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International Concrete Abstracts Portal

Showing 1-5 of 70 Abstracts search results

Document: 

SP212-15

Date: 

June 1, 2003

Author(s):

M. S. Konsta-Gdoutos, J. K. Dattatreya, and S. P. Shah

Publication:

Symposium Papers

Volume:

212

Abstract:

This paper illustrates the effect of silica fume, ultra fine fly ash and ground gran- ulated blast furnace slag on the compressive strength, shrinkage and the development of pore structure of high performance concrete. Shrinkage measurements were carried out using a modified version of ASTM C-341, as proposed by Tarawa and Mirawaya. The experimental data obtained demonstrates how the material composition, the water to binder ratio, and the distribution of pore volume influence strength, autogenous, drying and total shrinkage. High strength mixtures containing ultra fine fly ash, silica fume and ordinary Portland cement exhibited an increased drying shrinkage rate, when compared with the slag mixture. By using a 10% replacement of UFFA, a large improvement with respect to autogenous shrinkage, relative to a 10% silica fume replacement in high strength concrete occurs, without any noticeable effect on compressive strength. The pore structure of the matrix paste at early ages of hydration appears to have a strong effect on autogenous shrinkage.

DOI:

10.14359/12688


Document: 

SP212-25

Date: 

June 1, 2003

Author(s):

T. Callanan and M. Richardson

Publication:

Symposium Papers

Volume:

212

Abstract:

Performance-based specifications for concrete exposed to chlorides may involve the determination of long-term material parameters by relatively short-term laboratory tests. The first generation of chloride environment durability models are likely to be based on diffusion theory, despite the fact that chloride ingress is both by absorption and diffusion. This paper compares chloride resistance values from laboratory experiments and from field trials, derived solely on diffusion-based modelling. Concrete prisms were exposed to sodium chloride solutions in laboratory tests for a period of 12 months. The trials included both continuous immersion and cyclical wetting and drying cycles. Chloride values were determined at 3, 6 and 12 months. Material variables included normal portland cement, fly ash, crushed limestone aggregate, natural sand, and natural gravels. Diffusion coefficients were derived through best-fit curves based on Crank’s error function solution of Fick’s second law of diffusion. It was found that the laboratory test diffusion coefficients diminished significantly with increase in test duration and stabilised between 6 and 12 months, by which time they yielded values of a similar order of magnitude to those from the structures in service. The coefficients for gravel aggregate con- crete specimens were more variable than those for crushed rock aggregate concretes and could exceed the in-service values by a factor of at least two. The beneficial influence of fly ash was reflected in the results.

DOI:

10.14359/12698


Document: 

SP212-27

Date: 

June 1, 2003

Author(s):

J. Schlumpf

Publication:

Symposium Papers

Volume:

212

Abstract:

Switzerland is a leading country in Europe regarding the use of Self Compacting Concrete. The current world's largest tunnelling project, the 56km Gotthard base tunnel, which is crossing the Alps from North to South, is designed for a service life of 100 years with only minor maintenance allowed during this period. SCC, as well as conventional concrete have been tested. On the basis of studies effected in 1998 at the TFB, and of the knowledge gained since 1998 with applications in practice, concrete mixtures for SCC were elaborated according to the AlpTransit prequalification specifications for the first time in 1999. The differences in the composition of the mixtures are principally the content of the < 0 .125 mm fines fraction and in the grading of the aggregate. Further differences are in the type and quantity of the high-performance plasticisers (Polycarboxvlate) and the water content in the concrete. On the basis of gained knowledge and past practical experience, it can be said that under the conditions as described here, water content for durable SCC mixtures should not exceed 180 l/m3. With the mixtures presented in this paper it is possible to manufacture SCC meeting the durability specications of AlpTransit Gotthard.

DOI:

10.14359/12700


Document: 

SP212-23

Date: 

June 1, 2003

Author(s):

T. Ozturan and M. E. Bastopcu

Publication:

Symposium Papers

Volume:

212

Abstract:

When concrete is properly cured, pozzolanic reaction products of fly ash fill in the spaces between the hydrating cement particles, thus lowering the permeability to water and aggressive chemicals. This paper describes the durability of fly ash concrete subjected to different curing conditions. Sorptivity, chloride-ion penetration, and resistance to deicing-salt scaling were tested for concretes containing 0, 15.30, and 45 percent Class C fly ash by weight of cement. Specimens were tested at 28 and 56 days after being subjected to three different curing conditions. It was seen that increasing the fly ash content decreased the sorptivity, chloride-ion penetration and deicing-salt scaling of concretes with the exception that they were increased for the specimens that were not properly cured. Highest durability performance was observed for concrete specimens subjected to hot water curing. Moist cured specimens came next.

DOI:

10.14359/12696


Document: 

SP212-18

Date: 

June 1, 2003

Author(s):

G. Moriconi and F. Tittarelli

Publication:

Symposium Papers

Volume:

212

Abstract:

The environmental attack on reinforced concrete structures can he reduced by preventing water penetration into the concrete pores using hydrophobic agents as concrete admixtures. In order to point out problems related to their practical use, the effectiveness of hydrophobic admixture on cement pastes with different w/c, and in the presence of other commonly used chemical admixtures, was studied. Capillary water absorption and the contact angle between water drops and the cement paste surface were evaluated. Changes in the cement paste porosity due to the hydrophobic admixture were studied by porosimetric analysis. The results obtained show that the hydrophobic admixture is able to reduce the prolonged capillary water absorption in all cement pastes by about 70%. regardless of how it is added. The hydrophobic agent appears even more effective during the initial phase of water absorption, especially with increasing w/c. The simultaneous presence of either plasticizing or air-entraining admixtures does not negatively affect the effectiveness of the hydrophobic agent even if different ways of addition are used. An appreciable increase in the cement paste porosity, related to an ex- pected reduction in mechanical strength, is observed only for cement paste with the highest w/c (0.50).

DOI:

10.14359/12691


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