[논문]Experimental and SEM Analyses of Ground Fly Ash in Concrete

Brueggen, Beth; Kang, Thomas H.K.; Ramseyer, Chris

doi:10.4334/ijcsm.2010.4.1.051

Experimental and SEM Analyses of Ground Fly Ash in Concrete 원문보기

International journal of concrete structures and materials, v.4 no.1, 2010년, pp.51 - 54

Brueggen, Beth (School of Civil Engineering and Environmental Science, University of Oklahoma) , Kang, Thomas H.K. (KCI Member, School of Civil Engineering and Environmental Science, University of Oklahoma) , Ramseyer, Chris (School of Civil Engineering and Environmental Science, University of Oklahoma)

Abstract ▼ AI-Helper

Fly ash is used in concrete to improve the fresh and hardened properties of concrete, including workability, initial hydration temperature, ultimate strength and durability. A primary limitation on the use of large quantities of fly ash in blended cement concrete is its slow rate of strength gain. Prior studies investigated the effects of grinding fly ash and fly ash fineness on the performance of concrete containing fly ash. This study aims to discover the sources of those effects, to verify the compressive strength behavior of concrete made with raw and processed Class C fly ash, and to investigate the properties of fly ash particles at the microscopic level. Concrete cylinder test results indicate that grinding fly ash can significantly benefit the early age strength as well as the ultimate strength of concrete with ground fly ash. Therefore, it is demonstrated that grinding fly ash increases its reactivity. Scanning Electron Microscopy was then used to investigate the physical effects of the grinding process on the fly ash particles in order to identify the mechanism by which grinding leads to improved concrete properties.

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문제 정의

have investigated the effects of grinding the fly ash and fly ash fineness on the performance of concrete using significant amounts of fly ash; however, the sources of those changes have not been well described. The objective of this research is to investigate the properties of fly ash particles at the microscopic level while verifying the compressive strength behavior of concrete made with the investigated fly ash.

가설 설정

2) Grinding the fly ash decreases volume of particles greater than 40 µm, breaking them up into smaller particles.

제안 방법

In this study, an experimental program was carried out to verify the effect of grinding on the compressive strength of concrete made with fly ash and to investigate the properties of fly ash particles at the microscopic level. Both conventional concrete cylinder compression tests and novel Scanning Electron Microscopy analyses were used.
The fly ash used in this study was ground in a ball mill for 30 and 120 minutes and replaced 0% and 20% of the portland cement by weight. To determine the effectiveness of grinding the fly ash, the Blaine fineness of each sample was measured.
The samples replacing 20% of the portland cement with fly ash ground for 30 minutes had compressive strengths 7 and 8.3 N/mm² higher than the samples with un-ground fly ash at 3 days and 28 days, respectively. These samples had compressive strengths 4.
The results of the compressive strength tests indicate that most of the benefits of grinding were achieved after grinding the fly ash for 30 minutes. Therefore, the un-ground sample and 30 minute ground fly ash samples were carefully compared under the microscope to search for indications of the physical effects of the grinding operation. The most obvious difference was that grinding appeared to remove the bumps from the surfaces of the particles.

대상 데이터

presented a mathematical model describing fly ash as a two-component, perfectly spherical particle with material deposited in uniform layers. In this model, the outer layer consists of non-reactive glasses, including K₂O, Na₂O, CaO, MgO, and Fe₂O₃. The core of the fly ash particle is much more reactive, but cannot begin to hydrate until the outer shell has dissolved, and consists primarily of SiO₂ and Al₂O₃.
plant in Midlothian, Texas, Class C fly ash from Red Rock, Oklahoma, and tap water were used in this research. The coarse aggregate used in this research was 21 mm maximum size gravel, and the fineness modulus of fine aggregates was 2.5. A carboxylate superplasticizer was used to increase the workability of all mixtures.
Type-I portland cement from the Holcim, Inc. plant in Midlothian, Texas, Class C fly ash from Red Rock, Oklahoma, and tap water were used in this research. The coarse aggregate used in this research was 21 mm maximum size gravel, and the fineness modulus of fine aggregates was 2.

