International Concrete Abstracts Portal

Many of the current standards for fly ash to be used in portland cement suffer from prescriptive requirements not necessarily related to the material's performance in concrete. The development of performance specifications is being encouraged, and classifying fly ash by reference to type of coal is being questioned. To use fly ash as a mineral admixture, the potential strength contribution to a reference mortar seems to be the most important consideration. To overcome the inconsistency with cement in the ASTM C 311 pozzolanic activity index, many countries have revised the test by incorporating fixed fly ash/cement ratio by weight, fixed water/cement + ash ratio, and accelerated curing at various temperatures for up to 7, rather than 28, days. Various studies to improve pozzolanic test methods are summarized, and recommendations made to simplify present fly ash standards, and to change their orientation from prescriptive to performance.

In drafting the durability section of the Australian concrete code, the committee faced both an urgent problem and a lack of precise data. This paper outlines the concepts in the draft code with a particular emphasis on the protection of reinforcement and the influence of fly ash on durability. Based on a qualitative understanding of the fundamental parameters, some engineering decisions and classifications are made. Where ample curing or self-curing is available, fly ash is a desirable component of durable reinforced concrete. For building exteriors where minimal curing is provided, achieving quality concrete cover is difficult. In this respect, concrete containing fly ash may be more affected than plain concrete.

Extensive technical work has established that high-performance concrete and cementitious materials can be proportioned practically and economically by using condensed silica fume additives. These hybrid chemical/mineral admixtures can be used for applications ranging from bridge overlays, concrete roof tiles, and fiber reinforced cements to structural uses, both on land and offshore. First significant applications began some ten years ago in Norway, with cement replacement as the main benefit. While cement replacement still continues as the main end use in the Scandinavian markets, performance enhancement of cementitious and concrete applications is the dominant attraction for users outside of Scandinavia. After a brief consideration of the history, a range of durability and high-strength applications are reviewed. It is shown that this range of varied applications is generally driven by particular features of performance enhancement.

In the United States, blast furnace slag was first used as a cementitious material in 1896. Since that time its use has followed a course of limited and sporadic success. Recently, however, world-wide attention has been drawn to the technical advantages of ground granulated blast furnace slag used as a separate cement to be added at the concrete mixer. Recognizing its potential, the ASTM Subcommittee E38.06.02 developed a specification to cover three grades of ground granulated slag. This paper discusses the development of the specification and presents round-robin test data leading to the adoption of a test method for evaluating the hydraulic characteristics of slags. Adopted in 1982 as ASTM C 989, the specification has played an important role in market growth which is approaching 1.0 million tons annually. Test results from another ASTM cooperative test program demonstrating the usefulness of a rapid (24 hr) hydraulicity test method are also given.

Silica fume has been used commercially for five years in Canada, particularly in the province of Quebec where most of the material is produced. Field problems such as plastic shrinkage that were experienced in the early stages and the distinct nature of this pozzolan caused some concern among prospective users who, while recognizing the unique properties and potential of silica fume, were hesitant to specify it. Added to their apprehension was the unavailability of a recognized standard. These considerations prompted the Concrete Materials and Construction Committee of the Canadian Standards Association (CSA) to develop a specification for silica fume. Findings from research by the University of Sherbrooke, Quebec, and the Canadian Center for Mineral and Energy Technology, Ottawa, Canada, provided input for the new specification which is now part of CSA Standard A23.5, Supplementary Cementing Materials and Guidelines for their Use in Concrete. During the preparation of the specification, close contact was maintained with Committee 226 and ASTM Committee C618 which are in the process of preparing a state-of-the-art report and a specification, respectively. The Canadian specification, believed to be the first of its kind in the world, will eventually be updated particularly as regards to the ASTM C 311 methods of tests which were originally developed for pozzolans that are not as finely divided as silica fume.