International Concrete Abstracts Portal

Tests of portland cement concretes contain-ing Class F and Class C fly ashes from ten different sources were conducted to evaluate mixing water requirement, time of setting, bleeding, compressive strength, drying shrinkage, abrasion resistance, and absorption. The effects of moisture availability and temperature during curing were also examined. Mixing water requirement was reduced for concretes with Class C fly ash. There was no consistent water reduction when Class F fly ashes were used. Slight to signifi-cant retardation of setting time was noted for concretes with fly ash. Setting time generally increased as concrete mixing water requirement increased. Concretes with fly ash showed less bleeding than control concretes. Concretes with Class C fly ash showed less bleeding than concretes with Class F fly ash. Concretes containing Class C fly ash developed higher early age compressive strength than concretes with Class F fly ash. Compressive strengths of concretes with Class F fly ash were more susceptible to low curing temperatures than those for concretes with Class C fly ash. At early ages, compressive strength of concretes with fly ash, regardless of class, was essentially unaffected by moisture availability. Abrasion resistance of control concretes and concretes containing fly ash was dependent on compressive strength. Drying shrinkage and absorption of the concretes were generally unaffected by the use o f f l y ash.

SP91 This contains 78 symposium papers, bringing together the expertise of representatives from industry, government and universities. These volumes present the latest advances in the use of fly ash, silica fume, slag and natural pozzolans in concrete. New technologies are explored to provide ways in which these valuable mineral by-products can best be used to conserve both resources and energy. Case studies include: the effect of fly ash on physical properties of concrete; evaluation of kiln dust in concrete; effect of condensed silica fume on the strength development of concrete, and the influence of slag cement on the water sorptivity of concrete.

In order of the PF potential The relea HF, blend The pozzo try and f pozzolani The examination EDAX has lanic reagenerated ysical and mine ralo ashes (PFA'S) areave a better un dersworkability of fre PFA particles is sulfates and alka cement, and lime -sat activity of PFA lime determinate ion tivity was observed of hydrated blended some interestin n between the PFA cement hydration.gical characte performed.tanding of the sh mortars and measured in diff li oxides from urated solutio was investigate of the mixture after 14 days ded cement by information particles and trization of Belgian favourable concrete, erent condi PFA in watn is discus d by microc. A signif SEM coupled, with concerning the pozzo he calcium hydroxide effect the Zeta tions. er, HCl, sed. Alorimeicant

The effect on the properties of portland cement binders due to the addition of volcanic tuff, calcined clay, fly ash, coarse coal bottom ash and diatomaceous earth, are compared and evaluated for pozzolanic activity. Durability studies carried out for two years on mortars with addition of fly ash, in different aggressive environments, are also reported. Volcanic tuff is a highly reactive pozzolan, fly ash yields compressive strengths higher than the control after 60 days. The calcined clay reactivity is proportional to the calcination temperature. Coarse coal bottom ash has a pozzolanic activity similar to the calcined clay. Diatomaceous earth failed to produce pozzolanic activity.

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.