Page 143 - Handbook of Surface Improvement and Modification

138 Water Repelling (Hydrophobization)

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static contact angles (150 ) PTFE-SiO 2
coating surface had contact angle of 163.1 o
and a considerably denser structure than
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SiO . The PTFE-SiO coating also had
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2
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excellent water and acid resistance.
The mechano-chemical activation and
surface treatment of limestone filler influ-
enced properties of construction compos-
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ites. Mortars were prepared from cement
and calcite aggregate and limestone filler
(10 wt%) was added to the mixture after its
mechano-chemical activation in an ultra-
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centrifugal mill. The filler and aggregate
were also coated with stearic acid via dry
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procedure. Limestone aggregate led to
lower compressive strength but it had neg-
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ligible shrinkage at 1000 C. The hydro-
phobization with stearic acid decreased the
water absorption and caused the formation
of needle-like micro-network that filled
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structural voids reducing porosity.
A sprayable polydimethylsiloxane
solution have been applied on granite to
produce durable surface coating that mini-
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mized weathering effects. Due to the
excellent water and salt-blocking behavior
of PDMS, the protected stones display an
overall better stability against weathering
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than untreated stones.
The chemical functionalization of
ultrahigh-performance concrete, UHPC,
with a low surface energy material was
obtained by transferring residues from the
PDMS mold or by spraying siloxane-based
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compounds. The latter method gave super-
Figure 9.2. 3D topographic profiles of (a) micro-pillared hydrophobic properties with static contact
PDMS mold; (b) UHPC/micro-pillared PDMS; (c) angles reaching 164 and contact angle hys-
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UHPC/microtextured UHPC. [Adapted, by permission,
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from Horgnies, M; Chen, JJ, Cement Concrete Compos., teresis as low as 2.5 for microtextured sur-
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52, 81-90, 2014.] face (Figure 9.2). The process resulted
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with water-repelling, self-cleaning concrete. Raindrops slide off the concrete surface, car-
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rying debris away.
The infiltration of water into the porous structure of the concrete matrix is one of the
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main factors leading to the deterioration of concrete. Sealers or water repellants are often
applied to reduce the ingress of water but, if the material develops microcracks, water can
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easily penetrate and saturate its bulk. Incorporation of a hydrophobic admixture into the