Chloride Ion Permeability In The Concrete With PCMs And Nano Silica

With the common understanding of the increasing building energy consumption,the development and application of building energy-saving technologies and energy-saving materials has become a research hotspot.According to statistics,about one-third of the energy consumption in most countries comes from building-related energy consumption.In order to reduce the energy consumption of buildings and improve our living environment,building energy conservation is an urgent task.In recent years,the research on the use of PCM（Phase Change Materials）phase change energy storage materials in concrete structures to improve the energy consumption and temperature regulation performance of buildings has developed rapidly.PCM refers to a phase change material that transforms from one physical form to another with endothermic energy storage or exothermic energy release within a certain temperature range.The energy stored or released during the phase transition of PCM is called latent heat of phase transition.During the phase transition,the temperature of the PCM material itself remains almost unchanged until the phase transition is completed.Although the temperature remains unchanged,the latent heat absorbed or released by the PCM is quite large.Incorporating PCM into concrete will reduce the mechanical properties of concrete to a certain extent.In order to ensure and promote the application of PCM concrete in building structures,suitable reinforcing materials can be added to improve the mechanical properties of PCM concrete.In this study,nano-silica（Nano-silica）reinforcement was used to mix PCM concrete to properly improve the matrix strength of PCM concrete.The basic mechanical properties,resistance to chloride ion diffusion and diffusion mechanism of composite nano-silica PCM concrete with 9%MPCM（Micro-encapsulated Phase Change Materials）microcapsules were studied in depth.In this paper,the 28d compressive strength and thermal properties（specific heat capacity,specific heat capacity,heat capacity and thermal performance of MPCM concrete reinforced with（4%,7%,9%）MPCM concrete and（2%）nano-silica reinforced（4%,7%,9%）MPCM concrete were investigated in this paper.Thermal conductivity,thermal diffusivity）test,as well as strength and thermal properties phase change cycle stability,resistance to chloride ion penetration test research,The chloride ion diffusion coefficient（D₀）of MPCM concrete and nano-silica MPCM concrete was obtained by regression according to the test data,and the chloride ion diffusion theoretical model of nano-silica MPCM concrete considering the main influencing factors such as temperature and humidity was established,and the finite element analysis was carried out by ABAQUS.The software performs numerical simulations of chloride ion diffusion.The main research contents and conclusions are summarized as follows:（1）With the increase of MPCM content（4%,7%,9%）,the 28d compressive strength of MPCM concrete gradually decreased,and the addition of nano-silica can significantly improve the compressive strength of MPCM concrete.（2）With the increase of MPCM content,the thermal conductivity of MPCM concrete and nano-silica MPCM concrete gradually decreased,the specific heat capacity gradually increased,and the thermal diffusivity gradually decreased;At the same ambient temperature,with the increase of MPCM content,the internal temperature peak of nano-silica MPCM concrete gradually decreased,and the heating and cooling showed a lag,and MPCM played the role of cutting peaks and filling valleys.（3）After 100 thermal cycles of phase change,the compressive strength of MPCM concrete and nano-silica MPCM concrete increased,the compressive strength remained basically unchanged after 200 thermal cycles,and slightly decreased after300 thermal cycles.After 100,200,and 300 phase change thermal cycles,respectively,the temperature regulation performance of MPCM concrete and nano-silica MPCM concrete remained unchanged,indicating that the thermal properties of MPCM concrete and nano-silica MPCM concrete phase change cycle Excellent stability.（4）According to ASTM C1556-11a,the natural immersion method chloride ion diffusion experiment was carried out on MPCM concrete and nano-silica MPCM concrete,and it was found that the natural diffusion method was used in the test.The test results show that with the increase of MPCM content,the chloride ion diffusion depth in MPCM concrete and nano-silica MPCM concrete gradually decreases,and the chloride ion concentration at the same depth also decreases.At the same time,the chloride ion diffusion coefficient of nano-silica MPCM concrete gradually decreased,it can be seen that MPCM concrete and nano-silica MPCM concrete have better chloride ion permeability resistance than ordinary concrete.（5）Based on the experimental data,a theoretical model of chloride ion diffusion in nano-silica MPCM concrete was established considering the main influencing factors such as temperature and humidity,and the numerical simulation analysis of chloride ion diffusion in nano-silica MPCM concrete was carried out by using ABAQUS finite element analysis software.The numerical simulation results of ABAQUS were compared with the experimental data of chloride ion diffusion,and it was found that they were consistent with the experimental data and had a high correlation,which verified the applicability of the chloride ion diffusion model of nano-silica MPCM concrete.