Beneficiation of Waste Fly Ash and Phosphogypsum— The Development of a New Material

2021 ◽  
Vol 47 (1) ◽  
pp. 70-81
Author(s):  
Tebogo Mashifana ◽  
Felix Okonta ◽  
Freeman Ntuli
Keyword(s):  
Fly Ash ◽  
Citric Acid ◽  
Chemical Composition ◽  
Detrimental Effect ◽  
Pozzolanic Reaction ◽  
Building Construction ◽  
Strength Development ◽  
Material Strength ◽  
Minimum Requirements ◽  
New Material

Waste phosphogypsum (PG) was treated with citric acid, oxalic acid, sodium carbonate and sodium bicarbonate to reduce the contaminants in the material and render the material applicable for other applications. The chemical composition revealed that the material was laden with contaminants such as fluorides and phosphorous which have a detrimental effect on the development of material strength. Citric acid was the best leaching reagent to reduce the radionuclides in PG and it was selected as the leaching reagent to treat PG. The chemical composition of both the raw PG and treated PG showed that there was insufficient pozzolans in the materials to trigger the pozzolanic reaction for strength development. Therefore the PG had to be stabilized with fly ash and lime. The optimum mix ratio of the raw PG composite that yielded the highest UCS was made up of 50% raw PG and 30% FA, while 30% treated PG and 50% FA yielded the highest strength. The variation in strengths between the raw and treated PG was due to differences in the microstructure of the materials and the particle size distribution. The strength obtained met the minimum requirements for the material to be used in bulk as building construction elements.

Fly-Ash Concretes of 50% of the Replacement Ratio to Reduce the Cracking in Concrete Structures

2013 ◽  
Vol 405-408 ◽  
pp. 2665-2670 ◽  
Author(s):  
Ming Jie Mao ◽  
Qiu Ning Yang ◽  
Wen Bo Zhang ◽  
Isamu Yoshitake
Keyword(s):  
Fly Ash ◽  
Concrete Structures ◽  
High Volume ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Early Age ◽  
Replacement Ratio ◽  
Fly Ash Concrete ◽  
Massive Concrete ◽  
Normal Strength

Fly-ash concrete used in massive concrete structure has superior advantages to reduce hydration heat. On the other hand, the fly-ash concrete has negative property of low strength development at early age because pozzolanic reaction of fly-ash activates at mature age, such as after 28 days. To investigate these characteristics of fly-ash used in concrete, the present study discusses thermal cracking possibility of fly-ash concrete by using FE analysis software. The present study employs prediction formulae proposed by Zhang and Japanese design code in the simulations. The objects in this study are normal strength concrete mixed of fly-ash up to 50% of replacement ratio to cement. The comparative investigations show that temperature effect is more significant than strength development at early age. Based on the analytical study, high volume fly-ash concretes of 30-50% of the replacement ratio can be concluded as effective and useful materials to reduce the cracking possibility in massive concrete structures. Keywords-Fly-ash concrete; Early Age, Prediction Formulae for Strength; Thermal Stress Analysis

Evidence for Minimal Pozzolanic Reaction in a Fly Ash Cement During the Period of Major Strength Development

1988 ◽  
Vol 136 ◽  
Author(s):  
Sidney Diamond ◽  
Qizhong Sheng ◽  
Jan Olek
Keyword(s):  
Fly Ash ◽  
Plain Concrete ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Inert Material ◽  
Microscope Examination ◽  
Intimate Contact ◽  
Cement Pastes ◽  
Minimal Evidence ◽  
Water Contents

ABSTRACTStrengths developed in fly ash concretes usually equal or exceed that of similar plain concrete after a few months, with much of the response usually attributed to “pozzolanic” reaction between ash and secondary calcium hydroxide (CH). The CH contents of pastes made with five different fly ashes were determined by DTA for periods up to six months. The CH contents found did not decrease notably over the period, and were substantially identical to that expected for plain cement pastes diluted with the same amount of inert material as the amount of fly ash used. Scanning electron microscope examination of the pastes showed only minimal evidence of reaction even up to 1 year of age, although many fly ash grains were in intimate contact with CH. Non-evaporable water contents of the fly ash pastes were substantially higher than expected at each age, suggesting that the fly ash promoted more complete cement hydration or that the hydration products formed bound substantially greater amounts of water than plain cement paste ordinarily does.

