International Concrete Abstracts Portal

This paper presents a critical evaluation of the use of fly ash and ground granulated blast-furnace slag in concrete. In order to develop a rational concrete mixture incorporating these siliceous materials, their inherent characteristics are assessed, including their limitations and weaknesses. Based on the mixture proportioning methodology advocated, it is shown that fly ash and slag concretes, having the same three-day cube strength as concrete without them, can be produced. Engineering implications of using these materials such as increased bleeding and times of setting, reduced heat of hydration, low-early strength, and slow rate of gain of strength are addressed, and the need and role of a minimum period of moist curing to mobilize the chemically-bound qualities of these materials are fully emphasized. It is shown that both high-early strength and high-strength concrete can be achieved with fly ash and slag. Even with all their limitations, the durability properties of concretes with fly ash and slag are superior to those of concrete made with portland cement alone. It is shown further that extremely fine siliceous materials are only of limited use in concrete, but that a moderate increase in fineness, about thrice that of portland cement, can not only preserve and fully use the benefits of fineness on a variety of engineering properties such as bleeding, time of setting and heat evolution, but also lead to excellent chemical resistance and durability with high strength at early and later ages. It is shown that a slag fineness of about 1200 m2/kg can produce concretes of high strength and exceptional durability.

This paper presents an overview of the Quality Assurance and Quality Control for the construction of the Confederation Bridge in Eastern Canada. The bridge was unique not only in that it was designed, financed, constructed and operated by the private sector but also in the innovative approach to the design and construction. Private sector partnering with Government was a relatively new concept in Canada, and this project was an excellent example of the merits of such ventures. The design life of the Confederation Bridge is 100 years with a target reliabilitv . index, p, of 4.0. The contractor implemented a rigid Quality Management Plan (QMP) to ensure that the factors which impact on durability and service life were documented and that the specifications were met or exceeded.

Performance-based specifications are increasingly used to complement traditional prescriptive specifications in an effort to improve service life perform-ance of major infrastructure assets such as bridges. The water sorptivity of concrete, which relates to the moisture transport properties of near-surface concrete, has recently been adopted for trial application as a performance specification of concrete for bridge construction. Whilst data on water sorptivity of concretes cured under normal conditions are available, those of concrete subjected to heat curing are not yet widely available. This is particularly pertinent given that heat-cured precast structural elements are frequently used in bridge construction. This paper discusses the water sorptivity concept, its adoption in bridge specifications in New South Wales, and the performance of heat-cured concretes that could potentially be used in bridge construction.

The transition zone which is formed at the interface between cement paste and aggregate affects decisively the properties of hardened concrete. The transition zone in ordinary concrete consists mainly of a highly porous three dimensional network structure of calcium hydroxide crystals with pores from 50 nm to 2pm in diameter. Its thickness is usually 30 to 4Opm. The structure of the transition zone is closely related to the conditions of concrete manufacturing, including composition and structure of materials, proportions and curing conditions. The effects on concrete properties by the formation of the transition zone and the measure to reduce the formation of the transition zone, which causes the deterioration of concrete quality, are also described.

Results from a three year experimental study of the behavior of a high-strength (60 MPa) lightweight aggregate (LWA) concrete at elevated temperatures, including simulated hydrocarbon fire exposure, are described. Mechanical properties as a function of temperature (to 800 C) are also presented, as well as a summary of behavior in fire, and a comparison with normal density high performance and ordinary LWA concretes under similar conditions is made. In addition a simple and practical method for limiting the propensity of very low permeability, high performance concretes to explosively spa11 at elevated temperatures is demonstrated. Finally, the first application of this concrete in a major floating oil platform, the quarter-million ton Eeidrun TLP, is highlighted. High performance LWA concrete is shown . to possess all the best physical, mechanical, and durability characteristics of normal density high performance concretes while still retaining the superior high temperature and fire resistance properties of ordinary lightweight concretes--an ideal combination of properties for construction of offshore platforms.