Three natural pozzolans, a fly ash, and a sample of silica fume have been characterized by means of chemical analysis and nitrogen adsorption. lanic activity i.e. the The pozzo-lime consuming capacity of each of these pozzolans has been evaluated by making portland cement - pozzolan paste and determining free calcium I : hydroxide contents after different intervals of hydration. Mechanical strengths of the above portland cement -pozzolan mixtures have also been determined. The results indicate why previous workers in this area have obtained discordant results.

Since before the first utilization of imported fly ash by Ontario Hydro as a pozzolan in mass concrete in 1950, research programs on many aspects of its influence on durability were undertaken. Majo. areas addressed have been: 1. thermal crack resistance in mass concrete; 2. reduction of alkali reactivity; 3. freezing and thawing resistance, and 4. sulphate resistance (preliminary). When the first fly ash was produced by Ontario Hydro from thermal plants used for peak load power, the problems with utilizing variable and often high carbon content fly ash were also studied. This problem was overcome by selective storage along with provisior for fineness and carbon content checks for each tanker of ash leaving the plant. Major findings of the research include: 1. Fly ash has and is being used successfully in lieu of both CSA Types 20 and 40 (ASTM Types II and IV) moderate and low-heat cements to control temperature rise and thermally induced cracking in mass concrete. 2. The replacement of 25 percent of normal portland cement with fly ash has been found to be effective in reducing alkali silicate expansions. 3. As long as adequate air contents are obtained, carbon content does not adversely affect the freezing and thawing resistance of concrete at least within the 12 percent CSA and ASTM limits. As long as carbon contents are established for each delivery of fly ash, dosages of air entraining agents can be modified easily.

Methods of production, placement and strength requirements of mine fill are briefly described. The chemical composition and details of the mineralogical nature of a particular quenched copper reverberatory furnace slag, successfully used in fill operations at Mount Isa Mine, Queensland, Australia are discussed. Experimental work on slag reactivity in the presence of Ca(OH)2 is described, and includes studies on the heat of hydration, non-evaporable water and x-ray intensity variations. The reaction product, which is also observed in the presence of hydrating portland cement appears to be a 7.34 & hydrate. Information on hydration characteristics may eventually allow advantageous modifications to be made to the present compositions of the fill material.

Little basic oxygen slag is used as a portland cement concrete aggregate because of its unsoundness in concrete. However, soundness of basic oxygen furnace slag in concrete appears to largely depend upon the mineralogical and chemical compositions of the slag. Several experiments concerning workability, compressive strength and dimensional stability of concrete made with basic oxygen furnace slag were conducted for investigating the possibility of the use of basic oxygen furnace slag as a concrete aggregate. The concrete made with weathered slag showed a much higher slump for a given mix proportion than natural aggregate concrete and the concrete prepared using unweathered slag. The longer the periods during which the slag used wasplaced outdoors, the lower the compressive strength of the slag concrete. The changes in the mineralogical and chemical compositions and the surface texture of basic oxygen furnace slag particles were determined by X-ray diffraction, differential thermal analysis, SEM and EDAX. The results of these experiments show that reduction in compressive strength and high slumps in the concrete made with the weathered slag aggregates arise from slow hydration of C2S and C2F on and/or near the surface of basic oxygen furnace slag during weathering. It may be concluded that basic oxygen furnace slag can be used as a concrete aggregate if the grading of fine slag aggregates coarsened by its slow hydration is improved by adding river sand so as to obtain a workable concrete.

Extensive investigations at the Concrete Research Institute of the Dutch Cement Industry have shown that the difference in resistance to the alkali-aggregate reaction and sulphate attack between OPC and blastfurnace cement concretes is caused by the difference in permeability to ions and water. In this paper an investigation is described on the effect of high curing temperatures on the above mentioned difference in permeability. A model is given which explains both the difference in permeability between OPC and blended cements and the effect of temperature on this difference.