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.

Low Cement/High Fly Ash Concretes: Their Properties and Response to Chemical Admixtures

1987 ◽  
Vol 113 ◽  
Author(s):  
V. H. Dodson
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Calcium Hydroxide ◽  
Pozzolanic Reaction ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Fly Ashes ◽  
Chemical Admixtures ◽  
Reaction With Water

ABSTRACTIn practice, the amount of fly ash added to portland cement concrete varies depending upon the desired end properties of the concrete. Generally, when a given portland cement concrete is redesigned to include fly ash, between 10 and 50% of the cement is replaced by a volume of fly ash equal to that of the cement. Sometimes as much as twice the volume of the cement replaced, although 45.4 kg (100 lbs) of cement will only produce enough calcium hydroxide during its reaction with water to react with about 9 kg (20 lbs) of a typical fly ash. The combination of large amounts of certain fly ashes with small amounts of portland cement in concrete has been found to produce surprisingly high compressive strengths, which cannot be accounted for by the conventional “pozzolanic reaction”. Ratios of cement to fly ash as high as 1:15 by weight can produce compressive strengths of 20.7 MPa (3,000 psi) at I day and over 41.4 MPa (6,000 psi) at 28 days. Methods of identifying these “hyperactive” fly ashes along with some of the startling results, with and without chemical admixtures are described.

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.

scholarly journals Influence of Cement Replacement with Fly Ash and Ground Sand with Different Fineness on Alkali-Silica Reaction of Mortar

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1528
Author(s):  
Suwat Ramjan ◽  
Weerachart Tangchirapat ◽  
Chai Jaturapitakkul ◽  
Cheah Chee Ban ◽  
Peerapong Jitsangiam ◽  
...  
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Partial Substitution ◽  
Alkali Silica Reaction ◽  
Inert Material ◽  
Fly Ashes ◽  
River Sand ◽  
Concrete Materials

The alkali-silica reaction (ASR) is an important consideration in ensuring the long-term durability of concrete materials, especially for those containing reactive aggregates. Although fly ash (FA) has proven to be useful in preventing ASR expansion, the filler effect and the effect of FA fineness on ASR expansion are not well defined in the present literature. Hence, this study aimed to examine the effects of the filler and fineness of FA on ASR mortar expansion. FAs with two different finenesses were used to substitute ordinary Portland cement (OPC) at 20% by weight of binder. River sand (RS) with the same fineness as the FA was also used to replace OPC at the same rate as FA. The replacement of OPC with RS (an inert material) was carried out to observe the filler effect of FA on ASR. The results showed that FA and RS provided lower ASR expansions compared with the control mortar. Fine and coarse fly ashes in this study had almost the same effectiveness in mitigating the ASR expansion of the mortars. For the filler effect, smaller particles of RS had more influence on the ASR reduction than RS with coarser particles. A significant mitigation of the ASR expansion was obtained by decreasing the OPC content in the mortar mixture through its partial substitution with FA and RS.

scholarly journals Predicting the Compressive Strength of Portland Cement Concretes with the Addition of Fluidized Bed Combustion Fly Ashes from Bituminous Coal and Lignite

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 753
Author(s):  
Jacek Śliwiński ◽  
Artur Łagosz ◽  
Tomasz Tracz ◽  
Radosław Mróz ◽  
Jan Deja
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Portland Cement ◽  
Fluidized Bed ◽  
Bituminous Coal ◽  
Pozzolanic Reaction ◽  
Fluidized Bed Combustion ◽  
Fly Ashes ◽  
Binder Ratio ◽  
Water Binder Ratio

This paper presents the results of an extensive experimental study on the effect of the addition of two types of fly ash produced during fluidized bed combustion of bituminous coal and lignite, which differ substantially in their chemical and mineral compositions, on the compressive strength of concrete. Concretes with water/binder ratios of 0.65, 0.55 and 0.45 made with CEM I 42.5 R Portland cement and gravel aggregate were tested. The analyzed amounts of fly ash added to the binder were 0, 15% and 30% by weight. Based on the results of compressive strength testing after 28 and 90 days of curing, the relationships with the water/binder ratio and fly ash content in the binder were determined. The fly ashes used were highly active and capable of pozzolanic reaction. The relationships established allow the compressive strength of concretes based on composite cement-fly ash binder to be predicted with sufficient accuracy. The results presented in this study are an important contribution to the knowledge of concretes with combined binders. They have the exploratory value of establishing the dependence of compressive strength at 28 and 90 days on binder composition and water-binder ratio. In addition, they could be used almost directly in practical applications.

Microstructure of Cement Blends Including Fly Ash, Silica Fume, Slag and Fillers

1986 ◽  
Vol 86 ◽  
Author(s):  
Micheline Regourd
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Silica Fume ◽  
Blended Cement ◽  
Cement Clinker ◽  
Microstructural Development ◽  
Limestone Filler ◽  
Portland Cement Clinker

ABSTRACTThe hydration of a blended cement through hydraulic or pozzolanic reactions results in heterogeneous polyphase materials. Because portland cement clinker is the major component in most cement blends, the microstructural development of portland cement hydrates, including C-S-H and pore structures, is first discussed. Slag, fly ash, silica fume and limestone filler cements are then compared to portland cement with regards to C-S-H morphology and composition, aluminate crystallization, cement paste interfaces and pore size distribution.

