Effect of Internal Activation Using Porous Ceramic Aggregate on Hardness and Pore Structure of Fly Ash Cement Paste

Abstract:

The utilization of fly ash not only reduces the environmental impact but also improves some mechanical properties and durability of concrete. However, the early-age strength of fly ash concrete is sometimes lower than that of normal concrete due to the slow pozzolanic reaction of fly ash. In recent years, some researchers have suggested alkali or sulfate activation to accelerate the pozzolanic reaction. Some studies have used sodium hydroxide (NaOH) solution, while others have applied potassium sulfate (K₂SO₄) or sodium sulfate (Na₂SO₄) as activators which are effective in accelerating the pozzolanic reaction and increasing the strength at early age. On the other hand, the early-age strength of fly ash concrete is also improved by using porous ceramic aggregate (PCA) as an internal curing agent. Therefore, the present study aims at investigating the effect of an internal activating agent using PCA on hardness and pore structure of fly ash cement paste. In the experimental program, PCA immersed in two kinds of solution (K₂SO₄ and Na₂SO₄) was placed in the center of specimen with dimension of 21x21x20 mm. In addition, normal aggregate (NS) was used for reference. As a result, internal sulfate activation using PCA improved the hardness of interfacial transition zone (ITZ) between paste and PCA, and reduced the Ca(OH)₂ content in cement paste with 40% replacement with fly ash significantly at the age of 1 day, but negligibly at the ages of 7 and 28 days when compared with reference specimen. K₂SO₄ was more effective in improving hardness of ITZ as an internal activating agent than Na₂SO₄. Although the total pore volumes of the fly ash cement pastes using PCA imbibing sulfate activators were not reduced at the age of 28 days, their pore volumes with diameters less than 0.05 µm were increased.

• Periodical: Key Engineering Materials (Volume 711)
• Pages: 95-102
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.711.95
• Online since: September 2016
• Authors: Kazuki Ootaishi*, Phuong Trinh Bui, Yuko Ogawa, Kenji Kawai
• Keywords: Activation, Fly Ash, Hardness, Internal Curing, Pore Structure, Sulfate

References

[1] V.M. Malhotra, Durability of concrete incorporating high-volume of low-calcium (ASTM class F) fly ash, Cem. Concr. Compos. 12 (1990) 271-277.

DOI: 10.1016/0958-9465(90)90006-j

[2] J. Bijen, Benefits of slag and fly ash. Constr. Build. Mater. 10 (1996) 309-314.

[3] R. Siddique, Performance characteristics of high-volume class F fly ash concrete, Cem. Concr. Res. 34 (2004) 487-493.

DOI: 10.1016/j.cemconres.2003.09.002

[4] P. Nath, P. Sarker, Effect of fly ash on the durability properties of high strength concrete, The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction, Procedia Engineering 14 (2011) 1149-1156.

DOI: 10.1016/j.proeng.2011.07.144

[5] H. Toutanji, N. Delatte, S. Aggoun, R. Duval, and A. Danson, Effect of supplementary cementitious materials on the compressive strength and durability of short-term cured concrete, Cem. Concr. Res. 34 (2004) 311-319.

DOI: 10.1016/j.cemconres.2003.08.017

[6] G.S. Ryu, Y.B. Lee, K.T. Koh, Y.S. Chung, The mechanical properties of fly ash based geopolymer concrete with alkaline activators, Constr. Build. Mater. 47 (2013) 409-418.

DOI: 10.1016/j.conbuildmat.2013.05.069

[7] D. Li, Y. Chen, J. Shen, J. Su, X. Wu, The influence of alkalinity on activation and microstructure of fly ash, Cem. Concr. Res. 30 (2000) 881-886.

DOI: 10.1016/s0008-8846(00)00252-0

[8] P.T. Bui, Y. Ogawa, K. Nakarai, K. Kawai, A study on pozzolanic reaction of fly ash cement paste activated by an injection of alkali solution, Constr. Build. Mater. 94 (2015) 28-34.

DOI: 10.1016/j.conbuildmat.2015.06.046

[9] P.T. Bui, Y. Ogawa, K. Nakarai, K. Kawai, Effect of internal alkali activation on pozzolanic reaction of low-calcium fly ash cement paste, Mater. Struc. (2015) doi 10. 1617/s11527-015-0703-6.

DOI: 10.1617/s11527-015-0703-6

[10] C. Shi, R.L. Day, Acceleration of the reactivity of fly ash by chemical activation, Cem. Concr. Res. 25 (1995) 15-21.

[11] C. Shi, Early microstructure development of activated lime-fly ash pastes, Cem. Concr. Res. 26 (1996) 1351-1359.

DOI: 10.1016/0008-8846(96)00123-8

[12] A. Abdullah, M.S. Jaafar, Y.H. Taufiq-Yap, A. Alhozalmy, A. Al-Negheimish, J. Noorzaei, The effect of various chemical activators on pozzolanic reactivity: A review, Scientific Research and Essays. 7 (2012) 719-729.

DOI: 10.5897/sre10.858

[13] D.P. Bent, J. Weiss, Internal curing: A 2010 State-of-the-Art Review. NISTIR 7765 (2011). Information on http: /concrete. nist. gov/~bentz/NISTIR7765. pdf.

[14] T.P. Bui, Y. Muragishi, Y. Ogawa, K. Kawai, R. Sato, Effects of porous ceramic waste aggregate as an internal curing agent on steam-cured high strength fly ash concrete, Proc. The International Conference on Sustainable Structural Concrete, Argentina, (2015).

DOI: 10.1016/j.conbuildmat.2019.117462

[15] P.T. Bui, Effects of internal alkali activation on chemical and mechanical properties of fly ash cement systems, in: Doctoral thesis, Hiroshima University (2015).

[16] E. Sakai, S. Miyahara, S. Ohsawa, S.H. Lee, M. Daimon, Hydration of fly ash cement, Cem. Concr. Res. 35 (2005) 1135-1140.

DOI: 10.1016/j.cemconres.2004.09.008

[17] C.Y. Lee, H.K. Lee, K.M. Lee, Strength and microstructural characteristics of chemically activated fly ash-cement systems, Cem. Concr. Res. 33 (2003) 425-431.

DOI: 10.1016/s0008-8846(02)00973-0