International Concrete Abstracts Portal

Although the cement-paste matrix is intrinsically protective to steel, it also permits the ingress of deleterious agents that leads to its own progressive deterioration and consequent destabilisation of steel. Further, the development of a highly impermeable cement matrix, per se, may not ensure a high- performance concrete structure in practice, since the development of strength and pore structure are both time-dependent phenomena and aggressive elements somehow find a means of penetrating concrete and initiate a cumulative process of structural damage. This paper advocates an integrated design philosophy from concept to completion and during service life of a concrete structure. It is shown that by selecting concrete constituents that encourage synergic interactions, it is possible to develop a concrete matrix of high strength and excellent durability. However, concrete also needs to be protected from aggressive agents to enable it to attain its full potential and examples are given to show how such techniques can be adopted to ensure durable service life even in the most unfriendly environment. The application of this integrated design strategy is further illustrated with the design of columns exposed to alkali-silica reactivity and the production of cost-effective, fiber-reinforced thin sheets.

This paper presents a summary of a four-year research program sponsored by the Strategic Highway Research Program under contract C-205. The program included plain and fiber reinforced concrete. This paper summarizes the results of plain concrete. The paper covers the literature search and review, the development of mixture proportions of three categories of high performance concrete, the laboratory studies and field trials of the concretes. An assessment is made of how the research met its objectives and the limitations of the research are pointed out. Finally, the paper is concluded with a list of future research needs.

Australia is a dry warm continent. The major population centres are located close to the coastline. This paper examines the predictions for future building and construction activity in Australia. Based on the physical situation, for example climate and geography, and the anticipated needs for HPC arising from the forecast trends in construction activity it tries to forecast the research needs for HPC in Australia. It also endeavours to assign priorities for these research needs in terms of the size of the market likely to be affected.

This paper discusses recent research on high performance concrete with a focus on cemenentitious materials designed for durability. A major key to suchp erformance originates with the concrete microstructure. Recent advances in optimizing cement and concrete materials by using calculated packing diagrams offer the promise of superior products achieved by increased packing efficiency. A high packing density coupled with adequate processing and cement binder characteristics makes possible the formation of a fine microstructure. In turn, this fine microstructure results in a low permeability and therefore provides a resistance to aggressive forces from the environment, which together enhance its long term durability. The favorable interaction among physical and chemical phenomena gives rise to better long term performance, whether the application is structural, or chemical, such as in waste management.

Fly ash, a by-product from the coal-burning power generation process, is often used, for its pozzolanic properties and its fineness, to enhance the strength and durability of concrete and high-strength concrete. The quality assurance of fly ash is frequently questioned since its properties tend to vary depending on the source of coal, type of boiler, pulverizing equipment, and the removal efficiency of the air pollution control devices. Since fly ash is cornmonly used as one of the main components in the development of high-performance concrete, a closer look at the effects of fly ash on the properties of high-performance concrete is critical. In this study, two types of fly ash, dry and wet bottom ashes of different particle size distributions, were used. Physical and chemical properties of these fly ashes were tested and compared with the original feed fly ashes received directly from the utility. The effects of these fly ashes on the strength of concrete were studied when used as 15, 25, 35, and 50 percent cement replacement by weight of cement. The results show that fly ash, when proportioned properly, can enhance the properties of concrete. The chemical composition of fly ash of different particle size distributions varies slightly. For the same type of fly ash, the finer the particle, the higher the specific gravity. The smaller fly ash particle has a faster reactivity rate than the coarser one. The compressive strengths of several selected mixes of fly ash concrete are equal to, or higher than, the control concrete before the age of 28 days. For fly ash with large particle size distribution, the fly ash concrete reaches only 85 percent of the control concrete strength at the age of 180 days. It was also found that fly ash concrete exhibits excellent acid resistance when compared to conventional concrete.