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International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

Document: 

SP207-27

Date: 

October 7, 2002

Author(s):

G. Menendez, V.L. Bonavetti, H. Donza, M. Trezza, and E.F. Irassar

Publication:

Symposium Papers

Volume:

207

Abstract:

This paper analyzes the mechanical behavior and its relation with the development of the hydration reaction in concretes with low water-to-cementitious material ratio made with binary and ternary cements containing limestone filler and blast furnace slag. It explores the maximum level of replacement of portland cement by both additions to obtain high early strength concrete. At 3 days, the compressive strength was 43 to 45 MPa and it was greater than 60 MPa at 28 days. All studied concretes present a very similar strength development. Results show that the combination of limestone filler and blast furnace slag is complementary: the limestone filler improves the early strength of concrete while the slag improves the later strength achieving to an optimal strength development. The concrete performance analyzed in terms of water penetration test also classified these concretes as very low permeability.

DOI:

10.14359/12405


Document: 

SP207-11

Date: 

October 7, 2002

Author(s):

A.T.C. Guimaraes and P.R.L. Helene

Publication:

Symposium Papers

Volume:

207

Abstract:

The application of deterministic models based only on Fick's Laws can show considerable differences compared to the effective chloride profiles in existing marine structures. An important factor to be taken into consideration is the influence of the concrete saturation degree (SD). In the research, a laboratory test method for the influence of the SD on chloride diffusion in hardened cement paste was developed. Test results were applied to an existing marine structure with 22 years old. Results indicate that the concrete SD has a great influence on chloride diffusion and requires further research. It also shows that the SD should be taken into account when estimating the service life of concrete structures and a model is proposed.

DOI:

10.14359/12389


Document: 

SP207-22

Date: 

October 7, 2002

Author(s):

D. de Lima Araujo and M.D. El Debs

Publication:

Symposium Papers

Volume:

207

Abstract:

This paper shows a study on the connection between precast beams and precast slabs using push-out tests. The connection is formed by steel bars associated with shear-key. The steel bars are bent in hoop shape and inserted in the pockets in slab, which are filled with cast-in-place concrete. The strength of cast-in-place concrete ranges from 50 MPa to 100 MPa and a maximum volume of 1.50 % of steel fibers is added. Results show the strength of the connection increases when the concrete strength increases, mainly when steel fibers are added. It is also observed that addition of steel fibers to high strength concrete in connections transfers failure from the shear-key to the precast concrete. This result suggests the definition of an upper limit to the relationship between the strength of cast-in-place concrete and the strength of precast concrete.

DOI:

10.14359/12400


Document: 

SP207-23

Date: 

October 7, 2002

Author(s):

V.S. Caland, M.S.L. Velasco, and R.A. Einsfeld

Publication:

Symposium Papers

Volume:

207

Abstract:

In this work, some experimental results for determination of fracture energy and brittleness number for high-performance concrete are presented. Three-point bend tests were conducted for different concrete mixture proportions, with compressive strengths of 70 MPa to 90 Mpa. The tests were performed using crack mouth opening displacement control in a closed-loop servo-hydraulic system. The experiments involved the testing of 75 single-notched beams of four different sizes in order to study the size effect. The compositions of the concrete were established according to, those specified by IBRACON (Brazilian Concrete Institute) in order to match the concrete commonly used by companies that operate in Brazil. The results found in this work by the method proposed by RILEM show that the size of the specimens influences the value of the obtained fracture energy, it being larger as the size of influences the value of the obtained fracture energy, it being larger as the size of the specimen increases, thus suggesting that the RILEM method is not valid in characterizing fracture energy as a material parameter. The results from this work found that the fracture energy obtained by the method proposed by Bazant and Pfeiffer can be adopted as a fracture parameter of the material, since its value is independent of the size of the specimen.

DOI:

10.14359/12401


Document: 

SP207-04

Date: 

October 7, 2002

Author(s):

A.N.M. Lopes, M.A. Pimenta, M.A.S. Andrade, A.S. Barbin, R.M. Bittencourt, and W. Pacelli de Andrade

Publication:

Symposium Papers

Volume:

207

Abstract:

The concrete studies for the Cana Brava Hydroelectric Plant were conducted on the basis of the following provisions: the prescriptions of the project’s Technical Specifications, with emphasis on the durability of the structures; the control of thermal-originated cracking; the use of alkali-reactive aggregates and on the Construction Consortium’s plan, which prioritized pumped concrete. These aspects led to the choice of a cementitious material ‘composed of blast furnace slag cement with addition of silica fume in all concretes used in the project. Therefore, this work will focus on the study of mixtures and the characterization of the Cana Brava concrete, both of which were held to meet the project provisions. The studies showed that the use of silica fume, through its beneficial effect in increasing concrete strength, enabled a reduction in the amount of cementitious materials, thus benefically contributing to thermal cracking control; furthermore, it proved advantageous in preventing the alkali-aggregate reaction and in reducing permeability.

DOI:

10.14359/12382


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