Increase In Fly Ash Content Research Articles

Removal of dyes from aqueous solutions by adsortion on mixtures of fly ash in batch and column techniques

Adsorption and removal of commercial dyes were studied in aqueous suspensions of fly ash mixtures with a sandy clay loam soil of low organic matter content. The commercial dyes, acid orange 7, acid yellow 23, disperse blue 79, basic yellow 28 and direct yellow 28 represent the widely used nitroazo structures. Batch and column experiments were carried out at equilibrium conditions for concentrations of dyes between 5 and 60 mg l-1. The logarithmic form of Freundlich equation gave a high linearity and the k constants are increasing with the increase of fly ash content in adsorbent mixtures and the affinity between the adsorbent surface and adsorbed solute. The mean removed amounts of dyes by adsorption batch experiments in soil mixture with 20% fly ash content were up to 53.0% for acid yellow 7, 44.9% for acid yellow 23, 99.2% for direct yellow 28, 96.8% for basic yellow 28 and 88.5% for disperse blue 79. The removal of dyes from column experiments decrease with the increase of the solution concentration form 10 to 50 mg l-1 at 20 °C, showing the process to be highly dependent on the concentration of the solution. The mean removed amounts of dyes by adsorption on columns of soil mixture with 20% fly ash content and for initial concentration of dye solutions 50 mg l-1 were up to 33.8% for acid yellow 7, 59.4% for acid yellow 23, 84.2% for direct yellow 28, 98.2% for basic yellow 28 and 60.3% for disperse blue 79.

Mix design for fly ash based oil palm shell geopolymer lightweight concrete

This paper presents the experimental results of an on-going research project to produce geopolymer lightweight concrete using two locally available waste materials – low calcium fly ash (FA) and oil palm shell (OPS) – as the binder and lightweight coarse aggregate, respectively. A total of 32 mixes using different mixture proportions were prepared to get an appropriate mix design for fly ash based oil palm shell geopolymer lightweight concrete (OPSGPC). A mixture of sodium hydroxide and sodium silicate in different molarities was used as an alkali activator. The variables used in this investigation include the fly ash content, molarity and condition of OPS. The proposed mix design differs widely from the procedure used for mix proportioning of concrete produced with conventional lightweight and normal weight aggregates. The increase in FA content reduces the strength significantly due to additional water used for workability. The increase in molarity from 14M to 16M did not have desired effect on the compressive strength. However, the use of OPS with SSD condition produced higher strength than that of AD condition. The OPSGPC with 14M, FA content of 480kg/m3 and water to FA ratio of 0.34 produced 28-day compressive strength of about 32MPa and is recommended for producing structural grade 30 OPSGPC. The demoulded densities of OPSGPC were within the limit of 2000kg/m3 for lightweight concrete.

Freezing–thawing durability of fly ash concrete composites containing silica fume and polypropylene fiber

A parametric experimental study has been conducted to investigate the combined effect of fly ash, silica fume and polypropylene fiber on freezing–thawing durability of concrete composite. Four fly ash contents, four silica fume contents and five different fiber volume fractions were used. Results reveal that the addition of fly ash has lowered the freezing–thawing durability of concrete composite containing fly ash and that the freezing–thawing durability is decreasing gradually with the increase of fly ash content. It is evident that the addition of silica fume and polypropylene fiber can greatly improve the freezing–thawing durability of the concrete composite containing fly ash and the freezing–thawing durability is enhanced as the silica fume content and the fiber volume fraction increases gradually, with the fiber volume fraction below 0.08%. However, the freezing–thawing durability of concrete composite begins to decline after the fiber volume dosage exceeds 0.08%.

Removal of carbamazepine from aqueous solution by adsorption on fly ash-amended soil

Carbamazepine (CBZ), nonbiodegradable pharmaceutical residue, has become an emerging pollutant in several aquatic environments. The effectiveness of the mixture of soil and fly ash (FA) in adsorbing CBZ from aqueous solution has been studied as well as agitation time, FA content, initial CBZ concentration and desorption as a function of FA content. The adsorption kinetics fits a hyperbolic or pseudo-second-order model. The maximum adsorbed amounts for natural soil and a mixture of soil/FA ranged from 77 to 158 mg kg(-1). Rate constants were considered relatively low (4.15-15.59 × 10(-4) kg mg(-1) min). The logarithmic form of the Freundlich equation gave a linearity and the Kf constants increased with the increase of FA content in adsorbent mixtures and with the affinity between the adsorbent surface and adsorbed solute. The mean removed amounts of CBZ by adsorption batch experiments in a soil mixture with 30% FA content were up to 92.8% for coal FA and 33% in natural soil. This work proved that the mixture of the coal FA and soil can be used as an efficient adsorbent material for removal of CBZ from water.