Evidence for Minimal Pozzolanic Reaction in a Fly Ash Cement during the Period of Major Strength Development

1988 ◽  
Vol 137 ◽  
Author(s):  
Sidney Diamond ◽  
Qizhong Sheng ◽  
Jan Olek
Keyword(s):  
Fly Ash ◽  
Plain Concrete ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Inert Material ◽  
Microscope Examination ◽  
Intimate Contact ◽  
Cement Pastes ◽  
Minimal Evidence ◽  
Water Contents

AbstractStrengths developed in fly ash concretes usually equal or exceed that of similar plain concrete after a few months, with much of the response usually attributed to “pozzolanic” reaction between ash and secondary calcium hydroxide (CH). The CH contents of pastes made with five different fly ashes were determined by DTA for periods up to six months. The CH contents found did not decrease notably over the period, and were substantially identical to that expected for plain cement pastes diluted with the same amount of inert material as the amount of fly ash used. Scanning electron microscope examination of the pastes showed only minimal evidence of reaction even up to 1 year of age, although many fly ash grains were in intimate contact with CH. Non-evaporable water contents of the fly ash pastes were substantially higher than expected at each age, suggesting that the fly ash promoted more complete cement hydration or that the hydration products formed bound substantially greater amounts of water than plain cement paste ordinarily does.

Analysis of the Cementitious and Pozzolanic Properties of a Silico-Aluminous (Class F) Fly Ash

1985 ◽  
Vol 65 ◽  
Author(s):  
Andre Carles-Gibergues ◽  
Pierre-Claude Aitcin
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Chemical Composition ◽  
Pure Water ◽  
Mineralogical Composition ◽  
Pozzolanic Reaction ◽  
Strength Increase ◽  
Lime Water ◽  
Physico Chemical ◽  
Class F

ABSTRACTA silico-aluminous (Class F) French fly ash has been studied during the last ten years. While over this period the fly ash was produced from different bituminous coals, it has demonstrated high constancy in terms of its chemical and physical composition as well as cementitious properties. The first part of this paper gives a complete physico-chemical characterization of this fly ash, including chemical composition, mineralogical composition of its crystallized fraction, chemical composition of its glass, grain-size distribution, specific surface area, and bulk density. The second part deals with physico-chemical experiments performed to determine the cementitious components of this fly ash through its dissolution in pure water and in lime water. The lime water experiment was also carried out on a washed sample containing few residual sulfates. This series of experiments demonstrates the importance of sulfates in this particular fly ash, especially during the early stages of hydration. Their action results in the formation of ettringite. The cementitious role of these sulfates has been confirmed by comparing the compressive strength of mortar cubes containing washed and nonwashed fly ash. After 7 days, mortar cubes made with this fly ash showed a slight compressive strength increase when compared to a reference mix containing the same amount of quartz. This compressive strength increase can be related to the formation of C-S-H due to the pozzolanic reaction. After 8 months, the pozzolanic reaction had consumed most of the lime generated by the hydration of C2S and C3S, so that practically no portlandite remained in the mortar.

scholarly journals Resilient performance of expansive subgrades stabilized with nanosized and activated fly ash

2021 ◽  
Author(s):  
Frank Ikechukwu Aneke ◽  
Mohamed Mostafa Hassan
Keyword(s):  
Fly Ash ◽  
Resilient Modulus ◽  
Morphological Changes ◽  
Expansive Soils ◽  
Pozzolanic Reaction ◽  
Exchange Capacity ◽  
Degree Of Saturation ◽  
Strength Development ◽  
High Plasticity ◽  
Test Result

Subgrades across arid and semi-arid region are known for its random swelling, with high plasticity due to moisture infiltration of the pavement structures. Subgrades materials are significantly influenced by the cahnges in degree of saturation, which is unavoidable. Studies in the past, have reported several positive results on the stabilization of expansive soils with additives like lime, cement, fly ash, etc. In this study, resilient performance of expansive subgrades treated with 0.5%, 1.0%, 1.5% and 2.0% of nanosized and activated fly ash (NFA and AFA) is presented. Series of cation exchange capacity tests, zero swelling tests (ZST) and resilient modulus (M_R ) tests were performed to study the effects of NFA and AFA on resilient modulus (M_R) and swelling index of the subgrades material respectively. Scanning electron microscopy (SEM) tests was conducted to evaluate the morphological changes in the subgrades, and compounds responsible for resilient strength development. The result showed that, NFA and AFA inclusions in the treatment of expansive subgrades caused an increase in resilient strength and decrease in swelling stress to a limiting stabilizer content of 0.5% and 1.0% beyond which, the resilient modulus values increased triggering a significant decrease in swelling stress. The test result revealed that the reduction was caused by the pozzolanic reaction between the stabilizers and available moisture required for full completion of pozzolanic process. Based on the test result, nano-fly ash exhibite high potential in improving resilient strength and reducing swelling stress to 58.7% and 63% respectively on the average compared to activated fly ash. This study suggest a feasible solution to improve the quality and performance of expansive subgrades.

