Effectiveness of fly ash in preventing deleterious expansion due to alkali-aggregate reaction in normal and steam-cured concrete
✍ Scribed by A. Shayan; R. Diggins; I. Ivanusec
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 966 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0008-8846
No coin nor oath required. For personal study only.
✦ Synopsis
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/m3 and fly ash/binder ratio of 0.25. The specimens were stored either at 23°C (fog room) or 40°C 100% RI-I. Some specimens were steam cured at 75°C for eight hours, and then transferred to 40°C 100% RI-I. The expansion behaviour 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,O equiv./m3, the fly ashes only had a delaying effect (one to several years), whereas at 6.9 kg NqO equiv./m3 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. At lower alkali levels and for less reactive aggregates, the temperature was not important. Fly ashes were also effective under steamcuring conditions. 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 (based on six-year results and the shapes of expansion curves) that the two fly ashes can be used to prevent deleterious AAR expansions in practical situations.