Research On Hydrophobicity And Surface Superhydrophobic Modification For Cement-Based Materials

The penetration of water into the cement-based material is one of the important factors affecting its durability,especially for some projects that require higher resistance water penetration.In this paper,according to the water penetration characteristics of cement-based materials,the hydrophobic and superhydrophobic surfaces of the cement-based materials were studied respectively,based on the concept of structure-function integration.For the hydrophobic matrix of cement-based materials,we overcame the problem of dispersion of liquid oleic acid in cement-based materials.Oleic acid-fly ash（OA-FA）with hydrophobic function was prepared by oleic acid（OA）and fly ash（FA）.And then,hydrophobic cement-based material（HCBM）with good impermeability was prepared,using OA-FA as functional aggregate.In the meanwhile,we prepared silica gel mold（SGM）by copying the surface structure of sandpaper,and the hydration characteristics of needle 518 phase,interlapped jointing,were combined.Superhydrophobic structure was constructed on the surface of magnesium oxychloride cement.The main research contents and achievements are as follows:For cement-based material matrix resistance water permeability,oleic acid was used as hydrophobic functional modifier,and fly ash was used as collection carrier.carboxyl group of oleic acid and silicon hydroxyl of fly ash were composited.So,the oil acid with hydrophobic alkyl chain was introduced into the fly ash to get the OA-FA.Finally,HCBM with good resistance water permeability was prepared by introducing OA-FA into cement-based materials.The dispersion of liquid oleic acid,in cement-based materials,was overcame.FTIR analysis revealed that OA-FA contains both the characteristic peaks of oleic acid and fly ash.HCBM,introduced OA-FA,shows excellent hydrophobic function.The contact angle increased from 0 to87°,due to the combined function of OA-FA hydrophobic and rough structure composed of OA-FA.The gas permeability coefficient decreased by 87%.Moreover,the capillary absorption test of 9d showed that the lowest value was introduced at12%,and decreased by 63%compared with the control.It is proved that the introduction of OA-FA greatly increases the hydrophobicity of cement-based materials.Surface superhydrophobic modification is the most direct and effective way to improve the waterproofing property of cement-based materials.we combined the micro-nano soft confinement function of SGM and the 518 phase hydration growth characteristics,and constructed of multi-scale micro-nano gas solid composite surface structure on the surface of magnesium oxychloride cement,which thickness is between 50¹00μm and consistent with the Cassie-Baxter model.The maximal water contact angle was 154.6°,rolling lagging 3°.According to the Cassie-Baxter equation,the actual solid-liquid interface ratio is f₁=0.05,and reduced by 95%compared to ordinary magnesium oxychloride cement.The super hydrophobic surface structure of SSHMOC is sensitive to the service environment,due to the characteristics of magnesium oxychloride cement.This paper explores those factors.High humidity environment,immersion and water erosion will destroy its multi-scale micro-nano gas-solid composite structure.The superhydrophobic structure destroyed due to hydrolysis of the 518 phase with the ambient humidity increased from RH50%to RH100%,the contact angle decreased from 150.1°to 81.5°.Mg（OH）₂ was discovered,and the partial decomposition of the518 phase in high humidity environment was also proved.As the immersion time increases to 28d,the contact angle decreases from 150.1°to 30°,and the superhydrophobic structure basically disappeared at 28d.With the water washing time increasing to 10min,the contact angle decreased to 122.4°.Compared with the magnesium oxychloride cement,the water resistance of SSHMOC was improved,but the lifting was limited.How to further modify its super hydrophobic structure and prolong its water resistance is the key point of the next step.Further modification of its super hydrophobic structure was the key work to improve its water resistance.