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.

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.

Evolution of Lime and Microstructural Development In Fly Ash-Portland Cement Systems

1989 ◽  
Vol 178 ◽  
Author(s):  
Joseph A. Larbi ◽  
Jan M. Bijen
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Dilution Effect ◽  
Pozzolanic Reaction ◽  
Microstructural Development ◽  
Inert Material ◽  
Interfacial Region ◽  
Interfacial Zone ◽  
Fly Ashes ◽  
Intimate Contact

AbstractThe evolution and distribution of calcium hydroxide, CH, and the development of microstructure during the hydration of three low-calcium fly ash-Portland cement blends with water-solids ratio (w/s) of 0.40 have been investigated. During the first month of hydration, the CH content of the blends was found to be relatively higher than the plain mix, if a dilution effect due to replacement of cement by an inert material is taken into account. After 28 days of hydration the CH content in the blends began to decrease. SEM observations of specimens revealed the occurrence of large, well-crystallized CH plates in intimate contact with some of the fly ash particles at younger ages and even after six months of aging. The study also showed that the chemistry of the pore solution in contact with the hydrating cement system and the characteristics of the fly ashes, such as the glass content and the fineness of the ash particles seem to exert major influences on the rate of evolution of CH in the fly ash blends. Semi-quantitative X-ray diffraction analyses performed on specimens cast against polypropylene plastic plates used to “model coarse aggregates” showed reduction in the thickness of the interfacial zone for the fly ash-Portland cement pastes from about 60μm to less than 15μm within one month of hydration. In the case of the plain Portland cement paste no significant change was observed. The degree of orientation of CH crystals within the interfacial region also was significantly affected by the fly ashes, although by this age of hydration the CH data showed little or no evidence of pozzolanic reaction.

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

Synergistic Effect of High Temperature Fly Ash with Fluidized Bed Combustion Fly Ash in Cement Composites

2016 ◽  
Vol 722 ◽  
pp. 113-118
Author(s):  
Martin Ťažký ◽  
Rudolf Hela
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Fluidized Bed ◽  
Fossil Fuels ◽  
Cement Composite ◽  
Pozzolanic Reaction ◽  
Cement Composites ◽  
Fluidized Bed Combustion ◽  
Cement Pastes ◽  
Free Cao

Using high temperature fly ash for his pozzolan properties to cement composite production is known a few years ago. New ways combustion of fossil fuels also creates a new type of fly ash, named fluidized bed combustion fly ash. However, this fly ash has same pozzolan properties as has high temperature fly ash, this type is not using for production of cement composites. Fluidized bed combustion fly ash has highly variable chemical composition but usually it has a higher amount of free CaO together with sulphates. This higher amounts of free CaO after mixing of fluidized bed combustion fly ash with water to some extent becomes an activator for the beginning of the pozzolanic reaction, during which is consumed the extinguished CaO. If there is also present high temperature fly ash in cement composite, it could be accelerated his pozzolanic reaction in the same manner using a fluidized bed combustion fly ash. In this experiment was tested a synergy effect in the use of fluidized bed combustion fly ash with high temperature fly ash as an additive. The experiment was carried out on cement pastes that have been studied in particular the progress of hydration processes, pointing to a possible acceleration of pozzolanic reactions of both types of fly ash.

Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes

2012 ◽  
Vol 27 (1) ◽  
pp. 560-569 ◽  
Author(s):  
Qiang Zeng ◽  
Kefei Li ◽  
Teddy Fen-chong ◽  
Patrick Dangla
Keyword(s):  
Fly Ash ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Cement Pastes

scholarly journals Durability Assessment of Concrete with Class-F Fly Ash by Chloride Ion Permeability

2019 ◽  
Vol 8 (4) ◽  
pp. 8831-8836
Keyword(s):  
Fly Ash ◽  
Chloride Ion ◽  
Pozzolanic Reaction ◽  
Chloride Ions ◽  
Permeability Test ◽  
Reaction Products ◽  
Chloride Permeability ◽  
Cement Pastes ◽  
Rapid Chloride Permeability ◽  
Class F Fly Ash

This paper discusses on Rapid Chloride Permeability Test investigations on penetration of chloride ions included with replacement of cement by flyash material. By weigth of cement, the fly ash content is replaced from 0% to 60%. Concrete mixes with different binder content varies from 350, 400 and 450 kg/m3 were proportioned with different water binder(w/b) ratios = 0.4, 0.45 and 0.50. Specimens were casted and tested for 28 days. For all the combinations, RCPT was carried out and the charge passed through the specimens was noted. Rapid Chloride Permeability Test value of concrete without fly ash was found to be more than the concrete with fly ash. The Rapid Chloride Permeability Test values are found to be decreased if the percentage of flyash increases. The reason could be the pozzolanic reaction products (CSH) fill the pores between the cement pastes and cause a denser concrete matrix, resulting in better durability. Hence, it can be suggested that the fly ash concrete up to 50% replacement can be used for variety of applications.

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.

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