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International Concrete Abstracts Portal

Showing 1-5 of 55 Abstracts search results

Document: 

SP199-05

Date: 

June 1, 2001

Author(s):

C. Hubert, W. Wieker, and D. Heidemann

Publication:

Symposium Papers

Volume:

199

Abstract:

Binder systems containing large amounts of fly ash have become interesting for the building material industry because of their relatively low cost, the high resistance against aggressive solutions, durability against alkali-silica reaction, low hydration heat and ecological friendliness. The hydration mechanism of these systems differs from that of neat portland cement pastes, mainly in type and amount of solid hydration products and the composition of pore solution. It was the aim of this work to compare the hydration reactions of binder systems containing fly ashes from brown coal combustion and portland cement in mixture proportions of 60% fly ash /40% portland cement with corresponding 70/30, 85/15 and zero-fly ash mixtures. Investigations of the solid hydration products by high resolution solid 29 Si MAS NMR spectroscopy, molybdate method, DTA/DSC and the chemical analysis of the pore solution showed that the pozzolanic reaction of the ash leads to a decrease of the hydroxide ion concentration in the pore fluid and the amount of solid calcium hydroxide, and increased formation of aluminosilicate hydrates. When all the Ca(OH)z is consumed, the sulfate ion concentration in the pore solution begins to rise. The influence of the activity of fly ash, the mixture ratio of fly ash/Portland cement, and the hydration time on the chemical structure of the C-S-H and C-S-A-H phases is discussed.

DOI:

10.14359/10485


Document: 

SP199-52

Date: 

June 1, 2001

Author(s):

Ali Akbar Ramezanianpour and Amir Tarighat

Publication:

Symposium Papers

Volume:

199

Abstract:

Corrosion is one of the dominating causes of deterioration of reinforced concrete structures. Carbonation of concrete can initiate the corrosion of reinforcements. Many parameters are affecting the concrete carbonation process. Due to the combination of these parameters, phenomenon of concrete carbonation is very complex. It is therefore necessary to implement numerous experimental works to find the relationship between input and output parameters. These tests are slow and time-consuming. On the other hand t h e great number __ of __ r eq uir ed tests makes the investigations costly. Thus it is worth to use numerical methods as new tools to find the relationships between input and output parameters. Neural Networks are capable of showing the relationships of inputs and outputs even in complex nonlinearity. They can be used even in the cases of little background of the theoretical rules, which govern the phenomenon. Due two these advantages of neural networks, a new model of concrete carbonation (NNCC) have been developed to show the appropriateness of the neural networks in civil engineering fields especially in advanced concrete technology, together with its usage as a new prediction model instead of conventional fitted type models.

DOI:

10.14359/10555


Document: 

SP199-16

Date: 

June 1, 2001

Author(s):

K. K. Sideris and A. E. Savva

Publication:

Symposium Papers

Volume:

199

Abstract:

The durability of five mortar and concrete mixtures was investigated in this study. A normal portland cement and four blended cements incorporating different pozzolanic materials, two natural pozzolanas and two lignite fly ashes, were used. The properties measured were compressive strength development, sulfate and chloride resistance as well as the carbonation depth. The results available until the age of 1.5 years show that the replacement of normal portland cement by a pozzolanic material usually has beneficial effects on cement’s durability, especially when the sulfate resistance of mixtures is of primary interest. The carbonation depth of the pozzolanic mixtures was greater than the control’s at all ages up to 1.5 years. Among the four pozzolanic materials examined, the treated lignite fly ash from Ptolemaida gave the best performance in all the tests.

DOI:

10.14359/10499


Document: 

SP199-19

Date: 

June 1, 2001

Author(s):

Bruce W. Ramme, Bryan C. Fisher, and Tarun R. Naik

Publication:

Symposium Papers

Volume:

199

Abstract:

Several new coal-fired combustion system modifications have been designed to improve the quality of air emissions from power plants. These plant modifications have led to changes in the character of fly ash, and presented challenges for many of it’s conventional uses. For example, low NOx burner systems improve air emissions but also have the side effect of increasing the carbon in the fly ash. Wisconsin Electric Power Company (WE) has developed three new coal ash beneficiation processes for carbon and/or ammonia removal. These new processes have been demonstrated at various Wisconsin Electric coal fired-power plants located in Michigan and Wisconsin. The processes take advantage of utilizing the residual energy in high carbon fly ash and bottom ash; while also producing high quality fly ash for use as a supplementary cementing material for the concrete industry. These beneficiation processes are also designed to remove any residual ammonia contained in the fly ash from advanced NOx reduction systems such as Selective Catalytic Reduction (SCR), Selective Non-Catalytic Reduction (SNCR), and Amine Enhanced Fuel Lean Gas Rebum (AEFLGR). These new ash beneficiation processes are designed both as stand alone systems or potential additions to existing power plants. In some cases it may be advantageous to rebum high carbon coal ash from one power plant by transporting it to another where more complete combustion normally occurs.

DOI:

10.14359/10502


Document: 

SP199-08

Date: 

June 1, 2001

Author(s):

M. S. Mathews, S. Somayaji2, and G. S. B. Ambedkar3

Publication:

Symposium Papers

Volume:

199

Abstract:

:The effects of cement and sand replacement by two classes of fly ash (C and F) on the strength and durability characteristics of concrete made using three grades of cement are discussed. The compressive strength. permeability, and sulfate resistance of a large number of samples made from three grades of ordinary concrete - common to hydraulic structures - were studied. Effects of’ cement and sand replacement ( 10%. 15%, and 20%) by the two types of fly ash were compared with the results from control specimens. They show the dependence of durability characteristics - permeability and sulfate resistance - on the class and fineness of fly ash. the grade of concrete, the amount and type of replacement. and. to a lesser degree, on the grade of cement.

DOI:

10.14359/10489


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