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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Low-Calcium Fly Ash as a Mineral Admixture for Lean Concrete
Author(s): A. Verhasselt
Publication: Special Publication
Appears on pages(s): 803-820
Keywords: admixtures; age-strength relation; bearing capacity;
cement content; compaction; compressive strength; concretes; fly
ash; freeze-thaw durability; lime; portland cement; splitting-tensile
strength; ultrasonic tests.
Abstract:The use of fly ash as a mineral admixture for lean concrete (road base concrete) has aroused a rather limited interest until now. However this comparative study shows that there are so-me advantages in using low calcium fly ash in lean concretes. The compactibility of lean concrete is improved : the maximum level of compaction (Modified Proctor test) is achieved at about 5 % fly ash addition, whereas it is equal at 0 % and 10 % addition . The CBR-indexes of the mixes are similar at Proctor maximum, but the higher the fly ash content, the more sensitive the index is to an increase in moisture content. At an early stage, fly ash is not very effective in strength development : it is essentially the portland cement content (2 to 5 %) that governs the rate of strength evolution. On the other hand, at longer periods (more than six months), fly ash contributes very largely to strength : a factor of 1.5 between the weakest mix and the reference lean concrete without fly ash. Accordingly a reduction of the cement content in practice can be taken into consideration. Water stability which is obtained rapidly, is not much affec-ted by the presence of the admixture. On the other hand, resistance to repeated freezing and thawing cycles is delayed because of the slower strength gain for mixes containing more fly ash and less cement. The results on the whole show that the optimum low-calcium fly ash content in lean concrete for road base lies around 5 % by mass with the possibility of reducing the cement content appreciably.
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