International Concrete Abstracts Portal

This paper examines recent trends in European and British cement and concrete standards, concerning the production and use of blended cements and concrete mixer combinations of cements and additions, such as slag and pulverized fuel ash. The implications of the new categorization of six types of cement, changes in the definition of "cement," and acceptance of equivalence of performance in terms of concrete strength grade, are discussed. The principles being adopted in the UK for the approval of the use of additions in concrete include the adoption of the standard for blended cement as the basis, recognition of the cementitious properties of standardized additions and certification procedures for confirming compliance of concrete mixer blends with the standards of blended cements. Provided these procedures are followed, the answer to the question--blended cements or concrete mixer blends?--lies in a clearer definition of responsibility for their fitness for purpose, the relative costs of using blended cements or concrete mixer blends, and the local market demands.

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.

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.

Copper, nickel and lead slags of Canadian origin have been studied to evaluate the feasibility of their use as partial portland cement replacement in concrete and mine backfill. Pozzolanic activity of the slags was tested in mortars and the corresponding Ca(OH)2 and non-evaporable water contents at the same age were obtained by thermogravimetric analysis. The relationship between pozzolanic activity and glass content, measured by SEM and image analyzer, was assessed as well. It is concluded that non-ferrous slags could be used as partial Portland cement replacement in concrete and mine backfill if Portland cement and transportation costs justify it.

Laboratory test programmes have been carried out to assess the sulphate resistance of various Portland and Portland blast-furnace slag cements and of Portland cements blended with ground granulated blast-furnace slag ('slag'). Slag contents of between 30% and 80% were used. The test method was based upon the German 'Flat Prism' test. Tests were carried out on mortars containing ground slag from two sources, also pulverjsed fuel-ash (pfa - 'fly ash'), and with Portland blast-furnace cements. Control specimens contained either ordinary or sulphate resisting Portland cements. Prisms were tested at water-cement ratios (w/c) ranging from 0.45 to 0.60, using constant cement contents mortars. Supplementary tests used w/c ranging from 0.40 to 0.60 and constant water content mortars. Results are now available for mortars which have been immersed in sodium sulphate solution for periods of up to 3 years. The results confirm the inferior resistance to sulphate attack of ordinary Portland cements and of blends of both ordinary and sulphate resisting Portland cement containing lower slag replacement levels. Sulphate resistance increased as the slag content increased, and the 70% slag content mortars were found to have a superior resistance to those containing sulphate resisting Portland cements alone. The influence of slag content on sulphate resistance was found to be more significant than that of the w/c in the range examined.

Properties of heavy and light-weight concretes prepared with binders based on slag and activated ashes were studied as follows : fresh concrete; strength of concrete hardened both at normal temperature and by heat treatment; permeability and resistance to freeze-thaw cycling; behaviour of some concrete elements under various working conditions; preparation some technico-economic aspects related to and use of binders and practical conclu-sions for design and manufacture

This paper explains the concept of water sorptivity as a measure of concrete quality and discusses the effect of interrupted curing (as distinct from continuous curing) on the quality of concrete. Results of a pilot study on concretes incorporating ground granulated blast-furnace slag either as a blend or as an intergrind are presented. It was found that the response to interrupted curing varied depending on the constituents of the concrete. Plain concrete (i.e. without chemical or mineral admixtures) with a 28-day strength of 28 MPa showed a very slow response to interrupted curing, but could be improved by the incorporation of slag or by specifying a higher 28-day strength.

Two experimental houses, one of ordinary portland cement (OPC) concrete and the other of granulated blast furnace slag cement (GBFSC) concrete, were built under carefully controlled and documented conditions. After 20 years of exposure, cores were analysed and significant carbonation to 40 mm in depth was detected by TGA and the wet chemical method. More significantly, little Ca(OH)2 was found in the GBFSC concrete at all levels, so that any reinforcing steel would have to be considered susceptible to corrosion. According to Hg porosimetry results, the porosity of OPC concrete decreased after carbonation but that of GBFSC remained unchanged. In addition, increased permeability of GBFSC concrete with carbonation was indicated by coarsening of the pores, and the tensile strength of the surface region suffered a large decrease.

Diffusion of sodium chloride, cesium chloride and simulated sea water solutions across and into cement pastes and mortars blended with granulated blast furnace slag has been studied. The temperatures of hydration and diffusion were varied between 23and 6O C. Phase chemistry, depth profiles of chloride, and ion migration measurements across paste membranes were used to follow reaction and diffusion of the salt solutions. It was observed that cement mortars containing the slag showed lower penetration depths of Cl- compared to the control portland cement mortars at normal or moderate temperatures. The diffusion of cesium or chloride ions was retarded significantly through the use of slag blending in pastes. The porosity was lower and pore structure was finer in the case of the blended cement, which is considered to be the primary reason for the beneficial effect on diffusion. Phase chemistry studies of blended slag-cement mortars indicated an absence of detrimental reaction products such as gypsum or brucite after exposure, but the presence of Friedel's salt (tetracalcium aluminate dichloride-lo-hydrate) was detected. Comparisons are also made with blends with fly ash, which also showed relatively favorable effects. The electronegative nature of portland cement was elucidated by Cs+ and Cl- migration in pastes.

A second source of ground granulated blast-furnace slag ('slag') has become available in the UK, from Purfleet in South East England. The Purfleet slag has a slightly higher lime-silica ratio (c/s) and calcium content than the initial source at Scunthorpe. The slag has a potentially higher rate of hydration because of its chemical composition, but as a consequence can contain up to 30% by volume of merwinite crystallites included within its glass structure. The presence of these crystallites has been found to increase further the reactivity of the slag glass. Scanning election microscope (SEM) studies of concrete containing the slag have confirmed that the glassy particles containing merwinitic crystallites are more reactive than pure glass particles, also that an adequate supply of unreacted glass remains even in mature concrete. Testing of this merwinitic slag has shown no factors disadvantageous to slag reaction or performance and has confirmed that, when blended in appropriate proportions with Portland cement, it can for example, increase sulphate resistance and reduce expansion due to alkali-silica reaction. The results of the investigations reported are supported by a brief review of published literature which confirms that slag performance cannot be directly related to absolute glass content.