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Showing 1-5 of 63 Abstracts search results

Document: 

SP153-55

Date: 

June 1, 1995

Author(s):

S. NagatakiI and C. Wu

Publication:

Symposium Papers

Volume:

153

Abstract:

The workability, strength, and durability of concrete are affected by particle distribution and chemical composition of cement. So, a cement which has ideal particle distribution and chemical composition is needed is needed for making high performance concrete. This kind of cement can be realized by blending portland cement, silica fume, and blast furnace slag, because they have different particle distributions and chemical compositions. In this paper, the triple blended cement was composed of 10 percent silica fume, 30 percent blast furnace slag, and 60 percent portland cement as it had suitable chemical composition and the densest particle distribution in portland cement or portland cement admixed by silica fume or blast furnace slag in this research. The hydration process of the triple blended cement was similar to the portland cement, but the heat of hydration and Ca(OH) 2 content in the hydrates were much lower than that for portland cement. It was found that the porosity of the hardened paste was so low that it was half of that in portland cement paste. The R 2O in its pore solution was only 88 percent of that in pore solution of portland cement paste. This fact means the triple blended cement may reduce the alkali-silica reaction of concrete. The flows of the fresh mortars made by the triple blended cement were higher or lower than the flow of the control mortar depending on the specific surface area of silica fume used. The compressive strengths of the mortar were higher than that of the control mortar as its denser paste. Because of the low Ca(OH) 2 content in the hydrates and R 2O in the pore solution, the resistance of the mortars to sulfate attack and alkali-silica reaction was high. However, the drying shrinkage of the mortars made with the triple blended cement was higher than that of the control mortar.

DOI:

10.14359/1047


Document: 

SP153-27

Date: 

June 1, 1995

Author(s):

P. C. Taylor, P. E. Streicher, G. Goch, and L. Fliss

Publication:

Symposium Papers

Volume:

153

Abstract:

A test program was conducted to establish criteria for a performance- based specification of concrete quality, as a opposed to a prescriptive specification, for a major project in South Africa. Concretes containing different combinations of portland cement, fly ash, ground granulated blast furnace slag, and silica fume were prepared over a range of water/binder (W/CM) ratios. The samples were stored in water for three days to simulate the probable effects of site curing practice. Each concrete was then subjected to three different tests: air permeability and water sorptivity, both conducted in an "Autoclam," and a rapid chloride conductivity test. Time constraints prevented the preparation of a performance specification, but the results were used to prescribe a W/CM ratio and binder type. The results of the investigation also provide the basis for future evaluation of the site concrete by conducting similar tests on cores extracted from the structure. It was established that specifying only on the basis of concrete strength is insufficient to insure a high potential durability.

DOI:

10.14359/1084


Document: 

SP153-09

Date: 

June 1, 1995

Author(s):

R. B. Freeman and R. L Carrasquillo

Publication:

Symposium Papers

Volume:

153

Abstract:

Partial replacement of a moderately sulfate-resistant cement with a high-calcium fly ash may result in either increased or decreased sulfate resistance for concrete. These effects of fly ash have been related to, among other factors, changes in the permeability of concrete and changes in the stability of hydrated calcium aluminates in the presence of sulfate-bearing solutions. The objective of this study was to investigate the effects of using anhydrous sodium sulfate as a chemical admixture in concrete made with Class C fly ash. The sodium sulfate admixture was expected to influence the sulfate resistance of concrete by increasing the availability of sulfate ions during the hydration of calcium aluminates. The admixture was also expected to increase the rate of pozzolanic reactions by increasing the concentration of alkali ions in solution. In addition to studying the effects of the sodium sulfate admixture on sulfate resistance, its effects on mixing water requirements, compressive strength, and permeability were also examined. The fly ash was introduced into the concrete by two methods: partialre placement of portland cement with fly ash at the time of mixing concrete and intergrinding of fly ash with portland cement clinker and gypsum, as in the production of blended cements. A commercially available ASTM C 150 Type II cement and five ASTM C 618 Class C fly ashes were used. The fly ashes replaced the portland cement (or the cement clinker plus gypsum) at a level of 35 percent by volume. For each source of fly ash, 14 concrete mixtures were produced; seven mixtures included Type II cement and fly ash with various amounts of the sodium sulfate admixture and seven mixtures included blended fly ash cement with various amounts of the sodium sulfate admixture. The use of sodium sulfate as a concrete admixture, in amounts ranging from two to five percent by mass of cement, resulted in improved sulfate resistance for concrete containing Class C fly ash. In many cases, sulfate resistance exceeded that of Type II cement concrete without fly ash. Additional effects of the sodium sulfate admixture included increased compressive strengths at early ages and lower permeabilities at early ages.

DOI:

10.14359/1068


Document: 

SP153-24

Date: 

June 1, 1995

Author(s):

A. Hassaballah and T. H. Wenzel

Publication:

Symposium Papers

Volume:

153

Abstract:

The water-to-cementitious materials ratio (W/CM) is recognized as an important variable in understanding and controlling the quality of concretes containing pozzolan powder additives, such as fly ash. This paper presents part of a study to determine a correct way to evaluate the contribution of fly ash to concrete strength as is usually indicated by the W/CM ratio. A rational mathematical model of the form W/CM = W/(C + K * FA) is presented, in which W, C and FA are water, cement, and fly ash contents per m 3 of concrete, respectively. K is a pozzolan efficiency factor based on comparing the compressive strength of two concretes having the same workability and the same amount of cement. An experimental program was conducted to demonstrate the use of the proposed W/CM ratio model and corresponding K values. The variables studied were class and addition level of fly ash and slump, strength, and age of concrete. Results show that the model describes and considers the influence of fly ash on the rheological properties of fresh concrete and on the strength of hardened concrete. The model is also suitable for use as an equivalent to Abram's law to account for modern day powder additives.

DOI:

10.14359/1081


Document: 

SP153-20

Date: 

June 1, 1995

Author(s):

R. V. Ranganath, R. C. Sharma, and S. Krishnamoorthy

Publication:

Symposium Papers

Volume:

153

Abstract:

The authors have examined the lime-reactivity strength data of 14 samples of fly ash obtained from different thermal power plants of India. The sand-lime-fly ash mortars cured at 50 C and relative humidity of 90 percent were tested in compression at different ages up to 90 days. It was found that lime reactivity is best correlated with combined parameters of fineness and soluble silica content, rather than with each parameter considered individually. Also examined were the strength of concrete mixtures in which part of the cement is replaced by a low reactive fly ash. Fineness of fly ash and testing ages for strength were the variables. It is concluded that the soluble silica content was related to later-age strengths, while the early-age strength correlated better with fineness of fly ash. The mechanism for the latter may not be chemical, but physical, such as dispersion of cement particles or micro-filler effect.

DOI:

10.14359/1026


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