International Concrete Abstracts Portal

A superworkable concrete, which has excellent deformability and resistance to segregation and can be placed in heavily reinforced formwork without vibrators, was developed and employed in the construction of a 70-story building. The height of the building is 296 m, and the height of the superworkable concrete in the tubular columns is about 40 m. Some of the columns have two diaphragms with opening ratio of seven percent at each joint of column and beams. Before actual construction, the placing of the concrete into three model columns was conducted. From the tests, it was confirmed that the superworkable concrete had excellent filling ability and left no voids under the diaphragms. A 6-m high removable column was set on top of the 40-m high column of the building to check the quality of filled concrete. The superworkable concrete was placed successfully into 66 columns of the tallest building in Japan.

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.

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.

Presents basic information on a newly developed electrically conductive concrete. The concrete differs from previous inventions in that both high conductivity and mechanical strength are simultaneously achieved. The electrical and mechanical properties of the conductive concrete developed at Institute for Research in Construction, National Research Council of Canada are given. The material has superior electrical conductivity values and excellent mechanical strength. Experimental results of a laboratory-scale study on the application of conductive concrete to deicing and/or snow melting are presented in this paper. The results indicate that heat can be uniformly produced by the conductive concrete heating element when the element is activated by an external electric power supply. The new method is effective for deicing purposes. Power output of the conductive concrete heating element is stable over a wide range of temperature. The minimum heater power output required for deicing at various air temperatures was determined. This value is linearly dependent on the air temperature, ranging from 150 to 855 W/m 2 as air temperature varies from -5 C to -30 C.

During 1994, a new 50,000 m 2 warehouse and similar area of external pavement was constructed at Ingleburn near Sydney, Australia. The client required that the warehouse meet very onerous performance criteria that required the construction of a very flat, prestressed concrete floor that would be crack free, with excellent abrasion resistance, and having a minimal number of joints. The design required that the concrete base provide the wearing surface for the floor without application of a surface topping. A second industrial project which required the construction of high performance concrete floors is a new integrated printing facility for a major newspaper, commenced at Chullora near Sydney in late 1994. The plant is highly automated; sections of the floor are designed to be frequently loaded with turning transporters carrying full rolls of newsprint. Such floors require exceptional abrasion resistance. The designers decided to seek a level of abrasion resistance even higher than that provided at Ingleburn. To minimize joints and cracking, the concretes were designed to have 56- day drying shrinkage of less than 450 microstrain and to exhibit an abrasion resistance, when tested in situ using the Chaplin abrasion machine, of less than 0.10-mm depth of wear. This marks the first time such a direct measurement of abrasion resistance has been specified and assessed in Australia. Key elements of both projects were the high performance concrete floors, which were required to meet tolerances on surface flatness ¦ 2 mm on 3-m straight-edge and ¦ 4 mm overall. These and other strict performance criteria were met consistently during construction providing clients with world class low maintenance warehouses.