Use of Fluidized Bed Combustion Fly Ash as Addition Reducing Shrinkage of Concrete

2016 ◽  
Vol 865 ◽  
pp. 141-144 ◽  
Author(s):  
Lucia Osuská ◽  
Rudolf Hela
Keyword(s):  
Composite Material ◽  
High Temperature ◽  
Fly Ash ◽  
Fluidized Bed ◽  
Fresh Concrete ◽  
Fluidized Bed Combustion ◽  
Free Lime ◽  
Natural Properties ◽  
Temperature Combustion ◽  
High Temperature Combustion

Volumetric changes during ageing belong to natural properties of concrete. These changes, either growing or shrinking, can present a problem, which has to be taken into account during design and realization phases. This phenomenon is influenced by various factors and volumetric changes can be eliminated in many ways. One of the possibilities is setting appropriate combination of input materials and use of special additions and admixtures. This paper focused on verification of the method reducing shrinkage of concrete by means of using high temperature combustion fly ash combined with fluidized bed combustion fly ash as addition. The precondition is growth of new forms, in particular primary ettringite and monosulphate, which form because of the content free lime and sulphates in fluidized fly ash. If these minerals are formed in fresh concrete, they can positive prevent shrinkage without destruction of the composite material.

Influence of Use Fluidized Fly Ash Combined with High Temperature Fly Ash on Microstructure of Cement Composite

2016 ◽  
Vol 722 ◽  
pp. 146-150
Author(s):  
Lucia Osuská ◽  
Rudolf Hela ◽  
Martin Ťažký
Keyword(s):  
Electron Microscope ◽  
High Temperature ◽  
Fly Ash ◽  
Fluidized Bed ◽  
Cement Hydration ◽  
Cement Composite ◽  
Hardened Concrete ◽  
Hydration Products ◽  
Fluidized Bed Combustion ◽  
Free Lime

The constraint of using fluidized bed combustion fly ash as addition for concrete is mainly its chemical composition. Increased contents of sulphates and free lime in fluidized bed combustion fly ash causes development of undesirable ettringite during hydration. Expansive character of this mineral can have degrading effect on hardened concrete. Fluidized bed combustion fly ash as well as high temperature fly ash are considered pozzolanic addition, which is capable of reacting with Ca(OH)2 and form similar hydration products as cement hydration. Use of small amount of fluidized bed combustion fly ash can cause production of ettringite, however, when combined with high temperature fly ash, possible micro-failures could be healed with new hydration products - CSH gels. The paper deals with possibilities of confirming this theory mainly through examination of microstructure of cement composite with an electron microscope and clarifying observed hydration products.

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.

Effects of high-temperature fly ash and fluidized bed combustion ash on the hydration of Portland cement

2015 ◽  
Vol 78 ◽  
pp. 181-188 ◽  
Author(s):  
Pavel Šiler ◽  
Petr Bayer ◽  
Tomáš Sehnal ◽  
Iva Kolářová ◽  
Tomáš Opravil ◽  
...  
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Portland Cement ◽  
Fluidized Bed ◽  
Fluidized Bed Combustion

Development of Structural Concrete with Fly Ash

2014 ◽  
Vol 1054 ◽  
pp. 143-147 ◽  
Author(s):  
Rudolf Hela ◽  
Martin Ťažký
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Power Plants ◽  
Elasticity Modulus ◽  
Partial Replacement ◽  
Past Century ◽  
The Past ◽  
Temperature Combustion ◽  
Pozzolanic Properties ◽  
High Temperature Combustion

The paper describes problems of using fly ash in concrete. Using fly ash produced during high temperature combustion in power plants as addition for concrete has been known since the 60s of the past century. The Standard EN 206 Concrete - Specification, performance, production and conformity characterizes high temperature combustion fly ash as an addition of the type II, i.e. active addition with pozzolanic properties. Use of fly ash as an active addition also enables partial replacement of cement. The paper solves the extent of cement which can be replaced with fly ash in this manner. Influence of addition of fly ash on consistency of concrete, development of compressive strength and elasticity modulus at the age of 7, 28, 60 and 90 days of concrete are observed.

