Shrinkage and expansive strain of concrete with fly ash and expansive agent

Abstract

The effects of fly ash and MgO-type expansive agent on the shrinkage and expansive strain of concrete with high magnesia cement were investigated. The results show that high volumes of fly ash may reduce the shrinkage strain of concrete and inhibit the expansive strain of concrete with MgO-type expansive agent, but can not eliminate the shrinkage of concrete. MgO-type expansive agent may produce expansive strain and compensate the shrinkage strain of concrete, relieve the cracking risk, but the hydration product of magnesia tends to get together in paste and produce expansive cracking of concrete with high magnesia content according to SEM observation.

Keywords

high volumes of fly ash / MgO-bearing expansive agent / high magnesia cement / volume stability

References

[1] Schrader E., Mekinnon R. RCC Paving and Slabs-deeper[J]. Concrete International, 1989, 11(5): 64-66.

[2] Papayianni I., Valliasis T. Heat Deformations of Fly Ash Concrete[J]. Cement and Concrete Composites, 2005, 27: 249-254.

[3] Gao P. W. Production of MgO-type Expansive Agent in Dam Concrete by Use of Industrial by-products[J]. Building and Environment, 2008, 43(4): 453-457.

[4] Mehta P. K., Pirtz D. Magnesium Oxide Additive for Producing Selfstress in Mass-Concrete[C]. Proc of the 7th International Congress on the Chemistry of Cemen, Paris, France, 1980, 3: 6-9.

[5] Gao P. W. Using a New Composite Expansive Material to Decrease Deformation and Fracture of Concrete[J]. Materials Letters, 2008, 62(1): 106-108.

[6] Gao P. W., Tang M. S. Morphology of MgO Hydration Products under Different Curing Conditions[J]. Chinese J. of Inorganic Chemistry, 2007, 23(6): 1 063-1 068.

[7] Chatterji S. Mechanism of Expansion of Concrete Due to the Presence of Dead-burnt CaO and MgO[J]. Cement and Concrete Research, 1995, 25(1): 51-56.

[8] Kasselouris V., Ftikos C. Parissakis. On the Hydration of MgO in Cement Pastes Hydrated up to Eight Years[J]. Cement and Concrete Research, 1985, 15: 758-764.

[9] Gao P. W., Tang M. S. Effect of Different Expansive Agents on Mass Concrete Deformation Property[J]. J. of Nanjing University of Aeronautics & Astronautics, 2006, 38(2): 251-255.

[10] Deng M., Tang M. S. Expansive Characteristics of MgO in Different Cement Matrixes[J]. J. of Nanjing University of Chemical Technology, 1991, 13: 54-58.