Compressive Strength of Blended Portland Cement Mortars Incorporating Fly Ash and Silica Fume at High Volume Replacement

Fly ash has been widely used as a replacement of Portland cement at high content levels, but the compressive strength of Portland cement blended with fly ash is lower at early ages. Thus, this study compares the compressive strength of ternary blended Portland cement mortars incorporating fly ash (40-70 wt%) and silica fume (5-10 wt%) with binary blended Portland cement mortars incorporating fly ash only. Blended Portland cement mortars were designed with a constant water/binder ratio of 0.485 and the flow table tested was carried out. A fine aggregate to binder ratio of 2.75 was used. The compressive strength of all blended Portland cement mortars that cured in water at 23 °C was tested at 28 days. The results show that the flow of blended Portland cement mortars increased with increasing fly ash content and tended to decrease with increasing silica fume content, at the same replacement level. Moreover, the compressive strength of blended Portland cement mortars decreased with increasing fly ash content. However, compressive strength gains were obtained from ternary blended Portland cement mortars incorporating silica fume, tending to increase with increasing silica fume content.

Leaching Behavior of Aluminum, Arsenic, and Chromium from Highway Structural Fills Amended with High-Carbon Fly Ash

Coal combustion byproducts such as high-carbon fly ash (HCFA) are commonly used in highway construction as a stabilizing agent or soil amendment. Annually, 131 million tons of fly ash is produced in the United States. Unfortunately, only 40% of this fly ash is recycled, most of which are Class C and Class F types. These types of fly ash are generally used in concrete and cement production. However, HCFA cannot be used in such processes because of its high carbon content. Therefore, large amounts of HCFA are being put into landfills and causing significant economic loss and loss of valuable land space. Reuse of HCFA in geotechnical structures, particularly in road embankment construction, keeps these materials out of landfills. However, it is important to determine the environmental suitability of HCFA as a soil amendment because it poses a great potential for metal leaching. To evaluate environmental suitability, a series of column leach tests were conducted to determine the leaching of metals (aluminum, arsenic, and chromium) from soils amended with fly ash. In addition, numerical computer modeling programs were used to predict the metal concentrations in the soil vadose zone and ground-water. Results from laboratory tests indicated that metal concentrations increased with an increase in fly ash content and did not exceed the maximum concentration limits for drinking water, with few exceptions. Numerical modeling techniques predicted that leached metal concentrations decreased in the soil vadose zone with time and that concentrations of leached metals would be below environmental regulatory limits.

Effect of mineral admixtures on fluidity and stability of self-consolidating mortar subjected to prolonged mixing time

During continuous mixing of concrete in a truck mixer for its hauling to a construction site, concrete should remain workable without any signs of instability. Good workability at construction site is essential for high quality concrete since concretes of bad workability are prone to yield low strength and poor durability properties. This paper presents the effects of water to binder ratio, binary and ternary blends use of fly ash (FA) and metakaolin (MK) on fluidity, viscosity, and stability of self-consolidating mortars (SCMs) subjected to prolonged mixing time. The obtained results indicate that, by prolonged mixing time, flocculated cement particles are dispersed and as a result, fluidity is increased and so, the risk of instability increases. In addition, increasing FA content from 0 in the reference mixture to 20% and 50% of total binder mass increased the segregation index by about 48% and 160%, respectively. Furthermore, mixtures containing MK and FA have higher fluid capacity without any signs of instability. The addition of 7.5% MK has significantly improved the overall performance of the mixture, including the segregation stability.

Correlation studies on index properties of fly ash-stabilised expansive clay liners

The study of earthen barriers or clay liners has become very important in the field of geo-environmental engineering. The design of clay liners is based on the fact that leachate migration through clay liners depends on their hydraulic conductivity. The engineering behaviour of clay liners can be predicted through a proper estimation of some of the basic index properties like liquid limit which play a significant role in this study. An attempt at understanding the variation of index properties with the concentration of permeating fluids reveals useful facts about the clay liners. This paper proposes an innovative clay liner material in the form of fly ash-stabilised (or, fly ash-blended) expansive clay and presents a study on variation of index properties of the blend with varying fly ash content in the blend and concentration of salt solutions. The various permeating liquids used were deionised water and salt solutions such as CaCl2, NaCl and KCl. When expansive soils are stabilized with fly ash, index properties like liquid limit (LL) and swelling properties like free swell index (FSI) decrease; hydraulic conductivity also decreases because of a high dry density attained by the blend at increased fly ash contents. This paper presents experimental data on LL and FSI of an expansive clay soil stabilized with fly ash at 0%, 10%, 20% and 30% by weight of the expansive soil. The solution concentrations used in the test programme were 5 mM (or 5 milli Molar), 10 mM, 20 mM, 50 mM, 100 mM and 500 mM. LL and FSI decreased with increasing fly ash content in the blend and solution concentration for all the salt solutions. Useful correlations between LL and FSI for the salt solution concentration and the fly ash contents were obtained. Hydraulic conductivity decreased with increasing fly ash content in the blend and also with increasing solution concentration.

