Analysis Of Frost Resistance And Damage Deterioration Of MPCMs/NanoSiO₂ Composite Modified Concrete

In cold area projects,freeze-thaw damage is often one of the main factors that shorten the service life of concrete buildings.The traditional methods to improve the frost resistance of concrete mainly include adding admixtures,adding active mineral admixtures,improving the mix proportion,etc.Relevant scholars have made some achievements.Because of the particularity of engineering foundation in cold regions and the importance of engineering construction projects,improving the freeze-thaw resistance of cement-based composites has become the most important task of concrete durability in cold regions.Microcapsule phase change materials have great potential in overcoming freeze-thaw damage and structural looseness by exerting their own"regulation"role.At the same time,the filling effect of nano materials can effectively remedy the defects of phase change materials.Therefore,this paper studies the thermal mechanical properties,temperature control and frost resistance effects,the change rule of real-time compressive strength with external temperature under different temperature gradients,the evolution rule of internal pore structure distribution with freeze-thaw times,and the prediction of fractal damage characteristics evolution model under freeze-thaw cycle of mPCMs/NanoSiO₂composite modified concrete and ordinary concrete with the optimal content.The results show that:（1）The thermal conductivity,thermal diffusivity and adiabatic temperature rise of10mPCMs/1.5NanoSiO₂composite modified concrete are lower than that of ordinary concrete.The specific heat coefficient and linear expansion coefficient are higher than that of ordinary concrete,and the variation range is smaller than that of ordinary concrete.（2）Under temperature control environment,compared with ordinary concrete,the temperature drop rate of 10mPCMs/1.5NanoSi O₂ composite modified concrete is obviously smaller during freezing（15℃～-15℃）,and the temperature rise rate is slower during melting（-15℃～15℃）as time goes on.In the process of real-time compressive strength test under different gradients,the real-time compressive strength value of ordinary concrete changes greatly under freezing（10℃～-10℃）,and the real-time compressive strength value of 10mPCMs/1.5NanoSiO₂composite modified concrete changes slightly.In the process of freezing thawing,10mPCMs/1.5NanoSiO₂composite modified concrete,by mixing phase change materials and nano materials,the internal temperature change of composite modified concrete can be effectively alleviated,the internal structure damage of composite modified concrete can be improved,and the frost resistance of composite modified concrete can be improved.（3）In the freeze-thaw environment,with the continuous increase of the number of freeze-thaw cycles,the mass loss rate of 10mPCMs/1.5NanoSiO₂composite modified concrete and ordinary concrete increases,and the relative dynamic elastic modulus decreases.When the mass loss is used to evaluate the freeze-thaw failure of ordinary concrete and 10mPCMs/1.5NanoSiO₂composite modified concrete,the freeze-thaw times are 150 times and 300 times respectively;When the relative dynamic elastic modulus is used to evaluate the freeze-thaw failure,the number of times of reaching freeze-thaw is 100times and 300 times respectively.After the freeze-thaw cycle,the internal porosity and slice porosity of ordinary concrete and 10mPCMs/1.5NanoSiO₂composite modified concrete increase,and the fractal dimension increases,but the growth rate of10mPCMs/1.5NanoSiO₂composite modified concrete is less than that of ordinary concrete.After freeze-thaw cycles,the compressive strength loss of 10mPCMs/1.5NanoSi O₂composite modified concrete is less and the decline range is small,and its frost resistance and mechanical properties are better than ordinary concrete.（4）The compressive strength,axial peak strain and elastic modulus of10mPCMs/1.5NanoSiO₂composite modified concrete showed a decreasing trend during the freeze-thaw cycle.According to the test data of fractal damage variable D of10mPCMs/1.5NanoSiO₂composite modified concrete after different freeze-thaw cycles,the relationship curve of fractal damage variable D with axial pressure strain and the prediction model of fractal damage variable evolution under different freeze-thaw cycles are obtained,and the expression of fractal damage evolution model of10mPCMs/1.5NanoSiO₂composite modified concrete under freeze-thaw cycles is constructed.