Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering
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- 作者：Heloisa N. Bordallo ; Laurence P. Aldridge ; Arnaud Desmedt
- 刊名：Journal of Physical Chemistry B
- 出版年：2006
- 出版时间：September 14, 2006
- 年：2006
- 卷：110
- 期：36
- 页码：17966 - 17976
- 全文大小：449K
- 年卷期：v.110,no.36(September 14, 2006)
- ISSN：1520-5207
文摘
Portland cement reacts with water to form an amorphous paste through a chemical reaction called hydration.In concrete the formation of pastes causes the mix to harden and gain strength to form a rock-like mass.Within this process lies the key to a remarkable peculiarity of concrete: it is plastic and soft when newlymixed, strong and durable when hardened. These qualities explain why one material, concrete, can buildskyscrapers, bridges, sidewalks and superhighways, houses, and dams. The character of the concrete isdetermined by the quality of the paste. Creep and shrinkage of concrete specimens occur during the loss andgain of water from cement paste. To better understand the role of water in mature concrete, a series ofquasielastic neutron scattering (QENS) experiments were carried out on cement pastes with water/cementratio varying between 0.32 and 0.6. The samples were cured for about 28 days in sealed containers so thatthe initial water content would not change. These experiments were carried out with an actual sample ofPortland cement rather than with the components of cement studied by other workers. The QENS spectradifferentiated between three different water interactions: water that was chemically bound into the cementpaste, the physically bound or "glassy water" that interacted with the surface of the gel pores in the paste,and unbound water molecules that are confined within the larger capillary pores of cement paste. The dynamicsof the "glassy" and "unboud" water in an extended time scale, from a hundred picoseconds to a fewnanoseconds, could be clearly differentiated from the data. While the observed motions on the picosecondtime scale are mainly stochastic reorientations of the water molecules, the dynamics observed on the nanosecondrange can be attributed to long-range diffusion. Diffusive motion was characterized by diffusion constants inthe range of (0.6-2) 10-9 m2/s, with significant reduction compared to the rate of diffusion for bulk water.This reduction of the water diffusion is discussed in terms of the interaction of the water with the calciumsilicate gel and the ions present in the pore water.