POSSIBILITIES OF DETERMINATION OF OPTIMAL DOSAGE OF POWER PLANT FLY ASH FOR CONCRETE

2016 ◽  
Vol 78 (5-3) ◽  
Author(s):  
Rudolf Hela ◽  
Martin Tazky ◽  
Lenka Bodnarova
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Partial Replacement ◽  
Optimal Dosage ◽  
Test Results ◽  
Temperature Combustion ◽  
High Production ◽  
Positive Effect ◽  
High Temperature Combustion

The paper describes possibilities of making use of high temperature combustion fly ash for production of concrete more effective. Efforts for maximal utilization of high temperature combustion fly ash are supported by high production of fly ash worldwide. Use of high temperature fly ash for concrete has to take into account considerably lower speed of hydration reactions compared to pure Portland cement. The paper states results of experimental determination of optimal dosage of fly ash as partial replacement of cement. Dosage of fly ash for production of concrete was optimized. Test results proved positive effect of dosage of fly ash with respect to granulometry of used cement and fly ash. Taking granulometry of fly ash and cement into consideration improves physico-mechanical properties of concrete compared to concrete with fly ash designed standardly without considering granulometry. 

Hydration of Partially Sulphated CFBC Ash With Saturated Steam

2003 ◽  
Author(s):  
Yinghai Wu ◽  
Edward J. Anthony ◽  
Lufei Jia
Keyword(s):  
Fly Ash ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Bottom Ash ◽  
Size Fraction ◽  
Hydration Process ◽  
Saturated Steam ◽  
Fluidized Bed Combustion ◽  
Free Lime ◽  
X Ray

The hydration of partially sulphated fluidized bed combustion (FBC) ash with saturated steam was carried out in the laboratory. The ash samples were obtained from a commercial-scale 165 MWe circulating fluidized bed combustor (CFBC) firing a petroleum coke and coal blend. Both bottom ash and fly ash were tested, and in addition the bottom ash was also separated into five size fractions and tested. These solid streams and the “as-received” fly ashes were hydrated by steam produced in a pressure bomb for different lengths of time at different saturated temperatures. Samples of the ashes were analyzed for free lime and calcium hydroxide content before and after the hydration process. Scanning electron microscopy (SEM) with an energy dispersive X-ray system (EDX) was employed to determine physical characteristics of the samples. X-ray diffractograms (XRD) were also used to determine the phase composition. These results show that after hydration treatment with saturated steam at elevated pressures, the unreacted CaO in the partially sulphated material can be quantitatively converted to Ca(OH)2. However, the free lime content is also observed to change throughout the hydration process, which indicates that the hydration of CaO is not the only reaction occurring in this system. It is also clear that for fines, i.e., fly ash and <75 μm size fraction bottom ash, the effectiveness of the hydration depends much more strongly on hydration time and temperature than for coarser ashes and it is also clear that the behaviour of each particle size fraction is different.

Optimization of the Composition of the Binder Based on CFBC Fly Ash

2018 ◽  
Vol 760 ◽  
pp. 184-192 ◽  
Author(s):  
Petr Formáček ◽  
Rostislav Šulc
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Computer Programs ◽  
Fluidized Bed Combustion ◽  
Slaked Lime ◽  
Cfbc Fly Ash ◽  
Main Components ◽  
Circulating Fluidized Bed Combustion

This paper is bound to previous research of materials based on fly ash. The main objective was to design an optimal ternary (three-component) binder based on fly ash from Circulating fluidized Bed Combustion (CFBC). The design of the binder is based on the optimization of individual components. Main components of the binder are CFBC fly ash, high-temperature fly ash and slaked lime. The binder was progressively designed and optimized. The strength characteristics of the various binders were measured, evaluated and the results were inserted into computer programs Surfer 8 and Grapher 8 from which ternary diagrams with strength maps were created. The best binder mixture were selected from the optimization process.

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