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Showing 1-5 of 60 Abstracts search results

Document: 

SP178-03

Date: 

June 1, 1998

Author(s):

V. Sirivivatnanon and R.P. Khatri

Publication:

Symposium Papers

Volume:

178

Abstract:

Structural grade fly ash (FA) concrete and concrete with high volume of fly ash (HVFA) are well accepted and utilized in the Australian construction industry. These are concretes with fly ash (ASTM C 618 type F) making up between 10 and 50 % by weight of the total cementitious material. This paper is intended to demonstrate the importance of the selection of the appropriate amount of FA content for a range of applications. The durability performance of the FA concretes was compared with portland cement concretes of equivalent 28-day compressive strength, in terms of the resistance to carbonation, chloride penetration and sulfate attack. Some mixture design data for both FA and HVFA concretes and their mechanical properties are given. The likely optimum fly ash percentages for a range of applications are highlighted with respect to their properties and construction demands. It was found that a lower fly ash dosage would be more suitable for above-ground structures where a carbonation-related deterioration mechanism applied. However, for structures in aggressive sulfate ground condition or in marine environments, HVFA concrete was found to be much more suitable. Available field performance data have confirmed laboratory evaluated performance.

DOI:

10.14359/5971


Document: 

SP178-29

Date: 

June 1, 1998

Author(s):

K. Fukudome, N. Shintani, T. Saitoh, T. Kita and H. Sasaki

Publication:

Symposium Papers

Volume:

178

Abstract:

A pressurized fluidized-bed combustion power plant (PFBC) is a coal-fired thermal power plant specially developed for the enhancement of generating efficiency and the reduction of environmental loads. The physico-chemical properties of coal ash produced from this type of power plant (PFBC ash) are different from those of ordinary fly ash, because coal is mixed with pulverized limestone and burnt at a lower temperature than that in the conventional power generation system. This study explores the feasibility of utilizing PFBC ash as a concrete mineral admixture. It has been found that the coal ash from a secondary cyclone dust collector enhances the strength of concrete although it cannot improve the fluidity. A series of tests, including those for durability and changes in length, show that the durability of concrete containing the coal ash so produced is adequate for practical applications.

DOI:

10.14359/5997


Document: 

SP178-34

Date: 

June 1, 1998

Author(s):

R.N. Swamy and A.A. Darwish

Publication:

Symposium Papers

Volume:

178

Abstract:

The overall objective of this paper is to establish the engineering properties of concrete containing combinations of fly ash/silica fume and slag/silica fume. Six concrete mixtures were tested, with total cementitious materials content of 350 kg/m3 and 450 kg/m3, and a constant water/cementitious materials ratio of 0.45. The effect of three curing conditions was investigated, and the tests were performed up to about 260 days. The results reflect conclusively that cement replacement materials reduce slightly the engineering properties of portland cement concrete, and that the exposure conditions have a strong influence on flexural strength, dynamic modulus, and ultrasonic pulse velocity. Slag was generally found to be slightly superior to fly ash in the development of these engineering properties. The key to developing fly ash/silica fume and slag/silica fume concretes without suffering a reduction of strength gain when exposed to drying environmental conditions is to incorporate within the mixtures adequate amounts of portland cement and water to ensure the continuation of pozzolanic reactivity and hydration.

DOI:

10.14359/6002


Document: 

SP178-26

Date: 

June 1, 1998

Author(s):

A. Bilodeau, V.M. Malhotra and D.M. Golden

Publication:

Symposium Papers

Volume:

178

Abstract:

Canada Centre for Mineral and Energy Technology (CANMET) has an ongoing project dealing with the role of supplementary cementing materials in concrete. As a part of this program, a new type of concrete known as high-volume fly ash concrete has been developed. In this type of concrete, the water and cement contents are kept very low, i.e. about 115 and 155 kg/n?, respectively, and the proportion of low-calcium fly ash is about 56 per cent of the total cementitious materials. This type of concrete has excellent mechanical properties and durability characteristics. The objective of this study was to investigate the application of the high-volume fly ash system to the production of structural lightweight concrete. In this study, high-volume fly ash concrete mixtures were made using ASTM Type I portland cement, fly ashes from sources in the U.S.A. and lightweight coarse aggregates from four different producers, three from the U.S.A., and one from the U.K. A reference concrete mixture without fly ash was also made for comparison purposes. A large number of test specimens were cast to determine the mechanical properties and durability characteristics of the concrete. The test results show that the structural high-volume fly ash concrete had mechanical properties similar to those of the reference concrete. The fly ash concrete generated significantly less heat of hydration, and showed noticeably better resistance to chloride-ion penetration than the reference concrete of similar 2%day strength. All concretes investigated demonstrated an excellent resistance to the freezing and thawing cycling

DOI:

10.14359/5994


Document: 

SP178-59

Date: 

June 1, 1998

Author(s):

M.A. Berube, J. Duchesne and J. Frenette

Publication:

Symposium Papers

Volume:

178

Abstract:

Cement paste samples incorporating various amounts of silica fume were made and stored in humid air at 23°C and 38°C. Their pore solution was expressed under high pressure at different times, then analyzed for its alkali content. The storage temperature did not significantly affect the alkali concentration in the short term (O-28 days), where most reaction products (hydrates) are formed. However, all control and blended pastes stored at 38°C recycled very significant amounts of alkali in the pore solution between 28 days and 1.5 years, while not those stored at 23°C. Consequently, the longter effectiveness of silica fume against ASR should be better than expected from a number of recent experimental studies all involving concrete expansion tests conducted at 38°C for field concretes exposed at an average lower temperature, e.g. in many regions of the world. This would explain at the same time why satisfactory field performance is reported in Iceland, for instance, while the only one case reported until now relating to poor field performance of silica fume against ASR took place under the hot South African climate. Results from concrete prism expansion tests also indicated that ASR expansion can develop in high-performance concrete, even with moderately reactive aggregates. Other expansion results confirmed that the higher the degree of reactivity of the particular reactive aggregate to counteract, the alkali content in the silica fume, the alkali content in the portland cement used, and the cement dosage, in other words the higher the total concrete alkali content, the higher is the amount of silica fume required to counteract ASR expansion. The study also indicated that pelletizing the silica fume before mixing with the clinker at the grinding stage did not reduce its effectiveness against ASR, provided the grinding process is effective in dispersing the silica fume.

DOI:

10.14359/6027


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