International Concrete Abstracts Portal

A research program was conducted in which the temperature rise of mortars and the durability of concrete containing fly ash were studied. The study of the effect of fly ash on the temperature rise of mortars included the use of both ASTM C 618 Class C and Class F fly ashes. Control tests were conducted on mortars containing ASTM C 150 Type I, Type I-II, and Type III cements, and comparison tests were conducted on mortars containing 20, 27.5, and 35 percent fly ash by volume of cement. It was found that the use of Class F fly ash resulted in a reduction in the temperature of the mortar, whereas the partial replacement of cement with Class C fly ash did not lower the mortar temperature, regardless of the type of cement used. Resistance to scaling in the presence of deicing salts and abrasion resistance tests were conducted on concrete samples cast from 21 batches of concrete. Variables studied included fly ash type, fly ash content, and curing conditions. Both ASTM Class F and Class C fly ashes were used to replace 25 or 35 percent of the cement by volume, and curing conditions included combinations of 50, 75, and 100 F with 50 and 100 percent relative humidities.

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

Cements consisting of 60 percent ground granulated blast furnace slag and 40 percent fly ash activated by 7 percent sodium hydroxide have been investigated. Various slags were used, including some laboratory-made synthetic slags. The influence of additives like superplasticizers and defoaming agents has been examined. The most favorable composition with respect to strength development has been subjected to a durability testing program. A negative aspect appeared to be the carbonation resistance, which is low in comparison with portland cement. Carbonation leads to a decrease in strength. Other properties were favorable.