| Reinforced concrete is complex and harsh marine environment is prone to structural failure,the key factor is that concrete can't effectively inhibit the transport of water and salt.Water and salt transport rate can be significantly reduced by surface coating,which is economical and efficient.The organic-inorganic composite coating has gained widespread attention due to its strong design in composition and synergistic strengthening in performance.Polymer cementbased coating has both high elastic and high toughness of polymer and excellent interface compatibility and mechanical properties of cement,cost-effective and environmental friendliness make it has been widely used in all kinds of protection projects.However,the existing polymer cement-based waterproof coating is difficult to serve in the marine environment for a long time,because it is easy to absorb water and swell in the high humidity environment,inadequate waterproof and impermeability,and poor weather resistance.Given the above problems,this paper intends to improve the impermeability and weather resistance of polyacrylate emulsion by the excellent material compatibility and hydrophobicity of PDMS.On this basis,the hydrophobic alloy powder was used to synergistically strengthen the microstructure of the polymer cement-based coating and build an excellent three-dimensional hydrophobic network structure,aiming to achieve the effective performance improvement of the polymer cement-based coating in the marine environment.The main research contents are as follows:(1)Firstly,the critical process parameters of the hydrophobically modified polyacrylate latex particles by PDMS were identified,and the correlation between the properties of the physical cold-assembling modified polyacrylate latex film and the content of PDMS was established.Finally,the hydrophobic modification mechanism was explained.The molecular weight of PDMS is one of the key parameters of a hydrophobic modification.When the molecular weight of PDMS is 38000,the comprehensive modification effect was better.Compared with the blank sample,the contact angle(CA)increased by about 21.25% and the water absorption rate decreased by 16.53% under 6% PDMS dosage.The shear rate significantly affected the particle size distribution of hydrophobically modified latex particles.With the increase of shear rate,the average particle size of modified emulsion gradually decreased,and the stability improved,the water absorption of the film showed a good positive correlation with the shear rate.When the rotation speed is 7000 rpm,the comprehensive modification effect was best.Under the 10% content of PDMS,the water absorption rate was24.63% lower than that of the blank sample.With the increase of the content of PDMS,the CA of the latex film increased gradually,the water absorption and tensile strength decreased gradually,and the elongation at break reached the maximum value of 656.73% at 8%,which increased by 22.94% compared with the blank sample.The average particle size increased gradually.OP-10 significantly reduced the average particle size of the emulsion.When the amount of OP-10 was 0.5% of PDMS,the average particle size of the emulsion decreased to3.165 um,however,the CA decreased by 3.95% and the water absorption increased by 21.72%.The tensile strength of the latex film also gradually decreased with the increase of the amount of OP-10.The effective hydrophobic modification of latex particles by PDMS is based on sufficient dispersion of PDMS and sufficient emulsifier.PDMS can reduce the surface energy of latex particles,prevent water from spreading on the surface of the latex film,and improve the hydrophobicity of the latex film.(2)The effects of PDMS hydrophobic modified polyacrylate emulsion on the basic physical properties,UV aging resistance,and salt spray aging resistance of the coating were investigated.With the increase of the content of PDMS in polyacrylate emulsion,the waterproof and impermeability of the prepared cement-based polymer coating are improved.When the content of PDMS was 6%,the rolling angle(RA)of the coating was 52.27% lower than that of the blank sample,and the water absorption and water permeability reached the lowest values of 16.10% and 0.21 m L,which were 13.86% and 53.3% lower than that of the blank sample,respectively.The tensile strength decreased gradually with the increase of the content of PDMS,but the flexibility was improved.The elongation at break reached the maximum value of 61.77% at 6%,which increased by 41.38% compared with the blank sample.After UV aging for 1000 h,the structure of the coating doped with PDMS was more complete.When the content of PDMS was 6%,the lowest rate of change of tensile strength,the loss rate of elongation at break,and water absorption of the coating were 8.64%,103.8%,and 59.57%,respectively,which were reduced by 30.32%,8.0%,and 16.27% compared with the blank sample,respectively.After salt spray aging for 28 days,the sample with PDMS showed a more complete membrane structure than the blank sample.When the content of PDMS was 6%,the loss rates of water absorption and elongation at break of the coating were the lowest,which were 14.57% and 61.95%,respectively,and decreased by 15.10% and 28.36% compared with the blank sample,respectively.Under the optimal content of 6% PDMS,the coating prepared by PDMS hydrophobic modified emulsion has better waterproof performance than that by PDMS directly modified coating.The water absorption and water permeability were reduced by 31.67% and 41%,respectively,and the surface membrane structure was more complete.(3)The effects of hydrophobic powder on the basic physical properties,UV aging resistance,and salt spray aging resistance of the coating were investigated.With the increase of the hydrophobic powder content,the water absorption of the coating decreased gradually,and the water permeability at 3% had the lowest value of 0.259 m L,which was 42.44% lower than that of the blank sample.The tensile strength and elongation at break first increase and then decrease,and the tensile strength at 2% increases to the maximum,which is 12.75% higher than that of the blank sample.The elongation at break reached the maximum value at 3% and increased by 37.92% compared with the blank sample.After UV aging for 1000 h,the film structure of the coating with alloy powder was relatively complete.When the alloy powder content was 3%,the change rate of the tensile strength of the coating was the least 131.68%,which was 5.99% lower than that of the blank sample.At this time,the water absorption of the coating decreased the most.The loss rate of elongation at break was the lowest in the coating with 4% alloy powder content,which was 62.74%,about 11.80% lower than that of the blank sample.After salt spray aging for 28 d,the surface membrane structure of the coating with alloy powder was more complete than that of the blank sample.When the alloy powder content was3%,the water absorption rate of the coating decreased the most,the change rate of tensile strength and the loss rate of elongation at break were23.63% and 71.64%,respectively,which decreased by 47.74% and 17.15% compared with the blank sample.(4)High-performance polymer cement waterproof coating was prepared by compound 3%hydrophobic powder based on modified emulsion with PDMS content of 6%.Compared with four kinds of polymer cement waterproof coatings on the market,the self-made coating has better hydrophobicity,bonding strength,chloride ion penetration resistance,and UV aging resistance. |
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