Investigation on the Degree of Reaction and Strength Performance of Fly Ash Based Geopolymer Binder with Alternative Chemical Reagents

2014 ◽  
Vol 803 ◽  
pp. 115-119
Author(s):  
Norbaizurah Rahman ◽  
Andri Kusbiantoro
Keyword(s):  
Fly Ash ◽  
Citric Acid ◽  
Sodium Nitrate ◽  
Setting Time ◽  
Strength Development ◽  
Degree Of Hydration ◽  
Degree Of Reaction ◽  
High Calcium ◽  
Geopolymer Binder ◽  
Geopolymer Paste

The existence of high calcium contents in fly ash will contribute to the rapid stiffening and low workability of geopolymer paste. This study reports the feasibility of sodium nitrate and citric acid as the alternative admixtures for geopolymer binder. The effects of sodium nitrate and citric acid were independently evaluated at 0.5%, 1.5% and 2.5% of fly ash weight in geopolymer mixture. The effect of these admixtures on fresh geopolymer characteristic was evaluated through series of setting time and flow table workability tests, while degree of hydration, compressive strength and porosity tests were conducted to provide fundamental information on the hardened properties of geopolymer paste. Based on the result of degree of reaction, the inclusion of sodium nitrate in fly ash based geopolymer will increase the level of degree of hydration. Nevertheless, this result is in contrast with citric acid inclusion where degree of hydration decreased along with the increasing dosage of citric acid in the mixture. Strength development of geopolymer paste, particularly during the early age, appears to be affected by various geopolymerization rate presented by these admixtures.

Mechanical Properties and Thermal Resistance of High Volume Fly Ash Concrete for Energy Efficiency in Building Construction

2016 ◽  
Vol 678 ◽  
pp. 99-108 ◽  
Author(s):  
B. Balakrishnan ◽  
A.S.M. Abdul Awal
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Fly Ash ◽  
Elevated Temperatures ◽  
Value Added ◽  
High Volume ◽  
Building Construction ◽  
Strength Development ◽  
Fly Ash Concrete ◽  
High Volume Fly Ash

The utilization of waste materials in concrete is one of the best value added solutions to the construction industry. With the aim of sustability development, high volume fly ash (HVFA) were tested in concrete by substituting 40, 50 and 60% of OPC with fly ash. Properties studied in this research includes fresh concrete properties, mechanical properties and the resistance of concrete exposed to high temperature. The test result indicates that HVFA concrete positively influenced the workability; however, the setting times of the concrete were longer. It has been found that the development of strength of high volume fly ash concrete was relatively slower, but ahigher strength development at later ages was observed in concrete containing HVFA. The performance of concrete at elevated temperatures reveals that concrete without any fly ash has better resistance than HVFA concrete at high temperature. The use of high volume fly ash results in an acceptable concrete performance, which grants high potential for energy saving in the building construction.

Strength Development and Microstructural Investigation of Calcium Carbide Residue and Fly Ash Prepared with Optimized Alternative Green Binders

2021 ◽  
Vol 904 ◽  
pp. 429-434
Author(s):  
Papantasorn Manprom ◽  
Phongthorn Julphunthong ◽  
Pithiwat Tiantong ◽  
Tawat Suriwong
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Raw Materials ◽  
Extended Period ◽  
Calcium Carbide ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Chemical Compositions ◽  
Microstructural Investigation ◽  
Calcium Carbide Residue

The development of new environmentally friendly binder from calcium carbide residue and fly ash wastes were investigated in this study. The key point of this work is difference to several previous investigations in that the optimized mixture proportion of the raw materials were calculated based on their chemical composition and their reaction. The compressive strength development over the curing age was also compared with reference mortar created with OPC binder. Mortar cubes were cast from the mix containing the calcium carbide residue and fly ash, at the optimized ratio. The compressive strength of the mortar was then monitored over an extended period: at 56 days it was 10.66 MPa, which is approximately 47% of the reference mortar. The morphologies and chemical compositions of the developed mortar showed the presence of spherically shaped of unreacted fly ash powder particles embedded in a cement C–S–H gel resulting from the pozzolanic reaction of raw materials.

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