Pozzolanic reaction in portland cement, silica fume, and fly ash mixtures

1997 ◽  
Vol 24 (5) ◽  
pp. 754-760 ◽  
Author(s):  
J K Weng ◽  
B W Langan ◽  
M A Ward
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Silica Fume ◽  
Pozzolanic Reaction

Accelerated Diffusion Bonding Using Induced Forces

1976 ◽  
Vol 98 (1) ◽  
pp. 65-68
Author(s):  
T. J. Morin
Keyword(s):  
Magnetic Field ◽  
Diffusion Bonding ◽  
High Pressures ◽  
Interfacial Region ◽  
Interfacial Zone ◽  
Parent Metal ◽  
Intimate Contact ◽  
Intense Magnetic Field ◽  
Diffusion Bonds ◽  
Metal Properties

Classical diffusion bonding has always connoted nonproduction-like conditions such as extremely high pressures for long times, protective environments, and excessive cleanliness requirements. The attractive characteristics are that diffusion bonds are normally produced at comparatively low temperatures and they have parent metal properties. This paper presents a technique whereby high pressures are selectively applied to the interfacial region of the two parts being joined at temperatures approximately 90–95 percent of the parent metal melt range. The parts to be joined are heated rapidly using “induction heating” techniques. The mating surfaces and the areas immediately adjacent to them are the only portions of the parts that are significantly heated in most applications. As soon as the proper temperature range has been reached, the heating current is shut off and an intense magnetic field is forced or driven through the parts. The orientation and direction of this moving magnetic field is such that a large pulsed current is caused to flow on both sides of and parallel to the interface. These large currents attract each other and give rise to substantial pressures normal to the interface, thereby producing intimate contact on a microscopic scale, allowing for rapid diffusion. There is also some preferential super heating in the interfacial zone for a few milliseconds only but greatly enhancing diffusion conditions. Results of the application of this technique to several material combinations are discussed along with photomicrographs of joined sections.

Effect of Alkaline Solution to Fly Ash Ratio on Geopolymer Mortar Properties

2017 ◽  
Vol 733 ◽  
pp. 85-88 ◽  
Author(s):  
Amir Fauzi ◽  
Mohd Fadhil Nuruddin ◽  
Ahmad B. Malkawi ◽  
Mohd Mustafa Al Bakri Abdullah ◽  
Bashar S. Mohammed
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Portland Cement ◽  
Alkaline Solution ◽  
Similar Pattern ◽  
Ordinary Portland Cement ◽  
Setting Time ◽  
Pozzolanic Reaction

Geopolymer system is new binding materials in concrete industry that is produced by the alkaline solution and materials rich in aluminosilicate such as fly ash. The effect of the alkaline solution to fly ash ratios of 0.3, 0.4 and 0.5 on mortar geopolymer properties was an issue in this study. The results showed that the higher alkaline solution to fly ash ratio improves the workability and brings a longer setting time, whereas the lower alkaline solution to fly ash ratio gains the significant compressive strength. It was a similar pattern with conventional mortar used ordinary Portland cement, which the compressive strength at 7 days was 85%-90% for 28 days compressive strength, whereas conventional mortar is only 65%-75%. This was due to the higher reactivity in geopolymer system that was faster than the pozzolanic reaction.

The Effect of Fly Ash on the Hydration of Cements At Low Temperature Mixed and Cured in Sea-Water

1987 ◽  
Vol 113 ◽  
Author(s):  
H.-U. Jensen ◽  
P. L. Pratt
Keyword(s):  
Fly Ash ◽  
Sea Water ◽  
Quantitative Description ◽  
Pozzolanic Reaction ◽  
Heat Evolution ◽  
Partial Replacement ◽  
Microstructural Development ◽  
Hydration Products ◽  
Conduction Calorimeter ◽  
Mixing Water

ABSTRACTThe use of fly ash as a partial replacement in cements is widespread because of reduced costs and the reported improvement in performance. Fly ash/cement blends have been used offshore for underbase grouting of gravity platforms, although the cold marine exposure may slow the pozzolanic reaction which is very sensitive to temperature. Sea-water could be used as mixing water under these conditions. This paper looks at how curing at 8°C, the use of sea-water as mixing water, and direct exposure to sea-water, influence the hydration, strength and microstructural development of an OPC and an SRPC with 30% fly ash replacement. The early heat evolution was measured with a conduction calorimeter, while the presence and development of hydration products were identified by DTA, TG and x-ray analysis. Scanning electron microscopy was used in two modes; secondary electron images of fracture surfaces were examined, and a quantitative description of microstructure was made possible by analysis of backscattered electron images of polished sections. The morphology and distribution of hydration products in the wet state was studied using an environmental cell in a high voltage electron microscope.

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