The term "efficiency factor" for condensed silica fume in concrete can be defined as the number of parts of cement that may be replaced by one part of silica fume without changing the property studied. This factor was first introduced for concrete compressive strength after 28 days curing in water at 20 C. In this situation, factors around 3 to 4 are reported. However, if the concrete is exposed to other temperatures, other curing conditions, or other curing periods, the factor may be as low as zero. This is very important information for the practical application of silica fume, especially when forms have to be stripped very early in winter concreting. The durability of concrete structures is more in focus than ever. When studying durability, the efficiency factors of silica fume in concrete can be calculated at the same time. Durability efficiency factors are also affected by the curing conditions. A comprehensive research program has enabled efficiency factors to be calculated for different conditions. This has covered strength and durability parameters such as permeability, carbonation, and chloride penetration. This work will be a helpful indication of how silica fume can be used in the most efficient way in concrete structures.

Two granulated blast furnace slags were ground to different finenesses in a laboratory ball mill and in a vertical roller mill to produce products that differed in fineness level and shape of particle size distributions. The cementitious properties of the products were evaluated by the ASTM C 989 Slag Activity Index Test and the results correlated with the different fineness parameters. The narrower particle size distribution of the roller-mill products resulted in a slight reduction of the packing capacity of the pure slag powder and a slight increase in mortar water requirement with portland cement. The strength-contribution capacity was found to be highly correlated with the specific surface of the slag, irrespective of the way of grinding. Simultaneous drying during grinding did not influence the cementitious properties.

Presents results of research work on the evaluation of physical-chemical properties of fly ashes and their influence on physical and mechanical properties of cement mortars. Two types of fly ash were examined: a low-calcium and a high-calcium. Variability of chemical composition with grain size of the fly ashes was analyzed. When testing the influence of physical and mechanical activation (fly ash grinding process) on hydraulic activity of the two types of fly ash, it was found that grinding had an activating effect on the high-calcium fly ash. Consequently, cements containing ground high-calcium fly ash were comparable in strength to pure portland cement. The main factor affecting strength properties was the formation of ettringite and its stabilization in the structure of hardened mortars and pastes.

Chemical characteristics of the cement paste-aggregate interfacial zone have been considered to influence the durability and mechanical properties of concrete. Particularly, effects of mineral admixtures such as fly ash and slag on the microstructure of the interfacial zone deserve attention. An x-ray diffraction technique was used to evaluate the amounts of Ca(OH)2, ettringite, and the orientation of Ca(OH)2 crystals in the interfacial zone. Composite specimens with several types of rocks were broken to produce a fracture surface on the cement paste prism to which the x-ray diffraction analysis was applied. The analyses showed that the addition of fly ash or slag considerably affected the peak height and orientation of Ca(OH)2 crystals in the interfacial zone, which normally extends up to 50 to 100 æm from the interface. The formation of ettringite in the vicinity of the aggregate surface was restricted by the addition of the admixtures. These results also suggest that the addition of the mineral admixtures favorably affects the resistance of the interfacial zone against aggressive agents from the surroundings. The x-ray fluorescence analysis was conducted to quantify calcium and silicon in the zone. The results obtained complemented the conclusions described previously. 137-389

A study was conducted to determine whether pulverized fuel ash, granulated blast furnace slag, and natural pozzolana contribute effective alkalies and whether such alkalies lead to alkali-silica reaction (ASR) damage. Mortar bars were prepared in accordance with ASTM C 227 but stored at 20 C, and using three factory-produced cements, three Type F pulverized fuel ashes, three blast furnace slags, and four natural pozzolans at three or four different levels of substitution. The reactive aggregate component was Beltane opal substituted at the pessimum level, as well as zero and three near-pessimum levels. The selection of the materials and their substitution levels were adjudged to represent as wide as possible present-day usage. Deleterious expansion defined as > 0.0 percent within 4 years was taken as the criterion of failure. The results have been applied to demonstrate the deduction of practical guidelines for the use of composite hydraulic binders in situations in which ASR is a consideration. Limiting total alkali contents of composite hydraulic binders as function of the substitution ratio of the three mineral additives are suggested. The analysis of the results demonstrates that if the effective alkalies derived from portland cement are taken as 100 percent, then those derived from pulverized fuel ash and natural pozzolana can be taken as 17 percent and those derived from blast furnace slag as 50 percent of total alkalies. There is also evidence of somem mineral additives, particularly at high substitution levels, not simply acting as dilutents but exhibiting a positive ASR-suppressive effect.