Performances Of Permeable Concrete Mixed With Micro-nano Materials Based On "Sponge City"

With the rapid development of urbanization in China,environmental problems have become increasingly prominent.The backwardness of drainage network facilities and the shortage of sewage treatment facilities have led some cities in our country to be in an awkward situation of"water-logging when it rains" and"mixing rain and sewage".Therefore,the construction of"sponge city"is of great significance to improve the urban ecological pattern.In this paper,the permeable concrete is taken as the research object,and the cement paste is modified by adding nano-silica,nano-calcium carbonate and silica fume powder.According to the test procedure,the early performance of the modified cement paste and the mechanical properties and durability of the permeable concrete are studied.The main results are as follows:1.The addition of nano-materials will not significantly change the composition of the hydrated cement paste,but will accelerate the hydration degree of the cement paste,reduce the calcium hydroxide content and orientation distribution of the cement paste in the aggregate transition zone,and improve the structure of the transition zone2.When adding 1.5%nano-calcium carbonate alone,permeable concrete achieves the highest effective porosity and maximum permeability coefficient,and does not cause significant loss of cement paste fluidity.It shows that increasing the viscosity of cement paste properly is helpful to improve the vertical pore distribution and increase the permeability of permeable concrete.3.Both nano-materials and silica fume contribute to the increase of compressive strength and splitting tensile strength of permeable concrete.At the experimental design level,when 1%nano-silica,1%nano-calcium carbonate and 4%silica fume are added,permeable concrete achieves the highest compressive strength and splitting tensile strength.4.Nano-materials and silica fume can effectively improve the aggregate dispersion of permeable concrete in abrasion test by strengthening the interfacial zone and paste cohesion.When 0.5%nano-silica,0.5%nano-calcium carbonate and 8%silica fume are added,the mass loss rate is the lowest.5.The addition of micro-nano content can improve the frost resistance of permeable concrete.The pore distribution in cement paste is more uniform by filling effect.Nano-silica at 1%,nano-calcium carbonate at 3%and silica fume at 5%can reduce the freeze-thaw damage of cement paste and the loss of mass and dynamic elastic modulus in freeze-thaw cycle.