International Concrete Abstracts Portal

SP-178 This Symposium Publication contains the proceedings of the Fourth CANMET/ACI/JCI International Conference held in Tokushima, Japan, in June 1998. Sixty-two refereed papers were accepted for presentation at this conference and for this publication.

Structural grade fly ash (FA) concrete and concrete with high volume of fly ash (HVFA) are well accepted and utilized in the Australian construction industry. These are concretes with fly ash (ASTM C 618 type F) making up between 10 and 50 % by weight of the total cementitious material. This paper is intended to demonstrate the importance of the selection of the appropriate amount of FA content for a range of applications. The durability performance of the FA concretes was compared with portland cement concretes of equivalent 28-day compressive strength, in terms of the resistance to carbonation, chloride penetration and sulfate attack. Some mixture design data for both FA and HVFA concretes and their mechanical properties are given. The likely optimum fly ash percentages for a range of applications are highlighted with respect to their properties and construction demands. It was found that a lower fly ash dosage would be more suitable for above-ground structures where a carbonation-related deterioration mechanism applied. However, for structures in aggressive sulfate ground condition or in marine environments, HVFA concrete was found to be much more suitable. Available field performance data have confirmed laboratory evaluated performance.

The reduction in the useful-service life of reinforced concrete structures in the coastal areas of the Arabian Gulf is of major concern to the construction industry. The harsh climatic conditions, high level of chloride and sulfate contamination in the environment, low quality and contaminated aggregates, and substandard construction practices constitute the major causes of deterioration of reinforced concrete structures in less than 10 years in this part of the world. Since the concrete deterioration phenomena are strongly permeability dependent, mineral admixtures and industrial by-products, such as natural pozzolan, fly-ash, blast-furnace-slag, and silica-fume are increasingly used to improve its durability. Among the mineral admixtures and industrial by-products, fly-ash and silica-fume are considered to be more beneficial due to their superior performance in improving concrete durability. However, to attain beneficial properties, pozzolanic concrete needs early and extended curing compared with normal portland cement concrete. This is of particular concern in the Arabian Gulf environment, where the high ambient temperatures, solar radiation and blowing winds make curing a difficult process. Therefore in this study, the effect of temperature and drying as well as different curing conditions on the compressive strength development in normal Portland, silica-fume and fly-ash cement concretes was evaluated. The test specimens were cured in the laboratory and under field conditions, and tested 1,3,7, 14,28, 60 and 90 days after casting to evaluate the compressive strength development. The results indicated an increase in the compressive strength, in both the normal, fly-ash and silica-fume cement concrete specimens with the period of curing. Field curing had more negative effect on the strength development in concrete specimens containing fly-ash and silica-fume than in the plain concrete specimens. High temperature casting and curing increased the compressive strength in both plain and fly-ash concretes. Drying during curing produced the highest strength the silica-fume concrete specimens compared to plain and fly-ash concretes.

The Siberian State Academy for Mining and Metallurgy (SSAMM) and Uglestrinproject have developed a project for complex utilization of waste produced by burning brown coals from Kansk-Achinsk Power Complex at the Abakan thermal power plant. The project provides for total utilization of ashes and slags to the thermal power plant for producing finished ‘cementless’ binder and aggregate, finished ‘cementless’ fine ash/slag concrete and mortar, precast reinforced concrete structures and small products (silicate brick). Previous investigation of ash and slag from the thermal power plant and concretes on their base was completed in 1995. After grindiig and introducing silica mme, ash and slag to meet the requirements of State Standard 25818-91, concrete is in accordance with State Standard 26633-91. The technological complex providing loo-percent utilization of waste products from the TPP includes departments for grinding ash with a storage, for producing sand from slag with a storage, molding with concrete mixers and premises for admixtures. The project has been approved by a nature committee of the Khakass Republic and is in accordance with the ecological standards. The construction of the complex is currently under way.

In Thailand, the utilization of fly ash as a concrete admixture has been increasing gradually. However, there are no local standards regulating the use of fly ash. Mixing of concrete usually follows standards that contain requirements, especially temperature, that are difficult or sometimes impossible to satisfy. Therefore, this research was carried out to verify the influence of temperature, hot (Thailand) and temperate (Japan) climate, on the strength and durability properties of fly ash mortar. Also, to propose an optimum range of cement replacement percentage and water-binder ratio for each kind of fly ash under Thai (simulated) and Japanese climate conditions. From this investigation, it was found that fly ash exhibited advantages in strength and durability of mortar under high temperature. The strength activity index of both fly ash mortars were satisfied in accordance with ASTM C 618 under all temperatures considered. Furthermore, the optimum range of cement replacement and water-binder ratio became wider with increasing temperature. Thus, fly ash is recommended to be used under high temperature.