The use of hydrophobic additives is a relatively new development within the field of durability
design of concrete structures. This approach relies mainly on chemical modification of the
cement paste matrix. Another promising, but less well-studied approach is by adopting the
Cassie-Baxter mechanism. This can be achieved by creating a suitable micro texture on the
surface of the cementitious material, which traps air when in contact with water leading to the
separation between water and solid. The focus of this study is to develop concretes with
hydrophobic micro textured surfaces and to study the properties and durability of such
concretes. Hydrophobic Precipitated Calcium Carbonate (HPCC) made by dry ball milling
calcium carbonate and stearic acid is used to enhance hydrophobicity of the textured surfaces.
The effects of HPCC on the wettability and mass transport properties of cementitious materials
were investigated. By adopting soft lithography, micro textures on hydrophobic lotus and taro
leaves were transferred onto the surfaces of cementitious samples. Furthermore, research on
developing hydrophobic surfaces using a fine microgrid to mimic the micro texture of
hydrophobic plant leaves was undertaken. The hydrophobicity of micro textured surfaces was
enhanced by adding HPCC into cementitious mixture or by coating the surface with
Polydimethylsiloxane (PDMS). Water contact angle measurements were carried out to
determine the effect of surface micro textures on wettability and imbibition experiments were
carried out to determine the effect they have on water transport properties. Optical microscopy
was used to observe the formation and evolution of air trapped between the micro texture.
Furthermore, their durability and hydrophobicity when exposed to a range of conditions were
investigated. Changes in morphology due to continuous hydration, atmospheric carbonation
and abrasion, and wettability of deteriorated textured surfaces were investigated.
The research was successful in developing cementitious materials with micro textured
surfaces that displayed hydrophobicity, high water contact angle and strong adhesion between
droplets and substrate. The addition of HPCC to both micro textured and non-textured
samples showed decreasing wettability with increasing HPCC content. For example, taro
textured cementitious samples containing 16% HPCC had a water contact angle of 143˚,
compared to 123˚ for taro textured samples without HPCC. Furthermore, micro textured
samples containing 16% HPCC showed around 40% reduction in water sorptivity while the
textured samples with PDMS coating showed a reduction of 70% compared to non-textured
samples. The decrease in water absorption is mainly due to formation of trapped air cushions
when the sample is submerged underwater. However, samples containing less than 8% HPCC do not form such air cushion, and therefore, are less effective in decreasing water absorption.
This indicates that the performance of micro textures is related to HPCC content.
Durability studies showed that abrasion and efflorescence could affect the morphology of
textured surfaces and increase their wettability. In contrast, the influence of continuous
hydration and carbonation was negligible. Replacing 10% wt. of cement with silica fume can
prevent efflorescence and increase the abrasion resistance of surface textures, which yielded
a more durable textured surface. PDMS coating on micro textured surfaces was resistant to
cyclic wetting and elevated temperature of 50˚C, indicating that the coating was stable and
capable of providing long-term protection to cementitious materials. Overall, this research has
shown that the combination of hydrophobic treatments (HPCC / PDMS coating) and microtextured surfaces is a promising approach to deliver innovative hydrophobic concrete for
durable structures.