SUPERHYDROPHOBIC CONCRETE

Superhydrophobic Admixtures

To create the hydrophobic and superhydrophobic admixtures a water soluble polyvinyl alcohol (PVA) and a polymethyl-hydrogen siloxane oil (PMHS) were used as surfactant and as hydrophobic agent, respectively. Emulsion parameters such as the dosage of surfactant, admixture quantity and mixing speed for the emulsion preparation were evaluated on the performance in portland cement mortars. The mortars were also compared against a reference mortar and a mortar sample with air entrainment admixture (AE50). Each admixture was tested with either 2.2% or 4.4% PVA. The PMHS content was held constant at 25% and the emulsification speed was tested at 1,000 rpm and 10,000 rpm. A single or double dose of admixture was also tested (0.25 g/l and 0.50 g/l, respectively). Proportions of the portland cement mortars were kept constant with the water to cement ratio (W/C) and the sand to cement ratio (S/C) at 0.35 and 1.0, respectively.

Table 1. Experimental Matrix for Mortars with Air-Entrainment and Superhydrophobic Emulsions (Sobolev K. et. al, 2013)


Fig 1. Air Content (left) and Compressive Strength (right) of Mortars with
Air-Entrainment and Superhydrophobic Emulsions (Sobolev K. et. al, 2013)


Fig 2. Air Void Structure of Reference, Air-Entrained, and
PMHS-Based Hydrophobic Admixture Mortar Samples (Sobolev K. et. al, 2013)

Based on the air content, air void analysis, and compressive strength investigation, it was determined that the best admixture was produced with 4.4% PVA by mixing at high speed (10,000 rpm). This admixture provided minimal reduction in compressive strength, high air content, and enhanced air void structure with small, evenly spaced air voids. Combining this admixture with sub-micron particles further increases the hydrophobicity and provides a better air void distribution throughout a cementitious matrix. Two admixtures with sub-micron particles (Mk2 and Mk3) were produced and were tested on mortar tiles for the contact angle. These admixtures were compared with reference admixture (Mk1=Fast1) and an untreated plain mortar tile (REF).

Fig 3. Contact Angle of Mortar Tiles (Sobolev K. et. al, 2013)


Fig 4. Values of Contact Angle on Mortar Tiles (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.

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