Study On Concrete Surface Protection Materials Modified By Nano/Micro Particles

Promoting the"one belt and one way"construction and building a maritime power is a major development strategy of China.Advanced marine materials and ocean building engineering are the necessary material and important platform foundation for implementing marine strategy.Compared with the terrestrial concrete projects,the marine environment with high salinity,big temperature difference and high humidity has greatly reduced the service life of marine construction projects.In general,the erosion of harmful ions(such as Cl^-,SO₄^2-,Mg²⁺)in service environment is the main factor causing the damage of this kind of engineering.Therefore,reducing the invasion of harmful ions is of great significance for prolonging the service life of concrete.Concrete surface protection materials?CSPM?can form a layer of barriers on the concrete surface,which is the first and most important line of defense to prevent water and various erosion media from migrating to the concrete interior.Therefore,it is of great theory significance and engineering value to study CSPM with high efficiency for concrete protection.This paper relied on the National key R&D program of China during the Thirteenth Five-year Plan Period?2016YFC0701003-05?systematically studies the material design and performance control mechanism of nano-micron modified multiscale cement-based CSPM under ultra low water binder ratio based on the design principles of high crack resistance,high impermeability and high compatibility with concrete matrix,and then predicts the service life of concrete with CSPM,which provides a theoretical foundation and reference for the study and application of CSPM.The main work and the key scientific achievements are as follows:1.CSPM material design and performance control method based on high crack resistance.?1?The shrinkage of CSPM can be significantly reduced by shrinkage reducing agent?SRA?and crack-resistance and toughening component of PF in a certain range of dosage,improving the volume stability and cracking resistance of CSPM.The saturation content of SRA and PF is 1.5%and 2‰,respectively,and the optimal mixing ratio of 3 mm and 10 mm PF is 1:1.?2?Mixing high alumina silicon microspheres?HASM?with nano-SiO₂?NS?or nano-TiO₂?NT?can obviously improve the volume stability and cracking resistance degradation of CSPM caused by NS and NT incorporation.Compared with the sample single-added 30%HASM,when used 30%HASM and 3%NS or 3%NT together,the autogenous shrinkage and drying shrinkage would increase slightly,but compared to blank sample,the shrinkage rates decreased obviously.?3?The addition of styrene-acrylic emulsion?SAE?significantly reduced the elastic modulus,brittleness coefficient,elastic strength ratio,drying shrinkage and autogenous shrinkage of the specimen,which is beneficial to improve the volume stability and crack resistance of CSPM.?4?Compared with the reference sample,the crack resistance of CSPM is improved obviously by the adjustment of functional components and the modification of nano-micron materials,no visible cracks are found in the specimens after 14 days accelerated cracking test and 10 days temperature cycling test,but a large number of obvious cracks are discovered in the reference sample.2.CSPM material design and mechanism analysis based on high impermeability.?1?The chloride diffusion coefficient and electric flux were taken as indexes to study the effect of HASM,NS and NT on impermeability of CSPM under ultra low water binder ratio?0.22?.Results show that impermeability of CSPM can be significantly improved by addition of HASM,NS and NT,and the optimum mixing proportions are 30%,3%and 3%,respectively.HASM and NS or NT co-incorporated is able to achieve the superposition of advantages of them and further increase the impermeability of CSPM.Using 30%HASM and 3%NS or 3%NT together makes the chloride diffusion coefficient and 6 hours electric flux less than 3×10^-14 m²/s and100 C,respectively,and the sulfate corrosion resistance coefficient value greater than1.1 for 360 days.Based on the relationship between macroscopic properties and microstructure of cement-based materials,the influence mechanism of HASM,NS and NT on impermeability of CSPM was investigated:The addition of HASM with NS or NT can obviously promote the hydration of cementitious system,optimize the interface transition zone?ITZ?,reduce the concentration of calcium hydroxide?CH?and effectively improve the pore size distribution of CSPM,thus increasing its compactness and impermeability.?2?The influence of SAE combined with NS or NT on impermeability of CSPM was investigated for the first time.Results indicate that they have a good synergistic effect on improving the impermeability.The composite system mixing 5%SAE with3%NS or 3%NT makes the chloride diffusion coefficient and 6 hours electric flux less than 2×10^-14 m²/s and 100 C,respectively,and the sulfate corrosion resistance coefficient greater than 1.2 for 360 days.The mechanisms which improve the impermeability of CSPM by SAE/NS and SAE/NT systems were investigated through the influence of organic/inorganic nano-micron particle composites on the microstructure and phase of CSPM:The addition compound of SAE with NS or NT can significantly reduce the Ca/Si ratio and the enrichment degree of CH in ITZ,thus making it strengthened,and optimize the pore structure of CSPM so that the total pore volume and the amount of harmful and more-harmful pores decrease remarkably.The addition of NS and NT can promote the hydration of cementitious system and improve the film forming performance of SAE,which make up for the hindrance of SAE on hydration and increase the density of CSPM to a certain degree.?3?A hardening microstructure model of CSPM modified by inorganic nano-micron particles was established,which vividly reveals the inducement and control mechanism of HASM,NS and NT on CSPM microstructure.The time-variant hydration model of SAE modified CSPM was built,visually illustrating the development process of internal structure of CSPM system in the presence of SAE and the improving mechanism of SAE on ITZ and matrix.3.High compatibility control between CSPM and concrete matrix?C50?based on interface strengthening.?1?According to the requirement of high interfacial bond strength between CSPM and concrete matrix,the interface strength is enhanced by pouring surface protection materials after initial setting but before final setting,roughening the surface of concrete matrix and modification of CSPM with nano-micron materials,then the interfacial bond strength of the specimen with two molding process is equal to or slightly higher than that of concrete with one molding process.After 25 thermal shock cycles,the retention rates of interfacial bond strength of CSPM modified by nano-micron composites and concrete matrix has reached 90%or more.CSPM shows similar shrinkage rate to concrete matrix,indicating a good compatibility of volume deformation.?2?When CSPM is modified by HASM,NS,NT or SAE composites,the chloride ion diffusion coefficient of concrete can be reduced by about one order of magnitude or more with the thickness of 5 mm protective layer,and the 6 hours electric flux is reduced to below 400 C.?3?The influence mechanism of nano-micron particle modified protective material on the interface performance of CSPM and concrete matrix was revealed by the interface micro-analysis.Through the appropriate amount of HASM,NS,NT or SAE compound modification,the integration of matrix material and protective layer material can be realized,the Ca/Si ratio?less than 2?and the enrichment degree of CH near the interface bond zone can be evidently reduced,and the pore structure of the interface bonding area can also be optimized,making the microstructure of interface region become more compact and homogeneous.?4?The interfacial bonding models of different casting time and different nano-micron modification of CSPM were established,which iconically illustrate the influence mechanisms of casting time and nano-micron modification of protective layer on interfacial bonding properties of CSPM and concrete matrix.4.The concrete life prediction based on Cl^-diffusion theory model under the action of multi-factors.According to Cl^-diffusion theory model under the action of multi-factors,the service life of concrete in marine environment was predicted.Results show that the use of surface protection materials can greatly improve the service life of concrete.Even in the worse case,the predicted service life of concrete can reach more than 500years by using the CSPM modified by nano-micron materials.