International Concrete Abstracts Portal

Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete: Proceedings of the Third International Conference presents the latest technological advances in the use of these extremely valuable mineral by products. This two-volume set of 83 papers explores in detail how you can conserve energy and resource while increasing your profitability. The first volume contains papers dealing with fly ash and natural pozzolans, and the second volume details the use of condensed silica fume and ferrous and non-ferrous slags. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP114

The resistance to deicer scaling of lean concretes containing fly ash was evaluated using ASTM C 672-84. Concretes were prepared at cement contents of 250, 305, and 335 kg/m3. Six fly ashes were chosen for evaluation at cement replacement levels of 25 and 50 percent by mass in each of the mixtures. Specimens representative of residential flatwork were prepared and cured for 1 and 7 days under moist conditions, then air-dried until initiation of testing at 35 days of age. Results indicate that all mixtures containing fly ash exhibit more rapid and severe scaling than those mixtures prepared with cement alone at the same total cementitious material content. Scaling was found to increase with a decrease in the total cementitious content of the mixture and an increase in the amount of cement replaced. Data on compressive strength, and characteristics of air-void systems in these concretes are also presented.

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.

Paper presents the results of the tests conducted on reactive andesite produced to determine if Japanese fly ashes produced in Japan have an effect in controlling the alkali-aggregate reactions in concrete. Fourteen fly ashes produced were subjected to Japan Industrial Standard (JIS) alkali-silica reaction (ASR) mortar bar test (40 x 40 x 160 mm, alkali content in cement 1.2 percent, s/a = 2.25) with (c + f) ranging from 5 to 30 percent. With f/(c + f) at 20 percent or higher, all the mortar test bars incorporating fly ash had little expansion even after 6 months, but with f/(c + f) at 10 percent, different expansions were produced depending on the type used. The analysis of the data indicated that the component Na2Oeq of fly ash would accelerate the expansion while the component SiO2 will restrain the expansion. The controlling ability is also related to the alkali content of the cement: the greater the alkali from the cement and fly ash, the greater the quantity of fly ash required for preventing the expansion. An empirical formula expressing such a relationship has been derived. 123-389

Use of silica fume is an accepted technology in the Norwegian concrete environment and high-strength concrete incorporating silica fume is being used increasingly. However, in recent years, conflicting reports regarding the fire resistance of high-strength concrete have been published. This review indicates that eventual fire-safety problems seem to be linked less to the materials used than to physical properties of hardened concrete or conditions under which high strength concrete is used.