EFFECT OF ADDITION OF FLY ASH ON SHRINKAGE CHARACTERISTICS IN HIGH STRENGTH CONCRETE

This paper presents the results of an experimental investigation carried out to evaluate the shrinkage of High Strength Concrete. High Strength Concrete is made by partial replacement of cement by fly ash. The shrinkage of High Strength Concrete has been studied using the different mixes from a minimum of 10% to maximum of 70 %. From the test results of the above investigation it can be concluded that the shrinkage strain of High Strength Concrete increases with increase in fly ash content. The rate of increase in shrinkage with time is uniform for low fly ash content, whereas it generally increases after 28 days for high volume of fly ash and the high volume fly ash concrete yields slow strength development at an early age.

Combined effect of polypropylene fiber and silica fume on workability and carbonation resistance of concrete composite containing fly ash

A parametric experimental study has been conducted to investigate the combined effect of polypropylene fiber and silica fume on the workability and carbonation resistance of concrete composite containing fly ash. Five different fiber volume fractions, four contents of fly ash and four silica fume contents were used. The results indicate that the workability of the concrete composite becomes better and better by increasing the fly ash content. The addition of fly ash has lowered the carbonation resistance of concrete composite, and the carbonation resistance is decreasing gradually with the increase of fly ash content. Besides, the addition of silica fume can evidently improve the carbonation resistance of concrete composites containing fly ash, and the carbonation resistance is becoming better and better as the silica fume content is increasing gradually. In addition, polypropylene fiber can greatly improve the carbonation resistance of concrete composites containing fly ash and silica fume, and there is a tendency of increase in the carbonation resistance with the increase of fiber volume fraction as the fiber volume fraction is below 0.12%. However, the addition of silica fume and polypropylene fiber has a little adverse effect on the workability of the concrete composites.

Water impermeability of fly ash concrete composites containing silica fume and polypropylene fiber

A parametric experimental study has been conducted to investigate the combined effect of fly ash, silica fume and polypropylene fiber on the water impermeability of concrete composite. Four fly ash contents, four silica fume contents and five different fiber volume fractions were used. Fly ash and silica fume were mixed in concrete composites by replacing the same quantity of cement, and polypropylene fiber was mixed in concrete with the dosage of cementitious materials unchanged. Results reveal that the addition of fly ash, silica fume and polypropylene fiber can decrease the length of water permeability of the concrete composite evidently. The average length of water permeability is decreasing gradually with the increase of fly ash content, silica fume content, and fiber volume fraction, respectively. Silica fume and polypropylene fiber seem to play an important role to improve the water impermeability of concrete composites containing fly ash.

Impact properties of engineered cementitious composites with high volume fly ash using SHPB test

The split Hopkinson pressure bar (SHPB) testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites (ECCs) with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete (RPC) and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

Magnesium Phosphate Cement with Large Volume of Fly Ash

The accumulation of fly ash leads to severe problems in ecological environments. Various ways to excite the activity of fly ash in Portland cement based cementitious materials have been carried out for many years. In the present study, effect of large volume of fly ash in phosphate cement was studied. Dead burned magnesia, two phosphates (monoammonium phosphate and monosodium phosphate), and fly ash were used. The fabricated cement mortar specimens with different fly ash dosages were cured for 28 days in the lab air. Compressive strength was determined in 1d, 3d, 7d and 28d respectively. It is showed the compressive strength reduced with increase of fly ash content and increased with the curing time. After cured 28 days, the compressive strength of cement mortar developed to14MPa, when 80% fly ash was used. The reaction product, Na2HPO4•17H2O was found by X-ray diffraction analysis in sodium phosphate based cement. No ammonia gas was emitted and large volume of fly ash can be used in cement prepared from sodium phosphate. It is a new environmentally friendly cement material.

Behavior of High Performance PVA Fiber Reinforced Cement Composites under Uniaxial Compressive Load

Abstract. Based on an extensive experimental program, the paper studies the behavior of High Performance Fiber Reinforced Cement Composite (HPFRCC) under Uniaxial compression. The experimental parameters are: PVA fiber content by volume, fly ash and silica fume content. The compressive strength, peak strain as well as compressive stress-strain curves are obtained. The test results reveal that PVA fibers can greatly improve plastic deformation ability of HPFRCC, especially have significant impact on ductility after the peak stress, though fiber content has small influence on compressive strength. With the increase of fly ash content, peak stress of HPFRCC decreases, but toughness increases. 10% silica fume content has not obvious effect on compressive strength for HPFRCC with large quantities of fly ash , but leads to less ductile behavior.

