The objective of this study was to investigate the behavior of air flow through concrete and to make clear the effects of use of fly ash and condensed silica fume on the air permeability of concrete. The air permeability of concrete was estimated by means of the coefficient of air permeability, and the difference of the coefficient of air permeability between concretes with and without fly ash and condensed silica fume was investigated. Furthermore the improvement of the airtightness of concretes with fly ash and condensed silica fume was discussed from the view point of the internal structure of concrete such as porosity. As the results of this study, it was confirmed that the flow of air through concrete obeyed Darcy's law. It is possible to apply the coefficient of air permeability as the index of air permeability of concrete. In the case of use of fly ash, the coefficient of air permeability of concrete cured in water for the period of 28 days hadalmost the same value as concrete without fly ash when compared at the same level of compressive strength. However, the concrete with fly ash cured in water for the period of 91 days is more airtight than concrete without fly ash. In case of use of condensed silica fume, the coefficient of air permeability decreased with the increase of replacement ratio of condensed silica fume, and did not depend on the period of the curing in water. These results can be quantitatively understood by means of the internal structure of concrete.

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.

This report presents results from an investigation where fly ash has been used in cement to try to reduce an observed alkali-silica reactivity in tile covered mortar and concrete constructions such as swimming pools and larger shower cabinets. Examinations of ceramic tiles showed that soluble silica formed when the material was exposed to sodium hydroxide solution. For testing according to ASTM C227-81 "Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method)" concrete prisms were moulded using ordinary Portland cement or fly-ash cement with crushed ceramic tiles as aggregate. All the prisms showed changes in length; however, the changes are less in prisms made with fly-ash in cement. From these observations it seems that it is possible to reduce the damage caused by alkali-silica reactions in such structures by use of fly-ash in cement. Long term tests are being done on tile covered concrete slabs.

This paper describes an investigation of the use of industrial by-products such as bottom ash and silica fume with high silica content, as the admixture for mortar and concrete. The bottom ash used for this investigation was ground in a ball mill. At first, basic tests using mortars were conducted. Subsequently, the concretes containing different proportions of the two by-products were tested for strength development under accelerated curing, drying shrinkage, and water permeability. The results of the mortar strength tests indicate that the proper amount of ground bottom ash is about 5 percent if used to replace cement or 10 percent if used in addition to cement, and that of silica fume is approximately from 5 to 10 percent if used to replace cement and from 10 to 15 percent if used in addition to cement. When steam curing and autoclave curing are used, the concretes containing ground bottom ash and silica fume have higher early compressive strength than concrete without these materials. The coefficients of water permeability of the concretes using ground bottom ash and silica fume are lower than those of concrete without these materials. Paticularly, the water-tightness of silica fume concrete improved remarkably, although the concrete has a little higher drying shrinkage in comparison with concrete without silica fume. The use of these materials in amount of 5 to 10 percent to replace cement is effective for the improvement of concrete properties.

According to ASTM Standard C 618-84, fly ashes can be classified into two broad categories depending on their chemical composition. If Si02 + A1203 + Fe203 > 70%, the fly ash is said to be Class F; if 50% < Si02 + A1203 + Fe203 < 70%, it is said to be Class C. The physico-chemical properties of three Class F fly ashes - one French, one Canadian and one American - and of four Class C fly ashes - two American and two French - have been investigated. It has been found that fly ashes from one particular class can behave very differently. Two Class F fly ashes have been found to be pure1 Y Paz pozzolanic, whereas three others, one F and two C, were more or less hydrauli c at an early stage of hydration before behaving like a more or less pozzolanic material. One Class C French fly ash has been found to be hydraulic, then "auto-pozzolanic"; that is, in the presence of water, tis dissolution liberates enough lime to react with its own silica and alumina. Another Class C French fly ash was found to be hydraulic but non pozzolanic, its reactivity with the lime being directly associated to the formation of ettringite.these fly ashes has been explained In each case, the reactivity of by analyzing formation mechanisms of the different hydrates.