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.

SP-171 The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources of Canada, Ottawa, has played a significant role in Canada over 35 years in the broad area of concrete. In August 1997, CANMET in association with the American Concrete Institute and other organizations in Canada and New Zealand, sponsored the Third CANMET/ACI International Symposium on Advances in Concrete Technology in Auckland, New Zealand. The main purpose of the symposium was to bring together representatives from industry, universities, and government agencies to present the latest information in the subject area of the symposium, and to explore new areas of needed research and development. More than 50 papers from 15 countries were received and reviewed in accordance with the policies of the American Concrete Institute. Thirty-three of the papers were accepted for presentation and publication. In addition to the refered papers more than 20 other papers were presented and distributed at the symposium.

A natural amorphous silica with a purity of approximately 90% is mined from an extensive geothermal deposit near Rotorua, New Zealand. After refining and processing to remove impurities, the ‘Microsilica 600TM’ has properties which comply with Australian Standard AS 3582 Part 3 ‘Silica Fume’ as a supplementary cementitious material for use with portland cement. The performance characteristics of concrete incorporating the ‘Microsilica 600’ were evaluated at two cement levels of 320 and 400 kg/m 3 and two silica addition levels of 7 and 10%. Properties evaluated were compressive strength, tensile strength, concrete shrinkage, sulfate resistance, resistance against chemical attack, abrasion resistance, and chloride permeability. Performance improvement compared favorably with published data on concretes incorporating processed ‘conventional’ silica fume.