Improved geopolymerization of bottom ash by incorporating fly ash and using waste gypsum as additive

This research studied the improvement of the geopolymerization of bottom ash (BA) by incorporating fly ash (FA) and using flue gas desulfurization gypsum (FGDG) as additive. The BA:FA ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 were used as the blended source materials. The source materials were then replaced with 0%, 5%, 10%, and 15% of FGDG. NaOH, sodium silicate and temperature curing were used to activate the geopolymer . Test results indicated that the increase in FA content in the BA–FA blends improved the strengths of geopolymer mortars owing to the high glassy phase content and high reactivity of FA compared to those of BA. The use of up to 10% of FGDG as additive also significantly increased the strengths of geopolymer. In this case, the compressive strength enhancement was due to the increase in the Al 3+ leached from BA in the presence of SO 4 2 - and the formation of additional calcium silicate hydrate .

Study on the physical and mechanical property of ordinary portland cement and fly ash paste

An experimental investigation has been carried out to study the physical and mechanical property of high volume fly ash cement paste. Ordinary portland cement was replaced by 0, 20, 30, 40, 50, 60 and 70% class F fly ash (by weight). Water- binder ratio in all mixture was kept constant at 0.3. Cube specimens were compacted in table vibrator. As expected bulk density decreases with fly ash increment in the mixture. Apparent porosity and water absorption value increases with replacement of cement by fly ash. Results confirm the decrease in compressive strength at 3, 7 and 28 day with fly ash addition and it is more prominent in case of more than 30% fly ash content mixes. Ultrasonic pulse velocity test results indicate that the quality of the paste deteriorate with increase of fly ash content in the mixture.

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM–fly ash–lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM–fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.

Incorporation superabsorbent polymer (SAP) particles as controlling pre-existing flaws to improve the performance of engineered cementitious composites (ECC)

This paper concerns a new concept for introducing superabsorbent polymer (SAP) particles as pre-existing flaws into matrix to improve tensile property, flexural property, drying shrinkage and restrained shrinkage of engineered cementitious composites (ECC). The experimental results show that all ECC mixtures exhibit excellent ductility, more than 1.5%. Incorporating SAP particles in ECC matrix can apparently improve tensile strain capacity and toughness of ECC specimens. Compared to control specimens, tensile capacity and deflection of ECC with SAP particles can increase 92% and 77%, respectively. Moreover, SAP particles have an apparent effect on ECC with 50% fly ash (FA) compared with ECC with 70% FA. Meanwhile, introducing SAP in matrix is effective in reducing drying shrinkage and restrained shrinkage of ECC specimens, due to water-entrained capacity of SAP particles. However, SAP particles can reduce compressive strength of 5–15% compared to control specimens. In addition, increasing FA content can also increase tensile capacity and decrease drying shrinkage and restrained shrinkage of ECC specimens.

Experimental Study on the Effects of Addition of Excessive Volume of Fly Ash on Concrete Properties

This paper presents the results of experimental study on the effects of addition of excessive volume of fly ash on the strength characteristics of concrete. Crushed stone aggregate concrete with the replacement ratio of fly ash to Portland cement of 0, 10%, 20%, 30%, 40%, 60% and 80% were tested for compressive strength and modulus of elasticity at the ages of 7 days, 28 days and 91 days. The test result indicated significant reduction in compressive strength with the increase of fly ash content, indication 90% reduction at 80% fly ash replacement. Reduction in modulus of elasticity was found to be less than those of compressive strength, indicating 60% reduction at 80% fly ash replacement.

Study on the Freezing Resistance of HFCC

To the High fly-ash content concrete(abbreviated HFCC) whose fly-ash adding amount is 50%~70%, the influence of actual water-binder ratio, fly-ash content, quality of fly-ash and compression strength on the freezing resistance of HFCC were studied; The critical freeze-thaw cycle times in this paper involved with mass loss rate Wn=5% and relative dynamic elastic modulus P=60%, the relationship between the critical freeze-thaw cycle times and the 28d compression strength of HFCC was analyzed; To HFCC without air-entraining agent, the experiment results showed that the freezing resistance decreased with the increase of actual water-binder ratio, the increase of fly-ash content and the reduce of fly-ash quality. The freeze-thaw damage of HFCC dues to the freeze-thaw degradation results from surface denudation.