Research On Frost Resistance Of MPCMs Modified Cement-based Compmsite

In cold regions,due to the climate,the concrete is often in the freezing and thawing environment after the completion of the project,which greatly reduces the service life and safety of concrete.In recent years,the addition of phase change materials into concrete to enhance the frost resistance of concrete has been widely concerned.In this thesis,the same mass of microencapsulated phase change materials(m PCMs)were used to replace sand to prepare m PCMs concrete with the content of 0%,5%,7.5%,10%,15%,17.5% and 20%,respectively.The thermal properties,mechanical properties and frost resistance of phase change concrete with different m PCMs contents were studied:(1)With the increase of the content of m PCMs,the concrete’s temperature conductivity coefficient,thermal conductivity coefficient and adiabatic temperature appreciation all decrease,while the specific heat increases;(2)With the increase of m PCMs content,the compressive strength loss rate of concrete increases and the strength decreases;(3)With the increase of m PCMs content,the improvement rate of frost resistance of concrete increases immediately and then decreases.Considering the above conditions,the optimal content of phase change material is determined to be 10%.The loss rate of concrete strength is34.47%.The CT scanning analysis of concrete under different freeze-thaw cycles shows that with the increase of m PCMs content,the change of the internal pore growth rate of the specimens increases at first and then decreases as the content of m PCMs increases.Avizo software was used to analyze the CT scanning,and two-dimensional slices with different depths were compared.The results show that the freeze-thaw damage of concrete is from the outside to the inside.By adding nano-materials into the m PCMs modified concrete,the results show that with the increase of the content of nano-materials,the strength of m PCMs modified concrete immediately increases and then decreases.When the content of nano materials is1.5%,the reinforcement effect is the best.The results show that adding nano-materials is one of the methods to strengthen m PCMs modified concrete.This work lays a certain foundation for the further study of microencapsulated phase change materials.