in the silicate gel bonding environment of geopolymers immersed in MgSO4, attributed mostly to decalcification processes, but less changes upon exposure to sodium sulfate. It appears that the process of ‘sulfate attack’ on geopolymer binders is strongly dependent on the cation accompanying the sulfate, and it is suggested that a distinction should be drawn between ‘magnesium sulfate attack’ (where both Mg2+ and SO4
2− are capable of inducing damage in the structure), and general processes related to the presence of sulfate accompanied by other, non-damaging cations. The alkali-activated fly ash/slag binders tested here are susceptible to the first of these modes of attack, but not the second.
TL;DR: In this article, the main cementitious gels forming during the alkaline activation of hybrid cements (70% FA/30% OPC) were characterised by different techniques.
TL;DR: In this paper, the influence of limestone particle size and the type of (partial) cement replacement material on hydration and the mechanical properties of cement pastes was reported, and the synergistic effects of limestone and metakaolin incorporation results in improved properties at early ages, while maintaining later age properties similar to that of traditional OPC systems.
Abstract: This paper reports the influence of limestone particle size and the type of (partial) cement replacement material on hydration and the mechanical properties of cement pastes. Limestone powders having median particle sizes of 0.7, 3, and 15 μm, at OPC replacement levels between 0% and 20% (volume basis), and two other replacement materials of differing reactivity (i.e., Class F fly ash or metakaolin) at replacement levels between 0% and 10% (volume basis), are used to proportion ternary binder formulations. Fine limestone accelerates early-age hydration, resulting in comparable or better 1-day compressive strengths, and increased calcium hydroxide (CH) contents as compared to pure cement pastes. The incorporation of metakaolin in conjunction with limestone powder alters the heat release (i.e., kinetic) response significantly. A ternary blend of this nature, with 20% total cement replacement demonstrates the highest 1-day strength and lowest CH content. Thermal analysis reveals distinct peaks corresponding to the formation of the carboaluminate phases after 28 days in the limestone–metakaolin modified pastes, whereas the incorporation of similar levels of fly ash does not change the response markedly. It is shown that the synergistic effects of limestone and metakaolin incorporation results in improved properties at early ages, while maintaining later age properties similar to that of traditional OPC systems.
TL;DR: In this article, the compressive strength of MPC mortar with fly ash contents was measured at ages of 3h, 1d, 7d and 28d using XRD and SEM.
TL;DR: A parametric experimental study has been conducted to investigate the effect of polypropylene fiber on the workability and durability of the concrete composite containing fly ash and silica fume as discussed by the authors.
Abstract: A parametric experimental study has been conducted to investigate the effect of polypropylene fiber on the workability and durability of the concrete composite containing fly ash and silica fume. Four different fiber volume fractions (0.06%, 0.08%, 0.1% and 0.12%) were used. The results indicate that the addition of polypropylene fiber has a little adverse effect on the workability of concrete composite containing fly ash and silica fume. With the increase of fiber volume fraction, both of the slump and slump flow are decreasing gradually. However, the addition of polypropylene fiber has greatly improved the durability of the concrete composite containing fly ash and silica fume. The length of water permeability, the dry shrinkage strain and the carbonation depth of concrete containing fly ash and silica fume are decreasing gradually with the increase of fiber volume fraction as the fiber volume fraction is below 0.12%. Besides, freeze–thaw resistance of polypropylene fiber reinforced concrete containing fly ash and silica fume was found to slightly increase when compared to the concrete composite without fibers. Moreover, there is a tendency of increase in the freeze–thaw resistance with the increase of fiber volume fraction as the fiber volume fraction is below 0.08%. However, the freeze–thaw resistance begins to decrease slightly after the fiber volume fraction beyond 0.08%.
TL;DR: In this paper, a rational mix design method was developed for concrete with 20% to 80% fly ash replacement for cement, and the results confirmed the feasibility that up to 80 % of Class F fly ash can be suitably used as cement replacement in concrete.
TL;DR: This review considers among the most abundant the following materials - wood waste including demolition wood, phytoremediation scavengers and chromated copper arsenate (CCA) timber, sludges including de-inking sludge and sewage sludge, chicken litter and spent pot liner.
TL;DR: An overview of the published literature on the use of coal bottom ash in concrete can be found in this article, where the authors present an overview of concrete properties such as workability, bleeding and setting times.
