Effectiveness of fly ash in preventing deleterious expansion due to alkali-aggregate reaction [AAR] in normal and steam-cured concrete
- CSIRO, Highett, Victoria (Australia). Div. of Building, Construction and Engineering
A non-reactive and several reactive aggregates were used in concrete specimens with and without two fly ashes (varying in total alkali content) at binder (cement + fly ash) alkali levels ranging from 0.46 to 2.5% and a binder content of 500 kg/m{sup 3} and fly ash/binder ratio of 0.25. Some specimens were steam cured at 75 C for eight hours, and then transferred to 40 C, 100% RH. The expansion behavior of the specimens was monitored over nearly six years, and showed that the effectiveness of the fly ash in preventing deleterious AAR expansion depended on the alkali content of the concrete. At the highest alkali content of 12.5 kg Na{sub 2}O equiv./m{sup 3}, the fly ashes only had a delaying effect (one to several years), whereas at 6.9 kg Na{sub 2}O equiv./m{sup 3} they eliminated deleterious AAR expansions. Generally, for more highly reactive aggregates, and at the 2.5% alkali level, fly ash was less effective at 40 C than 23 C because the rate of AAR expansion was much higher at 40 C. A measurable amount of chemical shrinkage occurred in the first few months in concretes containing fly ash and with high alkali contents, although some of these concretes later expanded and cracked as a result of aggregate reactivity. Fly ash was used in mortar specimens prepared for the expression and analysis of the pore solution and was found to be very effective in reducing the alkalinity of the pore solution a factor contributing to its preventive effects on AAR. It is concluded that the two fly ashes can be used to prevent deleterious AAR expansions in practical situations.
- OSTI ID:
- 227990
- Journal Information:
- Cement and Concrete Research, Vol. 26, Issue 1; Other Information: PBD: Jan 1996
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effectiveness of mineral admixtures in reducing ASR expansion
Evaluation and beneficiation of high sulfur and high alkali fly ashes for use as supplementary cementitious materials in concrete