International Concrete Abstracts Portal

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

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.

Magnetic Resonance Imaging (MRI) is a nondestructive technique that can be used to spatially resolve distributions of certain nuclei. Lithium is a relatively sensitive nucleus for MRI. Therefore, it is possible to directly measure the distribution of lithium in cement based materials. Lithium salts are used in concrete to suppress alkali-silica reaction. The MRI relaxation parameters associated with lithium in cement-based materials are relatively short by traditional MRI standards. Due to the short relaxation parameters, special MRI measurement techniques and hardware considerations had to be developed in order to quantify lithium distributions in cement based materials. MRI has the potential to play an important role in concrete technology. While this method has been developed for laboratory studies, measurements could be made on cores extracted from existing concrete structures.

The working mechanism of a polycarboxylate superplasticizer (PC) which is a new generation of superplasticizer (NSP) is investigated. This NSP shows a shrinkage reducing effect as well as a water reducing effect with adequate slump retention in a wide range of water cement ratio by introducing a shrinkage-reducing component (SRC) into the molecular structure. Superplasticizers have been thought to be adsorbed on cement hydrates and to show their particle dispersing effects by modifying the inter-particle potentials. On the other hand, shrinkage reducing agents of the organic type have been thought to exist at the interface between the aqueous and the pore phases in hardened cement paste and to show their shrinkage reducing effects by reducing the surface tension, which occasionally results in the degradation of freezing and thawing (F/T) resistance. In this study, the mechanisms of NSP are discussed. By building a SRC into the molecular structure, the entrained air system is expected to be controlled successfully compared to traditional shrinkage-reducing agents (SRA) and so the degradation of F/T resistance can be avoided. With the progress of hydration, SRC is released from NSP and the surface tensions decreases, which results in the reduction of drying shrinkage.

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.