| The present paper is aimed to study the relation between apparent contact angle and micro-structure of super-hydrophobic cement materials.Firstly,SEM was used to observe the concrete surface under the admixture method and external coating method,the distribution of nanoparticles in cement concrete was analyzed,and the micro-structure of cement concrete pavement surface was qualitatively described.Based on this,2-D and 3-D mathematical model of micro-structure of hydrophobic and super-hydrophobic cement materials were constructed.The influence of apparent contact angle and surface roughness on hydrophobic cement materials was analyzed by mathematical model.Finally,by 2-D and 3-D CFD numerical simulation with Fluent,a CFD software which is widely used,the relation between apparent contact angle and surfacee roughness was provided.The main conclusions are as follows:(1)Three intrinsic contact angles,600,100°,110°,were set.The ratio of 1:2 to 2:1(solid particle diameter:spacing)was used to analyze the 2-D mathematical model.The analytical results showed that:when the spacing between nanomaterial particles was small,the diameter of nanoparticles was large,and the hydrophobic reagent dosage of 5%,the cement concrete road surface roughness was higher,along with the apparent contact angle stable at about 150°.(2)Three intrinsic contact angles,60°,100°,100° and 10μm for diameter and spacing of solid particles were adopted to 3-D mathematical model.The analytical results showed that:when the particle diameter and intrinsic contact angle were fixed,the apparent contact angle decreased with the increasing of particle spacing;when the particle spacing and intrinsic contact angle were fixed,the apparent contact angle increased with the increasing of particle spacing;when the surface roughness was constant,the apparent contact angle was obviously smaller than that of Cassie-Baxter.(3)10μm for diameter of the sphere and three intrinsic contact angles,60°,100°,110°were adopted to 2-D mathematical model.The observation results of ImageJ showed that the apparent contact angle fluctuated less with the change of particle spacing;the ratios of particle diameter to spacing,1:1,1:2,10:1,and the intrinsic contact angles,60°,110°,were used to simulate.The results showed that the air cushion existed in the case of 10:1 high roughness,and the air cushion was the reason that the apparent contact angle of the rough surface was larger than the intrinsic contact angle.(4)The ratios of particle diameter to spacing,1:1,10:1,and three intrinsic contact angles,60°,100°,110° were adopted to 3-D mathematical model.The results showed that the air cushion was almost invisible when the roughness was low;when the roughness was higher,and the intrinsic contact angle was smaller,the volume of the air cushion was smaller;when the surface roughness was higher and the intrinsic contact angle was larger,the volume proportion of the air cushion was larger,the liquid bridge was protruding upward,and the highly rough surface was the necessary condition for the preparation of super-hydrophobic materials.(5)By a comparison between the results of 2-D and 3-D simulations,the apparent contact angle predicted by the former was relatively large,while the simulation results of the latter were more consistent with the experimental results.When the roughness was high,the volume ratio of air cushion between them were not very different.When the roughness was low,the former air cushion ratio was obviously higher than the latter. |