성능/효과

1) Grinding the fly ash can significantly benefit the early age strength as well as the long-term strength of concrete. This demonstrates that grinding fly ash increases its reactivity, allowing for increased substitution of fly ash for portland cement.
Particles of similar size were used to minimize differences in curvature within the area counted. A T-test was used to determine that the ground sample did have a significantly lower surface bump density with at confidence of 99.1%. The average bump density of the fly ash particles was reported as 48.
The results of the compressive strength tests indicate that most of the benefits of grinding were achieved after grinding the fly ash for 30 minutes. Therefore, the un-ground sample and 30 minute ground fly ash samples were carefully compared under the microscope to search for indications of the physical effects of the grinding operation.
⁶ separated fly ash into various levels of fineness by using an air classifier machine. The results showed that the concrete pastes containing the finer fly ash have a higher compressive strength, lower total porosity and capillary porosity than those with the original fly ash.
As expected, the replacement of 20% of the portland cement with un-ground fly ash reduced the compressive strength of the specimens at all ages. The samples with un-ground fly ash exhibited 11.6 and 5.8 N/mm² lower compressive strength than 100% portland cement samples at 3 days and 28 days, respectively.
Tan and Pu⁴ ground fly ash in a ball mill to a Blaine fineness of 6021 cm²/g. Their results showed small changes in concrete compressive strength at an early age of 72 hours; however, significant compression improvement appeared at 28 and 56 days.
5 N/mm² higher) than 100% portland cement concrete at 28 days. These tests indicate that grinding the fly ash can significantly benefit the early age strength as well as the ultimate strength of the samples.
⁵ were able to grind fly ash to a fineness of 8800 cm²/g. This study concluded that the grinding converts spherical fly ash particles to irregular and crushed shaped particles, increasing their reactivity. Chindaprasirt et al.

후속연구

Chemical analysis was performed by Lafarge Canada, Inc. Finally, the authors would like to thank the Samuel Roberts Noble Microscopy Laboratory at the University of Oklahoma for allowing use of their equipment for the SEM portion of this study. The views expressed are those of the authors, and do not necessarily represent those of the donators or collaborators.

참고문헌 (8)

Mindess, S. and Young, J. F., Concrete, Prentice-Hall, Inc., New Jersey, 1981, 671 pp.
Slanika, S., “The Influence of Fly Ash Fineness on the Strength of Concrete,” Cement and Concrete Research, Elsevier, Vol. 21, 1991, pp. 285-296.

상세보기
Berry, E. E., Hemings, R.T., Langley, W. S., and Carette, G. G., “Beneficiated Fly Ash: Hydration, Microstructure, and Strength Development in Portland Concrete,” in V. M. Malhotra, Ed., Proceedings of Third International Conference on the Use of Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, ACI SP 114, 1989, pp. 241-273.
Pu, X. and Tan, K., “Strengthening Effects of Finely Ground Fly Ash, Granulated Blast Furnace Slag, and Their Combination,” Cement and Concrete Research, Elsevier, Vol. 28, No. 12, 1998, pp. 1819-1825.

상세보기
Kiattikomol, K., Jaturapitakkul, C., and Songpiriyakij, S., “A Study of Ground Coarse Fly Ashes with Different Finenesses from Various Sources as Pozzolanic Materials,” Cement and Concrete Composites, Vol. 23, Issues 4-5, 2001, pp. 335-343.

상세보기
Chindaprasirt, P., Jaturapitakkul, C., and Sinsiri, T., “Effect of Fly Ash Fineness on Compressive Strength and Pore Size of Blended Cement Paste,” Cement and Concrete Composites, Vol. 27, Issue 4, 2005, pp. 425-428.

상세보기
Brouwers, H. J. H. and Van Eijk, R. J., “Fly Ash Reactivity: Extension and Application of a Shrinking Core Model and Thermodynamic Approach,” Journal of Materials Science, Vol. 37, No. 10, 2002, pp. 2129-2141.

상세보기
Fu, X., Li, Q., Zhai, J., Sheng, G., and Li, F., “The Physical-Chemical Characterization of Mechanically-Treated CBFC Fly Ash,” Cement and Concrete Composites, Vol. 30, No. 3, 2008, pp. 220-226.

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Experimental and SEM Analyses of Ground Fly Ash in Concrete 원문보기

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Experimental and SEM Analyses of Ground Fly Ash in Concrete 원문보기

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