SUPERHYDROPHOBIC CONCRETE

The Concept of Superhydrophobization

To improve the durability of concrete, sealers are often placed on the surface of the material to reduce the water absorption. These sealers typically wear off over time and do not show high hydrophobicity. Moreover, when the concrete cracks, which inevitably happens, water can easily penetrate concrete greatly reducing the effectiveness of the sealer. By creating a 3-D (volume) hydrophobiziation, cracks that form will have a water repellant nature and, therefore, when water penetrates the crack, it will not be allowed to enter capillary pores ensuring excellent durability. Moreover, the small crack sizes produced due to the fiber reinforcement even further reduces the amount of water that infiltrates the material.


Fig 1. Lotus Effect (Poole, 2005 and Kock, 2008)

The addition of superhydrophobic or hydrophobic admixtures to the cementitious material known as superhydrophic hybridization can be very beneficial. Superhydrophobic hybridization of concrete engages interdisciplinary work combining biomimetics (lotus effect), chemistry (siloxane polymers) and nanotechnology (nano-SiO2 particles) to resolve fundamental problems of concrete such as insufficient durability and corrosion resistance for internal reinforcing (Sobolev and Bartrakov, 2007; Sobolev and Ferrada-Gutierrez, 2005; Poole, 2005; Kock et al., 2008). The superhydrophobic action is intended to change the volume, size, and distribution of air voids in concrete as well as to reduce the bond with PVA fibers realizing a controlled pull-out behavior. Furthermore, the controlled air void structure results in "preferred" fracture modes.

Fig 2. Contact angle of Hydrophobic Surfaces (Muzenski et. al, 2013)

Superhydrophobic surfaces, or surfaces that have a water contact angle (θ) larger than 150°, have generated much interest due to their potential in industrial applications (mainly for self-cleaning), but they have not yet been employed for enhancing concrete durability. In terms of enhancing concrete, this nature-inspired approach can improve the performance of hydrophobic materials that control wettability (Poole, 2005; Kock et al., 2008). To manufacture superhydrophobic admixtures, the hydrogen containing siloxane admixture (e.g. polyethyl hydrosiloxane (PEHSO)/polymethyl hydrosiloxane (PMHS)) is combined with small quantities of, submicro/nanosized particles (Sobolev et al., 2006 and Sobolev et al., 2013).


Fig 3. Concept of Superhydrophobization (Muzenski S. et al., 2013)



Fig 4. Air Void Structure of Reference, Air-Entrained, and PMHS-Based Hydrophobic Admixture Mortar Samples (Sobolev K. et. al, 2013)

References:

  • Sobolev, Konstantin, Habib Tabatabai, Jian Zhao, Michael G. Oliva, Ismael Flores-Vivian, Rossana Rivero, Scott Muzenski, and Rehan Rauf, 2013
    • "Superhydrophobic Engineered Cementitious Composites for Highway Applications: Phase I", No. CFIRE 04-09.

  • Muzenski S, Flores-Vivian I, Sobolev K., 2013
    • "Hydrophobic engineered cementitious composites for highway applications", Cement and Concrete Composites

  • Kock K., Bhushan B. and Barthlott W., 2008
    • "Diversity of structure, morphology and wetting of plant surfaces", Soft Matter, pp. 1943-1963

  • Sobolev K. and Bartrakov V., 2007
    • "The effect of a PEHSO on the durability of concrete with supplementary cementitious materials", ASCE Journal of Materials in Civil Engineering, pp. 809-819.

  • Sobolev K., Flores I., Hermosillo R. and Torres-Martinez L., 2006
    • "Application of nanomaterials in high-performance cement composites" in Prooceedings of the ACI session on nanotechnology of concrete: recent developments and future perspectives.

  • Sobolev K. and Ferrada-Gutierrez M., 2005
    • "How nanotechnology can change the concrete world: part 2", American Ceramic Society Bulletin, pp. 16-19.

  • Poole B., 2005

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