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International Concrete Abstracts Portal

Showing 1-5 of 17 Abstracts search results

Document: 

SP222

Date: 

May 1, 2004

Author(s):

V.M. Malhotra

Publication:

Symposium Papers

Volume:

222

Abstract:

The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources Canada, Ottawa, has played a significant role in Canada for over 40 years in the broad area of concrete technology. In recent years, CANMET has become increasingly involved in research and development dealing with supplementary cementing materials, high-performance normal-weight and lightweight concretes, and alkali-aggregate reactions. In May 2004, CANMET, in association with the American Concrete Institute and several other organizations in the United States, sponsored the Seventh CANMET/ACI International Conference on Recent Advances in Concrete Technology in Las Vegas, U.S.A. Seventeen refereed papers from more than 10 countries were presented and distributed at the conference. The proceedings consisting of refereed papers were published as ACI SP-222. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP222

DOI:

10.14359/14035


Document: 

SP222-02

Date: 

May 1, 2004

Author(s):

J. Assaad and K. H. Khayat

Publication:

Symposium Papers

Volume:

222

Abstract:

A comprehensive research program was undertaken to determine the influence of coarse aggregate concentration, binder type and content, and the use of set-modifying admixtures on lateral pressure exerted by self-consolidating concrete (SCC). Experimental columns measuring 200 mm in diameter and either 2100 or 2800 mm in height were used to determine the distribution of lateral pressure during the plastic stage of cement hydration. The effect of thixotropy of the concrete on pressure variations was investigated. Test results show that lateral pressure exerted by SCC is significantly affected by the development of shear strength properties of the plastic concrete, namely internal friction and cohesion. Mixtures incorporating greater coarse aggregate volumes and/or lower binder contents were found to exhibit higher degree of internal friction. This can reduce the mobility of the concrete and result in lower initial pressure. However, given that internal friction is an inherent property of the material which remains constant with time, the rate of drop in pressure was shown to depend mainly on the increase in cohesion. Therefore, mixtures containing higher binder contents and/or a set-accelerating admixture can exhibit sharper rate of pressure drop with time. Concrete with higher degree of thixotropy was found to develop lower initial lateral pressure and higher rate of pressure drop with time. This is attributed to the stiffening effect which enables the material to re-gain its shear strength when left at rest with-out any shearing action.

DOI:

10.14359/13302


Document: 

SP222-10

Date: 

May 1, 2004

Author(s):

I U. Mohammed, H. Hamada, and H. Yokota

Publication:

Symposium Papers

Volume:

222

Abstract:

Autogenous healing of cracks; and ingress of chloride and sulfate through the cracks in concrete were investigated utilizing 15 years old precracked prism specimens. The size of the specimens was100x 100x600 mm. The specimens were made with ordinary portland, slag (Types A, B and C), and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded in each specimen. W/C were 0.45 and 0.55. Crack widths were varied from 0.1 to 5 mm. The specimens were exposed to the tidal and sub-merged zones. Deposits along the path of the healed cracks as well. as the de-bonded areas over the steel bars located at the root of the crack were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). Mappings for chloride, sulfate, and magnesium oxide through the cracks in concrete were carried out by electron probe micro analyzer (EPMA). Autogenous healing is observed for narrower cracks (5 0.5 mm) irrespective of the cement types and exposure zones. Healing continues along the crack path. It extends to the debonded area over the steel bars at the cracked region. The deposits are con-firmed as calcium carbonate, ettringite, magnesium hydroxide, and rust. Accumulation of more chloride is found in the vicinity of the unhealed wider cracks (> 0.5 mm), especially for slag cements with a high amount of slag content. Sulfate ingress was limited over a very thin region from the crack plane. Interestingly, chloride concentration at the sulfate rich region is remarkably low. It indicates dissolution of chemically ad-sorbed chloride as well as the loss of ability of adsorption of chloride in the pore structures with the presence of sulfate.

DOI:

10.14359/13310


Document: 

SP222-13

Date: 

May 1, 2004

Author(s):

C. N. MacDonald and J. Trangsrud

Publication:

Symposium Papers

Volume:

222

Abstract:

This paper presents the introduction of a steel fiber made by a pre-cast manufacturer suitable for plant-produced products and transit-supplied concrete. The fiber con-figuration allows fiber manufacturing to be done in-house as are the other concrete products. Toughness test results indicate equivalent or improved performance with lab mixtures compared with other steel fibers available and tested. Tests were conducted with both wet (laboratory and transit mixture) and dry cast techniques for testing samples and full-scale three-edge bearing tests for dry cast pipe. Performance issues were identifiable for the sample casting techniques, compression strength, maturity, and toughness tests with fiber reinforcement. Pipe tests were conducted for the first visible crack, the first 0.25 mm crack, and the ultimate load with fabric reinforcement only, fiber reinforcement only, and then with both fabric and fiber reinforcements. Concrete mixture proportions for the pipe were constant with three dosages of fiber used: 0.25, 0.50, and 0.75 percent by volume.

DOI:

10.14359/13313


Document: 

SP222-15

Date: 

May 1, 2004

Author(s):

A. Hassan, M. Kawakami, S. Matsuoka, and H. Tanaka

Publication:

Symposium Papers

Volume:

222

Abstract:

The use of precast panels made of new ultra-high performance reactive powder composite materials (RPCM) in civil construction as permanent formwork for concrete structures and buried forms for bridge slabs is a new application that has great applicability prospects due to the high strength and durability of these new materials. The bond at the interface between RPCM and fiber-reinforced ordinary cement concrete is studied in this paper using slant shear tests. The program aimed at testing the bond between a substrate of RPCM with different surface treatments and an overlay of ordinary concrete with different fiber contents. This study concluded that casting the bonding surface of the substrate on air-cell plastic sheets produces a rough surface with concavities and thus provides an easy and effective way to increase the bonding strength. The results of this method of surface preparation are comparable to conventional methods like sand-blasting or grinder treatment. Increasing the fiber content of the concrete overlay in-creases the bond strength with the RPCM substrate if the surface of RPCM is not treated. When the surface of RPCM is roughened to obtain mechanical interlock, the high fiber content of the concrete overlay negatively affects the bond strength. A volumetric fiber content of 0.1% in the concrete overlay is found to be adequate in all surface types.

DOI:

10.14359/13315


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