Abstract: Coal bottom ash (CBA) is formed in coal furnaces. It is made from agglomerated ash particles that are too large to be carried in the flue gases and fall through open grates to an ash hopper at the bottom of the furnace. Bottom ash is mainly comprised of fused coarser ash particles. These particles are quite porous and look like volcanic lava. Bottom ash forms up to 25% of the total ash while the fly ash forms the remaining 75%. One of the most common uses for bottom ash is as structural fill. Published literature shown that there is a strongly possibility of coal bottom ash being used as substitute/replacement of fine aggregate (sand). Its use in concrete becomes more significant and important in view of the fact that sources of natural sand as fine aggregates are getting depleted gradually, and it is of prime importance that substitute of sand be explored. This paper presents an overview of the published literature on the use of coal bottom ash in concrete. Effect of coal bottom ash on the properties of concrete such as workability, bleeding, setting times, compressive strength, split tensile strength, flexural strength, shrinkage, and durability are presented.
TL;DR: In this article, the influence of glass content, color and particle size on ASR expansion of mortar was determined by the accelerated mortar bar method, and two approaches were investigated for green, brown and clear glass sand mortar, and they were: (1) replacing cement with pozzolans, that is, 30% fly ash, 60% GGBS, 10% silica fume, or 20% glass powder; (2) adding a suppressor, that are, plain steel fibers, and lithium chloride and lithium carbonate compounds.
Abstract: Waste glass may be used in concrete provided that the potential deleterious expansion caused by alkali–silica reaction (ASR) could be mitigated. In this study, the influence of glass content, color and particle size on ASR expansion of mortar was determined by the accelerated mortar bar method. Two approaches to control ASR expansion were investigated for green, brown and clear glass sand mortar. They were: (1) by replacing cement with pozzolans, that is, 30% fly ash, 60% GGBS, 10% silica fume, or 20% glass powder; (2) by adding a suppressor, that is, plain steel fibers, and lithium chloride and lithium carbonate compounds. Test results showed that the ASR expansion increased with higher glass content in the case of clear glass sand mortar, but would decrease with increasing content for green and brown glass sand mortar. The ASR expansion also decreased with smaller glass particle size, regardless of glass color. Fly ash and GGBS were the most effective in mitigating ASR expansion, followed by silica fume, steel fibers and lithium compounds.
TL;DR: In this paper, the influence of limestone particle size and the type and extent of (partial) cement replacement on the yield stress and plastic viscosity of ternary pastes are studied.
TL;DR: In this article, a mixture of Ca(OH)2-rich and pozzolanic materials was used for soil stabilization instead of ordinary Portland cement, and the results showed that the mixture of CCR and FA can produce a cementitious material.
TL;DR: In this article, the compressive strength and capillary water absorption of Cement Mortars containing fly ash (FA) were investigated using nano-SiO 2 (NS), nano-Al 2 O 3 (NA) and nano-Fe 2 O 4 (NF) powders and their binary and ternary combinations.
TL;DR: In this paper, the authors investigated the properties of high strength self compacting concrete (HSSCC) containing nano TiO 2 and industrial waste ash namely as fly ash (FA) for strength enhancement and durability-related characteristics along with rheological, thermal and microstructural properties.
TL;DR: Fly ash, a coal combustion byproduct with a predominantly aluminosilicate composition, is modified to develop an inexpensive sorbent for oil spill remediation and had high buoyancy critical for economic cleanup of oil over water.
Abstract: Fly ash, a coal combustion byproduct with a predominantly aluminosilicate composition, is modified to develop an inexpensive sorbent for oil spill remediation. The as-produced fly ash is a hydrophilic material with poor sorption capacity. A simple two-step chemical modification process is designed to improve the oil sorption capacity. First, the fly ash was transformed to a zeolitic material via an alkali treatment, which increased the specific surface area up to 404 m2 g–1. Then, the material was surface functionalized to form a hydrophobic material with high contact angle up to 147° that floats on the surface of an oil–water mixture. The reported oil sorption capacities of X-type zeolite sorbent with different surface functionalization (propyl-, octyl-, octadecyl-trimethoxysilane and esterification) were estimated to 1.10, 1.02, 0.86, and 1.15 g g–1, respectively. Oil sorption was about five times higher than the as-received fly ash (0.19 g g–1) and also had high buoyancy critical for economic cleanup o...
TL;DR: In this article, the effect of temperature on the hydration of Portland cement pastes blended with 50% of siliceous fly ash was investigated within a temperature range of 7 to 80°C.
TL;DR: In this paper, the effect of slag addition to the geopolymerization reaction and consequent structural rearrangement has been studied using Isothermal Conduction Calorimeter and Fourier Transform Infrared Spectroscopy.