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International Concrete Abstracts Portal

Showing 1-5 of 33 Abstracts search results

Document: 

SP154-29

Date: 

May 1, 1995

Author(s):

W. S. Langley, R. Gilmour, and E. Tromposch

Publication:

Symposium Papers

Volume:

154

Abstract:

Presents an overview of the technical aspects of concrete for a major bridge project in Eastern Canada. The bridge is unique in that it is being designed, finances, and constructed by the private sector; it will also be subsequently operated by the private sector. Private sector partnering with government is a relatively new concept in Canada. This project is an example of the merits of such agreements. The design life of this structure being constructed in a marine environment is 100 years. The length of the bridge will be 12.9 km, constructed in upwards of 35 meters of water. Ice floes throughout the winter and early spring have a major influence on the design and resultant configuration of the structure. Durability of the concrete with respect to chloride ingress, sulfate attack, freezing and thawing, abrasion resistance, and alkali-aggregate reactivity are addressed in the proportioning of concrete mixtures and in the structural design. Extensive use is made of silica fume and fly ash as a measure to reduce chloride diffusivity and heat rise in the more massive sections.

DOI:

10.14359/1032


Document: 

SP154-02

Date: 

May 1, 1995

Author(s):

E. G. Nawy and B. Chen

Publication:

Symposium Papers

Volume:

154

Abstract:

This paper covers analytical and experimental investigation of high- strength concrete beams reinforced with high-strength prestressed concrete prisms as main reinforcement. Fiber optics technology has been developed and used in this investigation to measure the flexural crack widths developed throughout the full loading history of the specimens. Thirteen beams, 8 in. x 12 in. (200 x 300 mm) is cross section and having a 9.0 ft (2.74 m) span were tested to failure. The embedded prestressed prisms had a length of 9 ft, 6 in. (2.90 m) and cross-sectional dimensions ranging between 1.5 in. x 3.0 in. (38 mm x 76 mm) and 4.5 in. x 3.0 in. (114 mm x 76 mm). The prisms were prestressed with 7-wire, 3/8 in. (10 mm) diameter, 270 ksi (1860 MPa) tendons. Concrete strength in both the prisms and the beams was in excess of 14,000 psi (100 MPa) using silica fume as a partial cementitious replacement, as well as a high-range water reducer (superplasticizer) to attain the desired workability and compressive strength. A study of the extensive data accumulated in this research program, supported by the National Science Foundation, resulted in expressions for the evaluation of flexural crack widths in ultra-high-strength concrete composite beams. Test results also showed that the embedded prisms delayed the development of cracks, while the additional use of non-prestressing steel significantly reduced the crack spacing in the beams and limited the crack width at the onset of prism cracking.

DOI:

10.14359/948


Document: 

SP154-10

Date: 

May 1, 1995

Author(s):

J. Marchand and B. Gerard

Publication:

Symposium Papers

Volume:

154

Abstract:

Cement-based composites are used in the construction of a wide range of structures. During their service life, many of these structures are exposed to various types of aggression; their durability is generally controlled by their diffusivity and permeability of the cement-based composite. Since the assessment of these two properties by laboratory or in situ tests is often difficult and generally time-consuming, a great deal of effort has been made towards developing microstructure-based models to predict them. A critical review of the most recent developments in this field is presented in this paper. The report begins with a survey of the various mathematical concepts developed to characterize the structure of porous media. Empirical and physical models are reviewed in separate sections. Special emphasis is placed on recent innovations in the field of numerical and digital image analysis based modeling. Each model is evaluated on the basis of its ability to predict the mass transport properties of a wide range of cement-based composites and its potential application to the study of other micro- and macro-structural properties.

DOI:

10.14359/1056


Document: 

SP154-28

Date: 

May 1, 1995

Author(s):

P. K. Mehtra and K. J. Folliard

Publication:

Symposium Papers

Volume:

154

Abstract:

Presents a review of recent research focusing on the durability of concrete and mortar containing rice husk ash (RHA). The purpose of the investigation was to determine the effects of RHA in cement products exposed to hostile environments. Included are the results of laboratory research on hydrochloric acid attack, sulfate attack, alkali-silica reaction, and frost action on mortar or concrete mixtures containing RHA. The results showed that mortar or concrete containing RHA showed a substantial reduction in mass loss on exposure to a hydrochloric acid solution and considerable reduction in alkali-silica and sulfate expansions. Also, the frost resistance of non-air- entrained concrete containing RHA was found to be considerably higher than similar concrete mixtures containing silica fume.

DOI:

10.14359/968


Document: 

SP154-25

Date: 

May 1, 1995

Author(s):

C. Wang and W. H. Dilger

Publication:

Symposium Papers

Volume:

154

Abstract:

As a result of the very low water-cement ratio in a high-performance concrete, the rate of cement hydration at early ages is significantly different from that in a normal strength concrete. The ultimate degree of cement hydration is lower in a high-performance concrete; the hydration process will terminate earlier because of the rapidly diminishing water supply. Another characteristic of high-performance concrete is caused by the relatively high dosage of superplasticizer which delays the onset of the cement hydration. This paper presents the extension of the research on temperature and strength development in hardening concrete from normal strength concrete to high- performance concrete. It models the development of heat of hydration in high-performance concrete, taking into account the effects of water-cement ratio, superplasticizers, and temperature changes. General formulations of the rate of heat of hydration as functions of concrete maturity (hydration stage) and current temperature are provided. Comparison with some test results verifies the theoretical model.

DOI:

10.14359/965


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